A) Why does the inlet temperature of the of the cold water seem to decrease at higher flowrate.B) How is the logarithmic mean temperature difference affected increasing the heat exchange surface area by increasing pipe length.Thanks in advance?
Normally the inlet cooling water temperature is fixed. Only the outlet cooling water temperature is subject to change and with higher flow rates you get a better heat transfer coefficient and you can transfer the required heat without the cooling water temperature getting as warm. With a longer exchanger you have more time and more surface area to effect the heat transfer. This results in the delta T being smaller and the LMTD should also be smaller.
