Heat Transfer

In general, heat transfer increases with velocity, though the effect is far from linear. There are empirical correlations for this phenomenon covering a range of configurations. Please refer to a good textbook on heat transfer. "Fundamentals of Momentum, Heat and Mass Transfer" by Welty, Wicks & Wilson ISBN 0 471 93356 2 would be a good start.

Dear Sir

I saw your suggestion about Fundamentals of Momentum. I am trying to set up a system where seawater pipes are heated by solar power. Do you have any suggetions on books that would cover pipe materials and their properties. Thank you cryptic

Heat transfer in your case is not really a problem since the density of energy coming from the sun (W/m²) is small with respect to the capacity to take heat from a wall by a water flow. The convection coefficients of water being very high the temperature drop at the inside wall will be small. You could envisage to increase the lighted area in contact with the tube.

Basiccaly..increase the fluid velocity will increase the heat transfer...for example..when increase the velocity..more friction will produce then this will contibute increases in heat transfer....

the fluid at centre of tube will cooled 1st because it far from wall... while the outer tube still hot coz its have contact with the wall/shell side..that is why..some problem like shrinkage will occur..this effect by cooling system

Not so fast guys! Volume is essential and when rheology is involved, too fast is detrimental for cooling or heating! Some processess need exposure or contact time to transfer heat effectively.

Thats correct, one normally wants to create a turbulent flow, which is define by the Reynolds number.

Having designed HX and written programs for heat transfer in counter flow, u-tube, double and triple tubes, the amount of information can be seemingly endless as well as solving a number of variables simultaneously through iterations.

If you are familiar with process that you are developing, you can eliminate some of the criteria and number of iteration to define some of the variables, and come up with a very close estimation.

The effects are different if flow is laminar or turbulent.

The higher the turbulence the higher the transfer. Since turbulence is important the way the flow goes through the heat exchanger makes the difference. This is the reason why the re baffles to direct the flow perpendicularly to the tubes. As a very very rough indication convective heat transfer is proportional to velocity ^0.8.

From a practical standpoint, it is also important ensure that the design velocity is not; too low such that fouling is promoted or; too high such that erosion or corrossion is encouraged. TEMA is a good source for velocity limits.

You are correct!

During an IQ/OQ validation of an Arburg 350, due diligence drove us to perform some testingof this efect on the molds/parts. The curves showed drastic differences which lead us to "Optimize" and find the best settings. Accordingly, falling between two extremes to comply with the PQ's and achieving the best fit and results.