Thermo-Hydraulic Design of Single and Multi-Pass Helical Baffle Heat Exchangers

Helical baffle heat exchangers offer and attractive option in terms of reduced heat transfer area for the same pressure drop and heat duty compared to conventional exchangers. Besides, the flow patterns inside the helical shell promote higher heat transfer coefficients and even reduced fouling. This type of technology has successfully been used in crude processing. Open literature design methodologies for helical baffle exchangers make use of the Bell-Delaware approach and applications deal with the design single shell and single tube pass arrangements. In certain applications the fluid velocity and the pressure drop can be increased by increasing the number of passes and even the number of units in series, thus giving rise to complex thermal arrangements. In such applications a correction factor for the logarithmic mean temperature difference must be determined. Figure 1 shows a two shell pass and one tube pass unit. As the hot fluid enters and flows along the length of the exchanger, it encounters the opposite fluid flowing in parallel flow fashion whereas as the shell fluid enters the outer section of the shell it flows counter-currently. A shortcut design approach based on the simplified determination of the correction factor of the log mean temperature difference is developed and demonstrated on case studies.