Numerical dynamic simulation of optimized cross-flow heat exchanger with various refrigerants

Abstract

Dynamic behaviors of fluid flow and interaction with the pipe material as well as the temperature are very useful in the design of heat exchangers. The information can be used to determine the effective operating condition and the limitation of the heat exchanger which will then benefited the manufacturers and consumers in terms of economy and safety. A single pass cross flow heat exchanger with conduction and forced convection heat transfer was represented by a mathematical model consist sets of partial differential equations. The equations were then transformed to non-dimensional form for the solution. A computer program was developed to solve the problem numerically. The governing equations were solved by finite difference method using implicit method. Five different types of refrigerant were used in the study; water, R-134a, R-23, R-22 and ammonia. Time response for steady state temperature then was determined and compared between the refrigerants which were then shows that ammonia has the shortest time response and water is the lowest steady state temperature. The results also showed that the tube length affects the air final temperature difference with the increase of temperature difference along with the tube length. The working fluid temperature difference was also affected by tube length with unique behaviors of the increase in temperature with respect to tube length. Finally, maximum air velocity showed the increase with working fluid velocity up to certain magnitude then the air velocity showed negligible change with the increase of working fluid velocity.