An application of non-compressible flowing in thermoplastic pipes in installations for fire prevention.

Pop, Petru ; Lazar, Liviu ; Marcu, Florin 等

1. INTRODUCTION

For fire prevention in special places, such as: medical stocks depot, warehouse, etc. as active medium is used cold water [Dubbel, 1988]. The cold water has capacity, under jet form or pulverization after warm bodies in burn, of heat absorption and evaporation, followed by cooling of bodies due to fire extinguishing. In general, the feed inner installations with cold water are equipped with special devices as sprinklers, for initiation and distribution of water for fire extinguisher. The sprinklers got in pipe section have fed with water, being special casings, which are automatic open at a predictable temperature of fire due to pulverization of water on burned place.

The constructions of sprinklers are complicate and expensive. A new, simple and efficient construction of hydrodynamic resistance this paper has presented. This construction has at base of polyamide property treated with gamma ray to be thermocontractible [Hutte, 1995]. Under pipe form, at flame temperature produced by fire the polyamide has contracted formed a necking, which under impulse force, pressure difference from pipe zone is broken assuring water circuit opening, which due to fire extinguishing.

2. THEORETICAL ASPECTS

Today, at fire extinguishing technique in water circuit have used sprinklers, which have to open themselves at predictable temperature by:

* Melting of low-fusible alloy, which closed sprinkler orifice [Carp&Ungur,2003;Dubbel,1988;Hutte,1995];

* Melting of low-fusible chemical composition, which supports of holding valve support [Ghimus,1984];

* Broken of glass bulb filled with a liquid, which has expanded at a higher temperature [Covrig,1996].

[FIGURE 1 OMITTED]

The most used sprinkler is with low-fusible alloy (Fig.1-a: ensemble, Fig1-b: fusible support device). Its construction is complicated, has formed by: 1-sprinkler body, 2-bronze ring, 3supported frame, 4-copper diaphragm, 5-valve, 6-shutting, 7,8,9-small plates of fusible alloy, 10-rosette. During fire braking out, shutting material is melting due to spurt open, on which the water get out under the pressure acting rosette and water pulverization is near uniform on desired surface.

A new, cheap and efficient device, which can change the sprinkle this paper has presented. At the base of new device construction is stand the continuity equation of Bernoulli for non-compressible fluids, impulse force in nozzles, and some thermoplastics and thermocontractible material's properties under pipes form narrow the section in heated portion, due to diminished hydrodynamic strength of pipe and its broken, and opening the water circuit which fire extinguishing [Dubbel,1988;Hutte,1995]. At water flowing through circular pipes with different sections, have different medium flow speeds, flow rates and pressures, the variations being function of section's size.

The main equations, which described the physical phenomena, have presented in following:

* The continuity equation [Hutte,1995]:

[??] = [rho] x [??] = [[rho].sub.1][v.sub.1][A.sub.1] = [[rho].sub.2][v.sub.2][A.sub.2] = [[rho].sub.0][v.sub.0][A.sub.0] (1)

, or:

[??] = [??]/[rho] = [A.sub.0][v.sub.0] = [A.sub.1][v.sub.1] = [A.sub.2][v.sub.2] (2)

, where: [??]-is volumic flow rates, [??]-masic flow rates, [[rho].sub.1][[rho].sub.2][[rho].sub.0]-fluids densities, that for non-compressible mediums are constant ([[rho].sub.1] = [[rho].sub.2] = [[rho].sub.0]), and [v.sub.1] [v.sub.2][v.sub.0]-fluid speeds within sections- [A.sub.1], [A.sub.2], [A.sub.0] of a narrow stream tube.

* Bernoulli equation [Hutte, 1995] for stationary flow is:

[v.sup.2]/2 + p/[rho] + g x z = ct. (3)

From continuity and Bernoulli's equations for flowing in narrow tubes have determined the medium flow speeds and flow rates in circular pipes. So, on (1-0)-way from Fig.2, it has: [v.sup.2.sub.1]/2 + [p.sub.1]/[rho] = [v.sup.2.sub.0]/2 + [p.sub.0]/[rho] (4)

, which can obtain the speed-vo from section-0:

[v.sub.0] = 1/[square root of 1 - [A.sub.0]/[A.sub.1]] x [square root of 2/[rho]([p.sub.1] - [p.sub.0])] = [alpha] x [square root of 2/[rho]([p.sub.1] - [p.sub.0])] (5)

, where the constant-a depends only of surface's ratio-([A.sub.0]/[A.sub.1]).

[FIGURE 2 OMITTED]

At section reducing from (1) to (0), the water speed-[v.sub.0] is raising significant, so and water flow rates due to broken of narrow thinner walls of pipe from themocontractible polyamide with small section-[A.sub.0]. At suddenly decrease of section has produced the contraction of stream fluid.

* The acting force of narrow water jet: From continuity and Bernoulli's equations of flow on (0-2)-way from Fig.2, for flow results:

[p.sub.0] - [p.sub.a] = 1\2 [rho]([v.sup.2.sub.2] - [v.sup.2.sub.0]) = 1/2 [rho][v.sup.2.sub.2](1 - [A.sup.2.sub.2]/[A.sup.2.sub.0]) (6)

From which the action force of waterjet is:

[F.sub.A] = -1/2[rho][v.sup.2.sub.0][A.sub.0][([A.sub.0]/[A.sub.2] - 1).sup.2] (7)

The force-[F.sub.A] is orientated in negative direction of X-axis as [A.sub.2] > [A.sub.0] , action on (0-2)-way to narrow tub's walls from thermoplastic and thermocontractible material going on tub's wall broken and opening the water circuit for fire extinguishing.

3. NEW DEVICE FOR FIRE PREVENTION

The sprinkler substitution with pipes from thermocontractible polyamide is easy and efficient, having the advantage of simple construction and easy fabrication [Argeseanu, 1999; Ghimus, 1984; Hornn, 1988].

In these installations, the thermocontractable pipe has the role of thermodynamic resistance, with a diameter-d0 and thickness-[a.sub.o], the length-[l.sub.o] is pre-established. At breaking of fire, as hot, the pipe has contracted altering the hydrodynamic flow parameters of water. Therefore, the narrow pipe zone has subjected of great speeds of water, an impulse force and a difference of pressure due to broken of wall's pipe and relieved the water from installation circuit of fire extinguishing. In Fig.3 has presented all phases process of thermocontractible pipe narrow and broken at hot temperature. The destroy phases of thermocontractable tub are: a-hydrostatic balance, b-narrow tub under adds heat, c-broken tub (hydrostatic unbalance).

The fast change of hydrostatic balance at thermocontractable pipe deformation due to gain of its hydrodynamic strength and its deterioration. At damaged tub under add heat, the hydrodynamic resistance from broken zone has narrowed, due to a hydraulic shock of tub.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

This phenomena is possible as a difference of pressure and contraction of stream fluid due to broken of pipe and relieved the waterjet, which fire extinguished [Dubbel,1988; Hutte, 1995].

In Fig.4 has depicted a partition from thermocontractable pipe, used as hydraulic resistance in installation of fire prevention.

In present, these tubs have used in decoration and anticorrosive actions, fixed on pipes, rods, shank by contraction and heat contribution [Rufe, 2002].

In inner hydraulic circuit of prevention and extinguishing fire can be mounted in parallel the pipes by screw, joining type DIN 3930, or by joining with closed muffle or tapped muffle, metallic tapped snap rings, or stick by adhesives (fig.5). Where: (Fig.5-a) 1-is pipefitting, 2-junction, 3-nut, 4-snap ring, 5-thermoplatics tub, and (Fig.5-b) 1-nipple, 2-nut, 3-thermoplastics tub.

4. CONCLUSIONS

The solution of thermoplastic and thermoconductible resistance for substitution of sprinklers in installations of fire prevention and extinguishing from depots assures great economy and efficiency.

The construction of limitative hydraulic resistances from thermoplastic and thermoconductible tubs is simple, robust, a lightweight and low cost, with large perpective using in fire installations.

5. REFERENCES

Argesanu, V. et al. (1999), Elements of Mechanical Engineering, pp. 37-42, 173-193, Eurostampa Editor, Timisoara

Carp, V. & Ungur, P. (2003), Study of Materials, pp. 70-82, Didactical and Pedagogical Editor, Bucharest

Covrig, M. (1996), Technology of Non-metallic Materials, pp. 112-144, Lux Libris Editor, Brasov

Ghimus, D. & Ivanoff, M. (1984), Plastically Materials in Installations", Technical Editor, Bucharest

Hornn, S., et al. (1988), Vade-mecum of Plastical Materials, Tehnical Editor, Bucharest

Rufe, P.D. (2002), Fundamentals of Manufacturing, SME Editor, Dearborn, Michigan, USA

***Dubbel, (1988), Handbook of Mechanical Enginnering, Fundamentals, pp. D74-D99, G23-G24, N1-N38, Tehnical Editor, Bucharest

***Hutte, (1995), Handbook of Mechanical Enginnering, Fundamentals, 29th Edition, pp. B80-B84, D26-D27, E123 E125, Tehnical Editor, Bucharest.