PROBLEM OF THE WEEK - Mechanical: Thermal & Fluids NCEES Problem 139

Problem 139 in the NCEES Mechanical Practice Exam for Thermal & Fluids Systems is a classic problem that involves finding the coefficient of performance (COP) of a heat pump. You are given a table of the pressure, temperature, and most importantly the enthalpy at all four points in the cycle. (Note the enthalpy at point 4 equals that at point 3.) The problem and NCEES solution are very straightforward and you should have no trouble following the steps.

However, there have been problems where you are told that the evaporator has so many “degrees of superheat,” or the condenser has so many “degrees of subcooling.” What do these terms mean? The purpose of this presentation is to explain how these fit into the standard heat pump cycle. By the way, these terms could also show up for an air conditioner or refrigerator, but they mean the same for the respective elements of the cycle. - Dr. Tom

Dr. Tom’s Solution to Mechanical: Thermal & Fluids NCEES Problem 139
 

DTC recommends that anyone taking the PE Exam purchase the NCEES Practice Exam for the exam they are taking. It is an essential exam review resource. https://account.ncees.org/exam-prep/

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