Internal Vapor Pressure Research Articles

Study of Ultra-High Performance Concrete Mechanical Behavior under High Temperatures.

The main concern with concrete at high temperatures is loss of strength and explosive spalling, which are more pronounced in high-strength concretes, such as Ultra-High Performance Concrete (UHPC). The use of polymeric fibers in the mixture helps control chipping, increasing porosity and reducing internal water vapor pressure, but their addition can impact its mechanical properties and workability. This study evaluated the physical and mechanical properties of UHPC with metallic and PVA fibers under high temperatures using a 23 central composite factorial design. The consistency of fresh UHPC and the compressive strength and elasticity modulus of hardened UHPC were measured. Above 300 °C, both compressive strength and elasticity modulus decreased drastically. Although the addition of PVA fibers reduced fluidity, it decreased the loss of compressive strength after exposure to high temperatures. The response surface indicates that the ideal mixture-1.65% steel fiber and 0.50% PVA fiber-achieved the highest compressive strength, both at room temperature and at high temperatures. However, PVA fibers did not protect UHPC against explosive spalling at the levels used in this research.

Evolution and Modelling of the Moisture Diffusion in Walnuts during the Combination of Hot Air and Microwave–Vacuum Drying

To understand the moisture transfer mechanism of walnuts during the combination of hot air (HA) and microwave–vacuum (MV) drying (HA-MVD) process, the drying characteristics and moisture diffusion characteristics of walnut during HA-MVD were investigated. The results indicated that the HA-MVD of walnuts occurred mainly in the falling-rate stage. The value of effective moisture diffusivity (Deff) dropped continuously with the decrease in moisture content (MC) during the HA drying, while switching to MV drying could truncate the decrease in Deff and still maintain a high value until the end of drying. The HA temperature, MC of the transition point, microwave power, and MV thermostatic temperature have significant effects on the moisture diffusion characteristics of walnuts. The values of Deff for walnuts ranged from 2.33 × 10−9 m2/s to 6.89 × 10−8 m2/s. The third-order polynomial prediction model of Deff related to the sample MC and drying conditions was established to describe the dynamic change in the Deff of walnuts during the HA-MVD process. The application of MVD in the final stage of drying could rapidly increase the internal vapor pressure of the walnuts, accelerate the diffusion speed of the internal moisture, and re-enhance the drying rate. The findings have practical value for the development of efficient and energy-saving drying methods in the walnut industry.

Experimental analysis of temperature and vapor core pressure for an annular heat pipe

The main contribution of this study is the effects of the operating conditions on the internal vapor pressure and temperature in an annular screen wick heat pipe, using distilled water as the working fluid. High-resolution pressure transducers, optical fiber distributed temperature sensors, and K-type thermocouples were employed to measure the internal and external temperatures as well as the local static pressures at different axial positions of the heat pipe. Temporal and frequency analysis using a one-dimensional continuous wavelet transform was performed on the differential pressure data to characterize flow behavior and infer the flow regime occurring within the heat pipe. The heat pipe was tested in multiple orientations with respect to the horizon (θ=0°, 45°, and 90°), heat loads (25, 50, and 75 W), and condenser coolant temperatures (Tw,in= 10 °C, 20 °C, and 30 °C). To estimate the vapor-phase flow friction factor for multiple Reynolds numbers, the Lockhart–Martinelli correlation was employed. This study provides critical experimental data and analyses for complex two-phase flow behavior in an annular wick heat pipe geometry. The thermal resistance and effective thermal conductivity were estimated as a function of the heat pipe orientation and power input. The experimental investigation revealed that power input and orientation influence both the internal vapor core and external surface temperatures, as well as the local pressure response. The outcomes from this study provide a valuable database that supports the advancement of heat pipe design, modeling, and validation.

An ultra-porous g-C3N4 micro-tube coupled with MXene (Ti3C2TX) nanosheets for efficient degradation of organics under natural sunlight

It remains as a challenge for realizing efficient photo-responsive catalysts towards large-scale degradation of organic pollutants under natural sunlight. This work reports a new pore engineering strategy for creating ultra-porous g-C3N4 micro-tubes with an unprecedentedly high specific surface area of 152.96 m2/g. This is mainly associated with releasing internal vapor pressure in the autoclave where the hydrothermal treatment of the urea/melamine mixture is processed. Supported by microscopic observation, porosity measurement and spectroscopic characterization, it is found that releasing the pressure at halfway of hydrothermal process is vital for forming exfoliated rod-like precursors and the de-aggregation of these rods presents substantial benefits on the production of mesopores on g-C3N4 micro-tubes during the calcination of precursors. This offers a large number of reactive sites required by photocatalytic reaction. Coupling these micro-tubes with Ti3C2TX nanosheets via electrostatic interaction yields a 1D/2D heterojunction with a close interfacial contact. The addition of metallically conductive Ti3C2TX nanosheets accelerates the separation between electrons and holes, and also enhances the light absorption. All these merits of structural design lead to forming a group of highly efficient catalysts demonstrating an excellent photocatalytic degradation rate of k = 0.0560 min−1 for RhB dyes under 100 mW/cm2 visible light radiation that micks sunlight outdoors. This laboratory valuation is further supported by an outdoor test that shows a fast degradation rate of 0.0744 min−1 under natural sunlight.

Stress analysis and thermal performance of ultra-thin heat pipes for compact electronics

The ultra-thin heat pipe (UTHP) has been established as a highly effective thermal control component for cooling electronics with large heat generation rate and limited space for cooling. However, UTHP has been severely limited in application because of buckling or breaking on the shell of UTHP during the flattening process. In this study, a series of high-accuracy UTHPs with a thickness of 0.38–0.47 mm were fabricated by the phase-change flattening process. An internal vapor pressure model of the heat pipe during flattening was constructed and the heat transfer performances of UTHPs under different working conditions were experimentally investigated. According to the internal vapor pressure model, the pipe wall stress after flattening was the first to reach the yield strength of the material, and the upper limit heating temperature of UTHPs decreased with the decrease of flattened thickness. The maximum heat transfer capacity decreased with the decreased flattened thickness. UTHP with a thickness of 0.47 mm has a maximum heat transfer capacity of 4.5 W and a minimum thermal resistance of 0.64 °C/W. Moreover, gravity appeared to impose minimal effects on the heat transfer performance of UTHPs and the heat transfer capabilities of the UTHPs fluctuated within ±0.5 W for different gravity orientations.

Experimental study on dual-evaporator based microchannel flat loop thermosyphon (DE-MFLTS) waste heat recovery system

Multi-evaporator flat loop thermosyphon is multi-source heat exchange equipment with favourable application prospects in data centers. A new dual-evaporator microchannel flat loop thermosyphon (DE-MFLTS) system was presented in this article to improve the thermal environment of data centers. Two evaporators made of microchannel flat plates were innovatively installed inside the data cabinet to enable efficient and precise cooling for different servers, where the condenser is installed outside the data center room by a water-cooled separated loop construction. The temperature characteristics, heat recovery efficiency, and internal vapor pressure of the DE-MFLTS system were analyzed by experiments at various cooling water supply temperatures (from 15 °C to 24 °C) and various cooling water flow rates (from 200 l/h to 600 l/h) respectively. The two evaporators could maintain excellent temperature homogeneity under various operating conditions. The system demonstrated the best heat recovery efficiency of 82% under identical conditions when the cooling water supply temperature was 15 °C and the cooling water flow rate was 300 l/h. Compared with the single-evaporator system, the DE-MFLTS system had better performance in heat recovery efficiency. This research has significant implications for data centers’ energy efficiency and emissions reduction.

Nucleate boiling of thin liquid films on nanostructured surfaces with hybrid wettability using molecular dynamics simulation

The development in nanotechnology and bionics has increased the application of hybrid wettable nanostructured surfaces in engineering and science research. This study employed molecular dynamics to investigate the phase changes of thin liquid films on nanostructured surfaces with hybrid wettability. The liquid film and nanostructured surfaces were consisted of Lennard–Jones (LJ) fluid and LJ solid atoms, respectively. The simulation results indicate that the microscopic mechanism of nucleate boiling is facilitated by the original residual vapor nuclei. Additionally, the competition mechanism between the hybrid surface wettability and nanostructure is identified. The initial nucleation temperature for a solid wall with a hydrophobic nanocavity is 1.09ε/kB, which is 0.04ε/kB less than that for a hydrophilic nanocavity. This phenomenon can be attributed to the original residual vapor nuclei generated by hydrophobic nanocavities, which induce a piston-like effect at the vapor–liquid interface. As the nanocavity hydrophobicity increases, the piston-like effect increases the internal vapor pressure within the cavity and reduces the initial waiting time for bubble nucleation. For the hydrophilic nanocavities with contact angles greater than 18°, the bubbles are initially generated on the smooth surface rather than the nanocavity. Moreover, the smooth surface wettability is instrumental in bubble nucleation and growth. When the contact angle of the nanocavity is less than 18°, the nanostructures are dominant, and the bubbles are generated only in the nanocavity. These findings can aid the design, manufacture, and performance optimization of micro/nano-systems and devices.

Strategy for preventing explosive spalling and enhancing material efficiency of lightweight ultra high-performance concrete

The highly dense structure which causes the risk of explosive spalling is one of the major limitations of using ultra high-performance concrete (UHPC). This study developed a lightweight UHPC (L-UHPC) and proposed a strategy to improve its material efficiency and lower the risk of explosive spalling. High-strength hollow glass microspheres and fine lightweight aggregates were jointly used in the UHPC system to achieve light weight and ultra high strength. The L-UHPC was cured at different curing regimes to maximize its material efficiency and prevent its spalling after exposure to high temperature. The experimental results showed that the combination of lightweight materials and dry heat curing was effective in reducing the density (<1800 kg/m3) and enhancing the compressive strength (>150 MPa) of the L-UHPC. By means of minimizing the amount of internal free water, the heat curing approach contributed to avoiding the thermal spalling of the L-UHPC exposed to fire conditions. Microstructural results indicated that the elevated temperature curing promoted the pozzolanic reaction and increased the microhardness of the paste matrix by increasing silicate polymerization of the C-S-H structure. The created voids of the collapsed glass microspheres might accommodate some internal vapor pressure and mitigate the degradation caused by the high temperature exposure. The synergetic effect of the porous materials and the dry heat curing lowered the thermal conductivity and significantly improved the material efficiency of the L-UHPC.

Reinforcing effects of gypsum composite with basalt fiber and diatomite for improvement of high-temperature endurance

In this study, plaster materials composed of gypsum, basalt fiber (BF), and diatomite additives were produced, and the combined effects of high-temperature-resistant BF and porous, lightweight siliceous diatomite on the thermal and mechanical endurance of the resulting composite at high temperatures were studied. At room temperature, the incorporation of 0.5 wt% BF improved the bending and compressive strength by 43% and 16%, respectively, which showed a better improvement than the 1 wt% BF incorporation, with the respective numbers of 8% and 7%. The reinforcing effect of BF is discernible at elevated temperatures; however, the reinforcing effect is lost up to 600 ℃ due to fiber failure. Diatomite significantly alleviated the formation and propagation of cracks in the gypsum composite at high temperatures by forming a porous structure that created pathways for releasing internal vapor pressure at high temperatures. The thermal conductivity values decreased from 0.411 to 0.364 W/mk as the diatomite content increased to 20 wt%, however, the polar surface energy of BF modified the growth of the gypsum crystals, resulting in an increased thermal conductivity of the composite. Furthermore, changes occurring in the morphology and chemical composition of the gypsum composite following heat-treatment were analyzed by the differential scanning calorimetry, X-ray diffraction, and scanning electron microscope. The results obtained validate the usage of BF and diatomite as potential additives for improving the performance of gypsum composites as fire protection materials in building construction.

A comprehensive evaluation of fracture toughness, fracture energy, flexural strength and microstructure of calcium aluminate cement concrete exposed to high temperatures

In this study, a comprehensive experimental program was developed to determine the microstructural, mechanical, and fracture features of calcium aluminate cement concrete (CACC) after exposure to high temperatures. The residual fracture parameters, including fracture toughness, fracture energy, and characteristic length, were obtained based on RILEM recommendations. In addition, XRD and SEM were used to evaluate microstructural changes after exposure to different temperatures. Mechanical properties such as the residual compressive, tensile, and flexural strengths, as well as the elastic modulus, were also assessed. The SEM images revealed that the voids among the particles increased due to increasing internal vapor pressure, indicating that the number of pores in the concrete structure increased. Furthermore, the results showed that after subjecting the specimens to high temperatures, the concrete became more ductile, which may be due to the increase in the number of pores after water evaporation. The residual fracture energy of CACC was observed to increase with increasing temperature. However, the residual fracture toughness and flexural strength decreased as temperatures increased. In addition, the results demonstrated that, above 400 °C, the weight loss in the concrete is mainly due to the evaporation of chemically bound water and decomposition of cement hydration compounds, which are chemical processes.

Explosive Spalling Behavior of Single-Sided Heated Concrete According to Compressive Strength and Heating Rate.

In this study, the effects of heating rate and compressive strength on the spalling behavior of single-sided heated ring-restrained concrete with compressive strengths of 60 and 100 MPa were investigated. The vapor pressure and restrained stress inside the concrete were evaluated under fast- and slow-heating conditions. Regardless of the heating rate, the concrete vapor pressure and restrained stress increased as the temperature increased, and it was confirmed that spalling occurred in the 100-MPa concrete. Specifically, it was found that moisture migration and restrained stress inside the concrete varied depending on the heating rate. Under fast heating, moisture clogging and restrained stress occurred across the concrete surface, causing continuous surface spalling for the 100-MPa concrete. Under slow heating, moisture clogging occurred, and restrained stress continuously increased in the deep area of the concrete cross-section owing to the small internal temperature difference, resulting in explosive spalling for the 100-MPa concrete with a dense internal structure. Additionally, while the tensile strength of concrete is reduced by heating, stress in the heated surface direction is generated by restrained stress. The combination of stress in the heated concrete surface and the internal vapor pressure generates spalling. The experimental results confirm that heating rate has a significant influence on moisture migration and restrained stress occurrence inside concrete, which are important factors that determine the type of spalling.

Influence of three stage ultrasound—intermittent microwave—hot air drying of carrot on physical properties and energy consumption

Innovative drying technologies are frequently introduced to minimize various disadvantages of hot air dryers such as high energy consumption and low quality dried products. The aim of this study was to investigate the influence of ultrasound (40 kHz for 10, 20, and 30 min) and intermittent microwave (360, 600 and 900 W at pulse ratios of 1, 2, 3 and 4) on physical properties of carrot during low temperature hot air drying at 40˚C. Drying time decreased during continuous microwave drying (pulse ratio of 1) due to higher internal temperature and water vapor pressure of the samples. The lowest bulk density was observed when ultrasound was applied for 30 min at 900 W microwave power with pulse ratio of 1. This result was attributed to a higher number of micro-channels created in the samples, which led to generate a higher porosity. Shrinkage of the samples decreased by increasing microwave power due to a shorter application time of microwave at higher powers. By extending ultrasound application time, rehydration increased by 17.8% as a result of enhanced cell permeability and higher capacity for water absorption. In addition, specific energy consumption decreased by 38.1% by increasing microwave power owing to lower drying time. Overall, the combined drying method improved physical properties of dried carrots and decreased energy consumption, suggesting a suitable alternative for industrial applications.

Mechanism of Increasing the Permeability of Water-Bearing Coal Rock by Microwave Steam Explosion

Microwave heating of water-bearing coal can promote pore water evaporation. The pores are broken under the action of steam pressure, increasing the permeability of the coal. This study is aimed at investigating the mechanism of permeability improvement of water-bearing coal rock by microwave steam explosion. First, a microwave oven was used to irradiate and heat five groups of coal rock with different water contents; the NMR test was then conducted on the heated sample. Second, the internal vapor pressure and temperature changes during the heating process were obtained through the T-connector for samples with different water contents. Finally, a numerical experiment was used to explore the deformation characteristics of pores under three filling conditions. The experimental results showed that the total porosity increased significantly when the water content of coal increased from 0% to 8%, while the permeability increased by nearly 4.78 times. The extreme value of gas pressure inside the sample showed an increasing trend. The gas pressure and temperature were in line with the equation of state for an ideal gas during the rising phase. Numerical experiments showed that the pore boundary shrunk inward under vacuum conditions, and compressive stress appeared at the tip. The saturated humid air and liquid water conditions expanded the pore boundaries outward and caused tensile stress at the tip, with the latter being nearly 2.3 times larger than the former, making it more conducive to the development of pores. The findings of this study can be used as a reference value for the expansion of coalbed methane extraction technology.

Control of Heat Capacity of Moisture Sensor by Galvanic Arrays with Micro/Nano Gap

1. IntroductionDew condensation causes plant disease, metal corrosion, glass fogging and so on. In order to prevent dew condensation, its detection in early stages and preferably in advance should be followed by lowering relative humidity on the target. However, it is difficult to realize early and advanced detection of dew condensation accurately and in a short time by using current technologies such as hygrometer. Therefore, we have developed a sensor to detect fine water molecules directly. It has different metal arrays which are alternately arranged at fixed intervals (minimum distance: 100 nm). When water droplet or molecules cross over the adjacent arrays of the sensor, electric current flows spontaneously by the galvanic effect [1,2]. In addition, wettability of this sensor’s surface was changed [3]. Furthermore, the surface condition of the sensor could be made closer to that of the target for dew condensation if its surface temperature was controlled. So far, the temperature of the sensor surface was able to be changed from the back of silicon chip by using a Peltier device [2]. Taking into account actual application of this sensor, however, such Peltier device should not be adopted because the electric circuit for measurement and control becomes more complicated and the power consumption increases. Instead, it is suggested that heat capacity of the sensor can be close to the target by attaching a heat sink on the back of the silicon chip. Therefore, the purpose of this study was to clarify the influence of the material and weight of the heat sink on changing behaviour of the temperature of the sensor surface.2. Experimental methodSilicon wafer covered with a silica layer was used as the substrate of a sensor chip. Arrays of Al and Au were alternately arranged with 1 μm in width and 0.2 μm in thickness on the substrate to form an opposing interdigit structure and used as the electrodes. After fabrication of the electrodes, the wafer was cut into a 5mm square chip after Pt wires was also placed on the chip surface near the edge of the chip. The sensor chip was adhered on an aluminum lead frame. Except areas for the arrays, the rest surface of the chip was covered with the resin to make a sensor package. Electric current between two electrodes of Al and Au were measured by the hand-made device with precise amperemeter. The temperature of the sensor chip was estimated from after calibrated straight line of electric resistance of Pt as a function of changing temperature. Heat capacity of the sensor was varied by attaching a heat sink directly to the backside of a sensor package through a window which was open in the resin of the package. In this study, aluminum and copper were used as the heat sink and their volume was varied; 109 (cylindrical), 378 and 818 (cylindrical with rectangular) mm3. Temperature of a sensor was changed by putting it into a chamber and its internal temperature and water vapor pressure were controlled for 840 sec at 1 kPa from 25℃, respectively.3. Results and discussionTemperature changing rate of the sensor was calculated from the slope of temperature with the square root of time. It was plotted as a function of additional heat capacity of the sensor with and without heat sink and results at cooling process were shown in Fig. 1. The temperature changing rate of the sensor was decreased by adding heat sinks to the sensor and it seems to be related almost linearly with the additional heat capacity. This means that it is possible to make temperature change of the sensor with close to that of the target when it becomes important on application such as dew condensation detection.4. ConclusionThis study clarified that the heat capacity of moisture sensor could be controlled by attaching heat sink of metals directly on a part of the sensor. Since the wettability of the sensor had been already controlled successfully, the surface status of the sensor could be made closer to the target on application that this sensor is needed even when the temperature of the target is changed.5. Reference[1] J Kawakita et al., ECS trans., 75 (2017) 51.[2] Y. Kubota et al., Sensors and Actuators A: Phys., 303 (2020) 111838.[3] R.G. Shrestha et al., Sensors, 19 (2019) 4500. Figure 1

Mechanical Properties of Ultra-High Performance Concrete before and after Exposure to High Temperatures.

Compared with ordinary concrete, ultra-high performance concrete (UHPC) has excellent toughness and better impact resistance. Under high temperatures, the microstructure and mechanical properties of UHPC may seriously deteriorate. As such, we first explored the properties of UHPC with a designed 28-day compressive strength of 120 MPa or higher in the fresh mix phase, and measured its hardened mechanical properties at seven days. The test variables included: the type of cementing material and the mixing ratio (silica ash, ultra-fine silicon powder), the type of fiber (steel fiber, polypropylene fiber), and the fiber content (volume percentage). In addition to the UHPC of the experimental group, pure concrete was used as the control group in the experiment; no fiber or supplementary cementitious materials (silica ash, ultra-fine silicon powder) were added to enable comparison and discussion and analysis. Then, the UHPC-1 specimens of the experimental group were selected for further compressive, flexural, and splitting strength tests and SEM observations after exposure to different target temperatures in an electric furnace. The test results show that at room temperature, the 56-day compressive strength of the UHPC-1 mix was 155.8 MPa, which is higher than the >150 MPa general compressive strength requirement for ultra-high-performance concrete. The residual compressive strength, flexural strength, and splitting strength of the UHPC-1 specimen after exposure to 300, 400, and 500 °C did not decrease significantly, and even increased due to the drying effect of heating. However, when the temperature was 600 °C, spalling occurred, so the residual mechanical strength rapidly declined. SEM observations confirmed that polypropylene fibers melted at high temperatures, thereby forming other channels that helped to reduce the internal vapor pressure of the UHPC and maintain a certain residual strength.

Improvement of in-situ Fe/MgB2 monofilamentary wires by internal Mg-coating process

In the present work, we have studied on the use of internally Mg-coated and uncoated iron tubes in processing of in-situ mono filamentary Fe/MgB2 wires by means of transport measurements and structural analysis methods. For coated wires, the starting Fe tube is internally coated by magnesium before PIT process is applied and these wires with 0.81 mm in diameter are heat treated at different annealing temperatures and times. The main idea behind this work is to investigate the possible role of Mg coating on inhibition of Fe2B phase formation and its contribution to granular structure of MgB2 core. The transport and superconducting properties in the presence of external magnetic field are well improved for Mg-coated wire samples in comparison to the uncoated wire samples. The structural and surface analyses of Mg-coated wires reveal that the Fe2B formation still exists at the interface region. The results are interpreted in terms of effects of excess magnesium, internal Mg vapor pressure, homogeinity of Mg coating process, and heat treatment conditions. The highest engineering critical current density Jce(4.2 K) is obtained as greater than 5.4 × 104 A/cm2 at μ0H = 4 T among the coated samples.

Identifying drivers of leaf water and cellulose stable isotope enrichment in Eucalyptus in northern Australia.

Several previous studies have investigated the use of the stable hydrogen and oxygen isotope compositions in plant materials as indicators of palaeoclimate. However, accurate interpretation relies on a detailed understanding of both physiological and environmental drivers of the variations in isotopic enrichments that occur in leaf water and associated organic compounds. To progress this aim we measured δ18O and δ2H values in eucalypt leaf and stem water and δ18O values in leaf cellulose, along with the isotopic compositions of water vapour, across a north-eastern Australian aridity gradient. Here we compare observed leaf water enrichment, along with previously published enrichment data from a similar north Australian transect, to Craig-Gordon-modelled predictions of leaf water isotopic enrichment. Our investigation of model parameters shows that observed 18O enrichment across the aridity gradients is dominated by the relationship between atmospheric and internal leaf water vapour pressure while 2H enrichment is driven mainly by variation in the water vapour-source water isotopic disequilibrium. During exceptionally dry and hot conditions (RH<21%, T>37°C) we observed strong deviations from Craig-Gordon predicted isotope enrichments caused by partial stomatal closure. The atmospheric-leaf vapour pressure relationship is also a strong predictor of the observed leaf cellulose δ18O values across one aridity gradient. Our finding supports a wider applicability of leaf cellulose δ18O composition as a climate proxy for atmospheric humidity conditions during the leaf growing season than previously documented.

Formulation of SrO-MBCUS Agglomerates for Esterification and Transesterification of High FFA Vegetable Oil

Musa Balbisiana Colla Underground Stem (MBCUS) catalyst was treated thermally mixing with 5:1 w/w of Strontium Oxide (SrO) and the dynamic sites were reformed. The MBCUS-SrO showed sharper crystalline phases as evidence from XRD and TEM analysis. The composition and morphology were characterized from BET, SEM, EDX thermo-gravimetric analysis (TGA) and XRF analysis. The optimization process for biodiesel production from Jatropha curcas L oil (JCO) having high percentage of free fatty acids was carried out using orthogonal arrays adopting the Taguchi method. The linear equation was obtained from the analysis and subsequent biodiesel production (96% FAME) was taken away from the JCO under optimal reaction conditions. The biodiesel so prepared had identical characteristics to that with MBCUS alone, but at a lower temperature (200˚C) and internal vapour pressure. Metal leaching was much lower while reusability of the catalyst was enhanced. It was also confirmed that the particle size has little impact upon the conversion efficacy, but the basic active sites are more important.

내화피복공법 적용 고강도 콘크리트의 내화성능 확보 방안에 관한 실험적 연구

Owing to the dense internal organization of high-strength concrete, water vapor generated within the concrete cannot be easily discharged to the outside. The increased internal vapor pressure leads to a phenomenon known as spalling. This study investigated the use of fire-protection covering methods for preventing the spalling of high-strength concrete in order to inhibit temperature transmission to concrete structure by covering the material and to minimize the increase in cross-section. The fire-protection covering methods considered included fireproof plaster boards, high-performance fireproof plaster boards, and a composite covering method (fireproof plaster board + intumescent coating system). Among these, the high-performance fireproof plaster board exhibited 20~40 % higher fire protection performance compared to the regular fireproof plaster board. If the composite covering material is exposed to high-temperature fires, especially above <TEX>$500^{\circ}C$</TEX>, a 4 mm-thick intumescent coating system extends up to at least 50 mm, thereby blocking most of the heat transferred inside the board and suppressing the temperature increase within the concrete. The above-mentioned mechanism leads to more than 40 % decrease in the coating thickness. The restrictive application of this method could reinforce fire protection performance on finishing parts of gypsum board in existing buildings.

Preparation and Characterization of Musa balbisiana Colla Underground Stem Nano-material for Biodiesel Production Under Elevated Conditions

A high free fatty acid (FFA) containing Jatropha curcas L. oil (JCO) was used for biodiesel production using Musa balbisiana Colla underground stem (MBCUS) ash catalyst, in a high pressure–high temperature (HT) reactor. The composition of the MBCUS catalyst was ascertained using XRF analysis and found that the ash obtained at 550 °C contain about 36 % silica (SiO2), 25 % potassium oxide (K2O), 10 % each of lime (CaO) and magnesia (MgO) and 4 % each of phosphorous pentoxide (P2O5) and alumina (Al2O3) as the major component for catalytic activation. The catalyst was characterized by SEM–EDX image analysis and found that the composition of the catalyst is versatile and consist of several alkali and alkaline earth metal chlorides, oxides, carbonate and silica. The BET surface area was found to be about 39 m2/g. The catalyst was further calcined in a TGA and observed that a maximum of 10 % losses were possible at 991 °C. The catalyst structure was further characterized from TEM images and found that the structural dimensions are identical (less than 100 nm length) and brick like (70 nm × 20 nm × 15 nm). The catalyst was found very effective during transesterification under HT (275 °C) and internal pressure (4.2 MPa) and 98.0 % fatty acid methyl ester (FAME) could be obtained from JCO with an initial acid value (AV) 18.4 mg KOH/g. There was a drastic reduction of FFA (AV 3.4 mg KOH/g) in the FAME obtained. The reduction of FFA may be attributed to the HT and high internal vapour pressure of the reaction mixture that resulted conversion of FFA to FAME and water. The fuel properties of the FAME were analysed as per ASTM and EN-standards.