A thin-walled tube with a diameter of 6 mm and length of 2 0 m is used to carry exhaust gas from a smoke stack to the laboratory in a nearby building for analysis. The gas enters the tube at 2 00 ° C and with a mass flow rate of 0.00 3 kg / s . Autumn winds at a temperature of 15 ° C blow directly across the tube at a velocity of 5 m / s . Assume the thermophysical properties of the exhaust gas are those of air. (a) Estimate the average heat transfer coefficient for the exhaust gas flowing inside the tube. (b) Estimate the heat transfer coefficient for the air flowing across the outside of the tube. (e) Estimate the overall heat transfer coefficient U and the temperature of the exhaust gas when it reaches the laboratory.
A thin-walled tube with a diameter of 6 mm and length of 2 0 m is used to carry exhaust gas from a smoke stack to the laboratory in a nearby building for analysis. The gas enters the tube at 2 00 ° C and with a mass flow rate of 0.00 3 kg / s . Autumn winds at a temperature of 15 ° C blow directly across the tube at a velocity of 5 m / s . Assume the thermophysical properties of the exhaust gas are those of air. (a) Estimate the average heat transfer coefficient for the exhaust gas flowing inside the tube. (b) Estimate the heat transfer coefficient for the air flowing across the outside of the tube. (e) Estimate the overall heat transfer coefficient U and the temperature of the exhaust gas when it reaches the laboratory.
Solution Summary: The author calculates the average heat transfer coefficient for exhaust gas flowing in the tube based on table A-4 "Thermo physical properties of air at atmospheric pressure".
A thin-walled tube with a diameter of 6 mm and length of
2
0
m
is used to carry exhaust gas from a smoke stack to the laboratory in a nearby building for analysis. The gas enters the tube at
2
00
°
C
and with a mass flow rate of
0.00
3 kg
/
s
. Autumn winds at a temperature of
15
°
C
blow directly across the tube at a velocity of
5 m
/
s
. Assume the thermophysical properties of the exhaust gas are those of air.
(a) Estimate the average heat transfer coefficient for the exhaust gas flowing inside the tube.
(b) Estimate the heat transfer coefficient for the air flowing across the outside of the tube.
(e) Estimate the overall heat transfer coefficient U and the temperature of the exhaust gas when it reaches the laboratory.
Liquid ammonia is transported from a production plant to a processing center via a 0.6-m diameter pipeline
at a mass flow rate of 0.15 kg/s. Surface temperature of the pipe is maintained 0°C by using a cooling jacket
with ice-cold water. Ammonia enters the pipeline at -17°C and exits at -3°C. Assume the flow is both
hydrodynamically and thermally fully developed in the pipe. What is the length of the pipe?
185.7m
Q11)
Air is to be heated by passing it over a bank of 3 m long tubes inside which steam is
condensing at 100ºC. Air approaches the tube bank in the normal direction at 20°C
and 1 atm with a mean velocity of 5.2 m/s. The outer diameter of the tubes is 1.6 cm,
and the tubes are arranged staggered with longitudinal and transverse pitches of S, =
Sp = 4 cm. There are 20 rows in the flow direction with 10 tubes in each row.
Determine (a) the rate of heat transfer, (b) and pressure drop across the tube bank,
Air at 0.8 atm enters at 18 C. Flows across bank of tubes 13 rows high and 7 rows deep at velocity of 9 m/s .The surfaces of tubes are maintained at 78 . The length of tubes is 1.2 m and the diameter of 1.5 cm .They are arranged in staggered manner so that the spacing in both the vertical and horizontal direction are 3cm and 2.25cm respectively. Calculate the total heat transfer and the exit air temperature.
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