Forced air at 250C and 10 m/s is used to cool electronic elements mounted on a circuit board. Consider a chip of length 4 mm and width 4 mm located 120 mm from the leading edge. Because the board surface is irregular, the flow is disturbed and the appropriate convection correlation is of the form
Estimate the surface temperature of the chip,
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Fundamentals of Heat and Mass Transfer
- Air at 2 bar and 40°C is heated as it flows through tube of diameter 30mm at a velocity of 10 m/s. Calculate the heat transfer per unit length of the tube when wall temperature is maintained at 100°C all along length of the tube. How much would be the bulk temperature increase over one metre length of the tube ? Use the following relation : Nu = 0.023 Re08 Pr04 u = 20.6 x 106 N- s/m?: Pr = 0.694 c, 1.009 kJ/kg°C; k = 0.0297 kg/m°C;arrow_forwardAir at 20 ◦ C flows inside a pipe 18-mm-ID having a uniform heat flux of 150 W/m 2 on the surface, the average flow velocity at entry being 1.0 m/s. The air pressure is 2 bar. Determine the value of convection coefficient. If the pipe is 2.5 m long, determine the air exit temperature and the wall temperature at the exit. Assume fully developed hydrodynamic boundary layer.arrow_forwardA steam reservoir is covered by a rectangular plate (its length is 1 m and width 2 m). The steam temperature is 95o C, and it is in contact with the plate. Over the outside surface of the plate, water is flowing at a speed of 3 m/sec at a temperature of 25o C. What is the mean Nusselt number over the plate? What is the mean heat transfer convective coefficient over the plate? What is the heat transfer rate to the water?arrow_forward
- Compute the Nu numbers for air at 40°C flowing with 4 m/s speed over the following: 1) A Copper sphere of 5 cm in diameter with 80°C isothermal surface temperature 2) A circular Aluminum pipe of 6 cm in diameter with 80°C isothermal surface temperature 3) A bank of 20x20 5-mm diameter tubes arranged in-line with center-to-center distance of 20 mm. Each tube is assumed to have isothermal temperature of 80°C. Please show detailed calculations.arrow_forwardConsider two cases involving parallel flow of dry air at V = 4.5 m/s, T, = 45°C, and atmospheric pressure over an isothermal plate at T = 20°C. In the first case, Re= 5x 105, while in the second case the flow is tripped to a turbulent state atx = 0 m. At whatx -location, in m, are the thermal boundary layer thicknesses of the two cases equal? What are the local heat fluxes, in W/m?, at this location for the two cases? x = i m Jam i W/m? i W/m? I turbarrow_forwardcan you please work all these parts please pleasearrow_forward
- Water at 20 C flows in a smooth pipe 0.04 m indiameter at a Reynolds number of 50,000. Thewall temperature is maintained at 25C. The bulk temperature and film temperature are assumed to be at 20C. Using Colburn analogy find the value of heat transfer coefficient. The properties of water are: Density = 999 kg/m3; viscosity = 1 cp; Pr = 6.94; Specific heat 4182 K/kgK; k=0.603 W/mKarrow_forwardA printed circuit board with constant surface temperature dissipates 100 W from one side over an area (0.3 mx 0.2 m). A fan is use to cool this board with a flow speed of 12 m/s parallel to the longest dimension of the board. Calculate: 1. The surface temperature of the board for an air temperature of 30 C. 2. Thickness of hydrodynamic and thermal boundary layer. 3. Amount of change in heat transfer rate if the flow parallel to the short dimension. Cp-1000 J/kg.K, k-0.03 W/m.C, Pr-0.667, u = 2 x 105 kg/m.s, p=1.15 kg/m³ Laminar flow, Nu= 0.664Rel/2Pr1/3, Turbule flow, Nu= 0.037Re4/5Prl/3arrow_forwardConsider two cases involving parallel flow of dry air at V = 5 m/s, T = 45°C, and atmospheric pressure over an isothermal plate at T = 20°C. In the first case, Rex, = 5 x 105, while in the second case the flow is tripped to a turbulent state at x = 0 m. At what x-location, in m, are the thermal boundary layer thicknesses of the two cases equal? What are the local heat fluxes, in W/m², at this location for the two cases? x = d'am = qturb = Mc i m W/m² W/m²arrow_forward
- Air at 400C flows with a velocity of 7 m/s over a 5m long and 4m wilde surface of a flat plate whose surface temperature is 800C. Find the rate of heat transfer from the laminar flow region of the surface. (For air at 400C , V = 1.702 × 10-5 , pr = 0.7255, K = 0.02662 w/m . K).arrow_forwardAir with free stream temperature of 10 C is flowing over a flat plate (1.5m long and Im wide). The air is flowing along 1.5m side of the plate. The plate is maintained at 90 C. Find the velocity of air required to have a rate of heat dissipation as 3.75 kW. Use the correlations: Nu =0.664Res Pro3 for laminar flow Nu, = (0.037R *-871)Pr for turbulent flow Take the properties p = 1.0877 kg/m u=2.029x10 m/s, k=0.028 W/mK, C,-1.007KJ/kg.K and Pr=0.703 %3Darrow_forwardAir at 2 atm. and 20oC is heated as it passes through a tube of 25 mm ID with a velocity of 10m/s. The temperature of the tube wall is maintained at 100oC. Calculate heat transfer per unit length of the tube and the bulk temperature change over a 3m length of the tubearrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning