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For the purpose of taking full advantages of the District Cooling System (DCS), the mathematical model was established based on the principle of non-decreasing state of the energy efficiency grade of the refrigeration unit and high level of the transportation energy efficiency of the cooling pipeline. Based on the mathematical model, two formula were derived. One is suitable for the scientific research concerning the length of the DCS, and the other is appropriate for the design in engineering application. The determination of the maximum length of the pipe provides an alternative for the research and design of the DCS, therefore it is worth studying.

Settling velocity of sediment increases if flocculating occurred, and this enlarges deposition in reservoirs. According to water environmental factors in the Three Gorges reservoir, potential energy and forces between particles are evaluated based on DLVO theory. The critical water dynamics conditions were obtained by comparing extremum in synthetic potential curve and kinetic energy caused by relative velocity between particles. It is found that sediment flocculating is apt to happen when water level is high according to flow dynamics in the Three Gorges reservoir. The flocs are relatively loose and which is prone to be broken by water shear force. So the settling velocity of the flocculation is limited and the critical diameter of sediment is 0.019mm under which the sediments are affected by flocculating, and the settling velocity should be revised according to the limited settling velocity of flocculation when sediments are smaller than the critical diameter.

Taking the geothermal heat pump system in the campus of Hunan University of Technology for example, three technical solutions of the heat source of the system were analyzed in terms of the condensing heat load, the annual unbalanced heat load and the energy efficiency ratio (EER) of the system. In addition, comparison was conducted among the solutions. The results indicate that the solution 3, which has a cold and hot water integrative unit and hot water unit connected in series, meanwhile has a cooling tower for auxiliary cooling, shows better performance among all the solutions. The analysis on the solution of heat source of geothermal heat pump system, which usually contains the analysis on the condensing heat load, annual unbalanced heat load and EER, is of great significance for the design and development of the geothermal heat pump system with lower coat and higher EER.