A square isothermal chip is of width
If the coolant is air and the corresponding convectioncoefficient is
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Fundamentals of Heat and Mass Transfer
- 1.19 A square isothermal chip is of width w = front surface is exposed to the flow of a coolant at To = 15°C. From reliability considerations, the chip temperature must not exceed T = 85°C. 5 mm on a side and is mounted in a substrate such that its side and back surfaces are well insulated; the Coolant T, h Chip = 200 W/m2 · K, what is the maximum allowable chip power? If the coolant is a If the coolant is air and the corresponding convection coefficient is h dielectric liquid for which h = 3000 W/m² · K, what is the maximum allowable power?arrow_forwardFor details shown below the rate of heat transfer per unit length is Q is: T=350 K, T=700 K, d= 10mm, N,=50, N =4 00 -6 Air properties: v= 61.1 10 m /s, k =0.0524 W/mxK, , Pr. = 0.707,Pr=0.695, Cp=1075J/Kg.K 3 •p=0.498 Kg/m S,20mm Flue gas V=5m/s Too=700K=T; p=1atm S=20mmLi Select one: a. 701218 W/m b. 547649 W/m c. 206009 W/m d. 401528 W/marrow_forwardS is 6. A spherical shaped vessel of 1.4 m outer diameter is 90 mm thick. Find the rate of heat leakage, if the temperature difference between the inner and outer surfaces is 220°C. Thermal conductivity of the material of the sphere is 0.083 W/mK. (a) 0.2 kW (c) 1.088 kW (b) 0.5 kW (d) 1.6 kWarrow_forward
- t = 30 + 0.9563 (62.2- 30) = 60.79°C (Ans.) Example 4.14. A very thin glass walled 3 mm diameter mercury thermometer is placed in a stream of air, where heat transfer coefficient is 55 W/m2°C, for measuring the unsteady temperature of air. Consider cylindrical thermometer bulb to consist of mercury only for which k and a = 0.0166 m2/h. Calculate the time required for the temperature change to reach half its final or, %3D 8.8 W/m C %3D value.arrow_forwardQ2/ An aluminum sphere weighting 7kg and initially at a temperature of 533K is suddenly immersed in a fluid at 283K. if heat transfer coefficient between the sphere and fluid is 50W/m?.°C. Take density=2707kg/m3, specific heat=0.9KJ/kg.°C and thermal conductivity= 204W/m °C. إجابت * Determine the Bi number 0.00696 0.000696 0.0052 0.00052 0 أخری *.Determine the time required to cool sphere to 263K 26.28min 262.8min 52.56 min 525.6 min O أخریarrow_forwardA spherical shaped vessel of 1.2 m diameter is 100 mm thick. Find the rate of heat leakage, if the temperature difference between the inner and outer surfaces is 200° C. Thermal conductivity of material is 0.3 kJ /mh°C.arrow_forward
- 1 - A square chip, with side w = 5 mm, operates under isothermal conditions.The chip is positioned on a substrate so that its side and bottom surfaces are thermally insulated, while its top surface is exposed to theflow of a refrigerant at T∞ = 15°C. From reliability considerations, the chip temperature cannot exceed T = 85°C. The refrigerant being air, with a convection heat transfer coefficientcorresponding h = 200 W/(m2K), what is the maximum allowable power for the chip? Since the coolant is a dielectric liquid for which h = 3000 W/(m²K), what is the maximum allowed power?arrow_forwardO A vertical cylinder 6 ft tall and 1 ft in diameter might be used to approximate a man for heat-transfer purposes. Suppose the surface temperature of the cylinder is 78°F, h=2 Btu/h - ft2 .°F, the surface emissivity is 0.9, and the cylinder is placed in a large room where the air temperature is 68°F and the wall temperature is 45°F. Calculate the heat lost from the cylinder. Repeat for a wall temperature of 80°F. What do you conclude from these calculations?arrow_forwardThe 0.5 m x 1.2 m wall of an industrial furnace is constructed from L = 0.15-m-thick fireclay brick having a thermal conductivity of 1.7 W/m-K. The temperature distribution, at an instant in time, is T(x) = a + bxwhere a = 1400 K and b = -1050 K/m. Determine the heat fluxes, q, and heat rates, q,, at x = 0 and x = L, in W/m2 and W respectively. Do steady-state conditions exist? W/m2 1x=0 i W/m? i W Ix=0 = Ir=L = i W Steady-state conditions exist.arrow_forward
- A silicon chip is encapsulated so that, under steady-state conditions, all the power dissipated by it is transferred by convection for a fluid current with h=1000 W/(m2.K) and Tꚙ=25oC. An aluminum plate (k=237 W/(mK)), 2 mm thick, is placed on the chip surface, the contact resistance on the chip/aluminum interface is 0.5x10-4 (m2.K)/W. If the chip area is 100 mm2 and the maximum allowable temperature is 85 oC, what is the maximum allowable power dissipation on the chip?arrow_forwardA large 100-mm thick steel plate is initially at uniform temperature T = 180°C at time t = 0. Both sides of the plate are exposed to 30°C oil with convection coefficient h = 1500 W/m².K. The thermal conductivity, heat capacity, and density of the steel are k = 38 W/m-K, cp = 485 J/kg-K, and p = 7800 kg/m³. a) Find the temperature at the center of the slab when t = 125 s. b) Find the temperature at the surface of the slab when t=125 s.arrow_forwardA chromel–constantan thermocouple measuring the temperature of a fluid is connected by mistake with copper–constantan extension leads (such that the two constantan wires are connected together and the copper extension lead wire is connected to the chromel thermocouple wire). If the fluid temperature was actually 250 C and the junction between the thermocouple and extension leads was at 90 C, what e.m.f. would be measured at the open ends of the extension leads if the reference junction is maintained at 0 C? What fluid temperature would be deduced from this (assuming that the connection error was not known)?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning