EXERGY & ENERGY ANALYSIS OF THREE STAGE CASCADE REFRIGERATION SYSTEM FOR BIOMEDICAL APPLICATION USING NATURAL REFRIGERANTS

Abstract

Biomedical preservation requires the temperature for the storage of stem cell, blood, sperm & organs at a storage temperature of below -80°C.We can achieve effectively cooling of about -35°C with the help of simple vapour compression refrigeration system. With the help of compound vapour compression refrigeration system, temperature up to – 50 °C is achievable. The cascade refrigeration system is widely used where low temperatures are needed. The natural refrigerant CO2 makes it possible to achieve temperatures as low as -54°C in the low temperature stage. In this case propene is the refrigerant for the upper cascade stage.Using other refrigerants (e.g. ethane) in low temperature circuit temperatures as low as -88oC can be realized. So the required evaporating temperature below -80 °C can be achieved by cascade refrigeration system. Present work deals with thermodynamic analysis of cascade refrigeration system using ozone friendly hydrocarbon refrigerants Iso-butane (R-600a), Propane(R-290) & Ethane (R-170). Iso-butane (R-600a), Propane (R-290) & Ethane (R-170) are the natural refrigerants. These are hydrocarbons. These refrigerants are used as replacement to CFC refrigerant in low temperature applications. These refrigerants have zero ozone depletion potential and less global warming potential. Hydrocarbons are flammable but non toxic. System with charge mass sizes of 0.15 kg or less can be installed in any size of room. Since these refrigerants are pure natural gases, there is no problem of temperature glide as it occurs in azeotropic mixture. This study deals thermodynamically analysis of R-600a, R-290 & R-170, three stage cascade refrigeration system to optimize the operating parameters of the system. The operating parameters include: Condensing, evaporating, sub cooling and superheating temperatures in the high temperature circuit, temperature difference in the cascade heat exchanger, Condensing, evaporating, sub cooling and superheating temperatures in the low & medium temperature circuit. This article presents a thermodynamic analysis to optimize a cascade refrigeration system to be used for biomedical cold-storage application. It can also be used successfully for rapid freezing and storage of frozen food and liquidification of petroleum vapor. A combination of hydrocarbon refrigerants i.e. Isobutene, Propane and Ethane–(R600a, R290 & R170) cascade system has been promoted as a prospective alternative solution to the use of HFC refrigerants.