General aspects of carbon dioxide as a refrigerant

Carbon dioxide is an innocuous refrigerant for the environment. It is a substance of current interest in the refrigeration area. Its good thermodynamic and heat transfer properties have placed it in an excellent position for substituting refrigerants that contribute to global warming. This paper describes carbon dioxide as a refrigerant, the main characteristics that have made it a substance of current interest, its applications in subcritical and transcritical cycles, and a general vision of its usage at international level. Moreover, this paper presents the disadvantages of using this refrigerant and the upgrades made by the scientific community in order to improve the performance of those systems that work with this fluid. This paper is a reference for those interested in having a wider vision of frigorific technology based on carbon dioxide as a refrigerant

Modeling of the Compression Process for Refrigerants R134a and R1234yf of a Variable Speed Reciprocating Compressor

This paper presents a robust computational model to predict the behavior of a variable speed reciprocating compressor, incorporating infinitesimal displacements to calculate state by state according to the piston movement. The philosophy of the model is to consider eight sub internal processes: heat transfer on the suction and discharge internal lines, pressure drop across the suction and discharge valves, expansion, suction, compression and discharge. The input variables are: pressure and temperature on the suction (before starting the compression process), discharge pressure (after the compression process completed) and rotation speed, with this the model is able to compute the output parameters like: mass flow rate, power consumption and discharge temperature. With the development of the model, the behaviors of R1234yf and R134a are analyzed. Then the model is validated with experimental data using these both refrigerants, concluding that the model predict with an error of ±10% for the mass flow rate and power consumption, and with an error of ±1 K for the discharge temperature. In the validation, differences in energy behavior for the two refrigerants are discussed; the compressor with R1234yf as working fluid increases its power consumption and delivers greater mass flow rate with low temperature compared when the working fluid on the compressor is R134a

Modelado del evaporador de un sistema difusión-absorción: análisis energético y efecto sobre el diseño de un frigobar

En este artículo se presenta como aportación, el desarrollo del modelado de un evaporador que forma parte de un sistema de refrigeración difusión-absorción de pequeña capacidad volumétrica (frigobar). El modelo es basado en fundamentos físicos y correlaciones empíricas, además, se involucran parámetros geométricos de interés como la longitud y el diámetro del evaporador. Se realiza un análisis experimental para obtener los comportamientos térmicos del evaporador bajo tres posiciones del termostato; a través de estos resultados se lleva a cabo la validación del modelo, arrojando errores marginales por debajo del 10%. En base a la buena confiabilidad mostrada por el modelo, este se aplica para la simulación energética del sistema global. Entre los resultados relevantes se pueden conseguir reducciones en la longitud del evaporador sin alterar la capacidad frigorífica y el desempeño energético del sistema experimental, representando esto una oportunidad para los fabricantes en extender su análisis a los diferentes equipos que forman un sistema de difusión-absorción en la búsqueda de mejoras energéticas y condiciones de diseño óptimas

Modeling of the Compression Process for Refrigerants R134a and R1234yf of a Variable Speed Reciprocating Compressor

This paper presents a robust computational model to predict the behavior of a variable speed reciprocating compressor, incorporating infinitesimal displacements to calculate state by state according to the piston movement. The philosophy of the model is to consider eight sub internal processes: heat transfer on the suction and discharge internal lines, pressure drop across the suction and discharge valves, expansion, suction, compression and discharge. The input variables are: pressure and temperature on the suction (before starting the compression process), discharge pressure (after the compression process completed) and rotation speed, with this the model is able to compute the output parameters like: mass flow rate, power consumption and discharge temperature. With the development of the model, the behaviors of R1234yf and R134a are analyzed. Then the model is validated with experimental data using these both refrigerants, concluding that the model predict with an error of ±10% for the mass flow rate and power consumption, and with an error of ±1 K for the discharge temperature. In the validation, differences in energy behavior for the two refrigerants are discussed; the compressor with R1234yf as working fluid increases its power consumption and delivers greater mass flow rate with low temperature compared when the working fluid on the compressor is R134a

Applications of refrigerant R1234yf in heating, air conditioning and refrigeration systems: A decade of researches

International audienc

Applications of refrigerant R1234yf in heating, air conditioning and refrigeration systems: A decade of researches

HFC refrigerants as R134a, R404A, R407C and R410A are commonly used in heating, air conditioning and refrigeration (HACR) systems since Kyoto protocol. However, they are phased-out due to their high global warming potential (GWP). There are various options to replace high GWP refrigerants, among all hydrofluorolefin (HFO) fluids, such as R1234yf, represents an excellent alternative. With GWP <1, R1234yf is a promising substitute for R134a. This paper presents the most relevant researches concerning the application of R1234yf in the last decade. This review paper regroups experimental and theoretical studies which assess the performance of pure R1234yf as working fluid of the compression systems such as mobile and residential air conditioning, air and water heat pump, domestic refrigerator and freezer. Studies depict that R1234yf can be recommended for small-scale systems instead of R134a, but an optimization process is necessary to achieve the optimum operating conditions.Peer reviewe

Energetic and Exergetic Performance Comparison of a Compression-Absorption System Working with NH3-H2O, NH3-LiNO3 and NH3-NaSCN

 The inclusion of a compressor in absorption refrigeration systems is one of the practices that are becoming more common in the refrigeration field, since a lower generation temperature is required. Among the mixtures most used and studied in refrigeration-compression cycles (CARC) are NH3-LiNO3 and NH3-NaSCN. This is mainly due to the assumption that these two mixtures have a better energy efficiency than the conventional absorption refrigeration cycle working with NH3-H2O (BARC). Therefore, this work shows an energy and exergy study of a CARC cycle, in which its analysis extends to the use of the NH3-H2O mixture, to show the potential that presents the mixture for refrigeration and air conditions applications, as well as the advantages and disadvantages to operating in this type of configurations. The results obtained are compared with the mixtures NH3-LiNO3 and NH3-NaSCN at different evaporation, condensation, generation temperatures and different compressor pressure ratio. The results show that the generation temperature, as well as the energetic and exergetic efficiency are strongly dependent on the compressor pressure ratio. For compression ratio values lesser than 1.6, NH3-NaSCN mixture is energetically higher than NH3-H2O and NH3-LiNO3 at generation temperatures higher than 70°C. The results show the three mixtures have very similar exergetic behavior for almost all wide range of operating conditions. When the system works with rp=2.0, the COP of NH3-H2O mixture is 3.26% higher than the other two mixtures, while under the same operations conditions, the energetic behavior is very similar for the three mixtures for different generation and evaporation temperatures