GATE Overflow for GATE XE - Recent questions and answers in Thermodynamic Cycles

GATE XE 2026 | Question: 86

Tue, 24 Feb 2026 15:40:20 +0000

Consider an ideal Otto-cycle with cold-air-standard assumptions to be applicable. The temperature of the working fluid at the start and the end of the compression process is $300$ $\mathrm{K}$ and $750$ $\mathrm{K}$, respectively. For the working fluid take the ratio of the specific heat capacities as $1.4$. The thermal efficiency (in $\%$) of the cycle is $\_\_\_\_$ (rounded off to two decimal places).

GATE XE 2026 | Question: 90

Tue, 24 Feb 2026 15:39:22 +0000

Consider an ideal Rankine cycle with fixed conditions at the turbine inlet. If the condenser pressure is lowered, which of the following statements is/are CORRECT?

Pump work input remains the same.
Moisture content at turbine exit decreases.
Heat rejected in the condenser decreases.
Turbine work output increases.

GATE XE 2025 | Question: 92

Sun, 04 May 2025 19:05:58 +0000

If $\gamma$ refers to the ratio of specific heats, the air-standard efficiency of an Otto cycle is

$1-\frac{1}{(\text { Compression ratio })^{\gamma}}$
$1-\frac{1}{(\text { Pressure ratio) } ^{\frac{\gamma-1}{\gamma}}.}$
$1-\frac{1}{(\text { Compression ratio })^{(\gamma-1)}}$
$1-\frac{1}{(\text { Pressure ratio })^{(\gamma-1)}}$

GATE XE 2025 | Question: 97

Sun, 04 May 2025 19:05:50 +0000

For an ideal gas turbine cycle, $T_{1}$ and $T_{3}$ are the compressor inlet temperature and turbine inlet temperature respectively. The ratio $\frac{T_{3}}{T_{1}}$ is denoted by $t$ and the ratio of specific heats is denoted by $\gamma$. For any given $t$, the optimum pressure ratio for the maximum specific work output is

$t^{\frac{2}{(\gamma-1)}}$
$t^{\frac{\gamma}{2(\gamma-1)}}$
$t^{\frac{\gamma}{(\gamma-1)}}$
$t^{\frac{\gamma-1}{\gamma}}$

GATE XE 2025 | Question: 101

Sun, 04 May 2025 19:05:40 +0000

Air in an ideal Diesel cycle is compressed from $3 \: \mathrm{litre}$ to $0.15 \: \mathrm{litre}$. It then expands during a constant pressure heat addition process to $0.3 \: \mathrm{litre}$. If the ratio of specific heats, $\gamma=1.4$, the thermal efficiency (in $\%$ ) of the cycle is $\_\_\_\_\_\_\_$ (rounded to one decimal place).

GATE XE 2024 | Question: 93

Sun, 21 Jul 2024 16:41:27 +0000

Consider the following data from a Brayton cycle.

Enthalpy at inlet to turbine; $1400 \mathrm{~kJ} / \mathrm{kg}$

Enthalpy at exit of turbine: $880 \mathrm{~kJ} / \mathrm{kg}$

Enthalpy at exit of compressor: $600 \mathrm{~kJ} / \mathrm{kg}$

On adding a regenerator of effectiveness equal to $0.8$, the absolute value of percentage change in heat addition is __________ $\text{(rounded off to the nearest integer)}$.

GATE XE 2023 | Question: 88

Wed, 14 Feb 2024 18:08:57 +0000

\begin{tabular}{|l|l|}
Q.98 & \begin{tabular}{l}
An ideal Diesel cycle has a compression ratio of 20 and cut-off ratio of 1.5. At the \\
beginning of the compression stroke, air is at $100 \mathrm{kPa}, 300 \mathrm{~K}$. Use the \\
cold-air-standard assumptions with property value $c_{p}=1.005 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}$. Assume \\
$c_{p} / c_{v}=1.4$. For this cycle, the net work output per unit mass is
\end{tabular} \\
\hline

& $335 \mathrm{~kJ} / \mathrm{kg}$ \\
\hline
& $395 \mathrm{~kJ} / \mathrm{kg}$ \\
\hline
& $500 \mathrm{~kJ} / \mathrm{kg}$ \\
\hline
& $165 \mathrm{~kJ} / \mathrm{kg}$
\end{tabular}

GATE XE 2023 | Question: 95

Wed, 14 Feb 2024 18:08:51 +0000

Q. 105 A refrigerator operates on an ideal vapor compression cycle between the pressure limits of $140 \mathrm{kPa}$ and $800 \mathrm{kPa}$. The working fluid is the refrigerant R-134a. The refrigerant enters the compressor as saturated vapor at $140 \mathrm{kPa}$ and exits at 800 $\mathrm{kPa}$ and $60{ }^{\circ} \mathrm{C}$. It leaves the condenser as a saturated liquid at $800 \mathrm{kPa}$. The coefficient of performance (COP) of the refrigerator is (rounded off to two decimal places).
Use the following property data for R-134a:
At $140 \mathrm{kPa}$ :
$h_{f}=27.06 \mathrm{~kJ} / \mathrm{kg}$, $h_{g}=239.19 \mathrm{~kJ} / \mathrm{kg}$
At $800 \mathrm{kPa}$ :
$h_{f}=95.48 \mathrm{~kJ} / \mathrm{kg}$,
$h_{g}=267.34 \mathrm{~kJ} / \mathrm{kg}$
At $800 \mathrm{kPa}$ and $60^{\circ} \mathrm{C}: \quad h=296.82 \mathrm{~kJ} / \mathrm{kg}$

GATE XE 2023 | Question: 96

Wed, 14 Feb 2024 18:08:49 +0000

Q. 106
A steam power plant operates on a simple ideal Rankine cycle. The condenser pressure is $10 \mathrm{kPa}$ and the boiler pressure is $5 \mathrm{MPa}$. The steam enters the turbine at $600^{\circ} \mathrm{C}$. Mass flow rate of the steam is $50 \mathrm{~kg} / \mathrm{s}$. Neglecting the pump work, the net power output of the plant is MW (rounded off to one decimal place).

Use the following property data for water:
At $10 \mathrm{kPa}$ :
\[
\begin{array}{l}
h_{f}=191.81 \mathrm{~kJ} / \mathrm{kg}, \quad h_{f g}=2392.82 \mathrm{~kJ} / \mathrm{kg}, \quad h_{g}=2584.63 \mathrm{~kJ} / \mathrm{kg} \\
s_{f}=0.6492 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}, \quad s_{f g}=7.5010 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}, \quad s_{g}=8.1502 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}
\end{array}
\]

At $5 \mathrm{MPa}$ and $600{ }^{\circ} \mathrm{C}$ :
\[
h=3666.47 \mathrm{~kJ} / \mathrm{kg}, \quad s=7.2588 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}
\]