3 replies to this topic

[R_Gowtham]

Hi All,

 

What is the Mean metal temp of heat exchanger shell and tube side?

 

why mean metal temperature is required during various scenario like startup, shutdown and during any upset condition? 

[Pilesar]

Mean metal temperature of the tubes is the average temperature of the metal of the tubes. Similar definition for the shell. Because metal expands according to its temperature, the differences in mean temperature can result in internal stress if the tubes and shell are connected at two fixed locations. There is a risk of mechanical damage due to this stress which may require an engineered expansion joint in the shell. The type of metal affects the coefficient of expansion. The length of the exchanger is also used in the stress calculations. The expansion joint calculations are not required for U-tubes because they are attached at only one point of the shell.

[R_Gowtham]

is any way to calculate the Mean metal temperature(Approx) manually? or we have go for HTRI or others

[Pilesar]

There will be several cases to calculate. Precise calcs are usually not needed for every new design. Instead, conservative engineering judgment is often used to populate the matrix of temperatures and cases. If the result indicates no expansion joint is needed, then all is well. In my experience, the exchanger manufacturer performs the final calcs to determine expansion joint requirements based on the temperatures provided. HTRI helps since it provides the mean metal temperatures. But as long as your results are conservative then it is not that big a deal to get the temperatures super accurate. It is important to make sure each reasonable scenario is considered in order to find the controlling case. Metal temperatures can be non-intuitive since they are influenced by the heat transfer coefficient. Boiling and condensing fluids have more influence than single-phase fluids. I have never tried a full precise manual calc and instead either use HTRI results or make conservative assumptions like 'this is condensing steam on the tube side, so assume that with no flow on the other side that the tube metal is the same as the condensing temperature.'