9 replies to this topic

[badj]

Gents,

 

How can i calculate the outlet temprature of the hot fluid if i know the three remaininig ones (cold fluid IN/OUT temperature, and IN temperature of the hot fluid).

Thanks

 

[fallah]

badj,

 

You need to know also the exchanger duty and specific heat/mass flowrate of both cold and hot fluids...

[srfish]

I have a small program that is not quite ready for publication. It calculates two unknown temperatures when two known temperatures are given. Usually the two inlet temperatures are given. The heat load is part of the calculation.But it is necessary to know the overall heat transfer coefficient. 

[Zauberberg]

Read the attached document - Chapter 6 in particular.

 

Attached Files

•  Heat Exchangers Design Notes.pdf   7.06MB   4171 downloads

[badj]

 Fallah,The heat duty can be calculated from the cold fluid since i got the mass flow rate and temperatures, now to achieve this and having a hot source with known temperature, what will be the outlet temperature and mass flow rate needed?

Srfish, i'm curious to know how to calculate having only two temperature. since specific heat, thermal conductivity, viscosity are fonction of the average temperature.

Zauberberg very nice document thanks

[serra]

possibly you can solve

 

dH(cold side) = dH(hot side)

 

not difficult if you are able to calculate dH, for example, negleting change of phase and assuming constant cp  as cp*dT*w

if there is change of phase (vaporization, condensation)  add the contribute of latent heat

[srfish]

badj

 

Since it is software on a computing device, trial-and-error solutions can be done nearly instantly. Since it is necessary to know the heat transfer coefficient, you know the UA to start with. This is the main variable that the software test against. At the start  the two shell side temperatures are set equal to each other. Then one temperature is  changed in small increments and  the resulting heat flux is calculated. When this heat flux reaches the maximum (UA), then you have a solution.

Edited by srfish, 31 March 2015 - 09:32 AM.

[P.K.Rao]

Following high school physics, heat gained = heat lost

So, heat gained by cold medium = heat lost by hot medium (neglecting other small quantities)

[breizh]

Hi ,

 

Consider the excel sheet attached .

 

Hope this helps

 

Breizh

[badj]

Thanks to you all, i really appreciate your help