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(3.4) The gas heater shown below in cross-section consists of a square sheet-metal duct insulated on the outside and a steel pipe (5 cm OD, 4.85 cm ID, k = 56 W/m K) that passes through the center of the duct. A heat-transfer fluid will flow in the pipe, entering at 500 K and leaving at 450 K, with a heat-transfer coefficient of 200 W/m² K. Process air will enter the heater at 300 K with a flow rate of 0.35 kg/s, leave at 350 K, and flow counter currently to the heat-transfer fluid. The heat-transfer coefficient for the air has been calculated and its value is 55 W/m². K. Fouling factors of 0.00018 m² K/W for the air stream and 0.00035 m² K/W for the heat-transfer fluid are specified. (a) Calculate the value of the overall heat-transfer coefficient to be used for designing the heater. (b) What is the mean temperature difference in the heater? (c) Calculate the required length of the heater.

(3.4) The gas heater shown below in cross-section consists of a square sheet-metal duct insulated on the outside and a steel pipe (5 cm OD, 4.85 cm ID, k = 56 W/m K) that passes through the center of the duct. A heat-transfer fluid will flow in the pipe, entering at 500 K and leaving at 450 K, with a heat-transfer coefficient of 200 W/m² K. Process air will enter the heater at 300 K with a flow rate of 0.35 kg/s, leave at 350 K, and flow counter currently to the heat-transfer fluid. The heat-transfer coefficient for the air has been calculated and its value is 55 W/m². K. Fouling factors of 0.00018 m² K/W for the air stream and 0.00035 m² K/W for the heat-transfer fluid are specified. (a) Calculate the value of the overall heat-transfer coefficient to be used for designing the heater. (b) What is the mean temperature difference in the heater? (c) Calculate the required length of the heater.

Introduction to Chemical Engineering Thermodynamics
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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(3.4) The gas heater shown below in cross-section consists of a square sheet-metal duct insulated on the outside and a steel pipe (5 cm OD, 4.85 cm ID, k = 56 W/m K) that passes through the center of the duct. A heat-transfer fluid will flow in the pipe, entering at 500 K and leaving at 450 K, with a heat-transfer coefficient of 200 W/m² K. Process air will enter the heater at 300 K with a flow rate of 0.35 kg/s, leave at 350 K, and flow counter currently to the heat-transfer fluid. The heat-transfer coefficient for the air has been calculated and its value is 55 W/m². K. Fouling factors of 0.00018 m² K/W for the air stream and 0.00035 m² K/W for the heat-transfer fluid are specified. (a) Calculate the value of the overall heat-transfer coefficient to be used for designing the heater. (b) What is the mean temperature difference in the heater? (c) Calculate the required length of the heater. Ans. (a) 42 W/m². K. (c) 18 m. Air Insulated on all four sides 15 cm 15 cm Heat transfer fluid
Transcribed Image Text:(3.4) The gas heater shown below in cross-section consists of a square sheet-metal duct insulated on the outside and a steel pipe (5 cm OD, 4.85 cm ID, k = 56 W/m K) that passes through the center of the duct. A heat-transfer fluid will flow in the pipe, entering at 500 K and leaving at 450 K, with a heat-transfer coefficient of 200 W/m² K. Process air will enter the heater at 300 K with a flow rate of 0.35 kg/s, leave at 350 K, and flow counter currently to the heat-transfer fluid. The heat-transfer coefficient for the air has been calculated and its value is 55 W/m². K. Fouling factors of 0.00018 m² K/W for the air stream and 0.00035 m² K/W for the heat-transfer fluid are specified. (a) Calculate the value of the overall heat-transfer coefficient to be used for designing the heater. (b) What is the mean temperature difference in the heater? (c) Calculate the required length of the heater. Ans. (a) 42 W/m². K. (c) 18 m. Air Insulated on all four sides 15 cm 15 cm Heat transfer fluid
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