I have a heat exchange device here that is not working properly; could you tell me why?
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I have a small tank here; the coiled tubes are placed inside it, with almost no gaps between them. The heat transfer oil in this small tank can be heated to a maximum temperature of 600 degrees. The lower outlet of the coil is connected to a nitrogen cylinder, and the flow rate of nitrogen is very low. What I want is for the temperature at the coil’s outlet to be around 160 degrees. However, after building this setup, it turned out that no matter how low the nitrogen flow rate is, the outlet temperature remains around 60-70 degrees – a temperature that can be tolerated if touched for a short time. If I close the valve at the coil’s outlet for a while and then reopen it, the first stream of gas that comes out is hot, but the temperature of the gas that follows is very low. Why is this?
If a liquid flows through the coil, then there is absolutely no problem at all; but it won’t work if gas is used instead. Additionally, it should be noted that the coiled tubes are quite thin – roughly equivalent to 4 thick tubes. The tank used for heating is about 59 mm in diameter and approximately 300 mm in height. The coiled tubes are arranged very closely together, so it’s unlikely that gas can escape before it has a chance to exchange heat. The flow rate of gas is extremely low. I’m off work now, so I can’t send the drawings right away; I’ll try to do so tomorrow. Thank you everyone! Looking forward to everyone's answers!
The gas heat transfer coefficient is low, and the heat exchange area is too small. The temperature can rise when trapped inside with no circulation. It is recommended to use thicker pipes to increase the heat exchange area.
This post was last edited by sosoby on 2016-7-27 at 12:51. Thank you for your responses: I just checked, and it turns out that the heat transfer coefficient of nitrogen is indeed very low. The technician is currently working on two tanks, using a series connection of these tanks to heat the nitrogen; results should be available by tonight! Thank you
Other heat transfer methods are incorrect; even with a tank used for heat transfer, the coefficient remains low, resulting in poor heat transfer efficiency
The heat exchange area is far from sufficient; I think you should swap the media in the coil and the tank – use heat transfer oil in the coil and nitrogen in the tank, and ensure that the tank is properly insulated.
If the gas inside the pipe is nitrogen, use porous packing to reduce the flow rate and increase the heat exchange time ；
finned tube； Multi-pass design: reduces flow velocity and increases heat exchange time ；
I support those who suggested finned tubes with multiple tube passes; there’s no need to consider coiled tubes. Your heat exchange capacity is not sufficient, so you should use a heat exchanger design software to do some calculations, or at least perform simple manual calculations. Without relevant basic data, it takes a great deal of experience to design an appropriate heat exchanger.
It’s not good either if the coils are too dense, as this affects both the heat exchange surface and the flow of the heat transfer oil on the outside. Also, have the calculations for the coil wall thickness been done correctly?