Freezing Heat Transfer Theory Analysis And Freezing Heat Exchanger Development

There is a great lot of energy in urban sewage and surface water that can be used as lower heating or cooling source of heat pump for heating and air conditioning. In the process of exploitation there were two restrictions. First, in north china beyond Qinling mountain range and Huaihe River, surface water would be frozen in winter. Water under ice layer is 0℃, there is almost no sensible heat, and conditional heat exchanger would be frosted crack and destroyed. Second, the around sewage flux is always inadequate for building heating or air conditioning. This dissertation started from energy conservation and environment protection, has indicated the idea and method that is breaking through freezing point and obtaining freezing latent heat. Some correlative theory and technology had established, and the special heat exchanger has developed. So the unusable surface water and insufficient sewage would be usable and enough for heat pump. This new technology would greatly enlarge the application scale of water source heat pump. To develop the Freezing Heat Exchanger (FHE), there were several questions must be solved, such as judgment of freeze, freezing heat transfer, design of FHE, clear of ice layer, realization of mechanism. So the main work and produce of the dissertation are as following.(1) Used nucleation theory, the changes of nucleated work on cone pit and cone tip of rough surface had been researched. The concept of critical cone pit and condition of nucleus growth out had been given. The process of hetero-nucleation and influence to hetero-nucleation by surface energy and roughness had been analyzed and indicated that the high-energy surface and coarsening treatment can reduce the frozen degree of supercooling. Contrasted the velocities of homo-nucleation, hetero-nucleation and suspend particle nucleation, discovered that cold water can only be frozen on surface in low temperature. Deduced the growth velocity of ice phase and spread velocity of ice area, proved their correction by results in literatures. At last through experiment data, the minimum supercooling degree of water frozen on real steel surface, and it's the judgment of freezing.(2) On the basis of quasi-steady assumption, the energy conservation differential equation of phase interface under double dominative convection conditions has been established. By analysis of non-dimensional analytic method, the non-dimensional criteria formula of ice thickness, growth velocity and limited frozen thickness had been all given out. Through integral average of time, the calculated criteria formula of freezing heat transfer under continuously de-icing. Analyzed results indicated that the three modes freezing had different process and characteristics, and the quantity of freezing heat transfer was not only related to total temperature difference and total thermo-resistance, it's also related to the ratio of temperature distribution and ratio of thermo-resistance.(3) On the basis of freezing judgment and time-averaged heat transfer criteria formula, calculated method of freezing start point has been given. Established the internal heat source model of ice-slurry meltage and equation of cooling medium temperature, in order to solve them, the iterative method of temperature and heat has been created. The design method of parallel-flow, counter-flow and constant temperature of cooling medium had analyzed. Through the general program for FHE design and check called FHEDesign, the heat transfer performance and characteristics of FHE had been analyzed; results indicated that FHE is similar to other phase-changing heat-exchanger, such as evaporator or condenser. The flow mode and change of parameters of cold water had very little influence to total transferred heat, and FHE had very good stability of flux and temperature. The freezing degree of supercooling and period of de-icing is the most important factor to total transferred heat of FHE.(4) Through the establishment of stress balance equation and analysis of stress status, de-icing model and brittle fracture model under the conditions of vertical scraping and tilt scraping are presented respectively. According to material strength theory, the thesis analyses necessary external force to eliminate ice layer and its influencing factors, and then gains energy consumption forecast formula of mechanical scraping deicing, which provides the basis for motor selection of ice-scraping mechanism. Conclusion shows that tilt scraping can greatly reduce deicing energy consumption, that the smallest scraping force and energy consumption are obtained with tilt angle of 40o and that energy consumption of scraping ice is less than 1‰to 1% of heat exchange amount, which shows mechanical deicing owns economic feasibility. (5) Invents a kind of pulling-scraper online surfaces clean heat exchanger and heat exchanger to extract freezing latent heat of cold water, introduces its work principle and technical measures, presents design and calculation method of the initiative wring wheel and the cable diameter and designs the experimental prototype as an example. Through experiments on the heat pump heating and air conditioning system test-bed, validates the correctness of above freezing phase change heat exchange theory, the design and verification methods of FHE and deicing energy consumption forecast formula, at the same time validates reliability and technical feasibility of new heat exchange device. Through testing comprehensive properties of heat pump system, shows that heat pump of freezing latent heat has good technical and economic feasibility.Through the work of dissertation, the theoretical research and design development of Freezing Heat Exchanger to extract freezing latent heat of cold water had been done, and validated their correctness and feasibility of freezing latent heat source heat pump, which leads a new approach for heat energy utilization of surface water and sewage.