ISRO Scientist or Engineer Refrigeration & Air-Conditioning 2020

Instructions

For the following questions answer them individually

Question 71

A two stage centrifugal compressor operating at 3000 rpm is to compress refrigerant R134a from an evaporator temperature of $$O^\circ C (h_i = 398.6 kJ/kg)$$ to a condensing temperature of $$32^\circ C (h_e = 419.8 kJ/kg)$$. If the impeller diameter of both the stages have to be same, what is the diameter of the impeller?
Assume suction condition to be dry saturated, compression process isentropic, impeller blades radial and refrigerant enters impeller radially

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Question 72

Water with specific heat $$(c_p = 4 kJ/kgK)$$ is fed to a boiler at $$30^\circ C$$, the enthalpy of vaporization at atmospheric pressure in the boiler is 2400 kJ/kg, the steam coming from the boiler is 0.9 dry. The net heat supplied (in kJ/kg) in the boiler is

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Question 73

Subsonic and supersonic diffusers have the following geometry

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Question 74

The isentropic heat drop in the nozzle of an impulse steam turbine with nozzle efficiency 0.9, blade velocity ratio 0.5 and mean blade velocity 150 m/s in kJ/kg is

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Question 75

Consider a simple gas turbine (Brayton cycle) and a gas turbine with perfect regeneration. In both the cycles, the pressure ratio is 8 and the ratio of specific heats of working medium is 1.5. The ratio of minimum to maximum temperatureis 0.2 (with temperature in K) in the regenerative cycle. The ratio of the thermal efficiency of the simple cycle to that of tpseneralive cycle is

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Question 76

A simply supported beam PQ is loaded by a moment of 1 kN-m at the mid span of the beam of length 1 m. The reaction forces $$R_p and R_q$$ at supports P and Q respectively are

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Question 77

Two solid shafts โ€˜Aโ€™ and โ€˜Bโ€™ are made of the same material. The shaft โ€˜Aโ€™ is 50 mm diameter and shaft โ€˜Bโ€™is 100 mm diameter.The ratio of strength of shaft โ€˜Bโ€™ compared to shaft โ€˜Aโ€™is

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Question 78

Two simply supported beams โ€˜Aโ€™ and โ€˜Bโ€™ of same breadth and depth and same material carries constant central load W at the centre. The span of beam B is double that of beam A. The deflection of beam B compared to beam A will be

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Question 79

In a beam where shear force changes its sign, the bending moment will be

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Question 80

The rectangular beam โ€˜Aโ€™ has length l, width b and depth d. Another beam โ€˜B of same material has the same length and width but depth is double that of โ€˜Aโ€™. The elastic strength of beam B compared to that of A will be

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