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.

A household refrigerator is a major energy consumer in all homes. The paper aims to evaluate based, on experimental data, the COP of a 65-liter household refrigerator operating with R600a. The main components and instrumentation of the experimental setup are presented. A mathematical model based on the energy balance of the refrigerated enclosure is developed in order to evaluate the COP. Three experimental data sets have been obtained in quasi-steady-state operating conditions. The results point out that the compressor power absorbed from the grid was 60 [W]. The maximum value for the cooling capacity is 81.73 W while the minimum value is 80.24 W. In terms of COP, the maximum value obtained is 1.362, while the minimum one is 1.337. The COP values obtained in the present study are in good agreement with the ones displayed by the manufacturer in the compressor datasheet. Future development is discussed.

The paper presents a theoretical analysis from an energetic and exergetic point of view for a liquid air energy storage system (LAES). This paper identifies upper bounds on the energy and exergetic efficiency for this system. The system uses the simple Linde-Hampson liquefaction cycle for the liquefaction subsystem and the direct expansion method without heating above ambient temperature, for the power generation subsystem. It is known that as the temperature decreases, the destruction of mechanical work input increases due to the irreversibility of working processes. As a result, any irreversible process is very important to observe in cryogenic processes. The purpose of this paper is to develop an exergetic analysis which is then used in a procedure to optimize the Linde installation within the liquid air energy storage system when some functional parameters are changed. The analysis aims to find the functional parameters for which the exergetic efficiency of the installation is maximum. For each subsystem of the simple Linde installation an exergetic product and a fuel were defined and, based on their definition, the coefficient of performance of each functional area was calculated as well as the exergy destructions. Finally, the analysis of system components is presented in order to identify the components that have the greatest impact on energy and exergetic efficiency in an ideal environment. The analytical approach presented in this paper can be applied to other LAES configurations to identify the optimal operating points in terms of energy and exergetic efficiency.

The paper aims to compare and choose the most suitable criteria equation for the computation of the convective heat transfer coefficient on the refrigerant side of the evaporator. The comparison is carried out by considering a given air handling unit equipped with a specific evaporator operating with refrigerant R134a. A mathematical model is given. The results obtained for criteria equations available in the work of Shah (1982), Gungor and Winterton (1987) and Kandlikar (1999) have been compared. The first criterion equation of Shah (1982) is selected because it leads to a value for the evaporator pipe length close to the one measured on the air handling unit and also it can be applied for a wider range of refrigerants used in the field of air conditioning.