Changing flow rate and effect on U value in T&S HX
Changing flow rate and effect on U value in T&S HX
(OP)
Does anyboy have a rule of thumb that links changes in flowrate to a design U and flowrate.
Im specifically thinking of a gas heater with hot water on the shell side (so im assuming that all thermal resistance is on the gas side). The flow rate to vary is the gas flowrate both with regards to Sm3/hr but also a different pressure and temperature.
Best regards
Morten
Im specifically thinking of a gas heater with hot water on the shell side (so im assuming that all thermal resistance is on the gas side). The flow rate to vary is the gas flowrate both with regards to Sm3/hr but also a different pressure and temperature.
Best regards
Morten





RE: Changing flow rate and effect on U value in T&S HX
Re (Nu)(Pr-1/3)(visc ratio)-0.14
10000 40
20000 70
30000 95
100000 250
200000 450
500000 940
The variations are about a function of Re0.8.
So, if you change only the resistance of the gas side, you can estimate the new HTC on this side, and then recalculate the OHTC. J.P's Heat Transfer McGraw-Hill, tabulates the values of the thermal properties of the most common gases and liquids to facilitate the estimation.
RE: Changing flow rate and effect on U value in T&S HX