MET 3453 Heat Transfer Homework #1 Problems 1. Read the articles at the following links and then answer the below questions. https://www.nasa.gov/feature/ipl/how-cold-can-you-go-cooler-tested-for-nasa-telescope https://webbtelescope.org/contents/articles/how-does-webb-stay-cold https://webb.nasa.gov/content/observatory/sunshield.html https://webb.nasa.gov/content/about/innovations/cryocooler.html a. What temperature do the instruments need to maintain? b. What temperature is expected on the sun side of the shield? C. Name at least one use of each of the heat transfer methods (conduction, convection, radiation) on the James Webb space telescope. 2. A wood slab with a thickness of 0.05 m is subjected to a heat flux of 40 W/m2. The left and right surface temperatures of the wood slab are kept at constant temperatures of 40C and 20C, respectively. What is the thermal conductivity of the wood slab in [W/m-K]? 3. A square isothermal micro-processor is of width w = 0.05 m on a side and is mounted in a substrate such that its side and back surface are well insulated, while the front surface is exposed to the flow of a coolant at 15C. From the reliability considerations, the chip temperature must not exceed 85C. If the required heat dissipation from the chip is 45 W, what would be the required convection heat transfer coefficient in [W/m2-K]? Coolant Tooth Chip W 4. The roof of a house is 6 m long, 8 m wide, and 0.25 m thick. It is made of a flat layer of concrete whose thermal conductivity is 0.8 W/m-K. The temperatures of the inner and the outer surfaces of the roof are measured to be 15C and 4C, respectively. Calculate heat loss through the roof in [W]. Concrete roof 6 m 4C 15C 0.25 m 8 m MET 3453 Heat Transfer Homework #1 Problems 5. Consider a person whose exposed surface area is 1.7 m, emissivity is 0.5, and surface temperature is 32C. Determine the rate of heat loss [W] from that person by radiation in a large room having walls at a temperature of (a) 300 K and (b) 280 K. 32C Tsurr Qrad 6. A 20 cm thick granite (k=2.79 W/m-K) wall has a temperature on one side of 50 C while the other side is exposed to a 22 C air flow (h=15 W/mK). What is the equilibrium temperature on the second side? What is the heat flux through the wall? Neglect radiation.