【正文】 %,respectively.7 ConclusionThe characteristics of heat transfer and flow resistance forthe FBSTHX and the SBSTHX have been experimentally investigated. And performance parisons between the FBSTHX and the SBSTHX are conducted. The heat transfer and flow resistance correlation for SBSTHX and FBSTHX were developed based on the experiment results. The experimental results showed that under circumstanceof the sameRenumber both in shell and tube side, the Nusselt number Nufor FBSTHX is about 50% of that of SBSTHX while the pressure drop of the former is about 30% of the latter. But the prehensive performanceNu/Dp of the former is 60% higher than that of the latter. For the sake of energy saving in designing heat exchangers, both heat transfer enhancement and flow resistance increase should be taken into consideration. By properly designing FBSTHX the heat transfer and pressure drop performance can be improved relative to the traditional SGSTHX.References1. Qian SW (2002) Handbook for heat exchanger design. ChemicalIndustry Press, Beijing (in Chinese)2. Mukherjee R (1992) Use doublesegmental baffles in the shellandtube heat exchangers. Chem Eng Prog 88:47–523. Li H, Kottke V (1999) Analysis of local shell side heat and masstransfer in the shellandtube heat exchanger with discanddoughnut. Int J Heat Mass Transf 42:3509–35214. Li H, Kottke V (1998) Effect of baffle spacing on pressure dropand local heat transfer in shellandtube heat exchangersfor staggered tube arrangement. Int J Heat Mass Transf41(10):1303–13115. Lei YG, He YL, Rui L et al (2008) Effects of baffle inclinationangle on flow and heat transfer of a heat exchanger with helicalbaffles. Chem Eng Process 47(12):2336–23456. Lei YG, He YL, Pan C et al (2008) Design and optimization of heatexchangers with helical baffles. Chem Eng Sci 63(17):4386–43957. Dong QW, Wang YQ, Liu MS (2008) Numerical and experimental investigation of shell side characteristics for rod baffleheat exchanger. Appl Therm Eng 28:651–6608. Peng B, Wang QW, Zhang C et al (2007) An experimental studyof shellandtube heat exchangers with continuous helical baffles.J Heat Transf 129:1425–14319. Kara YA, Guraras OA (2004) Computer program for designing ofshellandtub。%, respectively,and the uncertainties involved in the Nunumber for FBSTHX and SBSTHX are within 177。 cp, specific heat under constant pressure, J/(kg K).According to Eqs. 2 – 5 , the overall heat transfer coefficient can be transfer performance on the tube side can beobtained by the following equation [13]Subscript f indicates the fluid temperature, and windicates the wall temperature. The thermal resistance of tube wall can be obtained by The tube material is chrome nickel steel and the its conductancek is W/(m K).After puting the heat transfer coefficient in tube side and thermal resistance for tube wall according Eqs. 6 and 7 , and substituting them and the total heat transfer coefficient k into Eq. 1 , we can get the heat transfer coefficient hoof shell Nu, f, and Reare defined as follows:where Dpo is the overall pressure drop on the shell side of the STHX, l is the effective length of tubes, do is the outer diameter of the tube.5 Experimental results and analysisThe experiments were conducted for the two types of STHXs described in , in which hot water flowed on the tube side and cold water flowed on the shell side of the STHXs. In order to verify the reliability of the experiment results, the heat transfer and fluid flow characteristics under three different tube inlet velocities (, and m/s) for SBSTHX and FBSTHX are investigated. And performances between the above two exchanger are pared.Proper evaluation is important for paring the prehensive performance of different heat exchangers. Both heat transfer coefficient and pressure drop are important parameters for performance evaluation of heat exchangers. It is desirable to obtain the highest heat transfer rate at the lowest pressure drop, so the ratio of Nusselt number Nuto pressure drop is used as a parison criterion in the present study.Figures 5 and 6 show the heat transfer correlation and flow resistance correlation for FBSTHX under the above three tube side inlet velocities. In the figures, the lines shown in these figures were fitted by the method of least squares, and the heat transfer correlation in the range of 7,000 B ReB 23,000 can be expressed as the correlation coefficient is r = .The flow resistance correlation in the ranger of 7,000 B ReB 23,000 can be expressed as – 14and the correlation coefficient for above equation is r = .It can be seen from Figs. 5 and 6 , that the Nusselt number Nu and pressure drop will increase with the increase of Renumber, and under the same shell side velocity and with different tube velocities for FBSTHX the heat transfer and flow resistance characteristic in shell side are almost the same, which prove the good repetition of the 7 and 8 show the heat transfer and flow resistance characteristics for SBSTHX. The lines shown in these figures were fitted by the method of least squares,and the heat transfer correlation in the range of 4,000 B ReB 15,000 can be expressed as the correlation coefficient for above equation is r = .The flow resistance correlation in the ranger of 4,000 B ReB 15,000 can be expressed as Eqs. 16– 17 and the correlation coefficients are r = ,r = respectively.As shown in Figs. 7 and 8 , the Nusselt number Nuand pressure drop will increase with the increase of Renumber.Under the same shell side velocity and with different tube velocity for SBSTHX the heat transfer and flow resistance characteristic are almost same, which prove the goodrepetition of the experiments. The parison of Nunumber and pressure drop D p inshell side between FBSTHX and SBSTHX can be seen in Figs. 9 and 10. Nusselt number Nu increases with the increase of Reynolds num