Please select the most appropriate answer for these multiple-choice questions.

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A surface has a spectral hemispherical emissivity of 0.6 for wavelengths from 0 to 1 m, and of 0.8 for wavelengths greater than 1m. The surface receives irradiation of 1368W/m2 from a blackbody at 5800K and is at a temperature of 300K. Select all correct answers. i. The surface can be approximated as a grey surface. ii. The surface is reflecting 897W/m2. iii. The surface is emitting 367W/m2. iv. If the surface is in a steady state, there is another mode of heat transfer transferring energy away from the surface. v. The net energy transport away the surface due to radiation heat transfer is 530W/m2 A plane wall is heating up to due being exposed (on both sides) to a gas stream at 100 C, with a convection coefficient of 16W/m2K. The oak wall is 20cm thick, has a density of 720kg/m3, a heat capacity of 1255J/kgK and a thermal conductivity of 0.16W/mK. The wall is initially at a uniform 20C. Select all correct answers. i. Lumped capacitance is the best way to analyse this problem. ii. The minimum temperature in the wall after 6 hours is 53.8C. iii. The minimum temperature in the wall after 6 hours is 18.0C. iv. The temperature will be constant throughout the thickness at each time, but will increase with time. v. If the thermal diffusivity of the wall were larger, the wall would heat up more quickly. A surface has a spectral hemispherical emissivity of 0.6 for wavelengths from 0 to 1 m, and of 0.8 for wavelengths greater than 1m. The surface receives irradiation of 1368W/m2 from a blackbody at 5800K and is at a temperature of 300K. Select all correct answers. i. The surface can be approximated as a grey surface. ii. The surface is reflecting 897W/m2. iii. The surface is emitting 367W/m2. iv. If the surface is in a steady state, there is another mode of heat transfer transferring energy away from the surface. v. The net energy transport away the surface due to radiation heat transfer is 530W/m2 A plane wall is heating up to due being exposed (on both sides) to a gas stream at 100 C, with a convection coefficient of 16W/m2K. The oak wall is 20cm thick, has a density of 720kg/m3, a heat capacity of 1255J/kgK and a thermal conductivity of 0.16W/mK. The wall is initially at a uniform 20C. Select all correct answers. i. Lumped capacitance is the best way to analyse this problem. ii. The minimum temperature in the wall after 6 hours is 53.8C. iii. The minimum temperature in the wall after 6 hours is 18.0C. iv. The temperature will be constant throughout the thickness at each time, but will increase with time. v. If the thermal diffusivity of the wall were larger, the wall would heat up more quickly