Heat transfer problem of temperature difference between cooling water inlet and outlet

As you said, if the cooling water flow rate remains constant, it indicates that the heat load initially changes before gradually stabilizing. The heat load calculation formula you provided is only applicable in a steady-state condition; therefore, to calculate the heat load more accurately, it is necessary to perform calculations for different periods, with △t being determined based on the actual conditions of each period.

The heat exchanger is scaled; I encountered this in China

The temperature after stabilization is the standard, so what about those high temperature differences earlier on? ? Should it be ignored? It should be taken into consideration. Moreover, it takes about 30 minutes for the cooling water to bring the system to a stable state – should the heat exchange that occurs during these 30 minutes not be counted? ? ? ? This post was last edited by lhxo524 on 2008-2-25 11:04.]

The temperature difference during the first 30 minutes can be determined using the arithmetic mean to find the temperature difference: handshake

It can be calculated using the average return water temperature at intervals of 5 minutes or less. The shorter the interval, the better. A more accurate method is the graphing approach: using time as the horizontal axis and the inlet water temperature and outlet water temperature as the vertical axes, a graph is drawn on paper, and the area between the two lines is then calculated. Draw it in AutoCAD: 1 mm on the x-axis represents 1 second, and 1 mm on the y-axis represents 1 degree; then simply calculate the area of the region.

Scaling, blockages, leaks, and other issues in the heat exchanger can all cause the temperature at the cooling water outlet to drop. △t is the average heat transfer temperature difference across the entire heat exchanger, and it depends on the flow direction of the cold and hot fluids. Is it co-current, counter-current, or something else?

It’s normal for the temperature to be high at first and then lower, right?

I am skeptical about the issue of scaling – 30 minutes is enough time to ignore its effects. I, on the other hand, strongly agree with the method suggested by the poster on floor 8

1. In the case of scaling, it is also necessary to use the value after stabilization, as this is when normal operating conditions prevail. 2. Since it’s not scaling, a transition period is required during operation; therefore, values after stabilization need to be used

The method on the eighth floor seems more scientific; if a rough approach is taken and a stable value is used, there should be no problem

Personal opinion: 1. I have reservations regarding the claim that \"the water temperature drops by 30 minutes due to scaling.\"； There is little possibility of scaling in such a short time ； 2. Will it be the same for the second time and subsequent attempts – high starting temperature, then stabilization after 30 minutes? 3. The original poster did not specify when cooling water was started to flow. If the water was introduced only when the temperature in the distillation vessel was high, then this phenomenon is quite normal. Because the temperature of the distillation kettle shell is relatively high when water flow is first established, this results in a high outlet water temperature as well ； Over time, it gradually decreases until equilibrium is reached ； 4. According to what was said above, the outlet water temperature is of course calculated based on the stabilized temperature! 5. During the stage of change in outlet water temperature, calculation is not very meaningful. It is changeable. Personal opinion, for reference only!

2. Will it be the same for the second time and subsequent attempts – high starting temperature, then stabilization after 30 minutes? Yes, it’s like this every time. 3. The original poster did not specify when cooling water was started to flow. If the water was introduced only when the temperature in the distillation vessel was high, then this phenomenon is quite normal. Because the temperature of the distillation kettle shell is relatively high when water flow is first established, this results in a high outlet water temperature as well ； Over time, it gradually decreases until equilibrium is reached ； Of course, cool water is supplied when the temperature remains constant. Thank you

In such a short period of time, scaling can be ignored; it takes some time to establish a steady-state heat transfer process. As for the calculations, the average temperature difference Δt should use the value after stabilization, as the values from the initial stages cannot be applied. Furthermore, the driving force for heat transfer depends on the logarithmic mean temperature difference between the two fluid streams; therefore, it takes time for equilibrium to be established. All chemical processes can be said to evolve from a non-steady state to a steady state gradually. :)

I’ve learned a lot :) :victory:

I wonder how long the original poster’s temperature measurement lasted? Is your cooling object operated intermittently or continuously?

Add a control valve to regulate the cooling water flow and meet the heat load

Why start circulating cooling water at a constant high temperature? I remember that in the units, cooling water is supplied first, followed by the feed material. If you wait until the equipment is at high temperature before introducing cooling water, could the equipment be damaged by the sudden drop in temperature? . I’m not familiar with heat calculations, so I have a small question – I hope everyone can help me answer it.