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The wall of a cold storage consists of three layers - an outer layer of ordinary bricks, 25 cm thick, a middle layer of cork, 10 cm thick, and an inner layer of cement, 6 cm thick. The thermal conductivities of the materials are - brick: 0.7, cork: 0.043, and cement: 0.72 W/m °C. The temperature of the outer surface of the wall is 30 °C, and that of the inner is -15 °C. Calculate (a) the steady state rate of heat gain per unit area of the wall, (b) the temperatures at the interface of the composite wall, and (c) the percentages of the total heat transfer resistance offered by the inidividual layers. (d) What additional thickness of cork should be provided to make the rate of heat transfer 30% less than the present value?

The wall of a cold storage consists of three layers - an outer layer of ordinary bricks, 25 cm thick, a middle layer of cork, 10 cm thick, and an inner layer of cement, 6 cm thick. The thermal conductivities of the materials are - brick: 0.7, cork: 0.043, and cement: 0.72 W/m °C. The temperature of the outer surface of the wall is 30 °C, and that of the inner is -15 °C. Calculate (a) the steady state rate of heat gain per unit area of the wall, (b) the temperatures at the interface of the composite wall, and (c) the percentages of the total heat transfer resistance offered by the inidividual layers. (d) What additional thickness of cork should be provided to make the rate of heat transfer 30% less than the present value?

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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1. The wall of a cold storage consists of three layers - an outer layer of ordinary bricks, 25 cm thick, a middle layer of cork, 10 cm thick, and an inner layer of cement, 6 cm thick. The thermal conductivities of the materials are - brick: 0.7, cork: 0.043, and cement: 0.72 W/m °C. The temperature of the outer surface of the wall is 30 °C, and that of the inner is -15 °C. Calculate (a) the steady state rate of heat gain per unit area of the wall, (b) the temperatures at the interface of the composite wall, and (c) the percentages of the total heat transfer resistance offered by the inidividual layers. (d) What additional thickness of cork should be provided to make the rate of heat transfer 30% less than the present value?
Transcribed Image Text:1. The wall of a cold storage consists of three layers - an outer layer of ordinary bricks, 25 cm thick, a middle layer of cork, 10 cm thick, and an inner layer of cement, 6 cm thick. The thermal conductivities of the materials are - brick: 0.7, cork: 0.043, and cement: 0.72 W/m °C. The temperature of the outer surface of the wall is 30 °C, and that of the inner is -15 °C. Calculate (a) the steady state rate of heat gain per unit area of the wall, (b) the temperatures at the interface of the composite wall, and (c) the percentages of the total heat transfer resistance offered by the inidividual layers. (d) What additional thickness of cork should be provided to make the rate of heat transfer 30% less than the present value?
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