| How to improve the heat exchange efficiency of heat exchangers is a hot research topic in the field of heat transfer.Twisted tape,as a means of passively enhancing heat transfer,have simple structures and low prices,and are widely used in various projects.The Comprehensive performance PEC,heat transfer characteristics and resistance characteristics of a heat exchanger with different Left-Right twisted tape(LRTT)inserts under laminar conditions were studied by experiments.Keep the twist rate of the traditional twisted tape(TT)unchanged,change the single twist of the traditional twisted tape to clockwise and counterclockwise alternate twist.The torsional periods of the Left-Right twisted tape are 90°and 180°,respectively.And three different types of notches are added to the LRTT with a 180°torsional period.In addition,this paper also studies the regularity of the length change of the Left-Right twisted tape and compares it with the traditional twisted tape.The laminar flow range of the experimental study is the Reynolds number of 500-1800.First,the reliability of the experimental table needs to be verified.The heat transfer characteristics Nu and friction characteristics f measured by the light tube are compared with the empirical formula.The results show that the error does not exceed 10%.The experiment studies and analyzes the TT with LRTT.The results show that Both the Nusselt number and the overall performance increase as the Reynolds number increases,the friction coefficient f decreases as the Reynolds number increases.The Nusselt number,the friction coefficient and the overall performance of LRTT and TT are reduced as the twisted rate increases.The Nusselt number of LRTT90° with a twist rate of 3 is the highest multiple of increase,which is 2.32-3.24 times.The increase ratio of the TT with a twist rate of 3 is 1.85-2.4 times that of the smooth tube,and the friction coefficient of the LRTT 90° with a twist rate of 3 is also the highest,and its increase is 3.9-7.3 times.The heat transfer effect of LRTT 90° with twist rate of 3 is also the best.Its comprehensive performance PEC can reach 1.46-1.67,and the comprehensive performance PEC of TT with a twist rate of 3 can reach 1.22-1.36.The experiment studies and analyzes the LRTT 90° and LRTT 180°,and adds three different types of notches to LRTT 180° : semicircle,rectangle and triangle.The results show that the heat transfer performance of LRTT with a twist period of 90° is better than that of LRTT with a twisted period of 180°.For the LRTT with a 180°torsional period,the research shows that the notched LRTT has the best heat transfer effect,and its comprehensive performance index can reach 1.35-1.6.The triangular notched LRTT is better than the rectangular and semi-circular notched LRTT,Its comprehensive performance index can reach 1.3-1.5.In the experiment,the length of LRTT 180° with semicircular notch and TT are studied and analyzed.The lengths of the study are 2400 mm,1800mm,1200 mm and 600 mm.The results show that the heat transfer performance of the four lengths of twisted tape is better than that of smooth tubes.The full-length twisted tape have the best heat exchange effect,and the friction coefficient is also the largest.The full-length LRTT 180° with semicircular notch is better than the full-length TT,and its comprehensive performance PEC value can reach 1.31-1.52.At the end of the experiment,the Nusselt number and the experimental correlation of the friction coefficient are fitted to the twisted tape of different structures.The error between the experimental correlation value and the experimental value does not exceed 10%,which provides guidance for the future research of this type of twisted tape. |
PDF Full Text Request