HEAT+MASS TRANSFER:FUND.+APPL.
6th Edition
ISBN: 9780073398198
Author: CENGEL
Publisher: RENT MCG
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Chapter 1, Problem 150P
Heat is lost through a brick wall
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A rectangular wall of length "L" m and height
"H" m is made from a thick bricklayer. The
rectangular wall has a surface area as 11 m2
& Thermal conductivity as 0.53 W/mK. The
wall is subjected to heat transfer due to the
outside temperature 43 °C and inside
temperature 24 °C. If the energy loss is 11219
kJ in 484 minutes. (HINT: 1 minute = 60
%3D
seconds)
Determine the following --
i) Heat transfer rate,
ii) Thickness of the wall.
A large plane wall has a thickness of 0.4 m, thermal conductivity k= 2.3 W/m.
°C, and surface area 30 m?. The left side of the wall is maintained at a constant
temperature of 90°C while the right side loses heat by convection to the
surrounding air at 25°C with a heat transfer coefficient of 24 W/m². °C.
Assuming constant thermal conductivity and no heat generation in the wall,
(i) Express the differential equation and the boundary conditions for steady
one-dimensional heat conduction through the wall
(ii) Obtain a relation for the variation of temperature in the wall
(iii) Evaluate the rate of heat transfer through the wall
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The thermal conductivity of Aluminum material at127°Cand 527 C are 240 and 218 W/m. K,
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Heat is generated in a slab of 120 mm thickness with a conductivity of 200 W/m K at a rate of
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find the heat flow rate at these planes and the temperature gradients at these planes.
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1. Determine the heat flow for (i) rectangular fins and (ii) triangular fin of 20 mm length
and 3 mm base thickness. Thermal conductivity = 45 W/m K. Conwection coefficient h=
100 W/m K, base temperature = 120°C surrounding fluid temperature = 35°C. Determine
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2. A circumferential fin on a pipe of 50 mm OD is 3 mm thick and 20 mm long. Using the
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Chapter 1 Solutions
HEAT+MASS TRANSFER:FUND.+APPL.
Ch. 1 - How does the science of heat transfer differ from...Ch. 1 - What is the driving force for (a) heat transfer,...Ch. 1 - How do rating problems in heat transfer differ...Ch. 1 - What is the difference between the analytical and...Ch. 1 - What is the importance of modeling in engineering?...Ch. 1 - When modeling an engineering process, how is the...Ch. 1 - On a hot summer day, a student turns his fan on...Ch. 1 - Consider two identical rooms, one with a...Ch. 1 - Prob. 9CPCh. 1 - Prob. 10CP
Ch. 1 - Prob. 11CPCh. 1 - An ideal gas is heated from 50C to 80C (a) at...Ch. 1 - What is heat flux? How is it related to the heat...Ch. 1 - What are the mechanisms of energy transfer to a...Ch. 1 - A logic chip used in a computer dissipates 3 W of...Ch. 1 - Consider a 150-W incandescent lamp. The filament...Ch. 1 - A 15-cm-diameter aluminum ball is to be heated...Ch. 1 - A 60-gallon water heated is initially filled with...Ch. 1 - Prob. 19PCh. 1 - Prob. 20PCh. 1 - Prob. 21PCh. 1 - Prob. 22PCh. 1 - Prob. 23PCh. 1 - Prob. 24PCh. 1 - Prob. 25PCh. 1 - Prob. 26PCh. 1 - A 5-m6-m8-m room is to be heated by an electrical...Ch. 1 - Prob. 28PCh. 1 - Air enters the duct of an air-conditioning system...Ch. 1 - Prob. 30PCh. 1 - Define thermal conductivity, and explain its...Ch. 1 - Which is a better heat conductor, diamond or...Ch. 1 - How do the thermal conductivity of gases and...Ch. 1 - Why is the thermal conductivity of superinsulation...Ch. 1 - Why do we characterize the heat conduction ability...Ch. 1 - What are the mechanisms of heat transfer? How are...Ch. 1 - Write down the expression for the physical laws...Ch. 1 - How does heat conduction differ from convection?Ch. 1 - Does any of the energy of the sun reach the earth...Ch. 1 - How does forced convection differ from natural...Ch. 1 - What is the physical mechanism of heat conduction...Ch. 1 - Consider heat transfer a windowless wall of house...Ch. 1 - Consider heat loss through two walls of house on a...Ch. 1 - Consider two houses that are identical except that...Ch. 1 - Consider two walls of a house that are identical...Ch. 1 - Define emissivity and absorptivity. What is...Ch. 1 - What is a blackbody? How do real bodies differ...Ch. 1 - A wood slab with a thickness 0.05 m is subjected...Ch. 1 - Prob. 49PCh. 1 - Prob. 50EPCh. 1 - The inner and outer surfaces of a 0.5-cm thick...Ch. 1 - Prob. 52PCh. 1 - Prob. 53PCh. 1 - The north wall of an electrically heated home is...Ch. 1 - Prob. 55PCh. 1 - Prob. 56PCh. 1 - Prob. 57PCh. 1 - A concreate wall a surface area of 20 m2 and a...Ch. 1 - Prob. 59PCh. 1 - Prob. 60PCh. 1 - Prob. 61PCh. 1 - Prob. 62EPCh. 1 - Air at 20C with a convection heat transfer...Ch. 1 - Prob. 64PCh. 1 - Prob. 65PCh. 1 - Prob. 66PCh. 1 - Prob. 67PCh. 1 - Prob. 68PCh. 1 - Prob. 69PCh. 1 - Prob. 70PCh. 1 - Prob. 71PCh. 1 - Prob. 72EPCh. 1 - Prob. 73PCh. 1 - Prob. 74PCh. 1 - Prob. 75PCh. 1 - Prob. 76PCh. 1 - Using the conversion factors between W and Btu/h,...Ch. 1 - The outer surface of a spacecraft in space has an...Ch. 1 - Consider a person whose expose surface are is 1.7...Ch. 1 - Prob. 80PCh. 1 - Two surfaces, one highly polished and the other...Ch. 1 - A spherical interplanetary probe with a diameter...Ch. 1 - Prob. 83PCh. 1 - Can all three modes of heat transfer occur...Ch. 1 - Can a medium involve (a) conduction and...Ch. 1 - The deep human body temperature of a healthy...Ch. 1 - We often turn the fan on in summer to help us...Ch. 1 - Prob. 88PCh. 1 - Prob. 89PCh. 1 - Prob. 90PCh. 1 - An electronic package with a surface area of 1 m2...Ch. 1 - Consider steady heat transfer between two large...Ch. 1 - Prob. 93PCh. 1 - Prob. 94PCh. 1 - A 2-in-diameter spherical ball whose surface is...Ch. 1 - Prob. 96PCh. 1 - Prob. 97PCh. 1 - A 3-m-internal-diameter spherical tank made of...Ch. 1 - Prob. 99PCh. 1 - Solar radiation is incident on a 5-m2 solar...Ch. 1 - Prob. 101PCh. 1 - Prob. 102PCh. 1 - Prob. 103EPCh. 1 - An AISI 304 stainless steel sheet is going through...Ch. 1 - Prob. 105PCh. 1 - Prob. 106PCh. 1 - Prob. 107PCh. 1 - Prob. 108CPCh. 1 - Prob. 109PCh. 1 - Prob. 110PCh. 1 - Prob. 111PCh. 1 - Prob. 112PCh. 1 - Prob. 113CPCh. 1 - Why is the metabolic rate of women, in general,...Ch. 1 - What is asymmetric thermal radiation How does it...Ch. 1 - How do (a) draft and (b) cold floor surfaces cause...Ch. 1 - Prob. 117CPCh. 1 - Why is it necessary to ventilate buildings? What...Ch. 1 - Consider a house in Atlanta, Georgia, that is...Ch. 1 - Prob. 120PCh. 1 - A 4m5m6m and room is to be heated by one ton (1000...Ch. 1 - Engine valves (cp=440J/kg.Kandp=7840kg/m3) are to...Ch. 1 - Prob. 123PCh. 1 - Prob. 124PCh. 1 - A 0.3 -cm-thick, 12-cm-high, and 18-cm-long...Ch. 1 - A 40-cm-long, 800-W electric resistance heating...Ch. 1 - It is well known that wind makes the cold air feel...Ch. 1 - An engine block with a surface area measured to be...Ch. 1 - Prob. 129PCh. 1 - Prob. 130PCh. 1 - Prob. 131PCh. 1 - Consider a person standing in a room maintained at...Ch. 1 - Prob. 133PCh. 1 - Prob. 134PCh. 1 - Prob. 135PCh. 1 - Prob. 136PCh. 1 - Prob. 137PCh. 1 - Prob. 138PCh. 1 - Prob. 139PCh. 1 - Prob. 140PCh. 1 - Prob. 141PCh. 1 - Prob. 142PCh. 1 - A 2-kW electric resistance heater submerged in...Ch. 1 - Prob. 144PCh. 1 - A cold bottled drink (m=2.5kg,cp=4200J/kg.K) at...Ch. 1 - Prob. 146PCh. 1 - Air enters a 12-m-long, 7-cm-diameter pipe at 50oC...Ch. 1 - Prob. 148PCh. 1 - Steady heat conduction occurs through a...Ch. 1 - Heat is lost through a brick wall (k=0.72W/m.K),...Ch. 1 - Prob. 151PCh. 1 - A 40-cm-long, 0.4-cm-diameter electric resistance...Ch. 1 - Prob. 153PCh. 1 - Prob. 154PCh. 1 - Over 90 percent of the energy dissipated by an...Ch. 1 - On a still, cleat night, the sky appears to be a...Ch. 1 - Prob. 157PCh. 1 - Prob. 158PCh. 1 - A persons head can be approximated as a...Ch. 1 - A person standing in a room loses heat to the air...Ch. 1 - Write an essay on how microwave ovens work, and...Ch. 1 - Using information form the utility bill for the...Ch. 1 - It is well know that at the same outdoor air...
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- 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.arrow_forwardShow that the rate of heat conduction per unit length through a long, hollow cylinder of inner radius ri and outer radius ro, made of a material whose thermal conductivity varies linearly with temperature, is given by qkL=TiTo(rori)/kmA where Ti = temperature at the inner surface To = temperature at the outer surface A=2(rori)/ln(ro/ri)km=ko[1+k(Ti+To)/2]L=lenthofcyclinderarrow_forward2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.arrow_forward
- 3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.arrow_forwardA cooling system is to be designed for a food storage warehouse for keeping perishable foods cool prior to transportation to grocery stores. The warehouse has an effective surface area of 1860 m2 exposed to an ambient air temperature of 32C. The warehouse wall insulation (k=0.17W/(mK)) is 7.5 cm thick. Determine the rate at which heat must be removed (W) from the warehouse to maintain the food at 4C.arrow_forwardA high-speed computer is located in a temperature-controlled room at 26C. When the machine is operating, its internal heat generation rate is estimated to be 800 W. The external surface temperature of the computer is to be maintained below 85C. The heat transfer coefficient for the surface of the computer is estimated to be 10W/m2K. What surface area would be necessary to assure safe operation of this machine? Comment on ways to reduce this area.arrow_forward
- A pipe carrying superheated steam in a basement at 10C has a surface temperature of 150C. Heat loss from the pipe occurs by radiation (=0.6) and natural convection (hc=25W/m2K). Determine the percentage of the total heat loss by these two mechanisms.arrow_forward1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.arrow_forward1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that dissipates 100 W. If the probe surface has an emissivity of 0.8, what is its surface temperature in outer space? State your assumptions in the calculations.arrow_forward
- Heat is transferred at a rate of 0.1 kW through glass wool insulation (density=100kg/m3) with a 5-cm thickness and 2-m2 area. If the hot surface is at 70C, determine the temperature of the cooler surface.arrow_forwardA steam pipe 200 mm in diameter passes through a large basement room. The temperature of the pipe wall is 500C, while that of the ambient air in the room is 20C. Determine the heat transfer rate by convection and radiation per unit length of steam pipe if the emissivity of the pipe surface is 0.8 and the natural convection heat transfer coefficient has been determined to be 10 W/m2K.arrow_forward3.17 A 1.4-kg aluminum household iron has a 500-W heating element. The surface area is . The ambient temperature is 21°C, and the surface heat transfer coefficient is . How long after the iron is plugged in does its temperature reach 104°C?arrow_forward
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