Evaporator Frosting in Refrigerating Appliances: Fundamentals and Applications

Christian J. L. Hermes, Joel Boeng, Diogo L. da Silva, Fernando T. Knabben and Andrew D. Sommers
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Christian J. L. Hermes: POLO Laboratories, Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis 88040-900, Brazil
Joel Boeng: POLO Laboratories, Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis 88040-900, Brazil
Diogo L. da Silva: Laboratory of Vehicular Refrigeration, Department of Mobility Engineering, Federal University of Santa Catarina, Joinville 89218-035, Brazil
Fernando T. Knabben: POLO Laboratories, Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis 88040-900, Brazil
Andrew D. Sommers: Department of Mechanical and Manufacturing Engineering, Miami University, 56 Garland Hall, 650 East High Street, Oxford, OH 45056, USA

Energies, 2021, vol. 14, issue 18, 1-23

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.

Keywords: frost; defrost; heat exchanger; refrigeration; appliance (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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