heat absorbtion vs tube size

[geoffthehammer]

We have a liquid flowing through a tube of given bore size. The tube is immersed in a heated liquid bath. If the volumetric flow rate through the tube remains constant, I need to compare the absorbtion of heat from the lquid in the bath through the tube wall into the flowing liquid for different tube bore sizes (assuming the tube wall thickness is constant.
To give you some idea of sizes, in our case the initial tubing may be 1/16" diameter with about 40" length of immersion. Liquid will be entering the tube at ambient temperature and the liquid bath temperature will be aroung 35/37 degree Celsius. we are trying to compare with tubing bores up to 1/8" dia.
if anyone can point me in the right direct it would be of great help.

 

[gr2vessels]

geoff,
The heat transfer area increase or decrease will have the efect of increased heat duty or decreased heat duty, for the same flowing conditions in the tube ( same liquid, same velocity, same temperature, same viscosity). Increasing the tube diameter, you also tend to increase the mass flow in the tube, hence larger mass can absorb more heat from the environment. The increase of the tube diameter will also increase the heat transfer area, thus allowing additional energy (heat) transfer from the bath to the liquid in the tube.
However, the outlet temperature of the tubeside fluid in the case of small and larger tube diameter might not be significantly different or even measurable, because the additional heat was absorbed in additional mass of fluid.
Given that you will have sufficient temperature differential between the bath and tubeside fluids, you will remove more heat from the bath with the larger diameter tube than with the smaller tube;- hence the temperature loss in the bath to the tube liquid will be higher in the case of larger dia tube. This bath temperature could be your measuring reference to quantify of energy loss from the bath to the tubeside fluid.
cheers,
gr2vessels