Science Questions

How should I align my laundry with the wind?

Sun, 2nd Aug 2009

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Adrian asked:

As I live in the U.K., I need to use the dry weather as cleverly as possible for drying my laundry because there ain’t much of this dry weather around. If the wind blows from West to East, would it be better to place the rope for the laundry North-South? Or would it be better to do West to East do the wind would dissipate the water vapours from both sides of the clothing? What’s your theory?




Dave -   I would have said you probably want it across the wind because if the wind’s running along your laundry then any moisture evaporates and the front end of the laundry is then going to reduce the evaporation further on.  And if you’re going across it then you get lots of turbulence so the air will get to the back fine because it will just go over the top and swirl in the back. If anyone has any bright ideas then I’d love to hear them.

Chris -   Yes, I would suggest using a tumble dryer inside which is guaranteed to work unlike the washing I know in this country.

Helen -   Oh, Chris, how about the sunshine?  Come on, think of the environment.  I hang my washing outside.

Chris -   Indeed.

Helen -   In between the rain showers.


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adrian asked the Naked Scientists: Hi naked scientists, As I'm living in the UK, I need to use the dry weather as cleverly as possible for drying my laundry.  If the wind blows from West to East, would it be better if I place the rope for the laundry from North to South, or it would be better to place it from West to East, so the wind could dissipate the water vapours from both sides of the clothes? So to place my laundry to oppose as much surface as possible to the wind (and the wind to force out the water from the inside of the material), or to be as aerodynamic as possible? Would this be different depending on the thickness of the material? Many thanks, Adrian  What do you think? adrian , Mon, 3rd Aug 2009

What a good question! 

I've currently got 2 loads of washing drying, I have no idea how my line is aligned, but I am guessing it is east to west going on how the sun hits my house.

I think the general flapping action of the wind blowing the washing about is enough to dry it, more than the actualy direction itself. Variola, Mon, 3rd Aug 2009

I agree. Surely the drying is caused not by the wind's "actualy direction" but just the presence of air all around the wet fibres. Herman Melville, Mon, 3rd Aug 2009

I think that the wind should blow across the line. That will 'inflate the articles of double thickness - bags and trousers and maximise the amount of 'fresh' air flowing over and through the clothes.
I recently erected a pair of conventional lines from an old sailing dinghy mast to the house, replacing a rotating airer. It is much quicker, as you might expect. One of the lines is about 4m in the air (pulleys etc. make the neighbours smile!) but it dries very fast as the clothes blow almost horizontal in even the lightest breeze. The lines are pretty much across the prevailing wind direction.
I would say (from experimental evidence!!!! good TNS stuff) that height is a bigger factor than line direction. lyner, Mon, 3rd Aug 2009

Would that be because the wind speeds are higher when you are higher up? And maybe also because the wind closer to the ground may be a bit more humid as a result of the proximity to the moist ground (and those thousands of lines full of wet laundry)? Karsten, Mon, 3rd Aug 2009

The wind direction is never constant, just look at a wind vain and it will always be shifting in direction. The reason why you site a vain high is to get a wind direction free (or as free as possible)from the influences from  taller buildings and structures.

In an urban area the wind direction you see on a forecast or even from a wind vein may not be the same you feel at your ground location, a building may deflect the wind, it may move down between buildings and so on.

As for humidity, again this is dependant on where you are taking your measurements. Air temperature is from inside a screen 1.2M high and ground is read from a thermometer sited horizontally at the height of the tips of freshly cut grass. So you need to know if what you are looking at is a ground or air reading/observation. for your humidity.

You may see on some weather outlets that current observations give a high, or even 100% humidity yet there is no precipitation. Again you need to know where the reading were taken, If they are straightforward radiosonde or model forecast figures then they may be from a high altitude that is not relevant to ground conditions.

I think the observation by SC may well be because a washing line at his height has a wind that is free from obstructions, and therefore more "blowey", Mon, 3rd Aug 2009

But if you continue in the same vein, talking about a wind vane it will all be in vain. FOG
But let's not wash our dirty linen in public. lyner, Mon, 3rd Aug 2009

I suspect, all else being equal, that laundry will dry faster when the lines are parallel to the wind than at right angles. Reason: The wind speed is less obstructed, so that when, at the ambient temperature, water molecules evaporate from the cloth, they are swept away quickly and are less likely to return to the cloth through diffusion, than when the wind speed is more obstructed. Arguably, if the wind speed is high enough that the clothes stands out almost at 90 degrees to the vertical, it will make little difference. However, for lesser winds I think I am right. One complicating factor: the direction of sunlight. If you have anything resembling a clear day, the clothes position will affect the solar cross-section substantially, which would be the most important facter in those conditions. Atomic-S, Tue, 4th Aug 2009

I'm always getting Fogged :-(

I am not old enough to understand this., Wed, 5th Aug 2009

This is how I dry my washing, it is a good way and always dries well !

neilep, Wed, 5th Aug 2009

...don't be fooled by the above photo...the scenic bacground to the washing is just a scenery prop !!..I just happened to place my washing in front of it...this is true !!

neilep, Wed, 5th Aug 2009

Thanks for the clarification; I would have never guessed. Atomic-S, Mon, 10th Aug 2009

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