The applicability of an existing tube condenser model when used with refrigerant R-407C
Abstract
The Montreal Protocol resulted in the phase out of ozone depleting refrigerants like chloroflourocarbons (CFC) and hydrochloroflourocarbons (HCFC) used in refrigeration and heat pump applications. In heat pump applications the environmentally friendly refrigerant mixture, R-407C, usually replaces these refrigerants. The use of these zeotropic refrigerant mixtures has technical implications when the performance of refrigeration systems in industry is evaluated. These zeotropic mixtures display a temperature glide during the condensation process, which can be exploited to improve heat exchanger performance. In the past decade, research also focused on the enhancement of the heat transfer area by applying passive schemes. Limited information is available on the condensation characteristics of R-407C inside fluted tube annuli. Nevertheless, Rousseau et al. (2003) claimed that their correlation could be used to simulate a zeotropic mixture inside fluted tube annuli. Therefore, a need exists to investigate the applicability of the correlation by Rousseau et al. (2003) for R-407C condensation inside fluted tube annuli.
In order to evaluate the correlation, experimental data was gathered from a fluted tube test facility. The test section consists of a pre-, test- and sub-cooler. The refrigerant's mass flow rate, temperature and pressure were measured at each inlet and outlet of the condensers as well as the water's temperature and mass flow rate. The experimental results proved that the correlation of Rousseau et al. (2003) was only 48% accurate in predicting the pressure drop and 95% accurate for the heat transfer of R-407C during the condensation process inside fluted tube annuli. Due to this inexactness, new enhancement factors for pressure drop and heat transfer were derived from comparing the experimental data against the simulation results. These newly generated enhancement factors were implemented in the conelation of Rousseau et al. (2003) and predicted the theoretical pressure drop with a 90.48% accuracy and the heat transfer with a 99.48% accuracy. Thus, this method is acceptable to predict the data for design applications.
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