Ciro Aprea

An evaluation of R22 substitutes performances regulating continuously the compressor refrigeration capacity

Abstract This paper presents the results of an experimental analysis which compares in terms of energetic performances the refrigeration capacity control obtained by means of a variable-speed compressor with the on/off control deriving from a classical thermostatic device. The compressor considered is semi-hermetic reciprocating and is a component of a vapour compression refrigeration plant subjected to a commercially available cold store. The compressor working with the fluids R22, R507 and R407C and designed for a revolution speed corresponding to the compressor supply current nominal frequency of 50 Hz, has been tested varying the frequency in the range 30–50 Hz. In this range, the most suitable working fluids proposed as substitutes of the R22 as the R407C (R32/R125/R134a 23/25/52% in mass), the R507 (R125/R143A 50/50% in mass) and the R417A (R125/R134a/R600 46.6/50/3.4% in mass) have been tested. The results show that, using the R407C, it is possible an average an electric energy consumption about 12% smaller when an inverter is employed to control the compressor refrigeration capacity instead of the thermostatic control which imposes on/off cycles on the compressor, working at the nominal frequency of 50 Hz. So the R407C confirms its superiority in comparison with the R417A and R507; only the R22 shows a better performance.

Experimental evaluation of electronic and thermostatic expansion valves performances using R22 and R407C

An experimental study to evaluate the energetic performances in steady-state and in transient operating modes of an electronic and thermostatic expansion valve is presented. Both valves have been assembled to feed an air cooled evaporator connected to an experimental vapour compression plant with a water cooled condenser operating with a semihermetic compressor. The performances of the valves have been examined at different conditions when the experimental plant works with R22 and with a substitute as the non-azeotropic blend R407C that is chlorine free. Indeed the HCFC designated as R22 contains chlorine that is harmful for the ozone layer and must be replaced in the future. The final results of this study show an overall better performance of the electronic expansion valve compared with the thermostatic expansion valve under transient conditions while in steady-state conditions both the valves are equal in performance. These results apply to both R22 and R407C.

A criterion for predicting the possible advantage of adopting a suction/liquid heat exchanger in refrigerating system

An analysis for evaluating the possible advantage of adopting a suction/liquid heat exchanger, from a thermodynamic point of view, is carried out. To this purpose, a simplified criterion is prented; this is also validated for many working fluids such as chlorofluorocarbon (CFC)s, hydrochlorofluorocarbon (HCFC)s and substitutes on the basis of their thermodynamic properties available in scientific and commercial literature.The criterion is also presented in a graphical form and two examples, referred to as R502 and R32, are given.

Experimental evaluation of R22 and R407C evaporative heat transfer coefficients in a vapour compression plant

The mean heat transfer coeAcients of R22 and R407C in the coaxial counterflow evaporator (20 mm ID) of a refrigerating vapour compression plant have been experimentally measured. The experimental conditions under which heat transfer coeAcients were determined reflect a typical working situation for small-scale refrigeration systems. The heat flux ranged from 1.9 to 9.1 kW/m 2 and the mass flux was varied from 30 to 140 kg/m 2 s. The results illustrate that the R22 heat transfer coeAcient is always greater than that of R407C. Furthermore, a comparison carried out between the experimental data and those predicted by means of the most credited literature relationships showed a strongly overprediction for R407C coeAcients. # 2000 Elsevier Science Ltd and IIR. All rights reserved.

Performance evaluation of R22 and R407C in a vapour compression plant with reciprocating compressor

Abstract In this paper, the problem of R22 phase-out in refrigeration plants is addressed. A comparison is performed between R22 and R407C. The latter seems to be a promising drop-in substitute for the former. Experimental tests are performed in a vapour compression plant with a reciprocating compressor. The objective of this paper is to evaluate the compressor performance using R407C in comparison to R22. The plant overall energetic performance is also evaluated. R22 performance is consistently better than that of its candidate substitute. The difference stems from the different irreversibilities of the plant components arising when using R22 and R407C, respectively. Specific attention is devoted to compressor irreversibilities. Performance indices related to the semi-hermetic compressor are evaluated when using either refrigerant fluid. The investigation has revealed that R22 performs better than R407C mainly because of a better compression process due to a number of factors, including the facts that the isoentropic and volumetric efficiencies of the semi-hermetic compressor are better than that of R407C.

An exergetic analysis of R22 substitution

This paper deals with the substitution of R22 in an experimental vapour compression plant with the most widely used drop-in substitute, i.e. the zeotropic mixture R407C. A comparative exergetic analysis, carried on with experimental tests, has been presented. The experimental tests are performed in a vapour compression plant working with water and air as secondary fluids in the condenser and in the evaporator, respectively. The overall exergetic performance of the plant working with R22 is consistently better than that of its candidate substitute. The performance of the individual components of the plant has been analysed, in order to pinpoint those contributing most to the decrease in the exergetic performance of R407C.

A numerical approach to a very fast thermal transient in an air cooling evaporator

A numerical study of the performance of an air cooling evaporator inserted in a climatic chamber in the presence of a very fast thermal transient is considered. The climatic chamber is a confined environment that allows one in the presence of air, to submit for a short time a certain product to a particular thermal stress. In fact, according to some international standards, it is necessary to analyse the response of some type of products, that then will be used under severe condition, such as a sudden heating and cooling, to obtain an acceptable future operative life. Heating and cooling cycles are obtained in the confined environment respectively by means of an electrical resistance and of an air cooling evaporator linked to a vapour compression system. To study the cooling thermal cycle an air cooling evaporator numerical model has been obtained according to the hypotheses of a homogeneous model for the refrigerant and of an incompressible and one-dimensional flow for the air flowing onto the evaporator. Finally, the numerical model results have been compared with the experimental ones in terms of the evaporator outlet refrigerant temperature, the air temperature and of the evaporator outlet air relative humidity. This comparison is very satisfactory, as it shows that this study is very useful to permit proper design of the vapour compressor plant and its particular control system.

An air cooled tube-fin evaporator model for an expansion valve control law

For control purposes, a mathematical model of a tube-fin evaporator of a vapour compression plant running with R22 is analyzed. The refrigerant behavior in an evaporating region is described by a homogeneous model. The balance equations, together with the constitutive equations, determine a differential system which makes explicit the mechanism of dynamic behavior. At first, the numerical solution of the steady state is obtained, both in evaporating and superheated regions. Moreover, the numerical analysis allows us to evaluate the transition phase and to locate the interface. Subsequently, various analytical aspects are discussed. For the nonlinear two-phase flow, the dependence of the solution on the boundary data is estimated by means of a qualitative analysis. Then, a linearized model for the single-phase flow is deduced and solved explicitly. The analytical solution is compared with the numerical results and the degree of superheating is estimated in terms of the model parameters.

Behaviour and performances of R502 alternative working fluids in refrigerating plants

Abstract This is an experimental study that aims to evaluate both general characteristics and system performances of the most credited fluids that are likely to substitute for R502 in a refrigeration plant. R402A, R402B, R403B and R408A (still containing HCFC) and R404A, R407A and FX40 (chlorine free) have been tested. Generally, both of them have showed performances very close to those of R502 except R403B, whose COP has been found to be about 8% lower than that of R502.

Condensation heat transfer coefficients for R22 and R407C in gravity driven flow regime within a smooth horizontal tube

Abstract The quasi local heat transfer coefficients of R22 and R407C in the coaxial counterflow condenser (20 mm ID) of a refrigerating vapour compression plant have been experimentally measured. The experimental conditions under which the heat transfer coefficients were determined reflect a typical working situation for small scale refrigeration systems. The plant runs with low mass fluxes of refrigerant within the range of 45.5–120 kg/m2/s. During the experimental tests the pressure at the inlet of the test condenser varies within a fixed range between 15.2 and 14.3 bar. The results illustrate that the R22 heat transfer coefficient is always greater than that of R407C. Furthermore, comparisons between the experimental data and the values predicted by means of the most credited literature relationships for gravity-driven condensation are reported.