Study On Heat Transfer Characteristic Of Pulsating Heat Pipe And Heat Exchanger

Pulsating heat pipe(PHP) is a new and efficient heat transfer components whichhas many virtues，such as good heat transfer performance、simple structure、small sizeof shape、good adaptability and so on. So far pulsating heat pipe has been used in airconditioning waste heat recovery， microelectronics cooling， drying and solarcollectors and many other fields. In this paper，the pulsating heat pipe which would beused in the boiler flue gas waste heat recovery is studied，on the basis of experimentalstudy of pulsating heat pipe heat transfer characteristics，an pulsating heat pipe heatexchanger is designed which would be used for flue gas heat recovery of10t steamboiler. Based on the heat exchanger，a model of two-dimensional cross-section thatprovides the basis for the design of heat exchanger optimization is set up forcalculating the parameter change of gas in the exchanger and analyzing the internalheat exchanger flow field distribution.First，in the experiment，according to its application background，a PHP isdesigned and a test bench is set up on which we analyzing the effect of the heat pipestructure and operating parameters (angle of inclination，heating power，filling rateand cooling capacity) on the heat transfer characteristics. On the different operatingconditions，by contrast of the heat pipe thermal resistance and distribution of thetemperature of evaporation and condensation side we can find: a copper PHP whoseworking fluid is water，inner diameter is3mm，thickness is0.6mm has the best heattransfer performance when its filling rate is around55%. When put horizontally thepipe still can work normally，but the thermal resistance is higher than the verticalplacement and the inclination angle of impact on the thermal resistance decreasesgradually with the increase of heating power. With the increase of the flow of coolingwater，the heat-pipe thermal resistance shows increasing trend，but compared withother factors，the affect is less.Second，based on traditional gravity heat pipe heat exchanger design，we explorethe pulsating heat pipe heat exchanger design calculation method combined with thepulsating heat pipe with its own characteristics. We give the designing process ofpulsating heat pipe heat exchanger and design a real exchanger for the flue gas wasteheat recovery system of a10t steam boiler.Finally，we create a two-dimensional numerical model of the pulsating heat pipeheat exchanger and do some simulation analysis. Through different arrangement anddensity of the bundle，different inlet velocity and temperature of fluid，we investigate the heat transfer characteristics of the exchanger. The results showed that the insertedrow heat pipe heat exchanger arrangement is better than alignments. With the increaseof tube row density, the pressure loss of heat exchanger has a trend of decreasing firstand then slowly increasing, and the temperature difference of imports and exports alsodecreases. When the flue gas inlet temperature is constant, exit temperature decreaseswith the reduced inlet velocity. Meanwhile, there is a velocity limit to obtain lowoutlet temperature and no condensation. When the flue gas outlet temperature isconstant, the corresponding inlet velocity limit is reduced with the increasing inlettemperature.In summary，as an energy-saving technology，the pulsating heat pipe used in theboiler flue gas waste heat recovery system shows better performance compared to thenormal pipes. The application of pulsating heat pipe can not only reduce flue gastemperature but also preheat boiler feed water，it’s a high-efficiency energy-savingmeasures.