Showing papers by "S.V. Prabhu published in 2021"

Performance of water mist system with base injection in extinguishing small container fires

Abstract: The purpose of the present work is the experimental investigation on the extinguishment of diesel container fires by a water-mist system with base injection through multiple nozzles placed symmetrically at various positions around the rim of the container. Experimental parameters selected are the orifice diameter of the nozzle, the number of nozzles, position of nozzles (angle of orientation, radial and vertical distance of the nozzle from the edge of the container), and injection pressure. Nozzles used in the present work are pressure-swirl nozzles with Z-type swirl-insert with solid-cone spray. Desirable properties of the system such as the non-clogging operation of the nozzle and uniform mass flux density in the spray are tested for the nozzles. The optimized solution is provided considering water consumption and the physical stability of the fuel surface in the container. Displacement of oxygen is observed as a predominant extinction mechanism due to the effective application of spray in the base region of the fire. The present work provides the parametric study of the extinction establishing the feasibility of the water mist system with a base injection for extinguishing tank fires. This may serve as guidelines for the preliminary design of the system with the extension for larger tank fires.

Performance by Various Water Mist Nozzles in Extinguishing Liquid Pool Fires

Abstract: Water mist based systems have emerged as potentially lucrative alternatives to Halon-based fire suppression systems and have been extensively studied in the literature. In the present work, experimental investigations are carried out on the performance of the water mist nozzles in extinguishing pool fires of diameter 0.1 m, 0.2 m, and 0.3 m with diesel and heptane as fuels. The growth of the fire is studied for these fires by measuring the transient mass burning rates. Water mist is generated by passing plain water at room temperature through single-head solid-cone pressure-swirl nozzles with X-type swirl-inserts. The nozzle is directed vertically downwards and operated at various heights (0.75 m to 2 m) from the fuel surface with the injection pressure ranging from 6 bar to 10 bar. The extinction performances of four nozzles with orifice diameters of 1.2 mm, 1.65 mm, 1.9 mm, and 2.45 mm are investigated through videography. A comparison of the extinction performances by all the nozzles is presented and the optimal nozzle based on the consumption of water is reported for a given fire. An empirical correlation for the extinction time is reported in both the dimensional and non-dimensional form. Observed interactions of the spray with fuel surface are reported depicting probable undesired phenomena in the application of the water-mist system with top injection.

Pressure drop, local heat transfer coefficient, and critical heat flux of DNB type for flow boiling in a horizontal straight tube with R-123

Abstract: As far as design safety and operation of heat exchangers with a horizontal flow are concerned, it is necessary to study local heat transfer coefficient, boiling pressure drop, and critical heat flux for flow in a horizontal tube. In the present experimental work, local axial distribution of heat transfer coefficient, two-phase pressure drop, and critical heat flux for the flow boiling in a horizontal straight tube with R-123 as working fluid has been studied. Experiments are performed in horizontal tubes of diameter 11.9 mm and wall thickness 0.4 mm of SS304, having a heated length of 400 mm, 600 mm, and 1000 mm for the mass flux of 180 to 1210 kg/m2s. The local wall temperature is measured using the Infra-Red thermal imaging technique. The local heat transfer coefficients are compared with six different well-known correlations. Also, the two-phase frictional pressure drop is measured and compared with eight different general correlations. In the present study, a sudden rise in wall temperature at any location of a test section is considered as the occurrence of a boiling crisis. The boiling crisis mechanism observed in the present study is of departure from nucleate boiling (DNB). It takes place in the subcooled, or low quality saturated boiling region and in-between the length of the test sections rather than at exit as in the dry-out type of CHF. The critical heat flux is compared with six different predictive correlations. The mechanism of occurrence of CHF in the present work is found to be a departure from nucleate boiling.

Influence of converging and diverging geometry on the pressure drop distribution in randomly packed beds

Abstract: Packed beds with diverging geometry find applications in packed bed reactors and converging geometry are used in the ethanol fermentation process. Experimental studies are conducted on pressure dro...