Engineering

Chemical EngineeringQ&A Library6.21. A refrigerator is the opposite of a heat engine: it uses work supplied from theenvironment to move heat from a cold to a hot reservoir, effectively keepingthe former at a lower temperature. The coefficient of performance measures the efficiency of this process, defined by omaximum value of o that is possible according to the second law.Qcl/W. Find anexpression for theQuestion

Asked Oct 6, 2019

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This problem is (6.21) from a book "Thermodynamics and Statistical Mechanics An Integrated Approach by M. Scott Shell"

Step 1

Efficiency of refrigerator is measured by coefficient of performance

COP of a refrigerator is written as:

Where Q_{C} = Heat removed from the cold reservoir

W = work required to lift the liquid

Step 2

From the second law of thermodynamic it is not possible to transfer heat from lower temperature to higher temperature.

From the first law of thermodynamic work required W is given as:

Where Q_{h} is heat transfer to the hot reservoir

Q_{c }is heat transfer from the cold reservoir

Step 3

Carnot engine is the most efficient engine. It is an ideal engine.

From the Carnot cycle it can be written as

Where Th = source temperatu...

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