Questions and Answers of Principles Of Heat Transfer

Repeat Problem 11.15 for a PV module in Arizona on a sunny day at noon in an environment at 100°F. State your assumptions.Data from in Problem 11.15A hypothetical PV solar cell in space can utilize
The diameter of the sun is 1.39 × 109 m. Estimate the percentage of the total radiation emitted by the sun, which approximates a blackbody at 5760 K, that is actually intercepted by the Earth. Of
Air at a static temperature of 21°C and a static pressure of 0.7 kPa (abs) flows at zero angle of attack over a thin, electrically heated flat plate at a velocity of 240 m/s. If the plate is 10 cm
A large manufacturer of domestic electric ovens wants to explore more energy-efficient means for cooking with electricity. The baseline is the standard oven with electric heating elements
Anticipating the next energy crisis, one forward looking company would like to investigate advanced insulation systems for their line of hot-water heaters. They believe that a segment of the market
An optical pyrometer is a device used to measure the temperature of high-temperature surfaces. In this instrument, an image of the hot surface is compared to the image of a heated filament whose
Design a radiation shield for the thermocouple described in Design Problem 1.2. Determine the accuracy of the thermocouple measurement with the shield as a function of air temperature and velocity.
(a) Show that Ebλ/T5 = ∫ (λT) only. (b) For λT = 5000 μm K, calculate Ebλ/T5.
Derive an expression for the geometric shape factor F1–2 for the rectangular surface A1 shown in the figure. A1 is 1-m × 20-m and is placed parallel to and centered 5 m above a 20-m square surface
Compute the average emissivity of anodized aluminum at 100°C and 650°C from the spectral curve in Fig. 11.17. Assume ελ = 0.8 for λ > 9 μm.
Two parallel plates of infinite extent perpendicular to the page are situated relative to each other as shown in the figure. The upper plate is at 300°C and the lower plate is at 100°C. Determine
As a result of the atmosphere surrounding the Earth trapping some of the incoming solar radiation, the average temperature of the Earth is approximately 15°C. Estimate the amount of radiation that
A hypothetical PV solar cell in space can utilize solar radiation between 0.8 and 1.1 μm in wavelength. Estimate the maximum theoretical efficiency for this solar cell facing the sun using the ideal
Two coaxial parallel plate discs are situated relative to each other as shown in the sketch. The diameter of the upper plate is 20 cm, and that of the lower plate is 40 cm. The lower plate is
Show that the temperature of the reradiating surface Tr in Fig. 11.41 isData from in Fig. 11.41 TR ALFIRT + A2F2RT 1/4 = A₁FIR + A₂F2R
Estimate the rate at which heat needs to be supplied to an astronaut repairing the Hubble telescope in space. Assume that the emissivity of the spacesuit is 0.5. Describe your model with a simple
Using basic shape-factor definitions, estimate the equilibrium temperature of the planet Mars, which has a diameter of 6600 km and revolves around the sun at a distance of 225 × 106 km. The diameter
Two 1.5-m-square, parallel flat plates are 30 cm apart. Plate A1 is maintained at a temperature of 1100 K and A2 at 500 K. The emissivities of the plates are 0.5 and 0.8, respectively. Considering
A 60-cm-square section of panel heater is installed in the corner of the ceiling of a room having a 2.7-m × 3.6-m floor area with an 2.4-m ceiling. If the surface of the heater, made from oxidized
In order to conserve energy, the inner surface of double-glazed windows are treated with a low emissivity coating that reduces the emissivity of theuncoated surface from 0.95 to 0.5 for the coated
Mercury is to be evaporated at 317°C in a furnace. The mercury flows through a 25.4-mm BWG no. 18 gauge 304 stainless-steel tube that is placed in the center of the furnace. The furnace cross
A small sphere (2.5 cm in diameter) is placed in a heating oven. The oven cavity is a 30 cm cube filled with air at 101 kPa (abs); it contains 3% water vapor at 810 K, and its walls are at 1370 K.
Prepare the thermal design for a refrigerated container truck to carry frozen meat from Butte, Montana, to Phoenix, Arizona. The refrigerated shipping container has dimensions of 6 m × 3 m × 2.5 m
There is worldwide concern that the availability of oil will diminish within 20 or 30 years. (See, for example, Frank Kreith et al., Ground Transportation for the 21st Century, ASME Press, 2000.) In
High-strength steel is required for use in building structures and equipment (e.g., cranes). It is produced by heat treating quench-hardened steel in a process called tempering that reduces
A standard 10-cm steel pipe (ID = 10.066 cm, OD = 11.25 cm) carries superheated steam at 6508C in an enclosed space where a fire hazard exists, limiting the outer surface temperature to 38ºC. To
Design a cooler that can be used on camping trips. Primary considerations in the design are weight, capacity, and how long the cooler can keep items cold. Investigate commercially available
Quenching is a rapid cooling process by which many metallic alloys are hardened. Brass (a copper alloy: 70 Cu, 30 Zn) plates that are 4 mm thick are quenched in a water bath at a heat treating plant.
Electrical resistance heaters are usually made from coils of nichrome wire. The coiled wire can be supported between insulators and backed with a reflector, for example, as in a supplemental room
A thermocouple is made up of a spherical bead bimetallic junction at the end of two very thin wires of different materials. For example, in a type-T thermocouple, a copper wire and a constantan wire,
In a ball-bearing production facility, steel balls that are each of 15 mm in diameter are annealed by first heating them to 870°C and then slowly cooling in air to 125°C. If the cooling air stream
In a sheet-metal rolling and stamping factory, a 2.5- mm thick strip of stainless steel is hot rolled, as is schematically depicted in the figure. The strip emerges from the furnace and the rolling
A heat exchanger for heating liquid mercury is under development. The exchanger is visualized as a 15-cm-long and 0.3-m-wide flat plate. The plate is maintained at 70°C, and the mercury flows
A 2.5-cm-diameter, 15-cm-long transit rod (k = 0.97 W(m K) ρ = 1647 kg/m3, c = 837 J/(kg K)) on the end of a 2.5-cm-diameter wood rod at a uniform temperature of 100°C is suddenly placed into a
A flat-plate heat exchanger operates in a nitrogen atmosphere at a pressure of about 104 N/m2 and 38°C. The flat-plate heat exchanger was originally designed to operate in air at 1 atm and 38°C
A refrigeration truck is traveling at 130 km/h on a desert highway where the air temperature is 50°C. The body of the truck is idealized as a rectangular box 3 m wide, 2.1 m high, and 6 m long, at a
Determine the rate of heat loss from the wall of a building resulting from a 16 km/h wind blowing parallel to its surface. The wall is 24 m long and 6 m high, its surface temperature is 27°C, and
Repeat Problem 5.40, but consider the 2.5-mm thick stainless steel strip to emerge from the rolling mill with a speed of 35 m/s. With the temperature of the strip and the surrounding air,
A thin, flat plate 15 cm square is tested for drag in a wind tunnel with air at 30 m/s, 100 kPa (abs), and 16°C flowing across and parallel to the top and bottom surfaces. The observed total drag
A series of tests in which water was heated while flowing through a 1-m-long electrically heated tube of 1.3-cm ID yielded the experimental pressure-drop data shown next.Isothermal pressure-drop data
In a metal wire manufacturing facility, continuously drawn copper wire with a 2.5 mm diameter is annealed by heating it from its initial temperature of 45°C to 400°C in a soaking oven. The oven
Green coffee beans, after harvesting, are dried and roasted in a fluidized-bed roaster. This type of roaster has hot air, typically at 250°C, and the air blows through a screen or perforated plate
In the heat treating process in a sheet-metal manufacturing plant, brass plates are annealed by first heating them in an industrial furnace oven the inside of which is maintained at a constant
A copper wire, 0.8-mm OD, 5 cm long, is placed in an air stream whose temperature rises at a rate given by Tair = (10 + 14t) °C, where t is the time in seconds. If the initial temperature of the
Dielectric heating, also known as RF or high frequency heating, is a process in which a high-frequency alternating electric field or microwave electromagnetic radiation heats a dielectric material.
In a curing process for plastic and other polymer-based materials, a plastic sheet, which initially is 25°C, is placed on a hot metal surface that is maintained at 250°C. If the back (or opposite)
This is the first step in a two-step problem. Assume that a long aluminum extrusion having dimensions shown in the following figure has been heated uniformly to 150°C. It is necessary to determine
Consider a heat treatment process in which steel rods with a 10 cm diameter at an initial temperature of 600°C are inserted into an oil bath at 25°C. Assuming a convection coefficient of 400
The preliminary design of a fast-response hot-water heater has been completed in Design Problem 2.4. In the sketch, a cross section of the heater is shown. An extruded heating element is located
Surface hardening of metallic machine components, such as ball and roller bearings, is carried out in a heat treatment process where the surface temperature is increased to a desirable level without
A cross-sectional view of a 1-m-long gas preheater is shown in the sketch. The device provides 14 g/min preheated gas at 150°C to a chemical reactor. The heater rods dissipate 700 watts each. To
Light-emitting diodes or LEDs are currently perhaps the most energy-efficient lighting systems. Finned surface heat sinks are used to cool high-intensity LED lighting that are used for spot and/or
A heat sink made of an array of fins that have a straight, rectangular cross section is used to cool an electronic micro-chip module, as schematically shown in the figure. The heat sink (base and
A novel method to cool high-powered microelectronic chips and chip modules is to etch the liquid coolant flow channels in silicon (Si) substrate itself [9–12]. A typical such arrangement with
A circumferential fin with a rectangular cross section is made of mild steel has an outer diameter of 3.7 cm OD, and a thickness of 0.3 cm. An array of these circular fins = are attached to a
In Design Problem 1.3, you calculated the heat loss from a small industrial building in the winter. In the initial calculations, you estimated the convection heat transfer coefficient from Table 1.3.
Refine the thermal design for the refrigerated shipping container from Design Problem 3.3 by calculating the convection heat transfer coefficient over the two sides and the top at 105 km/h from
Evaluate the Nusselt number for flow over a sphere for the following conditions: D = 0.15 m, k = 0.2 W/m K, h̅c = 102 W/m2 K.
Estimate the heat loss from the surface of a swimming pool with a 3-m × 10-m surface area and an average depth of 1.5 m and then design a solar heating system for it. Previously, the pool had been
Evaluate the Prandtl number from the following data: cp = 2.1 kJ/kg K, k = 3.4 W/m K, μ = 0.45 kg/m s.
A 4-m2 square flat-plate solar collector for domestic hot-water heating is shown schematically. Solar radiation at a rate of 750 W/m2 is incident on the glass cover, which transmits 90% of the
A flat plate solar collector is installed flat-flush on the surface of a roof that is inclined 30° from the vertical normal and facing south in order to maximize its performance. The solar collector
A flat plate test section, which is 0.5 m wide and has an electrically heated surface installed 0.5 m away from the leading edge, as depicted in the schematic given, is to be designed for a
Recent studies have shown that the supply of crude oil from Alaska's North Slope will soon decline to sub-economic levels and that production will then cease. Alternatives are under consideration
A blood warmer is often used in certain clinical transfusion procedures. While safely storing and preserving blood requires refrigeration, cold blood when used in rapid transfusion procedures could
A mercury-in-glass thermometer at 40°C (OD = 1 cm) is inserted through a duct wall into a 3 m/s airstream at 66°C. This can be modelled as a cylinder in cross-flow, as shown in the figure. Estimate
Motorcycle manufacturers offer engines with two methods of cooling: air cooling and liquid cooling. In air cooling, fins are applied to the outside of the cylinder and the cylinder is oriented to
Consider a microprocessor dissipating 50 W with dimensions 2-cm × 2-cm square and 0.5-cm high (see figure). In order to cool the microprocessor, it is necessary to mount it to a device called a heat
In Chapter 4, you were asked to determine the time required for an aluminum extrusion to cool to a maximum temperature of 40°C. Repeat these calculations, but determine the convection heat transfer
A stainless steel pin fin 5 cm long and with a 6-mm OD, extends from a flat plate into a 175 m/s airstream, as shown in the sketch. Estimate (a) The average heat transfer coefficient between air
A multitube heat exchanger is used in a process plant to pre-heat air before it is enters a combustion chamber, using low pressure steam that flows inside the tubes and condenses. The tube bundle is
The human body is typically modelled as a vertical cylinder that is 1.8 m high and is 30 cm in diameter, as shown in the figure. Calculate the average rate of heat loss from this body, which is
In a metal manufacturing plant and its heat treatment process, a long, hexagonal copper extrusion (or rod) comes out of a heat-treatment furnace at 400°C and is then quenched by immersing it in a
To reduce the carbon footprint of building energy consumption, photovoltaic (PV) cell panels are increasingly being used to provide a solar, self- sustaining source of electricity in both homes and
Reconsider the heat exchanger of Problem 6.38 with an inline tube arrangement, where the centerlines of the tubes are spaced 7.5 cm apart, both in the longitudinal and transverse directions. Compare
Compare the rate of heat transfer and the pressure drop for an in-line and a staggered arrangement of a tube bank consisting of 300 tubes that are 1.8 m long with a 2.5 cm OD. The tubes are to be
A microprocessor chip (10 mm × 10 mm square) is to be cooled by an impinging circular air jet that is directed on the chip surface by a 5-mm diameter nozzle, placed at a distance of 10 mm. The
Estimate the heat transfer coefficient for liquid sodium at 540°C flowing over a 10-row staggered-tube bank of 2.5-cm-diameter tubes arranged in an equilateral-triangular array with a 1.5
Reconsider the heat exchanger of Problem 6.38 with an externally finned-tube bundle used to enhance the air-side heat transfer coefficient in the pre-heater. If thin circular fins are attached on the
In many metal machining operations (cutting or turning) the contact surface at the interface of the tool and metal part is cooled by a liquid coolant that is delivered on the surface by a single
Design an internal cooling system for a chemical reactor. The reactor has a cylindrical shape 2 m in diameter, is 14 m tall, and is well-insulated externally. The exothermic reaction releases 50
Timothy L. Hoopman of the 3M Corporation described a novel method for cooling highpowered- density silicon chips (D. Cho et al., eds., Microchanneled Structures in DCS, Vol. 19: Microstructures,
A miniature heat sink heat exchanger is constructed with circular cross section channels, each of which has a diameter of 3.0 mm, drilled through a rectangular block. Cooling water at 20°C flows at
Water enters a small copper tube, with an inner diameter of 2.5 cm, at the rate of 0.025 kg/s and a temperature of 15°C. Steam is condensing on the outer surface of the tube at atmospheric pressure
Purified water, flowing at the rate of 45 kg/h is to be heated from 25°C to 75°C in a food processing plant before it is mixed with thickened tomato puree for sauce production. A thin-walled, 1.25
Lubricating oil is cooled in a tubular heat exchanger to maintain its viscosity and effectiveness in the journal bearings used in a large steam turbine of an electric power plant. Oil flows at the
In thermal management or cooling of microchip modules for high-powered computer systems, very high heat fluxes have to be accommodated in the design of the cooling method. For many such cases,
Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16°C, and the tube is
An aniline-alcohol solution is flowing at a velocity of 3 m/s through a long, 2.5-cm-ID thin-wall tube. Steam is condensing at atmospheric pressure on the outer surface of the tube, and the tube wall
A large high-power transformer is installed and operated in an electric-power distribution station. To maintain transform efficiency and prevent its failure (burnout), the transformer oil is cooled
In a pipe-within-a-pipe heat exchanger, water flows in the annulus and an aniline-alcohol solution having the properties listed in Problem 7.28 flows in the central pipe. The inner pipe has a
A 5000 m2 condenser is constructed with 2.5-cm-OD brass tubes that are 2.7 m long and have a 1.2 mm wall thickness. The following thermal resistance data were obtained at various water velocities
Reconsider the fin design from Design Problem 2.1, but calculate the natural-convection heat transfer coefficient from information presented in this chapter. As shown in the schematic diagram, the
A 3.05 m vertical cylindrical exhaust duct from a commercial laundry has an ID of 15.2 cm. Exhaust gases having physical properties approximating thoseof dry air enter at 316°C. The duct is
Baseboard heaters used in residential applications have not changed in over 30 years. In either electrical or hot-water heating systems, the baseboard heater is a horizontal tube with closely spaced
Consider Design Problem 1.3 and repeat the heat load calculations by employing the natural convection correlations presented in this chapter. In order to maintain the temperature at 20°C, it is
Physicians use the local temperature of the skin as an indicator of underlying inflammation. U.S. Patent 3,570,312, “Skin Temperature Sensing Device” by F. Kreith, March 16, 1971, describes such
The heat loss from uninsulated hot water pipes installed in homes can be considerable and hence increases the overall energy cost of the home. Consider a 5-m-long section of such a pipe that has an
Overhead electric transmission lines get heated (due to the electric resistivity of the cable material) and lose heat to the ambient air; this transmission energy loss due to heat transfer is
A laboratory apparatus is used to maintain a horizontal slab of ice at –2.2°C so that specimens can be prepared on the surface of the ice and kept close to 0°C. If the ice is 10 cm × 3.8 cm and

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