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,…

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

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.38P

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Air enters a 25-cm-diameter 12-m-long underwater duct at 50°C and 1 atm at a mean velocity of 7 m/s, and is cooled by the water outside. If the average heat transfer coefficient is 85 W/m2?K and the tube temperature is nearly equal to the water temperature of 10°C, determine the exit temperature of air and the rate of heat transfer. Evaluate air properties at a bulk mean temperature of 30°C. Is this a good assumption?
In the effort to increase the removal of heat from a hot surface at 120°C, a cylindrical pin fin (kf = 237 W/m.K) with diameter of 5 mm is attached to the hot surface. Air at 20°C (1 atm) is flowing across the pin fin with a velocity of 10 m/s. Determine the maximum possible rate of heat transfer from the pin fin. Evaluate the air properties at 70°C.
A 25-cm-diameter stainless steel ball (r = 8055 kg/m3, cp 480 J/kg·°C) is removed from the oven at a uniform temperature of 300°C . The ball is then subjected to the flow of air at 1 atm pressure and 25°C with a velocity of 3 m/s. The surface temperature of the ball eventually drops to 200°C. Determine the average convection heat transfer coefficient during this cooling process and estimate how long the process will take.
A stainless steel ball (ρ = 8055 kg/m3, cp = 480 J/kg·K) of diameter D = 0.15 m is removed from the oven at a uniform temperature of 350°C. The ball is then subjected to the flow of air at 1 atm pressure and 30°C with a velocity of 6 m/s. The surface temperature of the ball eventually drops to 250°C. Determine the average convection heat transfer coefficient during this cooling process and estimate how long this process has taken. The average surface temperature is 300°C, and the properties of air at 1 atm pressure and the free stream temperature of 30°C are Pr = 0.7282, μs at 300°C = 2.934 × 10–5 kg/m·s, μ∞ = 1.872 × 10–5 kg/m·s, v = 1.608 × 10–5 m2/s, and k = 0.02588 W/m·°C. The average convection heat transfer coefficient during this cooling process is ____ W/m2·°C and time taken is ____ minutes.
For air flow at a constant wall temperature of 100 ◦C and average bulk temperature of 40 ◦C through a 4-cm-ID pipe, determine the value of average convection coefficient for an inlet velocity of 0.8 m/s if the pipe length is (i) 1 m, (ii) 3 m, (iii) 10 m.
Hot carbon dioxide exhaust gas at 1 atm is being cooled by flat plates. The gas at 220oC flows in parallel over the upper and lower surfaces of a 1.5-m-long flat plate at a velocity of 3m/s. if the flat plate surface temperature is maintained at 80oC, determine (a) the local convection heat transfer coefficient at 1 m from the leading edge, (b) the average convection heat transfer coefficient over the entire plate, and (c) the total heat flux transfer to the plate.
Hot engine oil at 150°C is flowing in parallel over a flat plate at a velocity of 3.30 m/s. Surface temperature of the 1.800-m long flat plate is constant at 50°C. The properties of engine oil at Tf = (150°C + 50°C)/2 = 100°C are k = 0.1367 W/m∙K, v = 2.046 × 10−5 m2/s, Pr = 279.1. Determine the local convection heat transfer coefficient at 0.200 m from the leading edge and the average convection heat transfer coefficient. The local convection heat transfer coefficient at 0.200 m from the leading edge is ___ W/m2·K. The average convection heat transfer coefficient is ___ W/m2·K.
Air at 1 atm 5°C with a free-stream velocity of 2 m/s flows in parallel with a stationary thin 1x 1m^2 flat plateover the top and bottom surfaces. The flat plate has a uniform surface temperature of 35°C. Determine theaverage convection heat transfer coefficient. (Answer: 5.46 W/m2·K)
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Q3: Air flows across a 20-cm-square plate with a velocity of $ m/s. Free-stream conditions are 10-C and 0.2 atm. A heater in the plate surface furnishes a constant heat-flux condition at the wall so that the average wall temperature is 100-C. Calculate the surface heat flux and the value of h at an x position of 10 cm. Answers: Q= 1414 W, b= 13.3 Wm?.C

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