6.3. A solid steel sphere (AISI 1010), 300 mm in diameter, is coated with a dielectric materiallayer of thickness 2 mm and thermal conductivity 0.04W/m ⚫ K. The coated sphere is initially ata uniform temperature of 500°C and is suddenly quenched in a large oil bath for which To=100°C and h 3300 W/m² K. Estimate the time required for the coated sphere temperature toreach 140°C. Hint: Neglect the effect of energy storage in the dielectric material, since itsthermal capacitance (pcV) is small compared to that of the steel sphere.

Analyzing the Problem and AssumptionsWe are tasked with estimating the time required for a coated…

Answered: 6.3. A solid steel sphere (AISI 1010),…

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

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Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.35P

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5.10 A steel sphere (AISI 1010), 100 mm in diameter, is coated with a dielectric material layer of thickness 2 mm and thermal conductivity 0.04 W/mK. The coated sphere is initially at a uniform temperature of 500°C and is suddenly quenched in a large oil bath for which T = 100°C and h = 3000 W/m² K. Estimate the time required for the coated sphere temperature to reach 150°C. Hint: Neglect the effect of energy storage in the dielectric material, since its thermal capacitance (pcV) is small compared to that of the steel sphere.
A steel sphere (AISI 1010), 100 mm in diameter, is coated with a dielectric material layer of thickness 1.75 mm and thermal conductivity 0.04 W/m.K. The coated sphere is initially at a uniform temperature of 500°C and is suddenly quenched in a large oil bath for which T = 100°C and h = 3000 W/m².K. Estimate the time, in h, required for the coated sphere temperature to reach 150°C. Hint: Neglect the effect of energy storage in the dielectric material, since its thermal capacitance (pc)is small compared to that of the steel sphere. t = h
A long insulated tube is doped with an exothermic ma- terial which generates steady and uniform heat at rate of è [W/m³]. The tube has an inner radius r₁ and outer radius r₂. The temperature of the outer insulated sur- face is T₂. This tube is used to heat a liquid flowing through it. (a) Write the governing differential equation and boundary conditions to determine the tempera- ture distribution inside the tube. (b) What is the heat flux supplied to the liquid by the tube? e (√₂²-1₁²) / 21₁ 1 Fluid Figure 2: Schematic Insulation T₂ N
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Q2/ An aluminum sphere weighting 7kg and initially at a temperature of 533K is suddenly immersed in a fluid at 283K. if heat transfer coefficient between the sphere and fluid is 50W/m?.°C. Take density=2707kg/m3, specific heat=0.9KJ/kg.ºC and thermal conductivity= 204W/m°C. Determine th Bi number and And determine the time required to cool sphere to 263k
Example 3.3: The temperature at the center of a tender-boiled potato needs to be 98.9°C. Let's take a potato with 4 cm diameter at 5°C and and put it in vigorously boiling water at 100 °C, where convection coefficient is 1200 W/m². c. How much time will it take to cook the potato? Potato properties: density p=1070 kg/m³, conductivity k=0.8 W/m.°c, specific heat c = 3400 J/kg-°C.
5.6 Steel balls 12 mm in diameter are annealed by heating to 1150 K and then slowly cooling to 400 K in an air envi- ronment for which T325 K and h = 20 W/m².K. Assuming the properties of the steel to be k = 40 W/mK, p= 7800 kg/m³, and c = 600 J/kg K, estimate the time required for the cooling process.
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3.8 Determine (i) the pressure drop, and (ii) the convective heat transfer coefficient from hot air ( Tin = 500 K, Pin = 101.3 kPa, m sphere = 3.8 cm, o = 0.45, T init = 300 K, c sphere = 0.8 kJ/kgK, k sphere = 1.05 W/mK). = 3.5 kg/s) to a cold-packed bed of spheres (L vessel = 6.0 m, D vessel = 1.50 m, D Answer. (a) Ap = 9.46 kPa ; (b) h = 115
3.4 Estimate the rate of heat loss due to radiation from a covered pot of water at 95 ° C. How does this compare with the 60 W that is lost due only to convection and conduction losses? What amount of energy input would be needed to maintain the water at its boiling point for 30 minutes? The polished stainless steel pot is cylindrical, 20 cm in diameter and 14 cm high, with a tight-fitting flat cover. The air temperature in the kitchen is about 25 ° C. State any assumptions you make in deriving your estimates
1. Saturated steam at 500 K flows in a 0.20 m inside diameter, 0.21 m outside diameter pipe. The pipe is covered with 0.08 m of insulation with a thermal conductivity of 0.10 W/m-K. The pipe's conductivity is 52 W/m-K. The ambient temperature is 300 K. The unit convective coefficients are h; = 18,000 W/m²-K and ho = 12 W/m²-K. Determine the heat loss (kJ/min) from 4 m of pipe. • show conversions, units, and box in your final answers
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