Heat Transfer, Energy Resources and Environment

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Heat transfer is energy transfer due to a temperature difference.

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It occurs by three modes — conduction, convection and radiation.

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This section covers the basic laws, one-dimensional conduction through plane walls, tubes and spheres, radiation (electromagnetic spectrum, Stefan-Boltzmann law, reflectivity, absorptivity, transmissivity) and the overall heat transfer coefficient.

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Modes of Heat Transfer Mode Mechanism Law Conduction Energy transfer by molecular vibration and free electrons within a medium, without bulk motion (solids, stationary fluids) Fourier's law: q = −kA dT/dx Convection Conduction + bulk motion of a fluid over a surface; free (natural) — buoyancy driven; forced — pump/fan driven Newton's law of cooling: q = hA(Ts − T∞) Radiation Electromagnetic waves emitted by all bodies above 0 K; needs NO medium (fastest — travels at speed of light, works in vacuum) Stefan-Boltzmann:

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E = εσT⁴ Material Thermal conductivity k (W/m·K, approx.) Diamond / silver / copper ≈ 2000 / 429 / 385–400 Aluminium / brass ≈ 205 / 110 Carbon steel / stainless steel ≈ 45–55 / 15–16 Glass / brick / concrete ≈ 0.8–1.4 / 0.7 / 1.0 Water / engine oil ≈ 0.6 / 0.15 Air / insulation (glass wool, foam) ≈ 0.026 / 0.03–0.05 • Order of k: pure metals > alloys > non-metallic solids > liquids > gases.

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For metals k usually decreases with temperature; for gases it increases. • Typical convective coefficient h (W/m²·K): free convection in gases 2–25, in liquids 50–1000; forced convection in gases 25–250, in liquids 100–20,000; boiling and condensation 2500–100,000. • Thermal diffusivity α = k/(ρcp) (m²/s) — how fast heat diffuses through a material in transient conduction. • Thermal resistance (electrical analogy Q = ΔT/R): conduction R = L/(kA); convection R = 1/(hA); resistances add in series; in parallel 1/R = Σ1/Ri.

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Heat Transfer through Plane Wall, Tube and Sphere Geometry Heat flow Q Conduction resistance Temperature profile Plane wall (thickness L) Q = kA(T1 − T2)/L R = L/(kA) Linear Composite wall Q = (T1 − Tn)/ΣR ΣLi/(kiA) (+ 1/hA for fluids) Linear in each layer Hollow cylinder / tube (r1, r2, length L) Q = 2πkL(T1 − T2)/ln(r2/r1) R = ln(r2/r1)/(2πkL) Logarithmic Hollow sphere Q = 4πk r1r2(T1 − T2)/(r2 − r1) R = (r2 − r1)/(4πk r1r2) Hyperbolic (1/r) • Critical radius of insulation: cylinder rc = k/h; sphere rc = 2k/h (k of insulation, h outside).

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If outer radius < rc, adding insulation INCREASES heat loss (surface area effect dominates) — useful for cooling electric cables; for steam pipes r > rc, so insulation reduces loss. • Transient conduction — lumped capacitance: valid when Biot number Bi = hLc/k < 0.1 (Lc = V/A):

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(T − T∞)/(Ti − T∞) = e−t/τ, time constant τ = ρVc/(hA).

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Fourier number Fo = αt/Lc². • Dimensionless numbers:

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Biot Bi = hL/ksolid (internal conduction resistance / surface convection resistance);

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Nusselt Nu = hL/kfluid (convective / conductive heat transfer in fluid);

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Prandtl Pr = ν/α = μcp/k (momentum / thermal diffusivity — air ≈ 0.7, water ≈ 7, oils ≫ 1, liquid metals ≪ 1);

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Grashof Gr = gβΔTL³/ν² (buoyancy / viscous);

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Rayleigh Ra = Gr·Pr;

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Stanton St = Nu/(Re·Pr);

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Electromagnetic Spectrum and Laws • EM spectrum (decreasing wavelength): radio → microwave → infrared → visible (≈ 0.38–0.76 μm) → ultraviolet → X-rays → gamma rays.

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Thermal radiation ≈ 0.1–100 μm (part of UV, all visible and IR).

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All EM waves travel at c = 3 × 10⁸ m/s in vacuum; c = λν. • Black body: ideal body that absorbs ALL incident radiation and emits the MAXIMUM possible at a given temperature (perfect absorber and emitter; diffuse emitter).

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Approximated by a small hole in a large cavity. • Stefan-Boltzmann law:

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Eb = σT⁴, σ = 5.67 × 10⁻⁸ W/m²·K⁴ (T in kelvin).

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E = εσT⁴ (ε = emissivity, 0–1).

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Doubling absolute temperature increases emission 16 times. • Wien's displacement law: λmaxT = 2898 μm·K — hotter bodies peak at shorter wavelengths (sun at ≈ 5800 K peaks ≈ 0.5 μm, visible; earth at ≈ 300 K peaks ≈ 10 μm, infrared).

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Planck's law gives spectral distribution. • Kirchhoff's law: at thermal equilibrium, emissivity = absorptivity (ε = α) — good absorbers are good emitters. • Solar constant ≈ 1361–1367 W/m² (outside atmosphere); peak at earth's surface ≈ 1000 W/m².

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Reflectivity, Absorptivity and Transmissivity • Incident radiation is partly absorbed (α), reflected (ρ) and transmitted (τ): α + ρ + τ = 1. • Opaque body: τ = 0 → α + ρ = 1 (most solids).

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White (perfect reflector) body: ρ = 1.

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Transparent (diathermanous) body: τ = 1 (dry air, O2, N2 nearly).

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Grey body: α (= ε) same for all wavelengths, less than 1. • Reflection: specular (mirror-like, angle of incidence = angle of reflection — polished surfaces) and diffuse (scattered in all directions — rough surfaces). • Greenhouse effect: glass is transparent to short-wave solar radiation but nearly opaque to long-wave IR emitted by interior surfaces — used in flat-plate solar collectors and greenhouses; atmospheric CO2/H2O behave similarly. • Net radiation: small body 1 in large enclosure:

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Q = ε1σA1(T1⁴ − T2⁴).

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Two large parallel plates: q = σ(T1⁴ − T2⁴)/(1/ε1 + 1/ε2 − 1).

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Shape (view) factor F12: reciprocity A1F12 = A2F21; summation ΣF = 1.

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Radiation shields: n shields of equal emissivity reduce heat exchange to 1/(n + 1).

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Overall Heat Transfer Coefficient • Q = U·A·ΔT, where U combines all resistances between two fluids:

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U = 1/(A·ΣR). • Plane wall between two fluids:

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1/U = 1/h1 + L/k + 1/h2. • Tube (based on outer area Ao):

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1/Uo = ro/(rihi) + roln(ro/ri)/k + 1/ho (+ fouling resistances Rf,i, Rf,o).

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UiAi = UoAo. • U is controlled by the LARGEST resistance (smallest h) — e.g., gas side in a gas-to-liquid exchanger — so improvements (fins) are made on that side. • Typical U (W/m²·K): water-to-water 850–1700; steam condenser 1000–6000; gas-to-gas 10–40; water-to-air finned tubes 25–50.

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This section applies heat-transfer principles to free and forced convection, boiling and condensation, extended surfaces (fins) and heat exchangers — their types, LMTD analysis and effectiveness-NTU method.

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Free (Natural) Convection • Fluid motion caused by buoyancy forces arising from density differences due to temperature gradients (no external fan/pump). • Governing numbers:

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Grashof Gr = gβΔTL³/ν² and Rayleigh Ra = Gr·Pr.

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Nu = C·Ran — n = 1/4 laminar, n = 1/3 turbulent (vertical plate transition Ra ≈ 10⁹). • Examples: room heaters/radiators, cooling of transformers, hot pipes in still air, cooling of electronic components without fans, cooling of hot tea, atmospheric and ocean circulation. • Low heat-transfer coefficients (gases 2–25 W/m²K).

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Forced Convection • Fluid motion imposed by external means (pump, fan, blower, wind).

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Nu = f(Re, Pr). • External flow over flat plate (laminar): local Nux = 0.332 Rex 1/2 Pr1/3; average Nu = 0.664 ReL 1/2 Pr1/3. • Internal flow in tubes: laminar fully developed Nu = 3.66 (constant wall temperature) and 4.36 (constant heat flux); turbulent — Dittus-Boelter:

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Nu = 0.023 Re0.8 Prn (n = 0.4 when fluid is heated, 0.3 when cooled). • Thermal boundary layer vs velocity boundary layer: δ/δt ≈ Pr1/3 (thermal layer thinner than velocity layer for Pr > 1). • Mixed convection when Gr/Re² ≈ 1 (free convection negligible if Gr/Re² ≪ 1; dominant if ≫ 1). • Boiling (pool boiling curve — Nukiyama): free-convection → nucleate boiling (most efficient; ends at critical heat flux / burnout point) → transition → film boiling (vapour blanket, Leidenfrost).

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Condensation: dropwise (h 5–10 times higher) vs filmwise (usual in practice;

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Fins (Extended Surfaces) • Fins increase the surface area for convection where h is low (usually the GAS side):

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IC-engine cylinders and motorcycle engines, car radiators, air-cooled condensers, transformer tanks, electronic heat sinks, compressor cylinders. • Fin equation: d²θ/dx² − m²θ = 0 with m = √(hP/(kAc)) (P = perimeter, Ac = cross-section area, θ = T − T∞). • Heat transfer: infinitely long fin Q = √(hPkAc)·θb; fin with insulated tip Q = √(hPkAc)·θb·tanh(mL); convective tip → use corrected length Lc = L + t/2 (rectangular) or L + D/4 (pin). • Fin efficiency ηf = actual heat transfer / heat transfer if the entire fin were at base temperature = tanh(mL)/(mL) (insulated tip). • Fin effectiveness εf = heat transfer with fin / heat transfer from base area without fin; should be ≥ 2 to justify a fin.

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Effectiveness is higher for high k (Cu, Al), low h (gases), and thin, closely spaced fins (large P/Ac). • Increasing length beyond mL ≈ 2–3 adds little heat transfer (tanh mL → 1).

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Types: straight rectangular, pin (spine), annular (circumferential), triangular, parabolic.

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Types Basis Types Flow arrangement Parallel flow (co-current), counter flow (most effective), cross flow (mixed/unmixed — car radiator, AC coils), multi-pass shell-and-tube Heat transfer process Recuperator (fluids separated by a wall — most exchangers); regenerator (storage type — same matrix alternately heated and cooled, e.g., Ljungström rotary air preheater); direct contact (fluids mix — cooling tower, jet condenser, deaerator) Construction Double-pipe (tube-in-tube); shell-and-tube (most common in industry — baffles support tubes and increase turbulence;

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TEMA standards); plate heat exchanger (compact, high U, easy cleaning — dairy, food, HVAC); compact/finned-tube (area density > 700 m²/m³ — car radiators, gas-turbine regenerators) Function Condensers, evaporators, boilers, economisers, air preheaters, radiators, oil coolers, intercoolers • Parallel flow: both fluids enter at the same end; temperature difference largest at inlet; cold-fluid outlet temperature is always LOWER than hot-fluid outlet temperature. • Counter flow: fluids enter at opposite ends; more uniform ΔT; cold outlet CAN exceed hot outlet temperature; highest LMTD and effectiveness — smallest area for a given duty. • Fouling: deposits (scale, corrosion products, biological growth) add fouling resistance Rf, reduce U — allowed for by extra area and periodic cleaning.

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LMTD Method • Q = U·A·ΔTlm, with log mean temperature difference ΔTlm = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2) (ΔT1, ΔT2 = temperature differences at the two ends). • Parallel flow: ΔT1 = Th,in − Tc,in, ΔT2 = Th,out − Tc,out.

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Counter flow: ΔT1 = Th,in − Tc,out, ΔT2 = Th,out − Tc,in. • If ΔT1 = ΔT2 (counter flow with equal heat capacity rates), LMTD = ΔT.

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For the same terminal temperatures, LMTDcounter > LMTDparallel.

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When one fluid changes phase at constant temperature (condenser, evaporator), parallel and counter flow give the SAME LMTD. • Multi-pass and cross-flow exchangers:

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Q = U·A·F·ΔTlm,counter (F = correction factor ≤ 1). • Energy balance:

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Q = ṁhcph(Th,in − Th,out) = ṁccpc(Tc,out − Tc,in). • LMTD method is convenient for sizing (all four terminal temperatures known).

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Effectiveness-NTU Method • Effectiveness ε = Q/Qmax, Qmax = Cmin(Th,in − Tc,in), heat capacity rate C = ṁcp. • NTU = UA/Cmin (number of transfer units — 'size' of exchanger); capacity ratio Cr = Cmin/Cmax. • Parallel flow: ε = [1 − e−NTU(1+Cr)]/(1 + Cr) — maximum 50% when Cr = 1 even with infinite area.

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Counter flow: ε = [1 − e−NTU(1−Cr)]/[1 − Cre−NTU(1−Cr)]; for Cr = 1, ε = NTU/(1 + NTU). • For Cr = 0 (one fluid condensing/evaporating — condensers, evaporators, boilers): ε = 1 − e−NTU for ALL flow arrangements. • ε-NTU method is convenient for rating problems (outlet temperatures unknown).

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This section classifies energy resources, describes the properties of coal, oil and natural gas, and the harnessing technologies for solar, bio, wind, micro and small hydro, nuclear energy, fuel cells and hydrogen, together with their environmental impacts.

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Classification of Energy Resources Basis Types / examples Conventional vs non-conventional Conventional: coal, oil, natural gas, large hydro, nuclear fission, fuelwood.

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Non-conventional (alternative): solar, wind, small/micro hydro, modern biomass (biogas, biofuels), geothermal, tidal, wave, ocean thermal (OTEC), hydrogen, fuel cells Renewable vs non-renewable Renewable (replenished naturally): solar, wind, hydro, biomass, geothermal, tidal.

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Non-renewable (finite): coal, oil, gas, uranium Primary vs secondary Primary: found in nature (coal, crude oil, sunlight, water flow).

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Secondary: converted forms (electricity, petrol, hydrogen, coke) Commercial vs non-commercial Commercial: traded — electricity, petroleum, coal, LPG.

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Non-commercial/traditional: fuelwood, agricultural residue, animal dung • Nepal: traditional biomass still supplies the largest share of total energy consumption; all petroleum products and coal are imported; hydropower is the main source of electricity (commonly quoted potential ≈ 83,000 MW theoretical and ≈ 42,000 MW economically feasible).

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Solar insolation ≈ 4–5 kWh/m²/day with ≈ 300 sunny days a year.

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Alternative energy is promoted by the Alternative Energy Promotion Centre (AEPC).

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Coal • Formed from plant material by heat and pressure over millions of years.

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Rank (increasing carbon content and calorific value, decreasing moisture and volatiles): peat → lignite → sub-bituminous → bituminous → anthracite. • Proximate analysis (mass %): moisture, volatile matter, fixed carbon, ash.

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Ultimate analysis (elemental %):

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C, H, N, S, O (+ ash). • Calorific value: higher (gross) CV includes latent heat of the water vapour formed; lower (net) CV = HCV − latent heat of water formed (≈ 9H × 2442 kJ/kg of fuel, H = mass fraction of hydrogen).

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Measured by bomb calorimeter (solid, liquid fuels) and Junkers gas calorimeter (gaseous fuels). • Typical CV: anthracite ≈ 30–35 MJ/kg (≈ 90%+ C, low volatiles, smokeless), bituminous ≈ 25–35 MJ/kg (coking coal → coke for steel), lignite ≈ 10–20 MJ/kg (high moisture). • Other properties: caking/coking index, grindability, ash fusion temperature, sulphur content (→ SO2).

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Oil (Petroleum) and Natural Gas • Crude oil: mixture of hydrocarbons (paraffins, naphthenes, aromatics) with S, N, O compounds.

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Fractional distillation products (increasing boiling point): refinery gas and LPG (C3–C4) → petrol/gasoline (≈ C5–C10, 40–200 °C) → naphtha → kerosene/ATF (C10–C16) → diesel (C14–C20) → fuel oil → lubricating oil, wax → bitumen (residue). • Properties: specific gravity / API gravity, viscosity, flash point (lowest temperature at which vapours ignite momentarily when a flame is applied — Pensky-Martens/Abel apparatus), fire point (sustained burning; a few °C higher), pour point, cloud point, calorific value (≈ 42–46 MJ/kg), sulphur, carbon residue. • Natural gas: mainly methane (CH4, 70–95%) with ethane, propane, CO2, N2, H2S;

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CV ≈ 50–55 MJ/kg (≈ 35–40 MJ/m³); cleanest fossil fuel (lowest CO2 per unit energy).

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CNG — compressed to ≈ 200–250 bar;

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LNG — liquefied at −162 °C (≈ 1/600 volume).

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LPG = propane + butane (from refining/gas processing), heavier than air — household cooking fuel in Nepal.

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Solar Energy • Solar thermal: flat-plate collectors (black selectively-coated absorber, glass glazing — greenhouse effect, insulation; water heating up to ≈ 80–100 °C), evacuated-tube collectors, concentrating collectors (parabolic trough, dish, central tower, Fresnel — high temperatures for power), solar cookers, dryers, stills. • Solar photovoltaic (PV): photovoltaic effect in a semiconductor p-n junction (silicon) converts light directly into DC electricity.

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Cell voltage ≈ 0.5–0.6 V; cells → modules → arrays.

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Types: monocrystalline (highest efficiency ≈ 20–24%), polycrystalline (≈ 15–20%), thin film (a-Si, CdTe, CIGS; ≈ 10–18%). • Standard test conditions (STC):

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1000 W/m², 25 °C cell temperature, AM 1.5.

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Efficiency falls as cell temperature rises.

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MPPT (maximum power point tracking) controllers extract maximum power; fill factor measures cell quality. • Systems: stand-alone (with battery — solar home systems), grid-tied (net metering), hybrid, solar water pumping, mini-grids.

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Optimum fixed tilt ≈ latitude (≈ 27–30° in Nepal), facing south.

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Bio-energy • Biomass sources: fuelwood, agricultural residues, animal dung, energy crops, municipal organic waste. • Conversion routes: direct combustion (improved cooking stoves — reduce fuel use and indoor smoke); thermochemical — pyrolysis (charcoal, bio-oil), gasification (producer gas:

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CO + H2), briquetting; biochemical — anaerobic digestion (biogas), fermentation (ethanol); chemical — transesterification of vegetable oils (jatropha etc.) → biodiesel. • Biogas: ≈ 50–70% CH4, 30–40% CO2, traces of H2S;

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Anaerobic digestion stages: hydrolysis → acidogenesis → acetogenesis → methanogenesis.

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Optimum conditions: mesophilic temperature ≈ 30–40 °C (≈ 35 °C), pH ≈ 6.8–7.5, C/N ratio ≈ 20–30 :

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1, total solids ≈ 8–10% (dung : water ≈ 1 :

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1), retention time ≈ 30–60 days. • Plant types: fixed-dome (Chinese type;

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Nepal's standard GGC-2047 design), floating-drum (KVIC, India), bag digesters.

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Digested slurry is a good fertiliser.

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Gas production drops in cold hill climates.

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Wind Energy • Power in wind P = ½ρAV³ — proportional to the CUBE of wind speed and to rotor swept area (∝ D²).

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Doubling wind speed gives 8 times the power. • Betz limit: maximum fraction of wind power extractable = 16/27 ≈ 59.3%; practical power coefficient Cp ≈ 0.35–0.45. • HAWT (horizontal axis — most common, 2–3 blades, needs yaw control, high efficiency) vs VAWT (vertical axis — Darrieus (lift type, 'egg-beater') and Savonius (drag type, high starting torque, low efficiency); no yaw needed). • Operating speeds: cut-in ≈ 3–4 m/s, rated ≈ 12–15 m/s, cut-out ≈ 25 m/s.

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Wind speed increases with height; capacity factor ≈ 25–40%.

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Tip-speed ratio = blade-tip speed / wind speed.

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In Nepal the best wind resource is in high Himalayan corridors such as Mustang.

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Micro and Small Hydro • Hydropower P = η·ρ·g·Q·H (W) → P (kW) ≈ 9.81·η·Q·H (Q in m³/s, H in m). • Typical size classification (limits vary by country/policy): pico < 5 kW, micro ≈ 5–100 kW, mini ≈ 100 kW–1 MW, small ≈ 1–10 MW. • Components of a run-of-river scheme: diversion weir and intake → headrace canal → settling basin (desilting) — removes sediment to protect turbines → forebay → penstock → powerhouse (turbine, generator, controller) → tailrace → transmission/distribution. • Turbines:

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Pelton, Turgo, cross-flow (Banki-Michell) — widely manufactured locally in Nepal, good part-load efficiency;

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Francis, propeller; improved traditional water mills (ghatta). • Micro-hydro plants use an electronic load controller (ELC) that diverts surplus power to ballast (dump) heaters, keeping load and hence speed/frequency constant (instead of a mechanical flow governor). • Types: run-of-river (ROR), storage (reservoir), pumped storage.

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Advantages: renewable, local resource, rural electrification, low running cost.

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Limitations: seasonal (dry-season) flow reduction, sediment wear, floods/landslides, site-specific.

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Nuclear Energy • Fission of U-235 by slow (thermal) neutrons releases ≈ 200 MeV per fission plus 2–3 neutrons → chain reaction.

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Natural uranium contains ≈ 0.7% U-235; light-water reactors use fuel enriched to ≈ 3–5%. • Reactor components: fuel (UO2 pellets in zirconium-alloy cladding), moderator (slows neutrons — light water, heavy water D2O, graphite), control rods (absorb neutrons — cadmium, boron, hafnium), coolant (water, heavy water, CO2, liquid sodium), reflector, shielding (concrete, lead), containment building. • Reactor types:

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PWR (pressurised water — most common; water kept liquid at ≈ 155 bar, separate steam generator), BWR (boiling in core, direct cycle), PHWR/CANDU (natural uranium, heavy water), gas-cooled (graphite, CO2), fast breeder (no moderator, liquid-sodium coolant, breeds Pu-239 from U-238).

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Fusion (D-T, ITER) is under development. • Pros: no CO2 in operation, very high energy density, base-load power.

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Cons: long-lived radioactive waste, accident risk (Three Mile Island 1979, Chernobyl 1986, Fukushima 2011), proliferation, high capital and decommissioning cost, thermal pollution.

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Fuel Cells and Hydrogen • Fuel cell: electrochemical device that converts chemical energy of a fuel (H2) and oxidant (O2) DIRECTLY into DC electricity — not limited by Carnot efficiency.

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H2 → 2H⁺ + 2e⁻; cathode: ½O2 + 2H⁺ + 2e⁻ → H2O.

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By-products: water and heat.

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Cell voltage ≈ 0.7 V (theoretical 1.23 V); electrical efficiency ≈ 40–60% (≈ 80%+ with heat recovery). • Types:

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PEMFC (proton exchange membrane, ≈ 80 °C, Pt catalyst — vehicles), AFC (alkaline, KOH — spacecraft), PAFC (phosphoric acid, ≈ 200 °C), MCFC (molten carbonate, ≈ 650 °C), SOFC (solid oxide, ≈ 800–1000 °C — stationary, internal reforming), DMFC (direct methanol). • Hydrogen is an energy CARRIER, not a primary source.

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Highest energy per unit mass (LHV ≈ 120 MJ/kg, HHV ≈ 142 MJ/kg) but very low per unit volume.

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Production: steam methane reforming (most common, 'grey'), coal gasification, electrolysis of water with renewable electricity ('green'), reforming with carbon capture ('blue'), biomass gasification. • Storage: compressed gas (350–700 bar), liquid (−253 °C), metal hydrides, chemical carriers (ammonia).

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Uses: fuel cells, IC engines, fertiliser (ammonia), refining, steel.

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Safety: wide flammability limits (≈ 4–75%), very low ignition energy, invisible flame, hydrogen embrittlement, leakage.

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Nepal's surplus wet-season hydropower is seen as a potential source of green hydrogen.

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Environmental Impacts of Energy Sources Source Main environmental impacts Coal Highest CO2 per unit energy;

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SO2, NOx, particulates, fly ash, mercury; acid rain; mining land damage Oil CO2, NOx, SOx, VOCs; oil spills; refinery pollution Natural gas Lower CO2; methane leakage (strong GHG);

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NOx Large hydro Displacement, ecosystem and fish-migration disruption, sedimentation, reservoir emissions, dam-break/GLOF risk — but no fuel emissions Solar PV Land use, manufacturing energy and chemicals, end-of-life panel waste Wind Noise, bird/bat strikes, visual impact, land use Biomass Carbon-neutral only if sustainably harvested; deforestation; indoor air pollution from traditional stoves Nuclear Radioactive waste, accident risk, thermal pollution of cooling water Fuel cells / hydrogen Zero local emissions (only water); overall impact depends on how H2 is produced

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Combustion is the rapid oxidation of a fuel releasing heat and light.

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This section covers the combustion process and stoichiometry, conditions necessary for combustion, phases of combustion, methods of controlling fire, harmful effects of combustion products and their control, and engine emissions.

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The Combustion Process and Stoichiometry • Combustion: rapid exothermic chemical reaction of fuel (C, H, S) with oxygen.

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Complete combustion → CO2, H2O (and SO2); incomplete combustion (insufficient O2, poor mixing, low temperature) → CO, soot, unburnt hydrocarbons. • Reactions:

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C + O2 → CO2 (1 kg C needs 8/3 kg O2);

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2H2 + O2 → 2H2O (1 kg H2 needs 8 kg O2);

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S + O2 → SO2 (1 kg S needs 1 kg O2);

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CH4 + 2O2 → CO2 + 2H2O. • Air contains ≈ 23% O2 by mass and ≈ 21% by volume.

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Theoretical air per kg fuel = (100/23)[(8/3)C + 8(H − O/8) + S] kg. • Stoichiometric air-fuel ratio (by mass): petrol ≈ 14.7, diesel ≈ 14.5, methane ≈ 17.2, hydrogen ≈ 34.3.

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Excess air % = (actual − theoretical)/theoretical × 100 — boilers use ≈ 15–25% (gas/oil) to 20–50% (coal). • Equivalence ratio φ = actual F/A ÷ stoichiometric F/A: φ < 1 lean, φ > 1 rich; λ = 1/φ (excess-air ratio). • Flue-gas analysis by Orsat apparatus (dry basis):

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CO2 absorbed in KOH, O2 in alkaline pyrogallol, CO in cuprous chloride (in that order). • Flammability limits (by volume in air): methane ≈ 5–15%, petrol vapour ≈ 1.4–7.6%, hydrogen ≈ 4–75%.

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Adiabatic flame temperature is maximum for a slightly rich mixture.

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Conditions Necessary for Combustion • Presence of fuel, oxygen (air) in proportion within the flammability limits, and heat to reach the ignition temperature (fire triangle; plus sustained chain reaction — fire tetrahedron). • The three Ts of good combustion:

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Time, Temperature, Turbulence — enough residence time, high enough temperature, and thorough mixing of fuel and air. • Other requirements: correct air-fuel ratio, proper atomisation/vaporisation of liquid fuels and pulverisation of solid fuels, ignition source (spark, pilot flame, heat of compression).

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Phases of Combustion Engine / fuel Phases SI engine (Ricardo) (1) Ignition lag / delay period (preparation — chemical growth of flame kernel after spark);

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(2) flame propagation / main combustion (turbulent flame front, rapid pressure rise);

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(3) after-burning (combustion continues in expansion stroke) CI engine (1) Ignition delay — physical (atomisation, vaporisation, mixing) + chemical delay;

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(2) rapid (uncontrolled) combustion of premixed fuel — steep pressure rise (diesel knock if delay is long);

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(3) controlled (mixing-controlled) combustion — rate governed by injection;

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(4) after-burning Solid fuel particle Drying → devolatilisation (volatile matter released and burns with flame) → char (fixed carbon) combustion (glowing) → ash Fire development Ignition → growth → flashover → fully developed fire → decay Methods of Controlling Fire • Remove one element of the fire triangle/tetrahedron: starving (remove or isolate fuel — shut valves), smothering/blanketing (cut off oxygen — foam, CO2, sand, fire blanket), cooling (water to below ignition temperature), chain-breaking/inhibition (dry chemical powder, clean agents).

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Match the extinguisher to the fire class (see 7.2). • Fire prevention: housekeeping, safe storage of flammables, hot-work permits, proper electrical installations, no-smoking zones, detection (smoke/heat/flame detectors) and suppression systems (sprinklers, hydrants). • In furnaces and boilers: control of air-fuel ratio and excess air, burner management and flame-failure safeguards, dampers, purge before ignition; in plants handling gases/dusts: explosion vents, flame arrestors, inerting with N2/CO2.

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Harmful Effects of Combustion Products and Their Control Pollutant Source / formation Harmful effects Control CO2 Complete combustion of carbon Greenhouse gas → global warming Efficiency, fuel switching, renewables, CCS CO Incomplete combustion (rich mixture, poor mixing) Toxic — binds haemoglobin ≈ 200–250× more strongly than O2 (carboxyhaemoglobin), headache, death Adequate air, good mixing, catalytic converters, ventilation, CO detectors Unburnt HC / VOC Incomplete combustion, evaporation Photochemical smog with NOx; some carcinogenic (benzene) Catalytic converters, vapour recovery, better combustion NOx N2 + O2 at HIGH temperature (thermal/Zeldovich), fuel nitrogen Respiratory irritation, acid rain, smog and ground-level ozone EGR, low-NOx burners, staged combustion, lower flame temperature, SCR (NH3/urea), SNCR SO2/SOx Sulphur in fuel Acid rain, respiratory disease, corrosion Low-sulphur fuels, flue-gas desulphurisation (FGD) — limestone scrubbing, fluidised-bed combustion with limestone Particulates (PM10, PM2.5), soot, smoke Incomplete combustion, ash, diesel engines Lung and heart disease, reduced visibility Cyclones, bag filters, electrostatic precipitators (ESP), wet scrubbers, diesel particulate filters Lead Leaded petrol (TEL) — now phased out Neurotoxic, especially for children; poisons catalysts Unleaded fuel Engine Emissions • SI (petrol) engines: main pollutants CO, HC and NOx.

23

CI (diesel) engines: main pollutants NOx and particulate matter (smoke/soot);

24

CO and HC are low (excess air). • Sources in SI vehicles: exhaust (majority), crankcase blow-by (HC) and evaporation from fuel tank/carburettor (HC). • Effect of mixture: rich → high CO and HC; lean → low CO; very lean → HC rises (misfire);

25

NOx is maximum slightly lean of stoichiometric (high temperature + available O2). • Controls:

26

PCV (positive crankcase ventilation) for blow-by; charcoal canister for evaporative emissions; engine design (combustion chamber, timing, lean burn, fuel injection);

27

EGR (exhaust gas recirculation — lowers flame temperature → less NOx). • Three-way catalytic converter (TWC):

28

Pt, Pd, Rh on a ceramic honeycomb — oxidises CO → CO2 and HC → CO2 + H2O, and reduces NOx → N2.

29

Works only near stoichiometric (λ ≈ 1) with closed-loop oxygen-sensor control; needs unleaded fuel; light-off ≈ 250–300 °C. • Diesel after-treatment:

30

DOC (oxidation catalyst), DPF (diesel particulate filter), SCR with urea (DEF/AdBlue) for NOx, lean NOx traps. • Emission norms:

31

Euro standards (Euro 1–6), Bharat Stage (India);

32

Nepal enforces vehicle emission standards based on Euro norms and roadside smoke/emission tests ('green sticker').

1

This section covers the chemical structure of petroleum fuels and its effect on engine behaviour, rating of fuels (octane and cetane numbers), fuel supply and injection systems, engine lubrication systems, grading of lubricants, specific fuel consumption and conversions.

2

Chemical Structure of Petroleum Hydrocarbon family Formula / structure SI engine (anti-knock) CI engine (ignition quality) Paraffins — normal (alkanes) CnH2n+2, saturated straight chain (n-heptane, n-cetane C16H34) POOR — knock easily EXCELLENT — high cetane Iso-paraffins (branched) CnH2n+2, branched chain (iso-octane, 2,2,4-trimethylpentane) EXCELLENT — high octane Poor Olefins (alkenes) CnH2n, unsaturated (one double bond) — form gum on storage Moderate Moderate–poor Naphthenes (cycloalkanes) CnH2n, saturated ring Moderate Moderate Aromatics CnH2n−6, benzene ring (benzene, toluene, xylene) VERY GOOD — highest octane VERY POOR — low cetane, smoky • Rule:

3

SI fuels need RESISTANCE to auto-ignition (aromatics, iso-paraffins);

4

CI fuels need EASY auto-ignition (straight-chain paraffins).

5

Hence octane and cetane quality are roughly INVERSE. • Refining processes: fractional distillation; cracking (thermal/catalytic — break heavy molecules into lighter ones, more petrol of higher octane); catalytic reforming (naphtha → aromatics, raises octane); alkylation, isomerisation, polymerisation; hydrotreating (desulphurisation).

6

Rating of Engine Fuels • Octane number (ON): percentage by volume of iso-octane (ON = 100) in a mixture with n-heptane (ON = 0) that gives the same knock intensity as the test fuel in a standard CFR variable-compression engine. • RON (Research — 600 rpm, milder) > MON (Motor — 900 rpm, heated mixture, severe); sensitivity = RON − MON; anti-knock index (RON + MON)/2.

7

Fuels above 100 are rated by performance number.

8

Typical petrol ≈ 87–91 (regular) and 95–98 RON (premium). • Cetane number (CN): percentage by volume of n-cetane (CN = 100) in a mixture with α-methylnaphthalene (CN = 0) (modern secondary reference: heptamethylnonane, CN 15) that gives the same ignition delay as the test fuel.

9

Typical diesel CN ≈ 40–55.

10

Cetane index (calculated); diesel index = aniline point (°F) × API gravity / 100. • Other fuel properties: volatility (ASTM distillation curve — 10% point: cold starting and vapour lock;

11

50%: warm-up and acceleration;

12

90%: crankcase dilution and deposits), Reid vapour pressure, gum content, sulphur; for diesel — viscosity, cloud and pour point (waxing in cold), flash point (safety), carbon residue. • Additives: anti-knock (TEL — now banned;

13

MMT, MTBE, ETBE, ethanol), cetane improvers (amyl nitrate, 2-ethylhexyl nitrate), detergents, anti-oxidants (gum inhibitors), corrosion inhibitors, pour-point depressants, anti-icing agents. • Alternative fuels: ethanol (high octane ≈ 108 RON, lower CV ≈ 27 MJ/kg;

14

E10, E85), methanol, CNG (very high knock resistance, RON ≈ 120+), LPG (RON ≈ 105–110), biodiesel (FAME;

15

CN ≈ 50–60, blends B5–B20), hydrogen, DME (diesel substitute).

16

Fuel Supply and Fuel Injection Systems • Petrol supply: fuel tank → fuel pump (mechanical diaphragm pump driven by camshaft in older engines; electric in-tank pump in modern injected engines, ≈ 3–4 bar) → fuel filter → carburettor, or fuel rail with pressure regulator and injectors.

17

Motorcycles often use gravity feed. • Diesel supply: tank → feed (lift) pump → primary and secondary filters (with water separator) → injection pump → high-pressure pipes → injectors; leak-off (return) line to tank.

18

Air must be bled from the system before starting. • Injection-system requirements: accurate metering of fuel quantity, correct timing, controlled rate of injection, fine atomisation, adequate penetration and distribution, sharp start and end (no dribbling). • Injection pressures: petrol port injection ≈ 3–5 bar; gasoline direct injection ≈ 50–200+ bar; diesel ≈ several hundred bar, common-rail up to ≈ 2000–2500 bar.

19

System types (jerk pump, distributor pump, unit injector, common rail;

20

MPFI, GDI) — see 8.6.

21

Lubrication System • Functions of engine oil: reduce friction and wear, cool (carry heat from pistons and bearings), seal (piston rings), clean (detergents/dispersants hold soot in suspension), prevent corrosion, cushion shock loads, hydraulic actuation (tappets, variable valve timing). • Parts lubricated: main and big-end bearings, cylinder walls and pistons, gudgeon pins, camshaft and valve train, timing gears/chain, turbocharger bearings.

22

System Working Use Petroil (mist) Oil mixed with petrol (≈ 1 :

23

50); crankcase mist lubricates Small two-stroke engines Splash Dipper on connecting-rod big end splashes oil from sump Small single-cylinder engines Pressure (forced-feed) Gear/rotor oil pump draws oil through strainer, sends it via filter to main gallery and drilled passages to bearings; relief valve limits pressure Most automobile engines Semi-pressure Pressure to main bearings, splash elsewhere Some medium engines Wet sump vs dry sump Wet: oil stored in crankcase sump.

24

Dry: oil scavenged to a separate tank Dry sump in racing, aircraft, off-road (prevents oil starvation) • Components: sump, pick-up strainer, oil pump (gear or rotor type), pressure-relief valve, oil filter (full-flow or bypass), oil cooler, pressure gauge/warning lamp, dipstick, PCV system.

25

Grading of Lubricants • SAE viscosity grades (SAE J300): monogrades SAE 20, 30, 40, 50 (viscosity at 100 °C); winter grades 0W, 5W, 10W, 15W, 20W, 25W (low-temperature cranking and pumping limits — lower number flows better when cold). • Multigrade oil, e.g., SAE 15W-40: meets 15W cold-temperature requirements and SAE 40 viscosity at 100 °C (achieved with viscosity-index improvers).

26

(J306). • API service classification: 'S' series for spark-ignition (petrol) engines (e.g., SN, SP — later letter = newer, higher performance); 'C' series for compression-ignition (diesel) engines (e.g., CI-4, CK-4).

27

European ACEA (A/B, C, E);

28

JASO for motorcycles (MA, MB) and two-strokes (FC, FD). • ISO VG grades for industrial oils = kinematic viscosity (cSt) at 40 °C (VG 32, 46, 68, 100…).

29

NLGI consistency numbers for grease (000 to 6;

30

NLGI 2 most common). • Viscosity index (VI): resistance to viscosity change with temperature — ≈ 100 for good mineral oils, > 140 for synthetics; higher is better.

31

Specific Fuel Consumption and Conversion • Brake specific fuel consumption bsfc = ṁf / BP (kg/kWh or g/kWh); isfc = ṁf/IP.

32

Lower bsfc = better efficiency.

33

Typical: diesel ≈ 200–250 g/kWh (large marine diesels < 170), petrol ≈ 250–350 g/kWh. • Fuel conversion efficiency (= brake thermal efficiency) ηf = BP/(ṁf·CV) = 3600/(bsfc × CV) with bsfc in kg/kWh and CV in kJ/kg.

34

Example: bsfc = 0.25 kg/kWh, CV = 43,000 kJ/kg → η = 3600/(0.25 × 43,000) ≈ 33.5%. • Typical fuel data: petrol density ≈ 0.72–0.75 kg/L, LCV ≈ 43–44 MJ/kg; diesel ≈ 0.82–0.85 kg/L, LCV ≈ 42.5–43 MJ/kg;

35

LPG ≈ 46 MJ/kg; natural gas ≈ 50 MJ/kg; ethanol ≈ 27 MJ/kg; hydrogen ≈ 120 MJ/kg. • Unit conversions:

36

1 kWh = 3.6 MJ = 860 kcal;

37

1 metric hp = 0.7355 kW (1 British hp = 0.746 kW);

38

1 toe (tonne of oil equivalent) = 41.868 GJ;

39

1 US gallon = 3.785 L; fuel economy L/100 km = 100/(km/L). • Engine/vehicle fuel conversion: petrol engines can be converted to CNG/LPG with kits (bi-fuel); diesel engines to dual-fuel (gas + pilot diesel); electrification (e.g., battery-electric three-wheelers — 'Safa Tempo' in Kathmandu — and increasing EV use in Nepal).

1

Engineering activities affect air, water, soil and the acoustic environment.

2

This section covers air pollution and air quality, pollution dispersion, water pollution, noise pollution, solid waste, global environmental issues and national (Nepal) issues and regulations.

3

Air Pollution • Sources: natural (volcanoes, dust storms, forest fires, pollen) and anthropogenic — stationary (power plants, industries, brick kilns, cement), mobile (vehicles), area (open burning of waste and crop residue, domestic biomass cooking). • Primary pollutants (emitted directly):

4

CO, SO2, NOx, particulate matter, hydrocarbons/VOCs, lead.

5

Secondary pollutants (formed in atmosphere): ground-level ozone (O3), PAN (peroxyacetyl nitrate), sulphuric/nitric acid (acid rain), secondary aerosols. • Smog: classical/London smog (smoke + fog + SO2; reducing; cold humid winter) vs photochemical (Los Angeles) smog (NOx + VOCs + sunlight → O3, PAN; oxidising; sunny days). • Health effects: respiratory and cardiovascular disease, lung cancer, eye irritation;

6

PM2.5 (≤ 2.5 μm) penetrates deep into lungs and bloodstream. • Control at source: cleaner fuels, efficient combustion, process change, vehicle maintenance, public transport, electrification.

7

Control devices below; tall stacks only disperse (dilute) — they do not remove pollutants.

8

Control device Pollutant Remarks Gravity settling chamber Coarse particles (> 50 μm) Simple pre-cleaner Cyclone separator Particles > ≈ 10 μm Centrifugal; cheap, low efficiency for fine particles Fabric (bag) filter Fine particulates > 99% efficiency; limited by temperature and moisture Electrostatic precipitator (ESP) Fine particulates (fly ash) > 99% efficiency, low pressure drop; power plants, cement plants Wet scrubber (venturi) Particles and soluble gases Produces wastewater FGD (flue-gas desulphurisation) SO2 Limestone slurry scrubbing → gypsum SCR / SNCR NOx Ammonia/urea reduces NOx to N2 Adsorption (activated carbon), thermal/catalytic oxidation VOCs, odours Solvent recovery, incineration Catalytic converter CO, HC, NOx from vehicles Three-way catalyst (see 9.4) Air Quality • Criteria pollutants (US EPA):

9

PM (PM10, PM2.5), O3, CO, SO2, NO2, lead. • Air Quality Index (AQI) (US EPA scale):

10

0–50 good, 51–100 moderate, 101–150 unhealthy for sensitive groups, 151–200 unhealthy, 201–300 very unhealthy, 301–500 hazardous. • WHO Air Quality Guidelines (2021):

11

PM2.5 annual 5 μg/m³, 24-hour 15 μg/m³;

12

PM10 annual 15 μg/m³, 24-hour 45 μg/m³.

13

Nepal's National Ambient Air Quality Standards (2012) set 24-hour limits of about 40 μg/m³ for PM2.5 and 120 μg/m³ for PM10. • Monitoring: high-volume samplers, beta-attenuation monitors, gas analysers;

14

Department of Environment monitoring stations in Nepal. • Indoor air pollution from biomass cooking (CO, PM) is a major health problem in rural Nepal — improved cook stoves, LPG, biogas and electric cooking reduce it.

15

Pollution Dispersion • Dispersion depends on wind speed (concentration ∝ 1/u), wind direction, atmospheric stability, mixing height, stack height and terrain. • Stability is judged by comparing the environmental lapse rate (ELR) with the dry adiabatic lapse rate (DALR ≈ 9.8 °C/km ≈ 1 °C per 100 m):

16

ELR > DALR (super-adiabatic) → unstable, strong vertical mixing;

17

ELR ≈ DALR → neutral;

18

ELR < DALR (sub-adiabatic) → stable; temperature increasing with height (inversion) → very stable, pollutants trapped. • Mixing height and ventilation coefficient (= mixing height × mean wind speed) indicate the atmosphere's dispersion capacity.

19

Valleys such as Kathmandu have poor dispersion in winter due to night-time inversions and low winds.

20

Plume type Atmospheric condition Looping Highly unstable (super-adiabatic) — strong vertical eddies; high ground concentrations near stack at times Coning Neutral or slightly stable — plume spreads as a cone (cloudy, windy) Fanning Stable/inversion at all heights — little vertical spread; plume fans out horizontally Lofting Inversion BELOW stack, unstable above — pollutants carried upward; best condition Fumigation Unstable BELOW, inversion ABOVE stack — pollutants brought down to ground; worst condition Trapping Inversions above and below stack — plume trapped between them • Gaussian plume model:

21

C(x, y, z) = [Q/(2πuσyσz)]·exp(−y²/2σy²)·[exp(−(z − H)²/2σz²) + exp(−(z + H)²/2σz²)]; effective stack height H = physical height + plume rise (Holland, Briggs);

22

Pasquill stability classes A (very unstable) to F (very stable).

23

Maximum ground-level concentration ∝ Q/(uH²) — a taller stack greatly reduces ground concentration.

24

Water Pollution • Sources: point (industrial effluents, sewage outfalls) and non-point (agricultural runoff with fertilisers and pesticides, urban storm runoff). • Pollutants: biodegradable organic matter (oxygen-demanding), pathogens (faecal coliforms — E. coli indicator; cholera, typhoid, diarrhoea), nutrients N and P (→ eutrophication, algal blooms, oxygen depletion), toxic chemicals and heavy metals (mercury — Minamata disease; cadmium — itai-itai; lead; arsenic — Terai groundwater in Nepal), suspended solids (turbidity), oil, thermal pollution (hot cooling water lowers dissolved oxygen), plastics/microplastics. • Key parameters:

25

DO (dissolved oxygen — ≈ 9 mg/L saturation at 20 °C; fish need ≥ 4–5 mg/L);

26

BOD (biochemical oxygen demand — 5 days at 20 °C, biodegradable organics);

27

COD (chemical oxygen demand — dichromate;

28

COD ≥ BOD); pH (6.5–8.5 for drinking), TDS, TSS, turbidity (NTU), hardness, nitrate, fluoride, coliform count.

29

WHO arsenic guideline 10 μg/L (Nepal's drinking-water standard allows 50 μg/L). • Water treatment: screening → coagulation/flocculation (alum) → sedimentation → filtration (slow/rapid sand) → disinfection (chlorination, UV, ozone). • Wastewater treatment: preliminary (screens, grit chamber) → primary (sedimentation — removes ≈ 60% SS, ≈ 30–35% BOD) → secondary/biological (activated sludge, trickling filter, oxidation ponds, UASB, constructed wetlands — removes ≈ 85–95% BOD) → tertiary (nutrient removal, filtration, disinfection); sludge digestion and drying.

30

Kathmandu's rivers (Bagmati, Bishnumati) are heavily polluted by untreated sewage;

31

Guheshwori treatment plant serves part of the Bagmati.

32

Noise Pollution • Noise = unwanted sound.

33

Sound pressure level SPL = 20 log10(p/p0) dB, p0 = 20 μPa (threshold of hearing = 0 dB). dB(A) weighting approximates human ear response. • Reference levels: whisper ≈ 30 dB, normal conversation ≈ 60 dB, heavy traffic ≈ 80–90 dB, pneumatic drill ≈ 100 dB, threshold of pain ≈ 120–140 dB, jet take-off ≈ 140 dB. • Rules: two equal sources together → +3 dB; doubling distance from a point source (free field) → −6 dB; +10 dB is perceived as about twice as loud.

34

Leq (equivalent continuous level), L10, L90, Ldn. • Effects: noise-induced hearing loss, stress, sleep disturbance, hypertension, communication interference, reduced productivity.

35

Occupational exposure limit ≈ 85 dB(A) for 8 hours (many standards;

36

OSHA's legal limit is 90 dB(A)).

37

WHO community guideline ≈ 55 dB(A) daytime outdoors in residential areas. • Control: at source (quieter machines, maintenance, balancing, mufflers/silencers, vibration isolation, enclosures, damping); along the path (distance, barriers, absorbing materials, green belts, land-use zoning); at the receiver (ear plugs/muffs, sound-proof cabins, limiting exposure time).

38

Kathmandu's 'no-horn' rule (2017) reduced traffic noise.

39

Solid Waste • Types: municipal solid waste (MSW — in Nepal more than half is organic/biodegradable), plastics, paper, glass, metals, textiles; hazardous/industrial waste; health-care (biomedical) waste; e-waste; construction and demolition waste. • Functional elements: generation → on-site storage and segregation at source (degradable/non-degradable) → collection → transfer and transport → processing → disposal. • Waste management hierarchy (most → least preferred): prevention/reduction → reuse → recycling → recovery (composting, anaerobic digestion, waste-to-energy, RDF) → disposal (sanitary landfill).

40

Reduce, Reuse, Recycle. • Composting (aerobic — windrow, vermicomposting) suits Nepal's high-organic waste; incineration reduces volume ≈ 90% but emits dioxins and is unsuitable for wet, low-calorific waste; sanitary landfill needs liner, leachate collection and treatment, gas collection (CH4 ≈ 50%) and daily cover — unlike open dumping. • Nepal:

41

Solid Waste Management Act 2011;

42

Kathmandu's waste is disposed at the Sisdol/Bancharedanda landfill site in Nuwakot; biomedical waste needs segregation (colour coding) and autoclaving/incineration.

43

Global Issues • Climate change / global warming: enhanced greenhouse effect from CO2, CH4, N2O, HFCs, PFCs, SF6.

44

CO2 = 1, CH4 ≈ 28, N2O ≈ 265, SF6 ≈ 23,500.

45

Atmospheric CO2 has risen from ≈ 280 ppm (pre-industrial) to over 420 ppm; global temperature has risen ≈ 1.1–1.2 °C.

46

Impacts: glacier retreat, sea-level rise, extreme weather. • Ozone-layer depletion: stratospheric ozone (which absorbs UV-B) is destroyed by chlorine and bromine from CFCs and halons → Antarctic ozone hole, more skin cancer and cataracts.

47

Vienna Convention (1985), Montreal Protocol (1987) — the most successful environmental treaty;

48

Kigali Amendment (2016) phases down HFCs. • Acid rain (pH < 5.6) from SO2 and NOx: damages forests, lakes, crops and buildings (marble/limestone).

49

Others: deforestation, biodiversity loss, desertification, marine plastic pollution, South Asian 'atmospheric brown cloud'. • Agreements and milestones:

50

Stockholm Conference (1972, UNEP);

51

Brundtland Report (1987 — sustainable development: meeting present needs without compromising future generations);

52

UNFCCC (Rio Earth Summit 1992);

53

Kyoto Protocol (1997) — binding targets for developed countries, CDM;

54

Paris Agreement (2015) — limit warming well below 2 °C and pursue 1.5 °C through NDCs;

55

SDGs 2030 (SDG 7 clean energy, SDG 13 climate action);

56

Basel (hazardous waste, 1989), Stockholm (POPs, 2001), Minamata (mercury, 2013), Ramsar (wetlands, 1971) conventions.

57

National Issues (Nepal) • Air pollution in Kathmandu Valley: vehicles, road and construction dust, brick kilns, open burning of waste, forest fires; bowl-shaped valley with winter inversions;

58

PM2.5 often many times the WHO guideline. • Water pollution: untreated sewage in urban rivers (Bagmati clean-up campaign), arsenic in Terai groundwater, industrial effluents; solid waste management and landfill siting problems; noise in cities; unplanned urbanisation; sand and stone mining from rivers. • Climate-change vulnerability:

59

Himalayan glacier retreat, growth of glacial lakes and GLOF (glacial lake outburst flood) risk (e.g., Tsho Rolpa, Imja), erratic monsoon, floods, landslides and droughts.

60

Deforestation and soil erosion, though community forestry has raised forest cover to about 45%. • Energy-related issues: heavy dependence on imported petroleum, indoor smoke from traditional biomass, need to use surplus hydropower (EVs, electric cooking). • Policy and law:

61

Environment Protection Act 2019 (2076 BS) and Rules 2020 — require Brief Environmental Study (BES), Initial Environmental Examination (IEE) or Environmental Impact Assessment (EIA) depending on project size;

62

Climate Change Policy 2019;

63

National Ambient Air Quality Standards 2012; vehicle emission standards;

64

Solid Waste Management Act 2011;

65

Nepal's commitment to net-zero emissions by 2045. • EIA process: screening → scoping → baseline study → impact prediction and evaluation → mitigation measures → Environmental Management Plan → public hearing and review → approval → monitoring and auditing.