生物质导热系数测量系统设计

随着不可再生能源的日渐枯竭,生物质能源的研究工作受到越来越多的关注。想要充分了解和利用生物质能源,生物质材料的热物性分析必不可少。其中,导热系数表征就是研究的重点内容之一,设计出可靠便捷的测量系统至关重要。笔者以LabVIEW平台为基础,依靠其强大的测控功能,结合3ω法测量原理及具体的实验步骤,设计出一种固液相样品都适用的导热系数测量系统。实验中测量端的铂丝将产生电信号,经前置放大电路被锁相放大器SR830采集,然后通过GPIB接口卡与PC机通讯。其中,上位机LabVIEW的程控交互界面包括了前期准备、信息记录、数据采集和曲线显示4个部分,为研究人员提供了直观、便捷、高效的实验进程帮助。还从测量对象的性质和实验台搭建过程两个方面,分析了可能存在的误差来源。为了验证该导热系数测量系统的可靠性,对常见的生物质液体,包括存在固液相变化的样品,进行了测量实验。测量值与文献参考值比较显示,系统误差小于5%,说明该测量系统具有较高的可靠性和稳定性。

Biomass thermal conductivity measurement system design

With the increasing consumption of energy,traditional fossil resources are gradually depleted,and the utilization of the clean and renewable biomass energy has attracted the attention in many countries.To fully understand and utilize biomass energy,the thermophysical analysis of biomass materials is essential.The characterization of thermal conductivity of biomass has always been one of the key contents of research.It is important to develop a reliable and convenient measurement system.In this study,the thermal conductivity measurement system was designed and fabricated for solid-liquid phase samples based on the LabVIEW platform,which was relied on its powerful measurement and control functions,combined with the measurement principle of 3ωmethod and specific experimental steps.In the experiment,the measuring platinum wire was not only a heating element,but also a measuring element.An alternating current with an angular frequency ofωin the platinum wire generated a third harmonic electrical signal related to temperature fluctuations under the effect of the Joule effect.This signal was collected by the lock-in amplifier SR830 through the preamplifier circuit,and then the same communication address was set with the PC through the GPIB interface card to interact.Considering the complexity of the experimental process and the long-time span,relying on the powerful engineering assistance of LabVIEW,it was also very important to develop a host computer program that reduced the experimental intensity.The program control interaction interface of upper computer LabVIEW included four parts,i.e.,the preliminary preparation,information recording,data acquisition and curve display.These four parts included the convenient hardware control,flexible information storage,and timely experimental error correction functions.Not only can quickly configure the phase-locked amplifier to balance out 1ωvoltage,but also can reasonably arrange the experimental process to greatly reduce the experimental time and strength.These features increased the productivity and experimental accuracy of researchers.This study considered the impact of the dynamic response of the amplifier on the data acquisition of the hardware.This study also analyzed the effects of convective heat transfer of liquid and the disturbance of the experimental environment on the error from the aspects of the nature of the measurement object and the process of setting up the experimental bench,thereby further improving the accuracy of the experiment.In order to verify the reliability of the thermal conductivity measurement system,measurement experiments were performed on common biomass liquids,including samples with solid-liquid phase changes.The comparison between the measured values and the reference values in the literature showed that the system error was less than 5%,indicating that the measurement system had high reliability and stability.