Design Calculation And Application On Trisection Helical Baffle Heat Exchangers

In this paper,the structure optimization of helical baffle heat exchanger and the characteristics of trisection or sextant circumferential overlap helical baffles are introduced.The prediction correlations for performances of shell side resistance and heat transfer of helical baffle heat exchangers are proposed,and the helical channel is regarded as a spiral coil tube,and the performance data are calculated according to the forced convection heat transfer of spiral coil tubes.A new formula for hydraulic diameter Dh in helical baffle channel are delivered from the ratio of four times the cross-sectional area over wet perimeter length to the ratio of the net volume of the shell side Vnet over the shell side surface area As excluding the both ends.Thus both the numerator and the denominator are easily calculated.Also the cross-sectional area of helical baffle channel can be obtained from the net volume of the shell side Vnet divided by the average length of the spiral channel Lh.The prediction correlations are proposed for design and check of the performances of shell side resistance and heat transfer of helical baffle heat exchangers.At the same time.the calculation results of the models are compared with the available experimental test results of the trisection circumferential overlap helical baffle heat exchangers,in the transferring heat Q,the overall heat transfer coefficient K and shell side heat transfer coefficient ho,shell side pressure drop Apo,comprehensive indexes h0·△po-1/3 and ho·App-1 versus shell side flow rate.The comparison results show that their corresponding variation trends are about the same.Thus the proposed thermal design method has opened a new window to develop a simpler design method for helical baffle heat exchangers,even though the correction coefficients for different helical baffle structure have yet to be improved.In industrial applications,the primary criterion for the users is that under the same heat transfer area more heat can be transmitted or under the same heat load the heat transfer area of the heat exchanger can be reduced with the helical baffle heat exchanger in replacing the segment baffle one.In this thesis the optimized reformation project of heat exchange process of the atmospheric and vacuum distillation unit is taken as an opportunity.by comparing the heat transfer temperatures of intermediate products of crude oil,furnace fuel consumption changes before and after the project implementation unit.The results show that through the energy optimized reformation,the temperature of desalting crude oil tank raised 30 ℃;the temperature after desolation of crude oil entering into the flash tower raised 15 ℃;the terminal temperature of crude oil after heat exchange raised 20 ℃;thus the optimized heat exchange network has achieved good effect of heat transfer.Because of the raised temperature of 15 ℃ of crude oil into the flash tower,the bottom oil output is reduced,which makes the light components in the crude oil vaporized as far as possible in the flash tower.At the same time,the increase of the heat transfer terminal temperature of bottom oil reduces heating load in atmosphere furnace.