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Heat Transfer Coefficient

To calculate the coefficient α we need the relative easy accessible values of the temperature and the volume flow:

The transferred heat (Q) in a exchanger:
Q = α x A x (T2 - T1) x Δt
with: α = heat transfer coefficient, A = heat transfer surface, (T2 -T1)= temperature difference, Δt = examined time frame

The transferred heat (Q) of one of the liquids:
Q = cp x dm x (T2 - T1) x Δt
with: cp = heat capacity of the fluid, dm= volume flow of the fluid, (T2 - T1) = temperature difference, Δt = examined time frame

equalizing the both heat transfers as well as the average temperatures
ΔTm

      (T_Hot_In -T_Coldt_Out) - (T_Hot _Out- T_Coldt_In)
    ΔTm =
      ln T_Hot_In - T_Coldt_Out  
     
 
      T-Hot_Out - T_Coldt_In  


results in the heat transfer coefficient (α):

 

    α = cp x dm x (T2 - T1)
   
    A x ΔTm

 

For the control (development of heat transfer coefficient) are no absolute values required, so it is possible to set A as constant (=1), and assuming always the same liquid cp and hence the same density ρ and set both as well as constant(=1). Doing like this we will get the "qualitative" Heat transfer coefficient αm .

αm = 1 x dv x (T2 - T1) / 1 x ΔTm

    αm = 1 x dv x (T2 - T1)
   
    1 x ΔTm

 

    αm = dv x (T2 - T1)
   
    ΔTm


using: T2, T1 the inlet and outlet temperature of the fluids and the volume flow.
The heat loss is also taken as constant.

 

How to use?

To check your own values and performance of a heat exchanger, also to store and reload your values in the database, please enter your Email address. Of course we will not use the Email address for any other purpose.
To calculate a trend in minimum 2 sets of values are required. The date entered has to be of two different days. The trend line is calculated using the method of the "best fit curve" (smallest quadrate).


The chart is standardized, means the trend line will always start at 1, with the oldest date.
The volume flow, has to be the real values in order to get a valid result, because changes in the system or incrustations in the heat exchanger might result in changed volume flow. So when entering only e.g. the design value or what is written on the pump, might give wrong results. Please enter only one of the volume flows, otherwise the equation will won't work.
Please enter the values at the in the flow sheet of the heat exchanger below, once finished please click "use values". Same way the entered values are stored.
If you have already stored some values before, and you like to add more values, please just enter your Email, and click "reload chart", the stored values will be shown and you can continue entering new values.

If you need help, or have ideas how to improve this calculation, please contact us.

 

 

 

 

To see practical examples about controlling the heat transfer in heat exchangers, please see the case Refinery of Aramco, Refinery in Dubai, or more detailed information about heat exchanger cleaning, cooling water treatment or fouling.