This review paper explores the possibilities of the control of heat and mass transfer associated with drought tolerance and freeze tolerance. The accumulation of some metabolites, such as proline and trehalose, are effective for drought tolerance. The special microstructures on the surfaces of some plants and insects in deserts are effective for collecting moisture in the air. Methods of preserving crops will be improved by the mimetic of the drought tolerance. Calcium ions and a protein are effective for the retrieval of damaged cell membrane due to ice formation. Ice crystal growth is inhibited by some substances such as antifreeze proteins. The cryopreservation of foods and organs will be improved by the mimetic of the freeze tolerance.
With the developments of computer technologies, three-dimensional direct numerical simulations (DNS) of turbulent combustion have been realized with a detailed or reduced kinetic mechanism. The 3D DNS gives detailed information about turbulent flames, while there are few experimental techniques which have high accuracy enough to compare with DNS. In this paper, after showing summary of recent DNS of turbulent premixed flames, newly-developed laser diagnostics are presented. Simultaneous CH-OH planar laser induced fluorescence (PLIF) and stereoscopic particle image velocimetry (PIV) are used to investigate the local flame structure of the turbulent premixed flames. From CH-OH PLIF and PIV measurements, flame fronts are identified, and the curvature of the flame front and the tangential strain rate at the flame front are evaluated. The experimental results are compared with 3D DNS of hydrogen-air and methane-air turbulent premixed flames. The flame displacement speeds in turbulent premixed flames have been measured directly by the CH double-pulsed PLIF. Since the time interval of the successive CH PLIF can be selected arbitrarily, both of the large scale dynamics and local displacement of the flame front can be obtained. As an application of laser diagnostics for development of high-efficient and low-emission combustors, reconstruction of 3D flame structure is shown by using multiple-plane OH PLIF.
This study investigated the behavior of pressure drops and heat transfer coefficients for four sets of triangular microchannels. Results of this study indicated that for Reynolds numbers less than 100, the Nusselt number tends to be nearly linearly increasing as the Reynolds number increases. The product of the friction factor and the Reynolds number (fRe) is slightly lower than those predicated by the conventional theory. Besides, high temperature gradient exists in the regions between the inlet and the exit of the flow channel. Furthermore, the difference between the values for Nu of those obtained from the empirical correlation for triangular microchannel and those from the experimental measurements was found to be within 15%.
Recently, lipid bilayers attract a great deal of interest as a material with nanoscale structure. Various devices utilizing lipid bilayers, which include some kinds of sensors and molecular sorting devices, have been proposed. Understanding of thermal energy transfer in the lipid bilayers is important for utilizing the lipid bilayers as a new material for NEMS with nano structures. In this study, we have investigated the energy transfer along and across the bilayer membrane by molecular dynamics simulations of the lipid bilayer in liquid water. We found that along the bilayer membrane, thermal energy flux in the lipid bilayer is much smaller than that in the water layer. On the other hand, in case of thermal energy transfer across the membrane, total thermal resistance of the lipid bilayer-water system is composed of thermal resistances of various parts of the system, including water layer, head group of lipid, and tail hydrocarbon chain of lipid, which exhibit different magnitude of values. It is found that the tail hydrocarbon chains of lipid have the highest thermal resistance.
Opposed flame spread of electric wire in sub-atmospheric pressure is studied experimentally. Thin-polyethylene (PE) coated nickel-chrome (NiCr) and iron (Fe) wire are used as test samples in this study. Total pressure is reduced from atmospheric (100 kPa) to sub-atmospheric (40 kPa) and range of employed external forced-flow speed is from 0 cm/s to 40 cm/s. Results show that the spread rate monotonically decreases, or stays nearly constant, as the forced-flow speed increases regardless of the material of the wire. Dependence of the spread rate on the opposed-flow speed appears differently depending on the material of the wire; with high-conductive material (Fe), decrement trend of the spread rate with wind is suppressed. Importantly, under the conditions considered in this study, the spread rate tends to increase as the pressure decreases regardless of the pressure and the material of the wire. Dependence of the spread rate on pressure is more pronounced with less-conductive (NiCr) wire, whereas less-pronounced with high-conductive (Fe) wire. Qualitative discussions are made to explain the observed spread trend and the importance of the presence of wire to characterize the flame spread of the wire is addressed.
This paper discusses iterative calculation methods to determine the saturation state of pure fluids by using Helmholtz energy equations of state. The commonly used method is based on the successive substitution approach. This method is simple, but requires an aid of ancillary equations to estimate sufficiently accurate initial guesses for the saturation pressure and saturated liquid and vapor densities. In particular, in the vicinity of the critical point very accurate initial guesses are needed. This paper presents an alternative method based on the Newton-Raphson approach. The alternative method does not require accurate initial guesses. Therefore, the aid of ancillary equations is unnecessary. The iterative process is more stable than that in the commonly used method, even if rough initial guesses are given. The usability of the alternative method is demonstrated for several published equations of state.
In the present study, the robust thermal design of a power device package was accomplished using thermal conduction calculation, design of experiment, response surface method and Monte Carlo simulation. Initially, the effects of the design parameters on the solder strain were examined in terms of the thermal expansion difference as a result of unsteady thermal conduction simulation. From the factorial effects of design parameters, the design proposals were screened. Then, robustness of the thermal resistance was evaluated for the three design proposals obtained. The thermal resistances were calculated by solving the steady thermal conduction equation under the design of experiment conditions. The solder thickness, the substrate thickness, and the cooling fin performance were considered as the fluctuation factors, assuming the error associated with manufacturing process. Using a response surface method, the values of thermal resistance were expressed as a function of the design variables. The variances of the thermal resistance were examined based on Monte Carlo simulations. Related to the cooling fin design, the Pareto line showing the trade-off relation between the fin dimension and the fan velocity was obtained. By repeating the Monte Carlo simulations, the Pareto solution was calculated so that the thermal resistances satisfy the criteria in the position of 95 percentile of the thermal resistance variation. Under the same flow velocity conditions, the fin dimensions become about 10% higher compared to the case where the manufacturing error was not taken into account. By carrying out the thermal design following this Pareto line, even if the manufacturing error was taken into consideration, the thermal resistance could satisfy the desired value.
In this research, GTL spray combustion was visualized in an optically accessible quiescent constant-volume combustion chamber. The results were compared with the spray combustion of diesel fuel. Fast-speed photography with direct laser sheet illumination was used to determine the fuel liquid-phase length, and shadowgraph photography was used to determine the distribution of the sooting area in the fuel jet. The results showed that the fuel liquid-phase length of GTL fuel jets stabilized at about 20-22mm from the injector orifice and mainly depended on the ambient gas temperature and fuel volatility. GTL had a slightly shorter liquid length than that of the diesel fuel. This tendency was also maintained when multiple injection strategy was applied. The penetration of the tip of the liquid-phase fuel during pilot injection was a little shorter than the penetration during main injection. The liquid lengths during single and main injections were identical. In the case of soot formation, the results showed that soot formation was mainly affected by air-fuel mixing, and had very weak dependence on fuel volatility.
A micro-grid with the capacity for sustainable energy is expected to be a distributed energy system that exhibits quite a small environmental impact. In an independent micro-grid, “green energy,” which is typically thought of as unstable, can be utilized effectively by introducing a battery. In the past study, the production-of-electricity prediction algorithm (PAS) of the solar cell was developed. In PAS, a layered neural network is made to learn based on past weather data and the operation plan of the compound system of a solar cell and other energy systems was examined using this prediction algorithm. In this paper, a dynamic operational scheduling algorithm is developed using a neural network (PAS) and a genetic algorithm (GA) to provide predictions for solar cell power output. We also do a case study analysis in which we use this algorithm to plan the operation of a system that connects nine houses in Sapporo to a micro-grid composed of power equipment and a polycrystalline silicon solar cell. In this work, the relationship between the accuracy of output prediction of the solar cell and the operation plan of the micro-grid was clarified. Moreover, we found that operating the micro-grid according to the plan derived with PAS was far superior, in terms of equipment hours of operation, to that using past average weather data.
Thermocouples are widely used to measure the local gas temperature due to its accuracy and convenience. However, it is difficult to use thermocouples in a transient phenomenon such as reacting fields. In this study, the unsteady gas temperature inside a combustion chamber was measured by using an improved two-wire thermocouple technique. Based on previous two-wire methods, some modifications were examined. Firstly, numerical analysis of heat transfer between transient flow and thermocouple was performed to see what kind of modification was required. Secondly, a correction term was added to the basic equation, which was validated by experiments using a Rapid Compression and Expansion Machine. Finally, an improved two-wire thermocouple technique was evaluated by measuring the transient gas temperature inside a combustion chamber and compared to the estimated temperature using measured pressure data and assumptions of chemical equilibrium.
The distribution of solar cell modules is planned by referring to the configuration of plant shoots. The object is to develop a solar power generation system with low directivity and a small installation space. In this paper, the amount of insolation that reaches a plant shoot in an arbitrary period was investigated using the “Light received analysis algorithm of a plant shoot” (LAPS) described in a previous report. Based on the analysis, the optimal configuration of the shoot to maximize the amount of light received was determined. The position of the light source on a representative day in summer has a wide range of elevation angles and directions, and has a narrower range in the winter. This paper mainly examines the condensing system of low directivity using the plant shoot of a simple leaf. Based on the relation between the characteristics of these light sources, the shoot configuration for the summer season is optimized by a solar position at 12:00, with considerable solar radiation. The shoot configuration for winter, meanwhile, is arranged so that half the total leaves may absorb solar radiation at a small elevation angle. When the amount of light received by the leaves arranged horizontally and the optimized plant shoot configuration for every month is measured, the difference is found to be modest during the period from March to September. However, a greater amount of light is received in the plant shoot arrangement in January, February, and October to December, based on an optimal solution that is superior to that with the leaves arranged on the level surface.
It is thought that plants have evolved to modulate the amount of light received by the leaves in order to raise the photosynthetic rate. By investigating a plant condensing system, it is small and a directive low condensing system may be able to develop. A compact condensing system with low directivity may be able to be developed by investigating the condensing method by a plant. This paper presents the results of an investigation into light reception characteristics using the numerical-analysis program (LAPS), with emphasis on a kenaf plant (Hibiscus cannabinus) with division leaf of diversity. From this analysis, the relationship between the range of movement for the light source (sun) and the shoot configuration of a kenaf plant were clarified. There is a suitable shoot configuration, and the shoot configuration has a strong influence over the efficiency of light reception. The summer season is characterized by wide oscillations of the light source, and it is therefore necessary for the kenaf plant to adjust its shoot configuration in order to improve light reception.
Externally heated rotary kilns are the most appropriate furnaces to dispose of solid wastes using pyrolysis reactions. The goal of this study was to improve heat transfer in externally heated rotary kilns for waste pyrolysis. We experimentally evaluated the overall heat transfer coefficient km-w as it is an important property of heat transfer. The model wastes were pyrolyzed using an externally heated batch-type rotary-kiln pyrolyzer. Six pairs of thermocouples were attached to the inner and outer surfaces of the drum wall to measure the radial heat flux through it. The heat flux qm was calculated using the radial temperature gradient in the wall. km-w was calculated using the formula, km-w=qm/AdT, where A is the internal surface area of the wall, and dT is the difference in temperature between the inner surface of the wall and the wastes. qm and dT had the highest values when pyrolysis began. However, km-w had the lowest value when pyrolysis began and rose with an increase in waste temperature. When the mean temperature of the kiln's inner wall was 555 °C, km-w rose from 22 W/m2K to 55 W/m2K. Consequently, a higher km-w appeared closer to the end of the drum in a continuous-type kiln.
The effects of rotating speed and internal structure on the performance of an externally heated rotary kiln for waste pyrolysis were investigated. A newly developed method was adopted to evaluate the overall heat transfer coefficient km-w from the inner wall to the wastes for this purpose. The experimental results revealed that km-w monotonically increased with the number of lifters and their height. When six lifters 200 mm in height were attached to the inner wall of the kiln, the mean value of km-w increased from 38.6 W/m2K to 45.3 W/m2K at 2.7 rpm. In addition, km-w increased to 50.1 W/m2K when the rotating speed was increased to 4.0 rpm. In the water vaporization phase during the course of the pyrolysis process, the height of the lifters had a significant influence on km-w. However, the number of lifters had a significant impact on km-w in the pyrolysis phase of the plastic-based wastes. According to measurements, a 10 % increase in km-w could be obtained when installing lifters to attain a ratio of lifter height Hl to the thickness of the waste layer Hw larger than 0.45 or when arc length between two lifters Ll to the arc length of the interface between the wastes and the kiln wall Lw was larger than 1.
Numerical simulation of the hydrothermal process for growing two-inch bulk single crystals of ZnO has been done. The autoclave is assumed to be axisymmetric. The heat transfer by natural convection is discussed for flat and funnel-shaped baffles. The funnel-shaped baffle leads to a significant increase in the flow rate between the raw material zone and the crystal growth zone. However, the temperature difference between the two zones does not become very small. Therefore, the funnel-shaped baffle is effective in the hydrothermal crystal growth process from the viewpoint of transport phenomena. The calculations show that the optimum baffle angle about 20°. Similar results are obtained when the raw material is considered as a porous medium.
Edited and published by : The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan Produced and listed by : Showa Joho Process Co., Ltd.(Vol.8 No.3-) Sanbi Printing Co., Ltd.(Vol.1 No.1-Vol.8 No.2)