The develop of programming for reliable total heat transfer characteristics of a non-insulated double-pipe heat exchangerconsidering heat radiation effect

• Main Authors: Kuei-Chung Yu, 于貴中
• Other Authors: 黃景良
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/57145746680358786960

碩士 === 崑山科技大學 === 機械工程研究所 === 99 === The log mean temperature difference (LMTD) method neglecting heat radiation is conventionally used to calculate the total heat transfer rate for all types of heat exchangers. We discover that LMTD method can only obtained reliable solution in situations of insulated double pipe heat exchanger with high heat convection coefficient fluid located between inner and outer pipes. Thus, applying LMTD method to a non-insulated double pipe heat exchanger cannot obtain reliable solution. In this investigation, the log mean heat transfer rate (LMHTR) method considering heat radiation extended from the same concept in former study of single-pipe heat exchanger, is developed to calculate the total heat transfer characteristics of a non-insulated double-pipe heat exchanger. It is found that in this study that the total heat transfer rate of inner fluid obtained by LMHTR method is the same as that obtained by LMTD method while heat radiation effect is neglected but not for that of fluid between the inner and outer pipes. While air (or gas) with low convection coefficient is flowing between the inner and outer pipes, hence the heat radiation must be considered; it is found that the total heat transfer rate of fluid inside inner pipe and fluid between inner and outer pipes obtained by LMTD method are big different from that obtained by LMHTR method. LMTD assumed that the total heat transfer rate of fluid located in inner pipe is the same as that of fluid between inner and outer pipes; it is inaccurate for the non-insulated double pipe heat exchanger. Thus, the practical and complete results can only be obtained by LMHTR method, developed by this study, in any situations of a non-insulated double-pipe heat exchanger.