Energy Heat Transfer Research Articles

Catfish liver microwave dehydration modeling based on its kinetic patterns identification

Fish liver has unique properties, which opens up opportunities for creating specialized food ingredients. The quality of the dried product largely depends on the conditions of its dehydration. The aim of the study is to simulate micro wave drying of catfish liver under temperature restrictions and to study its kinetic patterns. The object of the study is the liver of the common catfish (Silurus glanis). The key aspect of this study is the adaptation of the mathematical model of heat energy and mass transfer to the conditions of microwave dehydration of a thin layer of catfish liver to determine the temperature distribution and control the process parameters. The article presents the plan and re sults of an experimental series to study catfish liver dehydration, the parameters affecting the drying rate, the curves of microwave drying of catfish liver at a drying layer thickness of 1.5 cm and a radiation frequency of 2.45 GHz. It has been determined the operating parameters for carrying out microwave drying of catfish liver in a thin layer: initial moisture content of the dried raw material (68 ± 2) %; the initial temperature of the raw material to be dried was (10 ± 1) °C; the thickness of the layer to be dried was (1.5 ± 0.1) cm; the area of the surface to be dried must be strictly within the range of the high-frequency electromagnetic radiation field with a frequency of 2450 MHz; the power of microwave radiation was (180 ± 10) W; the final moisture content of the raw material to be dried was (5 ± 1) %; the final temperature of the raw material to be dried was (85 ± 1) °C; the duration of dehydration was (28 ± 1) min. Comparison of the obtained results with the data for similar materials confirms their reliability and the possibility of successful application in engineering practice in the food industry.

A numerical study of the effect of different geometrical parameters on the cooling processes in electrical transformer

Proper thermal control is one of the most important aspects that should be considered when utilizing electrical transformers. This research work offers a numerical analysis of the effect of changing the shape of transformer fins on the heat exchange process. Based on the results of CFD simulations, several types of fin shapes such as rectangular, triangular and wavy are discussed to describe the improvements of heat transfer. The study examines the shape of an electrical transformer, determining the optimal distance between fins, fin shapes, transformer shape, rib type, and rib number. The results are then applied to a special case, representing the best of all variables on the transformer. The study also considers the effect of increasing the surface area of the ribs on the fins, and the number of ribs used on the fins. The temperature gradient of a coil, oil, and transformer varies depending on the distance between fins, fin shape, rib type, and number of ribs. The coil temperature is 383 K when the fins are 7 cm apart, 381 K when the fins are 5 cm apart, and 381 K when the fins are 3cm apart. The temperature gradient also varies depending on the rib type, with triangular ribs increasing the surface area for heat energy transfer and reducing the temperature value. The oil temperature gradient varies depending on the fins, ribs type, and number of ribs. The heat transfer coefficient gradient of the transformer surface varies depending on the fins, ribs type, and number of ribs. The surface heat transfer coefficient reaches 1.5 W/m2. K when the fins are l shape, 1.6 W/m2. K when the fins are c shape, 1.7 W/m2. K when the fins are z shape, 1.4 W/m2. K when the ribs are rectangular, 1.6 W/m2. K when the ribs are triangular, and 1.4 W/m2. K when the ribs are 9 ribs.

Transition from ballistic to diffusive heat transfer in a chain with breaks.

The transition from a ballistic to a diffusive regime of heat transfer is studied using two models. The first model is a one-dimensional chain with bonds, capable of dissociation. Interparticle forces in the chain are harmonic for bond deformations below a critical value, corresponding to the dissociation, and zero above this value. A kinetic description of heat transfer in the chain is proposed using the second model, namely, a gas of noninteracting quasiparticles, reflecting from randomly occurring barriers. The motion of quasiparticles mimicks heat (energy) transfer in the chain, while the barriers mimic dissociated bonds. For the gas, a kinetic equation is derived and solved analytically. The solution demonstrates the transition from the ballistic regime at small times to the diffusive regime at large times. In the diffusive limit, the distance traveled by a heat obeys square-root asymptotics as in the case of classical diffusion. However, the shape of the fundamental solution for temperature differs from the Gaussian function and therefore the Fourier law is not satisfied. Two examples are considered to demonstrate that the presented kinetic model is in good qualitative agreement with the results of the numerical solution of the chain dynamics. The presented results show that bond dissociation is an important mechanism underlying the transition from ballistic to diffusive heat transfer in one-dimensional chains.

A Novel Hydrogen-Nitrogen Heat Exchanger For Aeronautical Applications

Abstract Renewable fuels are playing an increasingly central role in shaping today’s energy landscape, and within the aviation sector there is a remarkable drive to research and develop engines that harness the potential of these sustainable resources. Looking specifically at hydrogen, a fuel with immense promise, there is a critical need to maximize storage capacity, prompting consideration of storing it in a liquid state. However, before this stored hydrogen can be used for combustion, it must undergo an important process of vaporization. To address this challenge, this paper presents an innovative heat exchanger model. In this model, nitrogen is used as a medium to transfer heat energy to the stored hydrogen, allowing it to be converted to a gaseous state and making it easily usable in the combustion chamber. In addition, to provide a comprehensive understanding of the thermodynamic processes involved, a detailed and thorough thermodynamic model is presented that properly captures the exchange of heat flow rates. Moreover, the pipe-in-pipe architecture is adopted, and the assumed geometrical data are validated numerically.

Supercritical retrograde solubility in R-14 and the second law of thermodynamics

A closed transcritical power cycle is described that uses a positive excess enthalpy of solution reaction differential between the reaction in the cycle’s high-density liquid state and low-density expanded gas state to internally transfer heat energy. The heat energy input to satisfy the solution reaction near the cycle’s low temperature is returned as heat during supercritical retrograde solubility near the cycle’s high temperature before that heat energy affects gas expansion. The power cycle format is used to frame this heat energy transfer so that Carnot efficiency can be used to calculate the maximum second law allowed amount of heat energy that can be transferred. If the amount of heat transfer exceeds the determined minimum threshold, the cycle’s Q efficiency will surpass the cycle’s T efficiency. The process demonstrates that the maximum positive excess enthalpy differential allowed by the second law is irreconcilably low.

Convection Heat Transfer and Performance Analysis of a Triply Periodic Minimal Surface (TPMS) for a Novel Heat Exchanger

Heat exchangers are necessary in most engineering systems that move thermal energy from a hot source to a colder location. The development of additive manufacturing technology facilitates the design and optimization of heat exchangers by introducing triply periodic minimal surface (TPMS) structures. TPMSs have shown excellent mechanical and thermal performance, which can improve heat energy transfer efficiency in heat exchangers. This current study intends to design and develop efficient, lightweight heat exchangers for aerospace and space applications. Using the TPMS structure, a porous construction encloses a horizontal tube that circulates heated fluid. Low-temperature water circulates inside a rectangular box that houses the complete system to remove heat from the horizontal pipe. Three porous structures, the gyroid, diamond, and FKS structures, were employed and examined. Porous models with various porosities and surface areas (15 cm2 and 24 cm2) were investigated. The results revealed that the gyroid structure exhibits the highest Nusselt number for heat removal (Nu max = 2250), confirming the highest heat transfer and lowest pressure drop among the three structures under investigation. The maximum Nusselt number obtained for the FKS structure is less than 1000, whereas, for the diamond structure, it is near 1250. A linear variation in the average Nusselt number as a function of the structure surface area was found for the FKS and diamond structures. In contrast, nonlinearity was observed in the gyroid structures.

Analysis of reducing thermal resistance between the PCM and ambient air for improving the power generation characteristics of PCM-based thermoelectric power generators

A power generator comprising a thermoelectric device (TED) and a phase change material (PCM) allows energy harvesting from ambient temperature variations, which exist ubiquitously; thus, such a device has received considerable attention as an energy harvester that can operate at any location. We developed a model for estimating the characteristics of a power generator in ambient air, whose temperature is forcibly changed between two temperature values, such as when an air conditioner is turned on and off. We calculated the influence of latent heat and thermal conductivity of the PCM on the characteristics of power generators with various thermal resistances between the TED/PCM interface and ambient air. Latent heat and thermal conductivity of the PCM affect the amount of heat energy (Q) transfer between the ambient air and PCM and the energy conversion efficiency (ηE), respectively, where the amount of electric energy is given by Q × ηE. The increase in Q caused by an increase in the latent heat of the PCM was almost independent of the thermal resistance between the TED/PCM interface and air. However, the increase in ηE caused by an increase in the thermal conductivity of the PCM decreased as the thermal resistance between the TED/PCM interface and air increased. These results indicate that the techniques to improve the power generation characteristics by increasing the thermal conductivity of PCM, which have been frequently investigated in recent years, are effective only when the thermal resistance between the TED/PCM interface and ambient air is small.

Evolving Thermal Energy Storage Using Hybrid Nanoparticle: An Experimental Investigation on Salt Hydrate Phase Change Materials for Greener Future

Thermal energy storage (TES) assisted with phase change materials (PCM)s seeks greater attention to bridge the gap between energy demand and supply. PCM has its footprint toward efficient storage of solar energy. Inorganic salt hydrate PCMs are propitious over organic PCMs in terms of energy storage ability, thermal conductivity, and fireproof, however the major issue of supercooling and poor optical absorbance remains. This research investigates commercialized inorganic salt hydrate PCM with phase transition temperature of 50 °C, thermal conductivity of 0.593 W m−1 K which is favoured with melting enthalpy of 190 J g−1, and 2–3 °C of supercooling. Mixture of graphene: silver at a proportion of (1:1) is used as the hybrid nanomaterial to further enhance the thermal conductivity, optical absorbance, and thermal stability. Hybrid nanocomposites are developed via two‐step process involving direct mixing and ultrasonication. Morphological behaviour, chemical stability, optical property, thermal property, thermal reliability, and stability of the developed nanocomposite samples are experimentally analysed. As a result, sustainable TES materials with thermal conductivity of 0.937 W m−1 K, optical absorbance of 0.8, increased energy storage potential is formulated. Subsequently a numerical simulation is conducted to illustrate the potential of the developed nanocomposite in transfer of heat energy.

Bone density estimation using tissue heat capacity.

Osteoporosis onset is relatively asymptomatic, the condition often being identified only once a significant fracture occurs, leading to a potentially serious prognosis. Currently, early identification of osteoporosis is complicated by the difficulty in measuring bone density without using x-ray absorptiometry or quantitative ultrasound, so a simpler method for estimating bone density is needed. Given that bone is reported to have a lower specific heat than other tissues, we investigated the possibility of estimating bone density using this difference in tissue thermal properties. The tibia medial surface (shin) and medial malleolus (ankle) of 68 healthy volunteers were cooled using an ice bag, and skin surface temperatures and heat flow were recorded. These measurements were then used to calculate the heat energy transferred per unit temperature. Bone density was estimated by quantitative ultrasound using the T score OSISD, which is the participant's osteo sono-assessment index (OSI) compared to the average OSI of young adults. The heat energy transfer per unit temperature at the shin, but not the ankle, showed a significant negative correlation with T score OSISD (r = -0.413, p = 0.001). Multiple regression analysis showed that heat energy transfer per unit temperature at the shin was a significant predictor of T score OSISD, along with age and height. These results show that tissue thermal property measurements are useful for estimating bone density.

THERMODYNAMIC MODEL OF STUDYING THE DYNAMICS OF THE TEMPERATURE BALANCE BY CALCULATING HEAT ENERGY IN AGRICULTURAL SECTOR

This work is the result of the simulation of a thermodynamic model that investigates the dy- namics of the temperature balance due to the transfer of thermal energy. A proposed scheme outlines the rheological heat transfer characteristics of an object featuring an insulated surface, along with accompany- ing graphs illustrating irreversible rheological transformations. The primary equation governing heat ex- change, incorporating a chemical reaction, is presented, and the equation dictating the rate of heat energy transfer along the object's length is derived. The subsequent step involves advancing physical- mathematical models to depict the conversion of thermal energy into various states of the object. This ad- vancement aims to facilitate an evaluation of the overall temperature regimen of agricultural entities and optimize the heating procedures. In recent years, the agricultural sector has faced substantial challenges attributed to climate change. Climate change impacts on agriculture encompass elevated temperatures, increased weather variability, shifting agroecosystem boundaries, invasive species, pests, and frequent ex- treme weather events. These changes possess the potential to disrupt agricultural yields and food security, underscoring the importance of comprehending and managing temperature dynamics within agricultural systems. This research delves into the core of temperature regulation within agricultural objects, employing a thermodynamic model that not only considers heat exchange but also incorporates the influence of chemical reactions. Through the derivation of equations characterizing the speed of heat energy transfer and the development of physical-mathematical models for thermal energy transformation, this study offers a robust framework for evaluating and refining the temperature regime of agricultural objects. This re- search paves the way for further advancements in the comprehension and management of temperature dynamics within agricultural systems. As climate change persists in posing challenges to the sector, the knowledge and models developed here will serve as invaluable tools in optimizing heating procedures, en- hancing agricultural resilience, and securing global food production. In summary, this study significantly contributes to our understanding of temperature balance and heat energy transfer within agricultural ob- jects. It represents a crucial stride towards addressing the challenges posed by climate change in agricul- ture.The suggested thermodynamic model, along with its corresponding equations, lays a robust ground- work for forthcoming investigations and practical implementations. Ultimately, this development stands to enhance the agricultural sector and contribute to global food production.

Quantitative Assessment of the Heat Transfer Capacity of Ice Bags and their Cooling Effects on the Skin Surface and Core Temperature.

Ice bags are frequently used in medical care settings for pain relief, comfort, and in some cases, whole-body cooling. This study quantifies heat energy transfer capacity of ice bags and evaluates their cooling effects on body temperature. Forty-eight healthy adults in their 20s were recruited. An ice bag wrapped in two layers of dry towel was applied to the forehead, neck, or palm of each participant for 10 min. The skin surface temperature, heat flow, and core temperature were recorded during the cooling and non-cooling periods, with energy transfer calculated by integrating heat flow over time. Over the non-cooling period, 31.4-53.6 kJ·m-2 of energy was dissipated over 10 min, whereas during the cooling period, the range increased to 180.0-218.7 kJ·m-2 over 10 min. Skin surface temperature decreased by 3.2-5.7°C, whereas core temperature was unchanged. Ice bag use augmented energy transfer by about 150-180 kJ·m-2 over 10 min, but this was insufficient for rapid whole body cooling due to the small skin-surface area in contact with the ice bag. The measured energy transfer indicated that topical ice bag application absorbs insufficient energy to affect core temperature. Quantitative assessment of energy transfer was shown to inform the safe and appropriate use of thermotherapy.

Thermocapillary convection modes and phase change heat transfer characteristics of three-dimensional metal foam composited phase change materials with different aspect ratios under microgravity

This work aims to investigate the flow, heat transfer and phase change characteristics of porous media composite phase change materials with different aspect ratios in the thermocapillary mode under microgravity. A three-dimensional hydrodynamic model of thermocapillary-enhanced phase change heat transfer in the composite is developed. The model considers the shear stress boundary conditions on the porous free surface, employing the enthalpy-porosity method and the Darcy–Forchheimer model to describe the phase change process and fluid flow within the porous matrix, respectively, and the local thermal non-equilibrium model to describe the transient heat energy transfer between the paraffin and copper foam. The effects of different Marangoni numbers (Ma), aspect ratios (AR), Darcy numbers (Da) and porosities (ε) on the phase change heat transfer are compared. The results show that the increase of Ma from 6 × 104 to 2 × 105 accelerates the thermocapillary effect, and positively affect the thermal transport inside the cavity. The total melting time of the composite is reduced by 22.6 %, the heat storage efficiency is improved by 31.1 %, and secondary vortices appear in the convection zone. The large AR is favorable to the development of thermocapillary convection, but it also causes the reduced temperature gradient and heat transfer area of the heat source as well as the increased heat transfer distance. Compared to AR = 1, the total melting time increased by 34.4 % and 46.9 % for AR of 1.95 and 2.25 at a larger Ma, while the heat storage efficiency decreased by 26.5 % and 33.7 %, respectively. For a fixed ε, the decrease in Da hinders the development of convection, thus weakening the heat transfer and storage performance of the composite, and also causes heat conduction to dominate the phase change process in advance.

Development of a thermodynamic model for optimization of processes in crop production

The agricultural sector faces serious challenges related to climate change. These changes have the potential to reduce yields and food security, highlighting the importance of understanding and managing temperature dynamics. This work is the result of development a thermodynamic model that investigates the dynamics of temperature balance through heat energy transfer. A scheme of rheological heat exchange of an object with an insulated surface and graphs of irreversible rheological transformations are proposed. The main equation of heat exchange with a chemical reaction is given and the equation of the speed of heat energy transfer along the length of the object is derived. Further development of physical-mathematical models of the transformation of thermal energy into a set of states of the object is proposed. The experimental results fully correlate with the heat transfer equation. Samples with tomato seeds were irradiated with a photon irradiator with wavelengths of blue 450 nm, green 550 nm, red 650 nm with an exposure of 12/24 h. As a result, 90 % under the influence of the red spectrum of the photon irradiator for 24 h, which is 24 % more than the control sample. This will make it possible to assess the general temperature regime of agricultural objects and optimize the heating process. This study reveals the essence of temperature regulation at agricultural facilities using a thermodynamic model, which not only takes into account heat exchange, but also includes the influence of chemical reactions. The proposed thermodynamic model and associated equations provide a foundation for future research and practical applications that will ultimately benefit the agricultural industry, global food production

PENGARUH GEOMETRI DAN PENAMBAHAN JUMLAH SIRIP TERHADAP DISTRIBUSI TEMPERATUR HEAT SINK SEBAGAI ALTERNATIF PENDINGINAN PADA PIRANTI ELEKTRONIK

This study aims to determine the effect of the geometry shape of the copper material heat sink fins on the surface temperature distribution of the heat sink. The material used in this research is pure copper, the shape of the heat sink fins is made rippled with the addition of the number of fins 5, 6, and 7 and the input temperature is varied from 40 C to 80 C with airflow variations from 0.2 m/s to 1 m/s. The first step is to create a heat sink design with Autodesk Inventor. Then the plan is simulated with Autodesk CFD to solve the continuity, momentum, turbulence, and energy equations. Based on the method that has been carried out, it is found that the addition of variations in the number of fins affects the decrease in surface temperature. The highest temperature drop on fin 5 ripples is 24.1 C. The heat energy transfer rate increased by 0.4657 W. The convection heat transfer coefficient increased by 3.47 W/m²C. Nusselt number shows an increase of 271. Fin performance has increased efficiency by 63.4 %, and effectiveness by 1.61. The results of this study are expected to provide practical alternatives that can be widely adopted on a heatsink plate that is very promising for future thermal developments.

Decoupling thermoelectric parameters by the energy-dependent carrier and phonon scattering based on the nano-structuring interface design

Thermoelectric materials can transfer heat energy to electricity energy or vice versa. However, the transfer efficiency is restricted by the interdependent thermoelectric parameters. In this work, all the thermoelectric parameters are simultaneously optimized via the energy-dependent carrier and phonon scattering based on the nano-structuring interface design. As a result, not only the electrical conductivity is significantly enhanced by increasing the electron concentration, the Seebeck coefficient is maintained in a high value due to the energy-dependent carrier scattering mechanism. Otherwise, based on the stronger phonon scattering by the nanoinclusions and dislocations, the lattice thermal conductivity is markedly suppressed. And thus, a peak ZT=1.5 and an outstanding conversion efficiency η=9 % are achieved for Pb0.995Bi0.005Te/0.1 wt.%Fe3O4 composite, indicating that the thermoelectric property of n-type PbTe can be elevated greatly by embedding Fe3O4 nanoinclusions. This strategy of nano-structuring interface design can also be highly applicable in improving the performance of other state-of-the-art thermoelectric materials.

Energy Conversion in Systems-Contained Laser-Irradiated Metallic Nanoparticles – Comparison of Results from Analytical Solutions and Numerical Methods

Abstract This work introduces the theoretical method of metallic nanoparticles’ (NPs’) heat and mass transfer where the particles are coated on a surface (base), together with considering the case wherein nanoparticles move freely in a pipe. In order to simulate the heat transfer, energy and radiative transfer equations are adjusted to the considered issue. NPs’ properties are determined following the nanofluidic theories, whereas absorption and scattering coefficients are described using either Mie-Lorenz theory or Rayleigh-Drude approximation. Thermal boundary conditions are implemented based on the microscale heat transfer and Smoluchowski theory. Results are compared with the classical Fourier transport differential solutions that have been adjusted to laser irradiation.

Micro-/nanohoneycomb-like porous silicon loaded with Ag particles leads to synergistic enhancement of photothermal and thermoelectric conversions for MEMS thermopile chip application

Infrared detection technology has extensive and important applications in both military and civilian fields. Due to the advantages including no refrigeration, wide spectral response range, no chopping, low cost, and simple output circuit, MEMS thermopile chip has become one of the research hotspots in the field of infrared detection. The working mode of the thermopile chip is based on the photothermal and thermoelectric conversions, which are achieved by the infrared absorber and thermocouples, respectively. Actually, the resulting complex multi-layer structure brings about the shortcomings of thermopile chips, such as large heat capacity, large loss of heat transfer, low stacking efficiency and long response time, which has become the bottleneck of performance improvement. This work proposes a new concept for achieving high-efficiency photothermal and thermoelectric conversions of the thermopile chip simultaneously by a monolayer of multi-functional material. Herein, a micro-/nanohoneycomb-like porous Si loaded with Ag particles was constructed by metal-assisted chemical etching. The etched Si/Ag was endowed with high-efficiency light absorption in a wide spectral range (2–20 µm) and thermoelectric conversion, with the help of synergistic effect of light trapping, phonon scattering, energy filtering, and plasmon resonance. Replacing the infrared absorption layer, thermocouple layer, and insulation layer of the thermopile chip by the as-constructed porous Si/Ag composite can significantly reduce the heat capacity and energy transfer loss of the chip. It is expected to acquire a leap in the performance of the thermopile infrared detectors, providing a new technical approach for breaking through the bottleneck of small-scale and high-performance thermopile chips.

Heat transfer in a non-isothermal walled square closed space filled with ternary hybrid nanofluids

The application of hybrid nanoparticles with the purpose of enhancing thermal processes is an important technology that could have ramifications for a wide range of interventions used in a variety of industries. In this research paper, the impact of a ternary hybrid type nanofluid on heat energy transfer and free convection flow in a square closed space is explored using numerical simulations with different wall conditions. The wall at the bottom side of the closed space is heated uniformly, the vertical wall at the left side is linearly heated or uniformly heated, and the vertical wall at the right side is either linearly heated or cooled, while the wall at the top is thermally insulated. The equations controlling the flow and heat energy transfer are resolved using the finite element method with quads and triangles as elements. With varying values of nanoparticle volume percentage and Rayleigh number, numerical results for the mean Nusselt numbers of various fluids are analysed in detail, along with the profiles of streamlines and isotherms.

Interface deciphering for highly interfacial adhesion and efficient heat energy transfer

Interfacial adhesion and interfacial thermal resistance (ITR) are two critical factors in the interfacial force and energy transfer, but it is difficult to simultaneously achieve the desirable interfacial adhesion and ITR. Here, we overcome this challenge by fabricating an elastomer composite consisting of polydimethylsiloxane (PDMS) and micro-scale spherical aluminum (Al) fillers, which offers the high adhesion strength (1.28 MPa), high interfacial adhesion energy (528.4 J/m2), and low ITR (0.028 mm2·K/W) between the PDMS/Al elastomer composite and substrates. We further propose a quantified physical model to establish the relationship between interfacial adhesion and ITR for low phonon mismatch interfaces. This work will contribute to the development of interface science and guide the regulation of force and energy transfer at interface for wide range applications, such as electronic packaging, thermal storage, sensors, and medicine.

MODELING A SYSTEM WITH SOLAR CONCENTRATORS AND THERMAL ENERGY STORAGE

Global climate change, which has upset the ecological balance, and the rate of population growth, causing an increase in the demand for electricity in the world, are accelerating the gradual transition of states to green energy. Energy generation and energy storage are two important elements in green energy systems. We select parabolic solar concentrators as instrument for energy generation and develop flat facet solar concentrators that approximate a parabolic shape surface. Not only the structure of solar concentrators is proposed, but also the structure of thermal energy storage is described and presented. Using our solar concentrators, small-scale thermal energy storage (TES), it is possible to make power plants for green buildings. Small solar power plants and the air dehumidification system based on solar concentrators have great practical potential, can provide all the energy needs of smart residential buildings in countries with a hot climate, regulate air humidity, improve agricultural productivity in mountainous areas, etc. We describe a small-scale TES and the heater based on a solar concentrator. Water can be used to transfer heat energy. Another variant of TES is based on grave. We describe not only the structure of the system with parabolic solar concentrator and TES but calculate their parameters.