Investigation of dehumidifaction permormance of air cooled heat exchanger in washer dryers

Thanks to the rapid improvements in technology, everyday either a new product becomes a part of daily life or a new version of an existing product comes onto the market. Today consumers begin to pay attention to the energy consumption values of the products beside all these technical improvements. This shows that consumers are becoming more aware of saving on energy. In addition to this awareness, diminishing energy resources also push European Union and non-governmental organizations to publish regulations related to the energy consumption of the home appliances. This progress also forces the manufacturers to carry on studies related to energy efficiency besides improving other technical specifications of their products. Laundry drying is one of the most energy consuming process that occures within houses, hence in this thesis the effect of the inlet conditions for a heat exchanger used in tumble dryers on dehumidification is studied. This thesis study is composed of seventh chapters. In chapter one, motivation and aim of this study were explained in general terms as an introduction. The method follewed during the study is also briefly explained within this chapter. In the second chapter , former literature studies about the plate type compact heat exchanger which are used as condensers within drying cycles are examined. At the end of literature research, it has been noticed that studies related to this topic have been mainly focused on offset strip compact heat exchanger. In the third chapter of the thesis , description about the systems and working principles of home appliance type textile drying cycles are presented. At the end of the chapter, some basic information about psychometry which is one of the main thermodynamic branches is given and the working principle of the closed loop drying with air cooled heat exchanger is explained on a psychometric diagram. In fourth chapter, experimental setup which is used for the thesis study was described with details. After describing the design, components and installation process of the testing unit, calibration studies and the measurement system is explained with details. And than consists of experimental studies that have been carried within the testing unit described on the previous chapter. The inlet conditions that were chosen as test parameters and parameter values were described in detail. At the end of the chapter how the inlet temperature and flow rate of drying air and cooling air to the heat exchanger effects the outlet conditions and the condensation rate is shown with diagrams and described in details. In the fifth chapter, the heat exchanger that had been examined experimentally is examined analytically. At the end of this chapter, a model that gives heat exchanger outlet conditions and heat transfer mechanism between the drying and cooling air is created. With the help of some assumptions this model helps to predict the outlet conditions for both cooling and process air and also the heat transfer and condensation rate. In the sixth chapter, experimental study results and the developed model outputs that are discussed and compared with each other. Critical parameters with regard to heat transfer were determined. In the final chapter results of this study have been evaluated and suggestions have proposed. The results achieved within this thesis can be summarized as follows:  In the case of fixed flow rates for drying and cooling ambient air and also fixed temperature and relative humidity for cooling ambient air heat exchanger inlet conditions; increasing the inlet temperature for drying air also increases the cooling air exit temperatures and condensation rate. Similarly, in case of fixing all the other parameters, increasing the heat exchanger inlet temperature for ambient cooling air decreases the condensation rate. Increasing the drying air flow rate causes a limited increase in the outlet temperatures while increasing the ambient air flow rate causes a very limited decrease in the outlet temperatures. An increase in the flow rates for both drying and cooling air also causes an increase in the condensation rate. The general linear model (GLM) analyses show that the variability for condensation rate is mostly depends on the inlet temperatures of the drying and cooling ambient air (94 per cent). The effect of the flow rates is only 4 per cent and the effect of the relative humidity of the cooling air is negligible. The GLM analyses also show that the variability of the exit temperatures is mostly depends on the inlet temperatures (99 per cent). Compared to the inlet temperatures, the effect of all the other parameters is negligible. With the help of the analyses it has been shown that, 69,5 per cent of the variability for ambient cooling air exit temperature depends on the drying air inlet temperature and 26,1 per cent depends on the ambient cooling air inlet temperature and flow rate. It has been shown that the outputs of the model that has been developed and the test results converge well. Test and model results both show that increasing the drying air inlet temperature, decreasing the ambient cooling air inlet temperature, increasing the flow rates for both air streams effect the condenser efficiency in a positive way. At the end of the study , it has been understood that dehumidification performance of heat exchanger depends on the working conditions and expectation from the system. Therefore dehumidification conditions and working temperature of heat exchangers should be evaluated well .Considering the increase in the condensation rate due to high inlet relative humidity conditions, it is very critical to determine the air inlet flowrates ann temperatures. When the result of the developed model and the test results are compared, it can be seen that the model gives successful results under different working conditions and it can be used as a tool for determining the effect of the critical input parameters that were mentioned above. As a continuation of this study is thought to be useful in the following proposals: In this study, experimental studies were done on the same heat exchanger. Working on different types of heat exchanger (such as various fin thickness, various fin spacing, various number of row and various fin surface coatings) may be beneficial for improving the model and the literature . It has been provided that heat exchanger performance can be investigated during whole drying process due to expanding fixed regime model with different drying air inlet temperature and outlet relative humidity. This model can help developing a new model for not only heat exchanger but also for washer dryers.