Intrinsic isotopic C labelling of polyphenols

The intrinsic isotopic labelling of plants with ¹³CO₂ is an effective method to generate highly labelled compounds using photosynthesis and avoiding labour-intensive complex organic syntheses. In this study, the intrinsic isotopic labelling of polyphenols in parsley, spinach and peppermint is shown for the first time. The plants were grown in an atmosphere where ¹²CO₂ was replaced by ¹³CO₂, in order to generate highly labelled compounds. The total content of ¹³C as well as the individual polyphenols were analysed by Isotopic Ratio-MS and HPLC–Iontrap-MSⁿ.     

Nusselt number correlations for a microchannel heat exchanger hot water supplier with S-shaped fins

Using 3D-CFD code, Nusselt number correlations for a microchannel heat exchanger (MCHE) with S-shaped fins used for hot water suppliers are obtained through numerical experiments and then validated. The supercritical carbon dioxide working fluid is assumed to operate around the pseudo-critical point, where fluid properties change radically. Calculations with 20 different temperatures are executed to produce Nusselt number correlations for each side. The fluid inlet temperature in each calculation is defined as 2 °C lower or higher than the constant wall temperature, respectively, for cold and hot side simulations. The small temperature difference of 2 °C is sufficiently small to regard thermal–hydraulic properties as constant. A new integrating method using the correlations to calculate the heat-transfer-performance is proposed. The resultant heat-transfer-performance is compared with that of another numerical result, which is reduced from large geometry and integration. The results agree within 3% error; the calculation accuracy of the method is confirmed. Experimental results with MCHE verify the correlations. The difference is approximately 5%. Using few computer resources, these Nusselt number correlations and the heat-transfer-performance calculation methods using correlation information are sufficiently accurate to evaluate heat exchangers.     

Three-dimensional numerical simulation of heat and fluid flow in noncircular microchannel heat sinks

A three-dimensional model of heat transfer and fluid flow in noncircular microchannel heat sinks is developed and analyzed numerically. It is found that Nusselt number has a much higher value at the inlet region, but quickly approaches the constant fully developed value. The temperature in both solid and fluid increases along the flow direction. In addition, the comparison of thermal efficiencies is conducted among triangular, rectangular and trapezoidal microchannels. The result indicates that the triangular microchannel has the highest thermal efficiency.     

Non-Fourier heat conduction in a hollow sphere with periodic surface heat flux

Presented is the analysis of non-Fourier effect in a hollow sphere exposed to a periodic boundary heat flux. The problem is studied by deriving an analytical solution of the hyperbolic heat conduction equation. Using the obtained analytical expression, the temperature profiles at outer and inner surfaces of the sphere are evaluated for various thermal relaxation times. By comparing the results of non-Fourier model with those obtained from Fourier heat conduction equation, the transition process from parabolic model to hyperbolic one is shown. The phase difference and amplitude ratio of boundary surfaces are calculated as functions of the thermal relaxation time and the results are depicted graphically.     

Assessment of potential for natural gas-based cogeneration in Thailand

Using the results of a comprehensive data analysis of final energy consumption in industry and commercial buildings, the assessment has been made of the potential for gradual implementation of cogeneration plants in these facilities. In doing so, plans for the expansion of the natural gas pipeline distribution network in Thailand are taken into consideration. The sample comprises of 2540 factories and 1651 commercial buildings from which it was found that 817 factories and 966 commercial buildings were suitable for the implementation of natural gas-based cogeneration technologies until 2020. By the implementation of cogeneration in these facilities, it is possible to save 3.2% of the total primary energy consumption in Thailand in 2003.     

Effect of static magnetic field on a thermal conductivity measurement of a molten droplet using an electromagnetic levitation technique

Recently, a novel method of measuring the thermophysical properties, particularly thermal conductivity, of high-temperature molten materials using the electromagnetic levitation technique has been developed by Kobatake et al. [H. Kobatake, H. Fukuyama, I. Minato, T. Tsukada, S. Awaji, Noncontact measurement of thermal conductivity of liquid silicon in a static magnetic field, Appl. Phys. Lett. 90 (2007) 094102]; this method is based on a periodic laser-heating method, and entails the superimposing of a static magnetic field to suppress convection in an electromagnetically levitated droplet. In this work, to confirm the fact that a static magnetic field really suppresses convection in a molten silicon droplet in an electromagnetic levitator, numerical simulations of convection in the droplet and periodic laser heating in the presence of convection have been carried out. Here, the convections driven by buoyancy force, thermocapillary force due to the temperature dependence of the surface tension on the melt surface, and electromagnetic force in the droplet were considered. As a result, it was found that applying a static magnetic field of 4 T can suppress convection in a molten silicon droplet enough to measure the real thermal conductivity of molten silicon.     

Effect of three-dimensional melt pool convection on process characteristics during laser cladding

A three-dimensional heat transfer model is developed to simulate the cladding process that include the different physical phenomena such as heat transfer, phase changes, addition of powder particles and fluid flow due to Marangoni–Rayleigh–Benard convection. It is found that the Rayleigh–Benard convection is insignificant and Marangoni–Benard convection is dominant for the studied cases. By varying the scanning speed and Marangoni number the melt pool size and strength of convection are changed and its influence on clad built-up geometry, dilution level, maximum and average melt pool temperatures and the form and scale of the microstructure of the solidified clad track has been studied.     

输水隧洞施工盾构管片修补措施

总结了输水隧洞盾构施工过程中盾构管片存在的主要缺陷，从材料选择和修补技术方面，阐述盾构管片修补措施。研究成果可为类似工程施工提供参考。     

Ventilation system with spiral recuperator

A new kind of longitudinal flow spiral recuperator for the heat recovery in ventilation systems of buildings was studied experimentally and analytically.The aim of this work is to analyze the possibility of using air handling units with new type of spiral recuperator in order to recover heat in ventilation systems of buildings. For the reason that the air flows are parallel to the symmetry axis of the longitudinal flow spiral recuperator, in this unit pressure drops are smaller than in commonly known spiral exchangers. Because of the counter flow, a greater value of thermal effectiveness ? is reached for the same value of the number of transfer units in comparison to cross-flow recuperators.The exploitation of the new type of spiral recuperator in winter periods brings significant savings. The results obtained from computations are very encouraging for a widespread use of these devices.     

Pre-treatment to Improve the Bake-hardening Response in the Naturally Aged Al-Mg-Si Alloy

This paper describes pre-treatment methods to improve the bake-hardening response of naturally aged AA6022(Al-0.6Mg-1.0Si),which is an alloy used in automotive body panels.These methods are used to accelerate the artificial aging process,which proceeds 30-day period of natural aging.The precipitation behavior of the sheets of this aluminum alloy was analyzed by differential scanning calorimetry(DSC) and electrical conductivity measurements,and subsequently confirmed by microstructure observations by transmission electron microscopy(TEM).Tensile tests and microhardness measurements were performed to determine the mechanical properties of the samples.Under simulated paint-baking conditions(30 min at 170 ℃),the microhardness and the yield strength(YS) of the pre-strained + pre-aged samples were found to be 113 HV and 225 MPa,respectively.These values are considerably higher than those of pre-aged samples,and they did not decrease significantly during the initial stage of artificial aging.