Optimum Control Of Shell-tube Heat Exchanger Based On Sewage Thermal Utilization

Today,with vigorous advocacy of "Low Carbon Economy", "Energy Saving and Emission Reduction", the sewage-source heat pump, a construction energy conservation application technology of utilizing renewable energy resources, is becoming more and more concern. For the indirect sewage-source heat pump system, the heat exchange efficiency ,operation and maintenance costs of shell-and-tube heat exchanger have a great effect on its actual efficiency of energy saving and system operation costs. Therefore, it is one of the hot topics how to achieve optimal control of shell-and-tube heat exchanger of the indirect sewage-source heat pump system in current sewage-source heat pump research field.From heat transfer principle and thermodynamic calculation principle of the sewage pipe heat exchanger, this paper analyses and deduces common calculation formulas on heat exchanger including the calculation formulas of heat transfer area , heat transfer coefficient, mean temperature difference and flow resistance, which establish a theoretical foundation for the subsequent design and production of heat exchanger. The article makes further analysis on the factors to the effective quantity of heat exchange in the indirect sewage-source heat pump system, and proposes five important factors to the effective quantity of the heat exchange system, which contain system heat transfer area at runtime, sewage temperature, the changes of system cooling and heating load, the fluid velocity and fouling resistance of shell and tube.Based on the effective factors of the sewage pipe heat exchanger and the optimal control principle, this paper puts forward optimal control strategy about the running numbers of pump, heat exchange, primary side circulation pump on account of sewage temperature and the load condition change in system; This paper also raises the control method and cycle concerning the flow direction change in the tube side and shell side of the sewage tube-shell heat exchanger aiming at dirt growth characteristics of heat exchanger tube passes. And then it presents comprehensive measures of optimal control and effect analysis of optimal control about the sewage- source heat pump system according to all the above considerations.Finally, according to theoretical analysis and derivation, we have designed and made the model of the sewage pipe heat exchanger, and put up experimental platform model of sewage source heat pump system. Through a series of experimental conditions arrangement and the relevant tests and researches, the optimal control strategy of shell-and-tube heat exchanger is analyzed and summarized qualitatively.Experiments show that:①As the sewage water temperature is increased 1℃, the sewage flow increased about 17%, and the logarithmic mean temperature difference was reduced 12.7%, and heat transfer coefficient was reduced a scale of 14%, so the sewage temperature influences the actual heat exchange greatly;②The flow change of heat exchanger being controlled can be relatively extended dirt induction period, meanwhile, if the dirt original growing environment is constantly destroyed during the medium term period of dirt growth , the growth cycle of dirt will be further extended.③In different load conditions, it is absolutely feasible that the running numbers of pump, heat exchange, primary side circulation pump of the system will be optimized and controlled , but in the practical project, A-L control strategy will be theoretically analyzed and post-test debugged according to heat exchangers, the number of pumps and circulating water pump in the actual engineering.