| China’s energy resources are relatively scarce,and the per capita energy resources are far lower than the world average level.China is also one of the countries with the highest per unit energy consumption in the world.Low energy efficiency is a status quo of China’s energy use.Heat exchanger is an equipment which transfers part of heat from hot fluid to cold fluid.In general,most heat exchanger systems are widely used in the heat transfer medium is water,the heat transfer pipe is smooth,however,these heat exchanger systems in some cases can not meet the high intensity of heat transfer requirements.In order to improve the heat transfer performance of heat exchanger system,nanofluids and reinforced heat exchange tubes are used instead of water and smooth tubes.This topic with TiO2-H2O nanofluids,twist tape and triangular tube as the research object,and through the experimental method,explored the flow and heat transfer characteristics of deionized water and nanofluids in different structure triangular tubes,different structure triangular tubes equipped with a same twisted tape,and the same structure triangular tubes equipped with different twisted tapes,using the thermal efficiency and exergy efficiency evaluation method on the thermal and hydraulic properties of the experiment system has carried on the comprehensive evaluation.Firstly,three kinds of TiO2-H2O nanofluids with different mass fractions of0.1wt%,0.3wt%,and 0.5wt%were prepared,and their stabilities were analyzed.The physical parameters of the nanofluids with different mass fractions were measured,including the thermal conductivity and viscosity.Secondly,the experimental platform is designed and built,and the relevant experimental comparison and analysis were carried out,including:Designing and building the enhanced heat exchange platform with different structure triangular tubes,and comparing the heat transfer effect of different structure tubes;Designing and building the enhanced heat exchange platform with triangular tubes equipped with different built-in twisted tapes,and comparing the heat transfer effect of the tubes equipped with different twisted tape pitches;Designing and building the enhanced heat exchange platform with different structure triangular tubes equipped with a same built-in twisted tape,and comparing the heat transfer effect of different structure tubes equipped with a same built-in twisted tape.Finally,the thermo-dynamic comprehensive evaluation methods of thermal efficiency（R3）and the exergy efficiency theory were applied to comprehensively evaluate the thermal and hydraulic performance of the experimental system in terms of quantity and quality.The experimental results were analyzed from three perspectives.From the perspective of nanofluids,nanofluids can enhance heat transfer,and when the mass fraction is 0.5wt%,the maximum heat transfer can be increased by 16.22;The flow resistance of nanofluids can be increased by 11.4%when the mass fraction is 0.5wt%;Nanofluid can improve thermal efficiency,but lower exergic efficiency.From the point of view of twisted tape,twisted tape can enhance heat transfer,compared with tubes without twisted tape,tubes with built-in twisted tape can increase heat transfer by 13.02%at most,and the smaller the twist distance of twisted tape,the better the heat transfer performance;Compared with tubes without twisted tape,the resistance of tubes with built-in twisted tape can increase by 91.08%at most,and the smaller the twisted tape are,the greater the resistance will be.The thermal efficiency can be improved by 11.18%,and the smaller the pitch,the greater the thermal efficiency.Twisted tape can reduce exergic efficiency.As for the structure of the tube,the equal-side triangular tube with twisted tape inside has the best heat transfer performance,the lowest resistance coefficient and the highest thermal efficiency,as a result of which exergic efficiency is good.The comprehensive evaluation methods and results in this paper provide a certain guiding significance for the design and operation of the operating conditions in the heat transfer systems and the evaluation and application of the new enhanced heat transfer technologies.There are 98 pictures,4 tables and 107 references in this paper. |
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