{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

hw1-solution

# hw1-solution - W/m 2 K The surface emissivity of the sphere...

This preview shows pages 1–2. Sign up to view the full content.

1. A square isothermal chip is of width w = 5 mm on a side and is mounted in a substrate such that its side and back surfaces are well insulated, while the front surface is exposed to the flow of a coolant at T = 20 ºC. From the reliability consideration, the chip temperature must not exceed T = 85ºC. (1) If the coolant is air and the corresponding convection coefficient is h = 200 W/m 2 K, what is the maximum allowable chip power? (2) If the coolant is a dielectric liquid for which h = 3000 W/m 2 K, what is the maximum allowable power? w = 5 mm Coolant chip Power = q = hA(T s - T ) (1) Power = 200 × (0.005 × 0.005) (85 – 20) = 0.325 W (2) Power = 3000 × (0.005 × 0.005) (85 – 20) = 4.875 W 2. A sphere 4.0 cm in diameter is heated to a temperature of 150ºC and is enclosed in a large room at 20ºC. Air in the room is also at 20ºC. The average convection heat transfer coefficient is 9.8

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: W/m 2 K. The surface emissivity of the sphere is 0.65. Calculate the total heat loss due to both convection and radiation. q = hA(T s – T air ) + σɛA(T s 4 – T sur 4 ) = (9.8)(4π × 0.02 2 )(150 – 20) + (5.67×10-8 )(0.65)(4π × 0.02 2 ) × (423 4 – 293 4 ) = 6.40 + 4.56 = 10.96 W 3. A wall 2.0 cm thick is to be constructed from material which has an average thermal conductivity of 1.3 W/m K. The wall is to be insulated with material having an average thermal conductivity of 0.035 W/m K, so that the heat loss will not exceed 1830 W/m 2 . Assuming that the temperature difference across the combined wall is 1270ºC, calculate the thickness of insulation required. ins w o i k x k x T T q            " 035 . 3 . 1 02 . 1270 1830 x    0238 .   x m 4....
View Full Document

{[ snackBarMessage ]}

### Page1 / 2

hw1-solution - W/m 2 K The surface emissivity of the sphere...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online