To assess the efficacy of different liquids for cooling an object of given size and shape by forced convection, it is convenient to introduce a figure of merit,
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Fundamentals of Heat and Mass Transfer
- An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.arrow_forward5.7 The average Reynolds number for air passing in turbulent flow over a 2-m-long, flat plate is . Under these conditions, the average Nusselt number was found to be equal to 4150. Determine the average heat transfer coefficient for an oil having thermal properties similar to those in Appendix 2, Table 18, at at the same Reynolds number and flowing over the same plate.arrow_forwardEngine Oil at 58.95 degrees celsius Flows over a 5m long flat plate whose temperature is 20.11 degrees celsius with a velocity of 2.2m/s. Determine the rate of heat transfer (W), considering forced convection, per unit width of the entire plate. Density = 876kg/m^3 Thermal conductivity = 0.144W/m-K Pr = 2870 dynamic viscosity = 0.21kg/m-s Q = ?arrow_forward
- During 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_forwardIn thermally fully developed flow of a fluid with constant properties, the local convection coefficient is .......................... , ........................ please fill the blank Blank 1( a constant or not a constant) Blank 2 ( dependent on or independent of)arrow_forwardThe boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm) is -196°C. Therefore, nitrogen is commonly used in low temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere will remain constant at -196°C until the liquid nitrogen in the tank is depleted. Any heat transfer to the tank will result in the evaporation of some liquid nitrogen, which has a heat of vaporization of 198 kJ/kg and a density of 810 kg/m3 at 1 atm. Consider a 3-m-diameter spherical tank initially filled with liquid nitrogen at 1 atm and 196°C. The tank is exposed to 22°C ambient air with a heat transfer coefficient of 22 W/m2 · °C. The temperature of the thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Disregarding any radiation heat exchange, determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air in kg/sec. Answer in…arrow_forward
- During air cooling of oranges, grapefruit, andtangelos, the heat transfer coefficient for combined convection,radiation, and evaporation for air velocities of0.11 < V < 0.33 m/s is determined experimentally and isexpressed as h = 5.05 kair Re1/3/D, where the diameter Dis the characteristic length. Oranges are cooled by refrigeratedair at 5°C and 1 atm at a velocity of 0.3 m/s. Determine(a) the initial rate of heat transfer from a 7-cm-diameterorange initially at 15°C with a thermal conductivity of0.50 W/m·K, (b) the value of the initial temperature gradientinside the orange at the surface, and (c) the value of theNusselt number.arrow_forward7. Air at 600 K, 1 atm is flowing across a flat plate kept at 300 K with a convection coefficient of 91 W/m2 K. If the Stanton number at this condition of flow is 0.039. what is the velocity of the air? Express your answer in m/s.arrow_forwardMercury at 25°C flows over a 3-m-long and 2-m-wide flat plate maintained at 75°C with a velocity of 0.01 m/s. Determine the rate of heat transfer from the entire plate.arrow_forward
- Cylindrical vessel of 1m diameter and 4 m length has hydrogen gas at pressure of 100 kpa and 27 °C. Determine the amount of heat to be supplied so as to increase gas pressure to 125 kPa. For hydrogen take Cp= 14.307 kJ/kg K, Cv= 10.183 kJ/kg K.arrow_forwardA heated plate, 20 by 20 cm, is inclined at an angle of 60°with the horizontal and placed in water. Approximately constant-heat-flux conditions prevail with a mean plate temperature of 40°C and the heated surface facing downward. The water temperature is 20°C. Calculate the heat lost by the plate.arrow_forwardA copper rod of 30 kg initially at the temperature of 300 °C needs to be immersed and fitted tightly into a ABA alloy ring with inner diameter 30.0015 mm found in tank of 100 liters water of 25 °C. (i) Determine the diameter copper when it is 300 °C. (ii) In your opinion, does the copper rod will still fit tightly into the ABA alloy ring inner diameter 30.0015 in the ambient air condition of 25 °C. Provide your answer in 4 decimal places. Assume the alloy ABA is very small with negligible effect in heat transfer. [Density for copper = 8890 kg/m3, Specific heat, Ccopper = 385 J/kg.°C;Coefficient of thermal expansion, αCopper = 18.0 × 10-6 (°C)-1]. [Density for ABA alloy = 8500 kg/m3, Specific heat, CABA = 138 J/kg.°C;Coefficient of thermal expansion, αABA = 13.3 × 10-6 (°C)-1]. [Density for water = 1000 kg/m3, Specific heat, Cwater = 4200 J/kg.°C].arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning