2. A furnace wall is made up of three layer of thickness 150 mm, 110 mm, and 125 mm with thermal conductivity of 1.65 W/m-K, k2, and 9.2 W/m-K respectively. The inside is exposed to gases at 1050°C with a convection coefficient of 25 W/m²-K and the inside surface temperature is at 900°C, the outside air temperature is at 30°C with convection coefficient of 12 W/m²-K. Calculate: a. the unknown thermal conductivity; b. the outside surface temperature and mid-plane temperatures in °F.

Round off the numbers in the following problems to three significant figures. Find the percent difference between each rounded-off number and the original number by using the original number as the reference.        26.394

Round off the numbers in the following problems to three significant figures. Find the percent difference between each rounded-off number and the original number by using the original number as the reference.      6471.9

2. Thermal Efficiency a. Planet Express Generating Station in New York, NY uses 8720 Btu of energy to generate each kilowatt hour of electricity. Find its thermal efficiency. Express as a percentage with no decimal point. b. Mystery Shack Generating Station in Gravity Falls, OR has a thermal efficiency of 43%. How many million cubic feet (MMcf) of natural gas are needed to generate 560 megawatt hours of electricity? Round to the nearest hundredth.