@moeinSj Regarding your interesting questions of heat transfer rate for fully-developed laminar pipe flow versus flow rate, I think one quick solution is to set up a CFD simulation and inspect the results, maybe we can gain good insights. As far as convection is concerned, the total heat transfer rates should be higher at higher flow rates, this is obvious from conservation of energy of an open system for the pipe flow.

@moeinSj Regarding your interesting questions of heat transfer rate for fully-developed laminar pipe flow versus flow rate, I think one quick approach is to set up a CFD simulation and inspect the results, maybe we can gain good insights. As far as convection is concerned, the total heat transfer rates should be higher at higher flow rates, this is obvious from conservation of energy of an open system for the pipe flow.