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4.1 Technique of experimental definition of air exchange in salon

Oscillation of speed and direction of air streams in windows and manholes of cars does not allow to define with an adequate accuracy magnitude of air exchange only sampling of speeds. More exact results can give antrakometrichesky a way of an experimental research of air exchange in cars at which in a car body create known density of gas-analyzer, and then, through certain time intervals fix its reduction.

Air exchange define on speed of lowering of density of gas - of the analyzer in which quality use carbonic gas, nitrogen and acetone steams. For fast distribution of gas-analyzer to salon it enter into a stream of going into fresh air.

In GSHI experimental researches by air exchange definition in salons of cars with use as gas-analyzer carbonic gas have been spent. The maintenance of this gas in atmosphere, under usual conditions is not enough 0,03 %). It allows to neglect at calculations magnitude of 0,03 % and it is easy to define density of carbonic gas even at its small case doses of introduction.

Fig. 4.1 Installation for air exchange definition in car salon

Carbonic gas put in car salon in a bulb 1 (fig. 4.1) from which through a hose 2 it arrives in a serpentine 3 air pipes 5. For prevention of freezing of a moisture available in gas and alignment of temperatures of gas and air in salon the heater 4 which air pipe organises a closed loop is provided.

The warmed-up gas through a reducer 6 governing it expenditure, and a diaphragm 8, arrives in a distributive pipe 11. Inspect gas expenditure under the index 7, and temperature on the thermometer 9. The gas temperature can be changed, regulating gasoline feeding in a heater. On handsets 10 gas take in in car salon in the same places where air streams go into, and then through certain time intervals in going out streams take air samples.

Amount of air arriving in salon in unit of time,

Where Q - gas-analyzer expenditure in l/s; Sc and SB - density of gas - of the analyzer in salon of the car and fresh air in %.

For a case of use as gas-analyzer of carbonic gas G, =Q (100/Sc).

4.2 Aerodynamics podkapotnogo spaces

Aerodynamic trials of models of cars usually spend without imitation of system of cooling that distorts the received results. Influence of degree of imitation of nature for car model on magnitude of factor sh a head resistance (according to SHmida) is displayed in tab. 4.1

Influence of an arrangement of the drive and reproduction of its system of cooling on magnitude of factor of a head resistance (according to Rikkerta, the Gauss, Weiss, Zavatsky and Romani) is displayed in tab. 4.2.

Table 4.1 - Degree of imitation of nature for the car Degree of imitation of nature Factor sh in absolute units in % the Prime model, a smooth bottom, are absent window recesses 0,506 92,5 Are imitated a bottom and okopnye recesses, but there is no pass for air cooling a heat sink 0,520 95,0 the bottom, window recesses, lattices of a heat sink and air passes Are imitated, but the heat sink is enclosed 0,530 97,0 Are imitated a bottom, window recesses, lattices of a heat sink and the heat sink is opened 0,547 100,0 the bottom and window recesses Is imitated, but there is no system of cooling 0,523 96,0 Table 4.2 - Influence of an arrangement of the drive on factor sd

The model Factor sh for model Contributors of the car the Arrangement without system with system otklo the drive of cooling of cooling nenija in % Weiss and "Adler" Forward 0,349 0,358-5 Zavatsky "Hansa" - 0,530 0,547-3 "Kamm" - 0,196 0,195 +1 Rikkert and proiz - 0,370 0,400-7 Gauss free - 0,244 0,285-14 model - 0,320 0,350-9 Romani "Reno" Back 0,416 0,387 +7 KDF - 0,485 0,485 0 BMW the Forward 0,255 0,364-30 Considerable aberration of the results reduced in tab.

4.1 and 4.2, is a consequence not so much of various conditions of holding of experimental researches, how many the big variety of shapes of the models put on trial. It is possible to consider, that the internal resistance arising at course of air through a heat sink and podkapotnoe space in which the drive finds room, makes at the car with bodies of not streamline shapes to 10 % of the common resistance of air, and at cars with bodies of streamline shapes to 20 %. Change

Constructions of liner of heat sinks last years it is accompanied by increase in resistance to air course.

For the analysis of magnitude of internal resistance in podkapotnom car space it is possible to use a way of measurement of pressure its various points. Thus the amount of leaking air can be defined in the sizes of a cross-section through passage and a difference of static air pressures ahead and behind a heat sink. The more the pressure gradient (resistance to air course), the is less amount of air arriving in podkapotnoe space, and more common aerodynamic resistance of the car. Therefore it is desirable, that the heat sink possessed, probably, smaller aerodynamic resistance.

The air inflow which is passing through, passing through a heat sink, can be presented as the sum of two streams, one of which is called by car movement, and another is created by the ventilator. Analytical definition of magnitude of aerodynamic resistance of a heat sink rather inconveniently and usually this resistance is defined experimentally. The road trials of car GAZ-21 "Volga" spent in LSHI, have displayed, that average speed of an air stream before heat sink front at small speeds of movement of the car (80 km/h) ventilator influence becomes a little notable. If to evaluate efficiency of operation of an air stream accumulating on the car a ratio of average speed of air before heat sink front, at the disconnected ventilator, to speed of an accumulating stream this magnitude for car GAZ-21 "Volga" will make ~ 0,4.

The circuit of installation for definition of internal resistance in podkapotnom car space is displayed on fig. 4.2. The air stream is created by the ventilator. Before a heat sink and behind it are established pezometry. Magnitude of resistance of heat sinks basically is defined

In the sizes available in them a hole for air pass.

Fig. 4.2 Circuit of installation for definition of internal resistance in podkapotnom car space

ON

80

Ar, mm SH.st 2*0 / f _ Ul * * У\/V / About *О SO 1Z0Ws/c

Fig. 4.3 Dependence of a gradient of pressure on amount of the past through a heat sink for 1 from air at various magnitude of holes in wire sitah, substituted a heat sink: 1,2 and 3 - grids with holes in diameter

Accordingly 10,20 and 30 mm On fig. 4.3 dependence is displayed dependence of a gradient of pressure on amount of the past through a heat sink for 1с air is displayed at various magnitude of holes in wire sitah, substituted a heat sink.

A.I.Matveev conducted aerodynamic trials of heat sinks on installation specially designed for this purpose (fig. 4.4), representing a wind tunnel with smooth transition from input 13 to the working part 15, ensuring a uniform field of speeds

Fig. 4.4 Installation for aerodynamic trials of heat sinks: 1 - throttle zaslonka; 2 - a centrifugal blower; 3 - the electric motor of the water pump; 4 - the water pump; 5, 8 and 9 - pipes for water delivery; 6 - a heat sink of heating of water; 7 — a tank for water heating up; 10 - spirit a vacuum gauge; 11 - the receiver of air pressure; 12 and 16 - mobile koordinatniki; 13 - an input part of a wind tunnel; 14 - the mercury thermometer; 15 - a working part of a pipe; 17 - a flywheel for control throttle zaslonkoj; 18 - a differential vacuum gauge; 19 - an automatic temperature regulator; 20 - a control panel; 21 executive mechanism; 22 - a pipe of a steam turnpike; 23 - a broad diffuser; 24 - the centrifugal blower electric motor

And possibility of trial of heat sinks of various depth. The section of a working part of a pipe made 400x400 mm. Mobile koordinatnik 12 allowed to define by means of handset Pito speed of an air stream in any point of section. Pressure measured by a differential vacuum gauge 18. Overfall of static pressure on either side of a heat sink measured by a vacuum gauge 10. Air temperature behind a heat sink measured as an average of observations of three mercury thermometers also put on the mobile

koordinatnike 16. Behind a working part of a pipe the diffuser 23 with the stream rectifier is.

Air in a pipe arrived immediately from a shop location in which it has been established. Speed of receipt regulated throttle zaslonkoj 1, operated a flywheel 17 from a control panel 20. Hot water from a tank 7 moved with the water pump 4 reduced by the electric motor 3 in a heat sink. The temperature regulator 19 maintained fixed temperature of water arriving in a heat sink in limits 90-92°С. The executive mechanism 21 temperature regulators has been established in a pipe 22 steam turnpikes. Water expenditure through a heat sink defined by means of double conic nasadkov and mercury vacuum gauges. Number powered up nasadkov changed depending on water expenditure.

As a result of trials established dependence of a head resistance of a heat sink on second expenditure air before it at a preset speed of air and oscillations of its temperature in limits 2,0 5,0°С. Second expenditure of air measured from 5 to 40 kgs / (sm2).

In the real conditions thanks to that air part passes under a cowl by a heat sink there are additional resistance, there is some lowering of speed of transiting of an air stream through a heat sink.

Operation of the ventilator put under a cowl of the drive behind a heat sink, disturbs uniformity of distribution of pressure in podkapotnom space and calls additional pressure decrease in a zone rotation of its lobes. In corners of the heat sink having the rectangular shape, a pressure gradient it is diminished owing to pressure heightening in podkapotnom the space, the ventilator called by operation. This phenomenon is illustrated by the dependences displayed on fig. 4.5. It is obvious, that for heightening k.p.d. The heat sink is important for achieving a pressure random distribution on its end face.

On internal resistance, temperatures, speed and a direction

Air stream the shape of the channels directing movement of air in podkapotnom space can render solving influence. However it is necessary to consider changes of density of air, linked with its heat and cooling. Therefore it is frequent as a metre use not a pressure absolute value, and height (in) Н=р/у.

Except a construction, magnitude and configurations of a cowl and the elements of the drive located under it, on an air stream in podkapotnom space influence also power setting and cooling systems. On fig. 4.6 the processes which are taking place on a path of cooling air in podkapotnom space are schematically displayed.

In section 1-1 selected before liner of a heat sink, level of pressure corresponds to a high-speed pressure of an opposing stream of air. Between sections 1-1 and 2-2 there is a reduction of speed and dynamic pressure, however static pressure raises. On a site between sections 2-2 and 3-3 from heat sink liner there is some pressure decrease owing to boundary layer formation. Between sections 3-3 and 4-4, within directing the mounting attachment, pressure is saved invariable, and at air course through a heat sink between sections 4-4 and 5-5 there is a considerable loss of energy by an air stream.

The increase in dynamic pressure behind a heat sink is a consequence of increase in volume of air at its heating up about transiting time through a heat sink. From section 5-5 to section 6-6 there is a further lowering of the common pressure though contraction of a cross-section of a stream and calls heightening of dynamic pressure. Ventilator operation calls pressure heightening between sections 6-6 and 7-7. In section 7-7 the air stream goes out an air pipe in podkapotnoe space and on a site between sections 7-7 and 8-8 there is the fast lowering of dynamic pressure which are not accompanied by heightening of static pressure.

Practically speed of an air stream becomes almost equal to zero. On a site between sections 8-8 and 9-9 at a constant of the common pressure its dynamic component raises, and static is reduced. Thus magnitude of a static component is defined by a condition of an external stream in a place of an exit of cooling air from podkapotnogo spaces.

Thus, the resistance met by an air stream at transiting through a heat sink, is linked with a heat transfer from water to air whereas se other resistance on its path are "harmful" and they are necessary for lowering whenever possible. Obviously, best result can be reached at the closed circulation of an air stream eliminating heightening of resistance, linked with sudden expansion of a stream in section 7-7 and pressure decrease on a site between sections 7-7 and 9-9. Possibility of origin of a high pressure in podkapotnom the space, heat promoting penetration and gases in car salon is besides, eliminated.

j / And 7 And V / g / at 4.

J / t with,

At / And At J IS And sh zio zoo tso

iZO

so *0 about

Fig. 4.6 Change of pressure on length of a path of transiting of air in

podkapotnom space

go is zo zi / *fi*zc/M*c a Fig. 4.7 Aerodynamic resistance of heat sinks of cars: 1 - М-20 "Victory" (the heat sink has 30 plates); 2 - ГАЗ-51; 3 - ГАЗ-11; 4 - М-20 "Victory" (the heat sink has 38 plates) Aerodynamic resistance Arr of a trubchato-lamellar heat sink depends on its depth, number of rows and an arrangement of handsets, distance between these handsets and between cooling plates. Aerodynamic resistance of a heat sink

Where Apjj, - losses of pressure upon a friction: Drs - the losses of pressure called by change of section and an air stream.

Thus &рс it is proportional to number p rows of handsets and depends on their shape and an arrangement, and also from the shape of cooling plates and depth of a heat sink, i.e.

2

Having meant depth of a heat sink e, and equivalent diameter of the channel for air pass between the next plates d, for a cold heat sink we will receive

For cars aerodynamic resistance nagretyh and cold heat sinks practically differ a little.

Aerodynamic resistance of a heat sink (84) increases proportionally to quadrate of speed of an air stream, that proves to be true dependences (fig. 4.7), received as a result of experimental researches. These dependences characterise also influence on resistance of air of a construction of a heat sink and amount of the plates falling to 100 mm of height of a heat sink. It is characteristic, that the increase in number of plates for a heat sink of car M-20 "Victory" with 30 (a curve 1) to 38 (кривая4) leads to sharp increase of resistance.

Design features of heat sinks can make considerable impact on turbulence of an air stream. The greatest aerodynamic resistance is rendered by heat sinks with narrow spljusnutymi the handsets ensuring at the same time sufficient section for course of water with small hydraulic resistance.

The arrangement of handsets and configuration of plates have bolshee value for degree of turbulence of an air stream passing through a heat sink. The arrangement of handsets in a heat sink can be koridornym (handsets are established under a corner or to in parallel air stream), chess or special. The greatest

Aerodynamic resistance takes place at koridornom an arrangement of handsets under a corner to a stream. Satisfactory results can be received at a special arrangement of handsets when each subsequent number is a little displaced concerning previous that cold air could wash handsets of all rows. The big turbulence of an air stream arises at a chess arrangement of handsets in comparison with koridornym an arrangement.

Application of individual cooling plates augments aerodynamic resistance by 15-20 % in comparison with resistance of the heat sink having the common plates. It is necessary to mean, that at transition from laminar to turbulent movement teplootdacha an air stream passing through a heat sink increases.

Turbulence of an air stream depends on number of plates on 100 mm of height of a heat sink and increases with its increase. Usually this number varies in limits from 20 to 50.

At perfecting of a construction of cars rushing to heightening of power of drives is characteristic at preservation of small overall dimensions. It leads to increase in depth of heat sinks, that, in turn calls increase of their aerodynamic resistance. It is better to expand a heat sink heat-absorbent surface, augmenting not its depth, and number of plates as it carries on to smaller aerodynamic losses.

Receipt in podkapotnoe space of enough of not dusty air is defined by a construction of air channels and a choice of places of a fence of external air. It is especially difficult to realise sufficient receipt of air in podkapotnoe space at a back arrangement of the drive. The successful decision of a similar problem is impossible without holding of aerodynamic trials of various variants of constructions. During such trials define pressure at an input in vozduhopriemnye holes and air expenditure at various speeds

Car movements. These trials usually spend in a wind tunnel.

Speed v (in km/s) an air stream (speed of the car) define under observations h mnkroampermetra: v = (4,5/ylp) yJh. At comparative trials this speed should remain a constant and correspond to the highest thermal intensity of the drive of the car.

Equation Bernulli for section 2-2 and 4-4 (fig. 4.6 see) will become:

Where Si With - factor of resistance of liner of a heat sink and an airline, difiniendums experimentally.

Pressure r and expenditure Q of air are linked by the equation

Where Sb - the area of a total cross-section vozduhopriemnyh holes.

The big influence on magnitude of resistance of air liners of a heat sink and a construction of louvers (render fig. 4.8). It is necessary to mark, that usually throughput of slots in heat sink liner differs known non-uniformity. Uniformity of distribution of a stream on separate slots define during special trials.

Interesting results are received at trial vozduhopriemnnkov cars ZAZ-965, ЗАЗ-966 and ЗАЗ-970 at which the drive is located behind. Trials have displayed, that air expenditure immediately depends on change of magnitude of pressure before vozduhopriemnikami. However at the same pressure at an input it is possible to augment expenditure of air by construction respective alteration vozduhopriemnoj strips.

Fig. of 4.8 Dependences of resistance of air from a material of liners and a construction of louvers of heat sinks of cars: 1 - ГАЗ-51; 2 - М-20 "Victory" Recently the corporations which are letting out cars, aspiring to improve operation of systems of cooling of drives, often carry out aerodynamic researches podkapotnogo spaces as here it is possible to discover yet not determined redundancies of heightening of power of drives.

Fig. of 4.9 Performances of an air path and the ventilator: and and - accordingly at positive and negative overpressures at an input in vozduhopriemnik $//-it and

с* Considering performances of an air path and the ventilator at positive (fig. 4.9,) and negative (fig. 4.9,) an overpressure at an input in vozduhopriemnik, it is possible to conclude, that productivity of the ventilator increases at increase in this pressure. Ventilator performances (curves 1) and an air path (curves 2) are intersected in points And, defining necessary productivity of the ventilator.

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A source: Matveev Denis Viktorovich. WORKING out of TECHNIQUE of CALCULATION of SYSTEM of HEATING And CAR VENTILATION. The thesis on competition of a scientific degree of a Cand.Tech.Sci. Izhevsk - 2006. 2006

More on topic 4.1 Technique of experimental definition of air exchange in salon:

  1. 1.2.2. A graphic method of calculation of air exchange in salon
  2. definition of a technique theoretical and experimental researches
  3. 1.2.3 Method of calculation of system of heating and ventilatings of salon of the car, grounded on experimental data
  4. § 2.3. A technique of use of air photography in the Kislovodsk hollow.
  5. the Technique of experimental researches
  6. Definition of key parametres of a stream of a cement-air mix in an unloading pipe
  7. Definition of a kaltsievo-phosphoric exchange and markers of an osteal metabolism
  8. an organisation technique it is skilled-experimental research
  9. 3.2. The general questions of a choice of an experimental technique
  10. 2.2 Substantiation of a choice of a technique of carrying out of experimental researches
  11. a technique of carrying out of experimental researches
  12. dynamics of definition of a legal status and an establishment of an operating legal regime of the international air space
  13. a technique of handling of results of experimental researches
  14. Dynamics of definition of a legal status and an establishment of an operating legal regime of sovereign air space
  15. 1.2.1 calculations of ventilation of salon Simplified an analytical method
  16. the first stage of an experimental research with use of an associative design technique
  17. CHAPTER 2. THE EXPERIMENTAL TECHNIQUE
  18. CHAPTER 2. THE EXPERIMENTAL TECHNIQUE
  19. CHAPTER 2. THE EXPERIMENTAL TECHNIQUE
  20. the Experimental technique and instrumentation
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