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You’ve experienced convection cooling if you’ve ever put your hand out the window of a moving vehicle or into a flowing stream of water. With the surface of your hand at a temperature of 30 degree C, determine the convection heat flux for

(a) a vehicle speed of 45 km/h in air at -5 degree C and
(b) a velocity of 0.25 m/s in water at 10 degree C. Which condition will feel colder? Approximate the hand as a flat plate that is 10 cm long in the direction of flow.

User El Tomato
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Final answer:

To determine the convection heat flux on the hand in different scenarios, the student would use the heat transfer coefficient, surface area, and temperature difference. Without exact values for the coefficients, precise calculation is not possible, but water typically feels colder due to its higher heat transfer coefficient despite a smaller temperature difference compared to air.

Step-by-step explanation:

The student has experienced convection cooling by putting their hand out of a moving vehicle or into flowing water, leading to a heat transfer from the hand to the surrounding environment. To determine the convection heat flux in each scenario, the heat transfer coefficient, surface area, and temperature difference are typically used in the formula q = hA(ΔT), where q is the heat flux, h is the heat transfer coefficient, A is the surface area, and ΔT is the temperature difference between the surface and the fluid. However, without exact values of the heat transfer coefficients for both air and water, it is not possible to provide specific heat flux values for the given conditions. Generally, the condition with the higher temperature difference and the medium with the higher heat transfer coefficient would feel colder. Considering that water has a higher heat transfer coefficient than air, the hand will likely lose more heat in water at 10°C than in air at -5°C, despite the colder air temperature, making the water feel colder.

User Marc Ster
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