Consider design B of Problem 3.151. Over time. dust can collect in the fine grooves that separate the fins. Consider the buildup of a dust layer of thickness
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Fundamentals of Heat and Mass Transfer
- Current Attempt in Progress 40°C and the corresponding convection coefficient is h; = 30 W/m2.K, what are the inner and outer surface temperatures, in °C, of 4-mm-thick window glass, if the outside ambient air temperature is T, The rear window of an automobile is defogged by passing warm air over its inner surface. If the warm air is at T; = -10°C and the 0,0 associated convection coefficient is h, = 65 W/m2-K? Evaluate the properties of the glass at 300 K. °C Isi i °C Ts,0 i || ||arrow_forwardThe surface temperature of the hot side of the furnace wall is 1200 degrees C. It is desired to maintain the outside of the wall at 38 degrees C. A 152 mm of refractory silica is used adjacent to the combustion chamber and 10 mm of steel covers the outside. What thickness of insulating bricks is necessary between refractory and steel, if the heat loss should be kept at 788 W/m2? Use k=13.84 W/m-K for refractory silica; 0.15 for insulating brick, and 45 for steel.arrow_forwardThe rate at which energy must be dissipated away from single integrated circuits (computer chips) continues to increase as transitors continue to shrink in size and more and more computations are being completed in smaller and smaller volumes. The maximum chip temperature, however, has not changed much over time and remains around Tc = 75 °C. To increase the rate of dissipation of thermal energy away from a new chip, it is proposed to add a 5 x 5 array of copper pin fins to the chip. Each fin will be individually joined to the chip surface such that there is a minimal contact resistance between the fin and the chip. The diameter of the fins is df = 1 mm and the length is Lf = 15 mm. The chip is square, with a side length of W= 15 mm. It is so thin that it can be treated as having a single temperature. A dielectric liquid flows over the outer surface of the chip and around the fins, with a temperature of T»,f= 20 °C and a convection coefficient of hf = 1150 W/m²-K. The chip is joined to…arrow_forward
- Bebang owns a 830-mm-thick concrete brick table top that has an area of 10,000,000 mm^2 and a 0.750-cm-thick glass plate that has an area of 20,000 cm^2. Assuming the same temperature difference across each, what is the ratio of the rate of heat conduction through the plate with respect to the rate of heat conduction through the table top? Use Table 10.1(given below) for the value of Thermal Conductivity k. Table 10.1 Thermat Conductivities of Common Substances Values are given for temperatures near o °C. Substance Thermal Conductivity k (W/m-O Diamond 2000 Silver 420 Copper 390 Gold 318 Aluminum 220 Steel iron Steel (stainless) 14 Ice 2.2 Glass (average) 0.84 Concrete brick O.84 water 0.6 Fatty tissue (without blood) 0.2 Asbestos 0.16 Plasterboard 0.16 wood 0.08-0.16 Snow (dry) 0.10 Cork 0.042 Glass wool 0.042 wool 0.04 Down feathers 0.025 Air 0.023 Polystyrene foam 0.010arrow_forwardFor laminar free convection from a heated vertical surface, the local convection coefficient may be expressed as hy Cx-1/4, where h, is the coefficient at a distance x from the leading edge of the surface and the quantity C, which depends on the fluid properties, is independent of x. Obtain an expression for the ratio hx/hx, where x is the average coefficient between the leading edge (x = 0) and the x-location. Sketch the variation of h, and hy with x.arrow_forwardA furnace is required to sinter powder-metal parts. It operates continuously at 650 °C while the parts are fed through on a moving belt. You are asked to select a material for furnace insulation to minimize heat loss and thus to make the furnace as energy-efficient as possible. For reasons of space the insulation is limited to a maximum thickness of x = 0.2 m. Derive a material index for selecting the material for the insulation.arrow_forward
- Calculate the quantity of heat conducted per minute through a duralumin circular disc 143 mm diameter and 46 mm thick when the temperature across the thickness of the plate is 10 ℃. Take the coefficient of thermal conductivity of duralumin as 33,000 Btu/hr-ft-R.arrow_forwardThe fan circulates the warm air on the inside of the windshield to stop condensation of water vapor and allow for maximum visibility during wintertime (see images). You have been provided with some info. and are asked to pick from the bottom table, the right model number(s) that will satisfy the requirement.Your car is equipped with a fan blower setting that allow you to choose between speeds 0, 1, 2 and 3. Variation of the convection heat transfer coefficient is dependent upon multiple factors, including the size and theblower configuration.following image shows the parametersarrow_forwardThe Diamond Ring Solution. The processing chip on the computer that controls the navigation equipment on your spacecraft is overheating. Unless you fix the problem, the chip will be damaged and the navigation system will shut down. You open the panel and find that the small copper disk that was supposed to bridge the gap between the smooth top of the chip and the cooling plate is missing, leaving a 2.0 mm gap between them. In this configuration, the heat cannot escape the chip at the required rate. You notice by the thin smudge of thermal grease (a highly thermally conductive material used to promote good thermal contact between surfaces) that the missing copper disk was 2.0 mm thick and had a díameter of 1.2 cm. You know that the chip is designed to run below 65 °C, and the copper cooling plate is held at a constant 5.0 °C. (a) What was the rate of heat flow from the chip to the copper plate when the original copper disk was in place and the chip was at its maximum operating…arrow_forward
- The Diamond Ring Solution. The processing chip on the computer that controls the navigation equipment on your spacecraft is overheating. Unless you fix the problem, the chip will be damaged and the navigation system will shut down. You open the panel and find that the small copper disk that was supposed to bridge the gap between the smooth top of the chip and the cooling plate is missing, leaving a 2.0 mm gap between them. In this configuration, the heat cannot escape the chip at the required rate. You notice by the thin smudge of thermal grease (a highly thermally conductive material used to promote good thermal contact between surfaces) that the missing copper disk was 2.0 mm thick and had a diameter of 1.0 cm. You know that the chip is designed to run below 70 °C, and the copper cooling plate is held at a constant 5.0 °C. (a) What was the rate of heat flow from the chip to the copper plate when the original copper disk was in place and the chip was at its maximum operating…arrow_forwardAn electric heater in the form of a horizontal disc 0.192 m in diameter is used to heat the bottom of a tank filled with resting engine oil to a temperature of 5 °C. Calculate the value in modulus of the power (in W) required to maintain the heater surface at a temperature of 70 °C.arrow_forwardA plate is maintained at 74°C and this surface is facin an air having temperature of 30°C, then what will be th value of coefficient of volumetric expansion ß?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning