Conference Year
2016
Keywords
Finned tube evaporators, frosting, air flow rate, air and refrigerant side maldistribution
Abstract
Finned tube evaporators are used in a wide range of application such as commercial and industrial cold/freezed storage rooms with high traffic loading under frosting conditions. During the literature survey it has been realized that there is not enough experimental and visual data regarding the unit cooler tested with casing and fan integrated as in real operating conditions. As it is known, the usage of fan and evaporator external case and non-optimum distributor design may affect air and refrigerant side distribution, capacity and frost formation along the fins with respect to degree of maldistribution. In this paper, an evaporator with an integrated fan was manufactured and tested at under frosting conditions by only changing air flow rate at ambient balanced type test laboratory in contrast with testing at wind tunnel and more uniform flow distribution. During the test, operation performed according to three different air flow rate separately. The parameters concerning test operation such as the changes of air temperature, air relative humidity, surface temperature, air-side pressure drop and refrigerant side capacity etc. were followed in detail for each air flow rate. At the same time, the digital and thermal images were captured in front of heat exchanger; thus, the frost temperature distributions, blockage ratios and frost thicknesses occurring throughout all surfaces were investigated. In this study the effect of air flow rate on frosting has been investigated. The test and visual results showed that the trendline of air side pressure drop has increased slowly at the first stage of test operations, then this phenomena has increased linearly up to a top point and then the linearity has disrupted instantly and this point has admitted beginning of defrost operation for each case. On the other hand, the refrigerant capacities were declined continuously during the test operations. When examining visual and thermal images captured at certain time intervals, it was shown an uneven frost layers and detected the temperature distributions in front of evaporator as different degree for each case via thermal and digital camera. Similarly, the frost thicknesses distribution with time occurring at the specific area of each circuit was identified via macro lens and Matlab Image Process Program. Moreover, the initial period of frost growth, which have significant impact on further frost growth, was followed and the stages of frost growth has been determined. Â