Thermo-flow Performance Optimization Of Indirect Dry Cooling System Based On Entransy Dissipation Theory

With the large-scale application of dry cooling technology in power plants, indirect dry cooling system has been more and more researched. In this thesis, the thermo-flow performance of air-cooled heat exchanger and indirect dry cooling system network under ambient wind were researched based on the entransy dissipation-based optimization method.By means of the entransy dissipation based optimization method, two irreversible heat transfer processes, i.e. the heat transfer between circulating water and cooling air and the mixing process of circulating water, were firstly taken into account by analyzing the heat transfer process of heat exchangers in indirect dry-cooling tower. The total entransy dissipation rate, which indicated the mathematic relation between the geometrical parameters of air-cooled heat exchangers and operation parameters, was obtained. Then the problem to seek the optimal parameters was converted into conditional extremum problem. By means of Lagrange multiplier method, the conditional extremum problem could be converted into unconditional extremum problem and an optimization equation group was derived. Solving this optimization equation group, the optimal operation parameters under different optimization objective were obtained.The thermal performance of air-cooled heat exchanger was optimized with the method of the entransy dissipation based optimization and the entransy dissipation extremum principle, which showed the two optimization results were consistent with the one calculated by heat transfer equations. For the cooling delta with uneven distribution of cooling air, the optimal distribution to get the best thermal performance existed.A typical indirect dry-cooling tower was optimized by means of the entransy dissipation based optimization method to obtain the optimal circulating water distribution and the optimization result showed that the indirect dry-cooling system got greater heat transfer rate and the increment of heat transfer rate decreased with the increasing of ambient wind speed. Compared with the traditional method, the total heat transfer rate with the entransy dissipation based optimization method became higher. It showed that the entransy dissipation based optimization method had advantages in the optimization of complicated heat exchanger network.The indirect dry-cooling system with uneven circulating water distribution was optimized by means of the entransy dissipation based method to obtain the optimal heat transfer area distribution and the optimization result showed that the indirect dry-cooling system had less frictional head loss and with the increasing of ambient wind speed, the frictional head loss got less. The optimization result was then verified. Moreover, for different optimization objectives, the entransy dissipation based optimization method could still be adopted and obtain good results.