Numerical optimization of multi-stage cascaded refrigeration-heat pump system

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Abstract

A multi-stage cascades refrigeration-heat pump system is numerically optimized, with overall coefficient of performance and total operating costs as the objective function. System cycle considered includes the effects of subcooling, superheating, irreversibilities, approach, overlap and ambient temperatures, and costs of water and electricity are incorporated therein. To facilitate the estimation of optimum performance of the system, the main design parameters such as interstage and condensing temperatures, economic water rates, heating effects, power requirements and overall coefficients of performance are presented for unit tonnage capacity in the form of graphs over evaporator and ambient temperatures ranges of −70–−30°C and 10–60°C, respectively. The effects of various operating variables on the optimum design quantities are displayed in tables and figures as well. Most widely used and comparatively cheaper refrigerant R-12 is selected for the heat pump system and R-13 for the refrigeration subsystem. Besides, two-stage compression is followed for the former subsystem while single-stage compression is followed for the latter one. For the ranges of operating parameters/variables considered, overall COPs in the range of 2.5–7.4 can be achieved.

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