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physics
thermodynamics

Questions and Answers of Thermodynamics

Liquid water is to be heated from 60oF to 120oF in a smooth tube. The tube has an electric heat supplied that provides a constant heat flux such that the tube wall temperature is always 30oF above
An annulus consists of the region between two concentric tubes having diameters of 4 cm and 5 cm. Ethylene glycol flows in this space at a velocity of 6.9 m/s. The entrance temperature is 20oC, and
An air-conditioning duct has a cross section of 45 cm by 90 cm. Air flows in the duct at a velocity of 7.5 m/s at conditions of 1 atm and 300 K. Calculate the heat-transfer coefficient for this
Water flows in a 3.0-cm-diameter tube having a relative roughness of 0.002 with a constant wall temperature of 80oC. If the water enters at 20oC, estimate the convection coefficient for a Reynolds
Liquid Freon 12 (CC12F2) enters a 3.5-mm-diameter tube at 0oC and with a flow rate such that the Reynolds number is 700 at entrance conditions. Calculate the length of tube necessary to raise the
Air enters a small duct having a cross section of an equilateral triangle, 3.0 mm on a side. The entering temperature is 27oC and the exit temperature is 77oC. If the flow rate is 5 × 10−5 kg/s
Air at 90 kPa and 27oC enters a 4.0-mm-diameter tube with a mass flow rate of 7 × 10−5 kg/s. A constant heat flux is imposed at the tube surface so that the tube wall temperature is 70oC above the
Air at 110 kPa and 40oC enters a 6.0-mm-diameter tube with a mass flow rate of 8 × 10−5 kg/s. The tube wall temperature is maintained constant at 140oC. Calculate the exit air temperature for a
Calculate the flow rate necessary to produce a Reynolds number of 15,000 for the flow of air at 1 atm and 300 K in a 2.5-cm-diameter tube. Repeat for liquid water at 300 K.
Engine oil at 40oC enters a 1-cm-diameter tube at a flow rate such that the Reynolds number at entrance is 50. Calculate the exit oil temperature for a tube length of 8 cm and a constant tube wall
Water flows in a 2-cm-diameter tube at an average flow velocity of 8 m/s. If the water enters at 20oC and leaves at 30oC and the tube length is 10 m, estimate the average wall temperature necessary
Engine oil at 20oC enters a 2.0-mm-diameter tube at a velocity of 1.2 m/s. The tube wall temperature is constant at 60oC and the tube is 1.0 m long. Calculate the exit oil temperature.
Water flows inside a smooth tube at a mean flow velocity of 3.0 m/s. The tube diameter is 25 mm and a constant heat flux condition is maintained at the tube wall such that the tube temperature is
Liquid ammonia at 10oC and 1 atm flows across a horizontal cylinder at a velocity of 5 m/s. The cylinder has a diameter of 2.5 cm and length of 125 cm and is maintained at a temperature of 30oC.
Water enters a 3-mm-diameter tube at 21oC and leaves at 32oC. The flow rate is such that the Reynolds number is 600. The tube length is 10 cm and is maintained at a constant temperature of 60oC.
Water enters a 3.0-cm-diameter tube at 15oC and leaves at 38oC. The flow rate is 1.0 kg/s and the tube wall temperature is 60oC. Calculate the length of the tube.
Glycerin flows in a 5-mm-diameter tube at such a rate that the Reynolds number is 10. The glycerine enters at 10oC and leaves at 30oC. The tube wall is maintained constant at 40oC. Calculate the
A 5-cm-diameter cylinder maintained at 80oC is placed in a nitrogen flow stream at 2 atm pressure and 10oC. The nitrogen flows across the cylinder with a velocity of 5 m/s. Calculate the heat lost by
Air at 1 atm and 10oC blows across a 4-cm-diameter cylinder maintained at a surface temperature of 54oC. The air velocity is 25 m/s. Calculate the heat loss from the cylinder per unit length.
Liquid ammonia flows in a duct having a cross section of an equilateral triangle 1.0cmon a side. The average bulk temperature is 20oC, and the duct wall temperature is 50oC. Fully developed laminar
Air at 200 kPa blows across a 20-cm-diameter cylinder at a velocity of 25 m/s and temperature of 10oC. The cylinder is maintained at a constant temperature of 80oC. Calculate the heat transfer and
Water at 43oC enters a 5-cm-ID pipe having a relative roughness of 0.002 at a rate of 6 kg/s. If the pipe is 9 m long and is maintained at 71oC, calculate the exit water temperature and the total
A short tube is 6.4 mm in diameter and 15 cm long. Water enters the tube at 1.5 m/s and 38oC, and a constant-heat-flux condition is maintained such that the tube wall temperature remains 28oC above
Ethylene glycol is to be cooled from 65 to 40oC in a 3.0-cm-diameter tube. The tube wall temperature is maintained constant at 20oC. The glycol enters the tube with a velocity of 10 m/s. Calculate
Air at 70 kPa and 20oC flows across a 5-cm-diameter cylinder at a velocity of 15 m/s. Compute the drag force exerted on the cylinder.
A heated cylinder at 450 K and 2.5 cm in diameter is placed in an atmospheric airstream at 1 atm and 325 K. The air velocity is 30 m/s. Calculate the heat loss per meter of length for the cylinder.
Assuming that a human can be approximated by a cylinder 30 cm in diameter and 1.1 m high with a surface temperature of 24oC, calculate the heat the person would lose while standing in a 30-mi/h wind
Water at 15.56oC is to be heated in a 2-mm-ID tube until the exit temperature reaches 26.67oC. The tube wall temperature is maintained at 48.99oC and the inlet flow velocity is 0.3 m/s. Calculate the
Water flows in a duct having a cross section 5 × 10 mm with a mean bulk temperature of 20oC. If the duct wall temperature is constant at 60oC and fully developed laminar flow is experienced,
A 0.13-mm-diameter wire is exposed to an airstream at - 30oC and 54 kPa. The flow velocity is 230 m/s. The wire is electrically heated and is 12.5 mm long. Calculate the electric power necessary to
Air at 90oC and 1 atm flows past a heated 1.5-mm-diameter wire at a velocity of 6 m/s. The wire is heated to a temperature of 150oC. Calculate the heat transfer per unit length of wire.
A fine wire 0.025 mm in diameter and 15 cm long is to be used to sense flow velocity by measuring the electrical heat that can be dissipated from the wire when placed in an airflow stream. The
Helium at 1 atm and 325 K flows across a 3-mm-diameter cylinder that is heated to 425 K. The flow velocity is 9 m/s. Calculate the heat transfer per unit length of wire. How does this compare with
Calculate the heat-transfer rate per unit length for flow over a 0.025-mm-diameter cylinder maintained at 65oC. Perform the calculation for (a) air at 20oC and 1 atm and (b) water at 20oC; u∞ = 6
A 1-m-square vertical plate is heated to 300oC and placed in room air at 25oC. Calculate the heat loss from one side of the plate.
Some canned goods are to be cooled from room temperature of 300 K by placing them in a refrigerator maintained at 275 K. The cans have diameter and height of 8.0 cm. Calculate the cooling rate.
A 5.0-cm-diameter horizontal disk is maintained at 120oF and submerged in water at 80oF. Calculate the heat lost from the top and bottom of the disk.
A 10-cm-square plate is maintained at 400 K on the bottom side, and exposed to air at 1 atm and 300 K. The plate is inclined at 45o with the vertical. Calculate the heat lost by the bottom surface of
A vertical cylinder 50 cm high is maintained at 400 K and exposed to air at 1 atm and 300 K. What is the minimum diameter for which the vertical-flat-plate relations may be used to calculate the heat
A smooth glass plate is coated with a special coating that is electrically conductive and can produce constant-heat-flux conditions. One of these surfaces, 0.5 m square, is suspended vertically in
A 20-cm-square vertical plate is heated to a temperature of 30oC and submerged in glycerin at 10oC. Calculate the heat lost from both sides of the plate.
A vertical flat plate is maintained at a constant temperature of 120oF and exposed to atmospheric air at 70oF. At a distance of 14 in. from the leading edge of the plate the boundary layer thickness
A vertical cylinder 30 cm high and 30 cm in diameter is maintained at a surface temperature of 43.3oC while submerged in water at 10oC. Calculate the heat lost from the total surface area of the
A 1.0-cm-diameter horizontal cylinder is maintained at a constant surface temperature of 400 K and exposed to oxygen at 300 K and 1.5 atm. The length of the cylinder is 125 cm. Calculate the heat
Air is contained between two vertical plates spaced 2 cm apart, with the air space evacuated so that the mean free path is equal to the plate spacing. One plate is at 400 K with ϵ = 0.1 while the
A 40-cm-diameter sphere is maintained at 400 K and exposed to room air at 20oC. Calculate the free convection heat loss from the sphere. If the surface has ϵ = 0.9, also calculate the radiation heat
Two 20-cm-square plates are maintained at 350 and 400 K and separated by a distance of 2 cm. The space between the plates is filled with helium at 2 atm. Calculate the heat transfer through the gap
A 30-cm-square horizontal plate is exposed to air at 1 atm and 25oC. The plate surface is maintained at 125oC on both sides. Calculate the free convection loss from the plate.
A horizontal 1-mm-diameter stainless-steel wire having k = 16 W/m· oC and a resistivity of 70 μΩ· cm is exposed to air at 1 atm and 20oC. The wire length is 1 m. What is the maximum temperature
A vertical cylindrical surface has a diameter of 10.5 cm, a height of 30 cm, and is exposed to air at 1 atm and 15oC. The cylindrical surface is maintained at 100oC. Calculate the free convection
A wire having a diameter of 0.025 mm is placed in a horizontal position in room air at 1 atm and 300 K. A voltage is impressed on the wire, producing a surface temperature of 865 K. The surface
A flat surface having the shape of an equilateral triangle, 20 cm on a side, is maintained at 400 K and exposed to air at 1 atm and 300 K. Calculate the heat lost from the top surface of the triangle.
Condensing steam at 1 atm is used to maintain a vertical plate 20 cm high and 3.0 m wide at a constant temperature of 100oC. The plate is exposed to room air at 20oC. What flow rate of air will
A horizontal disk having a diameter of 10 cm is maintained at 49oC and submerged in water at 1 atm and 10oC. Calculate the free convection heat loss from the top surface of the disk.
Energy-conservation advocates claim that storm windows can substantially reduce energy losses (or gains). Consider a vertical 1.0-m-square window covered by a storm window with an air gap of 2.5 cm.
An evacuated thermal insulation is to be designed that will incorporate multiple layers of reflective sheets (ϵ = 0.04) separated by air gap spaces that are partially evacuated and have spacing δ
Aunt Maude frequently complains of a "draft" while sitting next to a window in her New York apartment in the winter, and she also says her feet get cold. She remarks that the window seems to leak
A circular air-conditioning duct carries cool air at 5oC and is constructed of 1 percent carbon steel with a thickness of 0.2 mm and an outside diameter of 18 cm. The duct is in a horizontal position
An experiment is to be designed to measure free convection heat-transfer coefficients from spheres by preheating aluminum spheres of various diameters to an initial temperature and then measuring the
A vertical flat plate 10 cm high and 1.0mwide is maintained at a constant temperature of 310 K and submerged in a large pool of liquid water at 290 K. Calculate the free convection heat lost by the
In a television weather report a "wind chill factor" is frequently stated. The actual factor is based on empirical data. You are asked to come up with an expression for wind chill based on the
A vertical cylinder 1.8 m high and 7.5 cm in diameter is maintained at a temperature of 93oC in an atmospheric environment of 30oC. Calculate the heat lost by free convection from this cylinder. For
The outside wall of a building 6 m high receives an average radiant heat flux from the sun of 1100 W/m2. Assuming that 95 W/m2 is conducted through the wall, estimate the outside wall temperature.
Assuming that a human may be approximated by a vertical cylinder 30 cm in diameter and 2.0 m tall, estimate the free-convection heat loss for a surface temperature of 24oC in ambient air at 20oC.
A 30-cm-square vertical plate is heated electrically such that a constant-heat-flux condition is maintained with a total heat dissipation of 30 W. The ambient air is at 1 atm and 20oC. Calculate the
A 0.3-m-square vertical plate is maintained at 55oC and exposed to room air at 1 atm and 20oC. Calculate the heat lost from both sides of the plate.
Calculate the free-convection heat loss from a 0.61-m-square vertical plate maintained at 100oC and exposed to helium at 20oC and a pressure of 2 atm.
A large vertical plate 6.1 m high and 1.22 m wide is maintained at a constant temperature of 57oC and exposed to atmospheric air at 4oC. Calculate the heat lost by the plate.
A 1-m-square vertical plate is maintained at 49oC and exposed to room air at 21oC. Calculate the heat lost by the plate.
What vertical distance is necessary to produce a Rayleigh number of 1012 in air at standard conditions and ΔT =10◦C?
A 25-by-25-cm vertical plate is fitted with an electric heater that produces a constant heat flux of 1000 W/m2. The plate is submerged in water at 15oC. Calculate the heat-transfer coefficient and
Assume that one-half of the heat transfer by free convection from a horizontal cylinder occurs on each side of the cylinder because of symmetry considerations. Going by this assumption, compare the
A horizontal cylindrical heater with d = 2 cm is placed in a pool of sodium-potassium mixture with 22 percent sodium. The mixture is at 120oC, and the heater surface is constant at 200oC. Calculate
A vertical flat plate 15 cm high and 50 cm wide is maintained at a constant temperature of 325K and placed in a large tank of helium at a pressure of 2.2 atm and a temperature of 0oC. Calculate the
Ahorizontal heating rod having a diameter of 3.0 cm and a length of 1 m is placed in a pool of saturated liquid ammonia at 20oC. The heater is maintained at a constant surface temperature of 70oC.
Condensing steam at 120oC is to be used inside a 7.5-cm-diameter horizontal pipe to provide heating for a certain work area where the ambient air temperature is 20oC. The total heating required is
A 10-cm length of platinum wire 0.4 mm in diameter is placed horizontally in a container of water at 38oC and is electrically heated so that the surface temperature is maintained at 93oC. Calculate
Show that β = 1/T for an ideal gas having the equation of state p = ρRT.
Water at the rate of 0.8 kg/s at 90oC flows through a steel pipe with 2.5-cm ID and 3-cm OD. The outside surface temperature of the pipe is 85oC, and the temperature of the surrounding air is 20oC.
A horizontal pipe 8.0 cm in diameter is located in a room where atmospheric air is at 25oC. The surface temperature of the pipe is 140oC. Calculate the free-convection heat loss per meter of pipe.
A horizontal 1.25-cm-OD tube is heated to a surface temperature of 250oC and exposed to air at room temperature of 20oC and 1 atm. What is the free-convection heat transfer per unit length of tube?
A horizontal electric heater 2.5 cm in diameter is submerged in a light-oil bath at 93oC. The heater surface temperature is maintained at 150oC. Calculate the heat lost per meter of length of the
A 0.3-m-square air-conditioning duct carries air at a temperature such that the outside temperature of the duct is maintained at 15.6oC and is exposed to room air at 27oC. Estimate the heat gained by
A fine wire having a diameter of 0.001 in (0.0254 mm) is heated by an electric current and placed horizontally in a chamber containing helium at 3 atm and 10oC. If the surface temperature of the wire
A heated horizontal cylinder having a surface temperature of 93oC, diameter of 10 cm, and length of 2.0 m is exposed to Helium at 1 atm and − 18oC. Calculate the heat lost by the cylinder.
A large circular duct, 3.0 m in diameter, carries hot gases at 250oC. The outside of the duct is exposed to room air at 1 atm and 20oC. Estimate the heat loss per unit length of the duct.
A 2.0-cm-diameter cylinder is placed in a tank of glycerine at 20oC. The surface temperature of the heater is 60oC, and its length is 60 cm. Calculate the heat transfer.
A 3.5-cm-diameter cylinder contains an electric heater that maintains a constant heat flux at the surface of 1500 W/m2. If the cylinder is inclined at an angle of 35o with the horizontal and exposed
A 1-ft-square vertical plate is maintained at 65oC and is exposed to atmospheric air at 15oC. Compare the free-convection heat transfer from this plate with that which would result from forcing air
A 30-cm-diameter horizontal pipe is maintained at a constant temperature of 25oC and placed in room air at 20oC. Calculate the free-convection heat loss from the pipe per unit length.
A 12.5 cm-diameter duct is maintained at a constant temperature of 260oC by hot combustion gases inside. The duct is located horizontally in a small warehouse area having an ambient temperature of
A horizontal cylinder with diameter of 5 cm and length of 3mis maintained at 180oF and submerged in water that is at 60oF. Calculate the heat lost by the cylinder.
A 2.0-m-diameter horizontal cylinder is maintained at a constant temperature of 77oC and exposed to a large warehouse space at 27oC. The cylinder is 20 m long. Calculate the heat lost by the cylinder.
Calculate the rate of free-convection heat loss from a 30-cm-diameter sphere maintained at 90oC and exposed to atmospheric air at 20oC.
A 2.5-cm-diameter sphere at 35oC is submerged in water at 10oC. Calculate the rate of free-convection heat loss.
A spherical balloon gondola 2.4 m in diameter rises to an altitude where the ambient pressure is 1.4 kPa and the ambient temperature is - 50oC. The outside surface of the sphere is at approximately
A 4.0-cm diameter sphere is maintained at 38oC and submerged in water at 15oC. Calculate the heat-transfer rate under these conditions.
Apply the reasoning pertaining to the last entry of Table 7-1 to free convection from a sphere and compare with Equation (7-50). Equation (7-50) Nuf = 2 + 0.43(Grf Prf)1/4
Using the information in Table 7-1 and the simplified relations of Table 7-2, devise a simplified relation that may be used as a substitute for Equation (7-50) to calculate free convection from a
A vertical flat plat maintained at 350 K is exposed to room air at 300 K and 1 atm. Estimate the plate height necessary to produce a free-convection boundary layer thickness of 2.0 cm.

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