How do you calculate overall heat transfer coefficient for a shell and tube heat exchanger?

Answer 1

When a cold object and a hot object are in direct contact (touching) heat will be transferred through thermal conduction.

Normally, heat transfer processes are categorized as thermal conduction, radiative transfer or convection.

Heat transfer through thermal conduction is the direct transfer of kinetic energy from one molecule to the nearby molecules. Because temperature is directly proportional to kinetic energy, interactions between neighboring particles exchange energy and that exchange energy gradually works it way from the higher temperature regions to the lower temperature regions. The process of the temperature becoming the same is called thermal equilibration.

Convective heat transfer occurs in fluids. If a gas, liquid, or other fluid, changes in fluid density change the buoyancy and will cause fluid to flow (a process called convection) and the heat contained in the warmer fluid is transferred to a new location by the physical movement of the fluid.

Radiative transfer occurs when a hot object radiates electromagnetic energy. While the sun is an obvious source of electromagnetic energy, it is also generated in smaller amounts by any object. The hotter objects radiate more electromagnetic energy and the cooler objects absorb it. This radiative transfer is important but not as noticeable usually as the other two. It does occur between objects whether they are in direct contact or not, but is usually so small as not to be important of the objects are touching.

Answer 2

The heat gain or loss in a fluid is [(the temperature rise or fall) x (fluid flow per second) x (specific heat capacity of the fluid)]. So if you can measure these quantities for both fluids, they should be equal apart from any losses to the surroundings.

Answer 3

The equation for the overall heat transfer coefficient of a shell and tube heat exchanger is:

1/U = 1/hi + Rfi + Rfo + Rw + 1/ho

Where

U= overall heat transfer coefficient

hi= inside convective heat transfer coefficient, determined by correlations

Rfi= inside fouling resistance, assume a value or tabulated in a text

Rfo= outside fouling resistance, assume a value or tabulated in a text (often neglected)

Rw= conductive resistance of the wall = ln(ro/ri)/kw

kw= thermal conductivity of the wall material, tabulated in a text

ro= inside radius

ri= outside radius

ho= outside convective heat transfer coefficient, determined by correlations

Answer 4

That very easy matter... u should find whether the modes of transfer... after finding modes u should find laminar or turblnt... & u should also find surface type of fow... then go to data book.. u ill get it