The heat exchanger shown in the figure consists of thin-walled copper tubes (k = 250 W/m-K) of 15-mm diameter located in a duct of H = 0.9 m x W = 0.75 m cross section. There are no fins attached to the tubes. Cold water enters the tubes at 20°C with an average velocity of 0.18 m/s, while hot air enters the channel at 350°C at an average velocity of 15 m/s. The tubes are arranged staggered with longitudinal and transverse pitches of SL = ST = 4.5 cm. There are 12 rows in the flow direction with 20 tubes in each row. Average surface temperature of the tubes is measured as 67.4°C. Evaluating the fluid properties at their inlet temperatures, determine (a) the convection heat transfer coefficient on the inner surface of the tube (b) the convection heat transfer coefficient on the outer surface of the tube (c) the overall heat transfer coefficient of the heat exchanger if the fouling factors, Rf, for the inner surface is estimated to be 0.0005 m?.K/W (d) the effectiveness of the heat exchanger, (e) the rate of heat transfer in the heat exchanger using e-NTU method (f) and the outlet temperatures of both fluids. (e) Propose at least three solutions in order to increase the effectiveness of the heat exchanger. State your reasons clearly. H Hot air Water 00
The heat exchanger shown in the figure consists of thin-walled copper tubes (k = 250 W/m-K) of 15-mm diameter located in a duct of H = 0.9 m x W = 0.75 m cross section. There are no fins attached to the tubes. Cold water enters the tubes at 20°C with an average velocity of 0.18 m/s, while hot air enters the channel at 350°C at an average velocity of 15 m/s. The tubes are arranged staggered with longitudinal and transverse pitches of SL = ST = 4.5 cm. There are 12 rows in the flow direction with 20 tubes in each row. Average surface temperature of the tubes is measured as 67.4°C. Evaluating the fluid properties at their inlet temperatures, determine (a) the convection heat transfer coefficient on the inner surface of the tube (b) the convection heat transfer coefficient on the outer surface of the tube (c) the overall heat transfer coefficient of the heat exchanger if the fouling factors, Rf, for the inner surface is estimated to be 0.0005 m?.K/W (d) the effectiveness of the heat exchanger, (e) the rate of heat transfer in the heat exchanger using e-NTU method (f) and the outlet temperatures of both fluids. (e) Propose at least three solutions in order to increase the effectiveness of the heat exchanger. State your reasons clearly. H Hot air Water 00
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Transcribed Image Text:The heat exchanger shown in the figure consists of thin-walled copper tubes (k = 250 W/m-K) of
15-mm diameter located in a duct of H = 0.9 m x W = 0.75 m cross section. There are no fins attached
to the tubes. Cold water enters the tubes at 20°C with an average velocity of 0.18 m/s, while hot air
enters the channel at 350°C at an average velocity of 15 m/s. The tubes are arranged staggered with
longitudinal and transverse pitches of SL = ST = 4.5 cm. There are 12 rows in the flow direction with
20 tubes in each row. Average surface temperature of the tubes is measured as 67.4°C. Evaluating
the fluid properties at their inlet temperatures, determine
(a) the convection heat transfer coefficient on the inner surface of the tube
(b) the convection heat transfer coefficient on the outer surface of the tube
(c) the overall heat transfer coefficient of the heat exchanger if the fouling factors, Rf, for the inner
surface is estimated to be 0.0005 m².K/w
(d) the effectiveness of the heat exchanger,
(e) the rate of heat transfer in the heat exchanger using e-NTU method
(f) and the outlet temperatures of both fluids.
(g) Propose at least three solutions in order to increase the effectiveness of the heat exchanger.
State your reasons clearly.
H
Hot air
Water
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