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as seen in problem 3.109, silicon carbide nanowires of diameter d 15 nm can be grown onto a solid silicon carbide surface by carefully depositing droplets of catalyst liquid onto a flat silicon carbide substrate. silicon carbide nanowires grow upward from the deposited drops, and if the drops are deposited in a pattern, an array of nanowire fins can be grown, forming a silicon carbide nano-heat sink. consider finned and unfinned electronics packages in which an extremely small, 10 m 10 m electronics device is sandwiched between two d 100-nm-thick silicon carbide sheets. in both cases, the coolant is a dielectric liquid at 20 c. a heat transfer coefficient of h 1 105 w/m2 k exists on the top and bottom of the unfinned package and on all surfaces of the exposed silicon carbide fins, which are each l 300 nm long. each nano-heat sink includes a 200 200 array of nanofins. determine the maximum allowable heat rate that can be generated by the electronic device so that its temperature is maintained at Tt <85oC for the unfinned and finned packages.

Sagot :

1.30×10 W is the maximum allowable heat rate that can be generated by the electronic device to maintain the temperature below 85°C for an unfinned package.

Write the equation conduction resistance

Rcond = d/kA.........(1)

Consider the following and substitute the values:

From the table of 'thermo physical properties of selected nonmetallic solids' at a temperature of 300K.

The thermal conductivity of Silicon carbide, k is given by 490 W/m - K

Dimension of the electronic device,

W=10x10⁻⁶m

Find the cross-sectional area

A=W²

= (10x10⁻⁶)² m²

Rcond = 100×10⁻⁹/490×(10×10⁻⁶)^2

           = 2.04 K/W

The equation Convection resistance is given as follows:

Rconv = 1/hA

Consider the following and substitute the values:

Heat transfer coefficient of coolant

h= 1×10 W/m² K and

A= (10×10⁻⁶)² m²

Rcond = 1/10⁵x(10x10⁻⁶)^2

           = 1×10⁵ K/W

Find the heat rate by using the following equation

q= T1- Tinfinity/ Rcond + Rconv...........(3)

  = 2(85-20)/ (2.04+10⁵)

q  = 1.30×10 W

Thus, the maximum allowable heat rate that can be generated by the electronic device to maintain the temperature below 85°C for the unfinned package is 1.30×10 W.

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