6 replies to this topic

[Mohamed Selim]

According to counter current temperature gradient diagram of Heat Exchanger, we will find that the inlet temperature of the cold stream always smaller than outlet temperature of the hot stream in the right side of the diagram. 

 

as you know counter current is preferred because cold stream outlet temperature will be higher than hot stream outlet temperature so maximum heat is extracted from hot stream .

 

my inquiry is about if i raised the inlet temperature of cold stream to be higher than  outlet temperature of hot stream exactly to locate the temperature in between the range was gained before raining inlet cold stream temperature??

 

for example ... if we have cold stream (water) that is temperature will increase from 20 to 100 C, so i can reduce temperature of hot stream (crude oil)  to 90 C ..... if i use water with 92 C upraising it to 100 C, why not intersection between two lines in diagram happens, and I get the same result as before 90 C (crude oil), that doesn't happen?

 

Please explain!

[VeryProfessionalEngineer]

Heat exchangers facilitate heat transfer from high temperature to low temperature. Driving heat from a lower temperature stream to a higher temperature stream requires work, such as the work required to run the compressor of a refrigeration cycle. Since a heat exchanger is only facilitating heat transfer and does not work itself, it cannot transfer heat from a fluid that is already 92 or below to a stream that is 92C (your cold inlet stream temperature from your hypothetical).

 

Does that make sense?

[srfish]

I don't believe that example is practicable. Cooling the crude to 90 C when the entering water temperate is 92 C creates a temperature approach of only 2 C. This would be difficult to obtain.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

table.

Edited by srfish, 04 September 2017 - 02:48 PM.

[VeryProfessionalEngineer]

I don't believe that example is practicable. Cooling the crude to 90 C when the entering water temperate is 92 C creates a temperature approach of only 2 C. This would be difficult to obtain.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

table.

The approach is actually -2C, making it impossible.

[VeryProfessionalEngineer]

If I understand the question correctly, that is, the approach is -2C and it's not just infeasible but not attainable in any way.

[srfish]

You are right. I left off the negative sign on the temperature approach.

[Padmakar Katre]

According to counter current temperature gradient diagram of Heat Exchanger, we will find that the inlet temperature of the cold stream always smaller than outlet temperature of the hot stream in the right side of the diagram. 

 

as you know counter current is preferred because cold stream outlet temperature will be higher than hot stream outlet temperature so maximum heat is extracted from hot stream .

 

my inquiry is about if i raised the inlet temperature of cold stream to be higher than  outlet temperature of hot stream exactly to locate the temperature in between the range was gained before raining inlet cold stream temperature??

 

for example ... if we have cold stream (water) that is temperature will increase from 20 to 100 C, so i can reduce temperature of hot stream (crude oil)  to 90 C ..... if i use water with 92 C upraising it to 100 C, why not intersection between two lines in diagram happens, and I get the same result as before 90 C (crude oil), that doesn't happen?

 

Please explain!

 

What is crude oil inlet temperature?