Search

• Novel mathematical model to predict the heat transfer rate of skin condensers. • Experimental validation with eigth hot-wall condenser designs. • Adhesive tape has the strongest impact on the heat exchanger performance. This paper comes out with an investigation of the thermal performance of skin-type hot-wall condensers for household refrigeration applications. Eight different hot-wall condensers were manufactured and installed in identical refrigerators. The condenser samples were constructed by varying the following design parameters: (i) adhesive tape (aluminum or polyethylene), (ii) tube O.D. (4.00 or 4.76 mm), (iii) total length (10 or 11.5 m) and (iv) condenser positioning. The refrigerators were placed inside a climate-controlled chamber and tested in steady-state conditions. A mathematical model that takes into account the heat transfer not only to the surroundings but also to the refrigerated compartments was also put forward. The model predictions were compared to the experimental data when deviations within the ±10% bounds were achieved. It was found that the adhesive tape thermal conductivity and the tube-outer sheet contact area have the strongest impact on the condenser performance. It was also found that the polyethylene tape increases the condensing pressure, due to its low thermal conductivity and thus to the smaller useful heat transfer area. It was thus concluded that the refrigerator foaming process must be carried out with an extreme care to avoid any negative impact on the tube-outer sheet contact resistance. Finally, it was noted that the heat transfer to the refrigerated compartments is directly affected by the condenser positioning and the thermal insulation thickness. [ABSTRACT FROM AUTHOR]

The heat transfer performance variations of condensers that are caused by non-uniform distributions of air flows are investigated using a numerical simulation method. A heat exchanger designed for the outdoor unit of a heat pump system is selected and represented using a numerical model. A non-uniform profile of the air velocity is constructed through measuring the air velocity at various locations on the outdoor unit. Numerical analyses are conducted for various refrigerant circuits and air flow conditions. The results demonstrate that the heat transfer capacity is reduced depending on the air flow rate and the refrigerant circuit configuration. It is also demonstrated that the capacity reduction rate is increased as the average air velocity decreases. [ABSTRACT FROM AUTHOR]

• Path number in heat exchanger was conventionally determined at rated load. • Number of refrigerant paths of condenser is determined with part load condition. • Path number optimized with part load leads large increase in heat transfer rate. • Optimal number of path was determined by weighting with load conditions. • The proposed method shows promising energy performance potential. Heat exchangers for heat pump condensers and evaporators are usually designed considering rated load conditions. Residential heat pumps and residential air conditioners operate considerably longer at part load conditions than at rated load conditions. This study investigated the difference between a design considering the part load condition and a design considering the rated load condition in heat exchanger path design. The optimal number of paths for each load condition was selected considering the thermal resistance ratio. Results show that the heat transfer rates of a condenser with the optimal number of paths based on thermal resistance under 84%, 51%, and 33% load conditions were 18.29%, 27.58%, and 42.58% greater than the heat transfer rate of a condenser with the number of paths optimized under rated load conditions, respectively. Considering all load conditions, the optimal number of paths with the maximum average heat transfer rate was derived using the weighting factor of the system performance evaluation criteria. The results demonstrated that the optimal number of paths changed when a part load condition was considered in the heat exchanger design. [ABSTRACT FROM AUTHOR]