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Over Design In Air Heater By Increasing Air Flow

extra margin increasing air flow

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#1 dattatray kolte

dattatray kolte

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Posted 21 March 2019 - 07:05 PM

Dear Experts, 


Please help me to understand the meaning of following notes,

" Vendor to consider 10% extra margin by increasing air quantity". How to satisfy this note? Does this means normal over design we  have in HTRI output or any other specific meaning?


Thanks for your input!

#2 Pilesar


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Posted 21 March 2019 - 09:11 PM

If I were designing an air heater and read that instruction, I would interpret it to mean that I should multiply the air flow by 1.1 in the design calcs while still achieving the same outlet air condition. This is not the same as 10% overdesign in HTRI. I have included similar notes on design spec sheets in the past. Using extra flow for the margin puts a safety factor on the pressure drop as well as the thermal heat transfer. The engineer who wrote the note understands that there will be a margin added to the exchanger but wants to make it clear how and where the margin is to be applied. A note like this leads me to suspect the specifying engineer is competent and thoughtful and would not resent it if if you communicated directly with them.

#3 dattatray kolte

dattatray kolte

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Posted 23 March 2019 - 06:05 AM

Thanks for the reply. Indeed the note is specific. I have misquoted the note and the correct note is "Vendor to consider 10% extra margin on surface area by increasing air quantity". By this i understand 1. First design heat exchanger without any margin. BY this we know the required surface area for design condition. 2. Increase air flow rate with outlet temperature of air and other side (GW) open. By this require surface area increase and this increased area can be compared with case 1 to get 10% additional area. Let me know you view.

Edited by dattatray kolte, 23 March 2019 - 06:06 AM.

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