The Effects of Fin Spacing and Tube Outer Diameter of Evaporator on System Performance in Heat Pump Tumble Dryers

摘要

In heat pump tumble dryers, moisture separates from the laundry and leaves the dryer system at the evaporator. Moist air goes out the drum and enters the evaporator whose outer surface is below the dew point temperature. Air cools and then leaves its moisture. At the airside of the evaporator the wet surface develops and simultaneous heat-mass transfer occurs. Fin-and-tube heat exchangers are used as evaporators in household heat pump tumble dryers. In addition to optimum operating conditions, optimum evaporator geometry can significantly affect system performance. In this study, a model was developed for household heat pump tumble dryer. The model was validated by experimental data collected from the literature. MATLAB software was used in programming, and fluid properties were taken from Refprop software. The model was run with different fin spacing (2-5 mm) and tube outer diameter (6-12 mm) for evaporator, whereas operating conditions and all other geometrical parameters stayed the same. Then, coefficient of performance (COP), moisture extraction rate (MER), and specific moisture extraction rate (SMER) were calculated. As a result, the effects of fin spacing and tube outer diameter of evaporator were determined depending on the input characteristics of the dryer model. In the working range, SMER was changed up to 20% and 15% depending on the fin spacing and the tube outer diameter of evaporator, respectively.