Abstract: The Montreal protocol and Kyoto protocol underlined the need of substitution of CFC’s and HCFC’s due to their adverse impact on atmospheric ozone layer which protects earth from U.V rays. The CFCs have been entirely ruled out since 1995 and a long-term basis HCFCs must be replaced by 2020. All this events motivated HFC refrigerants which are harmless to ozone layer. In this paper thermodynamic analysis of cascade refrigeration system has been done using three different refrigerant pairs R13-R12, R290-R23, and R404A-R23. Effect of various operating parameters i.e. evaporator temperature, condenser temperature, temperature difference in cascade condenser and low temperature cycle condenser temperature on performance parameters viz. COP, exergetic efficiency and refrigerant mass flow ratio have been studied. Thermodynamic analysis shows that out of three refrigerant pairs R12-R13, R290-R23 and R404A-R23 the COP of R290-R23 refrigerant pair is highest.
Abstract: The present work deals with optimization of cascade refrigeration system using eco friendly refrigerants pair R507A and R23. R507A is azeotropic mixture composed of HFC refrigerants R125/R143a (50%/50% by wt.). R23 is a single component HFC refrigerant used as replacement to CFC refrigerant R13 in low temperature applications. These refrigerants have zero ozone depletion potential and are non-flammable. Optimization of R507AR23 cascade refrigeration system performance parameters such as minimum work required, refrigeration effect, coefficient of performance and exergetic efficiency was carried out in terms of eight operating parameters- combinations using Genetic Algorithm tool. The eight operating parameters include (1) low side evaporator temperature (2) high side condenser temperature (3) temperature difference in the cascade heat exchanger (4) low side condenser temperature (5) low side degree of subcooling (6) high side degree of subcooling (7) low side degree of superheating (8) high side degree of superheating. Results show that for minimum work system should operate at high temperature in low side evaporator, low temperature in high side condenser, low temperature difference in cascade condenser, high temperature in low side condenser and low degree of subcooling and superheating in both side. For maximum refrigeration effect system should operate at high temperature in low side evaporator, high temperature in high side condenser, high temperature difference in cascade condenser, low temperature in low side condenser and higher degree of subcooling in LT and HT side. For maximum coefficient of performance and exergetic efficiency, system should operate at high temperature in low side evaporator, low temperature in high side condenser, low temperature difference in cascade condenser, high temperature in low side condenser and higher degree of subcooling and superheating in low side of the system.
Abstract: The present work deals with thermodynamic analysis
of cascade refrigeration system using ozone friendly refrigerants pair
R507A and R23. R507A is azeotropic mixture composed of HFC
refrigerants R125/R143a (50%/50% wt.). R23 is a single component
HFC refrigerant used as replacement to CFC refrigerant R13 in low
temperature applications. These refrigerants have zero ozone
depletion potential and are non-flammable and as R507A an
azeotropic mixture there is no problem of temperature glide. This
study thermodynamically analyzed R507A-R23 cascade refrigeration
system to optimize the design and operating parameters of the
system. The design and operating parameters include: Condensing,
evaporating, subcooling and superheating temperatures in the high
temperature circuit, temperature difference in the cascade heat
exchanger, Condensing, evaporating, subcooling and superheating
temperatures in the low temperature circuit.
Abstract: Capacity and efficiency of any refrigerating system
diminish rapidly as the difference between the evaporating and
condensing temperature is increased by reduction in the evaporator
temperature. The single stage vapour compression refrigeration
system is limited to an evaporator temperature of -40 0C. Below
temperature of -40 0C the either cascade refrigeration system or multi
stage vapour compression system is employed. Present work
describes thermal design of main three heat exchangers namely
condenser (HTS), cascade condenser and evaporator (LTS) of
R404A-R508B and R410A-R23 cascade refrigeration system. Heat
transfer area of condenser (HTS), cascade condenser and evaporator
(LTS) for both systems have been compared and the effect of
condensing and evaporating temperature on heat-transfer area for
both systems have been studied under same operating condition. The
results shows that the required heat-transfer area of condenser and
cascade condenser for R410A-R23 cascade system is lower than the
R404A-R508B cascade system but heat transfer area of evaporator is
similar for both the system. The heat transfer area of condenser and
cascade condenser decreases with increase in condensing temperature
(Tc), whereas the heat transfer area of cascade condenser and
evaporator increases with increase in evaporating temperature (Te).
Abstract: Capacity and efficiency of any refrigerating system
diminish rapidly as the difference between the evaporating and
condensing temperature is increased by a reduction in the evaporator
temperature. The single stage vapour compression refrigeration
system using various refrigerants are limited to an evaporator
temperature of -40 0C. Below temperature of -40 0C the either
cascade refrigeration system or multi stage vapour compression
system is employed. Present work describes thermal design of
condenser (HTS), cascade condenser and evaporator (LTS) of
R404A-R508B and R410A-R23 cascade refrigeration system. Heat
transfer area of condenser, cascade condenser and evaporator for
both systems are compared and the effect of condenser and
evaporator temperature on heat-transfer area for both systems is
studied under same operating condition. The results shows that the
required heat-transfer area of condenser and cascade condenser for
R410A-R23 cascade system is lower than the R404A-R508B cascade
system but heat transfer area of evaporator is similar for both the
system. The heat transfer area of condenser and cascade condenser
decreases with increase in condenser temperature (Tc), whereas the
heat transfer area of cascade condenser and evaporator increases with
increase in evaporator temperature (Te).