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 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. Deter- mine the average convection heat transfer coefficient during this cooling process and estimate how long this process has taken.
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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)Hot engine oil at 150°C is flowing in parallel over a flat plate at a velocity of 2 m/s. Surface temperature of the 0.5-mlong flat plate is constant at 50°C. Determine (a) the local convection heat transfer coefficient at 0.2 m from the leading edge and the average convection heat transfer coefficient, and (b) repeat part (a) using the Churchill and Ozoe (1973) relation.
- Liquid mercury at 250°C is flowing with a velocity of 0.3 m/s in parallel over a 0.1-m-long flat plate where there is an unheated starting length of 5 cm. The heated section of the flat plate is maintained at a constant temperature of 50°C. Determine (a) the local convection heat transfer coefficient at the trailing edge, (b) the average convection heat transfer coefficient for the heated section, and (c) the rate of heat transfer per unit width for the heated section.A 4-m x 4-m flat plate maintained at a constant temperature of 80°C is subjected to parallel flow of air at 1 atm, 20°C, and 10 m/s. The total drag force acting on the upper surface of the plate is measured to be 2.4 N. Using momentum heat transfer analogy, determine the average convection heat transfer coefficient, and the rate of heat transfer between the upper surface of the plate and the airQ3: 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