Numerical Investigations on Supercritical Heat Transfer Characteristics of Environmental Friendly Refrigerants

Abstract

The heat transfer of supercritical fluids is a vastly growing field, specifically to find suitable alternatives to replace conventional R134a, which can be beneficial for climate change. Most of the experimental and numerical investigations have been conducted to explore supercritical water, carbon dioxide and R134a as heat transfer working fluids. Hydrofluoroolefin (HFO) and refrigerants blends have been considered the most environment-friendly refrigerants to replace Chlorofluorocarbons (CFCs), Hydrochlorofluoro-carbons (HCFCs) and Hydrofluorocarbons (HFCs). Their main advantage of zero Ozone Depletion Potential (ODP) and comparatively lower Global Warming Potential (GWP) have attracted growing amount of attention to mitigate environmental issues. This work adopts the computational method and takes the environmentally friendly refrigerants to investigate the heat transfer characteristics under widely used shear-stress transport (SST) model. A comprehensive comparison was performed at reduced pressure of 1.10 for supercritical fluids R515A, R1234ze(E) and R134a. The peaks of heat transfer coefficient occurred in the vicinity of pseudo critical temperature for all of these considered fluids; however, R134a resulted in higher heat transfer coefficient, Reynolds number and Prandtl number in comparison with R515A and R1234ze(E). The higher heat transfer coefficient of supercritical fluid R134a is owing to its thermophysical properties and the specific heat plays crucial role in the heat transfer of supercritical fluids. Owing to environmental issues, R515A can be a considerable replacement of R134a. R1234ze(E) is also promising alternative to R134a; however, safety issues should thoroughly concern its mild flammable characteristics.

Current status of the thermohydraulic behavior of supercritical refrigerants: A review

“…As a continuation of the previous study, Ibrahim et al [88,89] published two works about numerical work on supercritical cooling as well. In the first work [88], R515A (blend of R1234ze and R227ea) was studied.…”

“…Again, a new correlation was suggested based on the simulation data (with a more accurate one when the correlation is region dependent, either T b < T pc or T b ≥ T pc ). In a second work [89], results on R515A, R1234zeE and R134a were published. In this work, the three refrigerants were compared to each other for different working conditions.…”