Section A
Q1. A researcher measures that a refrigerator consumes 2 kW power, has removed 30,000 kJ of heat from a refrigerated space, is maintained at -28°C. The ambient temperature is 22°C and the running time of the refrigerator for the process is 18 minutes. Determine if these measurements are reasonable. Explain the term chemical equilibrium. How are equilibrium products of combustion different from non-dissociated species? Also explain the effect of temperature on the equilibrium composition. What is adiabatic flame temperature? How is it calculated for a given hydrocarbon fuel? Explain the factors which influence the adiabatic flame temperature for a given fuel-air mixture at a particular equivalence ratio. What is the typical range of convective heat transfer coefficient for the following cases? A three-cylinder, four-stroke cycle SI engine having bore 68.5 mm and stroke 72.0 mm runs at 3000 rpm with air-fuel ratio 15:1 and develops indicated mean effective pressure 10 bar. Calorific value of the fuel used is 44,000 kJ/kg. Mechanical efficiency is 0.85, combustion efficiency is 0.97 and volumetric efficiency is 0.9. Density of air is 1.18 kg/m3. Determine:
(i) Gases in free convection
(ii) Liquids in free convection
(iii) Gases in forced convection
(iv) Liquids in forced convection
(i) Indicated power in kW
(ii) Rate of air flow into the engine in kg/s
(iii) Brake thermal efficiency
(iv) Brake specific fuel consumption in kg/kWh.