Chapter 6, Problem 6.4DP

A plastics plant manufactures larges pieces of plastic by continuously extruding thin sheets.As the sheets flow out of the extruder, they are cooled via forced convection and radiation.The plastic sheets are 1 mm thick, 1 m wide, and leave the extruder at a rate of 9 m/min.A fan blows air over the top and bottom surface of the sheet during the first meter after thesheet leaves the extruder. The fan accelerates the air to 3 m/s and the air is known to be at27°C at the fan outlet. At the exit of the extruder, the plastic is at 90°C. The plastic isestimated to have an emissivity of ? = 0.9 and the general surroundings are at 20°C. A)  Determine the rate of heat transfer via convection and radiation from the 1-m-longsection of the plastic sheet that is being force cooled. take the surface temperature to be 90°C overthe entire section of interest.  B) The density-specific heat product of the plastic is ?? = 1920 kJ m3– K⁄ . What is thetemperature of the plastic at the end of the cooling…

"You did calculations using the simplified HAZ time-temperature formulas, assuming 3D heat flow, and are presenting your final internship conclusions to management. You realize with horror, in the middle of your presentation, that you forgot to label your calculated curves (below). Which curve is which? Pick the best answer A: "Plot 1 is HYPERFILL® and Plot 2 is p-GMAW. Since HYPERFILL® has the higher heat input, it cools more slowly."     B: "Plot 2 is HYPERFILL® and Plot 1 is p-GMAW. Since HYPERFILL® has the faster travel speed of the two processes, it cools faster."     C: "Plot 1 is p-GMAW and Plot 2 is HYPERFILL®. Since p-GMAW has the slower travel speed, it cools more slowly."     D: "Plot 2 is p-GMAW and Plot 1 is HYPERFILL®. Since p-GMAW has the lower heat input, it cools faster"     Both (A) and (D)

a cylindrical can of bean puree, has a diameter of 70 mm and height of 126 mm, and is initially at a uniform temperature of 25 ° C. The cans are stacked vertically inside a retort into which steam is introduced at 120 ° C. Calculate the temperature in the center of the can after a heating time of 0.55 h at 120 ° C. Now suppose the can is in the center of a vertical stack, insulated at its two ends by the presence of the remaining cans. (The heat capacity of the metal wall of the can can be neglected.) The heat transfer coefficient of steam is estimated to be 4640 W / m2 ° K. The physical properties of the bean are k = 0.750 W / m ° K and the thermal diffusivity = 2.007 x 10-7 m2 / s.a) Calculate the temperature in the center of the product.