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engineering
heat and mass transfer fundamentals and applications

Questions and Answers of Heat And Mass Transfer Fundamentals And Applications

A cross-flow heat exchanger consists of 80 thin walled tubes of 3-cm diameter located in a duct of 1 m × 1 m cross section. There are no fins attached to the tubes. Cold water (cp = 4180 J/kg · K)
Reconsider Prob. 11–122. Using EES (or other) software, investigate the effects of the condensing steam temperature and the tube diameter on the rate of heat transfer and the rate of condensation
Consider a condenser unit (shell and tube heat exchanger) of an HVAC facility where saturated refrigerant R134a at a saturation pressure of 1318.6 kPa and at a rate of 2.5 kg/s flows through
There are two heat exchangers that can meet the heat transfer requirements of a facility. Both have the same pumping power requirements, the same useful life, and the same price tag. But one is
There are two heat exchangers that can meet the heat transfer requirements of a facility. One is smaller and cheaper but requires a larger pump, while the other is larger and more expensive but has a
A heat exchanger is to be selected to cool a hot liquid chemical at a specified rate to a specified temperature. Explain the steps involved in the selection process.
A shell-and-tube process heater is to be selected to heat water (cp = 4190 J/kg · K) from 20°C to 90°C by steam flowing on the shell side. The heat transfer load of the heater is 600 kW. If the
Reconsider Prob. 11–131. Using EES (or other) software, plot the number of tube passes as a function of water velocity as it varies from 1 m/s to 8 m/s, and discuss the results.Data from problem
A heat exchanger is to cool oil (cp = 2200 J/kg · K) at a rate of 13 kg/s from 120°C to 50°C by air. Determine the heat transfer rating of the heat exchanger and propose a suitable type.
Repeat Prob. 11–133 for a heat transfer load of 50 MW.Data from problem 133The condenser of a large power plant is to remove 500 MW of heat from steam condensing at 30°C (hfg = 2431 kJ/kg). The
A shell-and-tube heat exchanger is to be designed to cool down the petroleum-based organic vapor available at a flow rate of 5 kg/s and at a saturation temperature of 75°C. The cold water (cp = 4187
Water flowing through the tube side of a shell-and-tube cross-flow heat exchanger at a rate of 40,000 lbm/h is heated from 80°F to 110°F. On the shell side water at 175°F flows through one shell
Saturated liquid benzene flowing at a rate of 5 kg/s is to be cooled from 75°C to 45°C by using a source of cold water (cp = 4187 J/kg · K) flowing at 3.5 kg/s and 15°C through a 20-mmdiameter
Describe the cardiovascular counter-current mechanism in the human body.
Discuss the differences between the cardiovascular counter-current design and standard engineering countercurrent designs.
How do heavy clothing and extreme environmental conditions affect the cardiovascular counter-current exchanger?
Calculate the total thermal resistance of the cardiovascular heat exchanger, assuming that the thermal conductivity of the system is k = 0.670 W/m · K and the convection heat transfer coefficients
How would the answer to Prob. 11–141 be altered if we tried to approximate the heat transfer loss through the blood vessel with a fouling factor to describe physiological inhomogeneities? Assume
Cold water (cp = 4180 J/kg· K) enters the tubes of a heat exchanger with 2-shell passes and 20-tube passes at 20°C at a rate of 3 kg/s, while hot oil (cp = 2200 J/kg · K) enters the shell at
The cardiovascular counter-current heat exchanger mechanism is to warm venous blood from 28°C to 35°C at a mass flow rate of 2 g/s. The artery inflow temperature is 37°C at a mass flow rate of 5
During an experiment, a plate heat exchanger that is used to transfer heat from a hot-water stream to a cold-water stream is tested, and the following measurements are taken:The heat transfer area is
The cardiovascular counter-current heat exchanger has an overall heat transfer coefficient of 100 W/m2 · K. Arterial blood enters at 37°C and exits at 27°C. Venous blood enters at 25°C and exits
Consider a double-pipe heat exchanger with a tube diameter of 10 cm and negligible tube thickness. The total thermal resistance of the heat exchanger was calculated to be 0.025 K/W when it was first
Hot water coming from the engine is to be cooled by ambient air in a car radiator. The aluminum tubes in which the water flows have a diameter of 4 cm and negligible thickness. Fins are attached on
A heat exchanger is used to heat cold water entering at 8°C at a rate of 1.2 kg/s by hot air entering at 90°C at rate of 2.5 kg/s. The highest rate of heat transfer in the heat exchanger is(a) 205
Cold water (cp = 4.18 kJ/kg · K) enters a heat exchanger at 15°C at a rate of 0.5 kg/s, where it is heated by hot air (cp = 1.0 kJ/kg · K) that enters the heat exchanger at 50°C at a rate of 1.8
Hot oil (cp = 2.1 kJ/kg · K) at 110°C and 8 kg/s is to be cooled in a heat exchanger by cold water (cp = 4.18 kJ/kg · K) entering at 10°C and at a rate of 2 kg/s. The lowest temperature that oil
Cold water (cp = 4.18 kJ/kg · K) enters a counter flow heat exchanger at 18°C at a rate of 0.7 kg/s where it is heated by hot air (cp = 1.0 kJ/kg?K) that enters the heat exchanger at 50°C at a
A heat exchanger is used to condense steam coming off the turbine of a steam power plant by cold water from a nearby lake. The cold water (cp = 4.18 kJ/kg · K) enters the condenser at 16°C at a
An air handler is a large unmixed heat exchanger used for comfort control in large buildings. In one such application, chilled water (cp = 4.2 kJ/kg · K) enters an air handler at 5°C and leaves at
An air handler is a large unmixed heat exchanger used for comfort control in large buildings. In one such application, chilled water (cp = 4.2 kJ/kg · K) enters an air handler at 5°C and leaves at
In a parallel-flow, liquid-to-liquid heat exchanger, the inlet and outlet temperatures of the hot fluid are 150°C and 90°C while that of the cold fluid are 30°C and 70°C, respectively. For the
A counter-flow heat exchanger is used to cool oil (cp = 2.20 kJ/kg · K) from 110°C to 85°C at a rate of 0.75 kg/s by cold water (cp = 4.18 kJ/kg · K) that enters the heat exchanger at 20°C at a
The radiator in an automobile is a cross-flow heat exchanger (UAs = 10 kW/K) that uses air (cp = 1.00 kJ/kg · K) to cool the engine coolant fluid (cp = 4.00 kJ/kg · K). The engine fan draws 30°C
In a parallel-flow, water-to-water heat exchanger, the hot water enters at 75°C at a rate of 1.2 kg/s and cold water enters at 20°C at a rate of 0 9 kg/s. The overall heat transfer coefficient and
In a parallel-flow heat exchanger, the NTU is calculated to be 2.5. The lowest possible effectiveness for this heat exchanger is(a) 10%(b) 27%(c) 41%(d) 50%(e) 92%
Cold water (cp = 4.18 kJ/kg · K) enters a counter-flow heat exchanger at 10°C at a rate of 0.35 kg/s, where it is heated by hot air (cp = 1.0 kJ/kg?K) that enters the heat exchanger at 50°C at a
Steam is to be condensed on the shell side of a 2-shell-passes and 8-tube-passes condenser, with 20 tubes in each pass. Cooling water enters the tubes a rate of 2 kg/s. If the heat transfer area is
Water is boiled at 150°C in a boiler by hot exhaust gases (cp = 1.05 kJ/kg · °C) that enter the boiler at 400°C at a rate of 0.4 kg/s and leaves at 200°C. The surface area of the heat exchanger
An air-cooled condenser is used to condense isobutane in a binary geothermal power plant. The isobutane is condensed at 85°C by air (cp = 1.0 kJ/kg · K) that enters at 22°C at a rate of 18 kg/s.
Write an interactive computer program that will give the effectiveness of a heat exchanger and the outlet temperatures of both the hot and cold fluids when the type of fluids, the inlet temperatures,
Open the engine compartment of your car and search for heat exchangers. How many do you have? What type are they? Why do you think those specific types are selected? If you were redesigning the car,
Write an essay on the static and dynamic types of regenerative heat exchangers and compile information about the manufacturers of such heat exchangers. Choose a few models by different manufacturers
A cordless telephone is designed to operate at a frequency of 8.5 × 108 Hz. Determine the wavelength of these telephone waves.
Consider a radio wave with a wavelength of 107 mm and a g-ray with a wavelength of 10-7 mm. Determine the photon energies of the radio wave and the g-ray, and the photon energy ratio of the
Consider two identical bodies, one at 1000 K and the other at 1500 K. Which body emits more radiation in the shorter-wavelength region? Which body emits more radiation at a wavelength of 20 μm?
Reconsider Prob. 12–33. Using EES (or other) software, investigate the effect of temperature on the fraction of radiation emitted in the visible range. Let the surface temperature vary from 1000 K
Consider a 20-cm × 20-cm × 20-cm cubical body at 750 K suspended in the air. Assuming the body closely approximates a blackbody, determine(a) The rate at which the cube emits radiation energy, in
The sun can be treated as a blackbody at 5780 K. Using EES (or other) software, calculate and plot the spectral blackbody emissive power Ebλ of the sun versus wavelength in the range of 0.01 mm to
Consider a black surface at 2060°F. Determine the radiation energy emitted by the black surface per unit area (in Btu/h·ft2) for λ ≥ 4 μm.
Daylight and candlelight may be approximated as a blackbody at the effective surface temperatures of 5800 K and 1800 K, respectively. Determine the radiation energy (in W/m2) emitted by both lighting
What does a solid angle represent, and how does it differ from a plane angle? What is the value of a solid angle associated with a sphere?
For a surface, how is irradiation defined? For diffusely incident radiation, how is irradiation on a surface related to the intensity of incident radiation?
For a surface, how is radiosity defined? For diffusely emitting and reflecting surfaces, how is radiosity related to the intensities of emitted and reflected radiation?
When the variation of spectral radiation quantity with wavelength is known, how is the corresponding total quantity determined?
To understand the burnout phenomenon, boiling experiments are conducted in water at atmospheric pressure using an electrically heated 30-cm-long, 3-mm-diameter nickel-plated horizontal wire.
Reconsider Prob. 10–50. Using EES (or other) software, investigate the effects of the local atmospheric pressure and the emissivity of the wire on the critical heat flux and the temperature rise of
What is condensation? How does it occur?
What is the difference between film and dropwise condensation? Which is a more effective mechanism of heat transfer?
How does the presence of a non condensable gas in a vapor influence the condensation heat transfer?
What is the modified latent heat of vaporization? For what is it used? How does it differ from the ordinary latent heat of vaporization?
Consider film condensation on a vertical plate. Will the heat flux be higher at the top or at the bottom of the plate? Why?
Consider film condensation on the outer surfaces of four long tubes. For which orientation of the tubes will the condensation heat transfer coefficient be the highest:(a) Vertical,(b) Horizontal side
In condensate flow, how is the wetted perimeter defined? How does wetted perimeter differ from ordinary perimeter?
The Reynolds number for condensate flow is defined as Re = 4ṁ/pμl, where p is the wetted perimeter. Obtain simplified relations for the Reynolds number by expressing p and ṁ by their equivalence
A vertical 0.2 m × 0.2 m square plate is exposed to saturated water vapor at atmospheric pressure. If the surface temperature is 80°C and the flow is laminar, estimate the local heat transfer
Saturated steam at 1 atm condenses on a 3-m-high and 8-m-wide vertical plate that is maintained at 90°C by circulating cooling water through the other side. Determine(a) The rate of heat transfer by
Repeat Prob. 10–63 for the case of the plate being tilted 60° from the vertical.Data from problem 63Saturated steam at 1 atm condenses on a 3-m-high and 8-m-wide vertical plate that is maintained
Saturated steam at 100°C condenses on a 2-m × 2-m plate that is tilted 40° from the vertical. The plate is maintained at 80°C by cooling it from the other side. Determine(a) The average heat
Reconsider Prob. 10–65. Using EES (or other) software, investigate the effects of plate temperature and the angle of the plate from the vertical on the average heat transfer coefficient and the
Saturated steam at 30°C condenses on the outside of a 4-cm-outer-diameter, 2-m-long vertical tube. The temperature of the tube is maintained at 20°C by the cooling water. Determine(a) The rate of
Saturated water vapor at atmospheric pressure condenses on the outer surface of a 0.1-m-diameter vertical pipe. The pipe is 1 m long and has a uniform surface temperature of 80°C. Determine the rate
Saturated steam at 55°C is to be condensed at a rate of 10 kg/h on the outside of a 3-cm-outer-diameter vertical tube whose surface is maintained at 45°C by the cooling water. Determine the
Repeat Prob. 10–69 for a horizontal tube.Data from problem 69Saturated steam at 55°C is to be condensed at a rate of 10 kg/h on the outside of a 3-cm-outer-diameter vertical tube whose surface is
A 1.5-m-long vertical tube is used for condensing saturated steam at 60°C. The surface temperature of the tube is maintained at a uniform temperature of 40°C by flowing coolant inside the tube.
Repeat Prob. 10-71 for a horizontal tube. Compare the required diameters between a vertical tube and a horizontal tube to condense 12 kg/h of steam during the condensation process.Data from problem
Saturated ammonia vapor at 10°C condenses on the outside of a 4-cm-outer-diameter, 15-m-long horizontal tube whose outer surface is maintained at 210°C. Determine(a) The rate of heat transfer from
A 3-m spherical tank storing cold fluid has a uniform surface temperature of 5°C. The lower temperature of the tank surface is causing condensation of moisture in the air at 25°C. The tank is
Consider film condensation on the outer surfaces of N horizontal tubes arranged in a vertical tier. For what value of N will the average heat transfer coefficient for the entire stack of tubes be
A large heat exchanger has several columns of tubes, with 33 tubes in each column. The outer diameter of the tubes is 1.5 cm. Saturated steam at 50°C condenses on the outer surfaces of the tubes,
The condenser of a steam power plant operates at a pressure of 4.25 kPa. The condenser consists of 100 horizontal tubes arranged in a 10 × 10 square array. The tubes are 8 m long and have an outer
Reconsider Prob. 10–77. Using EES (or other) software, investigate the effect of the condenser pressure on the rate of heat transfer and the rate of condensation of the steam. Let the condenser
Saturated steam at 95°F is condensed on the outer surfaces of an array of horizontal pipes through which cooling water circulates. The outer diameter of the pipes is 1 in and the outer surfaces of
Repeat Prob. 10–79E for the case of 32 horizontal pipes arranged in a rectangular array of 4 pipes high and 8 pipes wide.Data from problem 79Saturated steam at 95°F is condensed on the outer
A horizontal condenser uses a 4 × 4 array of tubes that have an outer diameter of 5.0 cm and length 2.0 m. Saturated steam at 101.3 kPa condenses on the outside tube surface held at a temperature of
Saturated water vapor at a pressure of 12.4 kPa is condensed over 100 horizontal tubes in a rectangular array of 5 tubes high and 20 tubes wide, each with a diameter of 8 mm. If the tube surfaces are
Saturated water vapor at a pressure of 12.4 kPa is condensed over an array of 100 horizontal tubes, each with a diameter of 8 mm and a length of 1 m. The tube surfaces are maintained with a uniform
Saturated ammonia vapor at a pressure of 1003 kPa is condensed as it flows through a 25-mm tube. The tube length is 0.5 m and the wall temperature is maintained uniform at 5°C. If the vapor exits
A 10-m-long copper tube with a diameter of 25 mm is used for transporting cold coolant. The coolant flow inside the tube maintains the tube surface temperature at 5°C and causes moist air to
Reconsider Prob. 4–72. Using EES (or other) software, investigate the effect of the initial temperature of the apples on the final center and surface temperatures and the amount of heat transfer.
Air water slug flows through a 25.4-mm diameter horizontal tube in microgravity condition (less than 1% of earth’s normal gravity). The liquid phase consists of water with dynamic viscosity of μl
A two-phase flow mixture of air and silicone (Dow Corning 200® Fluid, 5 cs) is being transported in an 11.7-mmdiameter thin-walled horizontal tube. The liquid phase consists of liquid silicone with
An air-water mixture is flowing in a 5° inclined tube that has a diameter of 25.4 mm. The two-phase mixture enters the tube at 25°C and exits at 65°C, while the tube surface temperature is
A mixture of petroleum and natural gas is being transported in a pipeline with a diameter of 102 mm. The pipeline is located in a terrain that caused it to have an average inclination angle of θ =
An air-water mixture is flowing in a tube with a diameter of 25.4 mm. The two-phase mixture enters the tube at 15°C and exits at 75°C, while the tube surface temperature is maintained at 80°C. If
Consider a two phase flow of air-water in a vertical upward stainless steel pipe with an inside diameter of 0.0254 m. The two phase mixture enters the pipe at 25°C at a system pressure of 201 kPa.
Water is boiled at 120°C in a mechanically polished stainless-steel pressure cooker placed on top of a heating unit. The inner surface of the bottom of the cooker is maintained at 130°C. The cooker
Water is to be boiled at sea level in a 30-cm-diameter mechanically polished AISI 304 stainless steel pan placed on top of a 3-kW electric burner. If 60 percent of the heat generated by the burner is
Repeat Prob. 10–100 for a location at an elevation of 1500 m where the atmospheric pressure is 84.5 kPa and thus the boiling temperature of water is 95°C.Data from problem 100Water is to be boiled
A resistance heater made of 2-mm-diameter nickel wire is used to heat water at 1 atm pressure. Determine the highest temperature at which this heater can operate safely without the danger of burning

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