Modelling and Optimization of Heat Absorbed in the Evaporator of Low Temperature Cycle of Two-Step Cascade Refrigeration Systems
1,*Olafimihan, E. O., 1*Ogunsola, A. D., 1Adeyi, A. J., 2Adeyi, O., 1Aderibigbe, A. A., 3Aworanti, O. A.
1,Department of Mechanical Engineering, Ladoke Akintola University of Technology, P.M.B.4000, Ogbomoso, Oyo State. Nigeria.
2Department of Chemical Engineering, Michael Okpara University of Agriculture, P.M.B 7267, Umudike Abia State, Nigeria.
3Department of Chemical Engineering, Ladoke Akintola University of Technology, P.M.B.4000, Ogbomoso, Oyo State. Nigeria
A single-stage refrigeration system has a low Coefficient of Performance (COP), thus it becomes paramount to have cascade refrigeration systems when there is need to have an evaporator temperature that is below -25 oC. Heat absorbed (QE) in the evaporator of low temperature cycle of two-step cascade refrigeration systems is one of the two parameters that determine the COP of the lower temperature cycle of the two-step refrigeration systems which is also a function of the COP of the cascade refrigeration systems. This research aimed at modelling and optimizing QE of the lower temperature cycle of two-step cascade refrigeration systems using eco-friendly refrigerants. Thermodynamic of the cascade refrigeration systems was performed by varying seven operating parameters using refrigerants R-134a in the High Temperature Cycle (HTC) and R-23 in the Low Temperature Cycle (LTC). Heat absorbed in the evaporator of the lower temperature cycle (QE[LTC]) of the refrigeration systems was optimized using Half Factorial Design of Design-Expert 12.0.1. The influence of the evaporating temperature (TE,HTC), condensing temperature (TC,HTC), cascade temperature difference (ΔTCAS,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 QE[LTC] of the refrigeration systems. The numerical QE[LTC] value is 14.183 while the measured value is 14.81.The study revealed that all the factors having interaction with TC[HTC] and TE[HTC] have a great influence on the value of QE[LTC].
Keywords: Heat absorbed, Coefficient of Performance, High Temperature Cycle, Low Temperature Cycle, Refrigerants, Cascade