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- The two-layer system of blinds plus curtains allows only 33 percent of the Sun's energy into the room.
- At equilibrium, the curtain emits h each way; the blind emits 2h each way but supplies only 3h from the Sun.
- Solution assumes homogeneous materials, simplified model, and steady-state; neglects glass, colors, and room shape.
Earlier today I establish you a challenge concerning maintaining homes cool in a heatwave. Right here it is again with the remedy.
Think of a space with a set of curtains. When the Sunlight is shining, its energy comes with the home windows where it is absorbed by the curtains. The drapes get hotter and hotter until they get to a temperature level at which they are emitting as much heat as they soak up. The curtains emit 50 per cent of this warmth back towards the home window, and 50 percent of the warm into the room.
In other words, drapes quit 50 per cent of the power from the Sunlight.
Visualize an area with roller blinds and drapes. The blinds line the windows, and the curtains cover the blinds. There are hence 2 layers of protection from the Sun.
Currently what portion of the Sun’s power enters the room?
(Think the blinds and drapes are made out of homogeneous material, and that the system has reached stability. Also, this is a simplified model, so neglect the glass windows, the colour of the products and the shape of the area.)
Service 33 per cent.
Operations
Below is a diagram that shows the warm flow when the system reaches equilibrium, i.e. when both curtains and blinds reach their individual steady temperature levels.
The curtain is emitting the same amount inwards and in an outward direction. Allow the energy radiated in either direction be h.
If the curtain has actually taken in a total amount of 2 h , it has to have obtained this energy from the blind. We deduce that the blind is emitting 2 h forwards and in reverse.
The blind, however, is likewise getting h develop the curtain. So, of the 4 h that it is emitting, just 3 h comes from the Sun.
If 3 h is being available in, and h enters the area, the percent of the Sunlight’s energy is 33 per cent.
I hope you enjoyed this problem. I’ll be back in two weeks.
Thanks to Alan Williams-Key for today’s challenge.
I’ve been setting a problem here on alternate Mondays since 2015 I’m constantly on the look-out for terrific challenges. If you want to recommend one, email me
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