Wind chill is very relevant to washer jets ....
.... because they are inevitably wet, wind increases the rate at which moisture evaporates from a wet object, the phase change of water from liquid to vapor requires the molecules to reach a higher energy state, the energy is acquired by absorbing heat from the surface of the body upon which the moisture is sitting by conduction thus lowering the temperature of the object in question.
Hence untreated and unheated washer jets can freeze even if the ambient is a little over 0deg.
I made the same point when discussing diesel waxing last winter, the effect of moisture and windchill on fuel lines.
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>>Wind chill is very relevant to washer jets ....
Yes, airflow will make a significant difference, but it's not "wind chill" as reported on any weather forecast - there's no direct correlation.
Number_Cruncher
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The prankster in me is dying to re-route this thread to the "How do you thaw out a frozen windscreen, then?" one, as I am convinced there are some common solutions, e.g. keep the wife/mother-in-law under the bonnet overnight, kettle of boiling water at the ready. "I've been doing this for 95 years, don'tcha know. Never cracked a screen yet... Course my first Darracq didn't actually have what one could call a windscreen..." "Load of rubbish. Had six windscreens go in me during the blitz. Rots the rubber too..." "Poppycock." etc.
;-)
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Yes airflow will make a significant difference but it's not "wind chill" as reported on any weather forecast - there's no direct correlation.>>
It is windchill as reported my the met people, precisely the same NC.
As I said wind (or air flow) increases the rate at which moisture evaporates from a wet object, the phase change of the water requires energy which is acquired by absorbing heat from the surface of the body upon which the moisture is sitting by conduction thus lowering the temperature of the object in question.
Skin is subject to windchill because it is naturally moist, it contains moisture within its surface, the rate of which this moisture evaporates is hightened by wind thus the above effect occurs. Likewise wet washer jets etc etc.
Regards.
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>>precisely the same NC.
I disagree - please show me where you obtained this info.
Number_Cruncher
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>>please show me where you obtained this info.
>>
I could ask you that every time you try to astound us with science NC ;-)
I have looked into wind chill in the past in respect of sailing, in that instance it is the effect on the skin, I was interested in why wind chill seems to have such a great effect on exposed skin, relatively little and not excessively cold wind can cause the body to lose so much heat. Now clearly air passing across any surface will take away heat by convection (the same way that air passing through the fins of an aircooled engine cool it) however there seemed to be more to it - and there is.
It is the process I outlined before - wind increases the rate at which moisture evaporates from a wet object, the phase change of water from liquid to vapour requires the molecules to reach a higher energy state, the energy is acquired by absorbing heat from the surface of the body upon which the moisture is sitting by conduction thus lowering the temperature of the object in question.
We discussed wind chill on here a year or so ago in respect of diesel waxing and the effect of airflow over exposed and therefore often wet fuel lines. I made the point that the fuel line could be below ambient due to the above effect. In that instance I quoted Wikipedia to support my point though I cannot find the Wiki link now though the following appears to be from Ohio State Uni and covers the same point of page 7, you might find the formula interesting:
tinyurl.com/ytk2ds
It seems that this is related to the enthalpy of vaporization:
en.wikipedia.org/wiki/Heat_of_vaporization
long link vaporized via TinyURL
Edited by Pugugly {P} on 22/12/2007 at 09:56
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Blimey wish i hadn't mentioned wind chill, somebody tell me to shut up, me and my big trap.
Would wind chill affect the rear washer on an estate car?
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Ched
Yeah, what you're describing is what I would know as evaporative cooling, a good example being a porous pot wine chiller, which can achieve a true temperature drop below ambient through the evaporative processes you describe. And in theory, wet washer jets exposed to high wind speed similarly, although I would have thought the effect was very very small, given the small surface area where evaporation could occur-interesting!
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Well after 400 miles in the past three days in some cold freezing fog I can say
Freezing washer jets was not a problem on the touran and is not on the altea. Both employ the "mist" type of nozzle and both were run on halfords "blue" readymix.
The nozzles onthe altea are set down behind the trailing edge of the bonnet, so have no direct cold airflow, tho there may be a back vortex but its not significant.
------
< Ulla>
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I disagree, wind-chill is a perceived lower temperature which effects the human body only because it is heated from within. The wind-chill factor is a measure of how the wind strips the layer of warmer air away from the body making it feel a few degrees colder than it really is.
I suppose you could say wind chill applies to washers because it strips away the heat from the engine, but that just adds more confusion.
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I'm surprised that some manufacturer hasn't thought of heated water jets - thery're the sort of semi-usless extra that sells cars these days.
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"I'm surprised that some manufacturer hasn't thought of heated water jets"
My wifes 2000 Xantia HDi has them - I assumed most "upmarket" (that's upmarket compared to what I usually drive!) cars had them. Can't you also buy a kit to heat washer jets from Maplins? I'll have a look.
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Phil
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Actually, I just googled and came up with heated washer jets for Omegas, Cavaliers, Mondeos, VW/Audi, BMW to mention but a few
and Webasto do a kit (as mentioned here!!)
www.honestjohn.co.uk/forum/post/index.htm?f=2&t=28...2
--
Phil
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>>in that instance it is the effect on the skin,
Yes, and that's the point - Wind chill is the effect on the human body. Yes, there's vapourisation, but, as pointed out below, there isn't the effect of body heat. Wind chill is for people, not for inanimate objects - you can't link the two. Really!, you can't!
>>I could ask you that every time you try to astound us with science NC ;-)
In most cases, I either state my assumptions, or point to reference works that will enable people to check what I say. I post very little of what I "reckon", and if I do, I'll usually say that it's just my opinion.
Number_Cruncher
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I used to have problems in Scotland at -16C. Most things froze incl washers.#
It's never that cold in England below 300 metres.
I always use a proper mix.
And it froze at speeds between 10 mph and 50 mph. Above 50 was too scary. Black ice on back roads.
madf
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Yes, and that's the point - Wind chill is the effect on the human body.
Agree entirely with NC. Wind chill is purely to do with the apparent cold felt by the human face.
www.bbc.co.uk/weather/features/understanding/wind_...l
"The JAG/TI algorithm is now used, which measures 'face only wind chill' and is a Canadian method. The Met Office use this method as it has been clinically tested, it is simple to use and based on current research."
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NC & jbif, you are missing the point!
The point is that whether you apply the term or not the science that applies to wind chill as it pertains to the human skin also applies to inanimate objects.
Firstly NC I am a bit miffed by your dismissive "you can't link the two. Really!, you can't!" I am not pretending to be an expert though I have researched it to a reasonable degree.
"there isn't the effect of body heat" perhaps shows a lack of understanding, the actual temperature of the surface effected is not relevant, what is relevant is that wind passsing over a moist surface such as skin vapourises some of that moisture (water), the phase change in the water requires energy, that energy is taken via conduction from the surface thus cooling it beyond the level that it would be cooled by simple convection were it not moist.
This process also applies to wet inanimate object such as washer jets, the fact that the surface temp of the washer jet might be only slight above freezing (i.e much colder than skin) is irrelevant, the vapourisation of the water sitting on the surface requires energy (as per above), that energy is taken via conduction from the surface thus cooling it beyond the level that it would be cooled by convection as would be the case were it dry. Thus an unheated, untreated washer jet can freeze in ambient temps a little above freezing.
Regards.
Edited by cheddar on 22/12/2007 at 21:10
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Only until they reach thermal equilibrium.
If the wind/air is 1 deg C, the wind will not chill the nozzle below that.
If the nozzles are heated, say to 7 deg C , the wind can chill it anywhere down to the 1 deg C of the wind, but no lower.
Edited by Hamsafar on 22/12/2007 at 22:05
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Only until they reach thermal equilibrium. If the wind/air is 1 deg C the wind will not chill the nozzle below that.
Not if the nozzle is damp because the phase change in the water requires energy which is taken from the surface upon which the water is sitting as it vaporises hence cooling it a little below ambient.
Edited by cheddar on 23/12/2007 at 11:44
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My windscreen squirters stopped working yesterday morning. Come lunchtime they were ok.
Do I have an electrical or ecu problem ?
Edited by none on 22/12/2007 at 22:09
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My windscreen squirters stopped working yesterday morning. Come lunchtime they were ok. Do I have an electrical or ecu problem ?
Do you mean in relation to the frozen washer nozzles, or some unspecified problem unconnected with that incident? ;-)
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Two different things going on with this chilling.
Wind chill as per the met office is to do with the wind cooling a warm body faster (due to the exchange of air at the surface). If the body is at the same temp as the wind there is no wind chill. The temp of the human body being known helps the calculation of wind chill factor, which would be different for animals with a different body temp (assuming they were dressed like people or at least had fur with similar insulating properties to human togs). Anybody know what dog blood temp is?
The other thing is the evaporative cooling. I notice this on the screen when I have used the de-icer spray - the de-icer evaporates so well that the screen freezes over again after I have set off!
I dare say a damp, warm body will suffer from both as Cheddar suggests.
Edited by Manatee on 22/12/2007 at 22:11
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NC & jbif, you are missing the point!
No, not in any way. I am not denying that evaporation will cause freezing in a wind; what I am saying is that the numbers quoted on weather forecasts are related to the effect on humans, you can't use those numbers to tell what will happen to washer fluid, or any other inanimate object.
I stand by my clear statement that wind chill as reported in weather forecast and the freezing of washers jets is not directly linkable - there's more to it than that.
>>"there isn't the effect of body heat"
What I mean by that, and I think you've missed is that the wind chill numbers reported in weather forceasts, are numbers that are applicable only to humans, because, among other factors, humans have an internal source of heat, i.e., via our blood supply, new thermal energy is brought to beneath the area of skin which is exposed to the wind (note, I'm not talking about a temperature, I'm talking about a flow of heat, which cannot occur in an inanimate body). This is one of the biggest reasons why wind chill numbers as reported in a weather forecast do not apply to inanimate objects.
>>Firstly NC I am a bit miffed by your dismissive "you can't link the two. Really!, you can't!"
There is nothing dismissive there - it's just a statement, it doesn't make any judgement about your understanding or lack of understanding of the subject.
Number_Cruncher
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I am not denying that evaporation will cause freezing in a wind; >>
Good so we agree then!
>>what I am saying is that the numbers quoted on weather forecasts are related to the effect on humans you can't use those numbers to tell what will happen to washer fluid>>
I agree with that NC, however I have not been refering to numbers quoted on weather forecasts, rather the science behind wind chill.
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numbers quoted on weather forecasts, rather the science behind wind chill.
By definition, wind chill - and the science behind it - is all to do with the perception of cold felt by the human body, and how weather forecasters convey that to the lay public.
Edited by jbif on 23/12/2007 at 13:29
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By definition wind chill - and the science behind it - is all to do with the perception of cold felt by the human body and how weather forecasters convey that to the lay public.
The science behind wind chill, the phase change of water etc, applies to a much broader range of circumstances.
Wind chill is however the common term used to convey that science in respect of its effect on the human body.
Edited by cheddar on 23/12/2007 at 13:45
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>>The science behind wind chill, the phase change of water etc, applies to a much broader range of circumstances.
Wind chill is very specific - it's how the human body experiences cold and wind. Nothing else.
Heat loss via wind passing over a wet substance is generally applicable, but that isn't wind chill as reported on a weather forecast. Wind chill as reported in a weather forecast includes much more than just evaporative cooling. The two things are not the same.
Number_Cruncher
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>>.. evaporation will cause freezing in a wind; >>
Cheddar, you are entitled to believe what you think is true. I do not have the time or inclination to type out pages of calculations showing you why windchill which by definition is to do with humans has nothing to do with the phase change of water on inanimate objects (nor do I suppose the Backroom has any interest in reading it). I will instead direct you to just two pages out of thousands on the internet that deal with the subject and call it a day:
1. Freezing point of water based on wind chill.
answers.google.com/answers/threadview?id=605868
2. Can windchill impact my car's radiator or exposed water pipe?
www.nws.noaa.gov/om/windchill/windchillglossary.sh...l
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>>windchill which by definition is to do with humans has nothing to do with the phase change of water on inanimate objects>>
jbif, how can I put it more clearly - while wind chill is a term that applies to the effect on human skin - the science, the process that the moisture in the surface of the skin goes through is the same as in many other circumstances.
As to your examples, it does not apply to a bowl full of water, and re a car's radiator, if it were externally wet then the phase change of the vaporising water would have an additional cooling effect though clearly not below the freezing point of the internal coolant.
Here are a couple of examples of the science behind wind chill (that - yes - is a term that applies to humans) being used to practical effect - and with a motoring link ;-)
www.airpowersystems.com/wrx/my01/water_spray/water...m
autospeed.com/A_2720/hDg34uLtp_1/cms/article.html
To quote the latter:
"Evaporating a kilogram (ie a litre) of water requires 2257 kilo-joules of energy ? and that?s a lot! If the nozzle flows 400 ml/minute, and if all the water evaporates, each minute 903 kilo-joules of energy are extracted. One joule per second is the equivalent of 1 watt, so fully evaporating 400 ml/min of water provides a cooling power of 15 kilowatts! Even a 130 ml/min spray provides a potential cooling power of just under 5kW.
The key point is that the water must evaporate ? it is this change of state from water to a gas which absorbs the energy."
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"The science behind wind chill, the phase change of water etc, applies to a much broader range of circumstances."
You are right about the science cheddar, and so are jbif and NC about windchill. But as I intimated in my post above (it's about the 12th one in thread)
"I don't think that wind chill applies in this case since it is a measure of how much heat would be lost from the (human) skin in different windspeeds. In other words, how wind speed would affect loss of heat from your (human!) body."
Wind chill is defined as the effect of wind on the human body - I looked it up and all definitions I found were related to heat loss from the body.
However, I think you are right in what you say about heat loss from other "bodies" - washer jets etc - except it needs a term other than "wind chill"
Does that make sense? I hope so!! Happy Christmas.
(Does this thread qualify as the traditional Christmas argument - if so, maybe I can forego the one we always have while playing some games on Christmas night!)
--
Phil
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>>Does that make sense? I hope so!!
Perfect sense Phil - I think you've summarised the debate perfectly.
>>Happy Christmas.
Season's greetings!
Number_Cruncher
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>>Does that make sense? I hope so!! Perfect sense Phil - I think you've summarised the debate perfectly.
Agreed!
>>Happy Christmas. Season's greetings!
Likewise!
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I quite agree jbif.
Here's a link which provides more information.
www.msc.ec.gc.ca/education/windchill/science_equat...m
Number_Cruncher
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Surely, the important area is what happens at the nozzles. No point having toasting warm bottles and pipes if the nozzles are not heated. Now, if only water is present it will freeze. Full stop. But if a type of alcohol is present, the freezing point of the solution is only lowered as long as the alcohol is present. Now, alcohol has a lower vapour pressure than water and any present at or about the nozzle region will evaporate much more quickly than will the water. The result is that at the nozzles water only will exist and will stay frozen until warmed sufficiently to melt all crystals.
The only solution (sic) is to use neat ethanol or some other liquid that does not freeze until, say, at least -10°C.
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Freezing Point
Ethanol Concentration
(% by volume) 0 10 20 30 40 50 60 70 80 90 100
Temperature(oF) 32 25 15 5 -10 -25 -35 -55 -75 -110 -175
Temperature(oC) 0 -4 -9 -15 -23 -32 -37 -48 -59 -73 -115
I use this table to see how much of a rip off screenwash is. Halfords ready mixed is probably more expensive than the finest Kashmiri saffron.
Edited by Dynamic Dave on 23/12/2007 at 00:47
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Thanks for the information Hamsafar. Whenever the ambient temperature gets down to -175 degC I'll make sure I've got neat ethanol in my washer bottle. ;-)
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Any evaporative cooling effect will be linked to the moisture content of the airstream passing over the moist "heat source". If the air stream is saturated (100% humidity) there will be no evaporative cooling.
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With respect to Flanders and Swann, aka Millers and Armstrong
"Heat is work and work's a curse
And all the heat in the Universe
Is gonna cooool down 'cos it can't increase
Then there'll be no more work and there'll be perfect peace
Really?
Yeah - that's entropy, man!
And all because of the Second Law of Thermodynamics, which lays down:
That you can't pass heat from the cooler to the hotter
Try it if you like but you far better notter
'Cos the cold in the cooler will get hotter as a ruler
'Cos the hotter body's heat will pass to the cooler
Oh, you can't pass heat from the cooler to the hotter
You can try it if you like but you'll only look a fooler
'Cos the cold in the cooler will get hotter as a ruler
That's a physical Law!
Oh, I'm hot!
Hot? That's because you've been working!
Oh, Beatles - nothing!
That's the First and Second Laws of Thermodynamics! "
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I used to have a VW Caravelle and it wasn't until one day I was talking to somone and leant on the bonnet whilst the engine was running that I discovered it had heated washer jets! ouch! wow!
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I remember in the dim and distant past there used to be a couple of kits available
One took the water from the washed bottle, channeled it through tubing wrapped around the radiator pipe and then on to the washer jets, thus heating the water.
The other was a small heater that sat in the washer bottle to stop the water in it from freezing.
Both might of been some use in the past but nowadays the pipes are usually hidden so well inside the engine bay that finding them is a pain the posterior.
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The main difference is that inanimate objects will suffer evaporative cooling, if they are wet, until the moisture has gone. They will then rise to the prevailing ambient temperature.
Living beings have a feedback loop, the skin chills, the brain senses this and attempts to keep the temperature of the affected parts constant, thus pumping heat out of the body.
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I still don't agree that any appreciable evapourative cooling is taking place with wet nozzles in the wind, in order to freeze them or make their temperature lower than ambient. This process ceases as the temperature approaches 0 deg C anyway. I aver that you cannot cool the nozzle with this process to a temperature below the freezing point of that evapourate (0 deg C). What is more a temperature change across a phase change requires a lot of additional energy than just cooling alone. Even if we assume that the nozzle could be frozen in this way, there would be too much warming of them nozzle in the meantime, by the copious amounts of relatively warm air.
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