A radiation shield that has the same emissivity 3 on both sides is placed between two large parallel plates, which are maintained at uniform temperatures of T1 = 650 K and T2 = 400 K and have emissivities of E1 = 0.6 and E2 = 0.9, respectively. Determine the emissivity of the radiation shield if the radiation heat transfer between the plates is to be reduced to 15 percent of that without the radiation shield

Could you give me some explanation, the correct answer is at the bottom of the question.

A composite wall is comprised of two large plates separated by sheets of refractory insulation. In the installation process, the sheets of thickness L = 50 mm and thermal conductivity k = 0.05 W/mK are separated at 1-m intervals by gaps of width w = 10 mm. The hot and cold plates have temperatures and emissivities of T1 = 400 deg C, emissivity1 = 0.85 and T2 = 35 deg C, emissivity2 = 0.5, respectively. Assume that the plates and insulation are diffuse-gray surfaces. %3D Determine the heat loss by radiation through the gap per unit length of the composite wall (normal to the page). Recognizing that the gaps are located on a 1-m spacing, determine what fraction of the total heat loss through the composite wall is due to transfer by radiation through the insulation gap. Hot side Gap w = 10 mm A. 47 W/m, 9.2% T1 = 400°C B. 47 W/m, 10.2% L = 50 mm C. 37 W/m, 10.2% D. 37 W/m, 9.2% T2 = 35°C Cold side 1 m Insulation, k = 0.05 W/m-K

This experiment is conducted to determine the emissivity of a certain material. A long cylindrical rod of diameter D₁ = 0.01 m is coated with this new material and is placed in an evacuated long cylindrical enclosure of diameter D₂ = 0.1 m and emissivity 2 = 0.95, which is cooled externally and maintained at a temperature of 200 K at all times. The rod is heated by passing the electric current through it. When steady operating conditions are reached, it is observed that the rod is dissipating electric power at a rate of 16 W per unit of its length, and its surface temperature is 600 K. Based on these measurements, determine the emissivity of the coating on the rod. The emissivity of the coating on the rod is 0.1165