Research On Heat-moisture Process And Performance Of Closed Heat Pump Drying Dishwasher

It has become a trend to use dishwasher to replace the manual tableware cleaning.Currently,the drying mode of dishwasher is mainly residual temperature drying,which evaporates water to the surrounding environment through increasing the temperature of tableware.However,this mode has many disadvantages as follows:it easy to rot around the building materials;the energy consumption of the whole machine is very high;the drying duration is very long.To solve this problem,this paper applies the heat pump drying technology on dishwasher.The heat pump drying is a type of active hot air drying,which does not require a higher drying starting temperature for tableware.Therefore,at the rinsing stage,cold water can be applied to replace hot water to reduce the energy consumption of dishwasher in operation.In addition,it also possesses many other advantages,such as good drying effect,short drying duration,etc.The main research content of this paper is to establish a closed heat pump dishwasher drying process model,build a heat pump system for dishwasher,and conducts an experimental analysis on the dishwasher's drying system performance.The details are as follows:Firstly,by coupling the humid air heat and mass transfer model and the heat pump circulation model,we designed established a closed heat pump dishwasher drying process model.The MATLAB program was applied for model solving,in which the time step was set to 10s and the effective heat transfer area was set to 8.54 m~2.Analyzing the model results,we found that the mass of condensed water at the evaporator only accounts for 50.7%of the amount of water evaporated on the surface of the tableware.To achieve the aridity index of1.08,the drying time should be 30 minutes.Secondly,in this paper,we designed and established a set of the closed heat pump dishwasher drying system.According to the dishwasher's running process,the heat and humidity load of the drying process is 640.3 W.On the premise of meeting this requirement,the main components of the system were designed and selected according to the thermal calculation of the heating cycle.In addition,this thesis selected the R134a as the cycle fluid by comparing the physical property parameters of different refrigerants.Thirdly,we conducted the experimental research on the closed heat pump dishwasher drying system to understand the wet air running characteristics as well as the heat pump system performance during dynamic drying.Moreover,through the comparative experiment,the effects of heating capacity,air flow structure,and evaporation temperature on the drying effect were analyzed.The experimental results revealed as follows:improving the air flow organization was the most beneficial mode to increase the aridity index,while lowering the evaporation temperature and increasing the heating capacity could also improve the drying effect.The former had stronger influence than the latter.In addition,when the time was 800s before the dishwasher's drying,the main demand of the system was to improve the heating capacity;after drying for 800s,the main demand of the system was to improve the dehumidification ability of the evaporator.The experimental data showed that when the average heating capacity was 623 W and the superheat was 7.5?,the air supply method was25 minutes for the upper supply and 5 minutes for the lower supply with the aridity index of1.08,which could satisfy the drying requirement.However,under the whole climate experiment,the aridity index decreased when the ambient temperature was higher or lower than 23?.The experimental data was also applied for model verification.We compared the average experimental values and the average simulation values of supply air temperature,return air temperature,heating capacity and refrigerating capacity,and found that the difference between them was not more than 3%.Finally,the research solves three pain points of the dishwasher on the market as follows:at first,the system does not affect the surrounding environment;second,the dishwasher's overall energy consumption is very low.In contrast to the German Miele dishwasher,this system can save energy by 19.3%;third,the final drying time is very short,and the total time consumption is shortened to 30 minutes from the original 60 minutes.