Modelling and experimental validation of the hot-gas defrost process of an air-cooled evaporator

Simulation based identification of the ideal defrost start time for a heat pump system for electric vehicles

“…Liu et al (2003) showed simulation results of a model of an air-source heat pump during hot-gas defrost. Dopazo et al (2010) predicted the required time and needed energy of the hot-gas defrost process of an air-coil evaporator using a transient simulation model and validated it with experimental data. But none of these models was able to handle frosting as well as defrosting.…”

A modeling study on alleviating uneven defrosting for a vertical three-circuit outdoor coil in an air source heat pump unit during reverse cycle defrosting

“…Defrosting could be realized by a number of methods including: (1) compressor shut-down defrosting [18], (2) electric heating defrosting [19,20], (3) hot water spray defrosting [7], and (4) hot gas by-pass defrosting [21][22][23][24][25]. Currently, reverse cycle defrosting is the most widely standard defrosting method used for ASHP units [5,[8][9][10][11][12][13][14][15][16][17][26][27][28].…”

“…On the other hand, an effective alternative to experimentally studying the defrosting performance in an ASHP unit is via numerical approach and therefore, the last two decades saw a growing number of modeling studies [16,17,[23][24][25][26][27] on defrosting operations. Noticeable, Krakow et al firstly developed a hot gas defrosting model for evaporators [23,24], and later presented an idealized reverse cycle defrosting model for an ASHP unit with a receiver [26,27].…”

“…Noticeable, Krakow et al firstly developed a hot gas defrosting model for evaporators [23,24], and later presented an idealized reverse cycle defrosting model for an ASHP unit with a receiver [26,27]. Dopazo et al also developed a detailed transient simulation model for hot-gas bypass defrosting in an air-cooled evaporator [25]. In the above mentioned defrosting models, the effects of downwards flowing of the melted frost due to gravity along the surface of a multi-circuit outdoor coil on the defrosting performance all were neglected, by assuming either no water retention on coil surface or a stable water layer.…”

Modeling and Numerical Investigation of Hot Gas Defrost on a Finned Tube Evaporator Using Computational Fluid Dynamics

“…Despite these limitations, their model's energy distribution was validated against experimental data. Dopazo et al [8] divided the whole defrosting process into six consecutive stages: preheating, tube frost melting start, fin frost melting start, air presence, tube-fin water film and dry heating. Different governing equations are applied for each stage depending on the nature and physical phenomena occurring during the stage.…”