Vapor Compression Refrigeration Simulation And Tutorial

Calculation intensive courses lead to the need to integrate computer technology into the classroom, especially in courses such as Applied Thermodynamics at the University of Portland (ME 332). ME 332 is the second in the series of thermodynamics courses offered at the University of Portland; therefore the opportunity arises for the implementation of interactive tools for ease of calculations. Once the students have mastered the concepts and ability to perform the necessary manual calculations, computer programs can be used to allow the students to study more advanced topics in the material without being bogged down in the calculations. To ease the considerable calculations involved in solving vapor-compression refrigeration (VCR) cycle problems in the course, a text-based computer program was written, complete with property evaluation for 3 three substances, by L.J. Genik and C.W. Somerton at Michigan State University. This program has recently been revised to be compatible with the Microsoft Windows operating environment prevalent today in engineering software. In addition, a fourth refrigerant, R-134a, was added to account for the addition of new refrigerants in use today. Another modification made to the program was the addition of a tutorial for the thermal system analysis of a VCR cycle. This tutorial emulates the general solution methodology used in the course and reinforces the concepts with the students. The program is available via current web pages for the described course. Introduction The evaluation of thermodynamic systems can become a long and tedious process, though an important one for students to learn and master. Several cycles are continually taught in applied thermodynamics courses such as the Rankine cycle for steam power systems, the Brayton cycle for gas turbine systems, vapor-compression for refrigeration systems. Within the applied thermodynamics course at the University of Portland, these cycles are taught along with deviations from these cycles. A thorough investigation into the operation of these cycles can be facilitated with the use of the computer to ease the property evaluation process. There are several good, commercially available programs and solvers for implementing such solutions; however, for economic reasons we have chosen to developed an in-house program. Beyond the economics of the situation, it is also the belief of the authors that value exists in writing and understanding thoroughly the ’black box’ being used by students for solving problems. The computer program utilizes equations of state and fundamental thermodynamic relations to perform a systems analysis. The first law of thermodynamics P ge 512.1 is used to evaluate the energy transfers for the ideal vapor compression refrigeration (VCR) cycle with either the operating temperatures or pressures known, the mass flow rate and the isentropic efficiency of the compressor, Figure 1. The program was originally written in FORTRAN and has been recently converted to Microsoft Visual Basic to allow for a graphical user interface (GUI). Along with this conversion, a tutorial was added which defines the working components of the system and steps through the methodology for solving cycles using VCR as an example. The program allows for the user to do repeated calculations of the VCR cycle which would allow the student to begin to gain insight into how various changes effect the heat transfer, coefficient of performance (COP), and required work. Figure 1 Input Dialogue Box