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Abstract: The world community has committed to eliminate the HCFC-22 refrigerant to a series of deadlines according to the agreements taken during the 19th Montreal Protocol meeting in September 2007. This phase-out, which is already in progress in European Countries, has been accelerated in Article 5 countries. Refrigerant manufactures offer different drop-in refrigerants to replace R22 in existing equipment by non-ozone depleting substances in order to be able to make full use of the remaining life of the plants or different retrofit refrigerants, the use of which implies modifications to the existing systems. This work aims to contribute to the understanding of the implications of the process of R22 substitution, either with drop-in or retrofitting processes, by presenting a theoretical and experimental analysis of the performance of R22, of two drop-in fluids (R422A, R417B) and a retrofit refrigerant (R404A), in a two-stage vapour compression plant over a wide range of evaporating temperatures for a fixed condensing temperature of 40°C. In this communication the main energy parameters, such as cooling capacity and COP are analysed and discussed. [Copyright &y& Elsevier]

A new interactive tool for supporting practical learning in the educational field of refrigeration is presented in this paper. The application, called REFLAB, is used for on-line representation of the main operating variations in real refrigeration plants, such as cooling capacity, power consumption and coefficient of performance. The implementation of this interactive tool covers two groups of practical lessons, in which students operate with two refrigeration plants (a single-stage and a two-stage) and obtain, by means of its graphical interface, the effects produced by changes in the operating conditions. The use of REFLAB allows a quick comprehension of the theoretical concepts explained in class and an intuitive assimilation of the behaviour of the refrigeration plants. The aim of this paper is to explain how the interactive tool works and which are the main objectives pursued in the practical lessons. The paper includes a series of graphical animations that simulate the practice lessons received by the students. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present paper is to describe a general methodology suitable for analysing any intermediate configuration considered in staged vapour compression refrigeration cycles. This general methodology only depends on two basic parameters related to the subcooling and desuperheating obtained in the inter-stage system. A COP expression based on the two basic parameters was obtained from the general configuration. By means of its particularization to seven common configurations, it was then possible to make an energy comparison of the various configurations working with two fluids appropriated for the low temperature domain such as ammonia and R-404A. [Copyright &y& Elsevier]

Abstract: The performance of an Internal Heat Exchanger (IHX) operating in a CO2 transcritical refrigeration plant is analysed, from an energetic point of view, in this work. The evaluation is based on experimental data by contrasting the performance of the plant working with (44 tests) and without the IHX (46 tests) at the same operating conditions. The experimental evaluation covers three evaporating levels (−5, −10 and −15 °C), at two different gas-cooler outlet temperatures each (31, 34 °C), for a wide range of gas-cooler operating pressures (74.5–105.9 bar). The thermal effectiveness of the IHX is empirically analysed for the different operating conditions in the first part of the paper. Moreover, the relation of its effectiveness with the operating parameters is presented. The second part is devoted to analyse the modification of the energetic performance of the plant caused by the IHX. The results show a maximum increment on cooling capacity of 12%, an increment of the efficiency of the plant up to 12% and a maximum increase on discharge temperature of 10 °C at −15 °C of evaporating temperature. [ABSTRACT FROM AUTHOR]

Abstract: This work presents an experimental evaluation, from an energy analysis point of view, for two of the most used inter-stage systems in two-stage vapour compression cycles driven by compound compressors: the direct liquid injection and subcooler systems. The evaluation, considers the two-stage cycle with no intermediate systems as reference cycle and was performed on a plant, driven by a compound compressor using the refrigerant R404A for an evaporating temperature range of −36 to −20 °C and for a condensing temperature range of 30–47 °C. The analysis of the results shows that the inter-stage systems determine the performance of the energy parameters, which are discussed in the paper. The configuration yielding the best results was the two-stage compression cycle with subcooler, since the cooling capacity and COP values for this configuration were the highest. Conversely, the two-stage compression cycle working with direct liquid injection showed lower performance from an energy point of view, though this configuration allows a substantial reduction of the discharge temperature. [Copyright &y& Elsevier]

This 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. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Internal or liquid-suction heat exchangers are used in many refrigeration and air conditioning systems based on the vapour compression cycle, with the basic objective of assuring the entrance of refrigerant in liquid phase to the expansion device. This purpose is achieved by exchanging energy between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant exiting the condenser. These devices can have positive or negative influences on the plant overall energy efficiency, depending on the working fluid and the operating conditions. In this paper the experimental results obtained from a refrigeration test facility with and without the presence of an internal heat exchanger, using R22, R134a and R407C as working fluids, are presented and analyzed, including the impact of pressure drops and variations of refrigerant mass flow rate. A comparison between experimental and theoretical results is also enclosed. [Copyright &y& Elsevier]

In 2014, the Directive 517/2014 was introduced by European Parliament to reduce the use of high-GWP greenhouse gases in the European area in order to limit global climate change in accordance with the objectives marked by the EU Research and Innovation programme Horizon 2020. These restrictions affect the large majority of artificial refrigerants among which R134a is included due to its relatively high GWP 100 (1301). The widely used of R134a in the refrigeration and air conditioning fields reveals the need to identify new low-GWP alternatives. Accordingly, in this work five low-GWP R134a possible choices have been tested and compared in an identical refrigerating facility equipped with a hermetic compressor, under the same operating conditions. The refrigerants used in this analysis are: R290 and R600a (HCs); R134a and R152a (HFCs), and finally, R1234yf and R1234ze(E) (HFOs). All of them have been assayed without changes in the facility, that is, as direct drop-ins . The results obtained from the experimental tests are presented and commented in this work from the energetic point of view. [ABSTRACT FROM AUTHOR]

The EU Regulation 517/2014 has recently been approved in a further attempt to curb the effects of Global Warming. As a consequence, the refrigeration sector is moving towards refrigerants with a low Global Warming Potential (GWP 100 ) in accordance with the limit fixed by these regulations (150). In this regard, the old refrigerant R152a attracts renewed interest due to its low GWP (138) and its similarity to R134a. The present work shows the results of using R152a in a vapour compression plant equipped with a hermetic compressor and an IHX designed for R134a. The refrigerant was replaced by a conventional “drop-in” process in order to carry out an energy comparison. The results have revealed an improvement in the COP with R152a up to 13% despite a reduction in the cooling capacity of about 10%. During the test campaign, R134a hermetic compressors have been shown to be capable of operating with R152a. [ABSTRACT FROM AUTHOR]

Abstract: This work analyses and compares two approaches to evaluate the boiling heat transfer of CO2 in a real evaporation process: classical empirical correlations and flow pattern maps. We develop a finite-volume mathematical model of an evaporator to contrast both approaches and simulate it with four empirical correlations, not developed for CO2 but tested successfully with it, and a flow pattern map specific for CO2. We contrast the results of the simulation with 73 experimental steady-states performed with a transcritical CO2 refrigeration plant that incorporates a concentric counter current evaporator. We observe that both approaches can predict the evaporation process of CO2, nonetheless, in spite of the more complex mathematical formulation, the considered flow pattern map allows to obtain more precision. [Copyright &y& Elsevier]