Heat Exchanger Problem
Heat Exchanger Problem
(OP)
Hello I need some help with a heat exchanger calculations.
A counterflow H Ex uses combustion gases to heat air for a process.
The data T1 in(air)= 25C , T3 in (gases)=180C and T4 out (gases)= 85C
air mass flow= 1 kg/s, gases m= 1.8 kg/s
The combustion gases lose heat to the environment by 5 KW
If I consider 4.18 Kj/KgK as Cp for both streams what would be the heat transfered to the air and the S generated?
I got Q air to be = 714.8 KW but for the enthropy no answer yet.
Is S gen = m air (Cp ln T2/T1) x Q surround/T surrondings alright? in KW/K Do I consider Ts of air here?
Thanks for your comments,
S
A counterflow H Ex uses combustion gases to heat air for a process.
The data T1 in(air)= 25C , T3 in (gases)=180C and T4 out (gases)= 85C
air mass flow= 1 kg/s, gases m= 1.8 kg/s
The combustion gases lose heat to the environment by 5 KW
If I consider 4.18 Kj/KgK as Cp for both streams what would be the heat transfered to the air and the S generated?
I got Q air to be = 714.8 KW but for the enthropy no answer yet.
Is S gen = m air (Cp ln T2/T1) x Q surround/T surrondings alright? in KW/K Do I consider Ts of air here?
Thanks for your comments,
S





RE: Heat Exchanger Problem
I think though that you'd be best served by investing in some software to calculate your answer. While someone could answer your questions, are you really sure you want to base your design off of what an anonymous person on the Internet tells you? Isn't it better to get the software yourself and have your own answers?
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RE: Heat Exchanger Problem
RE: Heat Exchanger Problem
The second question would be, what is the basis for the 5 kW heat loss?
I disagree with the Cp value. Should be about 4 times lower for air, ald lower still for the hot gas.
RE: Heat Exchanger Problem
Nonetheless, if you have the correct specific heats, and the exit temperature of the air, you can calculate the amount of energy transferred.
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
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RE: Heat Exchanger Problem
Want to know the do's and don'ts of Eng-Tips? Read FAQ731-376: Eng-Tips.com Forum Policies.
English not your native language? Looking for some help in getting your question across to others or understanding their answers? Go to forum1529: Translation Assistance for Engineers.
RE: Heat Exchanger Problem
Thank you all..