Heat And Mass Transfer
5th Edition
ISBN: 9781259173301
Author: Çengel, Yunus A., Ghajar, Afshin J. (afshin Jahanshahi)
Publisher: Mcgraw Hill Education,
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Ethylene glycol at 40°C flows over a heated plate very wide, 6 m long, at velocity of 0.04 m/s. For a temperature = 90°C, determine:
1- the thickness of the hydrodynamic boundary layer at the end of the plate2- the thickness of the thermal boundary layer at the end of the plate3- the local and average heat transfer coefficient at the end of the plate4- the total heat flux transferred from the heated surface.
Calculate the rate at which the average friction coefficient, friction force and heat transfer rate will change if the free flow rate of the turbulent air flowing parallel to the plate over a smooth plate is doubled. Does the result change for constant temperature and constant heat flux conditions; Please evaluate.
Air at 300 degrees Celsius flows over a plate of dimension 0.5 m by 0.25 m. If the convection heat transfer coefficient is 250 Watts per Sq.m Kelvin, determine the heat transfer rate from the air to one side of the plate if the plate is to be maintained at 40 degrees Celsius.
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- Air at 200C and at a pressure of 1 bar is flowing over a flat plate at a velocity of 3 m/s. If the plate is 280 mm wide and at 560C, calculate the following quantities at x = 280 mm given that properties of air at the bulk mean temperature 20 + 56/2= 380C are: (i) Boundary layer thickness,(ii) Local friction coefficient,(iii) Average friction coefficient,(iv) Shearing stress due to friction(v) Thickness of the boundary layer,(vi) Local convective heat transfer coefficient,(vii) Average convective heat transfer coefficient,(viii) Rate of heat transfer by convection(ix) Total drag force on the plate, and(x) Total mass flow rate through the boundaryarrow_forwardQuestion No. 3: During a cold winter day, wind at 55 km/h is blowing parallel to a 4-m-high and 10-m-long wall of a house. If the air outside is at 5°C and the surface temperature of the wall is12°C, determine the rate of heat loss from that wall by convection. What would your answer be if the wind velocity was doubledarrow_forwardA Gasoline engine operating on an air standard condition has a clearance volume of 15cm3 and a displacement volume of 100cm3 . Determine the theoretical thermal efficiency of the engine.arrow_forward
- An average person generates heat at a rate of 84 W while resting. Assuming one-quarter of this heat is lost from the head and disregarding radiation, determine the average surface temperature of the head when it is not covered and is subjected to winds at 10°C and 25 km/h. The head can be approximated as a 30-cm-diameter sphere. Assume a surface temperature of 15°C for evaluation of ms. Is this a good assumption?arrow_forwardConsider laminar flow of air across a hot circular cylinder. At what point on the cylinder will the heat transfer be highest? What would your answer be if the flow were turbulent?arrow_forwardConsider laminar flow over a flat plate. How does the local friction coefficient change with position?arrow_forward
- Explain, motorcycle engine is either considered as free or forced convection. Justify your answerarrow_forwardFlue gases from an incinerator are released to atmosphere using a stack that is 0.6 m in diameter and 10.0 m high. The outer surface of the stack is at 40°C and the surrounding air is at 10°C. Determine the rate of heat transfer from the stack assuming (a) there is no wind and (b) the stack is exposed to 20 km/h winds.arrow_forwardDuring a cold winter day, wind at 55 km/h is blowing parallel to a 4m high and 10m long wall of a house. If the air outside is at 5 degrees Celsius and the surface temperature of the wall is 12 degrees Celsius , determine the rate of heat loss from the wall by convection. What would your answer be if the wind velocity has doubled? From Table A-1:thermal conductivity, k = 0.0246 W/m degrees Celsiusviscosity, v = 1.4 x 10^-5 m^2/sPrandtl no. Pr = 0.717arrow_forward
- What is lift? What causes it? Does wall shear contribute to the lift?arrow_forward....A journal bearing is to be used for a centrifugal pump where the shaft diameter is 50 mm and the bearing length is 80 mm. The ambient and bearing surface temperatures are 20°C and 45°C, respectively. Which of the following is the heat dissipated by the bearing if the heat dissipation coefficient is 280 W/m2-°C? Group of answer choices 56 W 14 W 73 W 28 Warrow_forwardA vehicle carrying refrigeration box is moving with a speed of 24 m/s on a road withambient temperature of 323 K. The dimensions of box are 3 m(H) × 4 m (W) × 10 m (L).Assume a wall temperature of 283 K and air flow is parallel to the longest side of the box.Neglecting the heat loss from the front side and backside of the box, calculate heat lossfrom four surfaces. For flow over flat surfaces useNu = 0.036(Re)0.8(Pr)1/3The properties of air at bulk mean temperature are : = 1.165 kg/m3, Pr = 0.701, cp = 1005 J/kg – K, = 16 × 10–6m2/sarrow_forward
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