Shell Side Pressure Drop

First the computer assembles the information necessary to compute the crossflow velocity and the baffle window velocity. From storage it brings the net free distance (NFD) for crossflow. The net 

Equation 33 is used to calculate the shell longitudinal mass velocity, G/, in Ibs./sq. ft. sec., where Wg = shell flow rate, Ibs./hr. 

Equation 35 calculates the low flow velocity, V/, in ft./sec., where = shell-side fluid density, Ibs./cu. ft. 

Equation 39 calculates the turbulent, shell cross-flow pressure drop, AP, psi, where N = number of rows in crossflow and B = number of baffles. 

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Calculate the shell-side pressure drop. (Refer to the later section on Pressure Drop Relations and Figure 10-140. If AP is too high, reassume unit (step 3). 

Determine the shell-side pressure drop however, it is usually insignificant. It can be evaluated as previously described for unbaffled shells. 

The friction factor, f, is determined using Figure 10-140 for shell-side pressure drop with D, used in determining R,. For bundles with hare tubes (plain tubes), f, = f/1.2 (see Figure 10-140), calculate pressure drop ... 

Apj = shell side pressure drop with no bafQes, psi... 

Shell Side Pressure Drop in Condensers Kem recommends Equation 10-228 as being conservative ... 

The method of Buthod has given unusually good checks with data from industrial units. In general this method appears to give results that are slighdy higher than field data but not as high as the other methods presented previously. For shell-side pressure drop ... 

Pj = shell-side pressure drop, psi friction factor, fP/ in. cross-flow mass velocity, lb/ (ft ) (hr) shell I.D., ft = number of baffles... 

Whitley, D. L., Galculating Heat Exchanger Shell-Side Pressure Drop, Chem. Eng. Prog, V. 57, No. 9, p. 59 (1961). 

Starczewski, J., Short Cut Method to Exchanger Shell-Side Pressure Drop, Hydro. Proc., V. 50, No. 6, p. 147 (1971). 

Wills, M.J.N. and JOHNSTON, D. 22nd Nat. Heat Transfer Conf, HTD., 36. (ASME, New York, 1984) A new and accurate hand calculation method for shell side pressure drop and flow distribution. 

The divided flow and split-flow arrangements (G and J shells) are used to reduce the shell-side pressure drop where pressure drop, rather than heat transfer, is the controlling factor in the design. 

For the calculated shell-side Reynolds number, read the friction factor from Figure 12.30 and calculate the shell-side pressure drop from ... 

The estimated overall coefficient is well above that required for design, 302 compared to 192 W/m2oC, which gives scope for reducing the shell-side pressure drop. 

The pressure drops in the cross-flow and window zones are determined separately, and summed to give the total shell-side pressure drop. 

Though Bell s method will give a better estimate of the shell-side pressure drop than Kern s, it is not sufficiently accurate for the design of exchangers where the allowable pressure drop is the overriding consideration. For such designs, a divided-flow model based on Tinker s work should be used. If a proprietary computer program is not available,... 

Appreciably lower than that predicted by Kern s method. This shows the unsatisfactory nature of the methods available for predicting the shell-side pressure drop. 

The shell-side pressure drop is high. The fluid velocity on the shell-side could be decreased and the calculation repeated until an acceptable pressure drop is obtained. However, the approach allows the pressure drop to be specified directly. 

Tube-side and shell-side pressure drop... 

Based on the computer output a number of curves were produced as shown in Figure 4. To generate the doto necessary to produce the curves it wos assumed thot the overall heat transfer coefficient wos constant for all cases examined and the shell side pressure drop and heat tronsfer coefficient could be maintained by keeping the active tube length constant ond varying the bundle diameter and the number of tubes in order to satisfy the surface area requirements. 

The shell-side pressure drop of the surface condenser is quite low. The vapor outlet flow consists of air drawn into the system through leaks, C02, and a small amount of uncondensed steam. The weight flow of vapor from the top of the condenser is 1 percent or less than the flow of condensate from the bottom of the condenser. 

Effect of shell-side pressure drop. Reducing the baffle spacing increases cross-flow velocity and improves heat transfer. But it also increases the shell-side pressure drop. Reducing the baffle cut also improves heat transfer, but increases AP. 

Too much shell-side pressure drop can create a problem. The problem is flow through the bypass area shown in Fig. 19.3. This bypass area is caused by two factors ... 

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