A cubical glass melting furnace has exterior dimensionsof width
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Introduction to Heat Transfer
- 1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4arrow_forward2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)arrow_forward2.51 Determine by means of a flux plot the temperatures and heat flow per unit depth in the ribbed insulation shown in the accompanying sketch.arrow_forward
- A chip that is of length L = 5.5 mm on a side and thickness t = 2.0 mm is encased in a ceramic substrate, and its exposed surface is convectively cooled by a dielectric liquid for which h = 150 W/m² K and To = 20°C. . Th Chip, q, T₁, P, Cp The time is Substrate In the off-mode the chip is in thermal equilibrium with the coolant (T; = T). When the chip is energized, however, its temperature increases until a new steady state is established. For purposes of analysis, the energized chip is characterized by uniform volumetric heating with a = 9 x 106 W/m³. Assuming an infinite contact resistance between the chip and substrate and negligible conduction resistance within the chip, determine the steady-state chip temperature Tƒ. Following activation of the chip, how long does it take to come within 1°C of this temperature? The chip density and specific heat are p = 2000 kg/m³ and c = 700 J/kg-K, respectively. The steady-state chip temperature Tf is i S. °C.arrow_forwardA glass with an area of 0.625 m² is fit in the wooden outside wall of a room. The dimension of wall is 25 x 3.05 m , The wood has a thermal conductivity of 0.151W/m.K and is 3.05 cm thick. The glass has a thermal conductivity of 0.692W/m.K and is 5.0 mm thick. The temperature of the inside room is 27°C and outside air temperature is 268K. calculate ,What is the heat loss through wooden wall and glass window? What are the total heat loss?arrow_forwardA semiconductor material has a conductivity of 0.0124 W/cm-K. It has the shape of a rectangular bar with cross sectional area of 1 cm2and length of 3 cm. One end is maintained at 300 °C and the other end at 100 °C. The bar carries a current of 50 A and has resistivity of 1.5x10-3ohm-cm. Assuming the longitudinal surface is insulated, calculated the midpoint temperature in the bar.arrow_forward
- A machine element as seen in the figure is made of pure copper. It has an inner diameter of D;=2.9 cm, outer diameter of Do=5.9 cm, and height of H=19 cm. The initial temperature of the element is 749 K, and then suddenly placed in an environment which has a temperature of Too=300O K. The temperature of the element is measured as 489 K, 4.8 minutes after the cooling process. If the lumped system method is applicable, determine the heat transfer coefficient of the environment, in W/(m²K). Note: All the surfaces should be considered to calculate the surface area. Not: Yüzey alanı hesaplamak için tüm yüzeyler dikkate alınmalıdır. Properties of pure copper: k=370 W/(mK), C=920 J/(kg°C), p=8933 kg/m³ H Dịarrow_forwardQ1/The thermal conductivity 14.4w/m.k for the block of stainless steel shown below is well insulated on the front and back surfaces, and the temperature in the block varies linearly in both the x- and y directions, Find: The heat fluxes and heat flows in the x- and y-directions. 5 cm 15°C 10°C -5 cm - 10 cm 5°C 0°C Q2-Consider a two layer composite wall of copper and Teflon as shown below. The copper has a thickness of 10cm but the thickness of the Teflon is to be determined. The temperature on the left boundary is equal to 200 C and on the right boundary 25C. Determine the thickness of the Teflon layer so that the heat flux is equal to 200W/m2. L2 T = 200C Te = 25 C L1 = 01m TA T3 %3D - 007 = 5 coper télon Tcarrow_forward(b) A hydrogen gas cylinder is situated in the cylinder cage. The cylinder wall is constructed from 15.5 mm carbon fiber (kcp = 0.75 W mK-¹). The outside of the cylinder is lagged with an inner 10 mm layer of ceramic insulation (kc = 0.08 W mK-¹) and an outer 80 mm layer of fiberglass insulation (kp = 0.15 W mK-¹). The temperature on the hydrogen gas is 150 °C and the temperature of the cylinder cage is 45 °C. Given that the walls of the cylinder can be assumed to be flat and neglecting the contribution of radiation, calculate: (i) the heat flux per square meter of the gas cylinder wall (ii) the temperature at the interface between the fibreglass and the ceramic insulation. 1.1arrow_forward
- A wall in a house contains a single window. The window consists of a single pane of glass whose area is 0.13 m2 and whose thickness is 8 mm. Treat the wall as a slab of the insulating material Styrofoam whose area and thickness are 19 m2 and 0.10 m, respectively. Heat is lost via conduction through the wall and the window. The temperature difference between the inside and outside is the same for the wall and the window. Of the total heat lost by the wall and the window, what is the percentage lost by the window?arrow_forwardOne vessel having a carbon-steel wall of thickness 5 mm carrying saturated steam and water at 423K. The vessel is insulated with magnesia of thickness 50 mm. If the ambient air temperature is 321 K, determine the heat loss from the vessel. Given: i. thermal conductivity of carbon steel is 52 W/m.K ii. thermal conductivity of magnesia is 0.5 W/m.K iii. surface coefficient of insulation surface is 3 W/m2.Karrow_forward[2] An array of electronic chips is mounted within a sealed rectangular enclosure, and cooling is implemented by attaching an aluminum heat sink (k = 180 W/m K). The base of the heat sink has dimensions of w1 = W2 = 100 mm, while the 6 fins are of thickness t = 10 mm and pitch S = 18 mm. The fin length is Lr = 50 mm, and the base of the heat sink has a thickness of Lb = 10 mm. L -Chips Water u T Electronic package, P elec If cooling is implemented by water flow through the heat sink, with uo = 3 m/s and To = temperature Tb of the heat sink when power dissipation by the chips is Pelec = 1800 W? The average convection coefficient for surfaces of the fins and the exposed base may be estimated by assuming parallel flow over a flat plate. Properties of the water may be approximated as k = 0.62 W/m-K, p = 995 kg/m3, Cp = 4178 J/kg-K, v = 7.73 x 10-7 m2/s, and Pr = 5.2. 17°C, what is the base a.) Base temperature. А. 37.8°C B. 43.9°C С. 31.4°С D. 46.2°Carrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning