Liquid accelerants including kerosene, motor gasoline, and diesel fuel are often encountered in arson cases. The investigator must discover the presence of accelerants at the fire scene. Methods for their detection have been a subject of forensic interest. Visualization of a liquid accelerant at the fire scene was studied. Excitation and fluorescence spectra of liquid accelerants were measured. Broad fluorescence band in the spectral range between ultraviolet and shorter-wavelength region of visible was obtained when the excitation was performed in the ultraviolet spectral range. It is difficult to detect this fluorescence by human eyes. An image intensified CCD camera was used to visualize the fluorescence of accelerants. The experimental results show the applicability of new method to detection of liquid accelerants at the fire scene.
Natural thermal convection of different unmixed liquids is quite different from that of a single liquid because of the existence of liquid-liquid interface. In order to clarify this phenomenon, it is necessary to know both flow and temperature fields of different unmixed liquids. In the present paper, natural convection of different unmixed liquids in a cubic enclosure with isothermal hot and cold walls was investigated. Influence of difference of kinematic viscosities and volume ratio of two liquids on flow and temperature fields were experimentally studied. Temperature distribution on a central cross section was visualized by thermosensitive liquid crystal particles. The conclusions derived from the above experiment are as follows: As the thermal movement occurs through the interface, the reverse speed of two kind of liquids near the interface was promoted. And beside the main circulation that occurred in the liquids of higher volume ratio and lower viscosity ratio, the secondary circulation was caused in the upper liquid.
A visualization study of pulsating laminar flows through U-tubes with a curved section of curvature radius ratios Rc =4, 9.5 and 29 is conducted in order to grasp the effects of Rc and flow parameters on their features. The instantaneous axial velocity profiles are visualized by hydrogen bubble method and are photographed at representative phases. The experiments are performed under the conditions of the Womersley numbers α=5.5, 10 and 18 and the mean Dean numbers Dm=200 and 400, and the flow rate ratios η=0.5 and 1. Detailed descriptions are given of a depression and reversing phenomena in the velocity profile of the flow near the entrance and exit of the curved section and also in the downstream tangent, and the influences of Rc and α on the flow characteristics are made clear. The flow patterns in the velocity profiles of Rc=9.5 similar to those in Rc=4 appear at smaller bend angle in the curved section and does at further station from the bend exit in the downstream tangent. The length required to recover a straight-tube flow in the downstream tangent is shorter than that of a steady flow with the same flow rate as the maximum one in the pulsating flow.
In order to evaluate influence of pad spacing and pad shape on the behaviour of Taylor vortices in submerged multi-pad journal bearings, fluid film flow in bearing clearance and cavity flow between pads were visualized experimentally. Critical Taylor number for the film flow decreased with an increase of pad spacing irrespective of pad shape. Two-dimensional cavity flow field between pads were measured by Particle Image Velocimetry.