New!!! 3 April 2017
ANTI CONDENSATION GLAZINGS (1)
ANTI CONDENSATION GLAZING (1)
SIMPLIFIED THEORY OF LOW E ICE FREE GLAZING. ( THEORIE GEL)
PATENT DE 28 33 234 /FR 2 399 331/GB 1 598 924 ( g.LAFFAY AND AL. 1978).
In conclusion, that type of low E windscreen is very efficient on winter on evening to return from an outdoor parking of the job or kino and in autumn/spring, on morning to go to the job office from an outdoor parking.
In summer, it lowers the greenhouse effect (10°C see DE 28 33 234) inside the car.
LAFFAY GUY on 28 january 2012. Condensation in Astronomia. (Albireo78 Abstracts).
Ce type de vitrage est basé sur le ralentissement du refroidissement de sa face extérieure grâce au dépôt d’une couche à faible émissivité (Low E).
IL est utilisé en face n°1 dans le bâtiment sur les double/ triple vitrage super isolants qui condensent beaucoup.
Dans les portes des armoires frigorifiques. La face n°1 Low E est celle tournée vers le froid.
Dans les pare brise des véhicules, en face avant n°1 et les vitres latérales.
Application sur les pare-brise Windscreen-Ice-free
1)BALANCE OF TEMPERATURES DURING THE COOLING
Powers concerned.
A motionless windscreen on winter, during a clear night lose many calories by radiating effect (Infra-red 5->15 microns) so that it can be cooler than the ambient air and therefore get calories by conduction/convection and condensation of humidity into water or ice
Loss of calories by emitting effect of an ordinary windscreen
(noted s after strahlung).
The temperature of the windscreen is ~0° or 273°K (maximum of radiating ~ 11 microns and
emissivity ~ 0,9) so STEFAN formula give us the loss energy 0.9*5.7*10^-8*273^4=284w/m2
The sky is ~minus 20°C=253°K (maximum of radiating ~12 microns and emissivity ~0,9) , the windscreen get only 0,9 of incoming downward sky radiation.
0,9*0,9*5,7*10^-8*253^4=190 w/m2
The formula Swinbank/Goforth which don’t use sky temperature , generally badly defined, but temperature of windscreen and humidity percentage , give us for a clear night.
On winter 8,78*10^-13*(273^5,852)*(95^0,07195)=220 w/m2
On autumn/Spring 8,78*10^-13*(273^5,852)*(85^0,07195)=218 w/m2
The windscreen get 0,9*219=197 w/m2 (mean).
So the radiating loss is 284-197=87 w/m2 or 87/20=4,3 w/m2/°C
Loss of calories by emitting effect of a low E windscreen.
Emissivity=0,2
The loss is 0,2*5,7*10^-8*273^4=63w/m2
Emission of sky is the same 219 w/m2. Windscreen gets 0,2*219=44 w/ m2
The emitting loss is 63-44=19w/m2 ie 1w/m2/°C
Emissivity=0,1 loss by emission is 32 w/m2. Windscreen gets 219*0,1=22 w/m2
The final loss 32-22=10 w/m2 ie~ 0,5 w/m2/°C
Gain of calories by konduktion /konvektion noted k after
These gains are computed by clear and calm weather ie generating ice.
They are estimated 11w/m2/°C (v<1,5 m/s). If there a lot of wind v, the gains are much greater
But the windscreen don’t ice. The formula from Granqvist (1987) and al is 5,7+3,8*v.
Gain of calories by kondensation of humidity
The part of condensation warming the windscreen is estimated 537 calories/g of water
Ie 2244 J/g if a condensation of thickness (ep) in ( 1/10 mm) is deposed on the windscreen (surface 1 m2) in 1,5 hour, It means that a volume ep/10 liter or 100*ep in g is deposed ie 41,4*ep w/m2.
That quantity of warmth is a major contribution.
Temperature balance during the cooling of an ordinary windscreen on a clear calm sky
During the cooling, power P concerned is P=konvektion*delta(tk)-strahlung*delta(ts)
Delta(ts)=tg-ts tg temperature of the windscreen (g for glass) and ts= -20°C emitting
Temperature of sky (s for strahlung)
Delta(tk)=ta-tg ta=0°C ambient temperature
When reaching the balance state P=0, 0=11*delta(tk)-4,3*delta(ts)
Or delta(tk) + delta(ts)=20
11*delta(tk)=4,3* (20-delta(tk))
Delta(tk)*(11+4,3)=4,3*20
Delta(tk)=86/15,3=5,6°C delta(ts)=14,4°C
The temperature of windscreen is decreasing to -5,6°C but is icing before if humidity HR>65%
If HR, by example, is 85% icing is taken place at -2°C, then cooling is according to ,if ep=1 ( thickness
Of water condensation) 0=11*delta(tk)+41,4-4,3*delta(ts)
11*delta(tk)=4, 3*(20-delta(tk))-41,4
Delta(tk)=44,6/15,3=2,9°C
The windscreen with ice stop cooling at -2,9°C
Temperature balance during the cooling of a windscreen LowE=0,2
P=0=11*delta(tk)-1*delta(ts)
Delta(tk)+delta(ts)=20°C
11*delta(tk)=1*(20-delta(tk))
Delta(tk)*(11+1)=20 therefore delta(tk)=1,6°C
Temperature of windscreen It is -1,6°C. It is icing if HR>90%
If Emissivity=0,1 delta(tk)=0,87°C temperature of windscreen is -0,87°C. It is icing if HR>95%.
So in our example no icing.
The differences of surface temperature 2,9-1,6=1 ,3°C and 2,9-0,87= 2°C are those mentioned
In patent DE 28 33 234
2)KINETIC OF THE COOLING
Very approximately, we have ( Hour TU+1, end of twilight, the first night of a period of nights of clear sky , frequent humidity) latitude 48,7.
January 18,2 H 90->99% the windscreen has to cool 1 degree to attain the dew point
February 19H 90->99% 1 degree.
Mars 20H 90->99% 1 degree
April 20,5 H 80->89% 2 degrees
September 20 H 80-> 89% 2 degrees
October 19 H 80->89% 2 degrees
November 18 H 90->99% 1 degree
December 18 H 90->99% 1 degree
End of twilight is one hour after sunset
We saw from C. Granqvist (1987) that conduction/convection coefficient k=5,7+3 ,8*v
V wind velocity in m/s. If v= 0 k=5,7 and if v=2 m/s k is 13,3 w/m2/°C
During the cooling in winter, on a clear night (90% HR), difference of temperature (windscreen Low E and air) is ~ 1 degree.
So if the wind is 0 m/s, the windscreen get from the air 5,7 w/m2
If the wind is 2 m/s , the windscreen get 13,3 w/m2
If we consider a windscreen of surface 1 m2 thickness=5 mm, its weight is 12,5 kg.
The massic heat of glass is 720 j/kg/°C. So 720*12,5=9000 joule are necessary to cool that windscreen 1 degree.
Emissivity 0,1. We saw that the radiating loss is about 10 w/m2 so with a wind 1, 33 m/s
The windscreen conduction/convection and radiating loss are identical.
the time to cool 1 degree is then 9000/0=infinite. The windscreen don’t ice.
If wind velocity is 1,2m/s, the gain is 10,26 w/m2, the radiating loss is 10,6 w/m2
Ie global loss is 0,34 w/m2 or 0,34 J/s/m2
The time to cool 1 degree will be 9000/0,34=26470s or 7,3 hours.
If the velocity of the wind is 1,12m/s the time to cool is 4 hours.
If wind is 0,m/s the gain is 5,7 w/m2, the radiating loss is 10,6 w/m2, the global loss
4,9 w /m2 or 4,9 J/s/m2.
The time to cool 1 degree will be 9000/4,9=1838s ie 0,5 hours.
A minor variation of wind velocity between 0 and 1,33 m/s induce ice with a delay of 0,5 hour to infinite. On a period of several hours, we have to choose mean temporal delay. It has been estimated very approximately from experiments with mean velocity of wind 1m/s, that, on a clear night (period from end of twilight to dawn) of nov, dec, jan fev ,mar, a windscreen of a car outdoor without coating is cooling 1°C/hour and a windscreen coated with 0,2 emissivity (epsi) 0,2°/hour.
0n april,sep, oct a car without low E is cooling 0,9°C /h and with low E 0,18°C/H.
With these values, we can estimate and report the time when the windscreen are icing.
Estimation DE 28 33 234
Epsi=0,9 Epsi=0,2
Jan 18,2+1=19,2h 18,2+5=23,2h
Feb 19+1=20h 19+5=24h
Mar 20+1=21h 20+5=25h
Apr 20,5+2/0,9=22,7h 20,5+2/0,18=7,6h Am**Sunrise(6h)
Sep 20+2/0,9=22,2h 20+2/0,18=7,1h Am**Sunrise(6h)
Oct 19+2/0,9=21,2 h 19+2/0,18=6,1h Am**Sunrise(7h)
Nov 18+1=19 h 18+1/0,2=23 pm
Dec 18+1=19 h 18+1/0,2=23 pm
Globally the delay of icing with low E , compared to without Low E is 4 hours in winter and 8/9 HOURS in autumn/spring.
On Apr,Sep,Oct, there are minor icings on Sunrise with LowE 0,2. With low E 0,1 there are no icing.
« Applied Optics » vol 26 n°11 from Hamberg/ Claes Granqvist tackled the subject in 1987.
Granqvist and al don’t point out the delay of icing with low E till midnight. All the meteo data are registered at 7 am.That delay is appreciable.
The efficiency according to Granqvist is 1-6/29=0,8 (calculated with a number of favorable icing days), the same given in DE 28 33 234 (0,8/0,9 at 7 am with true measures). We have to add that a low E windscreen is easier to de-ice than an Ordinary one because the ice is always thinner.
In conclusion, that type of low E windscreen is very efficient on winter on evening to return from an outdoor parking of the job or kino and in autumn/spring, on morning to go to the job office from an outdoor parking.
In summer, it lowers the greenhouse effect (10°C see DE 28 33 234) inside the car.
LAFFAY GUY on 28 january 2012 .Condensation in Astronomia. (Albireo78 Abstracts).
------
New!!! 18 April 2017
ANTI CONDENSATION GLAZINGS (2)
(Windscreens, windows glazings, cold chambers) ** guy Laffay patent 1977 DE 28 33 234_théorie G.E.L
See schemes in annexe 1 and 2
Les pare brise givrent couramment l’hiver sur la face avant dite n°1 mais aussi les façades verrières des bâtiments dans le nord de l’Europe du fait que l’isolation actuelle, maintenant excellente empêche la moindre perte de chaleur pour réchauffer la face N°1. Le verre anti condensation permet de garder par tous les temps la transparence du verre qui est sa qualité principale.
Windscreens on outside parking and multi glazings windows, on cloudy nights don’t ice because the temperature of their exterior surface named N°1 and the exterior air temperature are the same.
It is not the case of a simple glazing which gets an important lot of heat from the interior ~+20°C and when adding sheets of glass or plastic to obtain a multi glazings one, the N°1 surface is getting now the behaviour of a windscreen’s n°1.
if suddenly, the clouds disappear, the radiating loss
toward the sky (here -20°C) of an ordinary windscreen is 90 watts/m2 and the gain conduction/convection
induced is 5,7+V*3,8 w/m2/°C ie 11 watts /m2 if the
face n°1 of the windshield and exterior air have a difference of 1 degree and 0 w/m2 at the beginning. (V is by example 1 m/s.).
The heat transfer of n°1 of a triple glazing when k’=0,7
Is ~ 0,7*18=12 w/m2 if exterior temperature is 0°C and interior 18°C.
1/k’=Sum(1/k)
So we can dispose now of the first point on the cooling diagram.
Axis Oy describe radiated power lost and conduction/convection power gained in w/m2.
Axis Ox being difference of temperature of surface N°1 relevant to temperature of exterior air.
The crossing of Oy,Ox is the zero point of the cooling of the windshield when clouds disappeared ;
Concerning a triple glazing, the point 12w/m2 is the first point on Oy if clouds disappeared.
The evolution continue then with the gain of conduction/convection according to 5,7+V*3,8 when the sky is always clearing.
The evolution stop when that gain reach the loss by the radiating surface n°1, function of its emissivity.
( 0,9/0,2/0,1 etc).
IF condensation appears, specific heat (40 w/m2 )is added according to a parallel line to Oy like heat coming from the interior in the case of multi glazing windows .Emissivity is getting now the value 0,9 (emissivity of water) and evolution stop on line 0,9.
Parallels to Oy concerning dx equal -1/-2/-3°C define relative humidity ie the dew points.
Concerning cold chambers multiglazing windows if k’=1 by example, the interior being minus 20°C ie similar to the sky (but always clear) and if the exterior temperature is +18°C, the heat entering the cold chamber through the surface n°1 is 38w/m2. We see that an emissivity of 0,45 is enough to avoid condensation and see through the window all the time.
LAFFAY guy on 28 january 2012 ; Condensation in astronomia. (Albireo78_Abstracts).
|