You’ve experienced convection cooling if you’ve everextended your hand out the window of a moving vehicle or into a flowing water stream. With the surface ofyour hand al a temperature of 30°C, determine the convection heal flux for (a) a vehicle speed of 35 km/h inair at
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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_forwardA spherical communications satellite, 2 m in diameter, is placed in orbit around the earth. The satellite generates 1000 W of internal power from a small nuclear generator. If the surface of the satellite has an emittance of 0.3, and is shaded from solar radiation by the earth, estimate its surface temperature.arrow_forwardThe air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specifiedarrow_forward
- The heat transfer rate from hot air by convection at 100C flowing over one side of a flat plate with dimensions 0.1m0.5m is determined to be 125 W when the surface of the plate is kept at 30C. What is the average convection heat transfer coefficient between the plate and the air?arrow_forward1.21 In an experimental set up in a laboratory, a long cylinder with a 5-cm diameter, and an electrical resistance heater inside its entire length is cooled with water flowing crosswise over the cylinder at and a velocity of 0.8 m/s. For these flow conditions, 20 kW/m of power is required to maintain a uniform temperature of at the surface of the cylinder. When water is not available, air at is used with a velocity of 10 m/s to maintain the same surface temperature. However, in this case, the cylinder surface heat dissipation rate is reduced to 400 W/m. Calculate the convection heat transfer coefficients for both water and air, and comment on the reason for the differences in the values.arrow_forward1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.arrow_forward
- You've experienced convection cooling if you've ever extended your hand out the window of a moving vehicle or into a flowing water stream. With the surface of your hand at a temperature of 30°C, consider the two following conditions. Condition A: a vehicle speed of 35 km/h in air at -9°C with a convection coefficient of 40 W/m².K. Condition B: a velocity of 0.2 m/s in a water stream at 10°C with a convection coefficient of 500 W/m².K. What is the convection heat flux for the following? Condition A: W/m² d'air = i Condition B: dwater = i W/m²arrow_forwardYou've experienced convection cooling if you've ever extended your hand out the window of a moving vehicle or into a flowing water stream. With the surface of your hand at a temperature of 30°C, consider the two following conditions. Condition A: a vehicle speed of 35 km/h in air at -5°C with a convection coefficient of 40 W/m2.K. Condition B: a velocity of 0.2 m/s in a water stream at 10°C with a convection coefficient of 500 W/m²-K. What is the convection heat flux for the following? Condition A: Tair W/m2 i Condition B: Twater W/m? i Physical Properties Mathematical Functionsarrow_forwardWater at 5°C is being used to cool apples from an initial temperature of 25° to 10°C. Thewater flow over the surface of the apple creates a convective heat-transfer coefficientof 15 W/(m2-K). Assume the apple can be described as a sphere with a 10 cm diameterand the geometric center is to be reduced to 10°C. The apple properties include thermalconductivity of 0.45 W/(m-K), specific heat of 3.950 kJ/(kg-K), and density of 940 kg/m3.a. Determine the time that the apples must be exposed to the water.b. If the apple is submerged only for 2 hours, what will be its center temperature?arrow_forward
- A food product with 80% moisture content in a 10 cm diameter can wants to be frozen. The density of the product is 1000 kg / m³, the thermal conductivity is 1.0 W / (m K), and the initial freezing temperature is -2 ° C. After 14 hours in the freezing medium -30 ° C, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinder.arrow_forwardThere is an equipment that allows to measure the heat transfer in fins with at least three different geometric shapes. To develop analysis skills among the students, the Heat Transfer teacher asks them to compare the performance of different cylindrical fins. These are "pin fins" made of aluminum (? = 200 W/m°C) and must be analyzed in terms of their relative performance as a function of diameter. Turning on the equipment, a base temperature of 200°C is recorded, the air temperature in the laboratory is T_∞= 20°C and h = 40 W/m"°C. (a) obtain an expression or mathematical model that allows calculating heat transfer as a function of the diameter of each fin.(b) Five fins with diameters of 2, 5, 10, 15, and 20 mm are available with a length of 10 cm for all, and only heat transfer is considered. heat by convection which of them have a greater heat transfer? heat flux with the diameter of the pin? (d) what would be the main factor to consider during future analysis if the fins appear…arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning