The attributes of the inlet streams to the heat exchanger are as follow: The UA

Question

The attributes of the inlet streams to the heat exchanger are as follow: The UA product in Btu/hr degree F for the heat exchanger is: UA = 1/0.12/C^0.8_k + 0.06/C^0.8_c + 2 middot 10^-7 Where C_k and C_c are the capacities in Btu/hr degree F. Using the NTU method, Find the out let temperatures and rating for parallel-flow arrangement Find the outlet temperatures and rating for counter-flow arrangement Find the outlet temperatures and rating if two of these heat exchangers are placed in series (0ne after another) and are operated in parallel-flow arrangement. What are the interface temperatures? Find the outlet temperatures and rating if two of these heat exchangers are placed in series (one after another) and are operated in counter-flow arrangement. What are the interface temperatures? Find the outlet temperatures and rating if two of these exchangers are placed in parallel (even mass flow rate split) and are operated in parallel-flow arrangement. Find the outlet temperatures and rating if two of these heat exchangers are placed in parallel (even mass flow rate split) and are operated in counter-flow arrangement. Based on the results of the above, discuss the utility of placing parallel-and counter-flow heat exchangers in series and parallel for added heat transfer capability.

Explanation / Answer

We know that , NTU(Number of transfer units) = UA/Cmin

Heat capacity ratio can be given as : Cr= Cmin/Cmax

For parallel flow heat exchanger ,

Effectiveness ( rating) = [1- exp{-NTU(1+Cr)}] ÷ [1+Cr]

For Counter flow heat exchanger ,

Effectiveness = [1-exp{-NTU(1-Cr)}] ÷ [1-Crexp{-NTU(1-Cr)}]

Qmax= Cmin(Th,i-Tc,i)

Q = Ch(Th,i-Th,o)= Cc(Tc,o-Tc,i) = effectiveness×Qmax

By above equation you can find out outlet temperature .

The task is to put numerals in the equations only.

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