HTRI ---- tube length and heat transfer coefficient
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One of the statements in the HTRI guidelines is that, in the case of phase-change-free heat transfer, as the length of the tube increases, the heat transfer coefficient also increases. I simulated it, and it’s indeed the case. Why is this the case? What’s the theory?
Do you mean the shell side or the tube side? I also did some simulations, and the overall heat transfer coefficient is exactly the opposite of what you said. There must be conditions attached to your statement.
In the last sentence of the image, no constraints were visible.
The sentence marked is the condition. What this sentence means is that with longer tubes, it is possible to use a smaller diameter for the heat exchanger at the same area; the flow velocity inside the tubes can increase, and as a result, the heat transfer coefficient rises. However, being too slender also increases manufacturing difficulties. Moreover, as the heat transfer coefficient increases, the pressure drop also rises; this allows the number of tube passes to be reduced in order to lower the pressure drop. But this still requires further comparison, as the number of tubes has a significant impact on the flow velocity.