JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III THERMAL ENGINEERING II Previous Question Paper (February - 2022 - R13)

The adiabatic flame temperature is the maximum theoretical temperature reached by the products of combustion when a fuel is burned in a perfectly insulated environment (adiabatic process) with no heat loss to the surroundings and no work done by the system. It represents the temperature at which the chemical energy released by the combustion reaction is entirely absorbed by the products, raising their internal energy.

In a steady-flow combustion process, the adiabatic flame temperature is determined by the energy balance where the enthalpy of the reactants equals the enthalpy of the products:

The process is often represented on a temperature-enthalpy diagram where the heat released during combustion is plotted against the temperature rise of the gas mixture. The intersection of the heat release curve and the sensible heat capacity curve of the product gases indicates the adiabatic flame temperature. Factors influencing this temperature include the air-fuel ratio, the initial temperature of reactants, and the degree of dissociation of product gases at high temperatures.

The Rankine cycle is the fundamental thermodynamic cycle for steam power plants. It consists of four processes: 1-2 (Isentropic compression in a pump), 2-3 (Constant pressure heat addition in a boiler), 3-4 (Isentropic expansion in a turbine), and 4-1 (Constant pressure heat rejection in a condenser).

On a P-v diagram, the cycle is represented by a closed loop where the pump work is a small area on the left and turbine work is a larger area on the right. On a T-s diagram, the process 2-3 shows the heating of water to steam, 3-4 shows the expansion through the turbine, 4-1 shows condensation, and 1-2 shows the liquid compression.

The efficiency of the Rankine cycle is derived as follows:

1. Work done by turbine: W_t = h_3 - h_4
2. Work input to pump: W_p = h_2 - h_1
3. Heat added in boiler: Q_in = h_3 - h_2
4. Net work output: W_net = (h_3 - h_4) - (h_2 - h_1)
5. Thermal efficiency: η = W_net / Q_in = ((h_3 - h_4) - (h_2 - h_1)) / (h_3 - h_2)

Assuming the pump work is negligible compared to the turbine work, the efficiency simplifies to η ≈ (h_3 - h_4) / (h_3 - h_2).