3 replies to this topic

[kaidlut]

hello,everyone! In our ASU plant,we use the steam heated water bath vaporizer to heat the Cryogenic liquid，The design temperature of outlet pipe line is 65℃，My question is ：when there is no water in the vaporizer and the coil is heated directly by the steam, can the outlet exceed the design temperature？

Edited by kaidlut, 15 December 2022 - 02:32 AM.

[Pilesar]

You can find steam tables showing the condensing temperature of steam at different pressures. Steam condensing temperature at atmospheric pressure is nominally 100C.

[kaidlut]

You can find steam tables showing the condensing temperature of steam at different pressures. Steam condensing temperature at atmospheric pressure is nominally 100C.

Hi Pilesar, thank you very much for your response.

 

So you mean the upper limit temperature of heated stream is 100C, my understanding is that because the shell side(steam side) pressure is 1atm, condensing temperature at the surface of tube is 100C, and these water at the surface of tube prevent further heat transfer, is that right ?

[Pilesar]

Normally, the outside tube walls of water bath vaporizers only see hot water. The water level is to be maintained for proper operation. Without water, the outside of the tubes will see a higher temperature and much greater heat flux than with hot water. The condensing steam is normally used only to heat the water. In other words the heat exchanger has two separate functions: 1) Transfer heat from hot water to the process 2) Transfer heat from steam to water. This can be broken down further. For example, in function 1 heat is transferred from the hot water to a film on the outside of the tube. That film transfers heat to the outer tube wall. The outer tube wall transfers heat through the tube to the inner tube wall. The inner tube wall transfers heat to a film on the inside of the tube which then transfers heat to the bulk fluid inside the tube. Each of these heat transfer steps has its own resistance to heat transfer. The exchanger designer took these resistances into account when the exchanger was engineered for hot water on the outside of the tubes. It is possible the designer also considered 'what if the water was not there' in the design but I suspect their instructions were 'make sure there is always water there.' If you explain your technical background and your concerns you may get more useful answers.