| Organic Rankine’s cycle(ORC)is one of the main ways to effective utilization of resources in low temperature.In the ORC system,efficiency of heat transfer in the evaporator directly affects the thermal efficiency of ORC system as a whole,the ORC evaporator are mainly composed of boiling heat transfer.Based on this,this paper respectively for the two types of experiment :single tube boiling experiments and shelltube heat exchanger.In single tube experiments,chose four type of pipe,light pipe,corrugated pipe,sintering pipe(HIGH-FLUX)and Turbo-EHP type perforated pipe,and chose two experimental working fluid,R245 fa and R601 a,respectively.Through the single pipe experiments,got each working fluid in a variety of pipe type boiling experiment phenomena and its local heat transfer coefficient and average heat transfer coefficient outside the pipe and pressure drop.Through the single pipe experiment,after the comparison and analysis,in tube-shell heat exchanger experiments,choose the Turbo-EHP porous pipe as experimental pipe,using the structure of the fork row layout,the experimental results get the local heat transfer boiling coefficient outside pipe and LMTD logarithmic mean heat transfer coefficient.Get the following conclusion:In the single pipe experiments,by observing the experimental phenomena,the vaporizing core of HIGH-FLUX is the most,followed by Turbo-EHP perforated pipe,for corrugated pipe,after the worst for light pipe.In the corrugated tube experiments,found bubbles most concentrated in the trough of the first half,demonstrates the Turbo-EHP type perforated pipe.From LHTC numerical comparison,four pipe type LHTC all showed a trend of firstly increase after decreases consistent with the experimental phenomena.From AHTC numerical comparison,the four pipes AHTC most presented the trend after the first linear increase slowly decreasing.In particular,AHTC value of most R601 a experiment is greater than R245 fa experimental.Contrast the AHTC value with light tube experiment,Turbo-EHP tube for 4.82~7.75 times,corrugated pipe is 1.1~1.2 times.From the point of the pressure drop,all the pressure drop experiments are linear increase with the increase of the heat source temperature.Four types of pipe pressure drop of R245 fa experiment were greater than R601 a experiment.Secondly compared four types of pipe can be found : Δ PTurbo-EHP > Δ P bellows > Δ P sintering pipe > Δ P light tube.Through the experiment of single tube experiment phenomenon and the heat transfer coefficient,which can be roughly from bottom-up direction inside the heat exchanger is divided into three areas,namely,liquid,gas and liquid and the gas phase area.Supercooled liquid get into the first area,heat FLUX density is lower,is suitable for the HIGH-FLUX sintered tube;Secondly,saturated liquid into gas and liquid region,the heat flux density is high,suitable for Turbo-EHP tube,nucleate boiling speed up;In gas phase zone,working fluid is most gas,from the point of view of strengthening heat transfer,appropriate to increase heat exchange area,so as to improve in thermal efficiency,appropriately use high fin tube to increase the heat transfer area.Choose Turbo-EHP tube as heat exchanger pipe for experiment,and use the R245 fa as the working fluid.From the point of view of upper and lower tube LHTC,when heat source temperature is 50~60℃,along the length direction,LHTC first decreased after increase,up and down two tube of the heat transfer coefficient is very close;When the heat source temperature is 60~100 ℃,along the length direction,LHTC value increase after decreases first,due to the heat source temperature rises.from the experimental data,the local heat transfer coefficient is 3027.96~8936.80 W/(m2·K).Through the calculation of LMTD logarithmic average heat transfer coefficient,the LMTD logarithmic mean heat transfer coefficient value of 1529.76~ 2271.63 W/(m2·K),to the Turbo-EHP type perforated pipe heat exchanger to provide numerical reference,has a certain practical significance. |
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