View source for Example: Calculation of average bulk temperature for property determination

====Problem Statement:====
A pipe has flowing water at an inlet temperature of 80°C. Heat is removed using cooling water outside the pipe. The final outlet temperature of the water is 40°C. Calculate the average bulk temperature of the water. Determine the viscosity of the bulk fluid and compare this value to the viscosity of water at 80°C and 40°C.
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====Solution:====

To calculate the bulk average temperature of a material, find the average temperature of the material:

<math> T_{bulk} = \frac{T_{out} + T_{in}}{2} = \frac{80 + 40}{2} =  60^\circ C
</math>

Now find the viscosity of water at 40°C, 60°C and 80°C and compare.

at 60°C:
<math>
\mu= 0.4656 \, mPa \ast s
</math> 

at 80°C:
<math>
\mu= 0.3537 \, mPa \ast s
</math> 

at 40°C:
<math>
\mu= 0.6539 \, mPa \ast s
</math>


Clearly, there is a large difference between the viscosities at the three different temperatures. This shows the importance of using bulk material temperature when determining properties instead of inlet or outlet temperature only.