Akira Narumi

The Measurement of Transient Two-Dimensional Profiles of Velocity and Fuel Concentration Over Liquids

We recently developed two different optical techniques in order to simultaneously measure transient two-dimensional profiles of velocity, temperature, and fuel concentration that were generated by a spreading flame over liquid fuels. One technique employs a particle-track system combined with a laser-sheet system (LSPT) and a high-speed camera, while the other technique employs dual wavelength holographic interferometry (DWHI). The LSPT system revealed transient two dimensional profiles of flame-induced flow, while DWHI revealed two-dimensional profiles offuel concentration over liquids. In this paper we present a series of velocity profiles for a pulsating flame spread over I -propanol and concentration profiles for gaseous 1-propanol determined with LSPT and DWHI, respectively.

The effect of a cold temperature valley on pulsating flame spread over propanol

The transient three-dimensional structures of velocity and temperature created by a pulsating flame spread over normal propanol were constructed from five independent transient measurements using five different techniques: laser sheet particle tracking (LSPT): smoke tracing (ST); dual wavelength holographic interferometry (DWHI): infrared thermography (IR): and high-speed photography (HSP). These measurements showed that the pulsating flame spread consists of five distinctly different steps. The first step is the onset of pulsation created by the stagnation of flame spread over the liquid, which is followed by the second step, formation of a cold liquid valley near the flames leading edge, and the third step, accumulation of liquid fuel vapor over the liquid surface. In the fourth step, the flame jumps through the formed premixed gas layer, leading to the final step, the cessation of spread. After the fifth step, the process returns to the first step, completing the entire pulsation cycle. Our experimental data confirm the formation of a small gas-phase circulation cell, as predicted by the University of California, Irvine, numerical model, and support the idea that the pulsating spread is triggered by the subsurface liquid convection that affects the gas-phase flow and the fuel vapor concentration. The second result is unique and suggests that a cold temperature valley formed on the liquid surface would play an important role in the mechanism of pulsating spread.

Simultaneous measurement of temperature and chemical species concentrations with a holographic interferometer and infrared absorption.

What is believed to be a new technique that allows for the simultaneous measurement of 2D temperature and chemical species concentration profiles with high spatial resolution and fast time response was developed and tested successfully by measuring a thin layer of fuel vapor created over a volatile fuel surface. Normal propanol was placed in an open-top rectangular container, and n-propanol fuel vapor was formed over the propanol surface in a quiescent laboratory environment. An IR beam with a wavelength of 8-13 mum emitted from a heated plate and a He-Ne laser beam with a wavelength of 632 nm were combined and passed through the n-propanol vapor layer, and both beams were absorbed by the vapor layer. The absorption of the IR beam was recorded by an IR camera, and the He-Ne laser was used to form a holographic interferogram. Two-dimensional temperature and propanol vapor concentration profiles were, respectively, determined by the IR absorption and the fringe pattern associated with the holographic interferogram. This new measurement technique is a significant improvement over the dual wavelength holographic interferometry that has been used previously to measure temperature and fuel concentration, and it is ready for application under different types of fire and flame conditions.

A study on ice crystal formation behavior at intracellular freezing of plant cells using a high-speed camera.

Intracellular ice crystal formation (IIF) causes several problems to cryopreservation, and it is the key to developing improved cryopreservation techniques that can ensure the long-term preservation of living tissues. Therefore, the ability to capture clear intracellular freezing images is important for understanding both the occurrence and the IIF behavior. The authors developed a new cryomicroscopic system that was equipped with a high-speed camera for this study and successfully used this to capture clearer images of the IIF process in the epidermal tissues of strawberry geranium (Saxifraga stolonifera Curtis) leaves. This system was then used to examine patterns in the location and formation of intracellular ice crystals and to evaluate the degree of cell deformation because of ice crystals inside the cell and the growing rate and grain size of intracellular ice crystals at various cooling rates. The results showed that an increase in cooling rate influenced the formation pattern of intracellular ice crystals but had less of an effect on their location. Moreover, it reduced the degree of supercooling at the onset of intracellular freezing and the degree of cell deformation; the characteristic grain size of intracellular ice crystals was also reduced, but the growing rate of intracellular ice crystals was increased. Thus, the high-speed camera images could expose these changes in IIF behaviors with an increase in the cooling rate, and these are believed to have been caused by an increase in the degree of supercooling.

Effects of micro electric current load during cooling of plant tissues on intracellular ice crystal formation behavior and pH.

Cryopreservation techniques are expected to evolve further to preserve biomaterials and foods in a fresh state for extended periods of time. Long-term cryopreservation of living materials such as food and biological tissue is generally achieved by freezing; thus, intracellular freezing occurs. Intracellular freezing injures the cells and leads to cell death. Therefore, a dream cryopreservation technique would preserve the living materials without internal ice crystal formation at a temperature low enough to prevent bacterial activity. This study was performed to investigate the effect of micro electrical current loading during cooling as a new cryopreservation technique. The behavior of intracellular ice crystal formation in plant tissues with or without an electric current load was evaluated using the degree of supercooling, degree of cell deformation, and grain size and growing rate of intracellular ice crystal. Moreover, the transition of intracellular pH during plant tissue cooling with or without electric current loading was also examined using the fluorescence intensity ratio to comprehend cell activity at lower temperatures. The results indicated that micro electric current load did not only decrease the degree of cell deformation and grain size of intracellular ice crystal but also reduced the decline in intracellular pH due to temperature lowering, compared with tissues subjected to the same cooling rate without an electric current load. Thus, the effect of electric current load on cryopreservation and the potential of a new cryopreservation technique using electric current load were discussed based on these results.

Section B Fire and Explosion - Scale Modeling of Biomass Fire Associated with Hydrogen-Producing Bacteria

This paper details a fundamental study for developing a safe handling system for waste biomass fuels, especially for the prevention of fires and explosions associated with refuse-derived fuels (RDF). Unlike conventional solid fuel, RDF is a living fuel that contains various kinds of bacteria among which flammable gases such as hydrogen and methane may be produced during biological fermentation in the proper circumstances. The RDF storage silo at the Mie prefectural RDF power plant unexpectedly exploded in 2003, and firefighter deaths and injuries were reported. Though flammable gas production was the suspected cause of the explosion, there is disagreement about whether the flammable gas was produced by the biological fermentation or by thermal decomposition of the RDF materials. Due to the difficulties in conducting both the experiments and numerical simulations in a full-scale mock-up silo, the detailed explosion mechanism has not been explained since 2003. On the basis of scale modeling principles, this study begins with determining the physical or chemical laws which govern the phenomena of the accident. For this purpose, flammable gas production tests were conducted using two kinds of RDFs, which were provided from two manufacturers: Kuwana and Sakura. The RDF hydrogen production ability was affected by pH, moisture, and ambient temperature. The microbial colony count method revealed that aerobes occupied a dominant position in RDF on the second or third day from the beginning, whereas anaerobes occupied a dominant position hereafter. Bacillus sp. was superior to Clostridium sp. in Kuwana, whereas Clostridium sp. was superior to Bacillus sp. in Sakura after 3 days of cultivation. Scale effects on the temperature rise of RDF due to biological activities were examined using three different amounts of RDFs. It was found that the higher the amount of RDF, the higher the maximum temperature obtained after 50–85 h cultivation.

Measurement of Microclimate within Clothing Using the Combination Technique of Infrared Ray Absorption Method And Holographic Interferometry

The wear comfort depends on the condition of micro-space between cloth and skin of human body. Heat and mass transfer occurs through clothing due to heat and sweat evaporation release from human body in this space. This paper applied a new measurement technique that combines infrared ray absorption method and holographic interferometry to this space to obtain the transient temperature and concentration distributions without and within cloth. The porous films with known specification were used for cloth to verify the usefulness of this technique. The measuring results were visualized by superimposing infrared ray image and interferogram to understand easily the passing behaviors of vapor through cloth. The calculated results of temperature and concentration distributions showed some significant differences in the permeation behaviors of vapor due to film. They fundamentally agreed with the property of film. As a result, this measurement technique was proved to be useful for microclimate within and without clothing.

The passing behaviors of vapor through cloth

There occurs heat and mass transfer through cloth in the very small space from skin to the outside of cloth due to the release of heat and sweat evaporation from human body. The new simultaneous 2-D measurement technique of temperature and concentration distributions that combines infrared absorbing method (IR) with holographic interferometry (HI) was applied to this space. Cotton (porosity Φ=0.586, thickness t=324μm) and nylon (Φ=0.578, t=347μm) were used for the typical hydrophilic and hydrophobic clothes, respectively. N-propanol was used for liquid. The distance from liquid surface to cloth was 5mm. Liquid temperature was 40°C. The superimposed images of HI and IR show clearly that more vapor passes through cloth in the case of cotton than in the case of nylon. This fact demonstrates that this new technique is very useful for measuring the passing behaviors of vapor through cloth. We appreciate that this research was partially supported by funds of Grant-in-Aid for Scientific Research in Japan.

Simultaneous Visualization of Velocity and Temperature Fields of Transient Natural Convection

A new visualization technique to measure transient 2-D profiles of velocity and temperature was developed. Particle tracking velocimetry (PTV) and real time holographic interferometry (HI) are combined into the new technique, and it will be called as HI-PV. HIPV’s accuracy depends on the clarity of separation of PTV and HI images. We propose two different techniques to separate PTV and HI images: (1) separate two images using a digital image processing after recording the superimposed image with a digital video camera and (2) record the two images separately by two digital video cameras attached with blue or red color filter. HI-PV was applied to the transient natural convection of water around two cooling tubes. Water: initial temperature = 13C was cooled by two tandem cooling tubes: surface temperature = -4.3C, and natural convection with density inversion occurs. A numerical calculation was also made and its results were favorably compared to the corresponding visualized results by HI-PV. HI-PV is proven to be a very useful technique to measure simultaneously transient 2-D profiles of velocity and temperature. Separation Separation Superimposed and Separated Images Obtained by HI-PV

Cooling and Freezing of Water around Two Horizontal Tubes Placed in Vertical Arrangement. Effect of Tube Diameter and Vertical Separation Distance.

When water is cooled and frozen around two horizontal cooling tubes placed in vertical arrangements in an enclosure, natural convection with density inversion is caused. This natural convection has both downward and upward flow, and these flows interfere with each other between the two cooling tubes. The process of cooling and freezing the water is much influenced by this flow interference. We studied this influence by experimental visualization and numerical calculation, and already reported on the basics of this influence. In this paper, we discuss the effect of the tube diameter and the separation distance on the process of cooling and freezing the water with this flow interference. The tube diameter and the separation distance have the great effects on the development of the density inversion flow, the release of supercooling and the heat transfer characteristics.