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*21.1 Convert 45.0 Btu/lb to the following: (a) cal/kg (c) kWh/kg (b) J/kg (d) (A)(lb,)/bm

*21.1 Convert 45.0 Btu/lb to the following: (a) cal/kg (c) kWh/kg (b) J/kg (d) (A)(lb,)/bm

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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PROBLEMS *21.1 Convert 45.0 Btu/lbm to the following: (a) cal/kg (c) kWh/kg (b) J/kg (d) (ft)(lb,)/lbm *21.2 Convert the following physical properties of liquid water at 0°C and 1 atm from t given SI units to the equivalent values in the listed American Engineering units. (a) Heat capacity of 4.184 J/(g)(K) (b) Enthalpy of -41.6 J/kg (c) Thermal conductivity of 0.59 (kg)(m)/(s³)(K) Btu/(lb)(°F) Btu/lb Btw(ft)(hr)(°F) *21.3 Convert the following quantities as specified. (a) A rate of heat flow of 6000 Btu/(hr)(ft?) to cai/(s)(cm²). (b) A heat capacity of 2.3 Btu/(Ib)(°F) to cal/(g)(°C) (c) A thermal conductivity of 200 Btu/(hr)(ft)(°F) to J/(s)(cm)(°C). (d) The gas constant, 10.73 (psia)(ft³)/(ib mol)(°R) to J/(g mol)(K). *21.4 A simplified equation for the heat transfer coefficient from a pipe to air is 0.026G0.6 h = D0.4 where h = heat transfer coefficient, Btu/(hr)(ft?)(°F) G = mass rate flow, Ib/(hr)(ft?) D = outside diameter of the pipe, (ft) If h is to be expressed in J/(min)(cm?)(°C), and the units of G and D remain the sam what should the new constant in the equation be in place of 0.026? 538 Energy: Terminology, Concepts, and Units Chap. 21 *21.5 A problem for many people in the United States is excess body weight stored as fat. Many people have tried to capitalize on this problem with fruitless weight-loss schemes. However, since energy is conserved, an energy balance reveals only two real ways to lose weight (other than water loss): (1) reduce the caloric intake, and/on (2) increase the caloric expenditure. In answering the following questions, assume that fat contains approximately 7700 kcal/kg (1 kcal is called a "dietetic calorie" i nutrition, or commonly just a "Calorie"). (a) If a normal diet containing 2400 kcal/day is reduced by 500 kcal/day, how many days does it take to lose 1 lb of fat? (b) How many miles would you have to run to lose 1 lb of fat if running at a moder- ate pace of 12 km/hr expends 400 kJ/km? (c) Suppose that two joggers each run 10 km/day. One runs at a pace of 5 km/hr and the other at 10 km/hr. Which will lose more weight (ignoring water loss)? *21.6 The energy from the sun incident on the surface of the earth averages 32.0 cal/(min)(cm²). It has been proposed to use space stations in synchronous orbits 36,000 km from earth to collect solar energy. How large a collection surface is needed (in m?) to obtain 108 watts of electricity (equivalents to a 100 MW power plant)? Assume that 10% of the collected energy is converted to electricity. Is your answer a reasonable size? *21.7 Solar energy has been suggested as a source of renewable energy. If in the desert the direct radiation from the sun (say for 320 days) is 975 W/m? between 10 AM and 3 PM, and the conversion efficiency to electricity is 21.0%, how many square meters are needed to collect an amount of energy equivalent to the annual U.S. energy con- sumption of 3 x 1020 J? Is the construction of such an area feasible? How many tons of coal (of heating value of 10,000 Btu/lb) would be needed to provide the 3 x 1020 J if the efficiency of conversion to electricity was 70%? What fraction of the total U.S. resources of coal (estimated at 1.7 x 1012 tons) is the calcu- lated quantity? *21.8 Lasers are used in many technologies, but they are fairly large devices even in CD players. A mater als scientist has been working on procucing a laser from a mi- crochip. He claims that his laser can produce a burst of light with up to 10,000 watts,
Transcribed Image Text:PROBLEMS *21.1 Convert 45.0 Btu/lbm to the following: (a) cal/kg (c) kWh/kg (b) J/kg (d) (ft)(lb,)/lbm *21.2 Convert the following physical properties of liquid water at 0°C and 1 atm from t given SI units to the equivalent values in the listed American Engineering units. (a) Heat capacity of 4.184 J/(g)(K) (b) Enthalpy of -41.6 J/kg (c) Thermal conductivity of 0.59 (kg)(m)/(s³)(K) Btu/(lb)(°F) Btu/lb Btw(ft)(hr)(°F) *21.3 Convert the following quantities as specified. (a) A rate of heat flow of 6000 Btu/(hr)(ft?) to cai/(s)(cm²). (b) A heat capacity of 2.3 Btu/(Ib)(°F) to cal/(g)(°C) (c) A thermal conductivity of 200 Btu/(hr)(ft)(°F) to J/(s)(cm)(°C). (d) The gas constant, 10.73 (psia)(ft³)/(ib mol)(°R) to J/(g mol)(K). *21.4 A simplified equation for the heat transfer coefficient from a pipe to air is 0.026G0.6 h = D0.4 where h = heat transfer coefficient, Btu/(hr)(ft?)(°F) G = mass rate flow, Ib/(hr)(ft?) D = outside diameter of the pipe, (ft) If h is to be expressed in J/(min)(cm?)(°C), and the units of G and D remain the sam what should the new constant in the equation be in place of 0.026? 538 Energy: Terminology, Concepts, and Units Chap. 21 *21.5 A problem for many people in the United States is excess body weight stored as fat. Many people have tried to capitalize on this problem with fruitless weight-loss schemes. However, since energy is conserved, an energy balance reveals only two real ways to lose weight (other than water loss): (1) reduce the caloric intake, and/on (2) increase the caloric expenditure. In answering the following questions, assume that fat contains approximately 7700 kcal/kg (1 kcal is called a "dietetic calorie" i nutrition, or commonly just a "Calorie"). (a) If a normal diet containing 2400 kcal/day is reduced by 500 kcal/day, how many days does it take to lose 1 lb of fat? (b) How many miles would you have to run to lose 1 lb of fat if running at a moder- ate pace of 12 km/hr expends 400 kJ/km? (c) Suppose that two joggers each run 10 km/day. One runs at a pace of 5 km/hr and the other at 10 km/hr. Which will lose more weight (ignoring water loss)? *21.6 The energy from the sun incident on the surface of the earth averages 32.0 cal/(min)(cm²). It has been proposed to use space stations in synchronous orbits 36,000 km from earth to collect solar energy. How large a collection surface is needed (in m?) to obtain 108 watts of electricity (equivalents to a 100 MW power plant)? Assume that 10% of the collected energy is converted to electricity. Is your answer a reasonable size? *21.7 Solar energy has been suggested as a source of renewable energy. If in the desert the direct radiation from the sun (say for 320 days) is 975 W/m? between 10 AM and 3 PM, and the conversion efficiency to electricity is 21.0%, how many square meters are needed to collect an amount of energy equivalent to the annual U.S. energy con- sumption of 3 x 1020 J? Is the construction of such an area feasible? How many tons of coal (of heating value of 10,000 Btu/lb) would be needed to provide the 3 x 1020 J if the efficiency of conversion to electricity was 70%? What fraction of the total U.S. resources of coal (estimated at 1.7 x 1012 tons) is the calcu- lated quantity? *21.8 Lasers are used in many technologies, but they are fairly large devices even in CD players. A mater als scientist has been working on procucing a laser from a mi- crochip. He claims that his laser can produce a burst of light with up to 10,000 watts,
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