Theoretical Heat Research Articles

Experimental and theoretical heat transmission through a skin phantom using a Ruby IR therapeutic lamp.

A skin phantom model was developed and characterized to study the interaction of infrared radiation during photothermal therapy. The phantom consists of a platinum silicone matrix with polyethylene oxide containing encapsulated sodium alginate to mimic the concentration of water in human skin. The specific heat and thermal conductivity of each component were experimentally measured. A theoretical model was built with heat transfer equations to simulate the temperature distribution. The experimental results and numerical simulations show that the interaction phenomenon with infrared radiation is superficial, concentrating mostly in the epidermis and part of the dermis. This successfully replicates the actual thermal behaviour of the skin during photothermal therapy. The developed phantom adequately represents the thermal properties and response to infrared radiation of the skin, allowing its use as a surrogate model in thermal imaging and diagnostic applications.

Excess heat production of the pair annihilation of ionic vacancies in a copper redox reaction using a double bipolar MHD electrode.

Through a copper double bipolar magnetohydrodynamic (MHD) electrode (MHDE) producing twice the amounts of ionic vacancies than a conventional single MHDE, the molar excess heat of the pair annihilation of ionic vacancies, 702kJmol-1 at 10T on average was obtained in a copper redox reaction. It was about twice as large as that of a single MHDE, 387kJmol-1 at the same magnetic field. This result strongly suggests that a multi-channel bipolar MHDE will produce much greater excess heat. To conserve the linear momentum and electric charge during electron transfer in an electrode reaction, ionic vacancies are created, storing the solvation energy in the polarized core of the order of 0.1nm, and the pair annihilation of the vacancies with opposite charges liberates the energy as excess heat. The promoted excess heat by the double bipolar MHDE with a diffuser at 10T was 710 ± 144kJmol-1, whereas as mentioned above, 702 ± 426kJmol-1 was obtained by the same electrode without such a diffuser. From the theoretical excess heat of 1140kJmol-1, the collision efficiencies in pair annihilation were 0.623 ± 0.126 and 0.616 ± 0.374, respectively. From these results, the reproducibility of the thermal measurement was experimentally validated. At the same time, it was concluded that at magnetic fields beyond 10T, the concentration of ionic vacancy and the collision efficiency take constant uppermost values.

Heat transfer performance of single atom solution in carbon dioxide capture circulation system

In order to accurately assess the heat transfer performance of the new single atom solution for carbon dioxide capture, an experimental system and heat transfer model have been developed. This study focuses on the effects of flow rate and temperature on the heat transfer performance. It is found that the effect of temperature on their heat transfer characteristics is not significant, and increasing flow rate enhances heat transfer. The heat transfer coefficient is increased by 45% as the diameter of the heat exchange tube is reduced. The theoretical heat transfer performance of single atom solutions is 18∼37% higher than that of common solvents. Additionally, the numerical simulation results showed that single atom solutions greatly reduced desorption energy consumption to 1.447 GJ/t. The results provide new technological support for carbon capture.

Laser doping of n-type 4H-SiC with boron using solution precursor for mid-wave infrared optical properties

Laser doping of n-type 4H-silicon carbide (SiC) semiconductor substrates with boron (B) using a pulsed Nd:YAG laser (λ = 1064 nm) is reported. An aqueous boric acid solution was used as a boron precursor. A simple theoretical heat transfer model was employed to select the laser processing parameters, i.e., laser power and laser-substrate interaction time, and determine the appropriate temperature to dope 4H-SiC substrates. The selected processing parameters ensured that the temperature at the laser-substrate interaction zone was below the SiC peritectic temperature to prevent any crystalline phase transformations in SiC. Fourier-transform infrared spectrometry was conducted to determine the optical properties of both undoped and boron-doped 4H-SiC substrates within the mid-wave infrared (MWIR) wavelength range (3–5 μm). Boron atoms create an acceptor energy level at 0.29 eV above the valence band in the 4H-SiC bandgap, which corresponds to λ = 4.3 μm. Boron-doped 4H-SiC substrate exhibited reduced reflectance and increased absorptance for the MWIR range. An absorption peak at λ = 4.3 μm was detected for the doped substrate. This confirmed the creation of the acceptor energy level in the 4H-SiC bandgap and, thus, doping of 4H-SiC with boron. A notable decrease in the refractive index, i.e., from 2.87 to 2.52, after laser doping of n-type 4H-SiC with boron was achieved.

Analyzing the ignition capabilities of glowing firebrand accumulations

Firebrand spotting is a significant mechanism for structure losses in wildland–urban interface (WUI) fires. In this work, the ability of firebrand accumulations to cause flaming ignition of an engineered wood material, Oriented Strand Board (OSB), under different flow conditions was experimentally studied. The firebrands were emulated by burning wooden dowels of two sizes, 6.35 & 12.7 mm. Firebrands were dropped onto on the fuel to form accumulations, with the coverage densities of 0.06 to 0.16g/cm2 on the fuel surface. The surface temperature of glowing combustion on the firebrands was measured with color ratio pyrometry. The ignition outcome results show a similar hyperbolic relationship between air flow and coverage density for both firebrand sizes although accumulations of small firebrands can cause the ignition faster. A firebrand combustion model was adopted to predict the surface temperature of accumulated firebrands considering re-radiation between nearby firebrands. A correlation between the ignition time and characteristics of accumulations was also established based on a theoretical combustion and heat transfer analysis.

Fabrication and thermal properties of capric–stearic acid eutectic/nano-SiO2 phase change material with expanded graphite and CuO for thermal energy storage

With the booming development of energy storage technology, phase change materials (PCMs) provide more possibilities for building energy efficiency. In this paper, binary eutectic mixture of capric acid (CA) and stearic acid (SA) is PCM, nano silica (SiO2) is used as the nano-enhancer, and expanded graphite (EG) and nano CuO are used as the thermal conductivity enhancers. Different mass fractions of composite phase change materials (CPCMs) are prepared by melt impregnation method. The structure, thermal properties, stability, thermal conductivity properties, thermal storage/release properties and temperature response properties of the CPCMs are characterized. Results show the prepared CA-SA/SiO2/EG(CPCM5) melts at 30.62 °C and solidifies at 25.29 °C with latent heat of 156.50 J/g and 144.20 J/g, respectively, and CA-SA/SiO2/CuO(CPCM8) melts at 29.09 °C and solidifies at 25.30 °C with latent heat of 152.60 J/g and 140.70 J/g, respectively. The latent heats of melting are higher than the theoretical latent heat due to the enhancement of the nano SiO2. Good compatibility is observed between CA-SA, SiO2, CuO and EG. The thermal conductivity of CPCM8 and CPCM5 are 0.287 and 0.929 W/(m·K), respectively, and CPCM5 has better thermal storage/release and temperature response characteristics. Moreover, CPCM5 does not decompose at 100.00 °C, and shows good stability after 200 cycles of heating and cooling. Therefore, the composite has great potential for application in the field of building energy efficiency.

Thermite-for-Demise (T4D): Experimental analysis of heat transfer principles and preliminary sizing of an application

The use of exothermic reactions to aid satellite demise during re-entry is under investigation. An energetic material, if stored on board, could passively ignite thanks to the heat load experienced by the spacecraft during re-entry, and ease its complete ablation. Thermites are good candidates for this application because of their high energy density and relative stability. Their effectiveness is strictly related to the heat transfer efficiency between the ignited powder and its confining vessel. Experiments in non-relevant environment were conducted for Al+Fe2O3 thermite to quantify this value. The average heat transfer efficiency was quantified at 60%, with respect to the theoretical heat release of the mixture. A novel numerical model implementing a T4D application, named TRANSIT (TRANsatmosferic SImulation Tool), is presented and verified with respect to two commercial software packages. In particular, literature data for SAM and dedicated simulations for SCARAB have been used in this phase. TRANSIT is then employed to preliminarily size a thermite charge to aid spacecraft demise during re-entry for three simple re-entering objects. A genetic algorithm is employed to optimize the thermite to spacecraft mass ratio, assuring complete demise.

Design and experimental study of a novel vapor chamber for proton exchange membrane fuel cell cooling

Proper thermal management is the key to the efficient and safe operation of proton exchange membrane fuel cells. In this study, a novel vapor chamber was designed and experimentally tested to verify its potential application for proton exchange membrane fuel cell cooling. The thermal management design scheme of proton exchange membrane fuel cells based on vapor chambers was introduced, and the influence of structural parameters on the theoretical maximum heat transfer of the vapor chamber was discussed. Based on theoretical analysis, a vapor chamber matching the structural characteristics of proton exchange membrane fuel cells was designed and manufactured, and the influence of heat load, tilt angle, and cooling water flow rate on the heat transfer performance of the vapor chamber was investigated experimentally. The results showed that the designed vapor chamber had excellent thermal dispersion performance and temperature equalization ability. When the heat load was less than 35 W, the maximum temperature of the vapor chamber was always less than 33 °C, and the thermal resistance was less than 0.2 °C/W. The tilt angle affected the capillary limit of the vapor chamber, and then significantly affected the thermal performance of the vapor chamber. In addition, the results also indicated that increasing the cooling water flow rate led to an increase in the temperature difference and thermal resistance of the vapor chamber, but this effect was relatively limited. The results of this study will provide a new idea and reference for the efficient thermal management of proton exchange membrane fuel cells.

Finite integral transform with homogenized boundary conditions solution of transient heat conduction applied to thermal plug and abandonment of oil wells

After the end of productive life of a geological oil reservoir, a set of operations for well Plug and Abandonment (P&A) is performed to recover the soil layers to its natural state. As traditional P&A techniques are expensive activities, alternative technologies are gaining renewed interest for capital expenditure reduction and leak risks mitigation. Hence, the Thermal Plug and Abandonment (TP&A) procedure is here investigated by focusing on the fulfillment of two intermediate milestones, combining new technology with conventional P&A practices. The first milestone consists in applying a thermite exothermic reaction to generate enough heat for melting the entire thickness of the production tube. The second milestone aims to determine if the resulting molten section has sufficient dimensions to allow for the passage of the cement pumped downhole, thus ensuring the complete sealing of the oil well's cross-section. The thermal investigation was conducted by applying a homogenized form of the Finite Integral Transform (FIT) analytical framework to solve the transient heat conduction equation in 2-D polar coordinates. The well assembly was geometrically discretized as a multilayered circular domain. The thermite reaction was modeled as a theoretical volumetric heat source profile dependent on both time and space, placed in the innermost layer. While a pure FIT approach may only be used to solve Neumann boundary conditions, the combined scheme applied here copes with any type of boundary condition. Hence, the integration of FIT with homogenization satisfies the Dirichlet condition requirement of the TP&A procedure. The methodology was verified through an equivalent Finite Volume Method (FVM) solution obtained using a commercial code. The results evidenced that within the 5 min duration of thermite reaction, the entire circumferential section of the production tube exceeds the steel melting temperature by at least 227 °C, thus fulfilling both milestones set. The research outcomes are part of a series of investigation steps to thoroughly analyze the new TP&A technology with regard to its compliance with the regulatory norms established to P&A operations.

Contact engineering for graphene nanoribbon devices

Graphene nanoribbons (GNRs), when synthesized with atomic precision by bottom–up chemical approaches, possess tunable electronic structure, and high theoretical mobility, conductivity, and heat dissipation capabilities, which makes them an excellent candidate for channel material in post-silicon transistors. Despite their immense potential, achieving highly transparent contacts for efficient charge transport—which requires proper contact selection and a deep understanding of the complex one-dimensional GNR channel-three-dimensional metal contact interface—remains a challenge. In this study, we investigated the impact of different electron-beam deposited contact metals—the commonly used palladium (Pd) and softer metal indium (In)—on the structural properties and field-effect transistor performance of semiconducting nine-atom wide armchair GNRs. The performance and integrity of the GNR channel material were studied by means of a comprehensive Raman spectroscopy analysis, scanning tunneling microscopy (STM) imaging, optical absorption calculations, and transport measurements. We found that, compared to Pd, In contacts facilitate favorable Ohmic-like transport because of the reduction of interface defects, while the edge structure quality of GNR channel plays a more dominant role in determining the overall device performance. Our study provides a blueprint for improving device performance through contact engineering and material quality enhancements in emerging GNR-based technology.

Evaluation of thermal loss of Chinese solar greenhouse cover under all operating conditions

The solar greenhouses in China are composed of gables on the east and west sides, north walls, and north and south roofs. The south roof is the main heat dissipation surface of the greenhouse. To quantitatively and comprehensively analyse the heat transfer characteristics and heat loss pathways of the south roof of a solar greenhouse, based on the actual usage of the greenhouse, the heat transfer of the south roof is classified into two working conditions: heat transfer of the transparent covering material (TCM) and heat transfer of the composite thermal insulation coating (CTIC). A theoretical heat transfer model of the covering layer of the solar greenhouse under all working conditions is constructed by applying the heat transfer theory. The model was tested using field test data from two areas different regions in China: Beijing and Lhasa. The results show good agreement between the simulated and measured values, the relative errors between simulated and measured values were 18.54% and 8.17%, respectively, with root mean square errors of 1.69 and 1.92. The model can comprehensively and accurately reflect the comprehensive heat transfer coefficient and heat loss changes of the south roof of the solar greenhouse. It can be used to analyze the proportion of heat loss caused by radiation, convection, and water vapor condensation. The analysis shows that condensation heat loss cannot be ignored during the winter night period. Measures such as covering the roof with plastic film and controlled irrigation can help reduce condensation heat loss.

Performance evaluation of solar still using evacuated tube collector with and without nanoparticles.

Solar-thermal distillation is recognized as a low-cost, long-term technique of producing high-quality fresh water in the lack of energy and clean water infrastructure. Improvements to distillation have lately been developed by the application of three main phases depending on the transition of sunlight into heat energy, the generation of thermal vapor, and the condensation of vapor into water. The effectiveness of collected distillation water from evacuated tube collectors on nanoparticles was examined along with basic fluids including water and copper oxide, aluminum oxide, and zinc oxide. Additionally, an investigation of the relationship between specific heat and thermal conductivity, as well as between actual and theoretical heat generation, was conducted. For 11 h of operation, 2275 ml of distilled water was collected using evacuated tube collectors without nanoparticles. The efficiency of the nanoparticles compared to water was more than 17.4% CuO, 15.7% Al2O3, and 14.5% ZnO improved and an increase in overall efficiency of 66.6%. As a result of the experiment, the greatest actual heat generation, expressed in kilowatt-hour, exceeds the theoretical value.

Heat recovery opportunities from electrical substation transformers

The transformation of voltages in electrical substations leads to energy losses in the form of waste heat; the quantity of which depends on transformer size and electrical loading. This paper investigates how a novel waste heat source, namely transformer waste heat could be harvested and distributed via district heating networks. Firstly, the investigation considered nameplate heat loss factors to quantify the theoretical waste heat potential from electrical substation transformers in England, Wales and Northern Ireland, which varied from 3.0 to 5.4 TWh a−1, equivalent to between 0.7 and 1.25% of annual heat demand for these countries, depending on loading assumptions. A number of heat recovery approaches which could be integrated with existing transformer cooling systems were then proposed. A spreadsheet model was then developed to simulate heat recovery from a transformer, together with the upgrade of the recovered heat using a heat pump prior to delivery via district heating. The model was used to evaluate the merits of capturing transformer waste heat losses, estimated using industry supplied electrical loading data, to meet different heat network demands based on an existing network, compared to conventional heating technologies. Findings suggest that the system proposed can achieve levelised costs that are up to 17% lower than the running costs of air-source heat pumps, whilst reducing emissions by almost 80% when displacing gas boilers. The methodology hereby described can also be used to evaluate the feasibility of recovering transformer waste heat in other countries.

Assessment and Characterization of Duck Feathers as Potential Source of Biopolymers from an Upcycling Perspective

A comprehensive characterization of the physical and chemical properties of whole duck feathers from French mulard species, including their various categories and fractions (barbs, rachis, and calamus), was conducted to explore potential ways for utilizing this waste product. This analysis aimed to identify opportunities for valorizing these feathers and unlocking their untapped potential. Hence, the duck feathers were thoroughly characterized by a proximate analysis to determine their composition and theoretical heating value. Additionally, feathers underwent other analyses as Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis, solvent behavior and chemical durability assessment, hydrophobicity testing, Fourier Transform Infrared (FT-IR) spectroscopy, Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). The analyses revealed duck feather composition, molecular weight, stability in different environments, hydrophobicity, functional groups present, thermal behavior, crystallinity, and structural arrangement. Upon analysis, it was determined that duck feathers contain pure fiber keratin and possess characteristics that make them suitable for the production of high-value keratin-based products, including cosmetics, activated carbon for purification, materials for waterproofing, lightweight construction, and textile innovations, underscoring their potential to support sustainable and eco-friendly initiatives across various sectors.

Characterization of Magnetic Susceptor Heating Rate Due to Hysteresis Losses in Thermoplastic Welding

Welding techniques are emerging as a new method to join thermoplastic composite parts. They present a fast and efficient alternative to adhesives and mechanical fasteners. Induction welding is a welding technique that relies on the application of an oscillating magnetic field on the joining interface, where a material called a magnetic susceptor generates heat by interacting with the applied magnetic field. In this work, susceptors relying on magnetic hysteresis losses made of polyetherimide (PEI) and nickel (Ni) particles are investigated with varying Ni concentration. The materials are mixed using an internal mixer and pressed to form films approximately 500μm thick. To characterize the heating rates of the susceptor materials, samples are placed on an induction coil – a water-cooled copper tube in which AC current (frequency 388kHz), generates an alternating magnetic field – and the temperature evolution is measured using a thermal camera. An increasing concentration of Ni particles results in increased heating rate and maximum temperature reached by the samples. The temperature-time experimental curves are compared with theoretical heating curves to verify if the model can be used to predict the temperature evolution at the joining interface during a welding process.

A scientific report on Stokes' second problem for a transient nanofluid model with a heated boundary in the presence of a magnetic field

Stoke's second problem is a well-known classical boundary layer (BL) issue involving the time-dependent shear flow of viscous fluid about a flat porous plate in the magnetic field. This study has several applications, including chemical engineering, nanotechnology, heat conduction issues, and biological and medical sciences. A theoretical heat transfer (HT) analysis analyzes Stoke's second problem for an MHD time-dependent nanofluid flow through a porous plate. It produces a sinusoidal oscillation that is perpendicular to the flat plate. Copper (Cu) nanoparticles are suspended in water or ethylene glycol (EG), a base fluid. Modeling the fluid flow uses dimensional PDEs, which are then altered into dimensionless forms by adding the proper parameters. With no slip, the resulting non-dimensional PDEs are handled analytically by the Laplace transform approach (LTA). It is demonstrated that EG-Cu nanofluid has greater skin friction and higher HT rate than water-Cu nanofluid. Furthermore, skin friction is reduced by magnetic and porosity parameters, whereas the nanoparticle solid volume fraction and porosity parameters improve HT.

NiCo/SiO2 nanospheres for efficient synergetic decarboxylation of fatty acids and upgrading of municipal sludge HTL bio-crude to biofuels

Municipal sludge (MS) and derived HTL (hydrothermal liquefaction) bio-crude contains a large quantity of organics, including fatty acids, which may be a potential resource for producing biofuels via catalytic treatment. Herein, decarboxylation of fatty acids is chosen as the model reaction to screen a series of nickel-based bimetallic catalysts supported on homemade SiO2 nanospheres to investigate the synergetic effect. NiCo/SiO2 turned out with the best performance compared to NiCu-, NiZn-, NiMo- and NiFe/SiO2. An 83% conversion of stearic acid and an 84% selectivity of heptadecane via hydrothermal decarboxylation were achieved at 280 °C under 1 MPa H2. XPS results revealed the electron transfer from Co to Ni, leading to the formation of Niδ-, which is more accessible to bond with Cδ+ in the carboxyl group of fatty acids, thus facilitating the decarboxylation reaction. Compared to commercial SiO2, our homemade SiO2 showed a stronger carbon accumulation resistance, indicating a medium specific surface area was essential. Both the synergetic effect of NiCo bimetal and the carbon accumulation resistance of homemade SiO2 nanospheres contributed to the efficient hydrothermal decarboxylation. The NiCo/SiO2 catalyst was further applied for upgrading of MS HTL bio-crude to biofuels, and the theoretical higher heating value (HHV) was significantly improved from 34.4 to 37.2 MJ/kg, suggesting the potential application of converting MS bio-crude to biofuels.

A high-efficiency gas–liquid coupled heat-driven thermoacoustic heat pump

The search for a diversified and sustainable technology for energy utilisation is crucial for reducing the consumption of fossil energy. This research proposed a novel heat-driven thermoacoustic heat pump with a gas–liquid coupled resonator that exhibits high efficiency, compact structure and easy fabrication. A series of theoretical and experimental studies has been performed in this work, including numerical and experimental domestic heating performance, onset characteristics as well as the effects of different liquid masses and high and ambient temperatures on the performance of a heat pump. Results show that the theoretical and experimental heat pump performance exhibit good agreement, with a standard error of about 5%. Moreover, the gas–liquid coupled heat-driven thermoacoustic heat pump has a low onset temperature (70 °C at 3 MPa), offering a wide range of applications for low-grade thermal energy utilisation. With high, ambient and domestic heating temperatures of 300 °C, 10 °C and 50 °C, respectively, a maximum domestic heating power of 18.4 kW is obtained, corresponding to the maximum coefficient of performance of domestic heating based on heating power (COPh) of 1.48. Furthermore, a maximum relative Carnot efficiency of 50.9% and a COPh of 1.31 with a hot-end temperature of 300 °C are achieved under ambient and domestic heating temperatures of −20 °C and 50 °C, respectively. These results present a new domestic heating approach for the utilisation of medium- and low-grade thermal energy.

Effect of oxygen concentration on the velocity in buoyant turbulent diffusion flames

To better understand fire dynamics of buoyant turbulent diffusion flames under different oxygen concentrations (OCs, volumetric basis), we have recently conducted measurements on the flame temperature, radiation, and soot temperature and volume fraction under normal and reduced OCs. In the present study, particle image velocimetry (PIV) technique was employed to investigate the effect of OC (20.9%, 16.8%, and 15.2%) on the velocity field of the same flames with a theoretical heat release rate (HRR) of 15 kW. The statistics of the velocity field, such as mean and standard deviation of velocity, turbulent kinetic energy, Reynolds stress, and turbulent viscosity, were investigated and compared among different OCs. Results show that OC has minimal effect on the velocity distribution at heights close to the flame length. However, at lower heights above burner (HABs), turbulent mixing is reduced under reduced OCs, and the velocity shows an increased value at the flame centerline but with a narrower profile along the radial direction. Finally, a comparison with previous data was conducted and analyzed to further explore the fire dynamics. This study improves the physical understanding of related fire dynamics under reduced OCs and provides a comprehensive dataset for turbulent fire modeling validation.

Thermodynamic features of the regenerative system of direct fired sCO2 power cycles with oxygen combustion of methane

The article presents an analysis of the thermodynamic features of the operation of a regenerative system of sCO2 power cycles. The cycle with a two-stage pressure increase configuration is taken as a basis for calculation. The supply of energy to the working fluid is provided by the operation of the regenerative system and by oxy-fuel combustion. Methane is used as fuel. The issues of theoretically achievable heating temperatures of the working fluid in the cycle regenerative system are considered. The influence of thermodynamic parameters on the heat fluxes of the regenerative system is estimated. For the first time, an assessment was made of the relative and absolute contribution of water vapor, formed during fuel combustion, to heat flows. This study makes it possible to establish the physical quantities pressure, temperature and heat fluxes, which are necessary for further design calculations of heat exchangers to be used in industrial installations. As a result of multi-variant calculations of the cycle (when varying the temperature at the turbine inlet in the range of 500–1500 °C and pressure - from 100 to 400 bar), it was found that the temperature of the working fluid supply to the combustion chamber can be taken at the level of 2/3 of the temperature at its outlet. At operating temperatures of the working fluid at the level of 1000–1200 °C, the contribution of water vapor to regenerative heating will be 3–17%, depending on their mass content. The total theoretical heat flow to the cycle regenerative system will be 800–1000 kJ/kg CO2. The energy supply to the working fluid due to fuel combustion does not exceed 50% of the total energy supplied in the operating temperature and pressure ranges.