Q1: At a constant velocity of 20 m/s, air passes across a flat plate with ambient pressureand temperature of 20 kPa and 20°C. At a distance of 7.5 cm from the leading edge, theplate is heated to a constant temperature of 75°C. How much heat is transferred overallfrom the leading edge to a location 35 cm from the leading edge?Q2: The critical Reynolds number for flow over a flat plate in a particular application is106. This critical Reynolds number and an isothermal plate temperature of 400 K areencountered by air flowing across it at 1 atm, 300 K, and 10 m/s. At the end of the plate,the Reynolds number is 5 × 106. What will average heat transfer coefficient be for thissystem? What is the length of the plate? What is the plate's loss of heat?Q3: At 50 kPa and 300 K, air moves at an average velocity of 6 m/s across a 20-cm-square plate. To provide a steady flow of heat, an electrical heater is mounted within theplate. If the plate temperature is limited to 600 K, how much heat can be dissipatedoverall?

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Answered: Q1: At a constant velocity of 20 m/s,…

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.

Chapter5: Analysis Of Convection Heat Transfer

Section: Chapter Questions

Problem 5.65P

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Consider atmospheric air at 25 °C and a velocity of 25 m/s flowing over BOTH surfaces of a 1-m- long flat plate that is maintained at 125 °C. The width of the plate (into paper direction) is 1 m. Determine the rate of heat transfer if the critical Reynolds number is 5 × 105.
The fluid condition at the inlet and exit of a horizontal convergent nozzle is analysed. The nozzle is operating steadily and heat loss is assumed negligible. If the specific enthalpy of fluid and velocity of fluid at the inlet are 3,314 kJ/kg and 226 km/hr respectively. At the exit the specific enthalpy of fluid is 2,563 J/kg. Calculate the exit area (in mm-)of the nozzle when the specific volume at the nozzle exit is 0.61 m3/kg at the inlet area of 0.23 m2 and the specific volume at the inlet is 0.3 m3/kg.
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Consider a refrigeration truck traveling at 55 mph at a location where the air temperature is 80°F. The refrigerated compartment of the truck can be considered to be a 9-ft-wide, 8-ft-high, and 20-ft-long rectangular box. The refrigeration system of the truck can provide 3 tons of refrigeration (i.e., it can remove heat at a rate of 600 Btu/ min). The outer surface of the truck is coated with a lowemissivity material, and thus radiation heat transfer is very small. Determine the average temperature of the outer surface of the refrigeration compartment of the truck if the refrigeration system is observed to be operating at half the capacity. Assume the air flow over the entire outer surface to be turbulent and the heat transfer coefficient at the front and rear surfaces to be equal to that on side surfaces. For air properties evaluations assume a film temperature of 80°F. Is this a good assumption?
Q2) Air at 20°C flows over a flat plate having a uniform heat flux of 800 W/m². The flow velocity is 4m/s and the length of the plate is 1.2 m. Determine the value of heat transfer coefficient and also the temperature of the plate as the air leaves the plate.
Q1: Air enters a 7m long section of a rectangular duct of cross section 15 cm x 20 cm at 50°C at an average velocity of 7 m/s. If the walls of the duct are maintained at 10 C, determine (a) the outlet temperature of the air, (b) the rate of heat transfer from the air. Air properties from tables: p=1.127 kg/m' C,-1007 J/kg. C k 0.02662 W/m.°C Pr 0.7255 D=1.702x10 m'/s Answer: (a): Te 34.2 °C, (b): Q' 3776 W Hint: 1- Use the Logarithmic mean temperature difference relations. If Reer 2300, in pipes and ducts, the flow is turbulent. T-10°C Air duet 15 em x 20 em Air 50°C 7 m/s L-7m
Q3: A square flat plate of 1 m² area whose two surfaces temperature is 90 °C is cooled by air at 20 °C flowing over both sides parallel to the plate at 2 m/sec. Calculate the rate of cooling plate Air at 20°C 1111
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As shown in the figure, electrical heaters operating in the V-220 V are placed on the lower surface of the square-shaped horizontal aluminum plate with a length and width of 1.2 m. Air at a temperature of 27 °C flows from the upper surface of the plate in parallel at 15 m/s. Since the bottom surface of the plate is fully insulated, what should the value of the current () passing through the electrical elements be so that the temperature of the plate does not exceed 77 °C? Air Al plate Heaters L=1.2 m
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Q2: Air at standard conditions of I atm and 27°C flows over a flat plate at 20 m/s. The plate is 60 cm square and is maintained at 97°C. Calculate the heat transfer from the plate. Answers: Q= 681 W,

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