Some engineers have developed a device that provides lighting to rural areas with no access to grid electricity. The device is i
ntended for indoor use. It is driven by gravity, and it works as follows: A bag of rock or sand is raised by human power to a higher location. As the bag descends very slowly, it powers a sprocket-wheel which also rotates slowly. A gear train mechanism converts this slow motion to high speed, which drives a DC generator. The electric output from the generator is used to power an LED bulb. Consider a gravity-driven LED bulb that provides 16 lumens of lighting. The device uses a 10-kg sandbag that is raised by human power to a 2-m height. For continuous lighting, the bag needs to be raised every 20 minutes. Using an efficacy of 150 lumens per watt for the LED bulb, determine (a) the velocity of the sandbag as it descends and (b) the overall efficiency of the device.
1 answer:
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Answer:
0.00650 Ib s /ft^2
Explanation:
diameter ( D ) = 0.71 inches = 0.0591 ft
velocity = 0.90 ft/s ( V )
fluid specific gravity = 0.96 (62.4 ) ( x )
change in pressure ( P ) = 0 because pressure was constant
viscosity = (change in p - X sin∅ ) / 32 V
= ( 0 - 0.96( 62.4) sin -90 ) * 0.0591 ^2 / 32 * 0.90
= - 59.904 sin (-90) * 0.0035 / 28.8
= 0.1874 / 28.8
viscosity = 0.00650 Ib s /ft^2
Answer:
Hello
this is the answer
Answer:
1.
2.
Explanation:
1.
Given:
- height of the window pane,
- width of the window pane,
- thickness of the pane,
- thermal conductivity of the glass pane,
- temperature of the inner surface,
- temperature of the outer surface,
<u>According to the Fourier's law the rate of heat transfer is given as:</u>
here:
A = area through which the heat transfer occurs =
dT = temperature difference across the thickness of the surface =
dx = t = thickness normal to the surface =
2.
- air spacing between two glass panes,
- area of each glass pane,
- thermal conductivity of air,
- temperature difference between the surfaces,
<u>Assuming layered transfer of heat through the air and the air between the glasses is always still:</u>