7An electric heater is made of thin conducting wires forming a mesh. The diameter of the wire is0.5 mm and the total length of all the wires is 2 m. The temperature of the wire is 1,000 K. Theheat from the wire is dissipated to the air at 300 K flowing through the wire mesh at a velocity of5 m/s. Ignore radiation of the heater and assume it has a uniform temperature. T Const=(a) Calculate the convection heat transfer coefficient(h) between the air and the heater.(b) If the total electrical resistance of the heater is 10 2, what is the electrical current?(c) Calculate the Biot number of the heater. V=IR(d) The electrical current is suddenly cut off. How long does it take for the heatertemperature to drop to 500 K?Properties of the air: pa = 0.7 kg/m³, Cp,a= 1030 J/kg K, va = 38.8×106 m²/s, ka=0.041 W/m•K,aa =56.7×106 m²/s, and Pra = 0.684.Properties of the heater: ph = 8900 kg/m³, Cp,h= 380 J/kg K, and kn = 400 W/m.K.

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Answered: 7 An electric heater is made of thin…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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The front window of an automobile has a thickness of 4 mm and is defrosted by the passage of a stream of hot air through the inner surface. The thermal conductivity of glass is around 0.78 W/(m oC). Assume the ambient air temperature is -10°C and the external convection coefficient is 65W/(m2 K). If the hot air blowing to defog the glass internally is at 40 ºC and the internal convection coefficient corresponds to 30 W/(m2 K), the internal surface temperatures will be _____________. However, if the car accelerates and maintains high speed, the external convection coefficient should _____________ [increase or decrease?] and if the condition is maintained long enough the temperature of the inner surface of the glass should _____________ [increase or decrease?].
IMPORTANT!!! ONLY ANSWER PART D Parts A, B, and C are solved and the answers are in the picture.
* Energy Equation : (First law of thermodynamics) + (8-1). M? du u dT T =。
Water going into a pipe with a tempeture of T1 and going out T2 . ambient tempeture is T0. Develop an expression for T2 ( based on heat transfer) Length of the pipe Lh0 - convective heat transfer coefficient of the airhW -convective heat transfer coefficient of the waterk- pipe thermal conductivity (W/m·K)d – pipe diameter Use any other varilable that you need and can be found online easily .
A thick-walled cylindrical tubing of hard rubber (k=0.151 W/m*K) having an inside radius of 5 mm and an outside radius of 20 mm is being used as a temporary cooling coil in a bath. Ice water is flowing rapidly inside, and the inside wall temperature is 275 K. The outside surface temperature is 300 K. A total of 20 W must be removed from the bath by the cooling coil. How many meter of tubing are needed?
Problem 6. ART TAT Consider the cylindrical pipe shown in the figure. Heat is being generated in the pipe wall at a rate of R in units of W/m³, and the thermal conductivity of the wall is k, the heat transfer coefficients at the inside and outside of the pipe are h; and ho, respectively. At a given location along the pipe axis, the temperature of the fluid flowing inside of the pipe is Ti and that at the outside is To i. ii. Find the expression for the temperature distribution in the pipe wall. Find the total heat transfer rate from the pipe to both fluids.
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?

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