ET 314 Thermo/Heat Transfer - 14 Dec 2016 (K)=T(°C)+273.15 -5.67x10 W/(m²-°K*) elium R=0.2870 kPa-m'/(kg-"K) Cp 1.005 kJ/(kg-"K) R=2.0769 kPa-m'/(kg-"K) C-5.1926 kJ/(kg-"K) Name: unobtainium kpc,-20.9 kJ/(m²-"C) human flesh √/kpc,- 1.1 kJ/(m²-°C) vibranium kpc,-0.10 kJ/(m²-"C) For each problem, show all work including units in each step. PUT A BOX AROUND ANSWER. (23%) Helium is to be compressed from 120 kPa and 210 K to 700 kPa and 430 K. A heat loss of 20 kJ/kg occurs during the compression process. Neglecting kinetic energy changes, determine the power input required for a mass flow rate of 90 kg/min using the following steps. a) (3) Write out the givens, one per line and then the find b) (8) Write down the main equation needed to solve this problem and the assumptions you can make about some of the terms. Write the final formula. c) (2) What is m in kg/s? d) (10) What is the input power? 2. (22%) Heat is transferred to a heat engine from a furnace at a rate of 100 MW. If the rate of waste heat rejection to a nearby river is 70 MW, determine the work done by the heat engine and the thermal efficiency, n, for the heat engine. Label each step. a) (3 points) Write out the givens, one per line and then the find b) (3 points) Draw a schematic of the situation c) (8 points) What is the work done by the heat engine? d) (8 points) What is the thermal efficiency of the heat engine? 3. (25%) Consider a person standing in a breezy room at 23 °C. Determine the total rate of heat transfer from this person if the exposed surface area and the skin temperature of the person are 1.7 m² and 32 "C, respectively, and the convection heat transfer coefficient is 5 W/m²- "C. Assume the emissivity of the skin and the clothes is 0.9, and assume the temperature of the inner surfaces of the room to be the same as the air temperature. Label each step. a) (3) Write out the givens, one per line and then the finds b) (10) What is the radiative heat transfer? c) (10) What is the convection heat transfer? d) (2) What is the total rate of heat transfer? (23%) A person whose hands are at 32 °C puts one hand on a large block of unobtainium and the other hand on a large block of vibranium. Both blocks are at 20 °C. Determine the contact surface temperatures. Treat both the hands and blocks as semi-infinite solids. a) (3) Write out the givens, one per line and then the finds b) (10) What is the contact surface temperature for the unobtainium block? c) (10) What is the contact surface temperature for the vibranium block? (7%) In class we calculated that a concrete thermal wall exposed to the sun for a day increased temperature about 13 °C. Does the entire wall thickness raise 13°C? Explain why or why not.