一种微波加热装置的风冷散热研究

微波加热装置工作过程会散发大量的热量,如果不能及时排出,会造成输出功率的下降.本文以九个磁控管加热单元组成的微波加热装置为研究对象,首先提出一种风冷散热结构设计,接着通过Fluent热仿真软件验证结构设计的合理性,然后通过对比分析加热装置进风口位置、面积大小等因素对散热效果的影响,对散热结构进行改进,进一步提高了内部磁...     

HL-1装置等离子体特性的初步研究

HL-1装置在环向磁场2.3T下运行,获得135kA平衡稳定等离子体,平顶时间160ms。实验表明,环向磁场杂散分量约为纵场的万分之一,导体壳和平衡场基本上能保证等离子体的平衡。观察到的电子温度约500eV,平均电子密度2.8×10~(13)cm~(-3),能量约束时间10ms,有效电荷数小于3,最低稳定运行安全因子2.5,最长放电持续时间1040ms。在对MHD稳定性进行观察的基础上,确定了稳定运行区域;极限密度服从Murakami定标律。     

金刚石/ZnSe结构中瞬态热栅场的有限元法分析

利用有限元法分析计算了脉冲激光激发瞬态热栅在金刚石薄膜/ZnSe衬底双层结构中的三维温度场分布及变化。通过比较不同厚度金刚石薄膜样品的温度场分布,结果显示金刚石薄膜的厚度对样品中温度场的分布有较大影响,随着薄膜厚度的增大,峰值温度提高并且二次加热现象更加明显。     

Laser pulse heating: Cavity formation into steel, nickel and tantalum surfaces

The cavity formation during laser pulse heating of steel, nickel, and tantalum is examined and evaporation rate from the cavity surface is predicted. The mushy zones generated across the vapor–liquid and liquid–solid phases are modeled using the energy method. Temperature-dependent thermal properties are accommodated in the analysis and the laser pulse shape resembling the actual laser pulse is employed in the simulations. A numerical scheme using the control volume method is used to predict the cavity size, recession velocity of the vapor front, and temperature field in the laser irradiated region. It is found that cavity depth for steel is the largest, then follows nickel and tantalum. The recession velocity of the vapor front is high for steel due to the low evaporation temperature and latent heat of evaporation of steel.     

Measurements of the spatially resolved electron temperature and plasma potential in ferrite-core side type Ar/He inductively-coupled plasmas

Spatial distributions of the effective electron temperature (T_eff) and plasma potential were studied from the measurement of an electron energy probability function in a side type ferrite-core inductively coupled plasma with an argon–helium mixture. As the helium gas was diluted at the fixed total gas pressure of 5 mTorr in an argon discharge, the distribution of the plasma density and plasma potential changed from a concave to a flat profile, and finally became a convex profile, while all spatial profiles of T_eff were hollow shapes with helium dilution in the argon discharge. This evolution of the plasma potential with helium gas could be explained by the increased energy relaxation length (λ_ε), indicating the transition of electron kinetics from local to non-local kinetics.     

Simulation of elastic displacement of surface during laser short pulse heating of gold

The laser short pulse heating initiates nonequilibrium heating of the substrate material, which in turn results in the thermal stresses developing in the region below the surface. The surface temperature can be measured possibly through the monitoring of the resulting surface displacement. This requires in detail investigation into the surface displacement and surface temperature rises across the heated spot during the laser short pulse heating process. In the present study, the laser short pulse heating of gold surface is considered and the temperature rise at the surface and elastic displacement of the surface are investigated. The spatial and temporal distributions of surface displacement and surface temperature are predicted and the elastic response of the substrate material due to temperature rise is explored. It is found that the temporal and spatial distributions of the surface displacement do not follow the temperature rise at the surface. Consequently, care should be taken when measuring the temperature rise at the surface by means of monitoring the surface displacement during a laser short pulse heating process.     

Excimer laser accelerated hydrothermal synthesis of ZnO nanocrystals & their electrical properties

The synthesis of ZnO nanocrystals is reported using a hydrothermal chemical growth technique combined with 248 nm nanosecond excimer laser heating at fluences in the range 0-390 mJ cm⁻². The effect of laser heating in controlling the morphology of the nanocrystals is investigated using optical spectroscopy and electron microscopy characterization. Laser heating is shown to allow control of the crystal morphology from nanoparticles to nanorods as well as to modify the size distributions. The results indicate that not only does the laser accelerate the growth of nanocrystals, but can also produce crystals with a narrow size distribution possibly via photothermal size selection. An initial study of electrical conduction properties of ZnO nanocrystal thin films is also discussed.     

Electric current control of creation and annihilation of sub-100 nm magnetic bubbles examined by full-field transmission soft X-ray microscopy

The effect of electric current pulses on a sub-100 nm magnetic bubble state in a symmetric Pt/Co multilayer was directly observed using a full-field transmission soft X-ray microscope (MTXM). Field-induced evolution of the magnetic stripe domains into isolated bubbles with their sizes down to 100 nm was imaged under varying external magnetic fields. Electric current pulses were then applied to the created magnetic bubbles, and it was observed that the bubbles could be either created or annihilated by the current pulse depending on the strength of applied magnetic field. The results suggest that the Joule heating plays a critical role in the formation and/or elimination of the bubbles and skyrmions. Finally, the schematic phase diagram for the creation and annihilation of bubbles is presented, suggesting an optimized scheme with the combination of magnetic field and electric current necessary to utilize skyrmions in the practical devices.     

Transverse Transport of Polymeric Nanofluid under Pure Internal Heating: Keller Box Algorithm

The present work aims to investigate transverse Oldroyd-B nanofluid flow on a stretched panel with consideration of internal heat generation. Buongiorno model is utilized to study influence of thermophoresis and Brownian motion effects. A numerical procedure known as Keller box algorithm is used to solve the governed physical model. Graphically velocity, temperature and concentration of nanoparticles are expressed. Also, concerned physical measures such as heat and mass transfer are investigated numerically. The simulations performed revealed that fluid parameters play a significant role in heat transfer under Brownian motion and thermophoresis effects. Local heat flux is elevated while local mass flux is suppressed with enhancing Brownian motion parameter. Streamlines pattern exhibits that flow is more inclined in the presence of Deborah number effects. To the best of our knowledge, transverse flow of an Oldroyd-B type fluid which incorporates the thermal relaxation effects has never been reported before in the presence of Brownian motion and internal heating phenomenon. Therefore we intend to discuss these features in detail. The obtained results are a novel contribution, which can be benchmark for further relevant academic research related to polymer industry.     

Tip‐heating‐assisted Raman spectroscopy at elevated temperatures

We demonstrate tip‐heating‐assisted enhanced Raman spectroscopy to investigate the temperature dependence of the carbon nanotube G‐band with nanoscale resolution. The controllable and nanoscale heat generated at the tip apex was used to thermally perturb and characterize a small volume in a carbon nanotube sample that is precisely positioned underneath the tip. The dependence of tip enhancement with temperature was also experimentally examined, which is in good agreement with the enhancement calculated from the electromagnetic model of isolated spheroids. The technique presented may open up opportunities in the study of controlled heat‐assisted biochemical reactions and physical transformations of nanostructures. It can also be used for thermal characterization of various materials requiring site‐selective and controllable nanoscale heat source and could enable the realization of new photothermal devices. Copyright © 2010 John Wiley & Sons, Ltd.