Accurate measurement of temperatures with low power consumption with the highest sensitivity and smallest possible elements is still a challenge. The thermal, electrical, and mechanical properties of carbon nanotubes (CNTs) have suggested that their use as a very sensitive sensing element will allow the creation of different sensors, far superior to other devices of similar size. In this paper, we present a short review of different constructive designs of CNTs based resistive sensors used for temperature measurement, available in literature, assembled using different processes, such as self-assembly, drop-casting from a solution, thin films obtained by gluing, printing, spraying, or filtration over a special membrane. As particular cases, temperature sensors obtained from CNT-polymer nanocomposite structures, CNTs filled with uniformly dispersed Fe3O4 nanoparticles or with gallium, and carbon nanotube wires (CNWs) hybrids are presented. Using these preparation procedures, mixtures of CNTs with different dimensions and chirality, as well as with a variable level of impurities and structural defects, can be produced. The sensors’ performance charts are presented, highlighting a number of aspects regarding the applicability of CNT structures for temperature measurement ranging from cryogenic temperatures to high temperatures, the limitations they have, their characteristics and advantages, as well as the special situations that may arise given the particular structure of these new types of materials, together with basic relationships and parameters for CNTs characterization. Further research will be required to develop the techniques of manipulating and depositing individual CNTs on supports and electrodes for the development of temperature sensors.

We present an investigation consisting of single walled carbon nanotubes (SWCNTs) based cryogenic temperature sensors, capable of measuring temperatures in the range of 2–77 K. Carbon nanotubes (CNTs) due to their extremely small size, superior thermal and electrical properties have suggested that it is possible to create devices that will meet necessary requirements for miniaturization and better performance, by comparison to temperature sensors currently available on the market. Starting from SWCNTs, as starting material, a resistive structure was designed. Employing dropcast method, the carbon nanotubes were deposited over pairs of gold electrodes and in between the structure electrodes from a solution. The procedure was followed by an alignment process between the electrodes using a dielectrophoretic method. Two sensor structures were tested in cryogenic field down to 2 K, and the resistance was measured using a standard four-point method. The measurement results suggest that, at temperatures below 20 K, the temperature coefficient of resistance average for sensor 1 is 1.473%/K and for sensor 2 is 0.365%/K. From the experimental data, it can be concluded that the dependence of electrical resistance versus temperature can be approximated by an exponential equation and, correspondingly, a set of coefficients are calculated. It is further concluded that the proposed approach described here offers several advantages, which can be employed in the fabrication of a microsensors for cryogenic applications.

The electrical response of sulfonated single-walled carbon nanotubes (SWCNTs) to NO and NO₂, for gas sensing applications, at room temperature, is reported in this work. A specific configuration based on SWCNT deposition between double pair configuration gold electrodes, supported on a substrate, was considered for the sensing device; employed characterization technique where FTIR and SEM. The experimental results showed a p-type response of the sulfonated SWCNTs, with decrease in resistance, under exposure to NO gas (40–200 ppb) and NO₂ (40–200 ppb). Also, the sensor responses to successive exposures at NO₂ 800 ppb together with investigation of long term stability, at 485 ppb for NO, are reported. The reaction mechanism in case of NO and NO₂ detection with sulfonated SWCNTs is presented.

An integrated SWCNT-Pt-P₂O₅-based sensor type was fabricated by direct deposition of the films on a commercial planar sensor substrate without any conventional coating and using the dropcast procedure. For the humidity sensing experimental work, two sensors were prepared by the authors using this facile solution and a system for data acquisition. The measurements showed that the integrated SWCNT sensors exhibit high and fast response (of approximately 25 s) toward a humidity range from 1% to 90% AH. The high sensitivity and dynamic reproducibility of these sensors materials reveal that the proposed composition and morphology can be applied to fabricate sensing devices for detecting water humidity in nitrogen gas from low to medium concentration range. The experimental results also confirm that the proposed solution fits in the class of proper structures for humidity sensing in inert gas and can show remarkable sensing and recovery capabilities for industrial usage. The sensing mechanism is attributed to the fact that electrical changes in sensors resistance, as a function of the AH, are related to the attraction and trapping of water molecules produced on the surface of the film. Due to this physical behavior, a resistive path is formed between the microelectrodes. The resistivity of the system increases as the AH increases, or decreases when the AH values decreases due to an electrolysis process taking place under sensors supply voltage and using Pt catalyst.

We report on the experimental investigation of the magnetoresistance behavior of cryogenic temperature sensors based on single-walled carbon nanotubes (SWCNTs) as a function of temperature and magnetic flux density; one sensor was based on layers/networks of unsorted SWCNT of various chiralities, and one on SWCNTs layers of (7,6) chirality. SWCNT-based sensors were fabricated according to a straightforward method, and the electrical properties were measured from room temperature down to 2 K using a Quantum Design Physical Property Measurement System (PPMS). The two sensors present different magneto-transport behavior, with the magnetoresistance dependence on the magnetic field being a sum of two terms with positive and negative contributions respectively. The expression for magnetoresistance is derived together with its experimentally determined coefficients. For both sensors, the electrical resistance dependence on temperature below the 80 K mark is explained by Mott’s law of variable-range hopping. The experimentally obtained hopping dimension d values of 2.67 for the system comprised of purified (7,6) chirality SWCNTs and 2.97 for the system comprised of unsorted SWCNTs are in good agreement with the theory. As a second step, the magnetic field was kept constant and at different values, while the temperature was scanned over the investigated domain.

Hydrogen–methane gas mixtures are increasingly recognized as a viable path toward achieving carbon neutrality, leveraging existing natural gas infrastructure while reducing greenhouse gas emissions. This study investigates a novel static mixing device designed for blending hydrogen and methane, employing both experimental tests and three-dimensional computational fluid dynamics (CFD) simulations. Hydrogen was introduced into a methane flow via direct injection, with experimental mixtures ranging from 5% to 18% hydrogen. The mixture quality was assessed using a specialized gas chromatograph, and the results were compared against simulated data to evaluate the mixer’s performance and the model’s accuracy. The system demonstrated effective blending, maintaining uniform hydrogen concentrations across the outlet with minimal variations. Experimental and simulated results showed strong agreement, with an average accuracy error below 2%, validating the reliability of the CFD model. Smaller nozzles (0.4 mm) achieved greater mixing uniformity, while larger nozzles (0.6 mm) facilitated higher hydrogen throughput, indicating trade-offs between mixing precision and flow capacity. The mixing device proved compatible with existing pipeline infrastructure, offering a scalable solution for hydrogen integration into natural gas networks. These findings underscore the mixer’s potential as a practical component in advancing the hydrogen economy and achieving sustainable energy transitions.