A feed-water heater that supplies a boiler consists of a shell-and-tube heat exchanger with o1 shell pass and two tube passes. One hundred thin-walled tubes each have a diameter of 20 m and a length (per pass) of 2 m. Under normal operating conditions water enters the tubes at kg/s and 290 K and is heated by condensing saturated steam at 1 atm on the outer surface of tubes. The convection coefficient of the saturated steam is 10,000 W/m² ·K. Please use NTU method to determine the water outlet temperature. Hint: (1) please use the Dittus-Boelter correlation to determine the internal convection coeff hị; (2) Assuming thin wall tubes and ignore the conduction resistance of the tube walls; (3) F use Table A.6 to obtain all thermo-physical properties; (4) based on Table 11.3, choo: appropriate equation to obtain ɛ from NTU.

Elements Of Electromagnetics
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A feed-water heater that supplies a boiler consists of a shell-and-tube heat exchanger with one
shell
and two tube passes. One hundred thin-walled tubes each have a diameter of 20 mm
pass
and a length (per pass) of 2 m. Under normal operating conditions water enters the tubes at 10
kg/s and 290 K and is heated by condensing saturated steam at 1 atm on the outer surface of the
tubes. The convection coefficient of the saturated steam is 10,000 W/m2 K.
Please use NTU method to determine the water outlet temperature.
Hint: (1) please use the Dittus-Boelter correlation to determine the internal convection coefficient
h;; (2) Assuming thin wall tubes and ignore the conduction resistance of the tube walls; (3) Please
use Table A.6 to obtain all thermo-physical properties; (4) based on Table 11.3, choose an
appropriate equation to obtain ɛ from NTU.
TABLE 11.3 Heat Exchanger Effectiveness Relations [5]
Flow Arrangement
Relation
1- exp[-NTU(1 + C)]
1+C,
Parallel ow
(11.28a)
1- exp[-NTU(1 – C)]
1- C, exp[-NTU(1 – C,)]
Counterow
(C,< 1)
NTU
(C, = 1)
(11.29a)
1+ NTU
Shell-and-tube
1+ exp[-(NTU),(1+ C;)²]]-1
1- exp[-(NTU),(1 +C})!²j
One shell pass (2, 4, ... tube passes)
(1+ C}12 x
(11.30a)
-1
n shell passes (2n, 4n, . tube passes)
(11.31a)
E =
Cross-ow (single pass)
Both fluids unmixed
8 = 1- exp
|(NTU)" {exp[-CANTU)®7] – 1}
(11.32)
Cmar (mixed), Cin (unmixed)
(1– exp{-C,[1 – exp(-NTU)]})
(11.33a)
Cain (mixed), Cmax (unmixed)
6 = 1 – exp(-C,(1– exp[-C{NTU)]})
(11.34a)
All exchangers (C, = 0)
8 =1- exp(-NTU)
(11.35a)
Transcribed Image Text:A feed-water heater that supplies a boiler consists of a shell-and-tube heat exchanger with one shell and two tube passes. One hundred thin-walled tubes each have a diameter of 20 mm pass and a length (per pass) of 2 m. Under normal operating conditions water enters the tubes at 10 kg/s and 290 K and is heated by condensing saturated steam at 1 atm on the outer surface of the tubes. The convection coefficient of the saturated steam is 10,000 W/m2 K. Please use NTU method to determine the water outlet temperature. Hint: (1) please use the Dittus-Boelter correlation to determine the internal convection coefficient h;; (2) Assuming thin wall tubes and ignore the conduction resistance of the tube walls; (3) Please use Table A.6 to obtain all thermo-physical properties; (4) based on Table 11.3, choose an appropriate equation to obtain ɛ from NTU. TABLE 11.3 Heat Exchanger Effectiveness Relations [5] Flow Arrangement Relation 1- exp[-NTU(1 + C)] 1+C, Parallel ow (11.28a) 1- exp[-NTU(1 – C)] 1- C, exp[-NTU(1 – C,)] Counterow (C,< 1) NTU (C, = 1) (11.29a) 1+ NTU Shell-and-tube 1+ exp[-(NTU),(1+ C;)²]]-1 1- exp[-(NTU),(1 +C})!²j One shell pass (2, 4, ... tube passes) (1+ C}12 x (11.30a) -1 n shell passes (2n, 4n, . tube passes) (11.31a) E = Cross-ow (single pass) Both fluids unmixed 8 = 1- exp |(NTU)" {exp[-CANTU)®7] – 1} (11.32) Cmar (mixed), Cin (unmixed) (1– exp{-C,[1 – exp(-NTU)]}) (11.33a) Cain (mixed), Cmax (unmixed) 6 = 1 – exp(-C,(1– exp[-C{NTU)]}) (11.34a) All exchangers (C, = 0) 8 =1- exp(-NTU) (11.35a)
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