Current Issue

2024, Volume 68,  Issue 1

Research Progress
Abstract:
With increasing attention on environmental concerns, natural gas, as a clean energy source, is gaining a larger share in China's fossil energy consumption system. Recently, the consumption of natural gas has been characterized by a diversity of sources and a rise in imported gas, leading to a multi-source gas network pattern. Significant differences in calorific value among various gas sources pose challenges for China's existing measurement system in performing accurate trade measurement and carbon emission accounting. This calls for the development of a new measurement system. This article investigates the current status of domestic and international natural gas measurement systems, introducing three measurement methods: volumetric, mass, and energy measurement, along with their principles. A comparative analysis of current natural gas measurement technologies, including technical standards, measurement instruments, and traceability, is conducted. It highlights that the energy measurement method, based on natural gas calorific value combined with its volumetric or mass flow, offers a fairer and more accurate approach in the context of diverse gas sources. Additionally, the paper identifies shortcomings in China's natural gas quality analysis equipment, the construction of traceability for gas analysis, and pipeline network verification technologies.
Abstract:
Environmental particulate matter levels are closely linked to human health, with road traffic emissions being a significant source of urban particulate matter. As the mass concentration of particulates in vehicle exhaust approaches the measurement lower limit, the urgent need arises to develop more sensitive methods for measuring and evaluating particulate matter. Over the past two decades, motor vehicle particulate emissions have garnered increasing attention, leading to numerous changes in global emissions regulations. These include stricter standards, new indicators, and expansion to broader off-road applications, necessitating new requirements for real-time, highly sensitive, onboard instruments. The measurement of particulate matter number concentration serves as a crucial supplementary approach to evaluating vehicle emissions pollution. This paper reviews the evolution of this metric in relevant regulations and existing methods for measuring particulate number concentration in vehicle exhaust. It provides an overview of the principles and application ranges of both current and newly developed instruments, offering insights into the technical progression of measuring and evaluating particulate number concentration in motor vehicle exhaust emissions.
Measurement Methods and Techniques
Abstract:
Respirable dust, defined as particles with an aerodynamic equivalent diameter of less than 7.1 μm that can enter the human lungs during breathing, poses significant health risks and is a source of pneumoconiosis. Its concentration requires stringent monitoring. The respirable dust sampler, a crucial component at the front end of dust concentration measuring instruments in the coal industry, has its efficiency determined by the ability of dust to pass through its pre-separation device. This study introduces a novel detection method for sampling efficiency based on the aerodynamic method, accompanied by a newly developed detection device. This method was applied to test various imported and domestic products. Compared to current standards, this method simplifies the process, directly traces particle size and concentration to the aerodynamic particle size spectrometer, significantly reduces the detection cycle by at least 98%, and offers good repeatability. It is not affected by complex steps like sampling, elution, and solution fluorescence determination, thereby greatly reducing detection costs. Testing revealed that only one out of six models of sampling heads met the required standards, highlighting the urgent need for quality improvement in these products.
Abstract:
This paper addresses the issue of insufficient selectivity in electrochemical gas sensors within atmospheric miniature monitoring stations, which are susceptible to cross-interference from non-target gases. A data correction approach using a Genetic Algorithm (GA) optimized Back Propagation (BP) neural network (GA-BP model) is proposed. The GA-BP model enhances the BP neural network, adept at tackling nonlinear black-box problems, by integrating GA's global optimization capability. This integration optimizes the neural network's initial parameters, overcoming the BP network's tendency to fall into local minima, and thus enhances the model's overall accuracy and stability. Experimental results demonstrate that the miniature monitoring stations equipped with the GA-BP model can accurately quantify NO2, CO, O3, and SO2 concentrations in mixed gases. The goodness of fit (R2) between the computed values and actual measurements of these four gases exceeded 0.95. Compared to univariate, multivariate linear regressions, and traditional BP neural networks, the GA-BP model shows clear superiority. Moreover, the model exhibits strong generalization capabilities. When applied to new, untrained station data, it achieved R2 values above 0.88 for all four gas concentrations, affirming the method's robust applicability. This approach provides a beneficial reference for manufacturers to enhance equipment performance and for users to obtain accurate air pollutant concentration data.
Abstract:
This study aims to satisfy the testing needs for the collection efficiency of filtration membranes used in ambient air sampling and to ensure the consistency and accuracy of these tests. It analyzes the key influencing factors and the feasibility of the filtration membrane collection efficiency testing methods. Subsequently, two testing schemes based on particle number concentration and particle mass concentration are developed to assess the collection efficiency of ambient air filtration membranes. This paper presents the principles, experimental device requirements, and procedures of these testing schemes. Tests were conducted on various materials and applications of ambient particulate matter sampling filters. The experimental results show a high degree of consistency between the two methods in terms of collection efficiency test conformity. However, the method based on number concentration yields slightly lower results compared to the mass concentration-based method. The differences are attributed to the inherent limitations of the testing methods and deviations caused by various detection devices, though these impacts are negligible overall. Both methods demonstrate high reliability and equivalence, laying a foundation for their use in practical applications. Depending on the configuration of their experimental devices, users can choose either method for testing the collection efficiency of filtration membranes, ensuring the test's accuracy and reliability.
Abstract:
This paper introduces a calibration method for mask particle filtration efficiency testers, employing an in-situ aerosol dilutor as a standard device. This novel approach aims to address the limitations of operability and traceability inherent in traditional calibration methods such as standard photometers and filter membrane techniques. Characterized by a combination of multiple flow-limiting capillaries and in-situ aerosol dilution, the in-situ aerosol dilutor is designed to fit and function at the mask fixture position. When operating at a known flow rate, the calibrated dilutor calculates its dilution ratio based on the differential pressure data gathered during calibration. The article further discusses the calibration method for the dilution ratio, asserting that this ratio can be directly converted to a reference value for the dilutor's filtration efficiency. The calibration process is compared to coaxial non-uniform aerosol particle sampling, with a derived calculation of the Stokes number showing that the capillary suction efficiency is near 1. Additionally, the transport efficiency in the capillaries, accounting for diffusion loss, is calculated to be over 0.99. Calibration experiments were conducted with the in-situ aerosol dilutor on typical measurement objects, accompanied by an uncertainty analysis of the reference values. Collectively, these findings substantiate the feasibility and effectiveness of the dilution method calibration.
Abstract:
To cater to the diverse testing requirements of bioaerosol samplers in the market, and to advance the design, manufacturing, and practical application of these devices, this paper introduces two testing apparatuses — the fluorescence method and the counting method. These methods simulate microbial aerosols to assess the efficiency of microbial samplers. The composition, methodologies, and data processing steps of both testing devices are detailed. Subsequently, these methods were applied to evaluate the sampling efficiency of the domestically produced AGI-30 bioaerosol sampler and the Anderson six-stage microbial sampler under varying conditions. Results show that the AGI-30 sampler's efficiency increases with particle size, exceeding 90% for 5 μm particles, and decreases with higher flow rates. Sampling time also significantly impacts efficiency. The Anderson sampler exhibited high efficiency across eight particle sizes, approximately 99%, with a tendency to increase with particle size. The comparative analysis reveals that the fluorescence and counting methods, being more convenient than traditional microbial-culture methods, offer safe, reliable, and rapid results. The counting method, having fewer steps and no fluorescence quenching issues, is preferred for evaluating the efficiency of biological samplers.
Abstract:
High-precision vibration transducers, extensively employed in aerospace engine vibration monitoring, high and low temperature ground environmental testing, and modal testing, play a critical role in ensuring the reliability of tested equipment. Accurate measurement of these transducers' sensitivity to temperature variations and their transverse sensitivity is crucial for understanding transducer performance, enhancing manufacturing process quality, and guaranteeing the reliability of various ground testing data in product development and production. This paper presents research on key calibration techniques for high-precision vibration transducers, utilizing vibration comparison methods, point-by-point rapid temperature testing technology, and precise measurement of transverse sensitivity. An integrated rapid calibration device for key parameters of vibration transducers was developed using a PXI bus architecture, creating a comprehensive measurement IEWevaluation system. Control and calibration software were developed on the LabView platform to enable integrated control and measurement. This advancement addresses the challenges in rapidly calibrating critical parameters like temperature response and transverse sensitivity. Measurement uncertainty analysis and verification experiments of the calibration device demonstrate this method's ability to meet specific testing requirements for transducer temperature characteristics and transverse sensitivity, optimize transducer design, and ensure stability in high-precision vibration transducers' online operation.
Measuring Instruments and Systems
Abstract:
This paper introduces a novel calibration device for automatic monitors of water-soluble ions in atmospheric aerosols, aiming to address the lack of quality control technology in this field in China. While the United States and European Union have already issued test reports or developed standard substances for similar foreign equipment, this research contributes to the local development. The calibration device comprises three modules: an aerosol generation system, a sampling system, and an automatic test system based on the principles of HJ799 and HJ800. The final calibration relies on data from the automatic test system to provide correction values or coefficients for the front-end device. The performance of each module has been experimentally validated, confirming their suitability for the intended calibration roles. Due to the system's complexity, further investigation into factors affecting each module’s accuracy is necessary to enhance efficiency and achieve a stable calibration setup.
Abstract:
This study focuses on developing a method to evaluate the purification capacity of cooking fume purification equipment for non-methane total hydrocarbons (NMTHC) in a laboratory setting, aiming to enhance the scientificity and accuracy of the assessment process. A novel generating device capable of stably producing high concentrations of NMTHC has been developed. Suitable detection methods for NMTHC in cooking fumes were identified, and a laboratory test platform was established for evaluating the purification effect of NMTHC. The performance of the soot generator, capable of consistently producing NMTHC concentrations up to 40-50 mg/m3 with repeatability below 15%, was developed, overcoming the challenge of simulating high NMTHC concentrations emitted in the catering industry. Two detection methods, a portable hydrogen flame ionization detector and gas chromatography, were compared experimentally. Integrating the selected detection methods with the newly developed NMTHC generator and a laboratory standard bench, a testing platform was constructed to evaluate the efficiency of cooking fume purification equipment in handling NMTHC. Experimental verification of this platform demonstrated stable performance for both high and low concentrations of NMTHC, with repeatability below 15% and 20% respectively. The findings indicate that the developed detection system can reliably and effectively evaluate the performance of catering industry fume purification equipment in treating NMTHC, laying a foundation for standardized laboratory testing.