Refrigeration and Air-conditioning: Assignment 3

1. The optimum intermediate pressure P2 in a two-stage air compressor having P1 and P3 as a suction and delivery pressures respectively, equal to

 

 

 

 

Ans: a

1 point

2. In vapor compression refrigeration system, a refrigerant exists in the form of liquid between

 evaporator and compressor

 compressor and condenser

 condenser and expansion valve

 all of the above

Ans: c

1 point

3. A multistage air compressor as compared to single stage compressor

 Gives more uniform torque

 Reduces work done per kg of air

 Improves volumetric efficiency for a given pressure ratio

 All of the above

Ans: d

1 point

4. Phenomenon of choking in compressor means

 No flow of air

 Fixed mass flow rate regardless of pressure ratio

 Reducing mass flow rate with increase in pressure ratio

 Increased inclination of chord with air stream

Ans: b

1 point

 5. In a multistage compression system with flash gas removal, fluid at the entry of the expansion valve before the evaporator is

 dry and saturated vapor

 

superheated vapor

 vapor quality 0<x<1.0

 

saturated liquid

Ans: b

1 point

6. A single-acting two-stage compressor with inter cooling delivers air at 16 bar. Assuming an intake state of 1 bar at 15°C, the pressure ratio per stage is

 16

 8

 4

 2

Ans: 4

1 point

7. What is the highest possible theoretical efficiency of a heat engine operatingwith a hot reservoir of furnace gases at 2100°C when the cooling water available is at 15°C ?

 87.80 %

 78.67 %

 89.27 %

 87.52 %

Ans: a

1 point

Read the following and answer questions 8-10.

A refrigeration compressor of 50 mm bore and 40 mm stroke operates at a speed of 1460 rpm between condensing and evaporating pressure limits of 1.219 MPa and 0.151 MPa. The clearance ratio is 5% ratio of specific heats of refrigerant is 1.18, specific volume of refrigerant at suction is 0.11 m3/kg and the enthalpy change of refrigerant in the evaporator is 93.7 kJ/kg.


8. The Volumetric efficiency is

 

0.7564

 

0.2315

 

 0.06263

 

0.36515

Ans: a

1 point

 9. Mass flow rate of refrigerant, kg/sec

 

0.4605

 

 0.11753

 

0.07231

 

0.01314

Ans: d

1 point

10. Refrigeration load the compressor can serve, kW

 

1.862

 1.231

 2.32

 4.561

Ans: b