MODELLING AND OPTIMIZATION OF COEFFICIENT OF PERFORMANCE OF LOWER TEMPERATURE CYCLE OF TWO-STEP REFRIGERATION SYSTEMS

A. D. Ogunsola; M. Y. Kolawole; A. A. Aderibigbe; O. Olaogun; A. J. Adeyi; O. Adeyi; M. O. Ibiwoye; M. O. Adetunji

A. D. Ogunsola Department of Mechanical Engineering, Ladoke Akintola University of Technology, P.M.B.4000, Ogbomoso, Oyo State. Nigeria
M. Y. Kolawole Department of Mechanical Engineering, Kwara State University, Malete, Kwara State
A. A. Aderibigbe Department of Mechanical Engineering, Ladoke Akintola University of Technology, P.M.B.4000, Ogbomoso, Oyo State. Nigeria
O. Olaogun Department of Mechanical Engineering, Kwara State University, Malete, Kwara State
A. J. Adeyi Department of Mechanical Engineering, Ladoke Akintola University of Technology, P.M.B.4000, Ogbomoso, Oyo State. Nigeria
O. Adeyi Department of Chemical Engineering, Michael Okpara University of Agriculture, P.M.B 7267, Umudike, Abia State, Nigeria.
M. O. Ibiwoye Department of Mechanical Engineering, Kwara State University, Malete, Kwara State
M. O. Adetunji Department of Mechanical Engineering, Ladoke Akintola University of Technology, P.M.B.4000, Ogbomoso, Oyo State. Nigeria

Keywords: COP, Sub-cooling, Superheating, Refrigeration, Cascade, Refrigerant

Abstract

The coefficient of performance (COP) of a single-stage refrigeration system is low, thus there is a need for two-step refrigeration systems when there is a desire to have an evaporator temperature that is below -25 oC. The COP of the lower temperature cycle of the two-step refrigeration systems is a function of the COP of the refrigeration systems.This research aimed at optimizing COP of the lower temperature cycle of two-step refrigeration systems using eco-friendly refrigerants.Thermodynamic analysis of these refrigeration systems was performed by varying seven operating parameters. R-134a was used in the high-temperature cycle (HTC) and R-23 was used in the low-temperature cycle (LTC). The coefficient of performance of the lower temperature cycle (COP.REF[LTC]) of the refrigeration systems was optimized using Half Factorial Design of Design-Expert 12.0.1. The influence of the condensing temperature (TC,HTC),evaporating temperature (TE,HTC), cascade temperature difference (∆TCAS,DIFF), evaporating temperature (TE,LTC), superheating temperature (TSUP,LTC), sub-cooling temperature (TSUB,LTC), and refrigerant mass Flow rate (ṁHTC)was investigated on the values of COP.REF[LTC] of the refrigeration systems. The highest value of COP.REF[LTC] (18.1) was obtained under optimum conditions of the 30 TC,HTCoC , -40 TE,HTCoC, 0 ∆TCAS,DIFFoC, -50 TE,LTCoC, 0 TSUP,LTCoC, 20 TSUB,LTCoC and 0.01 ṁHTC kg/s.The study revealed that all the factors having interaction with TC[HTC] and TE[HTC] have a great influence on the value of COP.REF[LTC]