4 replies to this topic

[ndeer44]

I am tasked with evaluating the performance of several condensers around my unit and plan to compare my calculated overall heat transfer coefficients to clean U values.

 

I have the cooling water flow rate, inlet/outlet temperatures of both streams, the composition of the vapor that is to be condensed, and the total tube area. With this information I can calculate the total duty transferred, and back calculate the flow rate of the condensing stream (assuming complete condensing, which should be true for this stream)

 

From schooling I remember you can calculate the overall heat transfer coefficient U using 

U=Q/(A*(LMTD))

 

but for this scenario I expect the Log Mean Temperature Difference will be skewed as the hot side inlet and outlet temperature will be very close, assuming the hot side outlet is not sub cooled.

 

Are there any other equations I should be using to arrive at my U value or any correction factors that are needed when dealing with condensing streams?

 

 

[srfish]

What about the dewpoint of the condensing stream?

[ndeer44]

What about the dewpoint of the condensing stream?

 

Yes, with having the composition of the vapor I can find the dewpoint at the operating pressure.

[srfish]

I am puzzled by the expression used " expect the Log Mean Temperature Difference will be skewed as the hot side inlet and outlet temperature will be very close". Very close temperatures would not skew the LMTD.

 

If you don't have the fouling factors chosen, you could refer to TEMA or some other publication.

 

For a good condensing coefficient you need the size of the bundle. in  order to determine the number of vertical rows, assuming it is a horizontal heat exchanger.

[S.R.Shah]

ndeer44

 

SRFISH has rightly asked for dew Point

To find Clean Coefficient for condensation in existing plants;It requires process details

 

Different Heat transfer coefficient shall achieve for different type of condensations such as

1.Single Component condensation

2. Multicomponent condensation with out Non Condensable

3.Multi component condensation with non condensable.

 

Second ,Practically There is no 100% condensation and 100 % Sub cooling with single coolant  .You have to study practical situation.

 

 

You shall get your all answers in DQ Kern-Process Heat Transfer

 

SRSHAH