A dynamic mathematical model of a shell-and-tube evaporator. validation with pure and blend refrigerants

Abstract

SUMMARYThis work presents a mathematical model of a shell-and-tube evaporator based on mass continuity, energy conservation and heat transfer physical fundamentals. The model is formulated as a control volume combination that represents the different refrigerant states along the evaporator. Since the model is based on refrigerant and secondary fluid states prediction, it can be easily adapted for modelling any type of evaporator. The strategy of working with physical fundamentals allows the steady-and dynamic-state analysis of any of its performance variables. The paper presents a steady-state validation made with two pure refrigerants (HCFC-22, HFC-134a) and with a zeotropic blend (HFC-407C), and a dynamic validation with transient experimental tests using HCFC-22. The model prediction error is lower than 5% and it is well in accordance with actual dynamic behaviour.

Experimental evaluation of the energy efficiency of a CO2 refrigerating plant working in transcritical conditions

“…The second one, which is used to supply the evaporator with the refrigerant load, consists of a loop working with an ethylene-glycol mixture (50/50% by volume) that enables a constant pressure to be maintained in the evaporator. Further information about the auxiliary systems can be found in previous works presented by the authors [24].…”

Influence of the superheat associated to a semihermetic compressor of a transcritical CO2 refrigeration plant

“…Plant regulation and data validation are performed by two auxiliary systems [23]. The first one is devoted to control the heat rejected in the gas-cooler, which uses water as cooling fluid, and the second one is used to supply the refrigeration load to the evaporator, which operates with an ethylene-glycol water mixture (50%/ 50% by volume) as working fluid.…”

A dynamic model of a shell-and-tube condenser operating in a vapour compression refrigeration plant

“…It is therefore a good tool to understand how the condenser operates and its influence on the complete vapour compression system. This effect is analysed by comparing the theoretical response of a previously presented evaporator model [11] with the one obtained using the condenser model. …”