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I. What is a laminar flow differential pressure mass flow meter? The laminar pressure drop mass flow meter is designed based on Hagen-Poiseuille’s law, which describes the linear relationship between volumetric flow rate and pressure drop for incompressible fluids flowing in circular pipes in a laminar state, under conditions where parameters such as temperature and pipe diameter remain constant. By reading the pressure difference signal at both ends of the laminar flow element, the volumetric flow rate is calculated; this volumetric flow rate is then corrected for pressure and temperature to obtain the standard volumetric flow rate and mass flow rate. II. Applications of laminar flow differential mass flow meters: Since laminar flow differential mass flow meters can be used for the measurement and control of low-pressure gases and liquids, and they exhibit excellent performance, they are widely utilized in high-end manufacturing industries. 1. In the semiconductor industry, it is used in process equipment such as those for diffusion, oxidation, epitaxy, plasma etching, sputtering, and vapor deposition, to measure and control the flow rate of process gases. 2. Sterilization processes, ingredient preparation, gas distribution, exhaust gas detection, as well as flow measurement and control for bioreactors in the food and biological industries during production. 3. Analytical instrument samplers are used for precise measurement of the amount of gas to be sampled for gas chromatographs and other analytical instruments used in environmental protection, as well as for the collection of atmospheric samples. 4. Sealing performance testing and precise dimension measurement of precision components are used for the accurate measurement of gas leakage rates, which indicate the airtightness of mechanical components such as valves, as well as for measuring the size of small holes and the air permeability of filtering materials. 5. Process industries such as chemical and petroleum use them for the measurement and control of small gas flow rates in micro-reaction testing devices. 6. Surface treatment is used for vacuum coating, coating of automotive glass, automated painting, and the precise measurement and control of gases in plasma spraying. III. Advantages of laminar flow differential mass flow meters 1. Ability to switch between multiple gases arbitrarily. The most notable feature of laminar flow differential mass flow meters is their ability to switch between various gases without the need for conversion factors. Why can laminar flow differential mass flow meters achieve this functionality? According to Hagen-Poiseuille’s law, at constant temperature and pipe diameter, the volumetric flow rate of a gas is linearly related to the pressure difference as well as the viscosity of the gas. Therefore, once we know the viscosity of the gas that needs to be measured, we can determine its volumetric flow rate without the need for any conversion factors. 2. The response time of a laminar flow differential pressure mass flow meter depends crucially on the speed at which the pressure difference signals at both ends of the laminar flow element can be obtained; this speed is determined by the propagation speed of pressure waves (which are a type of sound wave). Therefore, the response time of a laminar flow differential pressure mass flow meter is very fast. 3. The high-precision laminar flow differential pressure mass flow meter determines the volumetric flow rate of gas by measuring the pressure difference; according to Hagen-Poiseuille’s law, there is an approximately linear relationship between the volumetric flow rate of gas and the pressure difference. The closer the physical properties are to linear, the higher the accuracy; therefore, laminar flow differential pressure mass flow meters have very high precision. 4. Repeatability: The repeatability of a repetitive high-layer flow differential pressure mass flow meter depends on the stability of the flow regime. In normal conditions, gases move in a turbulent state, whereas the core principle of a laminar flow differential pressure mass flow meter is to use laminar flow elements to make the gas flow in a laminar manner. Laminar flow of gases has the highest stability, which is why such meters exhibit very high repeatability. IV. Disadvantages of laminar flow differential pressure mass flow meters 1. They cannot measure high-pressure gases; the accuracy decreases rapidly when measuring such gases, so they are primarily used for measuring low-pressure gases. 2. It is necessary to know the main properties of the gas. As mentioned earlier, according to Hagen-Poiseuille’s law, the volumetric flow rate is related to the pressure difference as well as the viscosity of the gas; therefore, for a laminar flow pressure differential mass flow meter, it is essential to know the main properties of the gas in order to determine its viscosity coefficient. V. Development trends of laminar flow differential pressure mass flow meters As we all know, with the development of high-end manufacturing industries, fluid measurement and control has become a core technology in various manufacturing processes. Especially in the field of low-pressure gas measurement, the annual demand growth rate is over 30%. Following the Sino-US trade war, high-end manufacturing sectors such as semiconductors, new energy, and medical technology have begun to develop rapidly. Various research institutions and industry leaders are engaged in the development of key technologies and equipment, which will also drive the advancement of fluid measurement technologies in China. Here, there is another issue: when it comes to mass flow meters and semiconductors, the well-known foreign brands that come to mind are BronkHorst, Brooks, Horiba, and others. I once met a client who worked in the field of mass flow meters at an exhibition. When the topic of laminar flow differential pressure mass flow meters came up, he waved his hand and said, “Laminar flow differential pressure mass flow meters have too narrow an application range; they cannot be used in the semiconductor industry.” ”Whether it’s the foreign companies we mentioned earlier, such as BronkHorst and Horiba, or the domestic company Seven Stars Huachuang, they all initially adopted a technology approach based on the thermal principle. Therefore, many people assume that laminar flow differential pressure mass flow meters cannot be used in high-end manufacturing fields such as semiconductors. But is that really the case? Let’s start by looking at the manufacturers of mass flow meters. Among them are Brooks, MKS, Horiba, Bronkhost, vogtlin, Burkert, kofloc, Fujikin, Beijing Qixing Huachuang, and Houlibo. As for laminar flow differential pressure mass flow meters, the only manufacturers currently producing them are Alicat and Shaanxi Yidu. Indeed, in terms of market share, thermal mass flow meters have a very high proportion. It is undeniable that the mass flow meters exported to us by these foreign manufacturers are indeed based on the thermal principle. But few people know that the D500 series introduced by Horiba is a mass flow meter based on the differential pressure principle. As for its upgraded DZ500 series of mass flow controllers, although we don’t have access to the technical specifications, the term “laminar flow” is mentioned on the official website, which indicates that manufacturers of thermal mass flow meters have already begun developing mass flow meters using the laminar flow differential pressure principle. However, just like Horiba’s D500 and DZ500 products, these models are not available in the domestic market; yet it is these two types of mass flow meters that are widely used in semiconductor equipment. Thermal flowmeters have been in use for a long time, which has led to thermal mass flowmeters reaching a limit – it has become difficult to make further improvements. The laminar flow differential pressure mass flowmeter represents a completely new technical approach, and it offers significant advantages over thermal mass flowmeters in terms of certain performance aspects. Therefore, the development of laminar flow differential pressure mass flowmeters holds great promise; it is likely to see rapid growth thanks to the fast advancement of semiconductor and new energy technologies!