Tube-side pressure drop, heat

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. 

Prandtl number of coolant (-) tube pitch (m) pressure drop (N/m ) pressure drop of coil (N/m ) shell-side pressure drop (N/m ) tube-side pressure drop (N/m ) volumetric flow rate (m /s) heat load (W, kcal/s) product... 

Tube-side pressure drop and heat transfer coefficient ... 

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. 

If either the tube-side film coefficient or fouling coefficient is the controlling resistance to heat transfer, doubling the tube-side velocity can increase the overall heat-transfer coefficient by 50%. Be careful This modification will also increase the tube-side pressure drop (assuming noncompressible flow) by a factor of eight. Such an increase in pressure drop is frequently acceptable when operating at lower throughputs. 

The concept is that the tube-side fouling rate will be reduced by continuous scrubbing of the tube wall and also have a favorable impact on heat transfer. The associated increase in tube-side pressure drop with this device is about 1.5 psi per pass at 3 ft/s tube-side velocity, about half that of Spirelf or Fixotal. 

The concept is to increase turbulence in the tube-side flow, especially at the tube wall by constantly mixing slow moving fluid near the tube wall back into the bulk, thus increasing tube-side heat-transfer rate and reducing fouling. The additional tube-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 concept is that this vibration reduces fouling and increases flow turbulence, producing an improvement in heat transfer coefficient However, there is also an associated increase in tube-side pressure drop of about 3 psi per pass at tube-side velocities of 3 ft/s. 

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. 

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. 

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. 

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