Seek advice on heating air with steam
Thread Content
I would like to ask everyone: For air with a flow rate of 3000 m3/h, at temperatures ranging from 20 to 60 degrees Celsius, what size of heat exchanger is required? The heating is to be done using steam, with the air pressure at 0.3 MPa and the steam pressure also at 0.3 MPa. What is the heat transfer coefficient for gas-to-gas heat exchange? What is the typical inter-tube flow velocity?
It is recommended that the moderators take a look at the few posts on floor 2; they are all of this kind of confusing and meaningless posts. Giving lectures that are off-topic is a minor offense. . . . . Back to the topic: The original poster has provided too little information, and that can lead to ambiguity. If it’s simply 0.3 MPa of saturated steam heating 0.3 MPa of cold air, then it’s straightforward. If there is no need to recover the water formed by vapor condensation, then it’s sufficient to specify which type of heat transfer element will be used in order to calculate the heat transfer coefficient. The flow rate also corresponds to the heat transfer element. There are also requirements regarding material energy consumption, and so on. . . . Is it the poster’s question about \"what is the heat transfer coefficient between gases\" that causes ambiguity? It makes one wonder whether superheated steam is intended to be used to heat the air? Ensure no phase change of water vapor? So without a clear description, it’s difficult to answer questions. . .
There are two types of air preheaters in power plants: the first stage involves steam heating, while the second stage involves flue gas heating. For heat transfer in steam heating, in addition to theoretical calculations, model testing should also be carried out.
Thank you for the reply; saturated steam will do. Since this operating condition is used very rarely, I would like to ask about the values for the heat transfer coefficient and the flow rate.
Based on your requirements, it is generally acceptable to use a heat transfer coefficient of 35 kcal/(m2·h·°C) for the heat exchange between steam and gas. At a pressure of 0.3 MPA, the temperature of saturated steam is around 134°C; to achieve a temperature range of 20 to 60°C, approximately 70 kg/h of saturated steam is required.
35kcal/(m2*h*℃) = 40W/m2.℃?
Do heat exchangers also drain water through steam traps? The water vapor can be separated, and more steam can be extracted from the water for use in the heat exchanger. Since the temperature of the hot air is quite low, simple adjustments are sufficient to meet the requirements