According to the EU F-gas Regulation, the phase-out of the high global warming potential (GWP) refrigerants (with higher than 150 GWP value) had been established. The most currently existing household and commercial refrigerators and automobile air conditioners applications based on single-stage vapour compression systems operate with R134a as working fluid. The present paper aims, to review and evaluate the performance of a set of eco-friendly alternatives refrigerants to replace R134a, without change or with minor modifications in refrigeration equipment. The theoretical and experimental studies performed in this field of research were reviewed for this objective. These alternative refrigerants are some of HFCs, HFOs and HCs and their mixtures, which are expected to be an excellent candidates in many refrigeration applications. There are Many replacement possibilities had been proposed viz. drop-in replacement, retrofit refrigerant, and new systems. The results exhibited that the most suitable refrigerants as R134a drop-in substitutes are R1234yf, R152a, R450A, and R513A. The pure R1234ze and its mixtures are not suitable drop-in replacements of R134a but can be a good alternative to R134a only in new refrigeration systems. In terms of hydrocarbon refrigerants R290, R600, and R600a could replace R134a with some modifications to existing refrigeration systems to overcome the flammability issue. We should be using certain HFC and HC mixtures with the lowest TEWI index.

The paper presents a literature review regarding defrosting methods for household refrigeration and heat pumps. The literature review covers the period between 2008 and 2020. A number of 61 papers have been studied. The literature review was conducted by dividing the defrost methods into passive and active. Passive methods involve surface coating and off-cycle. The active defrost methods involve reverse cycle, ultrasonic vibration, hot–gas defrost, electric heating and hot fluid. Surface coating and ultrasonic vibration are recent defrost methods proposed in the literature. Also, recently, phase change materials have been used in household refrigerators to improve their efficiency. This is a topic that needs further investigation and is a subject of interest as it can lead to lower energy consumption during defrost cycles. From the present study, the research direction regarding the use of PCMs in defrost cycles can be highlighted.

This paper presents a mathematical model to simulate the effect of the coiling diameter, subcooling degree and internal diameter on the characteristics flow of the refrigerants R1234yf and R600a, flowing through an adiabatic helical capillary tube. The homogeneous flow model was developed in the two-phase region based on the fundamentals of conservation of mass, momentum and fluid energy in the capillary tube. To validate this model, a comparison with numerical data on helical capillary tubes obtained by previous investigators has been made. It was reported that the coiling diameter, the inner diameter and inlet temperature of the capillary tube significantly influence on the pressure drop and quality and temperature distribution of the refrigerants R1234yf and R600a flowing inside the adiabatic helical tube. To validate this model, a comparison with numerical data on helical capillary tubes obtained by previous investigators has been made. Finally, the outcomes obtained from the present model exhibit satisfactory agreement with the available numerical data of helical capillary tubes.

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