Thermal Conductivity Gas Sensor with Enhanced Flow-Rate Independence

Abstract

In this article, novel thermal gas sensors with newly designed diffusion gas channels are proposed to reduce the flow-rate disturbance. Simulation studies suggest that by lowering the gas flow velocity near the hot film, the maximum normalized temperature changes caused by flow-rate variations in the two new designs (Type-H and Type-U) are decreased to only 1.22% and 0.02%, which is much smaller than in the traditional straight design (Type-I) of 20.16%. Experiment results are in agreement with the simulations that the maximum normalized flow-rate interferences in Type-H and Type-U are only 1.51% and 1.65%, compared to 24.91% in Type-I. As the introduced CO2 flow varied from 1 to 20 sccm, the normalized output deviations in Type-H and Type-U are 0.38% and 0.02%, respectively, which are 2 and 3 orders of magnitude lower than in Type-I of 10.20%. In addition, the recovery time is almost the same in all these sensors. These results indicate that the principle of decreasing the flow velocity near the hot film caused by the two novel diffusion designs can enhance the flow-rate independence and improve the accuracy of the thermal conductivity as well as the gas detection.

Programmable and Modularized Gas Sensor Integrated by 3D Printing

“…The core component for the thermal conductivity gas sensors is a thermal element designed to heat the surrounding gas environment, facilitating the transfer of heat from the heater to the ambient atmosphere. 83,84 The distinct thermal conductivities of various gases enable the identification of specific gas species and concentrations, which is achieved by monitoring the heat transfer rate of the gases and comparing it with a reference gas (Figure 2d). These sensors feature remarkable stability, reproducibility, prompt response times, and long operational lifespans, attributable to their physical sensing mechanisms.…”

“…Thermal gas sensors operate by discerning gas species and concentrations through the detection of resistance variations in a thermistor, which arise due to changes in thermal conductivity across different gaseous environments or as a result of catalytic combustion reactions with flammable analytes. , These sensors are commonly categorized into two types: thermal conductivity gas sensors and thermochemical gas sensors. The core component for the thermal conductivity gas sensors is a thermal element designed to heat the surrounding gas environment, facilitating the transfer of heat from the heater to the ambient atmosphere. , The distinct thermal conductivities of various gases enable the identification of specific gas species and concentrations, which is achieved by monitoring the heat transfer rate of the gases and comparing it with a reference gas (Figure d). These sensors feature remarkable stability, reproducibility, prompt response times, and long operational lifespans, attributable to their physical sensing mechanisms.…”

Micromachined Thermal Gas Sensors—A Review

“…Artificial neural networks were then used to map the multi-parameter response to output both flow and thermal conductivity. Wang et al have presented a thermal conductivity sensor where they have ensured the heated element is exposed to gas by diffusion, this is by putting it out of the main flow path [ 54 ].…”

A Review of Hydrogen Sensors for ECLSS: Fundamentals, Recent Advances, and Challenges

“…The heat conduction-type hydrogen sensor belongs to the crossover class of electrical and physical thermodynamics sensors; its detection circuit is based on the design theory of a balanced bridge, while its detection principle is based on thermodynamics [34][35][36][37][38]. Figure 3 shows a heat conduction-type hydrogen sensor, which is designed based on the theory that each gas has a different thermal conductivity.…”