6.2__NTU-handout

6.2__NTU-handout - 6.2 Heat Exchangers NTU A.G.Ostrogorsky...

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6.2 Heat Exchangers –NTU A.G.Ostrogorsky 1 LMTD – advantages: - for problems for which temperatures are known (3 temperatures) - flow rate is known - select type/geometry… size, A, …calculate U Approach: use energy balance to find the 4 th temperature LMTD d, number of tubes, A. Check flow velocities and iterrate ---------------------------------------------------------- Number of Transfer Units (NTU) Method NTU - type, size, flow rates are known - outlet temperatures not known LMTD preferred for design calculations NTU preferred for performance calculations
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6.2 Heat Exchangers –NTU A.G.Ostrogorsky 2 Number of Transfer Units Approach: s C min /C max s NTU s ξ s max Q Q = s Get outlet temperatures Define 2 non-dimensional parameters: (i) Number of Transfer Units min C UA NTU = (ii) Effectiveness max actual Q Q rate HT imum max rate HT actual = = ξ ( ) max min in , c in , h min max T C T T C Q Δ = = ( ) ( ) c in out c h out in h actual T T C T T C Q
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6.2__NTU-handout - 6.2 Heat Exchangers NTU A.G.Ostrogorsky...

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