Thermal Resistance Characteristics Research Articles

Cellulose Nanocrystals and Lignin Nanoparticles Extraction from Lemna minor L.: Acid Hydrolysis of Bleached and Ionic Liquid-Treated Biomass.

Using biomass to develop and obtain environmentally friendly and industrially applicable biomaterials is increasingly attracting global interest. Herein, cellulose nanocrystals (CNCs) and lignin nanoparticles (LNPs) were extracted from Lemna minor L., a freshwater free-floating aquatic species commonly called duckweed. To obtain CNCs and LNPs, two different procedures and biomass treatment processes based on bleaching or on the use of an ionic liquid composed of triethylammonium and sulfuric acid ([TEA][HSO4]), followed by acid hydrolysis, were carried out. Then, the effects of these treatments in terms of the thermal, morphological, and chemical properties of the CNCs and LNPs were assessed. The resulting nanostructured materials were characterized by using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that the two methodologies applied resulted in both CNCs and LNPs. However, the bleaching-based treatment produced CNCs with a rod-like shape, length of 100-300 nm and width in the range of 10-30 nm, and higher purity than those obtained with ILs that were spherical in shape. In contrast, regarding lignin, IL made it possible to obtain spherical nanoparticles, as in the case of the other treatment, but they were characterized by higher purity and thermal stability. In conclusion, this research highlights the possibility of obtaining nanostructured biopolymers from an invasive aquatic species that is largely available in nature and how it is possible, by modifying experimental procedures, to obtain nanomaterials with different morphological, purity, and thermal resistance characteristics.

Automatic in-situ measurement of thermal resistance for GaN HEMTs

An automatic in-situ technique for thermal resistance measurement based on an electrical method is proposed in this paper. In contrast to the conventional thermal resistance measurement circuits of the electrical method, this method involves direct measurement of the thermal resistance of GaN high-electron-mobility transistor (HEMT) devices in an operating circuit by introducing a well-matched radio-frequency switching circuit into the operating circuit. The advantage of this method is that the thermal resistance can be measured periodically on the in-situ device without changing the electrical characteristics of the device. Based on this result, the cooling curve of the HEMT device in the power amplifier (PA) circuit is collected and the thermal resistance characteristics of the HEMT are determined via the structure function method. The purpose of this paper is to successfully obtain the thermal resistance of in-situ devices through an automatic in-situ measurement circuit of thermal resistance, and to verify the feasibility of periodic detection of thermal resistance of in-situ devices.

Prediction Model for Trends in Submarine Cable Burial Depth Variation Considering Dynamic Thermal Resistance Characteristics

Fault problems associated with submarine cables caused by variations in their burial depth are becoming increasingly prominent. To address the difficulty of detecting the burial depth of submarine cables and trends in its variation, a prediction model for submarine cable burial depth was proposed which considers the dynamic characteristics of thermal resistance. First, a parallel thermal circuit model of a three-core submarine cable was established, and a formula for calculating the submarine cable’s burial depth was derived based on a formula for calculating the submarine cable’s core temperature. Then, the calculation result was corrected by considering the dynamic characteristics of the thermal resistance of the submarine cable’s structural materials. On this basis, feature vectors associated with the seabed cable burial depth calculation data and time nodes were mined by a convolutional neural network and used as the input parameters of a long short-term memory network for optimization and training, and a prediction model for trends in seabed cable burial depth variation was obtained. Finally, an example analysis was carried out based on the actual electrical parameter data of submarine cables buried by an offshore oil and gas platform. The results showed that the prediction model for trends in variations in the burial depth of submarine cables based on the CNN-LSTM neural network can achieve high prediction accuracy and prediction efficiency.

Study on heat transfer of waxy crude oil melting phase change based on a novel model

The study of phase change heat transfer of crude oil melting is important for pre-heating and restarting of pipelines. Combining the characteristics of waxy crude oil characteristics of waxy crude oil melting, a novel mathematical model was established, which can accurately describe the non-linear release of latent heat, liquid-solid interface changes, natural convection, and other key heat transfer problems. In the process of heating and melting, the variation law of the solid-phase interface position in the pipe at different initial solidification states was analyzed. The results showed that in the partially solidified pipeline, the liquid crude oil in the pipeline has a higher temperature at the initial heating stage, and continuously loses heat to the low temperature crude oil, resulting in a decline in the liquid-phase ratio at the initial stage. Because crude oil was affected by different degrees of radial thermal resistance, latent heat release and porous medium characteristics at different positions of the pipeline, the temperature drop curves of the crude oil varies greatly.

Pressure drop and thermal resistance characteristics of plain-fin heat sink with impingement flow

Pressure drop and thermal resistance characteristics of plain-fin heat sink with impingement flow

Influence mechanism of the three-zone synergistic efficiency-enhancing pattern on the 3D flow field and thermal resistance characteristics for wet cooling towers

For a super-large natural draft wet cooling tower (S-NDWCT) equipped in a 1000 MW unit, a 3D numerical model of the three-zone synergistic efficiency-enhancing pattern (TSEP) was established and validated. This study focused on the influence mechanism of the three-zone parameters on the 3D flow field and thermal resistance characteristics, including the installation height h, installation angle θ, total coverage area S, length L and number n of the split-flow plate, water distribution partition radius R1, the proportion of inner zone water amount P, and fillings partition radius R2. The results showed that the TSEP reconfigures and comprehensively optimizes the airflow field, and presents the more uniform air-water ratio and water temperature fields. The volumetric heat transfer coefficient hv increases and then reduces as h, θ, S, n, R1, P and R2 increase, and increases continuously with increasing L in the range studied. Additionally, the ventilation G increases and then reduces with the increase of h, θ, R1 and P, increases with rising S, n and R2, and reduces with L increases. Finally, the relatively optimized values of the three-zone parameters are obtained. In this case, compared with a conventional tower, the hv and G increase by 11.3% and 10.6%, respectively.

Anti-leak, self-adaptive liquid metal-epoxy in-situ cured composites with ultra-low thermal resistance via flexible droplet inclusions

Generally, the function of thermal interface material (TIM) is filling rough surfaces, eradicating air pockets, decreasing thermal resistance, and improving heat dissipating effects. On this basis, we provide the TIM with another identity, “adhesion”, rendering it not only play a role of heat dissipation, but also serve as an adhesive to bond contacting surfaces. In this work, nano- to microscopic liquid metal (LM) droplets are embedded into the epoxy matrix to fabricate a LM-epoxy in-situ cured composite. By adding the curing agent, the LM-epoxy composite is cured into an entity structure, transforming from an amorphous grease state to a self-adaptive pad state. When the average droplet size is in a reasonable range of approximately 5–25 μm, the composite's thermal resistance (Rtotal) decreases to 2.19 mm2K/W at 70% volume fraction with its adhesive strength of 0.497 MPa, and the thermal conductivity (kTIM) could increase to 10.05 W/(m·K) at 85%. Both Rtotal and kTIM change rapidly for droplet size approximately ranging from 102 nm to 101 μm and then tend to level off when it further increases to 102 μm. A conception of equivalent contact thickness, δ, is presented to elucidate the contacting thermal resistance Rc, and set up predictive models of Rtotal for different volume fractions by considering the microscopic interfacial thermal resistance Rb between filler and matrix or not. This composite simultaneously possesses characteristics of the low thermal resistance like thermal grease, the whole entity like thermal pad, and the anti-leak characteristics by in-situ cured process. Actual cooling tests show it has a considerable temperature difference of 4.75 °C lower than the commercial thermal grease at 650 W heating power. This in-situ cured strategy, via decreasing the thermal resistance and solving the problem of LM leakage, remarkably promotes the LM-TIMs achieving a broader application prospect in the future.

Investigating the performance of conventional and hydrophobic surface heat sink in managing thermal challenges of high heat generating components

In the pursuit of optimizing heat dissipation and improving performance in electronic devices, liquid-cooled heat sinks have garnered significant interest due to their potential to improve heat transfer efficiency. Presented study set out to assess the effectiveness of straight channel heat sinks as a thermal solution for high heat generating electronics components, while also investigating the impact of applying a hydrophobic coating on their performance. A series of tests were conducted at different heating powers (50W-250 W) and flow rates (200–950 ml/min), while also considering different orientations and directions of flow. The investigation focused on analysing critical aspects such as heat transfer performance, wall temperature variations, thermal resistance, and pressure drop characteristics of straight channel heat sinks with conventional and hydrophobic-coated surfaces. The results showed that the Nusselt number increased with higher Reynolds numbers and heating powers, indicating improved heat transfer efficiency. However, the hydrophobic coating on the heat sink surface led to a reduction in the Nusselt number due to the formation and retention of bubbles, hindering heat transfer. The maximum average reduction of 20.85% in Nusselt number was noticed at 100 W for the vertically positioned hydrophobic-coated heat sink with downward flow compared to conventional surface (CS) heat sink. Additionally, the findings revealed that pressure drop is influenced by Reynolds number and the presence of bubbles, with gravity playing a role in reducing pressure drop in certain orientations. A hydrophobic coating shows a small decrease in pressure drop, but bubble formation limits its effectiveness to some extent. Comparisons also indicated that the highest average decrease in pressure drop about 11.92% was observed for the same configuration, vertically positioned hydrophobic heat sink with downward flow, at 50 W. Moreover, the study's findings have broader implications beyond electronics. Heat sinks are widely employed in various industries, including automotive, aerospace, renewable energy systems, and industrial processes.

Porous Material (Titanium Gas Diffusion Layer) in Proton Exchange Membrane Fuel Cell/Electrolyzer: Fabrication Methods & GeoDict: A Critical Review

Proton exchange membrane fuel cell (PEMFC) is a renewable energy source rapidly approaching commercial viability. The performance is significantly affected by the transfer of fluid, charges, and heat; gas diffusion layer (GDL) is primarily concerned with the consistent transfer of these components, which are heavily influenced by the material and design. High-efficiency GDL must have excellent thermal conductivity, electrical conductivity, permeability, corrosion resistance, and high mechanical characteristics. The first step in creating a high-performance GDL is selecting the appropriate material. Therefore, titanium is a suitable substitute for steel or carbon due to its high strength-to-weight and superior corrosion resistance. The second crucial parameter is the fabrication method that governs all the properties. This review seeks to comprehend numerous fabrication methods such as tape casting, 3D printing, freeze casting, phase separation technique, and lithography, along with the porosity controller in each process such as partial sintering, input design, ice structure, pore agent, etching time, and mask width. Moreover, other GDL properties are being studied, including microstructure and morphology. In the future, GeoDict simulation is highly recommended for optimizing various GDL properties, as it is frequently used for other porous materials. The approach can save time and energy compared to intensive experimental work.

Research of cooling tower filler based on radial basis function artificial neural network (RBF ANN)

AbstractThe filler is the core component of the cooling tower, filler performance refers to both its thermal and flow resistance characteristics, which use empirical formulas of tower characteristic N, volumetric mass transfer coefficient βxv, and pressure drop ΔP obtained through experimentation under specific conditions. However, the performance equations for identical countercurrent fillers can vary at different heights or seawater concentrations. Linear interpolation is the conventional method for obtaining the filler performance under different conditions, but its uncertainty limits the application. This paper explores the use of the radial basis function artificial neural network (RBF ANN) to analyze filler performance based on existing performance equations. The data set is generated by the filler performance equations. The results demonstrate that RBF ANN has a preferable prediction effect with high correlation (the determination coefficient R2 > 0.99) and prediction accuracy (the proportion of relative error within 10% N10 > 90%). Furthermore, the predicted results are consistent with the experimental results of the filler performance. Therefore, RBF ANN can accurately predict filler performance at varying heights and seawater concentrations, making it universal and providing a basis for cooling tower design.

Interface thermal resistance of micron-thin film

The utilize of multilayer stacked structure dielectric is very common in electrical engineering, such as thin film capacitor wound by multilayer dielectric, and oil paper cable insulation layer formed by multilayer oil paper winding. Interface thermal resistance between dielectric layers are crucial thermo-physical parameters, which are very important for the thermal management of electric devices to improve the operating stability. However, there are some difficulties in precisely measuring thermal resistance parameters between micron-thin films by conventional ways. In this paper, a novel method is proposed for measuring thermal resistance parameters between films based on the thermal pulse method, which is normally used for mapping space charge or electric field distribution. The sample in this paper is of a multilayer structure containing at least one insulating dielectric film. The parameters of the interface thermal resistance of the multilayer structure are obtained by simulating and analyzing the thermal response current characteristics of the dielectric film. To study the characteristics of interface thermal resistance, several different thin film interfaces were designed by changing the type of thermal interface materials and the roughness of the contact surface. The obtained data of the interface thermal resistance show well consistence with the theoretical expectation.

Thermal fatigue characteristics of 8Y2O3-ZrO2, La2Zr2O7, La2(Zr0.7Ce0.3)2O7 and La2Ce2O7 thermal barrier coatings in duplex, multilayer functionally graded and multilayer configurations

La2Zr2O7, La2(Zr0.7Ce0.3)2O7 and La2Ce2O7 pyrochlore plasma sprayable powders were synthesized and plasma spray coated on steel plates with NiCrAlY bond coat. Three different configurations were used: duplex, multilayer functionally graded and multilayer, with different combinations of commercial 8% yttria stabilized zirconia (8YSZ) and NiCrAlY (bond coat) layers. The prepared coatings were compared with the standard duplex 8YSZ thermal barrier coatings (TBCs) with a goal to study their suitability to serve as TBCs. TBCs? layer thicknesses and interfaces were studied via SEM on polished cross section metallographic samples removed from the spray coated TBCs. Thermal fatigue resistance was evaluated by directing a gas flame on the ceramic surface at 1200 and 1400 ?C, followed by its rapid withdrawal and forced cooling by pedestal fan. The maximum number of thermal shock cycles the coatings could withstand before failure was determined. The multilayered TBCs with lanthanum cerate composition stacked with 8YSZ exhibited the superior thermal fatigue resistance characteristics compared to all other studied TBCs. The findings were correlated with the crystalline phases of the ceramic coatings, obtained via XRD, and discussed in the light of existing literature.

Research on Transient Temperature Rise Measurement Method for Semiconductor Devices Based on Photothermal Reflection

In this article, a transient temperature rise measurement method for semiconductor devices based on photothermal reflection is proposed. The relationship between the reflectivity of a 360 nm laser beam and the device temperature is studied. Through the appropriate design of the optical circuit and the data acquisition system, measurement of the transient temperature rise characteristics of GaN-based microwave power devices is realized. In combination with resistor-capacitor network impulse response theory, the transient temperature rise curve is processed using the Bayesian iterative deconvolution method. By extracting the thermal time constant, nondestructive characterization of the temperature increase and thermal resistance characteristics of each material layer in the heat flow path is achieved, and the complementary relationship between the temperature change in the active region during heating and the device heat dissipation characteristics is verified. Additionally, the forward Schottky junction characteristics method and infrared thermal imaging are used to measure the channel temperature for verification of the proposed thermal reflection method. These measurements indicate that the proposed method can provide accurate results.

Manufacturing methods used to produce certain biocomposite materials – a mini-review

In recent years, interest in biocomposite materials has grown significantly, due to the potential to replace conventional materials. The increasing use of biocomposite materials in various fields (aerospace, automotive, maritime transport, sports equipment, energy, construction, medicine), is due to their characteristics, superior to those of conventional materials, the reduction of energy consumption required for their production, the increased resistance to corrosion, tear resistance, wear resistance, high temperature, strength, low density, controllable thermal conductivity, good deformability, exceptional dimensional stability, low thermal expansion, impact resistance and many other characteristics that, unlike classical materials, are convenient. This study reviews the manufacturing methods used to produce certain biocomposite materials.

SOME COMPARATIVE OPINIONS REGARDING THE EVALUATION OF MAXIMUM STRESSES IN LONG FIBER REINFORCED COMPOSITES

This paper falls within the scope of current concerns for scientific and technical research, relating to technical structures made of composite materials, recognized for their mechanical, thermal and chemical or erosive resistance characteristics. In this case, the study is characterized by the analysis of the bearing capacity of some composites: a) with fibers applied along them, b) in a certain direction, c) in a direction perpendicular to the fibers, d) the stability of the structure along the fibers, e) in a direction perpendicular to the fibers or f) combined stress.

Microstructural Characteristics, Modeling of Mechanical Strength and Thermal Performance of Industrial Waste Glass Blended Concrete

The need to get rid of solid waste in the environment necessitates the incorporation of waste glass powder (WGP) in mortar and concrete. The blending of WGP (G) with ordinary Portland cement (OPC) is a valorization technique that is not only cost efficient but also environmentally friendly. The replacement level is denoted as CxG10−x, where x is 0–20 wt.% at an interval of 5 wt.% in mortar (w/b = 0.4) and 0, 10, 20 and 30 in concrete (w/b = 0.42). The study investigates the effects of glass on the setting, workability, thermal resistance, microstructure, mineral phases and bond characteristics of silicon and hydroxyl-based compounds and C-O vibrations. It also provides the model equations for strength characteristics in terms of OPC, G and ages in mortar and concrete on one hand and investigates the residual strength and density of glass blended concrete at elevated temperature (550 °C) on the other. It is found that glass enhances the workability, reduces the setting time and density and enhances the residual strength and density of concrete. The presence of glass leads to the formation of coesite and microstructural distortion and decreases the Ca/Si ratio. Besides, the bond characteristics of the binder are significantly affected, while the thermal residual strength capacity in glass blended concrete (C80G20) is 40.4% and 75.14% lower than that in OPC concrete (C100G0) because of the low thermal conduction of glass particles. The optimum glass content in mortar and concrete to produce 33 MPa (28 days) and 47 MPa (90 days) is found to be 10 wt.% and 20 wt.%, respectively.

3D reactive inkjet printing of bisphenol A-polycarbonate

Additive Manufacturing (AM) techniques have gained extensive attention recently as they are able to directly produce 3D parts utilising a layer-by-layer manner. Inkjet printing is one such technique which can produce micron-scale features but is generally constrained to liquid viscosities of less than 30 mPa·s, therefore available materials are limited. A 3D reactive inkjet printing (3DRIJP) approach to deposit low viscosity monomers and polymerise in-situ to form polymer parts is emerging. In this work, a 3DRIJP approach has been developed to fabricate bisphenol A-polycarbonate (BPA-PC) for the first time by using a low viscosity reactive ink containing monomers, catalyst and solvent. A set of processing parameters were explored and optimised including temperature of droplet formation, substrate temperature and droplet spacing to print films. With a thermal post-curing process, BPA-PC was formed successfully with a molecular weight comparable to those which were manufactured by the conventional melt transesterification process. The thermal properties were evaluated suggesting good thermal resistance characteristics. Finally, a 3D ziggurat structure was printed to demonstrate the capability to fabricate BPA-PC by an AM method, thus broadened the library of AM materials to include engineering grade polymers via 3DRJIP. This approach was innovative in both the BPA-PC material formulation and the 3DRIJP process development from traditional inkjet printing methods, where a single printable formulation of monomers for thermoplastic optical-clear BPA-PC was able to be printed using one printhead to form 3D structures.

Determination of the inner forms of hollow blocks containing phase-changing material for different climate regions

Hollow blocks are used widely in buildings for their lightweight construction and high thermal resistance characteristics. When used with a phase change material (PCM), these blocks can reduce the heating and cooling loads of buildings compared to conventional hollow blocks. However, it is essential that the block inner forms and PCMs should be selected based on climate conditions. In this study, hollow blocks containing PCM in different climate types are thermally analysed. In the first step, ten different formed blocks are thermally analysed. In these blocks, the effects of hollow ratio (HR), inner form, and the number of cavities on heat flux and temperature distribution are investigated. The inner form of the hollow block with the least heat flux is determined in this step. The second step consists of optimization for the PCM melting temperature and layer thickness for the different provinces. The optimization results are evaluated on a building in terms of primary energy consumption and global costs. The best performing locations of the PCMs within the block are defined for all provinces in the last step. The results of the study are discussed in terms of the block surface temperatures and liquid fraction. The best PCM locations are found close to the block’s centerline in hot and warm climates and close to the indoor side in cold climates.

Effect Mechanism and Performance Evaluation of Flange Contact Thermal Resistance in an Aero-Engine

According to the discontinuous structural characteristics of a gas turbine, by considering the contact thermal resistance of the rough surface, a contact thermal resistance measurement experiment was conducted in this study. The main objectives of this work were to investigate the influence mechanism and change law of the contact thermal resistance characteristics on flange installation. Furthermore, this study conducted a theoretical analysis of contact thermal resistance and the calculation of a typical flange mounting edge based on actual operating conditions. The research results show that the contact thermal resistance of a typical flange mounting edge increases with an increase in flange clearance under different tightening torques, which is essentially proportional to the flange clearance. As the flange clearance increases, the unit contact thermal conductivity firstly decreases rapidly. Then, as the flange clearance reaches 0.4 mm, the decreasing rate of unit contact thermal conductivity tends to flatten. In addition, the contact thermal resistance of the typical flange mounting edge decreases with the increase in the tightening torque under different flange clearances. Furthermore, the contact area ratio is not related to the material, and the contact thermal resistance under actual working conditions can be calculated using the unit contact area.

Rapid detection and quantitation of dipicolinic acid from Clostridium botulinum spores using mixed-mode liquid chromatography-tandem mass spectrometry.

Analysis of the dipicolinic acid (DPA) released from Clostridium botulinum spores during thermal processing is crucial to obtaining a mechanistic understanding of the factors involved in spore heat resistance and related food safety applications. Here, we developed a novel mixed-mode liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for detection of the DPA released from C. botulinum type A, nonproteolytic types B and F strains, and nonpathogenic surrogate Clostridium sporogenes PA3679 spores. DPA was retained on a mixed-mode C18/anion exchange column and was detected using electrospray ionization (ESI) positive mode within a 4-min analysis time. The intraday and interday precision (%CV) was 1.94-3.46% and 4.04-8.28%, respectively. Matrix effects were minimal across proteolytic type A Giorgio-A, nonproteolytic types QC-B and 202-F, and C. sporogenes PA3679 spore suspensions (90.1-114% of spiked DPA concentrations). DPA recovery in carrot juice and beef broth ranged from 105 to 118%, indicating limited matrix effects of these food products. Experiments that assessed the DPA released from Giorgio-A spores over the course of a 5-min thermal treatment at 108°C found a significant correlation (R = 0.907; P < 0.05) between the log reduction of spores and amount of DPA released. This mixed-mode LC-MS/MS method provides a means for rapid detection of DPA released from C. botulinum spores during thermal processing and has the potential to be used for experiments in the field of food safety that assess the thermal resistance characteristics of various C. botulinum spore types.