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physics
thermodynamics

Heat Transfer 10th edition Jack Holman - Solutions

A horizontal tube having a diameter of 30 cm is maintained at a constant temperature of 204oC and exposed to helium at 3 atm and 93oC. Calculate the heat lost from the tube for a tube length of 10.4 m. Express in units of watts.
A large bare duct having a diameter of 30 cm runs horizontally across a factory area having environmental conditions of 20oC and 1 atm. The length of the duct is 100 m. Inside the duct a low pressure steam flow maintains the duct wall temperature constant at 120oC. Calculate the total heat lost by
A circular hot plate, 15 cm in diameter, is maintained at 150oC in atmospheric air at 20oC. Calculate the free-convection heat loss when the plate is in a horizontal position.
An engine-oil heater consists of a large vessel with a square-plate electric-heater surface in the bottom of the vessel. The heater plate is 30 by 30 cm and is maintained at a constant temperature of 60oC. Calculate the heat-transfer rate for an oil temperature of 20oC.
Small electric strip heaters with a width of 6 mm are oriented in a horizontal position. The strips are maintained at 500oC and exposed to room air at 20oC. Assuming that the strips dissipate heat from both the top and the bottom surfaces, estimate the strip length required to dissipate 2 kW of
The top surface of a 10-by-10-m horizontal plate is maintained at 25oC and exposed to room temperature at 28oC. Estimate the heat transfer.
A 4-by-4-m horizontal heater is placed in room air at 15oC. Both the top and the bottom surfaces are heated to 50oC. Estimate the total heat loss by free convection.
A horizontal plate, uniform in temperature at 400 K, has the shape of an equilateral triangle 45 cm on each side and is exposed to atmospheric air at 300 K. Estimate the heat lost by the plate.
A heated plate, 20 by 20 cm, is inclined at an angle of 60o with the horizontal and placed in water. Approximately constant-heat-flux conditions prevail with a mean plate temperature of 40oC and the heated surface facing downward. The water temperature is 20oC. Calculate the heat lost by the plate.
Repeat Problem 7-58 for the heated plate facing upward.Problem 7-58A heated plate, 20 by 20 cm, is inclined at an angle of 60o with the horizontal and placed in water. Approximately constant-heat-flux conditions prevail with a mean plate temperature of 40oC and the heated surface facing downward.
Plot the free-convection boundary-layer thickness as a function of x for a vertical plate maintained at 80oC and exposed to air at atmospheric pressure and 15oC. Consider the laminar portion only.
A double plate-glass window is constructed with a 1.25-cm air space. The plate dimensions are 1.2 by 1.8 m. Calculate the free-convection heat-transfer rate through the air space for a temperature difference of 30oC and T1 = 20oC.
A flat-plate solar collector is 1 m square and is inclined at an angle of 20o with the horizontal. The hot surface at 160oC is placed in an enclosure that is evacuated to a pressure of 0.1 atm. Above the hot surface, and parallel to it, is the transparent window that admits the radiant energy from
A flat plate 1 by 1 m is inclined at 30o with the horizontal and exposed to atmospheric air at 30oC and 1 atm. The plate receives a net radiant-energy flux from the sun of 700 W/m2, which then is dissipated to the surroundings by free convection. What average temperature will be attained by the
A horizontal cylinder having a diameter of 5 cm and an emissivity of 0.5 is placed in a large room, the walls of which are maintained at 35oC. The cylinder loses heat by natural convection with an h of 6.5 W/m2·oC. A sensitive thermocouple placed on the surface of the cylinder measures the
A 10-by-10-cm plate is maintained at 80oC and inclined at 45o with the horizontal. Calculate the heat loss from both sides of the plate to room air at 20oC.
A 5-by-5-cm plate is maintained at 50oC and inclined at 60o with the horizontal. Calculate the heat loss from both sides of the plate to water at 20oC.
Air at 1 atm and 38oC is forced through a horizontal 6.5-mm-diameter tube at an average velocity of 30 m/s. The tube wall is maintained at 540oC, and the tube is 30 cm long. Calculate the average heat-transfer coefficient. Repeat for a velocity of 30 m/s and a tube wall temperature of 800oC.
A small copper block having a square bottom 2.5 by 2.5 cm and a vertical height of 5 cm cools in room air at 1 atm and 15oC. The block is isothermal at 100oC. Calculate the heat-transfer rate.
A horizontal plate in the shape of an equilateral triangle 40 cm on a side is maintained at a constant temperature of 55oC and exposed to atmospheric air at 25oC. Calculate the heat lost by the top surface of the plate.
A small horizontal heater is in the shape of a circular disk with a diameter of 3 cm. The disk is maintained at 70oC and exposed to atmospheric air at 30oC. Calculate the heat loss.
Two vertical flat plates at 65oC are placed in a tank of water at 25oC. If the plates are 30 cm high, what is the minimum spacing that will prevent interference of the free-convection boundary layers?
A hot ceramic block at 400oC has dimensions of 15 by 15 by 8 cm high. It is exposed to room air at 27oC. Calculate the free-convection heat loss.
A magnetic amplifier is encased in a cubical box 15 cm on a side and must dissipate 50 W to surrounding air at 20oC. Estimate the surface temperature of the box.
A glass thermometer is placed in a large room, the walls of which are maintained at 10◦C. The convection coefficient between the thermometer and the room air is 5 W/m2∙oC, and the thermometer indicates a temperature of 30oC. Determine the temperature of the air in the room. Take ϵ = 1.0.
A horizontal air-conditioning duct having a horizontal dimension of 30 cm and a vertical dimension of 15 cm is maintained at 45oC and exposed to atmospheric air at 20oC. Calculate the heat lost per unit length of duct.
Two 30-cm-square vertical plates are separated by a distance of 1.25 cm, and the space between them is filled with water. A constant-heat-flux condition is imposed on the plates such that the average temperature is 38oC for one and 60oC for the other. Calculate the heat-transfer rate under these
An enclosure contains helium at a pressure of 1.3 atm and has two vertical heating surfaces, which are maintained at 80 and 20oC, respectively. The vertical surfaces are 40 by 40 cm and are separated by a gap of 2.0 cm. Calculate the free-convection heat transfer between the vertical surfaces.
A horizontal annulus with inside and outside diameters of 8 and 10 cm, respectively, contains liquid water. The inside and outside surfaces are maintained at 40 and 20oC, respectively. Calculate the heat transfer across the annulus space per meter of length.
Two concentric spheres are arranged to provide storage of brine inside the inner sphere at a temperature of - 10oC. The inner-sphere diameter is 2 m, and the gap spacing is 5 cm. The outer sphere is maintained at 30oC, and the gap space is evacuated to a pressure of 0.05 atm. Estimate the
A large vat used in food processing contains a hot oil at 400oF. Surrounding the vat on the vertical sides is a shell that is cooled to 140oF. The air space separating the vat and the shell is 35 cm high and 3 cm thick. Estimate the free-convection loss per square meter of surface area.
Two 30-cm-square vertical plates are separated by a distance of 2.5 cm and air at 1 atm. The two plates are maintained at temperatures of 200 and 90oC, respectively. Calculate the heat-transfer rate across the air space.
A 2.0-cm-diameter cylinder is placed horizontally in a pool of water at 70oF. The surface of the cylinder is maintained at 130oF. Calculate the heat lost by the cylinder per meter of length.
A horizontal air space is separated by a distance of 1.6 mm. Estimate the heat-transfer rate per unit area for a temperature difference of 165oC, with one plate temperature at 90oC.
Repeat Problem 7-80 for a horizontal space filled with water. Problem 7-80 A horizontal air space is separated by a distance of 1.6 mm. Estimate the heat-transfer rate per unit area for a temperature difference of 165oC, with one plate temperature at 90oC.
Two vertical plates 50 by 50 cm are separated by a space of 4 cm that is filled with water. The plate temperatures are 50 and 20oC. Calculate the heat transfer across the space.
Repeat Problem 7-83 for the plates oriented in a horizontal position with the 50◦C surface as the lower plate.Problem 7-83Two vertical plates 50 by 50 cm are separated by a space of 4 cm that is filled with water. The plate temperatures are 50 and 20oC. Calculate the heat transfer across the
An air space in a certain building wall is 10 cm thick and 2 m high. Estimate the free-convection heat transfer through this space for a temperature difference of 17oC.
A vertical enclosed space contains air at 2 atm. The space is 3 m high by 2 m deep and the spacing between the vertical plates is 6 cm. One plate is maintained at 300 K while the other is at 400 K. Calculate the convection heat transfer between the two vertical plates.
A vertical cylinder having a length of 30 cm is maintained at 100oC and exposed to room air at 15oC. Calculate the minimum diameter the cylinder can have in order to behave as a vertical flat plate.
Air at atmospheric pressure is contained between two vertical plates maintained at 100oC and 20oC, respectively. The plates are 1.0 m on a side and spaced 8 cm apart. Calculate the convection heat transfer across the air space.
A special section of insulating glass is constructed of two glass plates 30 cm square separated by an air space of 1 cm. Calculate the percent reduction in heat transfer of this arrangement compared to free convection from a vertical plate with a temperature difference of 30oC.
One way to reduce the free-convection heat loss in a horizontal solar collector is to reduce the pressure in the space separating the glass admitting the solar energy and the black absorber below. Assume the bottom surface is at 120oC and the top surface is at 20oC. Calculate the pressures that are
A horizontal tube is maintained at a surface temperature of 55oC and exposed to atmospheric air at 27oC. Heat is supplied to the tube by a suitable electric heater that produces an input of 175 W for each meter of length. Find the expected power input if the surface temperature is raised to 83oC.
A large vertical plate is maintained at a surface temperature of 140oF and exposed to air at 1 atm and 70oF. Estimate the vertical position on the plate where the boundary layer becomes turbulent. What is the average q/A for the portion of the plate preceding this location? What is the maximum
The horizontal air space over a solar collector has a spacing of 2.5 cm. The lower plate is maintained at 70oC while the upper plate is at 30oC. Calculate the free convection across the space for air at 1 atm. 1f the spacing is reduced to 1.0 cm, by how much is the heat transfer changed?
One concept of a solar collector reduces the pressure of the air gap to a value low enough to eliminate free-convection effects. For the air space in Problem 7-96 determine the pressures to eliminate convection; that is, Gr Pr < 1700.
A 2.5-cm sphere is maintained at a surface temperature of 120oF and exposed to a fluid at 80oF. Compare the heat loss for (a) Air and (b) Water.
Air at 1 atm is contained between two concentric spheres having diameters of 10 and 8 cm and maintained at temperatures of 300 and 400 K. Calculate the free-convection heat transfer across the air gap.
Using Equation (9-28) as a starting point, develop an expression for the average heat-transfer coefficient in turbulent condensation as a function of only the fluid properties, length of the plate, and temperature difference; that is, eliminate the Reynolds number from Equation (9-28) to obtain a
Saturated steam at 100 lb/in2 abs condenses on the outside of a horizontal 1-indiameter tube. The tube wall temperature is maintained at 280oF. Calculate the heat-transfer coefficient and the condensate flow per unit length of tube. Take Tsat = 328oF and hfg = 889 Btu/lb.
An un-insulated, chilled water pipe carrying water at 2oC passes through a hot, humid factory area where the temperature is 35oC and the relative humidity is 80 percent because of steam-operated equipment in the factory. If the pipe is 5 cm in diameter and the exposed length is 7.5 m, estimate the
A certain pressure cooker is designed to operate at 20 lb/in2 gauge. It is well known that an item of food will cook faster in such a device because of the higher steam temperature at the higher pressure. Consider a certain item of food as a horizontal 4-in diameter cylinder at a temperature of
Saturated steam at 690 kPa abs condenses on the outside of a horizontal 1-in-diameter tube. The tube wall temperature is maintained at 138oC. Calculate the heat-transfer coefficient and the condensate flow per unit length of tube.
Saturated steam at 1 atm pressure condenses on the outside of a 30-cm-diameter tube whose surface is maintained at 95oC. The tube is 15 m long. Calculate the amount of steam condensed per hour.
Condensing carbon dioxide at 20oC is in contact with a horizontal 10-cm-diameter tube maintained at 15oC. Calculate the condensation rate per meter of length if hfg = 153.2 kJ/kg at 20oC.
A square array of four hundred 6.35-mm tubes is used to condense steam at atmospheric pressure. The tube walls are maintained at 88oC by a coolant flowing inside the tubes. Calculate the amount of steam condensed per hour per unit length of the tubes.
Saturated water vapor at 1 atm enters a horizontal 5-cm-diameter tube 1.5 m long. Estimate the condensation for a tube wall temperature of 98oC.
Steam at 1 atm is to be condensed on the outside of a bank of 10 × 10 horizontal tubes 2.54 cm in diameter. The tube surface temperature is maintained at 95oC. Calculate the quantity of steam condensed for a tube length of 0.61 m.
Show that the condensation Reynolds number for laminar condensation on a vertical plate may be expressed as
A square array of 2.54-cm-diameter tubes contains 100 tubes each having a length of 0.91 m. The distance between centers is 45.7 mm and the tube wall temperature is 97oC. The tubes are exposed to steam at 1 atm. Calculate the condensation rate in kilograms per hour.
An ammonia condenser uses a 20 by 20 array of 6.35-mm-diameter tubes 0.305 m long. The ammonia condenses at 32.2oC and the tube walls are maintained at 27.8oC by a water flow inside. Calculate the rate of condensation of ammonia. hfg at 32.2oC is 1135 kJ/kg.
A condenser is to be designed to condense 10,000 kg/h of refrigerant 12 (CC12F2) at 37.8oC. A square 25 by 25 array of 12-mm-diameter tubes is to be used, with water flow inside the tubes maintaining the wall temperature at 32.2oC. Calculate the length of the tubes. hfg =130 kJ/kg at 37.8oC.
Refrigerant 12 (CC12F2) is condensed inside a horizontal 12-mm-diameter tube at a low vapor velocity. The condensing temperature is 32.2oC and the tube wall is at 26.7oC. Calculate the mass condensed per meter of tube length. hfg =133.5 kJ/kg at 32.2oC.
A heated vertical plate at a temperature of 107oC is immersed in a tank of water exposed to atmospheric pressure. The temperature of the water is 100oC, and boiling occurs at the surface of the plate. The area of the plate is 0.3 m2. What is the heat lost from the plate in watts?
The surface tension of water at 212oF is 58.8 dyn/cm for the vapor in contact with the liquid. Assuming that the saturated vapor inside a bubble is at 213◦F while the surrounding liquid is saturated at 212oF, calculate the size of the bubble.
A heated 30 by 30 cm square copper plate serves as the bottom for a pan of water at 1 atm pressure. The temperature of the plate is maintained at 119oC. Estimate the heat transferred per hour by the plate.
Develop an expression for the total condensate flow in a turbulent film in terms of the fluid properties, the temperature difference, and the dimensions of the plate.
Using Equations (9-14) and (9-7), develop Equation (9-26).Equation (9-14)Equation (9-7) Equation (9-26)
Water at 1 atm flows in a 1.25-cm-diameter brass tube at a velocity of 1.2 m/s. The tube wall is maintained at 110oC, and the average bulk temperature of the water is 96oC. Calculate the heat-transfer rate per unit length of tube.
Akettle with a flat bottom 30 cm in diameter is available. It is desired to boil 2.3 kg/h of water at atmospheric pressure in this kettle. At what temperature must the bottom surface of the kettle be maintained to accomplish this?
A5-mm-diameter copper heater rod is submerged in water at 1 atm. The temperature excess is 11oC. Estimate the heat loss per unit length of the rod.
Compare the heat-transfer coefficients for boiling water and condensing steam on a horizontal tube for normal atmospheric pressure.
A certain boiler employs one hundred 2-cm-diameter tubes 1 m long. The boiler is designed to produce local forced-convection boiling of water at 3 MPa pressure with ΔTx = 10oC. Estimate the total heat-transfer rate and the amount of saturated vapor that can be produced at 3 MPa.
A horizontal tube 3 mm in diameter and 7.5 cm long is submerged in water at 1.6 atm. Calculate the surface temperature necessary to generate a heat flux of 0.2 MW/m2.
Copper electric heating rods 2.5 cm in diameter are used to produce steam at 34-kPagauge pressure in a nucleate-pool-boiling arrangement where ΔTx = 4oC. Estimate the length of rod necessary to produce 908 kg/h of saturated vapor steam.
Estimate the nucleate-pool-boiling heat-transfer coefficient for a water-26% glycerin mixture at 1 atm in contact with a copper surface and ΔTx = 15oC.
Estimate the nucleate-pool-boiling heat flux for water at 1 atm in contact with ground and polished stainless steel and ΔTx =17oC.
How much heat would be lost from a horizontal platinum wire, 1.0 mm in diameter and 12 cm long, submerged in water at atmospheric pressure if the surface temperature of the wire is 110oC?
A horizontal pipe at 94oC is exposed to steam at atmospheric pressure and 100oC. The pipe is 4.0 cm in diameter. Calculate the condensation rate per meter of length.
Liquid water at 1 atm and 98oC flows in a horizontal 2.5-cm-diameter brass tube maintained at 110oC. Calculate the heat-transfer coefficient if the Reynolds number based on liquid bulk conditions is 40,000.
Estimate the peak heat flux for boiling water at normal atmospheric pressure.
A vertical plate 30 cm wide and 1.2 m high is maintained at 80oC and exposed to saturated steam at 1 atm. Calculate the heat transfer and the total mass of steam condensed per hour.
A horizontal tube having a 1.25-cm OD is submerged in water at 1 atm and 100oC. Calculate the heat flux for surface temperatures of (a) 540oC, (b) 650oC, and (c) 800oC. Assume = 0.8, and use Equation (9-41).Equation (9-41)
Water at a rate of 1.0 liter/h in the form of 0.4-mm droplets at 25oC is sprayed on a hot surface at 280oC with an impact velocity of 3 m/s. Estimate the maximum heat transfer that can be achieved with this arrangement.
A square array of 196 tubes 1.25 cm in diameter is used to condense steam at 1 atm pressure. Water flowing inside the tubes maintains the outside surface temperature at 92oC. Calculate the condensation rate for tube lengths of 2.0 m.
A vertical plate maintained at 91oC is exposed to saturated steam at 1 atm pressure. Determine the height of plate to just produce a Reynolds number of 1800. What would the condensation rate be under these conditions?
Determine the boiling heat flux for a water-ground and polished stainless-steel combination for a temperature excess of 15oC at 1 atm.
Calculate the heat-transfer coefficient for forced-convection local boiling of water at 5 atm in a vertical tube. The temperature excess is 10oC.
Calculate the condensation rate for saturated steam at 1 atm exposed to a horizontal 30-cm diameter cylinder maintained at 94oC.
A 20-cm-square vertical plate is maintained at 93oC and exposed to saturated water vapor at 1 atm pressure. Calculate the condensation rate and film thickness at the bottom of the plate.
Consider the copper-finned tube of Problem 2-121. Estimate the heat transfer that would result from submerging this tube in water at 1 atm with base tube temperatures at 108oC, 111oC, and 117oC.
A 40 by 40 cm plate is inclined at an angle of 30o with the vertical and exposed to water vapor at 1 atm. The plate is maintained at 98oC. Calculate the heat-transfer and mass-flow rate of condensate.
Water is placed in a stainless-steel pan on a kitchen stove. Estimate the heat transfer rate from a 25-cm-diameter pan when the bottom surface is maintained at 104oC.
A gas flame is placed around a shallow stainless steel pan having a bottom diameter of 12.5 cm and walls 5 cm high. The gas flame may be assumed to produce uniform heating, and the pan is filled with water to a depth of 2.5 cm. Estimate the heat transfer rate to the water if the surface temperature
Estimate the heat transfer coefficient from a horizontal Teflon-plated stainless-steel tube to water at atmospheric pressure with a temperature excess of 17oC. What would the heat transfer be for a 1-cm-diameter tube, 1 m long?
A horizontal tube bank employs 10 columns of tubes, with each column 15 rows high. The 12-mm-diameter tubes are exposed to condensing steam at 1 atm. If the tube wall temperature is maintained at 86oC, calculate the condensation rate per meter of tube length.
A vertical plate 25 cm wide by 50 cm high at 85oC is exposed to steam at 1 atm. Estimate the condensation rate in kg/h. Also estimate the film thickness at the bottom of the plate.
A condenser is to be designed to condense 1.3 kg/s of steam at atmospheric pressure. A square array of 1.25-cm-OD tubes is to be used with the outside tube walls maintained at 93oC. The spacing of the tubes is to be 1.9 cm between centers, and their length is 3 times the square dimension. How many
A heat exchanger is to be designed to condense 600 kg/h of steam at atmospheric pressure. A square array of four hundred 1.0-cm-diameter tubes is available for the task, and the tube wall temperature is to be maintained at 97oC. Estimate the length of tubes required.

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