Cooling of High Temperature Walls by means of Injection of Spray with Monodimensional Distribution of the Drops

Activity description
Experimental facility (Test Section)
Applications
Publications

Activity responsible: Dr. Andrea MARIANI
Address: ENEA C.R. Casaccia, Institute of Thermal Fluid Dynamics, Via Anguillarese 301 (S.P. 092), 00060 S. M. di Galeria RM, Italy 
Phone: +39 06 3048 3998Fax: +39 06 3048 3026 

Email: mariani_a@casaccia.enea.it


Activity description

The emergency of the transport on track and rubber of tanks containing dangerous and/or inflammable substances, must be guaranteed from hypothetical incidents that, developing a fire situation, could put in argument the previewed safeguards of emergency for the management of the transport. Typically, as a result of permanence in atmosphere with flames, the temperature of the walls of the tanks begins to go up, losing the property of mechanical resistance of metal, dangerous aspect in the case of container in pressure, until provoking the thermal yielding for overheating. The Institute of Termalfluid-dynamics of the ENEA is carrying out an activity for the determination of the rate of thermal exchange between drops of liquid and overheated walls. Such situation is typically that of a surface of a tank containing inflammable and/or dangerous substances in flame atmosphere as a result of fire, invested from a jet of extinguishing liquid. The purpose is the acquisition of information, derivatives on base experiences, regarding the thermal evolution of walls of tanks dipped in fire, in order to better manage the emergency of tanks containing dangerous substances, in the transport on rubber or tracks, as a result of hypothetical incident event. The peculiarity of the experiments in course is the use of a spray with a generation of monodimensional drops in order to cool a heated wall at variable temperature from test to test, and to measure the cooling rate of the system versus some geometric and fluiddynamic parameters. That allows to evaluate the effect of the diameter on heat transfer.
The working principle of such a spray is based on the varicose rupture of a liquid jet (Rayleigh-Weberinstability): imposing a periodic perturbation of appropriate amplitude and frequency on the jet surface, the flow is "constrained" to break in precise points, eventually obtaining constant diameter drops, depending, for a given liquid, on the nozzle diameter and liquid velocity. Dimensions of droplets used in the present work range from about 0.3 to 1.5 mm. The jets are obtained using nozzle disks with variable diameter and number of holes, Each nozzle disk is manufactured in order to have the same cross flow area independent of the number of nozzles in the disk.. A digital image system allows to know, for each nozzle, droplet diameter and aspect ratio. Tests are carried out varing the parameters to our disposition: nozzle disks (four different nozzle disks with holes from 0.15 to 0.90 millimeter), speed of the drops (from 2 to 5 m/s) and temperature of wall (from 100 to 700 °C). This activity is carried out STAF facility

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Experimental facility

The experimental program carried out on the STAF loop is devoted to study the influence of the geometrical and thermal-hydraulic parameter of a water spray on the rewetting of a high temperature surface. The configuration involves the study of the rewetting of a vertiical wall by fallinf liquid film.
The STAF loop is equipped with a visualized test section to obtain images of the phenomenon.


ImpBRIV.gif (12 K)

The test loop (STAF) is made of stainless steel, and the fluid refrigerant is deionized and demineralized water.
The main characteristic of the loop are:
Flow rate: up to 80 l/h (water)
Pressure: atmospheric
Inlet temperature: up to 75 °C
Dc power: up to 50 V and 1800 A.

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Test section

Vertical wall (AISI 316), heated length of 100 mm (total length 140 mm), width of 10 mm and depth of 5 mm.
Spray characteristic: distribution of the droplets: monodimensional, velocity of the droplets ranging from 1 m/s to 10 m/s, diameter of the dropltes: ranging from 0.1 mm up to 3.0 mm and wall temperature: ranging from 100°C to 700°C.

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Applications

  • Cooling of high temperature wall.
  • Emergency cooling.

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Publications

.P. CELATA, M. CUMO and A. MARIANI, Raffreddamento di Pareti ad Alta Temperatura Mediante Iniezione di uno Spray con Distribuzione Monodimensionale delle Gocce, Proc. XX National Heat Transfer Conference UIT, Maratea, Giugno 27-29, 2002 (in italian)
G.P. CELATA, M. CUMO and A. MARIANI, Rewetting of Hot Surfaces by Droplet Impingement, 40th European Two-Phase Flow Group Meeting, Stochkolm, 11-13 June, 2002, paper B1
G.P. CELATA, M. CUMO A. MARIANI and L. SARACENO, Rewetting of hot surfaces by droplet impingement: effect of the spray impact point, 41th European Two-Phase Flow Group Meeting, Tromso-Trondheim, 12-13 May 2003
G.P. CELATA, M. CUMO and A. MARIANI, Visualizzazione dell?impatto di gocce di acqua su superfici calde, effetto della altezza e dell?inclinazione della parete, Proc. XXI National Heat Transfer Conference UIT, Udine, Giugno 23-25, 2003 (in italian)
M. CASAMIRRA, F CASTIGLIA, M. GIARDINA, C. LOMBARDO, L. SARACENO, G. P. CELATA and A. MARIANI, Rewetting by liquid spray of a hot metallic wall, Proc. of the XXII UIT Conference, Genova, 21-23 June, 2004
G.P. CELATA, M. CUMO, C. LOMBARDO, A. MARIANI and L. SARACENO, Experimental result on rewetting of hot surfaces by droplet impingement, Experimental Thermal And Fluid Science Vol. 29, pp 275-285, 2005
M. CASAMIRRA, F CASTIGLIA, M. GIARDINA, C. LOMBARDO, G. P. CELATA, A. MARIANI and L. SARACENO Rewetting of a hot vertical surface by liquid sprays, Experimental Thermal And Fluid Science Vol. 29, pp 885-891, 2005
G.P. CELATA, M. CUMO, A. MARIANI and L. SARACENO, Parametric effects on rewetting hot surfaces by droplet impingement, 6thExHTFS Matsushima,, Miyagi, Japan 17-21 April, 2005
G.P. CELATA, M. CUMO, A. MARIANI and L. SARACENO, Flussi termici e coefficienti di scambio termico sperimentali nel ribagnamento di superfici ad elevata temperatura mediante impatto di gocce, Proc. XXIII National Heat Transfer Conference UIT, Parma, Giugno 20-22, 2005 (in italian)
G.P. CELATA, M. CUMO, A. MARIANI and L. SARACENO, Rewetting of hot surface: a comparison between "spray cooling" and "film flow cooling", ECI International Conference on Boiling Heat Transfer, Spoleto, 7-12 May 2006
G.P. CELATA and A. MARIANI, Parametric study of heat flux in the quenching of hot surfaces by spray impingement, DITICE workshop, Bergamo, 19 May 2006
G.P. CELATA, M. CUMO, A. MARIANI and L. SARACENO, Heat flux and heat transfer coefficient in quenching of hot surfaces by drops impingement, 13th International Heat Transfer Conference, Sydney, Australia, 13-18 August 2006
G.P. CELATA, M. CUMO, A. MARIANI and G. ZUMMO, Visualization of the impact of water drops on hot surfacie, effect of the height and the inclination of the wall, Heat and Mass Transfer Vol. 42, pp 885-890, 2006

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