Refine the thermal design for the refrigerated shipping container from Design Problem 3.3 by calculating the convection heat transfer coefficient over the two sides and the top at 105 km/h from information presented in this chapter. Heat loss from the front and the back of the truck is estimated from information in Table 1.3. Heat loss from the bottom of the container is relatively small because it sits close to the road on the bed of the truck.

Data from in Problem 3.3

Quenching is a rapid cooling process by which many metallic alloys are hardened. Brass (a copper alloy: 70 Cu, 30 Zn) plates that are 4 mm thick are quenched in a water bath at a heat treating plant. If a brass plate is initially at 450°C, determine the quench time needed for the plate to attain 90°C. The water bath temperature is 80°C and has an average convective heat transfer coefficient of 2500 W/m²•K. Also, if the rectangular plate is 1 m wide and 2 m long, determine the total amount of heat imparted to the bath during quenching.

Data from in Table 1.3

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TABLE 1.3 Thermal conductivities of some metals, nonmetallic solids, liquids, and gases Material Copper Aluminum Carbon steel, 1% C Glass Plastics Water Ethylene glycol Engine oil Freon (Liquid) Hydrogen Air Thermal Conductivity at 300 K (540 °R) W/m K 399 237 43 0.81 0.2-0.3 0.6 0.26 0.15 0.07 0.18 0.026 Btu/h ft °F 231 137 25 0.47 0.12-0.17 0.35 0.15 0.09 0.04 0.10 0.02