M.S. Thesis Presentation by Monifa F. Wright

(Dr. Samuel Shelton, advisor)

"Plate-Fin-and-Tube Condenser Performance and Design for a Refrigerant R-410a Air-Conditioner"

Abstract

Current residential air-conditioners and heat pumps use the hydrochlorofluorocarbon refrigerant, R-22, as the working fluid.  In accordance with the Montreal Protocol, a production ban of all equipment utilizing R-22 will begin in 2005, and a total ban on the production of R-22 is also impending.  A binary zeotropic mixture, R-410a, is a strong candidate for R-22 replacement due to its many favorable performance characteristics; e.g., non-flammability, high working pressures, and good cycle efficiency.

Since R-410a has significantly higher working pressure and vapor densities than R-22, current air cooled finned tube condenser designs are not appropriate. The optimum condenser and other high-pressure-side components are expected to employ smaller diameter tubes, which will effect other design parameters.  At this time, there is limited information about condenser coil design and optimization using R-410a as the working fluid.  Furthermore, the heat transfer and friction data are also limited.

This work includes an examination of the available refrigerant-side two-phase flow heat transfer and pressure drop models for refrigerants.  A model based on first principles is used to predict the performance of a unitary air-conditioning system with refrigerant R-410a as the working fluid.  The seasonal coefficient of performance of the air-conditioning system is used as the figure of merit.  The primary objective of this research was to provide guidelines for the design and optimization of the condenser coil for two distinct criteria:  (1) fixed condenser frontal area (size constraint), and (2) fixed condenser material cost (capital cost constraint).

This study concludes that for both design criteria, the velocity of air flow over the condenser ranges between 7.5 ft/s and 8.5 ft/s while the optimum sub-cool exiting the condenser is approximately 15? F.  It is also concluded that condensers employing tubes of smaller diameters yield the best system performance.  Recommendations for further research into the modeling of the in-tube condensation of refrigerant R-410a are outlined.  An exhaustive search optimization study could not be carried out do to computational limitations, therefore more advanced optimization search techniques are also recommended for further study.