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For laminar free convection from a heated vertical surface, the local convection coefficient may be expressed as
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- For laminar free convection from a heated vertical surface, the local convection coefficient may be expressed as hy Cx-1/4, where h, is the coefficient at a distance x from the leading edge of the surface and the quantity C, which depends on the fluid properties, is independent of x. Obtain an expression for the ratio hx/hx, where x is the average coefficient between the leading edge (x = 0) and the x-location. Sketch the variation of h, and hy with x.arrow_forwardA long wire of diameter D = 2 mm is submerged in an oil bath of temperature T∞ = 23°C. The wire has an electrical resistance per unit length of Re′=0.01 Ω/m. If a current of I = 180 A flows through the wire and the convection coefficient is h = 529 W/m2 · K, what is the steady-state temperature of the wire? From the time the current is applied, how long does it take for the wire to reach a temperature that is within 2°C of the steady-state value? The properties of the wire are ρ = 2,334 kg/m3, c = 537 J/kg · K, and k = 43 W/m · K.arrow_forwardA nuclear reactor is cooled by liquid sodium. The liquid sodium has the following properties: dynamic viscosity = 0.41 mPa·s, specific heat capacity = 1.2 kJ/kgK, thermal conductivity 82 W/mK. Which of the following statements is correct for this scenario? please explain A The thermal boundary layer is thicker than the hydraulic boundary layer. B Heat is transferred through the fluid more easily than momentum. C The velocity varies significantly from the surface to the thickness of the thermal boundary layer. D The hydraulic boundary layer is thicker than the thermal boundary layer.arrow_forward
- The next 8 questions are all related to the following problem statement and figure. Air at 27°C with a free stream velocity of u» = 10 m/s is used to cool electronic devices mounted on a printed circuit board (PCB). Each device dissipates 40 mW (rate of conversion of electrical energy into thermal energy), is thin, and can be modeled as isothermal with a square top that is 5 mm by 5 mm. Due to the low thermal conductivity of the PCB, all of the dissipated energy can be assumed to be transferred out of the devices from their tops. A turbulence promoter (turbulator) is located at the leading edge of the board, causing the boundary layer to be turbulent over the entire length of the PCB. Estimate the surface temperature of the fourth device located 15 mm from the leading edge of the board. Use properties of air at T= 52°C and atmospheric pressure. Air Turbulator Fourth device X = 15 mm Printed circuit board Ittarrow_forwardWhat’s the correct answer for this please ?arrow_forwardi need the answer quicklyarrow_forward
- QUESTION 4. Question 4.1 Consider two fluids, one with a large coefficient of volume expansion and the other with a small one with the same viscosity. Explain in which fluid will a hot surface initiate stronger natural convection currents?arrow_forward. An oil is acting as a lubricant for a pair of cylindrical surfaces. The angular velocity of the outer cylinder is 7908 rpm. The outer cylinder has a radius of 5.06 cm, and the clearance between the cylinders is 0.027 cm. What is the maximum temperature in the oil if both wall temperatures are known to be 70°C? The physical properties of the oil are assumed constant at the following values: Viscosity Density 92.3 cP 1.22 g/cm³ Thermal conductivity 0.0055 (cal/s)/(cm °C)arrow_forwardA water tank is completely filled with liquid water at 40°C. The tank material is such that it can withstand tension caused by a volume expansion of 5 percent. Determine the maximum temperature rise allowed without jeopardizing safety. Assume a volume expansion coefficient value at that of 65 °C. (Just write the numerical answer. Include - if the answer is negative. No need to put the unit.) Properties of saturated water Volume Specific Heat Jkg - K Thermal Conductivity k, Wim- K Prandti Enthalpy Dynamic Viscosity H. kg/m -s Expansion Coefficient Number Density P. kgim Saturation of Pr Temp. T, "C B. 1/K Liquid Pressure Vaporization P, kPa Liquid Vapor hg, k/kg Liquid Vapor Liquid Vapor Liquid Vapor Liquid Vapor 0.0171 1.792 x 103 0.0173 0.922 x 105 13.5 0.934 x 10-5 1.00 -0.068 x 10 3 1.00 1.00 0.01 0.6113 999.8 0.8721 0.0048 0.0068 2501 2490 2478 4217 4205 1854 0.561 0.571 1.519 x 10-3 1.307 x 10-3 0.946 x 10-5 1.138 x 10 3 0.959 x 10-5 1.002 x 10 3 0.973 x 105 999.9 1857 11.2 0.015…arrow_forward
- Q1: In a process water at 30°C flows over a plate maintained at 10 °C with a free stream velocity of 0.3 m/s. Determine the hydrodynamics boundary layer thickness, thermal boundary layer thickness, local and average values of heat transfer coefficient and refrigeration necessary to maintain the plate temperature. Consider a plate of 1m x 1m size. At the film temperature the property values are: Kinematic viscosity 1.006 x 106 m²/s, Thermal conductivity =0.5978 W/m.K, Prandtl number=7.02. =arrow_forwardt = 30 + 0.9563 (62.2- 30) = 60.79°C (Ans.) Example 4.14. A very thin glass walled 3 mm diameter mercury thermometer is placed in a stream of air, where heat transfer coefficient is 55 W/m2°C, for measuring the unsteady temperature of air. Consider cylindrical thermometer bulb to consist of mercury only for which k and a = 0.0166 m2/h. Calculate the time required for the temperature change to reach half its final or, %3D 8.8 W/m C %3D value.arrow_forwardQ5) For laminar free convection from a heated vertical surface, the local convection coefficient may be expressed as hy = Cxx-1/4, where h, is the coefficient at a distance x from the leading %3D edge of the surface and the quantity C, which depends on the fluid properties, is independent of x. Obtain an expression for the ratio hx/hx, where x is the average coefficient between the leading edge (x = 0) and the x-location. Sketch the variation of h, and h, with x.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning