Velocity-independent thermal conductivity and volumetric heat capacity measurement of binary gas mixtures

In this paper, we present a single hot wire suspended over a V-groove cavity that is used to measure the thermal conductivity ($k$) and volumetric heat capacity ($\rho c_p$) for both pure gases and binary gas mixtures through DC and AC excitation, respectively. The working principle and measurement results are discussed

Thermal Flow Meter with Integrated Thermal Conductivity Sensor

This paper presents a novel gas-independent thermal flow sensor chip featuring three calorimetric flow sensors for measuring flow profile and direction within a tube, along with a single-wire flow independent thermal conductivity sensor capable of identifying the gas type through a simple DC voltage measurement. All wires have the same dimensions of 2000 (Formula presented.) m in length, 5 (Formula presented.) m in width, and 1.2 (Formula presented.) m in thickness. The design theory and COMSOL simulation are discussed and compared with the measurement results. The sensor’s efficacy is demonstrated with different gases, He, N2, Ar, and CO2, for thermal conductivity and thermal flow measurements. The sensor can accurately measure the thermal conductivity of various gases, including air, enabling correction of flow rate measurements based on the fluid type. The measured voltage from the thermal conductivity sensor for air corresponds to a calculated thermal conductivity of 0.02522 [W/m·K], with an error within 2.9%.</p

Bi-Directional MEMS Thermal Flow Sensor for Respiratory Applications

This paper presents a MEMS bi-directional thermal flow sensor which consists of a pair of suspended thin wires. Wires are fabricated on both sides of the silicon wafer to form the upstream and downstream wires to measure the flow rate, and two more wires on the Si wafer to realize a Wheatstone bridge readout. Both wires are used as heater and sensor elements at the same time. In this paper we present a finite element analysis using COMSOL Multiphysics as well as measurement results on a fabricated device using air flow up to 2 m/s

Towards a Gas Independent Thermal Flow Meter

We present a novel potentially gas-independent thermal flow sensor chip that contains three two-wire calorimetric flow sensors to measure the flow profile and flow direction inside a tube, and a single-wire flow-independent thermal conductivity sensor which detects the type of the gas through a simple DC voltage measurement. All wires have the same dimensions of 2000 µm in length, 5 µm in width and 1.2 µm in thickness. Four different gases Ar, N 2 , Ne and He were used for the thermal conductivity measurement and the measured output voltage corresponds very well with a theoretical model

Gas Independent Thermal Flow Meter Based on Real-Time Velocity-Independent k and ρcp Measurement

A thermal flow sensor for gases is presented that measures the flow rate independent of the type of the gas by simultaneously measuring and compensating for the thermal conductivity (k) and volumetric heat capacity (ρc p ) of the gas. A suspended wire on a V-groove cavity is used to measure both fluid parameters independent of the flow rate. The output of the thermal flow sensor is automatically corrected for the medium using these measured parameters

Flow-Independent Thermal Conductivity and Volumetric Heat Capacity Measurement of Pure Gases and Binary Gas Mixtures Using a Single Heated Wire

Among the different techniques for monitoring the flow rate of various fluids, thermal flow sensors stand out for their straightforward measurement technique. However, the main drawback of these types of sensors is their dependency on the thermal properties of the medium, i.e., thermal conductivity (k), and volumetric heat capacity (ρcp). They require calibration whenever the fluid in the system changes. In this paper, we present a single hot wire suspended above a V-groove cavity that is used to measure k and ρcp through DC and AC excitation for both pure gases and binary gas mixtures, respectively. The unique characteristic of the proposed sensor is its independence of the flow velocity, which makes it possible to detect the medium properties while the fluid flows over the sensor chip. The measured error due to fluctuations in flow velocity is less than ±0.5% for all test gases except for He, where it is ±6% due to the limitations of the measurement setup. The working principle and measurement results are discussed