new principles for air curtains design for high efficiency

New principles for air curtains New principles for air curtains design for high efficiencydesign for high efficiency. .

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Air Curtains has become a standard way of Air Curtains has become a standard way of protecting the doorway openingprotecting the doorway opening..

Although air curtains are used for many applications, Although air curtains are used for many applications, mostly, they are used for temperature separation of the mostly, they are used for temperature separation of the air volumes in the vicinity of the open doorway.air volumes in the vicinity of the open doorway.

Nevertheless, today I will show that the thermal Nevertheless, today I will show that the thermal protection provided by air curtains is insufficient. This is protection provided by air curtains is insufficient. This is not because air curtains are made by manufacturers not because air curtains are made by manufacturers improperly or because physical principles employed in improperly or because physical principles employed in air curtains do not work. This is because those principles air curtains do not work. This is because those principles have limitations, which lead to a lack of efficiency of air have limitations, which lead to a lack of efficiency of air curtains.curtains.www.tropik.ru

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AIR CURTAINAIR CURTAIN – – OPERATION OPERATION PRINCIPLEPRINCIPLE..

EFFICIENCYEFFICIENCY. .

Unacceptable heat loss values takeUnacceptable heat loss values take place even in the optimal conventional air place even in the optimal conventional air

curtain.curtain.www.tropik.ru



Power which is loosing at the opening because of the temperature Power which is loosing at the opening because of the temperature difference on the sides of the opening is given by the formuladifference on the sides of the opening is given by the formula::

WW00 = = KK··ww··HH3/23/2·(ΔТ)·(ΔТ)3/23/2, ,

w – widthw – width, Н – , Н – heightheight, ΔТ – , ΔТ – temperature differencetemperature difference, ,

K ≈ 0,1K ≈ 0,1

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The efficiency of the device The efficiency of the device ee may be defined as part of the thermal may be defined as part of the thermal power which leakage was prevented by the operation of this devicepower which leakage was prevented by the operation of this device..

WWminmin = (1- = (1- ee)·K·w·H)·K·w·H3/23/2·(·(ΔТΔТ))3/23/2



What is the maximum possible value What is the maximum possible value of the effectiveness of the effectiveness ee in air curtains in air curtains??

In the article [A.M. Foster, M.J. Swain, R. Barrett, P. D'Agaro, L.P. In the article [A.M. Foster, M.J. Swain, R. Barrett, P. D'Agaro, L.P. Ketteringham, S.J. James. Three-dimensional effects of an air Ketteringham, S.J. James. Three-dimensional effects of an air curtain used to restrict coldcurtain used to restrict cold room infiltration. Applied Mathematical room infiltration. Applied Mathematical modeling, 31(6) 1109-1123, 2007.]modeling, 31(6) 1109-1123, 2007.]

Maximum effficiency is estimated as 71%Maximum effficiency is estimated as 71%..

By the data [Gregory Verhaeghe, Arnout Willockx, Marnix VanBy the data [Gregory Verhaeghe, Arnout Willockx, Marnix Van Belleghem, Michel De Paepe. Study of air curtains used to restrict Belleghem, Michel De Paepe. Study of air curtains used to restrict infiltrationinfiltration into refrigerated rooms. Heat Trasfer. Fluid Mechanics into refrigerated rooms. Heat Trasfer. Fluid Mechanics and Thermodynamics. and Thermodynamics.

77thth International Conference. Proceedings.(2010) pp. 1763-1769.] International Conference. Proceedings.(2010) pp. 1763-1769.], ,

Maximum effficiency is estimated as 8Maximum effficiency is estimated as 800%. %.


What parameters define the efficiency What parameters define the efficiency of the air curtainof the air curtain? ?


Efficiency as the function of initial air Efficiency as the function of initial air speedspeed

AirAir

speedspeed

4,25 4,25 mm//ss

6,75 6,75 mm//ss

14,0 14,0 mm//ss

Initial width of the nozzleInitial width of the nozzle 5 5 smsm, , heating power of air curtain 2heating power of air curtain 2,5,5kWkW, , additional poweradditional power 2,5 2,5 kWkW Tout =Tout = -10° -10°CC, , TinTin=20°=20°C,C, HH=2м, =2м, t = 180 st = 180 s www.tropik.ru www.tropik.ru


Real values of heat fluxReal values of heat flux I propose to compare the heat losses through the three types of I propose to compare the heat losses through the three types of

structures, the facade area of 3x3m, window area and an structures, the facade area of 3x3m, window area and an opening which is protected by an air curtain. Assume that all opening which is protected by an air curtain. Assume that all three areas are of the same size 3x3 meters and are used for three areas are of the same size 3x3 meters and are used for the same values of Tin = + 20the same values of Tin = + 2000C of the inside temperature and C of the inside temperature and Tout = -11Tout = -1100C of outside temperature. For values R of the C of outside temperature. For values R of the thermal resistance of the facade and windows Regulation of thermal resistance of the facade and windows Regulation of 23.02.2003 gives the recommended values R for the Moscow 23.02.2003 gives the recommended values R for the Moscow climate. Let us calculate the heat loss as square footage times climate. Let us calculate the heat loss as square footage times temperature difference divided by the value of thermal temperature difference divided by the value of thermal resistance. Heat losses for open aperture is calculated by the resistance. Heat losses for open aperture is calculated by the proposed formulas above with the lowest value of K = 0,06 proposed formulas above with the lowest value of K = 0,06 and the maximum efficiency of the air curtain 80%.and the maximum efficiency of the air curtain 80%.


Real values of heat flux.Real values of heat flux.

WWwallwall = = 85 85 WWт, т,

WWwinwin = = 500500 W W,,

WWacac ≈ ≈ 3322 000 000 W W, ,

WW0 0 ≈ ≈ 11660 0000 000 W W

1% 1% enhancement of the air curtain efficiency can save enhancement of the air curtain efficiency can save about about

11660000 W W..


Значимость задачи уменьшения Значимость задачи уменьшения теплопотери.теплопотери.

This huge difference in cost can be interpreted in this way This huge difference in cost can be interpreted in this way

1m1m22 of the doorway protected by the high performance air curtain of of the doorway protected by the high performance air curtain of the door in terms of heat loss can be compared with the heat loss the door in terms of heat loss can be compared with the heat loss through 60 m2 of the windows or through 375 m2 of the facade.through 60 m2 of the windows or through 375 m2 of the facade.

From the different point of view every percent of increase in the From the different point of view every percent of increase in the efficiency of the air curtain, which is mounted at 3x3 opening will efficiency of the air curtain, which is mounted at 3x3 opening will result in savings of heat of the same value that is lost through the result in savings of heat of the same value that is lost through the

window construction area of about 30mwindow construction area of about 30m22 or facade area of or facade area of approximately 170mapproximately 170m22..


Why heating of air is needed at air Why heating of air is needed at air curtain?curtain?

1. 1. The compensation of heat lossThe compensation of heat loss.. 2. 2. Imitation of the heating system (Secondary heating system)Imitation of the heating system (Secondary heating system).. 3. 3. Creating a comfort zone for people in the opening of the doorwayCreating a comfort zone for people in the opening of the doorway..


Efficiency of the air curtain with Efficiency of the air curtain with heatingheating. .

Why air curtain with heating of air steam has so low efficiency? Why air curtain with heating of air steam has so low efficiency?

Because the main part of the power doesn’t go into the room.Because the main part of the power doesn’t go into the room. I propose simple model of this phenomenon.I propose simple model of this phenomenon.

WW = 2 = 2kWkW//mm22

+20+2000CC +20 +2000CC +20 +2000CC -10 -1000CC

WW11= = WW22 = 1 = 1kWkW//mm2 2 WW11 ? ? WW22 ? ?


Efficiency of the air curtain with heatingEfficiency of the air curtain with heating. .

Why air curtain with heating of air steam has so low efficiency? Why air curtain with heating of air steam has so low efficiency?

Because the main part of the power doesn’t go into the room.Because the main part of the power doesn’t go into the room. I propose simple model of this phenomenon.I propose simple model of this phenomenon.

WW = 2 = 2kWkW//mm22

+20+2000CC +20 +2000CC +20 +2000CC Тст ≈ 30 Тст ≈ 3000CC -10 -1000CC

WW11= = WW22 = 1 = 1kWkW//mm2 2 WW11 ≈ 0,4 ≈ 0,4 kWkW//mm22 WW22 ≈ 1,6 ≈ 1,6 kWkW//mm22


How the efficiency of the air curtain without How the efficiency of the air curtain without heating can be increased sufficiently?heating can be increased sufficiently?

If we consider formula of heat loss for protected by air curtain openingIf we consider formula of heat loss for protected by air curtain opening

WWacac = (1- = (1- ee)·K·w·H)·K·w·H3/23/2·(·(ΔΔTT))3/23/2

Which of the variables in that formula could be changed for lowering of WWhich of the variables in that formula could be changed for lowering of W??



If we consider formula of heat loss for protected by air curtain openingIf we consider formula of heat loss for protected by air curtain opening

WWacac = (1- = (1- ee)·K·w·H)·K·w·H3/23/2·(·(ΔΔTT))3/23/2

We could change only the variable We could change only the variable ΔΔTT



WWminmin = (1- = (1- ee)·K·w·H)·K·w·H3/23/2·(·(ΔΔTT))3/23/2

::

ΔΔTT TT ≈ ( ≈ (TwTw++TcTc)/2)/2

ΔΔTT/2 Δ/2 ΔTT/2/2

WW 0,350,35W !!!W !!!www.tropik.ru www.tropik.ru


Under what conditions we can use appoximation Under what conditions we can use appoximation of average temperature?of average temperature?

Criterion of approximation possibilityCriterion of approximation possibility использования использования of average of average

temperaturetemperature TT is L is L ≈ ≈ HH

We can modify this schemeWe can modify this scheme

Then it can be used in compact construction of air curtainThen it can be used in compact construction of air curtain

For this case we canFor this case we can

supposesuppose, , αα ≈ 1 ≈ 1

((αα – – an angle between 2 air jetsan angle between 2 air jets))


For air curtain with heating. There is additional For air curtain with heating. There is additional limitation. We can not heat external jet which is close to limitation. We can not heat external jet which is close to outside airoutside air. .

Heating the outside air stream would reduce the effectiveness of the entire Heating the outside air stream would reduce the effectiveness of the entire scheme.scheme.

But we can use heating at theBut we can use heating at the

inner jetinner jet!!


Calculation in Calculation in 22D model ofD model of εε – – k turbulencek turbulence..

Conventional single jet airConventional single jet air

curtaincurtain. . Heating powerHeating power

55kWkW TTavav = 19,87 = 19,87 00CC. .

Double jet air curtainDouble jet air curtain

Heating powerHeating power 2 2 kWkW

40% 40% TT11 = 19,09 = 19,09 00CC

TT22 = 18,92 = 18,92 00CC

Double jet air curtainDouble jet air curtain

Heating powerHeating power 2 2,5,5 kW kW ВтВт

50% 50% TT11 = 23,21 = 23,21 00CC

TT22 = 20,62 = 20,62 00CC

Double jet air curtain with only 43% heating power allows gaining the same or Double jet air curtain with only 43% heating power allows gaining the same or better conditions as the standard single jet curtain with 100% heating!better conditions as the standard single jet curtain with 100% heating!


So, how do you ensure the comfort for people So, how do you ensure the comfort for people passing in the flow of the outer jet?passing in the flow of the outer jet?

If you surely do not have to heat outer jetIf you surely do not have to heat outer jet


For this purpose I propose now an entirely new For this purpose I propose now an entirely new principle of heating the outer jet (objects inside it) with principle of heating the outer jet (objects inside it) with

an infrared heateran infrared heater

I also suggest a name for this principleI also suggest a name for this principle

IR DOOR IR DOOR as the analogue of the Northas the analogue of the North

American name for air curtain American name for air curtain

AIR DOORAIR DOOR

While using this principle the importance is only in the personal feeling of comfort, not in the absolute values of While using this principle the importance is only in the personal feeling of comfort, not in the absolute values of energy flowenergy flow..


new principles for air curtains design for high efficiency

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study of air curtains

air curtains design

air volumes

physical principles

lack of efficiency

temperature difference

temperature separation

new principles