Heat exchanger tube-side pressure drop

Design a new shell-and-tube heat exchanger for the conditions of Example 13.7, but with maximum shell-side and tube-side pressure drops of 10 psi each. 

Heat exchanger pressure drop is mainly a function of velocity, that is, tube velocity for tube side pressure drop and bundle velocity for shell side pressure drop. 

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. 

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... 

The basic reason for using different control-valve trims is to keep the stability of the control loop fairly constant over a wide range of flows. Linear-trim valves are used, for example, when the pressure drop over the control valve is fairly constant and a linear relationship exists between the controlled variable and the flow rate of the manipulated variable. Consider the flow of steam from a constant-pressure supply header. The steam flows into the shell side of a heat exchanger. A process liquid stream flows through the tube side and is heated by the steam. There is a linear relationship between the process outlet temperature and steam flow (with constant process flow rate and inlet temperature) since every pound of steam provides a certain amount of heat. 

When considering the steam side of steam heated reboilers, it is best to think about the reboiler as a steam condenser. The steam, at least for a conventional horizontal reboiler, is usually on the tube side of the exchanger, as shown in Fig. 8.1. The steam is on the tube side, because the shell side was selected for the process fluid. If the reboiler is a thermosyphon, or natural-circulation reboiler, then low-process-side pressure drop is important. For a horizontal reboiler, it is easiest to obtain a low pressure drop for the fluid being vaporized by placing it on the shell side. 

For flow of a gas or liquid across the tubes on the shell side of a shell-and-tube heat exchanger, a preliminary estimate of the shell-side pressure drop can be made by the method of Grimison (1937). The pressure drop is given by a modified Fanning equation ... 

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