Research On Shell-tube Heat Exchanger That Used In Sewage Thermal Utilization

The urban residential sewage is a renewable resource that has not been utilized fully, which has a significant influence on the building energy saving in China. As one of the key problems in utilization of sewage cooling and heating resources, heat exchange received extensive attention. Shell-and-tube heat exchanger is a traditional kind of heat exchange equipment, which has been widely used in the process of thermal utilization of urban residential sewage. So it is useful to carry on research on shell-and-tube heat exchanger for urban residential sewage.This paper analyzed the heat transfer process of shell-and-tube heat exchanger, and selected calculation formula that fit the actual condition of the exchanger. There are two kinds of flow mode for the exchanger: flow mode 1—sewage flows in the shell and clear water flows in the tube; flow mode 2—sewage flows in the tube and clear water flows in the shell. The heat transfer coefficient and flow resistance in shell and tube of the two flow mode were compared and analyzed, seeking for the flow mode that would be beneficial to increase in heat and reduce flow resistance. The paper also introduced the formation mechanism and influence factors of fouling in exchanger, put forward control method for the fouling, and analyzed the scaling position and variation of the fouling in the two different flow modes.An experimental platform were put up to validate the theoretical analysis results, and further compare the effect of flow mode on heat transfer coefficient, flow resistance and fouling generation. Different experimental conditions were designed and carried out for the research and analysis, and the experiments showed that:①When the fluid flow quality are equal at the same flow space, and the flow quality is in design range of the exchanger, it is beneficial to increase the sewage shell-tube heat exchanger's heat transfer in flow mode 1.②For the same heat transfer quality, flow mode 1 makes flow resistance of heat exchanger on tube side drop and flow resistance on shell side rise. For the experimental system, decrement of flow resistance of heat exchanger on tube side is about 0.25~0.5mH2O, while recruitment of flow resistance on shell side is about 0.1~0.3mH2O. As far as the whole heat exchanger, flow mode 1 is beneficial to reduce flow resistance of the exchanger.③The generation of fouling deteriorates effect of heat transfer of the shell and tube heat exchanger. In the experimental system, the heat transfer quality reduced about 40%. In the process of the early operation of the heat exchanger, compared with flow mode 2, using flow mode 1 type can reduce the disadvantageous influence of fouling to the effect of heat transfer to some extent.④Periodic commutating flow has a positive effect on delaying detriment of dirtiness resistance, which can destroy primary growing environment of the fouling and extend the growth cycle of the fouling. Comparing the two flow modes, periodic commutating flow has an obvious and benefic effect on restraining the generation of fouling to heat exchanger when using flow mode 1.This paper suggests taking a different flow mode for heat exchange in the sewage pipe heat exchanger, and theoretical analysis and test the effect of flow mode on heat transfer quality, flow resistance and fouling generation. The research result is valuable for the utilization of tubular heat exchanger in sewage resources development and engineering application.