How to increase the heat transfer coefficient of a heat exchanger
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⑴Increase the turbulence level to reduce the thickness of the inner layer of the stagnant layer. Methods include: ① Increasing the fluid flow velocity. In a shell-and-tube heat exchanger, the flow velocity inside the tubes can be increased by raising the number of tubes in the tube side, while the heat transfer rate can be enhanced by adding baffles on the shell side. ②By changing the flow conditions, the fluid is forced to continuously change its direction of flow, thereby inducing turbulence. For example, in a plate heat exchanger, turbulence begins to occur when Re=200. ⑵Increase the thermal conductivity of the fluid. If liquid metals are used as heat carriers in the nuclear industry, their thermal conductivity is more than ten times greater than that of water. ⑶Descaling. After the heat exchanger has been in use for a long time, the scale layer thickens, affecting heat transfer, and it is necessary to remove this scale. Such as online cleaning technology, which can remove scale layers during the operation of heat exchangers.
The heat transfer coefficient of a heat exchanger is composed of the heat transfer coefficient in the tube side, the heat transfer coefficient in the shell side, the anti-scaling coefficient, etc., and it is determined by the smallest among these heat transfer coefficients. First, it is necessary to determine or calculate the heat transfer coefficients for each part, identify the minimum value – which represents the \"bottleneck\" – and then find ways to increase that value. If the heat transfer coefficient in the tube side is low, measures such as installing turbulators inside the tubes can be taken; if the coefficient on the shell side is low, baffles can be added, etc., to increase the turbulence coefficient. In short, as long as the pressure drop is acceptable, increasing the turbulence intensity of the medium is always effective, and there are many existing measures for this. Identifying the “bottleneck” factors and focusing on the main contradictions will yield very noticeable results.