Energy and Exergy Analyses of Different Transcritical CO2 Refrigeration Cycles

Year 2018, Volume: 5 Issue: 2, 425 - 436, 31.05.2018

Rabah Gomrı

https://doi.org/10.31202/ecjse.402904

Cited By: 3

Abstract

Carbon dioxide has received increasing
attention owing to its zero ODP and negligible GWP. Furthermore, carbon dioxide
also has desirable thermodynamic properties, such as large specific heat, low
viscosity, and large heat conductivity. Carbon dioxide
CO₂ has low critical pressure and temperature which are 7.36 MPa and
31.1°C, respectively. The low critical temperature causes the heat rejection
process to occur above the critical point and heat absorption process to happen
below the critical point. However, due to the high throttling loss, the energy efficiency of the
basic transcritical CO₂ cycle is lower than that of the conventional
low pressure refrigeration cycle.

In the present
study three different kinds of transcritical carbon dioxide cycles that are the
transcritical cycle with expansion valve (called also the conventional
transcritical cycle), the transcritical cycle with expander and the
transcritical cycle with ejector are analyzed. The effect of operating
parameters on the maximum performance and exergy efficiency of the three cycles
is investigated. Results reveal that replacing the expansion valve by an expander or an ejector does not
only improve the maximum COP and the exregy efficiency but also reduces the
optimal heat rejection pressure.

Keywords

Transcritical, CO2 Refrigeration Cycle, Expansion, COP

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