2023 · Paper 1

Complete GATE CH 2023 Paper 1 overview, original pages and practice · Timed previous-paper practice

Questions 55–57 of 65. Imported answers require review unless explicitly marked reviewed.

Question 55

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CHNAT2 marksNeeds review

A perfectly insulated, concentric tube countercurrent heat exchanger is used to cool lubricating oil using water as a coolant (see figure below). Oil enters the outer annulus at a mass flow rate of 2 kg·s



with a temperature of 100 °C and leaves at 40 °C. Water enters the inner tube at a mass flow rate of 1 kg·s



with a temperature of 20 °C and leaves at 80 °C. Use specific heats of oil and water as 2089 J·kg



·K



and 4178 J·kg



·K



, respectively. There is no phase change in both the streams. Under steady-state conditions, the number of transfer units (NTU) is ______ (in integer).



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Question 56

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CHNAT2 marksNeeds review

Partially saturated air at 1 bar and 50 °C is contacted with water in an adiabatic saturator. The air is cooled and humidified to saturation, and exits at 25 °C with an absolute humidity of 0.02 kg water per kg dry air. Use latent heat of vaporization of water as 2450 kJ·kg



, and average specific heat capacity for dry air and water, respectively as 1.0 kJ·kg



·K



and 4.18 kJ·kg



·K



. If the absolute humidity of air entering the adiabatic saturator is



kg water per kg dry air, the value of



is __________ (rounded off to two decimal places).

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Question 57

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CHNAT2 marksNeeds review

Distillation of a non-reactive binary mixture with components



and



is carried out in a batch still as shown in the figure below. The initial charge of the mixture in the still is 1 kmol. The initial and final amounts of



in the still are 0.1 kmol and 0.01 kmol, respectively. Use a constant relative volatility of 4.5. The mole fraction of



remaining in the vessel is ______ (rounded off to three decimal places).



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