Comprehensive Property Study Of The Large-And-Small-Hole Baffle Heat Exchanger

Large and small hole (LASH) baffle heat exchanger is a shell-and-tube heat exchanger with a new type of shell-side fluid-guided structure. By employing the LASH baffle structure, the cross flow in the shell-side of conventional heat exchangers is changed into longitudinally annular-gap wall jet flow with a profile of periodically contractiong and ejection. Thus, the induced vibration of the tube bundle can be greatly reduced, the pressure drop of fluid flow in the shell-side can be significantly decreased and the comprehensive heat transfer can be improved. In this dissertation, the LASH baffle heat exchanger is systematically studed. The major work and achievements are as follows.(1) A new type of shell-side fluid-guided structure or LASH baffle was studied. In the baffle, large and small holes are reasonably arranged. The small hole is an ordinary tube hole whose magnitude is the same as that for segmental baffles so as to support tubes. The large hole is designed to let the shell-side fluid go through the clearance between the hole and tube. Adjacent baffles have opposite large and small tube holes arrangements, thus the tube bundle can be effectively supported.(2) The concept of annular-gap wall jet was proposed. The annular-gap wall jet is a wall jet by which the fluid flows through annular gap and along the tube wall. Using numerical methods, velocity distribution, maximum velocity attenuation, half extended width variation, and surface heat transfer coefficient and skin friction coefficient along the tube axial variation, and so on, were studied. The parameters such as annular width and hole spacing were also studed for the influence on the flow and heat transfer of annular gap wall jet.(3) Fluid flow and heat transfer in LASH baffle heat exchangers with different large holes and two tube layouts were experimentally studied. Compared with the segmental baffle heat exchanger, results indicate that the shell-side pressure drop in the LASH baffle heat exchanger with the same layout and baffle pitch can be reduced by as much as50%. But the shell-side heat transfer coefficient is decreased in some extent. However, if evaluated with the heat transfer coefficient per unit pressure drop, the comprehensive performance of LASH baffle heat exchanger is generally higher than that of conventional heat exchanger.(4) Fluid flow and heat transfer in LASH baffle heat exchangers were also studied numerically. Influences of the parameters such as large hole diameter (LHD) and baffle pitch on the shell-side pressure drop and heat transfer coefficient were investigated. It is found that as a result of parallel flow, the local heat transfer coefficient and local friction coefficient outside the tube are low before the fluid passing through the clearance between large hole and the tube. But they increase very quickly when the fluid passing through the clearance and keep a high value for a certain length before falling down again. The shell-side pressure drop and heat transfer coefficient of LASH baffle heat exchanger increased with decreasing the LHD and baffle pitch. If the LHD and baffle pitches are reasonably chosen, the LASH baffle heat exchanger presents a larger shell-side heat transfer coefficient and lower shell-side pressure drop.(5) Based on the numerical simulation results, correlations of shell-side pressure drop and heat transfer coefficient of the LASH baffle heat exchanger were obtained, forming the basis for the industrial design of the LASH baffle heat exchanger.(6) By establishing fluid-solid coupling numerical models, the induced vibration of LASH baffle heat exchangers caused by fluid flow was analyzed. Comparing with the conventional heat exchanger, it is found that induced vibration of the tube bundle of the LASH baffle heat exchanger is significantly reduced compared with the segmental baffle heat exchanger.(7) Fluid flow and heat transfer in compound structures heat exchanger, which using LASH baffle and arc-tangent corrugated tubes, were experimentally studied. Compared with the segmental baffle heat exchanger, results indicate that it has a lower shell-side pressure drop and better comprehensive heat transfer ability.