Tube Side Pressure Drop

Pressure drop, tube side, from Figure 10-139. 

Figure 10-57. Effect of velocity on heat transfer rates and pressure drop shell-side and tube-side. (Used by permission Shroff, P. D. Chemical Processing, No.4, 1960. Putnam Publishing Co., Itasca, III. All rights reserved.)...

Step 5. Pressure drop (tube and shell side)... 

Tube pass Tube pass is a tool for heat exchanger designer to control the tube side velocity, pressure drop, and heat transfer, F.achtime tube side fluid flows from one head to the other is counted as one pass. For countercurrent flow heat exchanger, it has one tube pass and one shell pass. If tube side flow is low or there is enough allowable tube side pressure drop, tube pass should be Increased to increase tube side velocity and heat transfer. For tube pass mote than one, partition plates are required at inlet and outlet heads to direct the tube side fluid flow. 

APm.AP,., Pressure drop for ideal-tube-bank cross-flow and ideal window respectively AP for shell side of baffled exchanger kPa Itf ft ... 

For a given pressure drop, higher heat-transfer coefficients are obtained on the sheh side than on the tube side. 

Principal advantages are high rate of heat transfer, no internal pressure drop, short time of contact (very important for heat-sensitive materials/ easy accessibihty to tubes for cleaning, and, in some cases, prevention of leakage from one side to another. 

One device uses four baffles in a baffle set. Only half of either the vertical or the horizontal tube lanes in a baffle have rods. The new design apparently provides a maximum shell-side heat-transfer coefficient for a given pressure drop. 

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

Common to all air cooled heat exchangers is the tube, through which the process fluid flows. To compensate for the poor heat transfer properties of air, which flows across the outside of the tube, and to reduce the overall dimensions of the heat exchanger, external fins are added to the outside of the tube. A wide variety of finned tube types are available for use in air cooled exchangers. These vary in geometry, materials, and methods of construction, which affect both air side thermal performance and air side pressure drop. In addition, particular... 

There are many text books that describe the fundamental heat transfer relationships, but few discuss the complicated shell side characteristics. On the shell side of a shell and tube heat exchanger, the fluid flows across the outside of the tubes in complex patterns. Baffles are utilized to direct the fluid through the tube bundle and are designed and strategically placed to optimize heat transfer and minimize pressure drop. 

Tube holes cannot be drilled very close together, since this may struc-tually weaken the tube sheet. The shortest distance between two adjacent tube holes is called the clearance. Tubes are laid out in either square or triangular patterns as shown in Figure S-.i. The advantage of square pitch is that the tubes are accessible for external cleaning and cause a lower pressure drop when shell-side fluid flows perpendicularly to the tube axis. The tube pitch is the shortest center-to-center distance between adjacent tubes. The common pitches tor square putienis arc i-in. OD on... 

Example If the shell-side coefficient of a unit is 25 Btu/hr (ft )(°F) and velocity in the shell is doubled, read the new shell-side coefficient, h as 36 (line a). If the tube-side coefficient is 25 and velocity is doubled, read the new tube coefficient, h, as 43.1 (line a). In other cases, pressure drop would increase by a factor of 4. Note This may be used in reverse for reduced flow. 

Calculate the tube-side pressure drop. (Use Figure 10-139 for the end return losses. For water in tubes, use Figure 10-138 for tube losses. For other liquids and gases in tubes, use Figure 10-137. 

If the tube-side pressure drop exceeds a critical allowable value for the process system, then recheck by either lowering the flow rate and changing the temperature levels or reassume a unit with fewer passes on tube side or more tubes per pass. The unit must then be rechecked for the effect of changes on heat transfer performance. 

For the tube side pressure drop, refer to Figure 10-138 ... 

Tube side Determine heat transfer coefficient from Figure 10-46 (using tube-side curve) at Reynold s number calculated for pressure drop evaluation. If the hj calculated exceeds 300 for organics (Figure 10-103), use a value of 300 and correct to outside coefficient, hj. ... 

Inlet nozzles should be sized for 2.5 gpm liquid per tube with the inlet line pressure drop not to exceed 1.5 psi per 100 equivalent ft of inlet piping for total gpm. Nozzles may, in all cases, come into the side of the bottom channel. 

Pressure Drop for Plain Tube Exchangers A. Tube Side... 

Tube Side Condensation Pressure Drop Kem recommends the following conservative relation ... 

Figure 10-136. Tube-side liquid pressure drop for cascade cooler. For nonwater liquids, multiply pressure drop by (n, ) " (s) (Used by permission SGL Technic, Inc., Karbate Division.)...

Figure 10-139. Tube side end return pressure drop per tube pass viscosity close to water.

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 ... 

Tube-Side Heat Transfer and Pressure Drop... 

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