Study On Urban Scale Sewage Thermophysical Properties And Sewage Heat Transfer Model Of Vertical Evaporator And Its Applications

Energy saving and environment protection are the key issues concerned by all countries in the world,and building a resource-conserving society has become China’s future development strategy.Heat pump technology has the advantages of greatly reducing the consumption of traditional fossil fuels and solving the problem of heat supply for building heating and air conditioning,and has been widely applied in the field of building in China,especially in the field of heating in northern cities.Sewage water source heat pump has obvious superiority compared with other types of heat pump in northern cities and towns,and is more suitable for popularization and application in the field of heating in northern cities and towns in China.At present,sewage source heat pump technology in practical engineering applications also exist the following urgent problems to be solved.First of all,there are still few studies on the parameters of temperature,concentration,density,viscosity,thermal conductivity and specific heat of urban scale raw sewage,which play a very key role in the development and application of sewage source heat pump technology,and it is urgent to carry out the research on the thermal properties of urban scale raw sewage;Secondly,the existing sewage source heat pump projects almost have intermediate water system,which undoubtedly reduces the development and utilization efficiency of low-grade heat energy resources of urban raw sewage.It is very necessary to research and develop sewage source heat pump technology and special equipment that can directly allow urban raw sewage entering into heat pump units.It is urgent to study the heat transfer of raw sewage inside and outside the tube bundle of evaporator and the design method of sewage source heat pump system.For this reason,this article take the new type of sewage-source heat pump technology research and development that allow urban original sewage directly into the equipment as the goal,on the basis of systematically reviews the research progress both at home and abroad,using the combination of field investigation,theoretical analysis and experimental study.Based on testing and modeling research of an example of scale original sewage key parameters in thermal and physical properties in Shenyang city,a new type of sewage heat transfer technology and equipment suitable for urban raw sewage directly into the heat pump unit--vertical shell and tube sewage evaporator is proposed.The convective heat transfer characteristics of sewage in the vertical evaporator and the design method of this sewage source heat pump system are studied.The details are as follows.First of all,this paper takes Shenyang as an example,systematically studied the urban scale original sewage sampling and test method of seven key thermal physical property parameters including concentration,temperature,PH value,density,viscosity,thermal conductivity and specific heat,established binary regression mathematical model between the original sewage density,viscosity,thermal conductivity,specific heat and water temperature and the concentration.The engineering application parameter table of Prandt number,thermal diffusion coefficient and kinematic viscosity in Shenyang city at normal temperature.The variation rule of thermal physical property parameters of various primary sewage is compared and analyzed.Second,aiming at the present situation that sewage heat exchanger fouling resistance growth model research mainly consider the sewage temperature field and velocity field,seldom consider wastewater concentration field of fouling resistance to the influence of growth rule,this article analyzed the tube water flow characteristics from the perspective of mass transfer,theoretically researched the influence of sewage concentration field on the growth law of fouling thermal resistance,and finally established a dynamic mathematical model of fouling growth in pipes considering the key parameters of sewage temperature,velocity,concentration and so on.Third,for the experimental study on the vertical pipe sewage,wall fouling resistance,heat convection of refrigerant boiling heat transfer outside the vertical tube bundle key problems,this paper analyzed the test principle of internal and external flow and heat transfer of vertical tube bundle of vertical shell and tube sewage evaporator,put forward the test scheme,and designed and constructed the test system of internal and external flow and heat transfer characteristics of vertical tube bundle of vertical shell and tube sewage evaporator.The test system adjustment and test precision analysis are completed,which provides the test conditions for the subsequent test research.Fourth,using the established vertical sewage evaporator flow heat exchange characteristics test system,the experimental study of vertical sewage evaporator heat exchange tube beam in clean water and sewage conditions was conducted.Based on the test data,the mathematical model of boiling heat transfer coefficient outside the tube of vertical sewage evaporator,convective heat transfer coefficient of sewage inside the tube and fouling thermal resistance growth model of sewage side inside the tube are studied and established,which provide experimental basis for the development of vertical sewage evaporator and heat pump system.Finally,a vertical evaporator sewage source heat pump system with multiple vertical evaporators in parallel(multiple compressors in parallel)was proposed to meet the new technical development requirements of the urban primary sewage directly fed into the heat pump unit.The mathematical model of the key components and working medium of the heat pump system and the digital simulation system of the heat pump system design were established.Taking the development of a parallel sewage water source heat pump unit with double vertical evaporator and double compressors as an example,the orthogonal simulation test design method of this type of heat pump system and equipment was studied by taking the condenser area,evaporator area and evaporator aspect ratio as the key parameters.Research of this paper is to solve the problem of urban scale original sewage thermal physical properties,provides the specific sewage sampling,inspection,testing and modeling method,on the depth of further development of sewage-source heat pump technology,largescale exploitation and utilization of northern city of original sewage heat energy,promote the development of the northern cities clean heating work,has the important theoretical significance;It has provided basic mathematical model,experimental data and research methods for the research of revealing the internal and external heat transfer characteristics of vertical heat exchange tubes,the growth law of sewage fouling heat resistance in pipes,and the research and development of new sewage source heat pump technology suitable for direct urban raw sewage into heat pump units,which has important academic value.The work of this paper has important application value and market prospect for promoting the use of sewage source heat pump technology to realize clean heating and developing new sewage source heat pump technology and equipment in northern cities of China.