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engineering
heat and mass transfer fundamentals and applications

Questions and Answers of Heat And Mass Transfer Fundamentals And Applications

Repeat Prob. 14–132E for temperature of 60°F for both the air and water.Data from problem 132Air at 80°F, 1 atm, and 30 percent relative humidity is blown over the surface of a 15-in × 15-in
Benzene (M = 78.11 kg/kmol) is a carcinogen, and exposure to benzene increases the risk of cancer and other illnesses in humans. A truck transporting liquid benzene was involved in an accident that
Consider a 5-m × 5-m wet concrete patio with an average water film thickness of 0.3 mm. Now wind at 50 km/h is blowing over the surface. If the air is at 1 atm, 15°C, and 35 percent relative
Air at 40°C and 1 atm flows over a 5-m-long wet plate with an average velocity of 2.5 m/s in order to dry the surface. Using the analogy between heat and mass transfer, determine the mass transfer
A 2-in-diameter spherical naphthalene ball is suspended in a room at 1 atm and 80°F. Determine the average mass transfer coefficient between the naphthalene and the air if air is forced to flow over
Consider a 3-mm-diameter raindrop that is falling freely in atmospheric air at 25°C. Taking the temperature of the raindrop to be 9°C, determine the terminal velocity of the raindrop at which the
Consider a circular pipe of inner diameter D = 0.7 in. whose inner surface is covered with a thin layer of liquid water as a result of condensation. In order to dry the pipe, air at 540 R and 1 atm
Consider a 15-cm-internal-diameter, 10-m-long circular duct whose interior surface is wet. The duct is to be dried by forcing dry air at 1 atm and 15°C through it at an average velocity of 3 m/s.
Reconsider Prob. 14–140. Using EES (or other) software, plot the mass transfer coefficient as a function of the air velocity as the velocity varies from 1 m/s to 8 m/s, and discuss the results.Data
Does a mass transfer process have to involve heat transfer? Describe a process that involves both heat and mass transfer.
During evaporation from a water body to air, under what conditions will the latent heat of vaporization be equal to convection heat transfer from the air?
Jugs made of porous clay were commonly used to cool water in the past. A small amount of water that leaks out keeps the outer surface of the jug wet at all times, and hot and relatively dry air
Consider a shallow body of water. Is it possible for this water to freeze during a cold and dry night even when the ambient air and surrounding surface temperatures never drop to 0°C? Explain.
Reconsider Prob. 14–146. Using EES (or other) software, plot the water temperature as a function of the relative humidity of air as the relative humidity varies from 10 to 100 percent, and discuss
During a hot summer day, a 2-L bottle drink is to be cooled by wrapping it in a cloth kept wet continually and blowing air to it with a fan. If the environment conditions are 1 atm, 80°F, and 30
A water-soaked 10-cm × 10-cm-square sponge is experiencing parallel dry air flow over its surface. The average convection heat transfer coefficient of dry air at 20°C flowing over the sponge
Consider a thin layer of liquid water on a concrete surface. The surrounding air is dry with a convection heat transfer coefficient of 50 W/m2 . K. The liquid water has an emissivity of 0.95, and the
A soaked sponge is experiencing dry air flowing over its surface. The air is at 1 atm and zero relative humidity. Determine the difference in the air temperature and the surface temperature of the
One way of increasing heat transfer from the head on a hot summer day is to wet it. This is especially effective in windy weather, as you may have noticed. Approximating the head as a 30-cm-diameter
A 2-m-deep 20-m × 20-m heated swimming pool is maintained at a constant temperature of 30°C at a location where the atmospheric pressure is 1 atm. If the ambient air is at 20°C and 60 percent
Repeat Prob. 14–152 for a pool temperature of 25°C.Data from problem 152A 2-m-deep 20-m × 20-m heated swimming pool is maintained at a constant temperature of 30°C at a location where the
A glass bottle washing facility uses a well agitated hot water bath at 50°C with an open top that is placed on the ground. The bathtub is 1 m high, 2 m wide, and 4 m long and is made of sheet metal
Determine the mole fraction of the water vapor at the surface of a lake whose temperature is 15°C and compare it to the mole fraction of water in the lake. Take the atmospheric pressure at lake
Repeat Prob. 14–154 for a water bath temperature of 55°C.Data from problem 154A glass bottle washing facility uses a well agitated hot water bath at 50°C with an open top that is placed on the
Show that for an ideal gas mixture maintained at a constant temperature and pressure, the molar concentration C of the mixture remains constant but this is not necessarily the case for the density r
The diffusion coefficient of carbon in steel is given aswhere T is in K. Determine the diffusion coefficient from 300 K to 1500 K in 100 K increments and plot the results. DAB = 2.67 x 10-5
A gas mixture in a tank at 600 R and 20 psia consists of 1 lbm of CO2 and 3 lbm of CH4. Determine the volume of the tank and the partial pressure of each gas.
Consider a 30-cm-diameter pan filled with water at 15°C in a room at 20°C, 1 atm, and 30 percent relative humidity. Determine(a) The rate of heat transfer by convection,(b) The rate of evaporation
Consider a glass of water in a room at 20°C and 100 kPa. If the relative humidity in the room is 70 percent and the water and the air are at the same temperature, determine(a) The mole fraction of
Repeat Prob. 14–161 assuming a fan blows air over the water surface at a velocity of 3 m/s. Take the radius of the pan to be the characteristic length.Data from problem 161Consider a 30-cm-diameter
A membrane made of 0.1-mm-thick soft rubber separates pure O2 at 1 atm and 25°C from air at 3 atm pressure. Determine the mass flow rate of O2 through the membrane per unit area and the direction of
Consider a brick house that is maintained at 20°C and 60 percent relative humidity at a location where the atmospheric pressure is 85 kPa. The walls of the house are made of 20-cm-thick brick whose
A thick part made of nickel is put into a room filled with hydrogen at 3 atm and 85°C. Determine the hydrogen concentration at a depth of 2-mm from the surface after 24 h.
A tanker truck carrying liquid herbicide overturned and caused a spill over a field. The liquid herbicide remained on the soil for 30 minutes before evaporating into the air. The mass diffusivity of
Oxygen gas is forced into an aquarium at 1 atm and 25°C, and the oxygen bubbles are observed to rise to the free surface in 4 s. Determine the penetration depth of oxygen into water from a bubble
In an experiment, a sphere of crystalline sodium chloride (NaCl) was suspended in a stirred tank filled with water at 20°C. Its initial mass was 100 g. In 10 minutes, the mass of sphere was found to
Liquid toluene (C6H5CH3) was stored at 6.4°C in an open top 20-cm-diameter cylindrical container. The vapor pressure of toluene at 6.4°C is 10 mm Hg. A gentle stream of fresh air at 6.4°C and
Liquid methanol is accidentally spilt on a 1 m × 1 m laboratory bench and covered the entire bench surface. A fan is providing a 20 m/s air flow parallel over the bench surface. The air is
The top section of an 8-ft-deep 100-ft × 100-ft heated solar pond is maintained at a constant temperature of 80°F at a location where the atmospheric pressure is 1 atm. If the ambient air is at
Repeat Prob. 14-173E for a solar pond surface temperature of 90°F.Data from problem 173The top section of an 8-ft-deep 100-ft × 100-ft heated solar pond is maintained at a constant temperature of
A swimmer extends his wet arms into the windy air outside at 1 atm, 40°F, 50 percent relative humidity, and 20 mph. If the average skin temperature is 80°F, determine the rate at which water
A sphere of ice, 5 cm in diameter, is exposed to 50 km/h wind with 10 percent relative humidity. Both the ice sphere and air are at 21°C and 90 kPa. Predict the rate of evaporation of the ice in g/h
The basic equation describing the diffusion of one medium through another stationary medium is (a) JA = CD AB d(CA/C) dx d(C₂/C) dx (c) JA= - k- (e) none of them (b) JA= - DAB dT (d) JA
Benzene-free air at 25°C and 101.3 kPa enters a 5-cm-diameter tube at an average velocity of 5 m/s. The inner surface of the 6-m-long tube is coated with a thin film of pure benzene at 25°C. The
Air at 52°C, 101.3 kPa, and 10 percent relative humidity enters a 5-cm-diameter tube with an average velocity of 5 m/s. The tube inner surface is wetted uniformly with water, whose vapor pressure at
For the absorption of a gas (like carbon dioxide) into a liquid (like water) Henry’s law states that partial pressure of the gas is proportional to the mole fraction of the gas in the liquid–gas
A rubber object is in contact with nitrogen (N2) at 298 K and 250 kPa. The solubility of nitrogen gas in rubber is 0.00156 kmol/m3·bar. The mass density of nitrogen at the interface is(a) 0.049
Nitrogen gas at high pressure and 298 K is contained in a 2-m × 2-m × 2-m cubical container made of natural rubber whose walls are 4 cm thick. The concentration of nitrogen in the rubber at the
A recent attempt to circumnavigate the world in a balloon used a helium-filled balloon whose volume was 7240 m3 and surface area was 1800 m2. The skin of this balloon is 2 mm thick and is made of a
Carbon at 1273 K is contained in a 7-cm-innerdiameter cylinder made of iron whose thickness is 1.2 mm. The concentration of carbon in the iron at the inner surface is 0.5 kg/m3 and the concentration
The surface of an iron component is to be hardened by carbon. The diffusion coefficient of carbon in iron at 1000°C is given to be 3 × 10-11 m2/s. If the penetration depth of carbon in iron is
A natural gas (methane, CH4) storage facility uses 3-cm-diameter by 6-m-long vent tubes on its storage tanks to keep the pressure in these tanks at atmospheric value. If the diffusion coefficient for
Saturated water vapor at 25°C (Psat = 3.17 kPa) flows in a pipe that passes through air at 25°C with a relative humidity of 40 percent. The vapor is vented to the atmosphere through a 7-mm
When the __________ is unity, one can expect the momentum and mass transfer by diffusion to be the same.(a) Grashof(b) Reynolds(c) Lewis(d) Schmidt(e) Sherwood
Air flows in a 4-cm-diameter wet pipe at 20°C and 1 atm with an average velocity of 4 m/s in order to dry the surface. The Nusselt number in this case can be determined from Nu = 0.023Re0.8Pr0.4
Air flows through a wet pipe at 298 K and 1 atm, and the diffusion coefficient of water vapor in air is 2.5 × 10-5 m2/s. If the heat transfer coefficient is determined to be 35 W/m2 · K, the mass
Write an essay on diffusion caused by effects other than the concentration gradient such as thermal diffusion, pressure diffusion, forced diffusion, knodsen diffusion, and surface diffusion.
One way of generating electricity from solar energy involves the collection and storage of solar energy in large artificial lakes of a few meters deep, called solar ponds. Solar energy is stored at
You are asked to design a heating system for a swimming pool that is 2 m deep, 25 m long, and 25 m wide. Your client desires that the heating system be large enough to raise the water temperature
Consider an opaque horizontal plate that is well insulated on the edges and the lower surface. The plate is uniformly irradiated from above while air at T∞ = 300 K flows over the surface providing
Give examples for(a) Liquid-to-gas,(b) Solid-to-liquid,(c) Solid-to-gas,(d) Gas-to-liquid mass transfer.
What is the driving force for(a) Heat transfer,(b) Electric current flow,(c) Fluid flow,(d) Mass transfer?
Both Fourier’s law of heat conduction and Fick’s law of mass diffusion can be expressed as Q̇ = -kA(dT/dx). What do the quantities Q̇, k, A, and T represent in(a) Heat conduction(b) Mass
How does mass transfer differ from bulk fluid flow? Can mass transfer occur in a homogeneous medium?
What do(a) Homogeneous reactions(b) Heterogeneous reactions represent in mass transfer? To what do they correspond in heat transfer?
Mark these statements as being True or False for a binary mixture of substances A and B.____(a) The density of a mixture is always equal to the sum of the densities of its constituents._____(b) The
Fick’s law of diffusion is expressed on the mass and mole basis as ṁdiff, A = -ρADAB(dwA/dx) and Ṅdiff, A = -CADAB(dyA/dx), respectively. Are the diffusion coefficients DAB in the two
How does the mass diffusivity of a gas mixture change with(a) Temperature(b) Pressure?
At a given temperature and pressure, do you think the mass diffusivity of air in water vapor will be equal to the mass diffusivity of water vapor in air? Explain.
At a given temperature and pressure, do you think the mass diffusivity of copper in aluminum will be equal to the mass diffusivity of aluminum in copper? Explain.
In a mass production facility, steel components are to be hardened by carbon diffusion. Would you carry out the hardening process at room temperature or in a furnace at a high temperature, say
Determine the maximum mass fraction of calcium bicarbonate [Ca(HCO3)2)] in water at 350 K.
The molar analysis of a gas mixture at 290 K and 250 kPa is 65 percent N2, 20 percent O2, and 15 percent CO2. Determine the mass fraction and partial pressure of each gas.
A gas mixture consists of 7 lbm of O2, 8 lbm of N2, and 10 lbm of CO2. Determine(a) The mass fraction of each component,(b) The mole fraction of each component, and(c) The average molar mass of the
A gas mixture consists of 8 kmol of H2 and 2 kmol of N2. Determine the mass of each gas and the apparent gas constant of the mixture.
Determine the binary diffusion coefficient of CO2 in air at(a) 200 K and 1 atm,(b) 400 K and 0.5 atm,(c) 600 K and 5 atm.
Repeat Prob. 14–19 for O2 in N2.Data from problem 19Determine the binary diffusion coefficient of CO2 in air at(a) 200 K and 1 atm,(b) 400 K and 0.5 atm,(c) 600 K and 5 atm.
Determine the binary diffusion coefficient for(a) Carbon dioxide in nitrogen,(b) Carbon dioxide in oxygen,(c) Carbon dioxide in hydrogen at 320 K and 2 atm.
The diffusion coefficient of hydrogen in steel is given as a function of temperature as where T is in K. Determine the diffusion coefficients at 200 K, 500 K, 1000 K, and 1500 K. DAB = 1.65 x 10-6
Reconsider Prob. 14–22. Using EES (or other) software, plot the diffusion coefficient as a function of the temperature in the range of 200 K to 1200 K.Data from problem 22The diffusion coefficient
Consider the free surface of a lake exposed to the atmosphere. If the air at the lake surface is saturated, will the mole fraction of water vapor in air at the lake surface be the same as the mole
When prescribing a boundary condition for mass transfer at a solid–gas interface, why do we need to specify the side of the surface (whether the solid or the gas side)? Why did we not do it in heat
Write three boundary conditions for mass transfer (on a mass basis) for species A at x = 0 that correspond to specified temperature, specified heat flux, and convection boundary conditions in heat
Using properties of saturated water, explain how you would determine the mole fraction of water vapor at the surface of a lake when the temperature of the lake surface and the atmospheric pressure
What is an impermeable surface in mass transfer? How is it expressed mathematically (on a mass basis)? To what does it correspond in heat transfer?
What is permeability? How is the permeability of a gas in a solid related to the solubility of the gas in that solid?
Determine the mole fraction of carbon dioxide (CO2) dissolved in water at the surface of water at 300 K. The mole fraction of CO2 in air is 0.005, and the local atmosphere pressure is 100 kPa.
Consider a glass of water in a room at 20°C and 97 kPa. If the relative humidity in the room is 100 percent and the water and the air are in thermal and phase equilibrium, determine(a) The mole
Determine the mole fraction of the water vapor at the surface of a lake whose temperature at the surface is 70°F, and compare it to the mole fraction of water in the lake. Take the atmospheric
Determine the mole fraction of dry air at the surface of a lake whose temperature is 15°C. Take the atmospheric pressure at lake level to be 100 kPa.
Reconsider Prob. 14–37. Using EES (or other) software, plot the mole fraction of dry air at the surface of the lake as a function of the lake temperature as the temperature varies from 5°C to
Consider a carbonated drink in a bottle at 37°C and 130 kPa. Assuming the gas space above the liquid consists of a saturated mixture of CO2 and water vapor and treating the drink as water,
A wall made of natural rubber separates O2 and N2 gases at 25°C and 750 kPa. Determine the molar concentrations of O2 and N2 in the wall.
Hydrogen gas at 750 kPa and 85°C is stored in a spherical nickel vessel. The vessel is situated in a surrounding of atmospheric air at 1 atm. Determine the molar and mass concentrations of hydrogen
Consider a nickel wall separating hydrogen gas that is maintained on one side at 5 atm and on the opposite at 3 atm. If the temperature is constant at 85°C, determine(a) The mass densities of
Pure nitrogen gas at 200 kPa and 25°C is flowing inside a long circular rubber pipe. The atmospheric air surrounding the pipe is at 1 atm and 25°C, with 79 percent nitrogen and 21 percent oxygen.
Consider a rubber membrane separating carbon dioxide gas that is maintained on one side at 2 atm and on the opposite at 1 atm. If the temperature is constant at 25°C, determine(a) The molar
Hydrogen gas at 85°C is maintained at constant pressures of 5 atm and 3 atm on opposite sides of a 0.1-mm-thick nickel wall. Determine the molar diffusion rate per unit area through the nickel wall.
During cold weather periods, vapor in a room diffuses through the dry wall and condenses in the adjoining insulation. This process decreases the thermal resistance and degrades the insulation.
A 2-mm-thick 5-L vessel made of nickel is used to store hydrogen gas at 358 K and 300 kPa. If the total inner surface area of the vessel is 1600 cm2, determine the rate of gas loss from the nickel

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