Numerical investigations on unsteady flow of a scroll expander for compressed air energy storage

本工作以适应用于微型压缩空气储能（micro-CAES）系统的涡旋膨胀机为研究对象,采用计算流体力学（CFD）的方法对涡旋膨胀机工作过程进行非定常数值模拟,得到膨胀机内部温度场、压力场和速度场的分布,研究了吸气温度对涡旋膨胀机性能的影响规律及工作腔流场分布特点,结果显示：膨胀机吸气温度的升高,能够增加单位质量流量的输出功;随着吸气温度的下降,动涡旋盘所受轴向气体力增大,径、切向气体力减小;膨胀机工作过程中工作腔内的温度分布并不是沿涡旋盘半径方向逐渐下降,两侧背压腔存在较大的机械能损耗,背压腔温度会高于上游排气腔。该研究结果为涡旋膨胀机排气结构的设计提供了理论依据。     

关于涡旋膨胀机性能的数值模拟研究

本文建立了一种涡旋膨胀机三维模型,利用Pump Linx软件,以空气为工质,对其工作腔内的流场进行模拟研究。从内泄漏、进出口参数和入口形位等方面,对其输出功等性能进行了研究,并对空气的膨胀过程和多变指数进行拟合。结果表明:当径向间隙从0.04 mm增大至0.2 mm时,其单位质量流量的输出功将减少37%;腔内气体的温度、压力和密度从入口到出口均逐渐减小,且流体在旋转角为180°附近出现较剧烈的漩涡;空气膨胀过程的多变指数为1.141;膨胀机入口最大压力损失为6.07%;最后一个腔打开的瞬间,腔内压力会出现阶跃性突变,进而导致后期腔内压力存在一个较大的波动。     

分置式斯特林发动机热力性能的仿真

对斯特林发动机的压缩与膨胀过程进行了变质量系统热力学分析。利用等温模型分析法,引入流动阻力损失的计算模型,模拟了分置式斯特林发动机内部工质的压力等参数的动态变化规律。仿真结果表明：斯特林发动机在运行过程中压缩腔与膨胀腔的气体压力并不时时相等;提高发动机的转速和高温热源温度,可以增加发动机的输出功率。     

热导传感器在氢气测量中的影响因素研究

本文为提高热导传感器对待测气体中氢气浓度的测试准确度,通过实验对气体流量、温度、湿度等环境因素对传感器输出的影响进行了测试和分析,得出了各环境因素对传感器输出的影响规律。针对相应规律,提出了一种包含温度、湿度和输出电压等变量的多参数补偿方案,并对该补偿方案进行了实验验证,发现该补偿方案可使传感器在各温度点、各湿度点、各浓度点的测试准确度保持在±3%FS以内,使传感器的测试准确度获得极大地提高。     

一类有限热源多级连续卡诺热机系统的最大输出功

对高低温热源均为有限热源的多级连续卡诺热机系统最大输出功的最优温度曲线进行了研究,利用最优控制理论得出了其最优温度曲线为驱动流体温度随流速和过程时间成指数变化,求出了其最大输出功,并与低温热源为无限热源下的结果进行了比较。     

中压内缸进汽腔温度场的测试与分析

为了验证采用传热系数经验公式计算温度场的准确性,利用温度场测试和有限元计算2种方法对某在役超超临界1000 MW汽轮机中压内缸进汽腔的温度场进行了研究,得到了中压内缸进汽腔各测点温度的实测值,并与额定负荷工况下各测点温度的计算值进行了比较.结果 表明:进汽腔内壁的金属温度计算值与实测值拟合较好,经验传热系数设定合理;进...     

基于恒负载下太阳电池自身温度对其发电性能影响的实验研究

基于分布式太阳发电储热供暖系统,针对多晶硅太阳电池自身温度对其发电性能的影响进行实验研究。在自然条件下对太阳电池加恒阻值的远红外发热纤维软板进行实验,测试其输出电压、输出电流及其对应的光伏电池表面光照强度、太阳电池自身温度,并对测试数据进行整理、分析,研究太阳电池自身温度对其发电性能的影响。结果表明:太阳电池表面光照强度一定时,随着太阳电池自身温度的升高,太阳电池输出电压、电流及输出功率明显减小,太阳电池的光电转换率呈线性下降趋势。     

辐射传热时有限热源多级连续卡诺热机系统的最大输出功

对高低温热源均为有限热源、工质与高温热源间辐射传热、工质与低温热源间线性传热的多级连续卡诺热机系统最大输出功的最优温度曲线进行了研究,利用最优控制理论和"伪线性传热"模型得出了其最优温度曲线为驱动流体温度随流速和过程时间成单调递减变化,求出了其最大输出功,并与低温热源为无限热源下的结果进行了比较.     

反演高温腔体内壁面温度波动的辐射边界导热反问题

在工业生产中有很多情况需要获得高温腔体内壁温度波动,但在内壁面安装测温装置进行直接测量非常困难,一般通过测量外壁温度再进行反演计算间接获得。而已有反演计算方法未考虑高温壁面与周围环境之间的辐射传热,给反演计算结果带来一定误差,为此建立了考虑辐射边界条件的反演高温腔体内壁面温度波动的导热反问题数学模型,并构造了两组数值试验对数学模型的效果进行检验。计算结果表明,建立的数学模型能够很好的由高温腔体外壁面温度反演得到内壁面温度波动情况。     

无吸热管球形腔式集热器的设计与数值模拟

腔式集热器是点聚焦式太阳能集热系统的核心部件。目前,大多数腔式集热器均在腔体内壁上铺设吸热管,这样会导致该腔式集热器结构复杂、热损失严重。因此文章提出了一种新型的无吸热管球形腔式集热器,并对该腔式集热器的结构参数进行设计,而后采用Trace Pro,ANSYS软件对该腔式集热器进行光学仿真和热稳态分析。研究结果表明:无吸热管球形腔式集热器可以对聚焦光线进行多次反射和均匀吸收,光吸收率大于90%;当腔体内壁温度为500℃时,该腔式集热器的热效率为57.5%,随着腔体内壁温度的逐渐降低,热效率会逐渐升高;导热腔壁的热流主要集中在工质孔处,导致工质孔处工质获取热量的效率较高。     

Thermal model and thermodynamic performance of molten salt cavity receiver

The design of a global steady-state thermal model of a 100 kWt molten salt cavity receiver was developed as part of the key project of the Ministry of Science and Technology of People's Republic of China (MOST). In the design process, the following factors were analyzed: receiver area, heat loss (convective, emissive, reflective and conductive), number of tubes in the receiver panel, tube diameter and receiver surface temperature. The model was also used to calculate the receiver performance of the Sandia National Laboratories' molten salt electric experiment (MSEE). In addition, the thermal performance of the designed molten salt cavity receiver is presented for a fixed outlet flow rate and a fixed output temperature.     

Fuzzy-based estimation of mixed convection heat transfer in a square cavity in the presence of an adiabatic inclined fin

In this study, heat transfer from a square cavity in the presence of a thin inclined adiabatic fin is estimated using inputs–outputs generated from a CFD code with a fuzzy based identification procedure. The Reynolds number based on cavity length is 300 and the Richardson number is varied between 1 and 30. The top and bottom walls of the cavity are kept at constant temperature while the vertical walls are assumed to be adiabatic. The fin height, fin inclination angle, and Richardson number are considered as the input and the spatial averaged Nusselt number is taken as the output for the fuzzy model. Two data sets are used. One data set which contains 45 cases is used for estimation and another data set which contains 10 cases (not used in estimation) is used for validation purposes. The predictions using fuzzy model compare well with the CFD computations.     

An alternative solar pumping approach by a light guide assembly elliptical-cylindrical cavity

To improve solar laser output performance, what we believe to be a novel light guide assembly is proposed to pump a Nd:YAG laser rod within a two-dimensional elliptical-cylindrical (2D-EL-CYL) cavity with intervening optics. Based on refractive and total internal reflection principles, the concentrated solar radiation from a primary parabolic mirror is coupled through the square input face of a fused silica light guide assembly to its rectangular output end, located along the first focal line of the 2D-EL-CYL cavity. Optimized pumping conditions are found through ZEMAX™non-sequential ray-tracing software. By comparing with the laser performance of a two-dimensional dielectric compound parabolic concentrator (2D-DCPC) cavity, significant improvements in absorption distribution, TEM₀₀ laser power and tracking error dependent output power stability are obtained by the proposed pumping approach.     

基于新能源发电的电解水制氢直流电源研究

利用新能源发电进行电解水制氢是实现新能源就地消纳和氢能利用的重要途径,以匹配电解水制氢工作特性的制氢电源为研究对象,通过分析质子交换膜电解槽电解电流、温度与电解槽端口电压、能量效率、制氢速度之间的关系,得出制氢电源需具备输出低电流纹波、输出大电流、宽范围电压输出的特性。为满足新能源电解制氢系统需求,提出一种基于Y型三相交错并联LLC拓扑结构的制氢电源方案,该方案谐振腔三相交错并联输出,满足电解槽大电流低纹波工作特性,并采用脉冲频率控制实现谐振软开关,提高变换效率。最后,搭建仿真模型和6 kW模块化实验样机,验证所提出方案的合理性与可行性。     

Calculations of efficiencies achievable using gallium arsenide and silicon cells mounted together in cavities illuminated by single-stage concentration

Detailed calculations have been performed to predict the efficiencies achievable using gallium arsenide and silicon cells mounted in cavities with concentrated light entering. Prototype devices with power output of the order of 2 W are proposed and analysed. The concept of the elliptical cavity with restriction of the angle of the escaping rays is exploited in order to avoid having to use a secondary concentrator. The light first falls on the gallium arsenide cell, with a concentration of 720 suns, before being reflected onto a silicon cell. Arrangements using both one and two silicon cells are studied. Depending on the type of cells used, and whether a dichroic filter is included, the possible efficiencies (relative to the light entering the cavity) are in the range 30.4–36%. The effect of the cavity is to increase thepower output by about 5% when compared to a similar bandsplitting arrangement not using a cavity. It is concluded that the cavity effect should be of interest for practical photovoltaic converters.     

Detection of hot spot through inverse thermal analysis in superconducting RF cavities

An inverse heat conduction problem in a superconducting radio frequency (SRF) cavity is examined. A localized defect is simulated as a point-heating source on the inner surface (RF surface) of the evacuated niobium cavity. Liquid helium acts as a coolant on the outer surface of the cavity. By measuring the outer surface temperature profile of the cavity using relatively few sensors, the temperature and location of a hot spot on the inner surface of the niobium are calculated using an inverse heat conduction technique. The inverse method requires a direct solution of a three-dimensional heat conduction problem through the cavity wall thickness along with temperature measurements from sensors on the outer surface of the cavity, which is immersed in liquid helium. A non-linear parameter estimation program then estimates the unknown location and temperature rise of the hot spot inside the cavity. The validation of the technique has been done through an experiment conducted on a niobium sample at room temperature.     

Fluid temperature distributions in a rotating cavity with an axial throughflow

Radial and circumferential variations of cavity air temperature are presented for a rotating cavity with an axial throughflow of cooling air. Results show that the air temperatures are influenced significantly by the cavity surface temperature distribution. Strong (around 5°C) circumferential air temperature variations are observed showing the flow to be three-dimensional. Temperature time traces are used to infer flow structure features and also the variation of the fluid to cavity angular velocity ratio with temperature. Features and trends are found to be consistent with flow visualisation evidence, Laser Doppler Anemometry data, and also computations of other workers.     

Experimental study of unsteady supersonic flow interacting with porous cavity and jets or rods

In this study, an experiment was performed to clarify the flow field, in which the jets were normally injected into a main supersonic flow surrounded by a porous cavity, and this report figures out interaction between starting shock wave and porous cavity. In the experiment, a porous cavity is attached to a main duct and jets and rods are inserted to the main duct on the porous cavity. To reveal this flow field, the thermal tuft probe was adopted to ex- perimentally investigate the flow in the cavity. In the experiments, the effect of the porous cavity with jets or rods on the flow field is studied by means of visualization of schlieren method with a high speed camera and measurement of cavity flow with thermal tuft probe. As a results, frequency analysis of output of the thermal tuft probe revealed that some clear dominant frequencies were confirmed when the starting shock wave existed around the porous cavity in all cases of jets and rods arrangements. Moreover, visualization of schlieren method with a high speed camera clarified that a starting shock wave had the same dominant frequencies as that of the flow fluctuation in the cavity only around the cavity.     

Features of boiling on an artificial surface — Bubble formation, wall temperature fluctuation and nucleation site interaction

The artificial surfaces are applied to study the pool boiling features, including the bubble behaviors, the surface temperature fluctuation, the heat transfer characteristics and nucleate site interaction. Three sets of experiments are carried out to investigate the influences of cavity shape, cavity size, cavity spacing on the boiling phenomena. Experimental results reveal that bubbling from the cylindrical as well as reentrant cavity is generally stable. The influence of cavity diameter on the bubble behaviors and the temperature fluctuation seems very weak while the effect of cavity depth cannot be neglected. As for the two cavity conditions, the bubble behaviors show the different features depending on the dimensionless cavity spacing. Three significant factors (thermal interaction, hydraulic interaction, bubble coalescence) control the nucleation site interaction, and the competition and dominance of the factors yield four interaction regimes.     

Features of Boiling on an Artificial Surface—Bubble Formation, Wall Temperature Fluctuation and Nucleation Site Interaction

The artificial surfaces are applied to study the pool boiling features, including the bubble behaviors, the surface temperature fluctuation, the heat transfer characteristics and nucleate site interaction. Three sets of experiments are carried out to investigate the influences of cavity shape, cavity size, cavity spacing on the boiling phenomena. Experimental results reveal that bubbling from the cylindrical as well as reentrant cavity is generally stable. The influence of cavity diameter on the bubble behaviors and the temperature fluctuation seems very weak while the effect of cavity depth cannot be neglected. As for the two cavity conditions, the bubble behaviors show the different features depending on the dimensionless cavity spacing. Three significant factors (thermal interaction, hydraulic interaction, bubble coalescence) control the nucleation site interaction, and the competition and dominance of the factors yield four interaction regimes.