柴油机无压力室喷油器各孔喷射特性差异测量分析

在油泵试验台上用数据采集系统测量分析油泵-油管-油嘴燃油供给系统相同型号4个无压力室喷油器各孔喷射特性。研究结果表明:各喷油器及同一喷油器各孔的喷油喷射特性均存在差异;动态流量系数在喷油过程中随时间(凸轮转角)而变化;同一喷油器针阀全开时各孔流量系数差异与各孔循环喷油量差异变化趋势相同,随转速及循环喷油量的增加各孔循环喷油量及流量系数不均匀度均降低;但各孔流量系数不均匀度比各孔循环喷油量不均匀度要小,说明仅用各孔流量系数差异不能完全反映出各孔喷射特性差异。     

微波谐振腔蒸汽湿度测量系统不确定度分析

推导了微波谐振腔蒸汽湿度测量关系式的灵敏度系数;分析了压力和频率等直接测量参数的不确定度;以不同压力及湿度的湿蒸汽为例,分析湿度测量关系式中各计算参数的不确定度,合成了蒸汽湿度测量系统的标准不确定度,分析了蒸汽压力和湿度变化对系统不确定度的影响;确定了考虑参数测量、腔体热膨胀、取样误差、腔体内壁沉积水膜等因素时系统的综合不确定度.结果表明:系统综合不确定度uz≤0.764%;随着蒸汽湿度和压力值的增大,蒸汽湿度测量系统的合成标准不确定度变大;系统压力测量引入的不确定度较小,可以忽略,而频率测量引入的不确定度较大,谐振频率的准确测量是确保系统测量精度的关键.     

大型烟气转换装置流阻特性的试验与数值研究

在阀门动态性能测试系统上,对大型烟气转换装置的阀组试件进行了流阻特性试验,应用计算流体力学(CFD)软件对试件内部流场进行了数值模拟,并将试验结果和模拟结果进行分析和比较.结果表明:大型烟气转换装置的流量系数和流阻系数与气体的流动速度(流量)无关,主要取决于烟气转换装置的尺寸、结构及内腔形状;烟气转换装置的压力损失随流速的增大而增加;数值模拟结果与试验值吻合较好,说明采用的数学模型及算法具有较高的可靠性和精度.     

等径三通的应力与强度分析

本文对四个等径三通试件(β=D_o/D_i=1.07、1.20、无加强、焊缝加强试件各一)在五种典型外载作用下的弹性应力分布及对六个试件(再加以上两结构的β=1.50试件)在内压作用下的强度特性进行了实验研究。得到了最大相当应力系数。讨论了焊缝加强结构对应力分布及强度特性的影响。 本文还对β=1.07、1.11、1.15、1.20、1.35、1.50无加强等径三通作了有限元数值解计算。计算结果与试验值有良好的一致性;并得到了内压、外载作用下应力集中系数与β值的关系曲线。     

基于模拟光源的遮阳窗口系统太阳得热系数测试研究

为精确测量各种遮阳窗口系统的太阳得热系数,搭建一套遮阳窗口系统太阳得热系数测定实验平台。该平台主要由太阳辐射模拟器、环境室、热箱、试件、热计量箱、循环水温度控制及计量系统等组成。实验测试基于稳定传热原理测量2个恒温箱之间建筑围护的净热流值,平台对温度、流量、太阳辐射强度等热物理参数实时监控,能实现系统工况参数的自动检测、监控与存储,从而实现智能控制。接着,重点分析实验测试所需的3个标定测试以及测试方法。最后对典型试件进行测试,并与Windows 7.4的计算值进行对比,研究结果表明测试数据与计算数据具有较好的一致性,测试平台的可靠性较高。     

基于红外测温的内部缺陷尺寸、方位的计算方法研究

对具有内部缺陷的平板试件的传热建立了三维物理和数学模型,提出了通过表面红外测温确定内部缺陷尺寸、方位的计算方法。同时,分析了测量误差和缺陷导热系数对计算结果的影响。通过计算分析可以得到结论：本方法可以精确地确定内部缺陷的尺寸和方位,测量误差对内部缺陷估计的影响较小;在试件的导热系数远大于缺陷的导热系数时,缺陷导热系数的微小变化对缺陷尺寸和位置的计算没有明显的影响;适用于任何尺寸、方位可用有限个参数描述的内部缺陷的检测。     

点加热稳态导热系数测量方法研究

针对稳态导热系数测量方法测量过程时间较长、测量装置复杂、以及样品制备和加工工艺复杂等现状,提出了一种新型的点加热稳态导热系数测量方法,构建相应的三维稳态传热物理模型,使加热面温升只与热流密度、样品导热系数和测温点位置相关。通过聚焦连续激光加热样品,缩短样品达稳态时长至分钟量级;建立对照光路消除表面发射率和激光稳定性对温度测量的影响;红外热像仪测量加热表面稳态温度分布,结合物理模型实现导热系数测量。采用多种已知导热系数的标准材料和线性法对测量方法进行验证,并应用该方法测量硅藻土导热系数为0.49～0.60 W/(m·K),误差为6.06%。该方法的测量迅速及非接触特性使其可应用于工程实地测量。     

一种高密度辐射计的设计及性能分析

分析了辐照投射角、测量桥的传热特性、结构和材料等因素对一种高密度辐射计测量性能的影响.结果表明:铜制辐射计能完成10kW/m2～15MW/m2范围内的辐照测量,响应时间不超过5s,输出温差与投射辐射的密度值成正比;较长的测量桥适用于辐照密度低、分辨率要求高的场合,较短的测量桥则适用于辐照值较高的场合;用热扩散系数高的材料制造的辐射计,其测量上限值较高,而用热扩散系数低的材料制造的辐射计,则有较高的分辨率和较低的测量下限值.     

家用燃气灶热效率测量及不确定度评定

按照GB16410-2007家用燃气灶热效率的测量原理和方法,对测量结果进行了不确定度评定,分析了各输入量对评定结果的影响情况。作为对比,分析了标准状态改变和按旧国标测量时的热效率不确定度。结果表明:铝锅修正系数、上下限锅正投影面积、试验气标态低热值和水的温升对家用灶热效率测量结果影响较大,影响程度依次降低。折算系数、测量时间和实验水量的测量不确定度可忽略不计。标准状态的改变对热效率测量结果不确定度评定的影响很小。相比旧国标,新国标测量结果具有更大的不确定度。     

汽轮机螺栓园柱面上布氏硬度的测定方法

一、前言国标(GB)明确规定布氏硬度值的测定应在平面上进行。然而,生产上经常遇到的试件表面一般来说都不是平面,例如轴、钢管,链环、套筒等表面。所以要对这些试件进行硬度测定,就必须在试件的表面上加工出一个平面。而对于某些成品件来说,例如汽轮机螺栓,由于布氏硬度计的行程不够,不能在端平面上检查硬度,又不允许在其表面磨一平面进行硬度测定。在这种情况下,硬度检查应在曲面上进行。为此,本文在试验结果的基础上,介绍柱面布氏硬度的修正方法及修正系数的表达式,并给出     

隔热材料导热系数的数值模拟预测

对氧化锆空心球隔热材料进行合理的简化,用数值模拟方法计算氧化锆空心球隔热材料导热系数,并分析空心球半径、温度、发射率等对导热系数的影响。数值模拟结果表明,减小空心球半径,降低空心球表面发射率,抽真空等都有助于降低隔热材料导热系数。数值模拟与实验测量结果良好吻合,用数值模拟计算隔热材料导热系数是一个行之有效的方法。     

Influence of thermal stresses on thermal diffusion of hydrogen

Thermal diffusion of hydrogen atoms in zirconium taking into account thermal stresses is investigated. As mathematical model the steady-state temperature in the hollow cylinder is considered. The first invariant of the tensor of thermal stresses in the hollow cylinder has a logarithmic dependence on the radial coordinate. Such dependence permits an exact analytical solution of diffusion kinetics problem in view of thermal stresses.     

Simple thermal decomposition reactions for storage of solar thermal energy

Simple thermal decomposition reactions have been investigated for the purpose of solar thermal energy storage. Ten criteria regarding the thermodynamics and kinetics of the reaction and the physical properties of the components of the reaction have been established. One particular reaction, the decomposition of ammonium hydrogen sulfate, has been evaluated in a preliminary manner and appears to satisfy all of the established criteria. The efficiency of storage is high and the decomposition occurs in the vicinity of 500°C. Other compounds such as ammonium halides, alkali and alkaline earth metal hydroxides, carbonates, sulfates and oxides have also been examined.     

Modeling the thermal absorption factor of photovoltaic/thermal combi-panels

In a photovoltaic/thermal combi-panel solar cells generate electricity while residual heat is extracted to be used for tap water heating or room heating. In such a panel the entire solar spectrum can be used in principle. Unfortunately long wavelength solar irradiance is poorly absorbed by the semiconductor material in standard solar cells. A computer model was developed to determine the thermal absorption factor of crystalline silicon solar cells. It was found that for a standard untextured solar cell with a silver back contact a relatively large amount of long wavelength irradiance is lost by reflection resulting in an absorption factor of only 74%. The model was then used to investigate ways to increase this absorption factor. One way is absorbing long wavelength irradiance in a second absorber behind a semi-transparent solar cell. According to the model this will increase the total absorption factor to 87%. The second way is to absorb irradiance in the back contact of the solar cell by using rough interfaces in combination with a non-standard metal as back contact. Theoretically the absorption factor can then be increased to 85%.     

Dynamic modelling for thermal micro-actuators using thermal networks

Thermal actuators are extensively used in microelectromechanical systems (MEMS). Heat transfer through and around these microstructures are very complex. Knowing and controlling them in order to improve the performance of the micro-actuator, is currently a great challenge. This paper deals with this topic and proposes a dynamic thermal modelling of thermal micro-actuators. Thermal problems may be modelled using electrical analogy. However, current equivalent electrical models (thermal networks) are generally obtained considering only heat transfers through the thickness of structures having considerable height and length in relation to width (walls). These models cannot be directly applied to micro-actuators. In fact, micro-actuator configurations are based on 3D beam structures, and heat transfers occur through and around length. New dynamic and static thermal networks are then proposed in this paper. The validities of both types of thermal networks have been studied. They are successfully validated by comparison with finite elements simulation and analytical calculations.     

生物柴油与柴油热稳定性对比和热动力学分析

利用热重分析技术对生物柴油和0#柴油进行燃烧特性分析,比较两者的热稳定性。根据DTG-DTA曲线及实验数据,利用Achar微分法和Coats-Redfen积分法计算了活化能,并推断出生物柴油和柴油在低温段和高温段的非等温动力学方程。实验表明:生物柴油的挥发分较高,易于燃烧;但低温段表面活化能高于生物柴油,热稳定性优于柴油。     

Economic implications of thermal energy storage for concentrated solar thermal power

Solar energy is an attractive renewable energy source because the sun's energy is plentiful and carbon-free. However, solar energy is intermittent and not suitable for base load electricity generation without an energy backup system. Concentrated solar power (CSP) is unique among other renewable energy options because it can approach base load generation with molten salt thermal energy storage (TES). This paper describes the development of an engineering economic model that directly compares the performance, cost, and profit of a 110-MW parabolic trough CSP plant operating with a TES system, natural gas-fired backup system, and no backup system. Model results are presented for 0–12 h backup capacities with and without current U.S. subsidies. TES increased the annual capacity factor from around 30% with no backup to up to 55% with 12 h of storage when the solar field area was selected to provide the lowest levelized cost of energy (LCOE). Using TES instead of a natural gas-fired heat transfer fluid heater (NG) increased total plant capital costs but decreased annual operation and maintenance costs. These three effects led to an increase in the LCOE for PT plants with TES and NG backup compared with no backup. LCOE increased with increasing backup capacity for plants with TES and NG backup. For small backup capacities (1–4 h), plants with TES had slightly lower LCOE values than plants with NG backup. For larger backup capacities (5–12 h), plants with TES had slightly higher LCOE values than plants with NG backup. At these costs, current U.S. federal tax incentives were not sufficient to make PT profitable in a market with variable electricity pricing. Current U.S. incentives combined with a fixed electricity price of $200/MWh made PT plants with larger backup capacities more profitable than PT plants with no backup or with smaller backup capacities. In the absence of incentives, a carbon price of $100–$160/tonne CO_2eq would be required for these PT plants to compete with new coal-fired power plants in the U.S. If the long-term goal is to increase renewable base load electricity generation, additional incentives are needed to encourage new CSP plants to use thermal energy storage in the U.S.     

On the estimation of thermal resistance in borehole thermal conductivity test

Sizing of ground-coupled loop heat exchangers (GLHE) depends on the ground thermal conductivity and capacity, and the borehole thermal resistance. One popular method to estimate the thermal parameters is the interpretation of in situ thermal response tests. The modeled response is T_m=(T_in+T_out)/2, the average temperature of the fluid entering and leaving the ground. The T_m response corresponds to the physically unrealistic hypothesis of constant heat flux along a borehole. Using a 3D finite element model of the borehole, we show that T_m does not correspond to the fluid mean temperature within the borehole. Accordingly, with T_m, an overestimation of the borehole thermal resistance results. The resistance overestimation has a noticeable economic impact. We propose instead a new estimator we name “p-linear” average of T_in and T_out with parameter p→-1, as determined by numerical simulations. We show that the p-linear average closely fits the average fluid temperature computed with the numerical model, hence avoiding bias in estimation of borehole thermal resistance. Finally, we discuss the problem of collinearity arising in the estimation of thermal parameters.     

Experimental research on thermal characteristics of PCM thermal energy storage units

To explore thermal management integration in electric vehicles (EVs), a phase change materials (PCMs) thermal energy storage unit using flat tubes and corrugated fins is designed. The investigation focuses on the thermal characteristics of the PCM unit, such as the temperature variation, heat capacity, and heat transfer time, etc. Meanwhile, the heat storage and release process will be influenced by different inlet temperature, liquid flow rate, melting point of the PCM, and the combination order of the units. Under the same inlet temperature and flow rate condition, the PCM unit with higher melting point enters the latent heat storage stage slowly and enters the phase change melting release stage quickly. Furthermore, the heat storage and release rates increase with increasing liquid flow rates, but the effects are diminishing in the middle and later periods. The multiple PCM units with different melting temperatures are cascaded to help recycle low-grade heat energy with different temperature classes and exhibit well heat storage and release rates.