Research On Fouling Growth Characteristics Of Direct Sewage Source Heat Pump

The problem that heat exchanger fouling prevalent exist in industrial and civil heattransfer equipment, where the water in HVAC systems. Biofouling, wall corrosion,sedimentation prevalent exist in the heat exchanger of sewage source heat pumps, whichseriously affected the operational efficiency and service life of the equipment.According to statistics, because of fouling, the economic losses is0.28%to0.35%ofthe GNP of a country.The impact of fouling on the efficiency of heat transfer equipment makes thesewage source heat pump system easily bring various problems in engineeringapplications, such as heat exchanger inefficiencies, high-pressure failure of compressor,which seriously affecting the applications and promotion of sewage source heat pumps,the money per year spend to clean up the heat transfer equipment is a huge cost. Amongthe many forms of heat exchangers, because of wide range of selection, low productioncost, mature technology, high temperature, high pressure, shell and tube heat exchangersis widely used in sewage source heat pump systems, so the research of shell and tubeheat exchangers is particularly important.Depending on the kind of water sources, sewage can be divided into primarysewage effluent and renewable water. According to whether the sewage flowing into theheat pumps, sewage source heat pumps can be divided into the direct and indirect forms.In direct sewage source heat pump systems, because of the sewage directly into the unit,there is no loss of middle temperature difference which can improve the coefficient ofperformance of the unit, resulting in the development trend of sewage source heat pump systems gradually to the direct form. But now the research for the direct sewage sourceheat pumps is not enough, this paper will use a direct sewage source heat pump asobject to test and analysis.First, this article summarizes the ingredient, causes and influence factors of foulingof common types of fouling in shell and tube heat exchangers, and establish a predictivemodel based on the fouling resistance method. Under this theoretical guidance, asewage source heat pump system in Xi’an is for the test object, the system uses urbansecondary effluent as its water source. The continuous testing of the heat exchangerfouling growth is taken in each of the system’s cooling and heating period, obtainedpredictive models of thermal resistance and the decline law of efficiency with fouling.Then, a brief description of fouling prevention and cleaning methods is raised, andbased on the measured data, we establish the model of costs of the system, and calculatethe optimum heat exchanger cleaning cycle. Finally, a simple theoretical model isestablished in this paper on the energy efficiency of the direct and indirect forms tocalculate and analysis, and analysis the efficiency of sewage temperature, air conditionwater temperature to the two systems.