International Journal of Nanotechnology (12 papers in press)

Regular Issues

• A simulation-based study on the disc brake temperature distribution for optimizing hole geometry
  by Shyam Sunder Sharma, Hariharan Raju, Pranay Singh Tomar, Rajesh Jangid, Rahul Khatri 
  Abstract: Disc brakes used in automotive are responsible for braking to ensure a smooth and safe ride. This study deals with the thermal analysis of a disc brake rotor under various geometry of holes cut on the disc rotor surface. The friction on the disc escapes in the form of heat from the surface of the disc rotor. The temperature observed on the surface of the rotor, because of the friction developed between the brake pads and the rotor is analysed using ANSYS 18.1. The rotor is designed by assuming appropriate parameters in SOLIDWORKS 17. The temperature distribution and total heat flux were observed using ANSYS 18.1. The analysis was carried out on different hole geometries i.e. circular, square, 3/4th circular, straight slots, and rotor without holes. The dissipation of heat was found better in disc rotor with holes as compared to rotor without holes. The simulation study shows that the slotted holes on the disc rotor has surface temperature i.e. 89.356
  Keywords: Automotive disc brake; Simulation; Hole geometry; Heat dissipation.
  
  
• Effective thermal conductivity of La_0.9Ce_0.1Ni₅ metal hydride: effect of hydrogenation cycles, particle size and hydrogen concentration  
  by Pyoungjong Lee, Kwangjin Jung, Kyoungsoo Kang, Seonguk Jeong, Ki Bong Lee, Chusik Park 
  Abstract: Metal hydrides store hydrogen in a solid state through reactions with hydrogen, offering high storage density and safety as key advantages. Metal hydrides release heat during hydrogenation and absorb heat during dehydrogenation. To enable hydrogenation or dehydrogenation, it is important to promptly remove the heat generated during hydrogenation or supply the heat required during dehydrogenation. The effective thermal conductivity of the metal hydride is used to predict and evaluate the heat transfer performance, including both heat removal and supply. This study presents the effective thermal conductivity of La_0.9Ce_0.1Ni₅ metal hydride as influenced by hydrogenation cycles, particle size, and hydrogen concentration. An effective thermal conductivity measurement device based on the comparative radial heat flow method was designed and fabricated to perform the measurements. The effective thermal conductivity of La_0.9Ce_0.1Ni₅ metal hydride decreased with increasing hydrogenation cycles. It is expected to converge to 1.29 W/m·K after 23 cycles. With hydrogenation cycles, both the particle size and the effective thermal conductivity showed a similar tendency. With hydrogen concentration, the effective thermal conductivity variations of the metal hydride showed a similar tendency to the equilibrium pressure variations in the pressure-composition-temperature (PCT) curves.
  Keywords: metal hydride; effective thermal conductivity; comparative radial heat flow method; hydrogenation; particle size; hydrogen concentration.
  
  
• Thermophysical investigation of eicosane with expanded graphite shape-stabilised phase change material  
  by Veerakumar Chinnasamy, Tsogtbilegt Boldoo, Hyemin Kim, Jeongho Park, Honghyun Cho 
  Abstract: A shape-stabilised phase change material (SSPCM) was successfully synthesised using a microwave-assisted one-pot method, incorporating eicosane (EI) as the latent heat storage medium and expanded graphite (EG) as the supporting matrix. The process involved the microwave-induced expansion of EG in molten EI, promoting effective infiltration and encapsulation of the PCM. The resulting composites, prepared with EG concentrations ranging from 10 to 25 wt%, were thoroughly characterised to evaluate their thermal and structural properties. Differential scanning calorimetry (DSC) revealed that while the EG addition had minimal impact on the phase change temperatures, it led to a progressive decrease in latent heat with increasing EG content. Thermogravimetric analysis (TGA) indicated enhanced thermal stability of the composites due to the physical confinement of EI within the EG matrix. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analyses confirmed the physical blending of components without chemical bonding and preserved crystalline structures, respectively. The findings demonstrate that EG is an effective structural support, improving thermal stability and preventing leakage, though at the cost of reduced latent heat storage capacity.
  Keywords: thermal energy storage; phase change material; eicosane; expanded graphite; thermal conductivity; latent heat; shape-stabilised.
  
  
• CFD analysis of MWCNT nanocomposite PCM melting in the latent heat storage tank  
  by Seongmin Choi, Tsogtbilegt Boldoo, Nayoung You, Veerakumar Chinnasamy, Honghyun Cho 
  Abstract: In this paper, the low thermal conductivity of the phase change material (PCM) used in the latent heat storage tank was improved by adding multi-walled carbon nanotubes (MWCNTs) to enhance the heat storage capacity and release rate. MWCNT was mixed in amounts up to 2.0 wt%, and the thermal conductivity of the mixture was numerically calculated using the modified Maxwell model. The calculation results indicated that the specific heat slightly decreased as the mass fraction of MWCNTs increased, while the thermal conductivity improved by an average of 41.26%. Additionally, the heat storage process by the copper tube and copper fin in the latent heat storage tank was analytically examined. The PCM/MWCNT mixture, which has relatively high thermal conductivity, effectively absorbed heat and transitioned into a liquid phase faster than pure n-eicosane. The thermal conductivity decreased due to the phase change to a liquid state, and the outlet temperature tended to rise rapidly because the heat was not effectively absorbed after the phase change, confirming the low heat storage capacity. In conclusion, the addition of MWCNTs enhanced the thermal conductivity, and the total stored energy increased compared to pure n-eicosane due to the improved heat storage rate.
  Keywords: latent heat thermal energy storage; computational fluid dynamics; phase change material; multi-walled carbon nanotube; thermal conductivity.
  
  
• A dual-scheme MEMS Pirani vacuum gauge for high-precision and low-power applications  
  by Junki Jung, Seunghoe Koo, Jaehee Park, Kyeongtae Kim 
  Abstract: High-precision vacuum sensing is an essential element in various industrial fields such as semiconductor processing and vacuum based packaging. Accordingly, the advancement in vacuum sensing technology that enables both miniaturisation and low power operation is required. Here, we manufactured highly miniaturised Pirani vacuum gauge using the micro-electro-mechanical systems (MEMS) process and verified its performance using various signal processing methods. First, the fabricated gauge was used to measure the pressure response in the range of 10² Torr to 10^-5 Torr, and its reliability was verified. Furthermore, using the same measurement setup, we conducted a comparative analysis in the pressure range of 800 mTorr to 15 mTorr between the fabricated gauge and a commercial sensor. Subsequently, the gauge was operated using the unipolar square-wave heating method and its characteristics were compared with those obtained from the sine-wave heating method. Although the unipolar square-wave heating method exhibited slightly lower precision than the sine-wave heating method, it demonstrated reliable performance suitable for practical implementation, along with the benefit of low power operation. Therefore, this method can be effectively applied to various practical vacuum measurement systems due to its advantages such as simple circuit configuration and low power consumption. The fabricated MEMS Pirani vacuum gauge, featuring miniaturisation and low-power characteristics and integrated with the unipolar square-wave heating-based measurement technique, demonstrates potential for applications in industrial fields such as semiconductor processing and vacuum-based packaging.
  Keywords: MEMS Pirani sensor; unipolar square wave; vacuum measurement; MEMS process; pressure sensing; signal processing.
  
  
• Ni nanoparticle-based TLP sintering pastes for high-temperature joining of dissimilar electrodes in thermoelectric devices  
  by Hyukjun Youn, Kyeongho Lee, Hyeonbin Jo, Soonil Lee, Kyu-Mann Lee, Soon-Mok Choi 
  Abstract: A transient liquid phase sintering (TLPS) brazing method for high-temperature thermoelectric devices was investigated through the development of Ni-Sn-based pastes. A pressureless brazing process was also developed to address the challenge of uniform pressure application in complex structures of thermoelectric devices. A brazing evaluation method using a simplified thermoelectric module structure was established to assess paste performance. The tensile strength of joints brazed with the 43Ni-57Sn paste, corresponding to the stoichiometric composition of Ni3Sn4, was lower than expected. To improve tensile strength, a new TLPS paste with excess Sn (30Ni-70Sn) was formulated based on a mechanistic study. As a result, the tensile strengths of the Ni-Ni and Cu-Ni joints were significantly improved to 29.08 kgf/cm² and 14.49 kgf/cm², representing 1.81-fold and 3.5-fold increases, respectively. These results demonstrate that applying a Sn-excess composition in TLPS paste effectively enhances the tensile strength of pressureless TLPS brazing by promoting the formation of robust adhesive intermetallic compound (IMC) layers.
  Keywords: pressureless TLPS; Ni-Sn IMC; thermoelectric module; Sn excess composition; mechanical strength.
  
  
• Evaluation of heat transfer characteristics in cryogenic stage depending on the shape and material  
  by Myung Su Kim, Yojong Choi, Seunghyun Song, Yeon Suk Choi 
  Abstract: The heat transfer characteristics in cryogenic environments are critical in various fields such as semiconductors, aerospace, and superconducting applications. Minimising heat loss and ensuring efficient cooling performance are essential in cryogenic systems, necessitating the optimal design of the stage in terms of shape and material. In particular, maintaining temperature uniformity and reliability is crucial in experimental apparatus and precision equipment, requiring careful consideration of thermal shielding and conduction properties. This study aims to identify the optimal stage shape and material for effective heat transfer in cryogenic environments. Three stage designs and two materials were analysed through experiments. The experimental setup incorporated a cryocooler as the cooling source, along with multi-layer insulation (MLI) and a thermal link to reduce heat invasion and enhance thermal conduction. Temperature distribution and thermal performance were evaluated to identify the most efficient stage configuration. This study provides fundamental insights for optimising the thermal design of cryogenic stages and contributes to the advancement of cryogenic system performance.
  Keywords: cryogenic stage; cryocooler; conduction-cooling; heat transfer; cryogenic environment; thermal link; thermal conductivity; temperature distribution.
  
  
• Theoretical model of thermal contact conductance considering electron and phonon conduction in broad temperatures  
  by Duk Hyung Lee, Myung Su Kim, Dong-Hyun Kim, Yeon Suk Choi 
  Abstract: This study presents a thermal contact conductance (TCC) model that improves predictive accuracy across a wide temperature range, particularly in the region above the peak in thermal conductivity. In conduction cooled cryogenic systems that include current leads or resistive thermal components, heat is generated internally or transferred from external sources, requiring accurate estimation of TCC. Copper, a commonly used thermal conductor in such systems, exhibits nonlinear thermal conductivity with temperature, which makes precise prediction of TCC challenging, especially near and beyond the conductivity peak. The proposed model builds upon the Cooper-Mikic-Yovanovich (CMY) formulation by incorporating mechanical contact parameters along with thermophysical influences, such as size effects and heat carrier behaviour, through a modified thermal conductivity expression. The model was assessed using previously reported experimental data for oxygen-free high conductivity copper interfaces. Compared to conventional approaches, it demonstrates a significant reduction in deviation from measured values across the full temperature range, with improved agreement in the post-peak region of thermal conductivity.
  Keywords: thermal contact conductance; contact resistance; theoretical model; broad temperature; heat carrier; physical property.
  
  
• Experimental study on the 3-omega sensor depending on surface condition of forced convective heat transfer  
  by Chang-Ui Jeon, Dong-Wook Oh 
  Abstract: Accurate determination of gas-mixture composition is essential for stable and efficient operation of energy systems. Thermal-conductivity sensors are attractive for this task because, compared with catalytic or electrochemical sensors, they offer simpler structures and a wider measurable concentration range. Here, the three-omega (3ω) method was employed to quantify the influence of surface airflow conditions on the measured thermal conductivity of a gaseous sample. Two sensor architectures - a microheater on a polyimide-substrate and a suspended-bridge microheater - were fabricated and tested under forced convection conditions. The devices were operated in a flow chamber, where the inlet flow rate was varied up to 200 L/min, and the 3ω temperature-amplitude signal was recorded. For the polyimide sensor, comparison with theoretical predictions indicates that the surface airflow is insensitive to retrieved substrate thermal conductivity over the tested range. By contrast, the suspended sensor exhibited little change at moderate flow but a pronounced decrease in signal at the highest flow, consistent with enhanced convective heat removal and a modified thermal boundary condition. These results delineate the operating envelope in which 3ω measurements remain robust in flowing gases, providing guidance for gas-composition metrology under flow conditions.
  Keywords: 3ω method; forced convection; heat transfer coefficient; sensor calibration; thermal conductivity measurement.
  
  
• Flow visualisation of natural convection around a heated vertical plate using background oriented schlieren  
  by Su-Min Jeong, Dae-Hyun Kim, Dong-Wook Oh 
  Abstract: This study employed the background oriented schlieren (BOS) technique to visualise and quantify natural convection flow around a heated vertical plate. The BOS system comprised a camera, a heated plate, and a background image. The surface temperature of the vertical plate was set to 75, 100, 125, and 150°C, and natural convection was observed under ambient conditions. The recorded images were processed using a probabilistic optical flow algorithm to calculate pixel displacements and derive the velocity field, which was then calibrated by comparison with two-dimensional computational fluid dynamics (CFD) simulations of the same geometry and conditions. BOS successfully reproduced the velocity distribution in the high-temperature, high-speed core region, agreeing with CFD results within approximately 10% for peak velocity. However, in low-velocity and stagnant flow regions near the plate edges, minimal refractive index changes limited accurate velocity detection. These findings demonstrate the potential for extending BOS applications to thermal-fluid system monitoring and leak detection.
  Keywords: flow visualisation; BOS; background oriented schlieren; natural convection; heated vertical plate; velocity profile.
  
  

Special Issue on: Eco-Friendly and Sustainable Cognitive Green Nano-Technologies for the Mitigation of Emerging Environmental Pollutants

• Preparation of titanium dioxide composite nanomaterials using copper catalysis and their dynamic adsorption and photocatalytic performance in water treatment  
  by Ye Tian 
  Abstract: The aim is to investigate the dynamic adsorption performance of titanium dioxide (TiO2) nanocomposite materials in water treatment, providing direction for water purification. The copper-catalysed living free-radical polymerization method polymerizes the prepared TiO2 particles with tertiary amine polymer to manufacture the TiO2 polymer nanocomposite materials. The prepared TiO2 nanocomposite materials are then modified to obtain the quaternised TiO2 polymer nanocomposite materials (quaternised TiO2@poly(DEAEMA)), which are characterized and analysed. Finally, the water treatment performance of quaternised TiO2@poly(DEAEMA) is judged through photocatalysis and adsorption experiments, while the antibacterial performance of the prepared materials is judged using the common Escherichia coli and Staphylococcus aureus. Results demonstrate that the quaternised TiO2@poly(DEAEMA) polymer nanocomposite materials are completely and tightly wrapped, presenting a flower-like appearance, with a significantly-increased diameter and an average size of about 600nm, which can be utilized as the pollutant adsorbent. Water treatment simulation reveals the fastest adsorption rate and the highest adsorption capacity of quaternised TiO2@poly(DEAEMA), reaching 265 mg/g given the same reaction time. The catalytic removal rate in ultraviolet and visible light reaches 94%, and the photocatalysis of visible light reaches 69%. Until the reaction lasts for 45 minutes, its antibacterial activity is optimal, and the diameter of the inhibition zone against Escherichia coli and Staphylococcus aureus exceeds 16 mm. Therefore, the prepared TiO2 nanomaterials have high adsorption properties, good photocatalysis performance, and excellent antibacterial properties, which can provide an experimental basis for the treatment and purification of water resources in the industry.
  Keywords: titanium dioxide; water treatment; dynamic adsorption; photocatalysis; nanocomposite material.
  
  

Special Issue on: Smart Bio-Signal Acquisition System

• Deep learning-based feature extraction coupled with multi-class SVM for COVID-19 detection in the IoT era  
  by Auwalu Mubarak, Sertan Serte, Fadi Al-Turjman, Rabiu Aliyu, Zubaida Said, Mehmet Ozsoz 
  Abstract: The deadly coronavirus virus (COVID-19) was confirmed as a pandemic by the World Health Organisation (WHO) in December 2019. Prompt and early identification of suspected patients is necessary to monitor the transmission of the disease, increase the effectiveness of medical treatment and as a result, decrease the mortality rate. The adopted method to identify COVID-19 is the Reverse-Transcription Polymerase Chain Reaction (RT-PCR), the method is affected by the shortage of RT-PCR kits and complexity. Medical imaging using deep learning has proved to be one of the most efficient methods of detecting respiratory diseases, but efficient deep learning architecture and low data are affecting the performance of the deep learning models. To detect COVID-19 efficiently, a deep learning model based feature extraction coupled with Support Vector Machine (SVM) was employed in this study, Seven pre-trained models were employed as feature extractors and the extracted features are classified by multi-class SVM classifier to classify CT scan images from COVID-19, common pneumonia and healthy individuals. To improve the performance of the models and prevent overfitting, training was also carried out on augmented images. To generalise the model's performance and robustness, three datasets were merged in the study. The model with the best performance is the VGG19 which was trained with augmented images: it achieved an accuracy of 96%, a sensitivity of 0.936, a specificity 0f 0.967, an F1 score of 0.935, a precision of 0.934, a Yonden Index of 0.903 and AUC of 0.952. The best model shows that COVID-19 can be detected efficiently on CT scan images.
  Keywords: artificial intelligence; COVID-19; SVM; feature extraction.
  DOI: 10.1504/IJNT.2021.10040115