ME 341 HEAT TRANSFER FOR ENGINEERING Exam 3
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1) You are tasked to analyze the hydrodynamic and thermal behavior of H2 that is
flowing lengthwise (in x-direction) over a flat plate at a velocity of 3 m/s, and has a bulk temperature of 15°C. The width of the plate is z= 0.3 m (perpendicular into the picture) and the surface temperature of the plate is at 71°C. Assume steady-state conditions and constant fluid properties at Tfilm.
a) Calculate the thickness of the hydrodynamic and thermal boundary layers at x = 0.3m and at the distance x corresponding to the transition point considering Recritical = 5×105 (10 points)
ME 341 HEAT TRANSFER FOR ENGINEERING Exam 3
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b) Calculate the average friction coefficient along this plate between x=0 and x=0.3m and between x=0 and the distance x corresponding to the transition point considering Recritical = 5×105 (10 points)
ME 341 HEAT TRANSFER FOR ENGINEERING Exam 3
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c) Calculate the average convection heat transfer coefficient along this plate between x=0 and x=0.3m and between x=0 and the distance x corresponding to the transition point considering Recritical = 5×105 (10 points)
ME 341 HEAT TRANSFER FOR ENGINEERING Exam 3
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d) Calculate the rate of convection heat transfer off this plate between x=0 and x=0.3m and between x=0 and the distance x corresponding to the transition point considering Recritical = 5×105 (5 points)
e) Qualitatively draw the profile of the friction coefficient and the convection heat
transfer coefficient between x=0 and the distance x corresponding to the transition point considering Recritical = 5×105 (5 points)
ME 341 HEAT TRANSFER FOR ENGINEERING Exam 3
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2) As the engineer on the job you are tasked to determine the total heat transfer from the side of a building that is made entirely of glass when the temperature of the quiescent inside air is at 20°C and the outside surface of the glass is swept by cold air at -15°C at a velocity of 15 m/s parallel to its width. The dimensions of the glass and the system configuration are shown below. Assume that the conductive thermal resistance due to glass is negligibly small so that the inside surface temperature of the glass can be set equal to the outside surface temperature of the glass (Ts-inside = Ts-outside = Ts) (30 points)
ME 341 HEAT TRANSFER FOR ENGINEERING Exam 3
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3) In a heating application using a concentric tube configuration, light oil is flowing through a 25.4mm inner diameter, 0.6 m long thin-walled copper tube at a velocity of 0.03 m/s. The oil enters the tube at 15°C and is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11,300 W/(m2-K). The concentric tube heat exchange system is shown below. Light oil flows in the inner tube and steam is condensing in the annulus formed by the outer tube. Assume steady-state conditions, constant copper tube surface temperature and negligible copper tube wall thermal resistance. Determine the heat transfer per unit length of the copper tube.
The properties of the light oil as a function of temperature are tabulated below:
(30 points)
