Experimental Investigation On Heat Transfer Performance In Half-cylindrical Shell Space Of Different Structural Heat Exchangers

The development of energy-saving technology is of great significance to solve energy problems in our country.Heat exchangers are widely used in various industries as the core equipment for energy exchange,and the shell and tube heat exchangers are the most widely used ones.Therefore,how to improve the heat exchange performance of shell and tube heat exchangers is of great significance to the energy conservation and emission reduction.The superheated steam cooling section and condensate cooling section of a feedwater heater in power plants,as well as counter-flow U-tube heat exchangers,all involve heat transfer in the half-cylindrical space.In this paper,different baffle structure schemes in half-cylindrical space heat exchangers such as the ladder helical baffles and the orifice baffles to enhance heat transfer and the traditional segemental baffles were experimentally investigated.The testing cores of three ladder helical baffle types（single inclined ladder helical,dual inclined ladder helical and folded ladder helical）,three orifice baffle types（fillet triangle orifice,trefoil-orifice and quatrefoil-orifice）and segmental baffle ones with different baffle pitches in the half-cylindrical space heat exchangers were designed and manufactured.The testing platform was built and improved,and the heat transfer and flow resistance performance tests with water as the medium for both sides were carried out.The overall heat transfer coefficient,shell-side heat transfer coefficient,shell-side pressure drop,comprehensive performance h_oΔp_o^-1/3,Nusselt number,axial Euler number and other parameters of different baffle schemes were compared and analyzed,and the heat transfer enhancement effect and mechanism of the ladder helical baffles and the orifice baffles were further explored.Within the range of working conditions studied in this paper,the main research contents and results of the work are as follows:（1）The performances of half-cylindrical space heat exchangers of three kinds of ladder helical baffles and segmental baffles with different baffle pitches are compared and analyzed,and the results show that:The heat transfer performance parameters and shell-side resistance of the schemes with the baffle pitch of 40 mm are higher than those with the baffle pitch of50 mm,and the comprehensive performance h_oΔp_o^-1/3of the schemes with the baffle pitch of40 mm are lower than those with the baffle pitch of 50 mm.Under the same baffle pitch,the heat transfer performance and comprehensive performance of the ladder helical baffle schemes are all higher than those of the segmental baffle scheme,and the shell-side resistance is smaller than that of the segmental baffle scheme.Among the three ladder helical baffle schemes,the folded ladder helical baffle scheme F-40 has the best heat transfer performance,and the dual inclined ladder helical baffle scheme DH-40 has the smallest shell-side resistance and the best comprehensive performance.The shell-side heat transfer coefficient and comprehensive performance h_oΔp_o^-1/3of the scheme FH-40 are respectively 16.00%and14.26%higher than those of the segmental baffle scheme S-40,and the shell-side pressure drop is 5.32%lower than that of the scheme S-40;The shell-side heat transfer coefficient and comprehensive performance h_oΔp_o^-1/3of the scheme DH-40 are respectively 11.39%and17.58%higher than those of the segmental baffle scheme S-40,and the shell-side pressure drop is 18.09%lower than that of the scheme S-40.（2）The performances of three kinds of orifice baffles and segmental baffle half-cylindrical space heat exchanger with different baffle pitches are compared and analyzed,and the results show that:The heat transfer performance parameters and shell-side resistance of the schemes with the baffle pitch of 40 mm are higher than those of the baffle pitch of 50mm,and the comprehensive performance h_oΔp_o^-1/3of the schemes with the baffle pitch of 40mm are lower than those of the baffle pitch of 50 mm.Under the same baffle pitch,the heat transfer performance parameters of the orifice baffle schemes are slightly lower than that of the segmental baffle scheme,while the shell-side resistances of the orifice baffle schemes are much lower than that of the segmental baffle scheme,and the comprehensive performances of the orifice baffle schemes are much better than that of the segmental baffle scheme.The heat transfer performances of the three orifice baffle schemes are slightly different,and the resistance performances of the three orifice baffle schemes are almost the same.The shell-side heat transfer coefficient and shell-side pressure drop of the scheme F-40 are respectively 3.70%and 56.74%lower than those of the scheme S-40.And the comprehensive performance h_oΔp_o^-1/3of the scheme F-40 is 15.62%higher than that of the scheme S-40.（3）The performances of half-cylindrical space heat exchangers with three orifice baffles,three ladder helical baffles and segmental baffles with baffle pitch of 40 mm are compared and analyzed,and the results show that:The overall heat transfer coefficient,shell-side heat transfer coefficient and Nusselt number of the ladder helical baffle schemes are all higher than those of the orifice and segmental baffle schemes.The overall heat transfer coefficient and shell-side heat transfer coefficient of the ladder helical baffle scheme FH-40 which has the highest heat transfer performance are 9.55%and 25.52%higher than those of the scheme orifice baffle T-40,respectively;The comprehensive performance h_oΔp_o^-1/3of the ladder helical scheme is slightly higher than that of the orifice baffle scheme.The comprehensive performance h_oΔp_o^-1/3of the scheme DH-40 is 4.23%higher than that of the scheme T-40.The biggest advantage of the orifice schemes is that their pressure drop is very small,and their shell-side pressure drop and axial Euler number are much smaller than those of the ladder helical and segmental baffle schemes.The shell-side pressure drop of the scheme T-40which has the smallest shell-side resistance is 54.31%lower than that of the scheme FH-40.（4）The empirical correlations between the Nusselt number and the axial Euler number with respect to the axial Reynolds number for different baffle schemes are obtained by fitting the experimental data,which provides theoretical guidance for the design of the new half-cylindrical space heat exchangers.