List of top General Engineering Questions on Thermodynamics asked in GATE PI

In an air-standard Otto cycle, the pressure and temperature of air just before the compression stroke are 200 kPa and 26.85 °C, respectively. The combustion process is assumed to be a constant volume process, where 1.02 MJ/kg heat is added. The cycle efficiency is 50%. The adiabatic index \(γ\) and specific heat at constant volume \(C_v\) can be considered to be constant during the process (corresponding values taken at the mean cycle temperature).
Assuming that the ideal gas law is applicable, \(γ = \frac 43\) and \(c_v= 0.85\ kJ/kg-K\), the maximum pressure (in MPa) reached during the cycle is _____ . (Rounded off to 1 decimal place)
In an ideal air-standard Brayton cycle, air enters the compressor at 100 kPa and 300 K. Thermal efficiency of the cycle is 50 %. The heat added to air is 1000 kJ/kg. Air has constant specific heat \( c_p = 1.0 \, \text{kJ/(kg-K)} \) and \( \gamma = 1.4 \). Air temperature, in K, at the turbine inlet is ..................
Two metal sheets are joined using resistance spot welding. A welding current of 4500 A is applied for 0.2 s. The effective contact resistance at the sheet interface is \(400 \times 10^{-6} \, \Omega\). The thermal efficiency of the welding process is 50%. The amount of heat, in J, used for producing a spot weld is ................. (in integer).
An arc welding operation is performed at 25 V and 200 A at welding speed of 2 mm/s. The heat used for melting is 80% of the total heat generated. The unit melting energy of the metal to be joined is 10 J/mm$^3$. The volume of the weld metal produced per unit time, in mm$^3$/s, is ................. (in integer).
Water flows through a pipe of diameter 0.02 m. The Reynolds number of the flow is 1000. The pipe is heated from outside with a uniform heat flux. The flow and heat transfer in the pipe are steady and fully developed. The thermal conductivity of water is 0.66 W/(m-K). The convective heat transfer coefficient, in W/(m$^2$-K), is ................. (round off to 2 decimal places).
Under steady state conditions, superheated steam enters the turbine with enthalpy, $h_1 = 3200$ kJ/kg and wet steam leaves the turbine at pressure $p_2 = 0.1$ bar. The heat loss is 100 kJ/kg and work output is 1000 kJ/kg. Kinetic and potential energies for inflow and outflow are neglected. At pressure 0.1 bar, the enthalpy of saturated liquid is 200 kJ/kg and the enthalpy of vaporization is 2400 kJ/kg. The dryness fraction of the steam at the exit of the turbine is ................. (round off to 2 decimal places).
Two plane parallel surfaces exchange heat by thermal radiation. A radiation shield is placed in between at equal distance from the two surfaces to reduce heat transfer. All surfaces are black with infinite length and width. The ratio of heat transfer rate between surfaces with and without radiation shield is