Thermodynamics refrigeration Problem

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SUMMARY

The discussion focuses on solving a thermodynamics problem from "Thermodynamics: An Engineering Approach, 5th Edition," specifically problem 6-138. The scenario involves a refrigerated water fountain cooling water from 22°C to 8°C for a facility with 20 employees, requiring a compressor size calculation. Key parameters include a cooling rate of 0.4 L/hour per person, a heat transfer rate of 45 W from the surroundings, and a coefficient of performance (COP) of 2.9. The user has calculated the mass flow rate of water as 0.00222 kg/s and is seeking guidance on setting up an energy balance to determine the compressor size in watts.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the concept of Coefficient of Performance (COP).
  • Familiarity with energy balance equations in thermodynamics.
  • Knowledge of heat transfer principles and calculations.
  • Ability to perform calculations involving mass flow rates and specific heat capacities.
NEXT STEPS
  • Study the derivation and application of the Coefficient of Performance (COP) in refrigeration systems.
  • Learn how to set up and solve energy balance equations in thermodynamic systems.
  • Research the specific heat capacity of water and its implications in cooling applications.
  • Explore compressor sizing calculations for refrigeration systems, including factors affecting performance.
USEFUL FOR

This discussion is beneficial for mechanical engineers, thermodynamics students, and professionals involved in designing refrigeration systems, particularly those working with water cooling applications.

Bebalo
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Hey, I'm having a bit of trouble with a Thermo problem on a homework assignment. The problem is:

6-138 (Thermodynamics: An Engineering Approach, 5th Edition)

The drinking water needs of a production facility with 20 employees is to be met by a bobbler type water fountain. The refrigerated water fountain is to cool water from 22 C to 8 C and supply cold water at a rate of 0.4 L per hour per person. Heat is transferred to the reservoir from the surroundings at 25 C at a rate of 45 W. If the COP of the refrigeration system is 2.9, determine the size of the compressor, in W, that will be suitable for the refrigeration system of this water cooler.



Using the density of water, I first determined the mass flow rate of the water to be 0.00222 kg/s.

I know that I can use COP=(Ql)/(Qh-Ql)=(Ql)/(Win).

I think the next step I need to take is to set up an energy balance (Sum Ein = Sum Eexit) but I'm not entirely sure how to complete this step.

Thanks in advance for the help.
 
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The rate of Ql is \dot{m}\,c_p\,\Delta{T} ,
and you know COP, and heat out to environment, 45 W.
 
Last edited:

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