# Recent questions and answers in Thermodynamics

In an ideal Brayton cycle, atmospheric air (ratio of specific heats, $c_p$/$c_v$ = $1.4$, specific heat at constant pressure = $1.005$ $kJ/kg.K$) at $1$ $bar$ and $300$ $K$ is compressed to $8$ $bar$. The maximum temperature in the cycle is limited to $1280$ $K$. If the heat is supplied at the rate of $80$ $MW$, the mass flow rate (in $kg/s$) of air required in the cycle is _______
The thermodynamic cycle shown in figure ($T$-$s$ diagram) indicates reversed Carnot cycle reversed Brayton cycle vapor compression cycle vapor absorption cycle
Which of the following statements are TRUE with respect to heat and work? They are boundary phenomena They are exact differentials They are path functions both $(i)$ and $(ii)$ both $(i)$ and $(iii)$ both $(ii)$ and $(iii)$ only $(iii)$
The internal energy of an ideal gas is a function of temperature and pressure volume and pressure entropy and pressure temperature only
For an ideal gas, a constant pressure line and a constant volume line intersect at a point, in the Temperature $(T)$ versus specific entropy $\text{(s)}$ diagram. $C_{P}$ is the specific heat at constant pressure and $C_{V}$ is the specific heat at constant volume.The ratio of the slopes of the constant ... $\dfrac{C_{P}}{C_{V}} \\$ $\dfrac{C_{P}-C_{V}}{C_{V}} \\$ $\dfrac{C_{V}}{C_{P}}$
For an ideal gas, the value of the Joule-Thomson coefficient is positive negative zero indeterminate
In a new temperature scale degree(symbol)P ,the boiling point of water is 100 degree(symbol)P and the freezing point of water is 300 degree(symbol)P .Find the reading corresponding to 0 degree(symbol)P in centrigrade scale . Solve the question and explain each step properly with detailed solutions
If a mass of moist air contained in a closed metallic vessel is heated, then its Relative humidity decreases. Relative humidity increases. Specific humidity increases. Specific humidity decreases.
One kg of air, initially at a temperature of $127^{\circ}C$ , expands reversibly at a constant pressure until the volume is doubled. If the gas constant of air is $287\: J/kg.K$, the magnitude of work transfer is ________ $kJ$ (round off to $2$ decimal places).
Air (ideal gas) enters a perfectly insulated compressor at a temperature of $310\: K$. The pressure ratio of the compressor is $6$. Specific heat at constant pressure for air is $1005\: J/kg . K$ and ratio of specific heats at constant pressure and constant ... the difference in enthalpies of air between the exit and the inlet of the compressor is _________ $kJ/kg$ (round off to nearest integer).
For an ideal Rankine cycle operating between pressures of $30$ bar and $0.04$ bar,the work output from the turbine is $903\: kJ/kg$ and the work input to the feed pump is $3\: kJ/kg$. The specific steam consumption is _________ $kg/kW.h$ round off to $2$ decimal places).
The indicated power developed by an engine with compression ratio of $8$, is calculated using an air-standard Otto cycle (constant properties). The rate of heat addition is $10\: kW$. The ratio of specific heats at constant pressure and constant volume is $1.4$. The ... efficiency of the engine is $80$ percent. The brake power output of the engine is _________$kW$ (round off to one decimal place).
For a simple compressible system, $v, s, p$ and $T$ are specific volume, specific entropy, pressure and temperature, respectively. As per Maxwell's relations, $\bigg( \dfrac{\partial v}{\partial s} \bigg) _p$ is equal to $\bigg( \dfrac{\partial s}{\partial T} \bigg) _p \\$ ... $- \bigg( \dfrac{\partial T}{\partial v} \bigg) _p \\$ $\bigg( \dfrac{\partial T}{\partial p} \bigg) _s$
Which one of the following modifications of the simple ideal Rankine cycle increases the thermal efficiency and reduces the moisture content of the steam at the turbine outlet? Increasing the boiler pressure Decreasing the boiler pressure Increasing the turbine inlet temperature decreasing the condenser pressure
During a non-flow thermodynamic process $(1-2)$ executed by a perfect gas, the heat interaction is equal to the work interaction $(Q_{1-2} = W_{1-2})$ when the process is Isentropic Polytropic Isothermal Adiabatic
Air of mass $1$ kg, initially at $300$ K and $10$ bar, is allowed to expand isothermally till it reaches a pressure of $1$ bar. Assuming air as an ideal gas with gas constant of $0.287 \: kJ/kg.K$, the change in entropy of air (in $kJ/kg.K$, round off to two decimal places) is ______
A gas is heated in a duct as it flows over a resistance heater. Consider a $101 \: kW$ electric heating system. The gas enters the heating section of the duct at $100 \: kPa$ and $27^{\circ} C$ with a volume flow rate of $15 m^3/s$. If heat is lost from the gas in the duct to the surrounding at a ... $32^{\circ} C$ $37^{\circ} C$ $53^{\circ} C$ $76^{\circ} C$
If one mole of $H_2$ has occupies a rigid container with a capacity of $1000$ litres and the temperature is raised from $27^{\circ} C$ to $37^{\circ} C$, the change in pressure of the contained gas (round off to two decimal places), assuming ideal gas behaviour, is _______ Pa. $(R=8.314 \: J/mol \cdot K)$
Ambient air is at a pressure of $100 \: kPa$, dry bulb temperature at $30^{\circ} C$ and $60 \%$ relative humidity. The saturation pressure of water at $30^{\circ} C$ id $4.24 \: kPa$. The specific humidity of air (in $g/kg$ of dry air) is _______ (correct to two decimal places).
A standard vapor compression refrigeration cycle operating with a condensing temperature of $35^{\circ}C$ and an evaporating temperature of $-10^{\circ}C$ develops $15 \: kW$ of cooling. The $p-h$ diagram shows the enthalpies at various states. If the isentropic efficiency of the compressor is $0.75$, the magnitude of compressor power (in $kW$) is _________ (correct to two decimal places)
For an ideal gas with constant properties undergoing a quasi-static process, which one of the following represents the change of entropy $(\Delta s$) from state $1$ to $2$? $\Delta s = C_p \ln \bigg( \dfrac{T_2}{T_1} \bigg) - R \ln \bigg( \dfrac{P_2}{P_1} \bigg) \\$ ... $\Delta s = C_V \ln \bigg( \dfrac{T_2}{T_1} \bigg) + R \ln \bigg( \dfrac{V_1}{V_2} \bigg)$
A tank of volume $0.05 \: m^3$ contains a mixture of saturated water and saturated steam at $200 ^{\circ}C$. The mass of the liquid present is $8 \: kg$. The entropy (in $kJ/kg \: K$ ... $s_{fg}=4.1014 \: kJ/kg \: K, \: s_f=2.3309 \: kJ/kg \: K$
The volume and temperature of air (assumed to be an ideal gas) in a closed vessel is $2.87 m^{3}$ and $300 \: K$, respectively. The gauge pressure indicated by a manometer fitted to the wall of the vessel is $0.5$ bar. If the gas constant of air is $R=287 \: J/kg.K$ and the atmospheric pressure is $1$ bar, the mass of air (in $kg$) in the vessel is $1.67$ $3.33$ $5.00$ $6.66$
One kg of an ideal gas (gas constant $R= 287\: J/kg.K$) undergoes an irreversible process from state-$1$ ($1$ bar, $300 \: K$) to state-$2$ ($2$ bar, $300\: K$). The change in specific entropy $(s_{2} - s_{1})$ of the gas (in $J/kg.K$) in the process is _________.
A mass $m$ of a perfect gas at pressure $p_{1}$ and volume $V_{1}$ undergoes an isothermal process. The final pressure is $p_{2}$ and volume is $V_{2}$. The work done on the system is considered positive. If $R$ is the gas constant and $T$ ... $RT \ln \dfrac{V_{2}}{V_{1}} \\$ $-mRT \ln \dfrac{P_{2}}{P_{1}}$
A mixture of ideal gases has the following composition by mass: $\begin{array}{|c|c|c|} \hline N_2 & O_2 & CO_2 \\ \hline 60\% & 30\% & 10 \% \\ \hline \end{array}$ If the universal gas constant is $8314 \: J/kmol-K$, the characteristic gas constant of the mixture (in $J/kg-K$) is ________
Work is done on an adiabatic system due to which its velocity changes from $10$ $m/s$ to $20$ $m/s$, elevation increases by $20$ $m$ and temperature increases by $1$ $K$. The mass of the system is $10$ $kg$, $C_v$ = $100$ $J/(kg.K)$ and gravitational ... $kJ$) on the system is _______
A pure substance at $8$ $MPa$ and $400^0C$ is having a specific internal energy of $2864$ $kJ/kg$ and a specific volume of $0.03432$ $m^3$/$kg$. Its specific enthalpy (in $kJ/kg$) is _______