Homogeneous Temperature Distribution Research Articles

Thermo-Mechanical Behavior of Long-Bored Energy Pile: A Full-Scale Field Investigation

A geothermal energy pile is a revolutionary piling technique that combines a pile foundation with a ground source heat pump system that not only supports the structure but also provides heating and cooling for buildings and bridges. The thermo-mechanical behavior of long energy piles in soft clay has rarely been investigated, despite their increasing utilization. A long floating energy pile with a length-to-diameter ratio of 66.7 was evaluated on its own and monitored in service of the supported structure in the city of Kunshan, China. With vertical mechanical loads, the experiment involved alternate cooling and heating cycles, allowing for careful analysis and assessment of the pile's temperature, stress, and displacement. Temperature-induced stress, axial force, and friction resistance of the pile shaft, as well as the change in displacement of the energy pile throughout building, were all studied. The field observations revealed without any surprise that a longer energy pile outperformed a shorter one in terms of heating exchange capacity with a more homogenous temperature distribution along the pile. Following a quasi-linear relationship with the temperature variation, the thermo-induced additional axial force soared with the larger length-diameter ratio of the pile and may even reach four times that of the pile under pure mechanical loads. Important additional settlements were also observed especially in cooling conditions. The shaft frictions along the long bored energy pile were found to have a complicated distribution, which requires further investigations.

Biodegradable, Flexible Transparent Ordered Ag NWs Micromesh Conductor for Electrical Heater and Electromagnetic Interference Shielding Applications

Flexible transparent and biodegradable conductors with excellent performance are quite desirable for the development of portable electrical heaters and electromagnetic interference (EMI) shielding. As a promising candidate, electrical homogeneity and stability are required for a silver nanowire (Ag NW) network conductor to increase its reliability and robustness. Herein, an optimally well organized silver nanowire micromesh (Ag NMs) electrode embedded in biodegradable poly(l-lactic acid) (Ag NMs/ePLLA) is prepared without a template by virtue of the coffee-ring effect. The Ag NMs/ePLLA electrode possesses a low sheet resistance variation (<5%), leading to a highly homogeneous temperature distribution and a rapid response time of 6 s with a saturation temperature of 111.8 °C at a low driving voltage of 3 V. Moreover, the Ag NMs/ePLLA film also shows an outstanding EMI shielding efficiency of ∼27.6 dB in X-band with a sheet resistance of ∼10 Ω/sq to prevent electromagnetic radiation pollution and excellent biodegradable properties to avoid pollution by electronic waste. Therefore, the multifunctional portable Ag NMs/ePLLA electrode provides great opportunities in the application fields of thermal management and EMI shielding.

Quasi-equilibrium approximation of the solidification process for micro phase change materials taking into account curvature and surface tension

Phase change materials (PCMs) have superior energy storage properties, which can be used to solve the problem of energy absorption and release at various times, intensities and locations. Energy storage using PCMs is a promising way to make the rational use of energy, which could help improving our environment. Owing to their significant applications, we investigate the solidification process of microparticles, which is also known as the Stefan problem. Due to the tiny size of microparticles, quasi-equilibrium approximation of such Stefan’s problem is considered, where the effect of the curvature and the surface tension are incorporated. Here, we determine a simple but yet effective iterative model for the moving boundaries of micro PCMs (MPCMs) by assuming the homogeneous temperature distribution in molten regimes in order to avoid solving more complicated diffusion equations. We purposely investigate the solidification process of spherical and ellipsoidal MPCMs and find that both the curvature and the surface tension promote the solidification process. Due to these outcomes, peanut-shaped MPCMs are proposed to demonstrate the usage of both effects for fabricating smart MPCMs. Finally, the validity of the model is confirmed by a Computational Fluid Dynamics (CFD) method.

Channel to rib width ratio effect on thermal performance of cooling plate in polymer electrolyte membrane fuel cell

AbstractEnsuring a homogeneous temperature distribution inside a polymer electrolyte membrane fuel cell stack is crucial to fuel cell performance and durability, and cooling channels are responsible for this. In this study, a three‐dimensional numerical investigation is performed on a channel to rib width ratio (CR) based on serpentine flow field design. The cooling performance of various designs having different CR values is considered and compared according to the temperature uniformity index, the temperature difference between the maximum and minimum temperature, average bottom temperature, and pressure drop between the inlet and outlet of the cooling channels. Results demonstrate that the average temperature, temperature uniformity index, temperature difference, and pressure drop decrease by about 5%, 40%, 37%, and 79%, respectively, when CR is increased from 0.33 to 3.00. More uniform temperature distribution and thus, better cooling performance is achieved for CR = 3.00, especially at low Reynolds numbers and high heat fluxes. Also, the lowest pressure drops are obtained when CR is 3.00 under all considered operating conditions.

Validation of an extended objective function for the thermal optimisation of injection moulds

The central shaping element in the injection moulding process is the unique injection mould. The tempering channel layout inside the injection mould is the decisive factor in terms of cost-effectiveness and the resulting quality of the moulded parts. The aim of the present research is to further improve thermal mould design by an inverse approach. In the first part of this work, the improvement of the objective function as a central element of the inverse thermal mould design is explained based on theoretical evaluations. The aim of the revised objective function is a homogeneous temperature distribution in the moulded part at the end of the cooling phase and the achievement of a homogeneous morphology in the plastic. The inverse thermal mould design is applied for the first time to a practically relevant moulded part. The usability of the methodology also for complex geometries can be shown. Due to limitations in the choice of materials for additively manufactured injection moulds, conventionally designed cooling systems are usually equivalent in performance. The use of the developed method may reduce the dependence on the experience of the mould designer and results in moulded parts with low distortion.

Direct absorption nanofluid-based solar collectors for low and medium temperatures. A review

Solar energy is expected to play an important role in the decarbonization of the energy and industrial sectors. Low and medium temperature (<400 °C) solar thermal collectors have proved to be a reliable solution to supply heat and decarbonize the industrial sector, with over 800 Solar Heat for Industrial Processes (SHIP) plants put in operation in the last decade. Governmental support policy is a key factor for solar thermal energy to play a major role in CO2 emission reduction, which require improving the efficiency of solar collectors and reducing costs. Recent studies have demonstrated the potential of nanoparticles to enhance the optical properties of heat transfer fluids for direct absorption solar collectors (DASC). In a DASC the transfer fluid absorbs volumetrically the incident radiation, resulting in a more homogeneous temperature distribution and less heat losses than in conventional surface collectors. In this paper, the current state-of-the-art of SHIP installations and conventional surface collectors is presented, and a critical literature review dedicated to nanofluid-based DASC for both concentrating and non-concentrating collectors is provided. The key findings and the challenges to be overcome toward promoting the development of nanofluid-based DASC for SHIP applications are discussed.

Optimization of Aeration for Accelerating Municipal Solid Waste Biodrying

Biodrying technology is commonly used in Thailand to produce refuse-derived fuel (RDF), however, this technology remains ineffective on high-moisture waste. Air supply is key to ensuring homogenous temperature development within the waste matrix during biodrying, increasing RDF quality. This study investigated negative aeration during local municipal solid waste biodrying to meet RDF standards in reduced time. Lysimeter experiments were performed on pre-shredded waste (300 kg/m3) using different aeration patterns. The temperature, vent gas oxygen level, weight loss, and leachate volume during the biodrying process were monitored. In addition, the treated waste’s temperature, moisture, and heating values were evaluated to determine the biodrying process efficiency. The results indicate that shorter heating phases can be achieved during continuous aeration. No significant temperature variation was observed in the waste layers, with a low standard deviation of 1.96% during constant air supply, indicating homogeneous temperature development during the biodrying process. The vent gas contained 15–20% oxygen and non-detectable methane, evidencing sufficient air supply. The total heat development was independent of aeration pattern; therefore, biodrying was unaffected by excess air supply at a 95% confidence level. The highest weight loss and moisture content reduction were 25% and 66%, respectively. The optimal aeration was continuous mode with non-excessive aeration, increasing the lower heating value from 2,884.0 to 4,938.0 kCal/kg, and reducing the moisture content from 48.5% to 22.2%. RDF quality can be improved 1.7 times to meet Thailand’s standards within a short biodrying period of 7 days using homogeneous temperature distribution operated under continuous aeration

Temporal and spatial heat input regulation strategy for high-throughput micro-drilling based on multi-beam ultrafast laser

High-throughput laser drilling is crucial for the processing of large-area micro-hole arrays, but the local heat accumulation effect in the processing significantly limits the fabrication quality, especially for multi-beam laser micro-drilling. Although cooling methods such as water or airflow is applied to enhance heat dissipation, the heat input regulation is a convenient and effective way to improve the processing quality. In this work, a novel temporal and spatial heat input regulation strategy is proposed for multi-beam laser micro-drilling to effectively suppress the local heat accumulation during the processing. The strategy consists of a scanning path planning model and an optimization method of key drilling parameters. The scanning path planning model is established based on the temperature field of the workpiece, which is dynamically calculated using a transient finite-difference method (FDM). In addition, an optimization method is proposed to match the drilling parameters with the designated scanning path. Via this heat input regulation strategy, a more homogeneous temperature distribution can be obtained in the multi-beam laser drilling of micro-hole arrays. The maximum temperature and duration of overheating that causes material oxidation are decreased by 10%, and 50%, respectively. With the realization of high-quality (recast-free) and high-throughput (2430 micro-holes in 210 s, or 12 micro-holes/s), the proposed strategy showsa promising prospect in the multi-beam drilling of micro-hole arrays and other laser processing with possible heat accumulation, such as large-area surface texture and precise engraving of micro-nano structures.

Cooling performance optimization of supercritical hydrocarbon fuel via bi-directional flow pattern

• A novel bi-directional flow (BDF) pattern for regenerative cooling is proposed. • BDF achieves more homogeneous temperature distribution and higher fuel conversion. • BDF increases slightly pressure drop and surface temperature at the same time. • A hybrid flow pattern is recommended to maximize the cooling performance. Regenerative cooling is a promising method to meet the increasing heat management requirement of hypersonic vehicles. In contrast to the traditional co-directional flow (CDF) pattern, here we propose an innovative bi-directional flow (BDF) pattern inside rectangular parallel channels to improve the active regenerative cooling performance. Based on a reliable CFD model, the flow and heat transfer performance of n -decane under two types of thermal boundaries are analyzed. Three types of channels at different locations considering buoyancy effect are also investigated. By observing the contour of specific heat, mass fraction of n -decane, temperature distribution, velocity field and calculating the heat sink and surface heat transfer coefficient, the cooling performance of BDF pattern is discussed and compared with that of CDF pattern. Results reveal that compared to the CDF pattern a more homogeneous temperature distribution and a higher conversion of n -decane (around 14% increment under thermal boundary: 1.9 MW/m 2 and 1400 K) are obtained by BDF pattern. However, an increased pressure drop within a reasonable range and a higher surface temperature are observed for the BDF pattern. With overall consideration, a hybrid flow pattern is proposed which could maximize the cooling effect within the surface temperature constraint yet keeping its simple inner structure.

Numerical design of distributive mixing elements

This paper presents a novel shape-optimization technique for the design of mixing elements in single-screw extruders. Extruders enable the continuous production of constant-cross-section profiles. Equipped with one or several screw-shaped rotors, extruders transport polymer particles towards the outlet. Due to shear heating, melting is induced and a melt stream is created, which can be further processed. While many variants of multi-screw extruders exist, a significant share of all extrusion machines is made up of single-screw extruders due to their comparatively low operating costs and complexity. While the reduced complexity yields economic benefits, single-screw extruders' mixing capabilities, i.e., their ability to produce a melt with a homogeneous material and temperature distribution, suffer compared to multi-screw extruders. To compensate for this shortcoming, so-called mixing elements are added to the screw to enhance mixing by recurring flow reorientations. In view of the largely unintuitive flow characteristics of polymer melts, we present an optimization framework that allows designing these mixing elements numerically based on finite-element simulations of the melt flow. To reduce the computational demand required by shape optimization of a complete mixing section, we only focus on the shape optimization of a single mixing element. This paper presents advances in three aspects of numerical design: (1) A combination of free-form deformation and surface splines is presented, allowing to parameterize the mixing element's shape by very few variables. (2) The combination of this concept with a linear-elasticity-based mesh update method to deform the computational domain without the need for remeshing is demonstrated. (3) A simple yet robust and sensitive objective formulation to assess distributive mixing in laminar flows based on a measure for the interfacial area is proposed.

Analysis of the effect of nonuniform surface temperature distribution on the performance of a thermoelectric generator

The present paper analyses the effect of an inhomogeneous surface temperature distribution on the operation of a thermoelectric generator (TEG), experimentally and numerically. In the steady-state measurements, a spatially inhomogeneous temperature distribution is imposed on the colder surface of the TEG. The hotter surface temperature distribution is kept homogeneous. The maximum-to-minimum difference in the TEG cold side surface temperature distribution has been changing between 10 °C and 25 °C during the measurements, while the difference of the area averaged cold surface temperature to the hot side temperature has been varying within the range 70 °C and 150 °C. Tests are also performed with homogeneous cold side temperature distributions. Measurements with the variable and uniform cold side temperatures are compared. The comparison shows that a local surface variation within the considered ranges does not have a noticeable effect on the TEG performance.A finite element method (FEM) based computational model is developed and validated based on the measured data. Using the FEM model, it has been possible to increase the applied temperature inhomogeneity to higher levels beyond those, which were possible in the experiments. The FEM model predicts a deviation at very high temperature inhomogeneity on the cold side, which can be justified with the temperature dependency of the material properties.

Microfluidic Platform with Serpentine Geometry Providing Chaotic Mixing in Induction Time Experiments.

We present a droplet microfluidic platform mixing the contents of the droplet chaotically in microfluidic induction time measurements, a promising method for quantifying nucleation kinetics with minute amounts of solute. The nucleation kinetics of aqueous potassium chloride droplets dispersed in mineral oil without surfactants is quantified in the presence and absence of chaotic mixing. We demonstrate the ability of the proposed platform to dictate droplet size, to provide a homogeneous temperature distribution, and to chaotically mix the droplet contents. Chaotic mixing in induction time measurements is facilitated by the motion of droplets through serpentine micromixer bends, while the extent of mixing is controlled by how much droplets move. Different nucleation kinetics are observed in experiments where the droplets are static, mixed, and in motion. We hypothesize that the droplet motion induces formation of a thin-liquid Bretherton film surrounding the droplets. The thin film shields droplets from solid boundaries that are more efficient heteronucleant surfaces compared to liquid–liquid interfaces. We observed that repeated microfluidic induction time measurements, particularly with moving droplets, produce significantly distinct cumulative nucleation probability curves, indicating that the measured nucleation kinetics depend strongly on the details of the experimental procedure, which we discuss in detail. Finally, we compare the microfluidic experiments to well-mixed, milliliter volume, turbidity-based measurements in the context of classic nucleation theory.

Continuous microwave-assisted extrusion for high moisture texturized foods: A feasibility study

This study demonstrates a technical scale set-up for microwave-assisted extrusion of high moisture, texturized food systems. The set-up has been evaluated in a stationary study regarding the correlation of microwave tuner position and gap with the reflected microwave power and the product temperature, respectively. On that basis, a casein-based model food system has been plasticized by continuous microwave extrusion. The product outlet temperature and chemical composition have been investigated with varying screw speeds and power inputs.The stationary study resulted in specific tuner positions, giving an area of desired process parameters. This area was successfully transferred to a continuous product application, where desired gel-sol transition was achieved. With increasing power input, the product temperature increased, while it decreased with increasing screw speed and constant power input. The fat, protein, and dry matter content of the casein-based model system did not differ significantly throughout all trials. Industrial relevanceMicrowave heating is a promising alternative heating method for food applications. Within microwave extrusion it shows high potential for upscaling applications whilst maintaining a homogenous temperature distribution throughout the product. Moreover, microwave technology offers high efficiencies and the possibility to use green energy sources. Furthermore, the space saving design and easy application provide high potential for scale-up.

Multi-objective optimization of a mini channeled cold plate for using thermal management of a Li-Ion battery

Mini channeled cold plates (MCCP) are an impressive choice for electric vehicles with a liquid-based thermal management system to keep the battery temperature within the desired range and to achieve a homogeneous temperature distribution. This paper came up with an optimum solution for maximum battery temperature (MBT), maximum temperature difference on the battery surface (MTD) and pressure drops in the channels (ΔP), which are vital parameters. Multi-objective optimization of geometric parameters and coolant flow rate of a designed MCCP which is experimentally investigated is carried out using the Desirability Function Approach. Firstly, the design of experiments (DoE) is generated using response surface method after determining the input variables and their levels. Then, each sample of DoE are modeled and analyzed numerically. Furthermore, the regression equations of the objective functions (MBT, MTD and ΔP) depending on the design parameters are developed and their variance analyzes are performed. Prediction accuracies of model equations developed for MBT, MTD and ΔP are 97.75%, 95.49% and 97.15%, respectively. As a result, optimum values of design variables, namely channel width (mm), distance between branches (mm), channel depth (mm), number of crossovers in branches and coolant flow rate (l/min) are 5, 5, 10, 13 and 0.7061, respectively.

Thermal Behavior and Power Scaling Potential of Membrane External-Cavity Surface-Emitting Lasers (MECSELs)

Membrane external-cavity surface-emitting lasers (MECSELs) have great potential of power scaling owing to the possibility of double-side cooling and a thinner active structure. Here, we systematically investigate the limits of heat transfer capabilities with various heat spreader and pumping parameters. The thermal simulations employ the finite-element method and are validated with experimental results. The simulations reveal that double-side cooling lowers the temperature by about a factor of two compared to single-side cooling when diamond and silicon carbide (SiC) heat spreaders are used. In comparison, the benefit for a thermally worse conductive heat spreader is larger, i.e. a fourfold decrease for sapphire. Furthermore, we investigate the limits of power scaling imposed by the intrinsic lateral heat flow of the heat spreaders that sets how much the pump beam diameter can be enlarged while having efficient cooling. To this end, the simulations for sapphire reveal a limit for the pump beam diameter within the hundred micrometer range, while for SiC and diamond the limit is more than double. Moreover, pumping with a super-Gaussian beam profile could further reduce the temperature rise near the center of the pump area compared with a Gaussian beam. Finally, we investigate the benefits of double-side pumping of thick membrane gain structures, revealing a more homogeneous axial temperature distribution than for single-side pumping. This can be crucial for gain membranes with thicknesses larger than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1\,\mu \text{m}$ </tex-math></inline-formula> to fully exploit the power-scaling ability of MECSEL technology.

High-Performance Flexible Transparent Electrical Heater Based on a Robust Ordered Ag Nanowire Micromesh Conductor

High-performance electrical heaters with a rapid thermal response, homogeneous temperature distribution, and chemical and mechanical robustness are desirable for inevitable use in various areas such as defrosting windows and wearable thermotherapy. Herein, optimally engineered ordered Ag nanowire micromeshes are partially embedded in poly(ethylene terephthalate) matrix (Ag NMs/ePET) via a facile spray coating and transfer approach for flexible transparent conductor and electrical heater applications, which exhibit a slight sheet resistance variation of less than 5%. The resultant Ag NMs/ePET heater exhibits uniform heat distribution over the entire film and can achieve a saturation temperature of 134 °C with a rapid response time of 5 s under an input voltage of 6 V. In addition, owing to the large-diameter nanowire micromesh structure and the protective effect of PET encapsulation, the flexible transparent Ag NMs/ePET heater presents excellent mechanical and chemical robustness in extreme environments and still maintains a stable heating performance after 5000 repeated bending cycles (r = 5 mm) and exposure to a corrosive solution. This work lays the foundation for improving the electrical heater performance and provides a facile methodology to fabricate a high-performance flexible transparent conducting film for other innovative applications.

Thermal Protection Performances of the Macro and/or Nano Enhanced PCM in a Representative Battery Pack

ABSTRACT This experimental study focused on the comparison of thermal protection performances of macro and/or nano enhanced organic PCM in a representative battery pack from low to high discharge rates. The macro/nano enhanced RT-44 provides the desired battery thermal protection requirements in terms of criteria such as maximum temperature and maximum temperature difference restriction and uniform temperature distribution throughout the battery pack. It increases the effective battery thermal protection time by 117%-32% depending on the discharge rates. While PCM thermal protection provides a more homogeneous temperature distribution throughout the battery pack, nano and/or macro enhanced one provides it throughout the cell. The macro enhancement essentially makes a major contribution to shortening the cooling time for the next use.

Improved performance of polyimide Cirlex‐based dielectric barrier discharge plasma actuators for flow control

AbstractDielectric barrier discharge (DBD) plasma actuators are simple electrohydrodynamic devices, which are able to provide effective aerodynamic control. One of the main components of these devices is the thin dielectric layer, which allows to separate and prevent the arc between the high‐voltage electrodes. Different materials can be used as dielectric layer to reduce the power consumption or boost the flow controlling effect of the actuators. In this context, this report presents a comparative study of two commercial polyimides, Kapton and Cirlex, used as dielectric layer of surface DBD plasma actuators. The electrical, dielectric, mechanical, electromechanical, and thermal properties were obtained to evaluate overall performance. It was verified that Cirlex (8.3 W) consumes less power than Kapton (21.3 W) to generate higher induced flow velocity of ≈3.4 m/s for an input voltage of 11 kVpp and 24 kHz. During one AC cycle at 11 kVpp the charge transferred for Cirlex (70 nC) is lower than for Kapton (100 nC), as well as the dielectric breakdown voltage to ignite the plasma discharge, 1.5 and 2.2 kVpp, respectively. The Cirlex DBD presents a higher voltage operation limit (at least 14 kVpp) and a more regular plasma discharge, which results in a more homogenous thermal profile and temperature distribution during its operation. The Cirlex actuator delivered higher mechanical power (6.2 mW) and achieved higher electromechanical efficiency (0.004%). The polyimide Cirlex proved to be a suitable alternative for Kapton to fabricate DBD plasma actuators for flow control with improved performance.

Effects of Temperature (In)homogeneity during Hot Stamping on Deformation Behavior, Structure, and Properties of Brass Valves

Herein, assessing the effects of initial temperature (in)homogeneity on a hot‐stamped CuZn40Pb2 medical gas valve (fitting) via numerically and experimentally defining mutual relations of selected deformation parameters and optimizing temperature distribution within the original semi‐product heated via induction are focused. For these purposes, three preheating regimes are simulated, and deformation behaviors are evaluated. The predicted results are validated by experimental stamping and subsequent evaluation of the structure and properties of stamped fittings. The results show that preheating the semi‐product with a certain temperature gradient occurring between the axial and (sub)surface regions is favorable, as homogeneous initial temperature distribution results in rapid surface cooling by the effect of heat transfer from semi‐product to die, which imparts inhomogeneous stress distribution, local changes in structural phases, and possible occurrence of oxides. Too low (sub)surface temperature of the semi‐product can result in a significant (local) increase in flow stress, which consequently results in the danger of occurrence of forming defects. The brass fitting stamped with the optimized preheating procedure features an average grain size of 5.8 μm, uniform grains’ orientations with maximum texture intensity of two times random, and ultimate tensile strength of almost 400 MPa, while maintaining elongation to failure of more than 35%.

What causes the absence of pulsations in Central Compact Objects in supernova remnants?

Most young neutron stars belonging to the class of Central Compact Objects (CCOs) in supernova remnants do not have known periodicities. We investigated seven such CCOs to understand the common reasons for the absence of detected pulsations. Making use of XMM-Newton, Chandra, and NICER observations, we perform a systematic timing and spectral analysis to derive updated sensitivity limits for both periodic signals and multi-temperature spectral components that could be associated with radiation from hotspots on the neutron star surface. Based on these limits, we then investigated for each target the allowed viewing geometry that could explain the lack of pulsations. We find that it is unlikely (< 10−6) to attribute that we do not see pulsations to an unfavorable viewing geometry for five considered sources. Alternatively, the carbon atmosphere model, which assumes homogeneous temperature distribution on the surface, describes the spectra equally well and provides a reasonable interpretation for the absence of detected periodicities within current limits. The unusual properties of CCOs with respect to other young neutron stars could suggest a different evolutionary path, as that proposed for sources experiencing episodes of significant fallback accretion after the supernova event.