Hello, I am having some trouble trying to find an equation that would allow me to calculate the nusselt number for a laminar flow on the shell side for a heat exchanger with a tube bundle.

For the moment I've assumed a nusselt number of 4.3 for the sake of calculations in an excel spreadsheet.

I'm hoping to use this spreadsheet to design shell and tube heat exchangers so that the dimensions can be altered to obtain a desired output temperature for a fluid.

I've done research and I use this paper here:

http://homepages.wmi...r_corrected.pdf

For the basis for my calculations. In there its state the equation for the nusselt number for a turbulent flow is:

Nu= ho*De/kf =0.36*Re^0.55*Pr^(1/3) * (µ/µs)^0.14

(also here I am assuming µ is tube side fluid viscosity and µs is shell side fluid viscosity, please correct me if i'm wrong)

In this paper there is no mention of the equation for laminar flow, which is strange considering in my spreadsheet (see attached image) most of my results thus far has laminar flow for the shell side.

I do have experience with calculating nusselt number without an equation taken from table 8.2 in ''Fundamentals of Heat Transfer'' by incropera and Dewittbut that is for a concentric tube heat exchanger.

Also one final note, I have found that in my spreadsheet when the heat exchanger is above a certain length/ diameter/ or tube bundle, the outlet fluid temperatures doesn't make sense for a parallel flow heat exchanger. For example, one fluid at 20 degrees and another fluid at 80 degrees enters the heat exchanger, then exit at 30 degrees and 26.7 degrees respectively.

If anyone could lend some advice on how to obtain the nusselt number and my spreadsheet I'd be very grateful. Thank you