At the end of its manufacturing process, a silicon wafer of diameter d = 258 mm , thickness ô =1 mm is at an initial temperature of 325 C and is allowed to cool in quiescent, ambient air and large surroundings for which T =T= 25 C, What is the initial rate of cooling by convection (kJ/s) from the TOP surface ONLY (Watts)? 3 Silicon :p= 2330 kg/m , c = 813 J/kg · K, k= 87.8 W/m·K" 2 -6 Air: v = 32.15×10 m /s, k = 0.0372 W/m K, a = 46.8 ×10° m/s, Pr= 0.686 %3D Quiescent air T Tsur Silicon wafer D, 8, e, T

At the end of its manufacturing process, a silicon wafer of diameter d = 258 mm , thickness ô =1 mm is at an initial temperature of 325 C and is allowed to cool in quiescent, ambient air and large surroundings for which T =T= 25 C, What is the initial rate of cooling by convection (kJ/s) from the TOP surface ONLY (Watts)? 3 Silicon :p= 2330 kg/m , c = 813 J/kg · K, k= 87.8 W/m·K" 2 -6 Air: v = 32.15×10 m /s, k = 0.0372 W/m K, a = 46.8 ×10° m/s, Pr= 0.686 %3D Quiescent air T Tsur Silicon wafer D, 8, e, T

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.4P: An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a...

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An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.
Chips of width L _ 15 mm on a side are mounted to a substrate that is installed in an enclosurewhose walls and air are maintained at a temperature of Tsur=T∞=25oC. The chips have an emissivity ofε=0.60 and a maximum allowable temperature of Ts=85oC.(a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operatingpower of each chip? The convection coefficient may be approximated as h=11.7 W/m2K.(b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forcedconvection, with h=250 W/m2K, what is the maximum operating power?
An 8-m-internal-diameter spherical tank made of 1.5-cm-thick stainless steelAISI 302 is used to store iced water at 0°C. The tank is located in a roomwith temperature 25°C. The outer surface of the tank is black (emissivity, ε= 1), the heat transfer between the outer surface of the tank and thesurroundings is by natural convection and radiation. The convection heattransfer coefficients at the inner and the outer surfaces of the tank are 80W/m2K and 10W/m2K, respectively; and the outer surface temperature of thetank is 5°C. Draw the equivalent thermal circuit of the system. Determine the total heat transfer rate to the iced water in the tank and the total amount of ice at 0°C that melts after 24 hours.
pnts) Chips of width L _ 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur=T∞=25oC. The chips have an emissivity of ε=0.60 and a maximum allowable temperature of Ts=85oC. (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient may be approximated as h=11.7 W/m2K. (b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forced convection, with h=250 W/m2K, what is the maximum operating power?
Differentiate between free and forced convection with examples.
Experiment No. (5) Heat Transfer, Power Input and Surface temperature 4. In what functions does Nusselt number in natural convection differ from forced convection, Discuss.
The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.
(a) If the cost of producing the hot water is $0.10 per kWh, what is the representative daily costof heat loss from an uninsulated pipe to the air per meter of pipe length? The convectionresistance associated with water flow in the pipe may be neglected.(b) Determine the savings associated with application of a 10-mm-thick coating of urethaneinsulation (k = 0.026 W/m-K) to the outer surface of the pipe.
a) What regions show the largest oceanic latent heat loss? b) What regions show the saltiest surface waters? c) What is the main factor affecting the two radiation heat flux terms? Name the two fluxes. d) What is the main factor affecting the two turbulent heat flux terms? Name the two fluxes.
Exhaust gases from a manufacturing plant are being discharged through a 10-m-tall exhaust stack with outer diameter of 1 m. The exhaust gases are discharged at a rate of 0.125 kg/s, while temperature drop between inlet and exit of the exhaust stack is 30°C, and the constant pressure-specific heat of the exhaust gases is 1600 J/kg.K. On a particular calm day, the surrounding quiescent air temperature is 33°C. Solar radiation is incident on the exhaust stack outer surface at a rate of 500 W/m2, and both the emissivity and solar absorptivity of the outer surface are 0.9. Determine the exhaust stack outer surface temperature. Assume the film temperature is 60°C.
For the Convective Heat Transfer experiment, describe the difference in the procedures: Natural or FreeConvection and Forced convection. What makes the FORCED convection experiment as FORCED? Explain which, in your consideration should give the higher heat transfer rate? And REASON why? Did your results support your consideration?
A 3 m internal diameter spherical tank made of 1 cm thick stainless steel (k =15 W/mK) is used to store water at 4℃, as shown in Figure 2.2. Inner surfaceof the tank is 4℃, while the outer surface of the tank is painted with blackcolour paints with emissivity, ? = 0.88 measured at temperature 5℃. It islocated outdoor at 40℃ and is subjected to wind at 25 km/h. Determine the total heat transfer rate to the ice water.