A stainless steel ball (p = 8055 kg/m², C, = 480 J/kg -°C) of diameter D = 15 cm is removed from the oven at a uni-form temperature of 350°C. The ball is then subjected to the flowof air at 1 atm pressure and 30°C with a velocity of 6 m/s. Thesurface temperature of the ball eventually drops to 250°C. Deter-mine the average convection heat transfer coefficient during thiscooling process and estimate how long this process has taken.

Given: Diameter of ball D = 15 cm Velocity v = 6 m/s Cp = 480 J/Kg Uniform temperature T = 350°C…

Answered: A stainless steel ball (p = 8055 kg/m²,…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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What regime favors heat transfer and why?Laminar, Turbulent or Transitional
A hot steel ball of 5 mm in diameter initially at 100 oC is left to cool down in air at 20 oC. Assume a constant convective heat transfer coefficient h = 15 W/m2K through the course of the cooling process. Cp, steel = 0.49 kJ / kg K , k,steel = 45.0 W / m K , rho, steel = 7800 kg/m^3 Cp,air = 1.00 kJ/kg K ; k_air = 0.025 W / m K; rho,air = 1.2 kg/m^3 a) Calculate the rate of convective heat transfer when the steel ball is uniformly at 100 oC. b) Assuming the steel as a lumped system, find the temperature of the steel ball after 0.5 s.
A 65 kg beef carcass (k-0.47 w/mk and a-0.13 x10-6 m/s) initially at a uniform temperature of 37 "C is to be cooled by refrigerated air at -10 oC flowing at a velocity of 1.2 ms. The average heat transfer coefficient between the carcass and the air is 22 W/m²K. Treating the carcass as a cylinder of diameter 24 cm and the height 1.4 m and disregarding heat transfer from the base and top surfaces, Determine how long it will take for the centre temperature of the carcass to drop to 4 °C b. Also, determine if any part of the carcass will freeze during this process Hava- air -10 °C 12m/s Sider E Beef JTC
A short brass cylinder (p = 8530 kg/m³, cp=0.389 kJ/kg-K, k=110 W/m-K, and a = 3.39×10−5 m²/s) of diameter 4 cm and height 20 cm is initially at a uniform temperature of 140°C. The cylinder is now placed in atmospheric air at 20°C, where heat transfer takes place from the cylinder 15 min after the start of the cooling by convection with a heat transfer coefficient of 40 W/m2.K. Solve this problem using the analytical one-term approximation method. Interpolate table 4-2 to obtain constants ₁ and A₁. For Biot number values less than 0.01 approximate it as 0.01 for use in Table 4-2. NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. 20 cm Brass cylinder 4 cm TiºC Ambient air 20°C Calculate the center temperature of the top surface of the cylinder. The center temperature of the top surface of the cylinder is 61 °C.
The upper surface of a 50-cm-thick solid brass plate (k=109 W/mK) is being cooled by water with temperature of 10°C. The upper and lower surfaces of the solid plate maintained at constant temperatures of 60°C and 190°C, respectively. Determine the water convection heat transfer coefficient and the water temperature gradient at the upper plate surface. Water Ts.l · Ts.,2

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