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This mock test of Basics Of Refrigerating Machine - 2 for Mechanical Engineering helps you for every Mechanical Engineering entrance exam.
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QUESTION: 1

The COP of a heat pump can be increased either by decreasing T_{H} by ΔT or by increasing T_{L} by ΔT. The new COP of the heat pump is

Solution:

Assuming initially

If higher temperature is decreased by 5°C. New conditions

Then the COP of heat pump is

If lower temperature is increased by 5°C.

New conditions

Then the COP of heat pump is

Hence COP will be highest when lower temperature is increased rather than decreasing higher temperature by same amount.

QUESTION: 2

The expression for COP of reversed Brayton cycle is (r_{p} is the pressure ratio)

Solution:

Heat absorbed by the air during constant pressure expansion

= c_{p}(T_{1} - T_{4})

We know work done during the cycle

= Heat rejected - Heat absorbed

Coefficient of performance

We know that for isentropic compression process 1-2.

Similarly, for isentropic expansion process 3-4.

Since, p_{2} = p_{3} and p_{1} = p_{4}, therefore from equations (ii) and (iii)

Now substituting these values in equation (i), we get

QUESTION: 3

A reversible heat engine runs between high temperature T_{1} and low temperature T_{2}. The work output of this heat engine is used to run a reversible refrigeration cycle absorbing heat at temperature T_{3} and rejecting at temperature T_{2}.

What is the COP of the combined system?

Solution:

COP of the combined system

QUESTION: 4

If COP of a refrigerator is 5 and efficiency of a heat engine of the same temperature limit is 50%. Then what is the ratio of heat supplied to engine to heat absorbed by the refrigerator from the space

Solution:

By equating, we get

⇒

QUESTION: 5

COP of a Carnot heat pump operating between -3°C and 27°C is

Solution:

(COP)_{c.p.} = T_{1}/(T_{1} - T_{2})

= 300/(30)

= 10

QUESTION: 6

A condenser of a refrigeration system rejects heat at a rate of 120 kW, while its compressor consumes a power of 30 kW. The COP of the system would be

Solution:

QUESTION: 7

If an engine of 40% thermal efficiency drives a refrigerator having a coefficient of performance of 5, then the heat input to engine for each kJ of heat removed from the cold body of the refrigerator is

Solution:

QUESTION: 8

In the given figure E is a heat engine with efficiency of 0.4 and R is a refrigerator'given that Q_{2} + Q_{4} = 3Q., the COP of the refrigerator is

Solution:

QUESTION: 9

A refrigerator working on reversed Car not cycle absorbs 10 kW power and has a COP of 4. What will be the quantity of heat delivered to a building if it works as a heat pump

Solution:

Hence heat supplied to building

= 40 + 10 = 50 kW

QUESTION: 10

A water chiller with a capacity of 30 tons of refrigeration cools 20 m^{3}/hr of water entering at 12°C. What is the temperature of water leaving the chiller

Solution:

or

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