Research On Rheologic And Heat Transfer Characteristics Of Urban Sewage

Municipal sewage is a clean energy with excess heat. Sewage source heat pump could make full use of waste heat in municipal sewage to supply heat or cold for building. It could save fossil energy and also has much advantage in first cost and operating cost comparing with conventional air conditioning systems.In recent years, it is widespread concerned about the subject of using municipal sewage as hot and cold source of the heat pump, and is gradually developing in engineering field. With the consideration of municipal sewage would become the most important flowing material in heat pump system, it is of profound theoretical and practical significance that researching its resistance and characteristics intensively.Relative to the universal water used in heat pump system, the municipal sewage can be regarded as a kind of new flowing working material. When designing the sewage heat pump system, the basic data of designation is estimated as the clean water. Because of the difference between sewage and clean water, the head and flow of pump are both chosen exceeding the stander, so it is waste in electric energy. The loss in this field is much higher than the energy-consumption in water, so the sewage heat pump system doesn't present the effect of new energy; it is also the main obstacle of generalization. When designing the pipelines, the same problem appears. In order to reduce the resistance the diameter of pipe should be enlarged. So the first invest of system is higher, and the recovery period becomes long. Accurately mastering its resistance and heat transfer characteristics is a precondition for design the hydraulic and heat transfer conditions of sewage source heat pump system. It is also the theoretical foundation for the research of dirt in heat-exchanger. It is necessary to bring forward an easily method to calculate the flow and heat-transfer characteristics. Also, this method should be suitable for the actual flow characteristic and affect the system least. All of these form the basic theoretical problem of sewage in heat pump system.Through the experimental tables of horizontal-tube and revolution-flat rheometers, the relationship of shear rate and shear stress of sewage is determined. Based on the analysis of advantages and disadvantages for the two methods, it is found that municipal sewage had displayed non-Newton fluid characteristic. The municipal sewage belongs to the shear-thinning fluid and the constitutive equations can be obtained through system uncertainty analysis and identification theory. And then based on the certainty rheological characteristic, the experimental tables of flow and heat-transfer characteristics are designed and established, and also the error of it has been analyzed. The further researches the flow and temperature of laminar and turbulent in the sewage pipe, a series of equations about flow, resistance and pressure loss are developed. The numerical simulation of entrance effect in laminar flow and the feature has been given. Through the method of theoretical and experiment combination, the heat-transfer characteristic in laminar and turbulent currents has been obtained, and also the temperature and series of calculation formulas are given. The reliability and precision of the equations can be demonstrated.These formulas are complex in format and with the consideration of conveience for the designer, at last the differences between non-Newtonian and Newtonian flow of fluid characteristics are discussed for the complexity equations in engineering application. It is incorrect that taking the sewage as Newtonian flow with constant viscosity. But in the actual projects, the simplified formulas of Newtonian flow based on the concept of equivalent viscosity have been given. The differences of the results are small comparing with the accurate equations. It is much convenient for the designer.Through the research of the thesis, the flow and heat-transfer characteristics of urban sewage have been recognized. In the side of theory the reliability of the utilization is deeply analyzed. It supplies the foundation and guarantee for the techniques of sewage heat pump system.