TY - JOUR
T1 - Frost formation non-uniformity in a multi-circuit V-shape evaporator
AU - Alvandifar, Negar
AU - Kristofersson, Johannes
AU - Forooghi, Pourya
PY - 2024/1
Y1 - 2024/1
N2 - Formation of frost on outdoor evaporators poses a significant challenge for air source heat pumps operating in cold climates. It is widely recognized that uneven air-flow across an evaporator can have a negative impact on both the evaporator's performance and the overall efficiency of the heat pump. This study investigates the influence of non-uniform air-flow distribution on a V-shaped outdoor evaporator as a component of an air-source transcritical CO
2 heat pump when subjected to frosting conditions. To this end, we developed and validated against independent experiments a numerical frost-formation model, and used it to study a multi-circuit evaporator of interest under different ambient conditions. It is shown that the uneven air-flow distribution results in varying frost formation patterns across different circuits of the heat exchanger, including differences in the amount of frost accumulated and its distribution among the individual tubes; the circuit with the largest frost weight accumulates 18% more frost compared to the one with the smallest in one hour under the sever frosting condition. Non-uniform frost formation also leads to air-flow distribution changing over time, and the rate at which this change occurs depends on the ambient conditions. For the presently investigated case, frost formation suppresses the non-uniformity of air-flow distribution. Moreover, evaporators with non-uniform and ideal uniform air-flows are compared and it is revealed that the difference in their capacities is more noticeable at the beginning of the frosting period.
AB - Formation of frost on outdoor evaporators poses a significant challenge for air source heat pumps operating in cold climates. It is widely recognized that uneven air-flow across an evaporator can have a negative impact on both the evaporator's performance and the overall efficiency of the heat pump. This study investigates the influence of non-uniform air-flow distribution on a V-shaped outdoor evaporator as a component of an air-source transcritical CO
2 heat pump when subjected to frosting conditions. To this end, we developed and validated against independent experiments a numerical frost-formation model, and used it to study a multi-circuit evaporator of interest under different ambient conditions. It is shown that the uneven air-flow distribution results in varying frost formation patterns across different circuits of the heat exchanger, including differences in the amount of frost accumulated and its distribution among the individual tubes; the circuit with the largest frost weight accumulates 18% more frost compared to the one with the smallest in one hour under the sever frosting condition. Non-uniform frost formation also leads to air-flow distribution changing over time, and the rate at which this change occurs depends on the ambient conditions. For the presently investigated case, frost formation suppresses the non-uniformity of air-flow distribution. Moreover, evaporators with non-uniform and ideal uniform air-flows are compared and it is revealed that the difference in their capacities is more noticeable at the beginning of the frosting period.
KW - Air flow maldistribution
KW - CO heat pump
KW - Frost formation
KW - V-shape multi-circuit evaporator
UR - http://www.scopus.com/inward/record.url?scp=85182173196&partnerID=8YFLogxK
U2 - 10.1016/j.ijrefrig.2023.10.018
DO - 10.1016/j.ijrefrig.2023.10.018
M3 - Journal article
SN - 0140-7007
VL - 157
SP - 137
EP - 149
JO - International Journal of Refrigeration
JF - International Journal of Refrigeration
ER -