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Double Pipe Heat Transfer of Propylene glycol and Water

Question

A double-pipe heat exchanger uses water to cool propylene glycol. Use the data in Table 1 to answer the following questions.

Table 1 – Physical properties of water and propylene glycol  
 

 

Mass flow rate (lbm/hr)

Heat capacity  (Btu/lbm-°F) Temperature (°F)
entering
Temperature (°F) Leaving
Water   5000    1.00     60          -  
Propylene glycol  10,000    0.60    200       100  

(a) If the double-pipe heat exchanger is operated in counter current flow, what is the required heat exchange area if the heat transfer coefficient is 200 Btu/hr-ft2-°F?

(b) The heat transfer coefficient is 50Btu/hr-ft2-°F on the side of the heat exchanger with the water inlet (side “1”) and is 350 Btu/hr-ft2-°F at the water outlet (side “2”). Assume the heat transfer coefficient varies linearly with water temperature and the following equation applies:  Q = A (h1∆T2 – h2∆T1/In (h1∆T2/ h2∆T1))                          where ΔT = TPG - TWater. Calculate the required heat exchanger area.

(c) What are the minimum mass flow rates of water required to reduce the temperature of propylene glycol from 200°F to 100°F (as indicated in Table 1) for counter- and co-current flows?

(d) If the double-pipe heat exchanger is instead operated in co-current flow, what is the required heat exchange area if the water flow rate is 15,500 lbm/hr and the heat transfer coefficient is 200 Btu/hr-ft2-°F?  How do the water flow rate and area compare to your result from part (a)?

Summary

The question belongs to Chemical Engineering and the question is about using a double pipe heat exchanger for cooling down propylene glycol. Questions such as using double pipe heat exchanger to counter current flow, the required heat exchange are, the minimum mass flow rates of water required to reduce temperature from 200°F to 100°F, etc have been discussed with calculations in the solution .

Note: The answers are in handwritten format

 

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