 ## Summer 2022-VM335 Homework 8

### 12.1 Consider an opaque horizontal plate that is well insu-lated on its back side. The irradiation on the plate is 2500 W/m2, of which 500 W/m2 is reflected.  代写heat transfer作业

The plate is at 227°C and has an emissive power of 1200 W/m2. Air at 127°C flows over the plate with a heat transfer convection coeficient of 15 W/m2. K. Determine the emissivity, absorptivity, and radiosity of the plate.What is the net heat transfer rate per unit area?

### 12.6 Consider a small surface of area A =10-4m2, which emits diffusely with a total, hemispherical emissive powerof E=5 ×104 W/m2.  代写heat transfer作业

(a) At what rate is this emission intercepted by a small surface of area A2= 5 × 10-4m2, which is ori-ented as shown?  v

(b) What is the irradiation G2 on A2?

(c) For zenith angles of θ2 = 0, 30, and 60, plot G2 as a function of the separation distance for 0.25 ≤ r2≤1.0 m.

### 12.15 Determine the fraction of the total, hemispherical emissive power that leaves a diffuse surface in the directions π/4≤θ≤π/2 and 0≤ø≤π.  代写heat transfer作业

12.20 The energy flux associated with solar radiation incident on the outer surface of the earth’s atmosphere has been accurately measured and is known to be 1368 W/m2.

The diameters of the sun and earth are 1.39 ×109and 1.27 × 107m, respectively, and the distance between the sun and the earthis 1.5 × 1011m.

(a) What is the emissive power of the sun?  代写heat transfer作业

(b) Approximating the sun’s surface as black, what is its temperature?

(c) At what wavelength is the spectral emissive power of the sun a maximum?

(d) Assuming the earth’s surface to be black and the sun to be the only source of energy for the earth,estimate the earth’ s surface temperature.