Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations IDS on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Determining the flow on the counter-flow heat exchanger

Status
Not open for further replies.
_kon

_kon

Materials
Apr 26, 2024
2
I am trying to design a control system for a simple heating system (I am not en expert in this area) and I want to set the mass flow on both sides of the counter-flow heat exchanger at a given moment (in a simplified way for now). The cold water stream has temperature T1 and the mass flow is m1. I want to heat it to Tfinal temperature. The warm water stream has a temperature T2>Tfinal and the question is what should be the mass flow of the warm stream m2? I want to assume (for now) an ideal exchanger, which means that the overall heat transfer coeffisient OHTC can be as big as I want. For now, I used a simple equation:
m1*cp_water*(Tfinal-T1) = m2*cp_water*(T2-Tx)

I have two unknowns: m2 and Tx. I assumed that Tx can go down to T1, hence I can estimate (Tx_min = T1) that:
m1*(Tfinal - T1)<= m2(T2-T1)
hence:
m2 >= m1*(Tfinal-T1)/(T2-T1)

However, this is only an estimate (and I don't know if it is corrent)and does not take into account the flows in the exchanger.
Could someone help me (give me the right equation) or point me to a source that would allow me to correctly calculate m2?
 
Replies continue below

Recommended for you

Sort by date Sort by votes
Do you have a specific HX that you are working with?
Get the HEI (Heat Exchanger Institute) design manual for HX and use the sizing/rating equations there.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
Upvote 0 Downvote
If you have a theoretical pure countercurrent HX with infinite exchange area and /or infinite U, then your min value for m2 is correct.
 
Upvote 0 Downvote
thank you for your answers!

@EdStainless

Do you mean the book:
"STANDARDS FOR SHELL AND TUBE HEAT EXCHANGERS, 5TH EDITION" from:
?

@georgeverghese

I'm glad my estimates are right. Where would you recommend looking to be able to calculate the actual case for a concentric tube architecture exchanger?
 
Upvote 0 Downvote
Think you mean a double pipe exchanger, which is a pipe inside a pipe HX. These are pure countercurrent units. Thermal design of these is well covered in DQ Kern's Process Heat Transfer textbook.
Can you describe your service requirements ? Flows, max operating pressures, inlet / exit temperatures, service fluid type, total thermal duty, potential for fouling, corrosivity all play a role in HX selection.
 
Upvote 0 Downvote
Kern is a great source for these HX.
You can also find some manufactures web sites with sizing information
These are commonly used in sanitary service such as pasteurizers.
They are usually built serpentine because of how long they get.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

S
  • Question
Estimating steam flow through heat trace
Replies
4
Views
2K
goutam_freelance
goutam_freelance
I
  • Question
Heat Transfer with the sea
2
Replies
20
Views
8K
Snickster
Snickster
Jack Benson
  • Locked
  • Question
Counter Flow Plate Heat Exchanger Inlet / Outlets
Replies
12
Views
239
Jack Benson
Jack Benson
Samingme755
  • Question
Heat exchanger in hydrogen service
Replies
3
Views
1K
pvros
pvros
xlr8shun
  • Locked
  • Question
design of a counter-flow tube-in-tube supercritical steam heat exchanger 3
Replies
6
Views
230
EdStainless
EdStainless

Part and Inventory Search

Sponsor

Back
Top Bottom