A question about heat exchangers
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Can the flow velocity inside the tubes of a shell-and-tube heat exchanger be increased by adding more tubes in the tube side? ? ? What is the reason for this?
With the flow rate and the overall dimensions of the heat exchanger remaining constant, a reduction in the flow area occurs (an increase in the number of tube passes leads to a decrease in the flow area per pass); therefore, the flow velocity must increase in order to maintain a balance in the inflow and outflow of material
Because with more manifolds, less liquid flows into each channel, while the amount of liquid entering the heat exchanger remains the same; as a result, the flow velocity increases. However, it should be noted that as the flow rate increases, the corresponding pressure loss also increases; it is necessary to consider whether flow is possible.
With multi-pass pipes, the number of pipes decreases compared to before, and thus the cross-sectional area also decreases; as a result, the flow velocity increases for the same flow rate. Multi-tube passes are generally used to enhance heat transfer by increasing the flow velocity.
Flow rate is equal to velocity multiplied by cross-sectional area. With constant flow rate and a decreasing cross-sectional area, the flow velocity must increase.
In fact, it can be understood in this way: when the flow rate in the pipe network remains constant, the more pipe stages there are, the fewer pipes there are per stage (number of pipes per stage = total number of pipes / number of pipe stages). As a result, the flow area decreases while the flow velocity increases
The main purpose of increasing the number of tube passes is to increase the heat exchange area, reduce the total area occupied by the device, and lower the overall cost of the equipment. However, it is necessary to ensure that the sum of the cross-sectional areas of the heat exchange tubes in each tube pass is greater than the cross-sectional area of the connection pipes; otherwise, the system pressure will rise, increasing the system’s cost.