Evaporator Frosting in Refrigerating Appliances: Fundamentals and Applications

Abstract

Modern refrigerators are equipped with fan-supplied evaporators often tailor-made to mitigate the impacts of frost accretion, not only in terms of frost blocking, which depletes the cooling capacity and therefore the refrigerator coefficient of performance (COP), but also to allow optimal defrosting, thereby avoiding the undesired consequences of condensate retention and additional thermal loads. Evaporator design for frosting conditions can be done either empirically through trial-and-error approaches or using simulation models suitable to predict the distribution of the frost mass along the finned coil. Albeit the former is mandatory for robustness verification prior to product approval, it has been advocated that the latter speeds up the design process and reduces the costs of the engineering undertaking. Therefore, this article is aimed at summarizing the required foundations for the design of efficient evaporators and defrosting systems with minimized performance impacts due to frosting. The thermodynamics, and the heat and mass transfer principles involved in the frost nucleation, growth, and densification phenomena are presented. The thermophysical properties of frost, such as density and thermal conductivity, are discussed, and their relationship with refrigeration operating conditions are established. A first-principles model is presented to predict the growth of the frost layer on the evaporator surface as a function of geometric and operating conditions. The relation between the microscopic properties of frost and their macroscopic effects on the evaporator thermo-hydraulic performance is established and confirmed with experimental evidence. Furthermore, different defrost strategies are compared, and the concept of optimal defrost is formulated. Finally, the results are used to analyze the efficiency of the defrost operation based on the net cooling capacity of the refrigeration system for different duty cycles and evaporator geometries.

How Do Science Content Misconceptions Occur in Primary School Teachers with Teaching Certificates?

“…The misconception experienced by teachers on the concept of changes in the form of objects is that teachers think that the changes in the form of objects that occur in ice flowers in the freezer are changes in the form of objects by freezing, besides that there are also teachers who think that changes in the form of objects occur by condensing. Scientifically, the cause of ice flowers in the freezer is actually the change of water vapor to freeze through the desublimation process (Malik et al, 2020;Hermes et al, 2021). Desublimation is the process of changing the form of objects from water vapor to ice without going through the liquid phase (Jitendra et al, 2022;Qi et al, 2022).…”

Optimized Placement of Frost-Measuring Sensors in Heat Exchangers via Image Processing of Frost Formation Pattern

“…The presence of frost acts as a thermal barrier, reducing thermal performance and restraining heat transfer between air and refrigerant [4,5], besides increasing the energy consumption [6][7][8]. The influence of frost should be taken into account during the design and dimensioning of the HX, as without an appropriate design and defrosting method, the buildup of frost restricts or even blocks airflow between fins, resulting in increased energy consumption, lower performance, degradation of refrigeration conditions, decreased product safety and quality, or even system damage [9,10]. Figure 1 provides a visual representation of the frost formation process in a heat exchanger.…”