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# hw05-hints - ABE 484/584 CHOI HW5 1 Temperature and Food...

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Unformatted text preview: ABE 484/584 CHOI HW5 1. [ Temperature and Food Safety ] Most people think they know when food is done by trusting their experience or the color of meat. This can be misleading. One out of four hamburgers turns brown in the middle before it has reached a safe internal temperature, according to recent USDA research. Therefore, a recent USDA campaign features a cartoon thermometer called Thermy™ that proclaims "IT’S SAFE TO BITE WHEN THE TEMPERATURE IS RIGHT." Thermal engineers must ensure that food has reached a temperature high enough to destroy harmful bacteria. An international fast-food restaurant hired you as a consultant to estimate the time required to cook a hotdog in boiling water. Assume that the hot dog is initially at 6 o C, that the convection heat transfer coefficient is 100 W/m 2 ⋅ K and that the final temperature should be 80 o C at the centerline. Treat the hot dog as a long cylinder of 20-mm diameter having the properties shown in the figure. Estimate the minimum time required to cook a hot dog. Department of Agricultural and Biosystems Engineering, The University of Arizona T(r,0)= T i = 6 o C r o = 10 mm r T(0,t) = 80 o C T ∞ = 100 o C h = 100 W/m 2 ⋅ K c p = 3350 J/kg ⋅ K k = 0.52 W/m ⋅ K ρ = 880 kg/m 3 ABE 484/584 CHOI Department of Agricultural and Biosystems Engineering, The University of Arizona ABE 484/584 CHOI 2. [ Burn Injury and Supersonic Bullet ] The image at the right is a shadowgraph of a bullet at an approximate Mach number of 3. The recompression shock where the wake attains a constant width is nicely illustrated. An insurance company has hired you as a consultant to improve their understanding of burn injuries, and you need to determine bullet temperature. Consider a spherical lead bullet of 6 mm diameter moving at a Mark number of approximately 3. The resulting shock wave shown above heats the air around the bullet to 700 K, and the average convection coefficient for heat transfer between air and the bullet is 500 W/m 2 ⋅ K. The bullet leaves the barrel at 300 K and the time of flight K....
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hw05-hints - ABE 484/584 CHOI HW5 1 Temperature and Food...

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