Air (Cp=1005 J/kg.K) is to be preheated by hot exhaust gases in a crossflow heat exchanger before it enters the furnace.

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Air (Cp=1005 J/kg.K) is to be preheated by hot exhaust gases in
a crossflow heat exchanger before it enters the furnace. Air enters
the heat exchanger at 95 kPa and 20 °C at a rate of 0.8 m3 /s. The
combustion gases (Cp=1100 J/kg.K) enters at 180 °C at a rate of 1.1
kg/s and leave at 95 °C. The product of the overall heat transfer
coefficient and the heat transfer area is UA=12XX W/°C (4 digits,
example 1271 W/°C). Assuming both fluids to be unmixed (use the
graphs or equations below, show the values in the graphs),
determine the rate of heat transfer and the outlet temperature of
the air.
INSTRUTION: By XX use:
a) The two last digits of your student number if they are equal
or greater than 50, example S00000071 then XX=71
b) The two last digits of your student number plus 50 if they
are less than 50, example S00000034 then XX=34+50=84

Air Cp 1005 J Kg K Is To Be Preheated By Hot Exhaust Gases In A Crossflow Heat Exchanger Before It Enters The Furnace 1 (40.75 KiB) Viewed 17 times

Air Cp 1005 J Kg K Is To Be Preheated By Hot Exhaust Gases In A Crossflow Heat Exchanger Before It Enters The Furnace 2 (90.58 KiB) Viewed 17 times

Air Cp 1005 J Kg K Is To Be Preheated By Hot Exhaust Gases In A Crossflow Heat Exchanger Before It Enters The Furnace 3 (58.03 KiB) Viewed 17 times

Cross flow (both streams unmixed) Fig. 2-8(e) (2-32a) Cross flow (both streams mixed) ENTU NTU 1 - exp(- NTU) (2-33a) Cross flow (stream C unmixed) (2-34a) $ * 1 - exp {CINTU)671 [expl – C(NTU)07) – 11), ca 1 - exp| -" WATUMC) - 11" POSTUMIC $ = C11 - expl – C[1 – exp( - NTU)]], Č== NTU = ---In (1 + In (1 - EC)] 3 - 1 - exp{- @[1 – exp [ – (NTUMC)]); C- - In C In (1 - 5) + 1] Fig. 2-8(1) dashed curves (2-34b) Cross flow (stream in unmixed) Fig. 2-8(1) solid curves (2-35a) NTU = (2-35b)
1.0 200 1.0 0.9 சேன் 10.25 6 0.75 11.00 $ 0.7 0.6 0.5 04 0.3 0.2 0.1 0.0 0 1 3 4 1 2 3 4 5 5 NTU (b) Counter flow 0.25 0.7 0.6 0.76 0.5 11.00 0.4 0.3 0.2 0.1 0.0 0 1 2 3 4 5 5 NTU (a) Parallel flow 1.0 0.9 0.25 0.8 0.50 0.75 06 1.00 0.5 0.4 0.3 0.2 0.1 0.0 0 1 2 3 4 5 2 5 NTU (c) Shell and Tube with one shell and any multiple of two tube passes 2:00 1.0 0.9 0.8 0.7 Cri 026 10.50 0.75 1.00 5 $ 0.6 0.5 04 0.3 0.2 0.1 0.0 0 1 2 3 4 3 5 NTU (d) Two shell passes and any multiple of four tube passes
tube passUS 1.0 1.0 0.9 0.9 25 0.25 p.50 0.76 SET 0.8 0.7 0.6 Ce 60 bol 0.8 0.7 0.6 0.5 04 0.3 0.75 11.33 1.00 OS 9 04 0.3 02 0.2 0.1 0.0 5 0.1 0.0 0 1 2 3 4 5 0 1 2 3 4 NTU NTU (e) Cross flow with both fluids unmixed (d) Cross flow with one mixed and one unmixed. Where Cimbuna/Cumbed>1 NTU... is based on Cunetan FIGURE 2-8 Heat-exchanger effectiveness for various arrangements.