Dear friend

You should nevrer ignor them. Somehow it is similar to ignoring the friction and pressure drop in pipeline calculations. You should consider all thermal resistances. I suggest you take a look at TEMA standard.

in heat exchanger design the thickness is very important factor, Design parameters of elements such as shell diameter, tube length, sickness and pitch are required to be selected

Dear Undergrad Student,

* It must not be ignored.

Heat flows through solids at rates measured by their conductivity. The rate of heat flow is also proportional to the thickness of the material. Couple of experimental and theoretical model based results confirmed that conduction along the enclosure walls has a stabilizing influence on the convective motion in the enclosure and is therefore responsible for reduced average temperature differences across the cavity. It is found that the total heat transfer rate is an increasing function of the Rayleigh number, thermal conductivity ratio k* and a decreasing or increasing function of the wall thickness ratio t* according to the values of k* and Ra. The influence of critical parameters comprising of the Rayleigh number, Darcy number, Prandtl number, fluid to solid thermal conductivity ratio, and the heat transfer coefficient between the fluid and solid phases of the porous medium as well as the conjugate properties such as the wall thickness and the wall to fluid thermal conductivity ratio on the heat transfer rate possesses.

The rate of heat transfer is inversely proportional to the thickness of the cup. Thermal conductivity is not only affected by changes in thickness and orientation; temperature also has an effect on the overall magnitude. Because of the material temperature increase, the internal particle velocity increases and so does thermal conductivity. This increased velocity transfers heat with less resistance.

Refer this site which may be useful for you.

https://www.researchgate.net/publication/276354478_The_Effects_of_Wall_Thickness_and_Wall_Thermal_Conductivity_on_Natural_Convection_within_Square_Enclosures

Ashish

The need for the inclusion of tube wall thickness and conductivity depends on other factors including the exchanger layout/configuration, temperatures, internal and external heat transfer characteristics/coefficients, fouling factor(s), whether fining or other augmentation aids, etc. are employed. What you have with most models is a series of thermal resistances and if you tabulate them individually you can see which ones are critical and which can be ignored. I suspect that here you are experiencing good internal and external heat transfer so that the thermal resistance of the tubes is comparable to the other parameters, but you must check that you do not have a temperature cross with a single shell and that boiling is not happening.. Assuming that your parameters and arithmetic is without error, then in this case the tube properties and dimensions must be inserted.

Can you access a proprietory heat transfer package to check your results? I find that with certain packages it is better to sketch out a design with hand calc.s then ignore the "design" mode and input your numbers into a "check" rating mode. In doing this you will get an idea of your tube layout. Then make a few small changes and re-check to ensure that you are not in a sensitive region for the algorithms. A bit tedious but must be done. Fouling factors tend to be a very blunt approximation to real life.

Stephen

For precise calculation, it is not wise to ignore the wall conductivity in the heat exchanger.

Dear,

Practically, the tube wall thickness may be ignored when it is thin and has high thermal conductivity. But, for accurate estimations, they should be considered in the calculation.

Dear Undergrad Student

since you need the area and overall heat transfer coeffricinet then thickness can not be ignored.

1. thickness plays role in inner and outer heat transfer area

2. wall thickness and its thermal conductivity effect the overall U heat transfer coefficient

3. a 2 mm wall thichness is a typical value, not too thin so not to bee ignored

4. tube thickness has an impacat in total tubes volume and pitch between tubes so for a given shell diameter it puts a limit in number of shells

the above are some of the considerations one must think of.

but there is also the other side of things

for example if you need a general estimation of heat transfer area and have on specific information on the heat exchanger geometry then, a rough estimation can be made without considering wall thicness, you can be on the safe side by using an oversize factor in your design %30 to compensate for this

hope it helps