Thermal Energy Transfer Research Articles

Experimental study of Lannea microcarpa seed oil as a heat transfer fluid or thermal energy storage material for medium-temperature applications

In this study, we investigated the suitability of Lannea microcarpa seed oil (LaMSO) as a heat transfer fluid (HTF) and thermal energy storage material (TESM) for medium-temperature applications, focusing on its performance in concentrated solar power (CSP) plants. LaMSO demonstrated higher specific heat capacity than both Dowtherm A and Xceltherm 600 across the temperature range of 30 °C to 300 °C. It also exhibited a volumetric thermal energy storage density similar to, or approximately 10 % greater than, that of Dowtherm A and Xceltherm 600 at 210 °C. The oil was subjected to isothermal aging at 210 °C for 500 h and 1000 h, followed by analysis of its thermophysical and chemical properties. Thermogravimetric analysis demonstrated excellent thermal stability, with less than 3 % mass loss after 1000 h of aging. The density remained relatively unchanged, indicating consistent performance as a HTF or TESM. Despite an increase in viscosity at 40 °C, the viscosity at 100 °C remained comparable between the new and aged LaMSO samples. Furthermore, the flash point also showed no significant change, remaining high even after 1000 h of aging. However, challenges arise from the increase in the melting point due to oil saturation, which poses a risk of solidification in pipelines or tanks in certain climates. From the perspective of thermal storage cost per kWh, LaMSO is cheaper than Dowtherm A and Xceltherm 600, being approximately 8 times and 3 times less expensive, respectively. Overall, the findings suggest that LaMSO holds promise as an effective and sustainable alternative for HTF and TESM applications across a wide temperature range, contributing to advancements in renewable energy technology.

Bidirectional circulating preheating method harnessing engine and battery waste heat reuse in hybrid electric vehicles

In hybrid electric vehicles (HEVs), both the engine and power batteries experience reduced performance at low temperatures, necessitating the consumption of significant energy for preheating. The bidirectional preheating system method, which for the first time applies waste thermal energy to preheat both the engine and power battery in HEVs, utilizes the engine’s residual thermal energy to preheat the power battery and the thermal energy from the power battery to preheat the engine. To implement this method, a numerical model of the engine radiator and power battery waste heat is first established, and the temperature rise characteristics and temperature distribution of the waste heat system are simulated and analyzed. This analysis reveals the heat transfer law of the engine radiator and power battery waste heat. An automatic bidirectional thermal control device based on waste heat reuse is designed. The device utilizes a multi-stage series thermal energy transfer system with phase change materials (PCM) as the medium. A low-temperature experiment is conducted to assess the integration of heating and cooling between the engine and power battery. The results indicate that this method effectively utilizes the engine’s waste heat for both heating and cooling purposes. Specifically, a heat exchanger is used to preheat the power battery using the engine’s cooling residual heat, maintaining the internal battery temperature at 30 °C. Simultaneously, the residual heat from the power battery’s cooling system is circulated back to the engine body, preheating the engine coolant to 42 °C. Compared with existing HEVs, it can save more than 90% of the preheating energy consumption of the engine and power battery. This method can reduce power battery and engine warm-up time by more than 50%, while reducing emissions by more than 40% during engine cold start. This approach effectively addresses the challenge of low-temperature preheating for both power batteries and engines by utilizing cooling residual heat bidirectionally, thereby maximizing energy utilization efficiency in HEV systems and optimizing both battery and engine performance.

Molecular dynamics method to investigate the interaction energy and mechanical properties of the reinforced graphene aerogel with paraffin as the phase change material in the presence of different external heat fluxes

BackgroundGraphene aerogels (GA), known for their exceptional lightweight and sturdy characteristics, present a promising avenue for improving thermal energy (TE) storage and transfer efficiency. It might be possible to make better thermal management systems in fields like electronics, aerospace, and energy storage by studying how heat flux (HF) affects the strength and stability of graphene aerogels. MethodsThe study used molecular dynamics (MD) simulation to investigate how the mechanical properties of graphene aerogels strengthened with paraffin as phase change material (PCM) change in response to external heat flux (EHF). These simulation methods provided a detailed view of molecular interactions and dynamics at the atomic level, allowing researchers to understand the behavior of materials under various conditions. The change in toughness, interaction energy (IE), Young's modules (YM), and ultimate strength (US) was examined for this reason. Significant findingsThe results indicate that when the HF increased from 0.1 to 0.3 W/m2, the ultimate strength and Young's modules increased from 8.91 and 5.37 GPa to 14.546 and 8.59 GPa, respectively. These values declined when HF increased by more than 0.3 W/m2. When EHF went up to 0.3 W/m², these graphene aerogel properties went up. This was because the atoms moved around more and there were more bonding contacts among the graphene sheets, which made the structure of material stronger. However, at heat flux levels exceeding 0.3 W/m², excessive thermal energy may lead to thermal degradation, causing bond breakage and loss of structural integrity, ultimately resulting in a decrease in these mechanical properties. Also, the results reveal that interaction energy increased from -1522.098 to -1546.325 eV as external HF increased to 0.3 W/m2. The thermal motion of atoms enhanced as the HF increased, enabling closer clustering and better alignment of graphene sheets, thereby strengthening their interactions. This study gave us useful information about how to improve the mechanical properties of graphene aerogels in different HF conditions. This made it more likely that these materials can be used in energy storage systems and thermal management.

Microstructure and thermal properties of ternary chloride eutectic salts for high temperature thermal energy storage

Chloride molten salts are attractive candidate materials used for effective thermal energy transfer and storage in renewable energy system as concentrating solar power, but associated thermal properties at high temperature are still insufficient in research. In this work, eutectic point verification, microstructure and thermal properties of NaCl–KCl–ZnCl2 eutectic salts with four different contents are investigated by molecular dynamics simulation based on Born-Mayer-Huggins potential and experimental measurement. The density, specific heat capacity, viscosity, self-diffusion coefficient and thermal conductivity of four ternary eutectic salts are predicted with experimental validation and their correlations with different temperature and composition are proposed, and the mechanism of desirable thermal performance variation is revealed from the microscopic point of view. As ZnCl2 content increases, the thermal conductivity and specific heat capacity increase significantly, and eutectic salt #4 (18.6 %NaCl: 21.9 %KCl: 59.5 %ZnCl2) has maxima of density, specific heat capacity and thermal conductivity. The above phenomena can be attributed to the increase in potential energy and Columbic energy for more charge of Zn2+, which strengthens the interaction between atoms in the system and intensifies the collision. This work is expected to provide effective guidance on the design and application of molten salts for high temperature thermal energy storage.

Numerical analysis of hydrophobic surface effects on cavitation inception and evolution in high-speed centrifugal pumps for thermal energy storage and transfer systems

This study explores the influence of wettability surfaces on cavitation inception and evolution in high-speed centrifugal pumps used for thermal energy storage and transfer systems through numerical simulations. The simulations were conducted using the Kunz mass transfer model implemented in Fluent, combined with the Eulerian multiphase flow approach and the shear stress transport k–ω turbulence model. The cavitation dynamics were analyzed across contact angles ranging from superhydrophilic to superhydrophobic conditions. The results demonstrate that superhydrophobic surfaces delay cavitation onset compared to hydrophilic ones, reducing the critical cavitation coefficient by at least 28%. At flow rates of 1.11 Q0 and 0.89 Q0, cavitation numbers show distinct trends, with superhydrophobic surfaces enhancing cavitation stability and reducing the frequency of cavitation shedding. The reentrant jet dynamics are also affected, with increased hydrophobicity weakening the jets and stabilizing cavitation zones. This research aims to advance the understanding of using surface wettability to manage cavitation in high-speed centrifugal pumps, thereby improving the performance and reliability of thermal energy storage and transfer systems.

Повышение энергетической эффективности работы тепловых сетей за счет утилизации тепловых потерь

The efficiency of thermal energy transfer, which is inevitably accompanied by heat losses through the insulation of pipelines, directly characterizes heating networks and centralized heat supply systems in general. The most important task in terms of current approaches to energy efficiency is to improve the efficiency of thermal energy transfer in modern heat supply systems. Currently known technical solutions to reduce heat losses through insulation of pipelines reduce heat losses, but not significantly. So, the purpose of this study is to develop a technical solution to reduce (even eliminate) standardized linear heat losses in heat supply networks of industrial enterprises. The authors have used methods of experimental research of heat transfer processes and mathematical modeling of heat and power equipment. A device for recycling heat losses is proposed. It is designed to reduce (even eliminate) normalized linear heat losses in heat supply networks of industrial enterprises. The permissible heat absorption of the device collector is determined, and a method for its regulation is described. An engineering method for calculation of the proposed device has been developed. The effectiveness of application of heat-reflecting screens in heating networks has been determined. A number of problems have been solved to improve the efficiency of heat supply systems of industrial enterprises using a device for recycling heat losses in the heating system channel.

Understanding the thermodynamic effects of chemically reactive working fluids in the Stirling heat pump

Within the realm of sustainable heating technologies, this study examines the performance of a Stirling heat pump employing chemically reactive working fluids in contrast to conventional inert counterparts. Reactive working fluids are energy vectors that enable the conversion of not only thermal but also chemical energy within the heat pump. The investigation spans a wide range of theoretical reactive gaseous mixtures, leveraging the ideal gas mixture thermodynamic model. Each fluid is characterized by an equilibrated chemical reaction, denoted as A2(g)⇄2A(g), and distinguished by a set of reaction coordinates: the standard entropy change of reaction and standard enthalpy change of reaction. The chemical reaction evolution and thermodynamic properties are observed in each transformation, and the overall coefficient of performance (COP) of the system is evaluated and benchmarked against that of comparable inert working fluids. It is observed that the exothermic reaction during isothermal compression significantly increases the thermal energy supplied to the heat sink, as well as the thermal energy density per unit maximum volume, by up to 269 %, compared to an inert gas system. However, for the majority of reactive fluids studied, chemical reactions introduce irreversibility in the internal regenerator due to heat transfer across a finite temperature difference, contrary to the case of inert working fluids, penalizing the COP. Consequently, a reduction of up to 28 % in the COP is observed. Nevertheless, there exists a range of reactive fluids, characterized by reversible heat exchange in the internal regenerator, offering increased thermal energy transfer to the heat sink without compromising the COP.

Finite element method-based investigation of heat exchanger hydrodynamics: Effects of triangular vortex generator shape and size on flow characteristics

Heat exchangers (HEs) play a critical role in numerous industrial and engineering applications by facilitating efficient thermal energy transfer. In the pursuit of enhancing the performance of such systems, this study focuses on the hydrodynamic effects of two distinctive vortex generators (VGs) within a turbulent airflow channel, operating under steady-state conditions. Arranged in a staggered manner, the first vortex generator (VG) adopts a rectangular structure positioned in the upper section, while the second VG, triangular in shape, is situated on the opposing wall at varying heights, ranging from 40 to 80 mm in 10 mm increments. A further examination of the triangular VG includes two cases, one featuring an inclined front-face and the other showcasing an inclined rear-face. The turbulent airflow within the channel is accurately represented using the Newtonian fluid model and the standard k-epsilon turbulence model, while the governing equations are solved through the finite element method. A non-uniform mesh, consisting of triangular and square elements with a specific focus on refining the mesh near walls, is designed to capture boundary layer effects and effectively resolve intricacies in near-wall flow dynamics. The investigation unveils dynamic responses within the channel, characterized by notable flow distortions and prominent regions of recirculation, demonstrating the effectiveness of both rectangular and triangular VGs. Importantly, the analysis shows that tilting the triangular VG’s back-face notably improves the hydrodynamic structure of the HE channel, leading to enhanced recirculation cells and substantially increased performance. In particular, increasing the height of triangular VGs significantly enhances flow velocity within the channel. For instance, the axial velocity increased by 33.8% when the VG height was raised from 40 to 80 mm in the first triangular case, while an increase of about 37.9% was observed in the second triangular case at the lowest inlet velocity of 7.8 m/s. In addition, triangular VGs with an inclined back-surface achieved higher axial velocities compared to those with an inclined front-surface, with a 13.5% increase at the smallest height and a 17.0% increase at the maximum height. Furthermore, increasing the inlet velocity to 9.8 m/s resulted in a 17.1% higher axial velocity in the second model, reaching 55.4 m/s compared to 47.3 m/s in the first model. These findings underscore the importance of optimizing the triangular VG shape, height, and inlet conditions to maximize the hydrodynamic performance of HE systems, leading to potential energy savings and improved efficiency.

Modeling non-spherical hailstones

Abstract Hail research and forecasting models necessarily involve explicit or implicit – and uncertain – physical assumptions regarding hailstones’ shape, tumbling behavior, fallspeed, and thermal energy transfer. Whereas most models assume spherical hailstones, we relax this assumption by using hailstone shape data from field observations to establish empirical size-shape relationships with reasonable degrees of randomness considering hailstones’ natural shape variability, capturing the observed distribution of tri-axial ellipsoidal shapes. We also incorporate explicit, random tumbling of individual hailstones during their growth to simulate their free-falling behavior and the resultant changes in cross-sectional area (which affects growth by hydrometeor collection.) These physical attributes are incorporated in calculating hailstones’ fallspeeds, using either empirical or analytical relationships based on each hailstone’s Best and Reynolds numbers. Options for drag coefficient modification are added to emulate hailstones’ rough surfaces (lobes), which then modifies their thermal energy and vapor exchange with the environment. We investigate how applying these physical assumptions about nonspherical hail into the Penn State hail growth trajectory model, coupled with Cloud Model 1 supercell simulations, impacts hail production, and examine the reasons behind the resulting variability in hail statistics. The choice of hailstone size-mass relation and fallspeed scheme have the strongest influence on hail sizes. Using non-spherical, tumbling hailstones reduces the number of large hailstones produced. Applying shape-specific thermal energy transfer coefficients subtly increases sizes; the effects of lobes vary depending on the fallspeed scheme used. These physical assumptions, although adding complexity to modeling, can be parameterized efficiently and potentially used in microphysics schemes.

Thermal energy transfer for green urban development: numerical investigation on the heat transfer and flow noise in heat exchangers with different helical and segmental baffles

Thermal energy transfer for green urban development: numerical investigation on the heat transfer and flow noise in heat exchangers with different helical and segmental baffles

Improvement of Latent Heat Thermal Energy Storage Rate for Domestic Solar Water Heater Systems Using Anisotropic Layers of Metal Foam

Latent Heat Transfer Thermal Energy Storage (LHTES) units are crucial in managing the variability of solar energy in solar thermal storage systems. This study explores the effectiveness of strategically placing layers of anisotropic and uniform metal foam (MF) within an LHTES to optimize the melting times of phase-change materials (PCMs) in three different setups. Using the enthalpy–porosity approach and finite element method simulations for fluid dynamics in MF, this research evaluates the impact of the metal foam’s anisotropy parameter (Kn) and orientation angle (ω) on thermal performance. The results indicate that the configuration placing the anisotropic MF layer to channel heat towards the lower right corner shortens the phase transition time by 2.72% compared to other setups. Conversely, the middle setup experiences extended melting periods, particularly when ω is at 90°—an increase in Kn from 0.1 to 0.2 cuts the melting time by 4.14%, although it remains the least efficient option. The findings highlight the critical influence of MF anisotropy and the pivotal role of ω = 45°. Angles greater than this significantly increase the liquefaction time, especially at higher Kn values, due to altered thermal conductivity directions. Furthermore, the tactical placement of the anisotropic MF layer significantly boosts thermal efficiency, as evidenced by a 13.12% reduction in the PCM liquefaction time, most notably in configurations with a lower angle orientation.

Multiple shape factor effects of nanofluids on marangoni mixed convection flow through porous medium

This study explores the effects of multiple shape factors on nanofluids within Marangoni mixed convection flows through porous media. Nanofluids, containing nanoparticles in a base fluid, show unique thermal properties, making them valuable in cooling systems, energy storage, and medical devices. Marangoni mixed convection, driven by surface tension gradients, adds complexity to fluid dynamics and heat transfer in porous media. Analytical and numerical analyses examine how various particle geometries, nanoparticle volume fractions, and porous medium configurations influence transport phenomena. Entropy analysis calculates thermodynamic irreversibilities. Findings reveal relationships between shape factors, heat transfer rates, velocity profiles, temperature distribution, and entropy generation rates, offering insights for optimizing nanofluid-based systems. The study also investigates magnetic forces, heat source/sink effects, and viscous dissipation on thermal energy transfer in Graphene oxide/water and Molybdenum disulfide/water nanofluids. Using similarity transformations, Partial Differential Equations are converted into Ordinary Differential Equations, solved with HAM and NDSolver by using the Wolfram tools. Results graphically depict velocity, temperature, entropy, and skin friction values, providing practical insights for engineering applications.

Impact of thermal energy efficiency based on kerosene oil movement through hybrid nano-particles across contracting/stretching needle

This manuscript reveals the mathematical analysis of dual simulations in tangent hyperbolic rheology with heat transfer and mass diffusion mechanisms on the needle (expanding and shrinking). Further, Darcy's Forchhiermer law is employed with the occurrence of the magnetic field. The models of hybrid nanofluid utilized are Xue- and YO-hybrid nano-fluid models. Such models apply to optical fibers, solar systems, surgical implants, electronics and biological applications. Transfer of thermal energy and diffusion related to mass species occurs employing a non-Fourier approach. The transformed system of non-linear Odes is numerically tackled with the finite element method. Furthermore, because fluid and needle movement have opposite directions, the current model has dual solutions. It visualizes that such a complicated model is not solved numerically by FEM. The applications of Xue- and YO-hybrid nano-fluid model with non-Fourier's law on a needle are implemented for the first time. It concludes that adding YO-hybrid nanofluid with base fluid increases the entropy profile, temperature profile and Bejan profile rather than the Xue hybrid nanofluid model. Fields of concentration, velocity and heat energy for the case of upper solutions are higher than concentration, velocity and heat energy profiles for lower solutions.

Numerical simulation of insulated drilling technique with refrigerant fluid in the Arctic region

In recent years, there has been a gradual rise in the exploitation of the abundant oil and gas resources in the Arctic. Drilling operations in the permafrost regions of the Arctic can induce thermal energy transfer from the drilling fluid to the permafrost layer, causing permafrost thawing and potentially leading to wellbore instability. Especially when the reservoirs are in deeper formations, the challenge intensifies. In response, some researchers suggest a new drilling technique which adopts the method of injecting refrigerant fluid and vacuum insulated tubing (VIT) cementing for active and passive insulation, respectively. However, due to the novelty of this technique and the complex hydrothermal process in permafrost layers, current studies and numerical models struggle to accurately assess the insulation effect of this method during practical drilling operations. Therefore, referring to previous related research, this article establishes a coupled thermal modeling of this drilling method based on the hydrothermal theory of permafrost. The thermal insulation effect, as well as characteristics of wellbore and formation of this drilling method was investigated through numerical simulation. The findings reveal that compared to conventional drilling methods, this method can effectively delay heat transfer from the wellbore to the permafrost and ensure the volume of thawed permafrost less than 100 m3. Lastly, it is recommended to choose VIT with a thermal conductivity coefficient of less than 0.04 W/(m∙℃), or ensure a flow rate of refrigerant fluid above 7.5 L/s and an injection temperature of refrigerant fluid less than −5 °C when the thermal conductivity of VIT is above 0.04 W/(m∙℃). The model and calculations provided in this paper offer some insights for the implementation of this innovative insulated drilling technique in the Arctic region.

Heat and mass transfer analysis for bi-dimensional bioconvective MHD nanofluid with varying thermal traits

ABSTRACT Bioconvection phenomena offer practical applications in biomicrosystems, fuel cells, biosensors, biocomputing, electronic thermal management, and renewable energy systems, showcasing their relevance and potential impact across various engineering sectors. Consequently, this study delves into the examination of a bi-dimensional magnetohydrodynamic nanofluid flow model encompassing the intricate dynamics of gyrotactic microorganisms, subject to the effects of suction and thermal radiation. The primary objective of the investigation is to optimize the thermal energy transfer efficiency of the fluid while concurrently minimizing associated costs, with the secondary aim of diminishing the frictional resistance at the fluid-solid interface. The basis for energy and momentum equations incorporating radiation using Rosseland’s approximation is established by the Buongiorno nanofluid model. The foundational PDEs along with their BCs, are reformulated into ODEs utilizing similarity variables, then transformed into a set of first-order ODEs ensuring compatibility with MATLAB’s bvp4c solver, which offers high convergence rates and accuracy due to its efficient algorithms and precision handling. Heat transfer rate boosts up by increasing suction and radiation parameters, while it dwindles due to an increase in the magnetic field. Enhancing suction and the magnetic field lowers skin friction. Microbial concentration surges by increasing the magnetic field, while suction minimizes it. Intensifying the thermophoresis parameter increases the concentration of nanoparticles.

Employing ISPH simulations and artificial intelligence for enhanced heat and mass transfer in a core reactor with nano-enhanced phase change materials

This research investigates the heat and mass transfer characteristics of nano-enhanced phase change material (NEPCM) within a core reactor, employing both the incompressible smoothed particle hydrodynamics (ISPH) simulations and artificial intelligence (AI) analysis. NEPCM holds promise for enhancing thermal energy storage and transfer efficiency, with applications spanning various fields, including nuclear reactors. Through ISPH simulations, this study delves into the intricate fluid dynamics and phase change phenomena within the reactor, providing valuable insights into the thermal behavior of NEPCM. Eight embedded rods are initially settled inside a reactor with high temperature and concentration on four rods and the others are maintained at low temperature and concentration. The effects of various parameters including the Cattaneo–Christov heat parameter ( δ Heat ) , Cattaneo–Christov mass parameter ( δ Mass ) , Dufour number ( Du ) , Hartmann number ( Ha ) , Soret number ( Sr ) , and thermal radiation ( Rd ) are conducted in this work. δ Heat and δ Mass play critical roles in evaluating heat and mass transfer efficiencies. Raising the Dufour number improves temperature distribution while having a minimal impact on concentration. Additionally, increasing the Dufour number from 0 to 1.5 leads to a 30% increase in the velocity field. Elevating the Soret number significantly enhances velocity and concentration, while increasing the thermal radiation parameter improves temperature distribution. These findings are pertinent across multiple domains like combustion, chemical engineering, and geophysics, aiding in process optimization and system design. The ANN model exhibits high precision in predicting Nusselt and Sherwood numbers, highlighting its effectiveness in forecasting.

Molecular beam scattering from flat jets of liquid dodecane and water

AbstractMolecular beam experiments in which gas molecules are scattered from liquids provide detailed, microscopic perspectives on the gas–liquid interface. Extending these methods to volatile liquids while maintaining the ability to measure product energy and angular distributions presents a significant challenge. The incorporation of flat liquid jets into molecular beam scattering experiments in our laboratory has allowed us to demonstrate their utility in uncovering dynamics in this complex chemical environment. Here, we summarize recent work on the evaporation and scattering of Ne, CD4, ND3, and D2O from a dodecane flat liquid jet and present first results on the evaporation and scattering of Ar from a cold salty water jet. In the evaporation experiments, Maxwell–Boltzmann flux distributions with a cosθ angular distribution are observed. Scattering experiments reveal both impulsive scattering (IS) and trapping followed by thermal desorption (TD). Super‐specular scattering is observed for all four species scattered from dodecane and is attributed to anisotropic momentum transfer to the liquid surface. In the IS channel, rotational excitation of the polyatomic scatterers is a significant energy sink, and these species accommodate more readily on the dodecane surface compared to Ne. Our preliminary results on cold salty water jets suggest that Ar atoms undergo some vapor‐phase collisions when evaporating from the liquid surface. Initial scattering experiments characterize the mechanisms of Ar interacting with an aqueous jet, allowing for comparison to dodecane systems.Key Points Molecular beam scattering from flat liquid jets is a powerful technique to elucidate mechanistic detail at the gas–liquid interface. Previous dodecane scattering experiments have uncovered angularly‐resolved thermal desorption fractions and energy transfer at the interface for several small molecule scatterers. Preliminary results on scattering from cold salty water reveal mechanisms of interaction between argon and an aqueous jet.

Definition of a thermal conductivity map for geothermal purposes

The use of geothermal energy is spreading globally due to its many advantages, especially for heating and cooling. The correct design of a geothermal system requires knowledge of the parameters of the subsoil rocks, and particularly the thermal conductivity (k), which is the intrinsic ability of a material to transfer thermal energy as a result of a temperature gradient. A thermal conductivity map of the geological formations is time-consuming to produce, but can be of great help when selecting the location of a low-enthalpy geothermal installation, resulting in significant savings and an increase in the efficiency of that installation. The preferred option for determining k is an in situ thermal response test, but laboratory methods may be an alternative if it is not available or affordable. In this work, the needle thermal probe method has been used to measure the k of representative outcropping rocks in Oviedo (NW Spain), since it allows to obtain a rapid determination, its cost is comparatively low and it can be implemented in a portable device. 162 measurements have been carried out on a total of 27 samples, ranging from 0.2 (clay) to 5.4 W m−1 K−1 (quartzite). A relationship has been found between the k of the rocks and their characteristics, such as mineralogy, anisotropy or geological age and a thermal conductivity map was created.

Enhancement of thermal energy transfer behind a double consecutive expansion utilizing a variable magnetic field

This research focuses on utilizing non-uniform magnetic fields, induced by dipoles, to control and enhance thermal energy transfer in a two-dimensional cooling conduit including a double backward-facing step. The presence of electronic equipment along the straight channel path creates such arrangements, and cooling is often ineffective in the corners of the formed steps. The use of a non-constant magnetic field is a passive technique to improve the cooling rate in these sections without changing the internal geometry, thereby increasing the heat transfer rate. A commercial software based on the finite volume technique is employed to solve the governing equations of fluid flow and heat transfer. Multiple parameters are examined in this study, including the flow Reynolds number (12.5–50), dipole location and strength (0.1–5 A-m), and the number of dipoles (single or double). The results indicate that all of these parameters have a significant impact on the thermal energy transfer. The results of the study show that a single dipole increase the average heat transfer by about 22%, two magnetic fields by 40%, the strength of the magnetic source by 24% with respect to the non-magnetic field in the present study.

Theoretical simulation of steady flowing manifold in hybrid pneumatic power system

Improving the energy efficiency of existing power systems is part of energy conservation and carbon reduction efforts. Internal combustion engines (ICEs) are currently the most commonly used power source in transportation, and they can be combined with gas power sources to form hybrid power systems for enhanced energy efficiency and potential commercialization. This study introduces hybrid pneumatic systems that integrate energy from ICEs and exhaust gas through a manifold to reuse waste heat. However, the turbulence caused by compressed air in the manifold can prevent the smooth transfer and mixing of thermal energy, leading to reduced power at the final outlet. We use ANSYS Fluent software to conduct heat flow streamline analysis of the three-dimensional flow field in the manifold structure, with key parameters including throttle valve opening, manifold geometry, pressure, and temperature. Through this analysis, we explore the flow situation and heat transfer phenomenon inside the pipe, observe the flow field changes in the pipe, and adjust the diameter of the compressed air end channel for effective thermal energy. A backflow with velocity magnitude up to 72 m/s in high pressure case can be solved by compressing pipe and temperature increases from 349.9 K to 682.5 K with more efficient heat transfer and gas mixing. Thermal power, enthalpy, and mass flow rate of the hybrid power system are also investigated, enabling the ICE to operate at its optimal point. The waste heat from the ICE can also be recycled and converted into effective mechanical energy through flow work.