Flow rate for water-water heat exchange

This post was last edited by wiseboy on 2011-7-8 18:41, version 1. First, you need to consider whether there are any requirements regarding pressure drop in the process. If there is no requirement for voltage drop, then a higher voltage drop results in better heat transfer ； 2. Generally, when the water flow rate is between 1.5–2.0 m/s, the heat transfer coefficient is already quite high, and the pressure drop is around 0.03 MPa, which is sufficient ； 3. Furthermore, thermal equilibrium determines the flow rate of water on both sides, so it is not possible to determine the speeds on both sides simultaneously: you can only set one, with the other being a dependent variable. The specific details need to be carefully calculated; the above is just a rough estimate. Think about it: if, after performing a heat balance calculation, very little cold water is required while the hot water flow rate is high, how is it possible to increase the speed of the cold water? For example: Hot water: 10,000 kg/h, 70 ----> 68°C; Cold water: X kg/h, 12 ----> 58°C, where X can be calculated using heat balance. This kind of deformation problem is common in the chemical industry; let’s see how to determine the cold water flow rate

I’m checking your flow rate; it should generally be kept between 1 and 2.5 m/S. If the flow rate is very low, it doesn’t matter if the speed is a bit lower; consider all factors together.

This post was last edited by wiseboy on 2011-7-8 21:33. If the traffic is low, the flow rate is often very low, sometimes extremely so; there’s nothing that can be done about it. Experts hired by some owners often criticize my designs as having \"too low a design flow rate and lacking common sense,\" and sometimes they arbitrarily downplay the reliability of software calculations, claiming that they are not as good as their own experience. I faced severe criticism from these experts in Chongqing; it was one of the most baffling experiences in my design career. Key point: In such a situation, it might be possible to give up the shell-and-tube type and use some other type of heat exchanger to solve the problem properly. I don’t have time at the moment; I’ll talk about it in detail when I have time later.

This post was last edited by wiseboy on 2011-7-9 09:56, continuing from the previous post. If the flow rate is low, resulting in an excessively low velocity, the following actions can be taken: 1. Instead of a tubular heat exchanger, use another type of heat exchanger: 1) plate-type. The flow channel can be adjusted in size according to the flow rate to achieve an appropriate flow velocity; the downside is that it cannot withstand high pressures. It can be calculated using a certain Chinese plate heat exchanger software from the Northeast ； 2) Casing type. The inner and outer tube flow channels can be adjusted in size as appropriate according to the flow rate, in order to achieve an optimal flow velocity. It still retains the advantage of tubular heat exchangers in terms of withstanding high pressures, but its heat capacity is lower than that of tubular heat exchangers. The Chinese version of Xi’an Weiwei’s Dhem tube heat exchanger calculator can be used to carry out precise calculations very conveniently ； 2. Use a tube bundle, but not a standard design. If the fluid with lower flow rate flows through the tube side, the tube spacing can be increased, allowing for the use of fewer tubes. It’s a double-edged sword: the heat transfer coefficient increases (as the flow rate rises) while the heat transfer area decreases. Whether the overall effect is better or worse depends on specific calculations; generally speaking, the increase in the heat transfer coefficient has a dominant effect, resulting in an improved performance. Using Xi’an Weiwei’s Chinese version of Heat Exchanger Master (Them)’s verification mode, this optimization can be carried out very conveniently.

Modern coiled tubular heat exchangers can better address the aforementioned issues