HCFC-22 replacement with drop-in and retrofit HFC refrigerants in a two-stage refrigeration plant for low temperature

[EN] 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.The authors are indebted to the Spanish Ministry of Education and Science (CTM2008-06468-CO2-02/TECNO) and to the Spanish Ministry of the Environment and Rural and Marine Affairs (200800050084716) for their economic support for the present work.Llopis, R.; Torrella Alcaraz, E.; Cabello, R.; Sanchez, D. (2012). HCFC-22 replacement with drop-in and retrofit HFC refrigerants in a two-stage refrigeration plant for low temperature. International Journal of Refrigeration. 35(4):810-816. https://doi.org/10.1016/j.ijrefrig.2012.01.001S81081635

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

[EN] 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.Llopis, R.; Cabello, R.; Navarro-Esbrí, J.; Torrella Alcaraz, E. (2007). A dynamic mathematical model of a shell-and-tube evaporator. Validation with pure and blend refrigerants. International Journal of Energy Research. 31(3):232-244. doi:10.1002/er.1243S23224431

Second law analysis of two-stage vapour compression refrigeration plants

[EN] This paper describes a Second Law Analysis based on experimental data of a two-stage vapour compression facility driven by a compound compressor for medium and low-capacity refrigeration applications, which operates with the most usual inter-stage configurations (direct liquid injection and subcooler). The experimental analysis is performed for an evaporating temperature range between 36 degrees C and 20 degrees C and for a condensing temperature range between 30 degrees C and 47 degrees C using the refrigerant R-404A. The final results are compared with energy analysis from previous works. Additionally, a new criterion of equivalence between the simple vapour compression cycle and the two-stage compression cycle is given.The authors are indebted to the Spanish Ministry of Education and Science (CTM2008-06468-C02-02/TECNO) and to the Spanish Ministry of the Environment and Rural and Marine Affairs (200800050084716) for their economic support to this work.Torrella Alcaraz, E.; Llopis, R.; Cabello, R.; Sanchez, D.; Larumbe, J. (2010). Second law analysis of two-stage vapour compression refrigeration plants. International Journal of Exergy. 7(6):641-653. https://doi.org/10.1504/IJEX.2010.035512S6416537

Experimental comparison between R152a and R134a working in a refrigeration facility equipped with a hermetic compressor

[EN] The EU Regulation 517/2014 has recently been approved in a further attempt to curb the effects of GlobalWarming. As a consequence, the refrigeration sector is moving towards refrigerants with a low GlobalWarming Potential (GWP100) 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.The authors acknowledge Jaume I University of Spain, who financed partially the present study through the research project P1.B2013-10.Cabello, R.; Sanchez, D.; Llopis Doménech, R.; Armendáriz Araúzo, LM.; Torrella Alcaraz, E. (2015). Experimental comparison between R152a and R134a working in a refrigeration facility equipped with a hermetic compressor. International Journal of Refrigeration. 60:92-105. https://doi.org/10.1016/j.ijrefrig.2015.06.021S921056

Experimental evaluation of the energy performance of an air vortex tube when the inlet parameters are varied

The paper presents the analysis of the energy performance of an air vortex cooling tube under variations of the air inlet properties, with three independent experimental tests validated through the energy balance in the device. The experimental analysis includes the following variations of the input conditions: First, the effect of the air inlet pressure to the vortex tube, focused on the analysis of temperature variations in the output cold stream and in the cooling capacity when the cold flow fraction varies. Second, we studied air inlet temperature variations to the vortex tube under different cold flow fractions, which is an analysis not found in the literature. And finally, is studied the performance of the vortex tube when the insulation is provided or in absence of insulation.Torrella Alcaraz, E.; Patiño, J.; Sánchez, D.; Llopis, R.; Cabello, R. (2013). Experimental evaluation of the energy performance of an air vortex tube when the inlet parameters are varied. Open Mechanical Engineering Journal. 7(1):98-107. doi:10.2174/1874155X01307010098S981077

On-line quizzes to evaluate comprehension and integration skills

This work demonstrates the use of a 2.0 tool, namely, Socrative, to evaluate one of the cross-curricular competences indicated by the Universitat Politècnica de València, specifically, comprehension and integration. It has been applied to the courses in different areas: sciences, engineering and languages. As part of its implementation, activities were proposed that could be done at the beginning, during or at the end of the class to, on the one hand, help students acquire the knowledge associated with the course(s), and on the other, gather evidence that demonstrates acquisition of said competence. The results show a high level of satisfaction by the students with the use of the Socrative tool as an element to promote active participation and the acquisition of the cross-curricular competence of comprehension and integration; therefore, its extension to other courses has been suggested

Energy evaluation of R152a as drop in replacement for R134a in cascade refrigeration plants

An experimental comparison has been performed of a cascade refrigeration facility working with the refrigerant pairs R134a/R744 and R152a/R744. This kind of facility is suitable for industrial and commercial refrigeration applications. The high GWP refrigerant R134a has been substituted with the low GWP refrigerant R152a, in accordance with the new environmental regulations aimed at mitigating the Greenhouse effect. As both refrigerants belong to the family of HFC fluids, the replacement has been carried out as a drop-in. Apart from safety considerations, as R152a is included in the A2 group, the results of the wide range of tests conducted show that no special energy improvement or worsening is achieved, and that the replacement of R134a with R152a is technically and energetically feasible.The authors gratefully acknowledge the financial support for the present work provided by the Spanish Ministry of Economy and Competitiveness (research project ENE2014-53760-R)

Nuevos fluidos fluorados de bajo GWP (PCA)

El uso de refrigerantes fluorados de elevado GWP o PCA (Poder de Calentamiento Atmosférico), está siendo cuestionado por nuestra legislación tanto a nivel europeo como a nivel estatal, tal y como se pone de manifiesto en las últimas reglamentaciones aprobadas por la comunidad europea que van encaminadas hacia una mayor restricción en el uso de los mismos. Es evidente que las firmas comerciales fabricantes de dichos fluidos son muy conscientes del problema que esto supone, por lo que se encuentran en continuo proceso de desarrollo de nuevos fluidos que cumplan no sólo con la actual normativa, sino con futuras reglamentaciones de carácter más restrictivas. En este trabajo, se pretende pasar revista a las opciones disponibles actualmente o con previsiones futuras para la sustitución de los tres HFCs de mayor implantación industrial y elevado valor de PCA, esto es, el R404A (y el R507A), el R410A y el R134a

Experimental evaluation of the inter-stage conditions of a two-stage refrigeration cycle using a compound compressor

[EN] The aim of the present paper is to detail an analysis, based on experimental data, of the inter-stage working conditions of a two-stage vapour compression facility equipped with a compound compressor, which operates with the most usual inter-stage configurations (two-stage with direct liquid injection and two-stage with subcooler) in medium- and low-capacity commercial refrigeration applications. The experimental analysis is performed in an evaporating temperature range between -36 and -20 degrees C, and in a condensing temperature range between 30 and 47 degrees C, using one of the fluids most widely-used in Europe for low-temperature applications, the R-404a. The inter-stage working temperature/pressure obtained in the tests has been contrasted with the two usual criterion of the optimum working conditions definition: the arithmetical mean of the refrigerant condensing and evaporating temperatures and the criterion of equal pressure ratios in both stages. This paper presents the differences and affinities with the criterion and analyses the influence of the intermediate systems (direct liquid injection and subcooler) on the inter-stage operating conditions.The authors are indebted to the Generalitat Valenciana for partial support under project GV05/091.Torrella Alcaraz, E.; Llopis, R.; Cabello, R. (2009). Experimental evaluation of the inter-stage conditions of a two-stage refrigeration cycle using a compound compressor. International Journal of Refrigeration. 32(2):307-315. https://doi.org/10.1016/j.ijrefrig.2008.05.006S30731532

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

[EN] This work presents a mathematical model of a shell-and-tube condenser based on mass continuity, energy conservation and heat transfer physical fundamentals, whose methodology can be easily adapted for modelling any type of condenser. The model is formulated as a combination of control volumes that represents all the refrigerant states in the condenser and the liquid receiver function, which is carried out by the condenser of the experimental plant. Model validation is performed by using steady-state data and transient tests from an experimental vapour compression plant; the prediction error of the model is lower than 5% and a good representation of the dynamic performance of the condenser is achieved. A theoretical comparison involving the importance of the dynamic responses of the evaporator and the condenser at the plant is also presented.The authors are indebted to the Generalitat Valenciana for partial support under programme Formación de Personal Investigador (FPI) CTBPRB/2005/105 and project GV05/091.Llopis, R.; Cabello, R.; Torrella Alcaraz, E. (2008). A dynamic model of a shell-and-tube condenser operating in a vapour compression refrigeration plant. International Journal of Thermal Sciences. 47(7):926-934. https://doi.org/10.1016/j.ijthermalsci.2007.06.021S92693447