Thermal Heat Transfer Research Articles

Estimation of effective thermal conductivity and heat transfer coefficient of lithium orthosilicate pebble bed in carbon dioxide–air medium

ABSTRACT Lithium orthosilicate has the highest absorption capacity among other materials used to capture carbon dioxide (CO2) at a higher temperature. To design a CO2 adsorption system consisting of lithium orthosilicate pebble bed, effective thermal conductivity and heat transfer coefficient data are necessary, and till date, these are not reported in the literature. In the present study, experiments were conducted to estimate the effective thermal conductivity and heat transfer coefficient of lithium orthosilicate pebble bed in CO2–air medium. Effects of CO2 concentration in air, bed temperature, and gas flowrate on the hydrodynamic as well as heat transfer properties of the pebble bed of lithium orthosilicate pebbles were also studied. The effective thermal conductivity and heat transfer coefficients were found in the range of 0.2–0.75 Wm−1K−1 and 14–63 Wm−2K−1, respectively.

Significance of thermal conductivity and heat transfer mechanism through copper nanofluid with convective condition via heated Riga plate

This study investigates the heat and mass transfer of magnetohydrodynamic nanofluids via the Riga plate subjected to convective boundary conditions, including the thermal radiation parameter. Utilizing variable thermal conductivity and mixed convection effects, the heat transfer process is investigated. The peculiarity of the flow model enables us to investigate the importance of thermophoresis and Brownian motion to the kinetics of Newtonian fluids. The governing partial differential equations are converted into non-dimensional ordinary differential equations using proper similarity transformations and numerically solved using bvp4c in Matlab. The graphs explore the effects of pertinent parameters on the transference of heat, mass and velocity profiles. As the Biot number [Formula: see text] increases, so does the thermal boundary layer. The Nusselt number intensifies with radiation parameter but decreases with intensifying magnetic field parameter [Formula: see text], Eckert number [Formula: see text] and Brownian motion parameter [Formula: see text]. The influence of several physical quantities is illustrated and displayed through graphs and tables. Furthermore, it is observed that the thickness of the temperature profile is increased by combining the Biot number, the thermal radiation parameter, the thermal conductivity parameter and the modified Hartmann number.

Preparation and Characterization of n-Octadecane@SiO2/GO and n-Octadecane@SiO2/Ag Nanoencapsulated Phase Change Material for Immersion Cooling of Li-Ion Battery

Nanoencapsulated phase change materials (NePCMs) are promising thermal energy storage (TES) and heat transfer materials that show great potential in battery thermal management systems (BTMSs). In this work, nanocapsules with a paraffin core and silica shell were prepared using an optimized sol-gel method. The samples were characterized by different methods regarding chemical composition, thermal properties, etc. Then, the nanocapsules were used as the coolant by mixing with insulation oil in the immersion cooling of a simulative battery. The sample doped with Ag on the shell with a core-to-shell ratio of 1:1 showed the best performance. Compared to the sample without doping material, the thermal conductivity increased by 49%, while the supercooling degree was reduced by 35.6%. The average temperature of the simulative battery cooled by nanocapsule slurries decreased by up to 3.95 °C compared to the test performed with pure insulation oil as the coolant. These novel nanocapsules show great potential in the immersion cooling of a battery.

Analysis and modeling of heat and mass transfer and adsorption isotherms of the aqueous extracts vacuum contact drying

Vacuum contact drying is the most merit drying technology to ensure the quality and throughput of traditional Chinese medicine aqueous extracts. To study the heat and mass transfer of colloidal semi-solid porous media during vacuum contact drying, the sharp interface formulation was established to simulate the thin layer (4 mm) Lonicera japonica Thunb. aqueous extracts vacuum drying at high-temperature (110 and 120 ℃) and low-pressure (10, 15 and 20 kPa). And mathematical models were used to investigated drying kinetics and adsorption isotherms. Results show that the sharp interface model can predict final temperature and moisture ratio with the error is less than 20 %. The models of viscosity variation, specific heat capacity, heat capacity, effective thermal conductivity and heat transfer coefficient of boiling under different conditions were investigated to provide reference for subsequent research. When the vacuum drying superheat is between 50 ℃ and 75 ℃, the boiling heat transfer coefficient is among 6 to 9 W/ (m2·K). The Page is the most suitable semi-empirical model to describe the water migration law of the aqueous extracts. The adsorption isotherms of the extract powder were investigated by experiment and the Peleg is the most suitable model.

Study of thermal variation in a longitudinal exponential porous fin wetted with [formula omitted]/ hexanol hybrid nanofluid using hybrid residual power series method

This study aims to inspect the steady state thermal distribution and heat transfer within a longitudinal porous fin of exponential profile wetted with hybrid nanoliquid. The aggregate influence of conduction, radiation, and convection causes heat transfer in the fin. The Darcy model and the Fourier law of heat conduction are used for modeling the governing ordinary differential equation (ODE) that represents the corresponding fin problem. Through the use of non-dimensional terms, the formulated equation is further simplified into a dimensionless equation along with suitable boundary condition. The arising nonlinear dimensionless equation is solved analytically using the improved residual power series method with the Pade approximant (Hybrid residual power series method/HRPSM). The consequences of various dynamic thermal parameters on thermal behavior are explored using graphical portrayal. As per the observations of this investigation, the surface wet condition by hybrid nonliquid and porous nature of the exponential fin will have a significant effect on the temperature distribution. More specifically, as the values of these corresponding parameters increase, the rate of heat transfer intensifies. Finally, the obtained HRPSM results are compared with previous investigations, and a high level of consistency is observed.

Simulation of the Energy Performance of a Building with Green Roofs and Green Walls in a Tropical Climate

Global temperatures have continued to rise for decades, partly due to human-caused greenhouse gas emissions and subsequent urban heat island (UHI) effects. This current research examines the benefits of urban greenery by studying the impact of green roofs and walls of a building on thermal behavior and heat transfer in a warm and humid climate. This simulation study discusses the importance of greening systems in improving thermal comfort and minimizing the causes of UHI by assessing an integrated green building design. Using the simulation software DesignBuilder, the significance of greening systems, green roofs, and walls in enhancing thermal comfort and reducing the factors that contribute to UHI is investigated. The simulation results are based on the building’s energy usage in hot and humid regions while featuring green roofs and walls. The simulation results indicate a considerable positive impact of greening systems in improving the urban environment in hot and humid tropical climates. Air temperature, radiant temperature, humidity, and solar gain are decreased by urban greening. The total energy consumption and district cooling demand of buildings with green roofs and walls are reduced by 10.5% and 13%, respectively. The greening systems substantially improve air quality and building’s energy efficiency. Thus, the present study‘s findings can benefit urban designers and dwellers in devising strategies for establishing green spaces in congested urban environments by integrating green technologies and systems into built environments.

Aspects of Arrhenius kinetics and Hall currents on gyratory Couette flow of magnetized ethylene glycol containing bi‐hybridized nanomaterials

AbstractIncomparable thermal features of hybrid nanofluids (NFs) have been well recognized. Hybrid nanomaterials are prolifically used in chemistry processes, enzyme nanotechnology, pharmaceutical manufacturing, and so on. Motivated by numerous novel applications, in the present article, a theoretical study is conducted to demonstrate a time‐dependent hydro‐magnetic Couette flow and heat transport features inside a gyrating channel filled with a reactive second‐grade hybrid NF (copper–alumina–ethylene glycol) and Darcian porous medium under multiparty impacts of Hall currents, temperature‐dependent thermal conductivity, and Arrhenius chemical reaction. The modeled momentum equations are rendered nondimensional and solved analytically by means of the sophisticated Laplace transform technique. ND Solver in Mathematica is deployed to estimate the numerical solution of the energy equation. The computational outcomes are plotted and interpreted via physical constraints using line graphs and tables. The graphical outcomes assert that Hall currents significantly modify the gyratory flow dynamics and thermal features. The thermal profile and heat transfer rate manifest a diminishing pattern over widening Hall and rotation parameters. The change in thermal conductivity has a substantial impact on heat transmission. The novelty of the research study is a new insight into the hydro‐thermal manners of magnetized rotational non‐Newtonian hybrid NF.

Latent heat thermal energy storage in a shell-tube: A wavy partial layer of metal foam over tubes

The melting thermal energy storage and heat transfer of paraffin wax in a storage unit was modeled in the presence of a wavy copper foam. The phase-change energy and natural convection effects were modeled using the enthalpy porosity approach. The control equations were solved using the finite element method over a structured mesh. The energy storage was simulated for the wavenumber and amplitude of the foam layer. It was found that the higher wavenumber, the shorter the charging time and better energy storage power. A lower wave magnitude was also better than a longer wave magnitude. The shortest melting time was obtained for a flat foam layer, which was 20 % better than a low wave long amplitude foam layer. The current work intends to reduce the weight of applied metal foams in thermal energy storage applications by enhancing the geometry design. Here, a wavy form layer of metal foam was used to guide the natural convection flows and also boost the heat transfer mechanism. The phase change heat transfer has not been investigated in a wavy form metal foam layer.

The Synergistic Effect of Polystyrene/Modified Boron Nitride Composites for Enhanced Mechanical, Thermal and Conductive Properties

Thermal conductivity (TC) and thermal stability are the basic requirements and highly desirable properties in thermal management, heat storage and heat transfer applications. This work is regarding the fabrication of polystyrene/boron nitride composites and melt extruded to produce good thermal stability, increased thermal conductivity and enhanced mechanical properties. Our strategy is potentially applicable to produce thermally conductive composites of low cost over large scale. Boron nitride powder is bath sonicated in 10% NH3 solution to avoid its agglomeration and tendency toward entanglement in a polymer matrix. An approximately 67.43% increase in thermal conductivity and 69.37% increase in tensile strength as well as 56 multiple increases in thermal stability of the optimum samples were achieved. The developed polymeric composites are potentially applicable in the electronic industry, especially in electronic devices used for 5G, heat sink and several other aviation applications.

Enhancing Heat Transfer Performance: Nanofluids Application in Helical Microfin Tube Concentric Heat Exchangers

This manuscript explores the application of nanofluids in helical microfin tube concentric heat exchangers and investigates the potential for improved heat transfer performance. Helical microfin tubes offer enhanced heat transfer characteristics due to increased surface area and improved fluid mixing. When combined with nanofluids, which are base fluids with suspended nanoparticles, the thermal conductivity and convective heat transfer properties can be further enhanced. The objective of this present work is to investigate experimentally on heat transfer enhancement Al2O3/distilled water (0.05 vol.%) flowing through a helical microfin concentric heat exchanger in both parallel and counter flow in the vertical direction. The result is revealed that Al2O3/water nanofluids has enhanced thermal evaluation performance to water as base fluid. Counter flow might exhibit a more balanced performance, with a moderate enhancement in heat transfer while considering the pressure drop compared to parallel flow.

THREE TEMPERATURE MODEL FOR HEAT AND MASS TRANSFER IN NON-NEWTONIAN Cu-EG NANOFLUIDS EMBEDDED WITH PERMEABLE MEDIUM

In the current study, the impacts of local thermal non-equilibrium model and Cu-EG Oldroyd-B nanofluid layer on natural convective heat and mass transfer in a permeable medium are investigated. The transport equations are framed using modified Buongiorno two-phase Darcy model with different temperature profiles for fluid, particle, and porous-matrix phases. The thermophysical properties of the considered nanofluid are calculated using available experimental data. In the current situation, weak, non-linear analysis has been performed to find the Nusselt number and Sherwood number by solving finite amplitude equations using NDSolve in Mathematica 12.0. Influence of different parameters including viscoelastic parameters, LTNE parameters, thermal Rayleigh number, and nanoparticle volume fraction on heat and mass transfer mechanisms are explained graphically. An increase in the Nusselt number with the rising values of volume fraction of nanoparticles is registered and reach its maximum value at φ = 0.05 due to enhanced thermal conductivity. The significant findings for Oldroyd-B nanofluids are that the stress relaxation parameter declines heat transfer while strain retardation parameter promotes it. This study improves the theoretical understanding of heat transfer in porous media and facilitates the use of such theoretical models in practical applications.

Chemical reaction, Dufour and Soret effects on the stability of magnetohydrodynamic blood flow conveying magnetic nanoparticle in presence of thermal radiation: A biomedical application

Nowadays ferrofluids (magnetic nanofluids) are at the center of many researches because of their major biomedical applications such as drug delivery and cancer treatment. The effects of chemical reaction, temperature gradient induced mass transfer and concentration gradient induced heat transfer on the stability of ferrofluid flow are of great importance. This paper deals with a stability analysis of a ferrofluid composed of blood as base fluid and magnetic nanoparticles. The study integrates the effects of chemical reactions, the effects of mass transfer (Soret effect), the effects of heat transfer (Dufour effect) and the effects of the Buoyancy force. The flow is exposed to a magnetic field and thermal radiation. A system of eigenvalue equations governing the evolution of disturbances is derived by assuming a normal mode analysis. This system of equations is then solved numerically by the method of collocation. It appears from this study that the addition of nanoparticles to the blood increases its inertia, which dampens the amplitude of the disturbances and stabilizes the flow. The Casson parameter affects the stability of the flow by increasing the amplitude of the disturbances, which reflects its destabilizing effect. It appears from this study that taking into account the non-Newtonian nature of blood is very important when modeling the dynamics of the system because it shows more important and very different results than when blood is treated as a Newtonian fluid. The chemical reaction between the fluid and the nanoparticles leads to the redistribution of disturbances within the flow, which amplifies the instabilities and reflects the destabilizing character of the chemical reaction. On the other hand, temperature gradient induced mass transfer effects and concentration gradient induced heat transfer effects play an essential role on the stability of the flow because they attenuate the amplitude of the disturbances in the flow. The Darcy number exhibits a stabilizing effect on the flow. It appears from this analysis that the porosity of the medium increases the contact surface between the fluid and the nanoparticles. Buoyancy forces, thermal radiation parameter and wave number contribute to the stability of the flow. The magnetic field through the Lorentz force decreases the kinetic energy of the flow, which dissipates the disturbances and thus reflects the stabilizing character of the magnetic field. It should be noted that heat and mass transfer on magnetohydrodynamic flows through porous media taking into consideration the effect of chemical reaction appears in many natural and artificial transport processes in several branches of science and engineering applications. This phenomenon plays an important role in the chemical industry, power and cooling industry for drying, chemical vapor deposition on surfaces, cooling of nuclear reactors and petroleum industry. The effects of thermal radiation, mass and heat transfer are used in many situations in biomedical engineering and aerospace engineering.

Study on thermal protection characteristics of non-enclosed thermal cloak

The aerodynamic heat of hypersonic vehicle nose cone can reach MWm<sup>-2</sup> magnitude during flight, which could be transferred to the interior of hypersonic vehicle in the form of conduction and radiation. High efficient thermal insulation material is significant to keep internal electronic components working safely. Thermal metamaterials can regulate the macroscopic heat flow path, which have been developing rapidly and have a wide application prospect in the field of thermal protection. In this paper, a non-enclosed theoretical thermal cloak is designed to guide heat flow around hypersonic vehicle nose cone by using the transformation multithermotics, which can control thermal conduction and radiation simultaneously. A multi-layer structure is designed as cloak's simplified approximation due to the anisotropic parameters. Based on the software COMSOL, the thermal protection characteristics and heat transfer mechanism of the cloak and multi-layer structure are studied numerically. The results show that heat can flow around the object in the form of conduction and radiation in both theoretical thermal cloak and multi-layer structure, so the heat transferred to the inner area is decreased. Compared with the thermal insulation material, the heating rate of the protected area slows down, and the temperature at the front of the hypersonic vehicle nose cone is significantly reduced. However, the improvement of the thermal protection performance of cloak and multi-layer structures requires that the solid and radiative thermal conductivities of the material be lower than those of the original thermal insulation materials. To solve this problem, a non-enclosed theoretical extrapolation thermal cloak is further proposed. The solid and radiative thermal conductivities of extrapolation thermal cloak are non-singular, which could be higher than those of the original thermal insulation materials. Numerical simulation results show that the extrapolation thermal cloak can guide heat flow around object, so the thermal protection capability is improved significantly. Compared with the thermal insulation materials, the temperature of the front of the hypersonic vehicle nose cone is reduced by 100 K, and the temperature of the inner central zone of the hypersonic vehicle nose cone is reduced by 10 K. The non-enclosed extrapolation thermal cloak provides a new approach for thermal protection and is suitable for complex target areas, showing great application potential in thermal protection.

Experimental investigation on thermal efficiency augmentation of solar air heater using copper wire for discrete roughened absorber plate

Solar air heaters are used to heat the air, however their thermal efficiency is low due to the weak thermal conductivity between the air and the absorber plate. The thermal efficiency of solar air heaters can be improved by artificially roughening the absorber plate, which elevates the temperature of the plate and results in maximum thermal losses to the atmosphere.The performance of solar air heaters (SAH).is improved by using the largest range of solar flux and discharging heat energy from the absorber plate through air working fluid. In the outdoor experiment described in this article, artificial rib elements were added to the surface of the absorber plate to increase the heat transfer coefficient. In a recent study and outdoor experimental laboratory work done in view of the investigation of heat transfer coefficient and thermal efficiency parameters, a novel discrete double arc reverse form artificial roughness has been developed on the underside of the absorber plate. The roughness range of parameters used in the outdoor work are channel aspect ratio (W/H) of 8, relative roughness pitch (p/e) of 6.67–8.33, relative roughness height (e/Dh) of 0.027, angle of arc (α) of 60° and Reynolds number (Re) of 3000–14000, The test was run from morning 11 am until afternoon 2 pm, and the solar heat flux (I) was between 850 and 890 W per square metre. Under comparable working conditions, the artificially roughened channel performs well in comparison to the smooth channel. Over the smooth channel, the maximum ranges of thermal efficiency and heat transfer coefficient were noted to be 288 % and 129 %, respectively.

Effect of pasteurization on color, ascorbic acid and lycopene of crushed tomato: A computational study with experimental validation

Pasteurization of crushed tomato in glass bottles was evaluated using a multiphysics model, aiming to understand the temperature profiles and quality losses during the heating and cooling stages of the process. In order to rigorously simulate the pasteurization process, a finite element model was built using experimentally measured product and heat transfer parameters (thermal conductivity, density, specific heat, and convective heat transfer coefficient) and the kinetics of thermal degradation of the quality parameters (color, lycopene and ascorbic acid). The developed model was successfully validated by considering both the temperature profile (R 2 = 0.99) and quality losses (relative differences <10%). After validation, equivalent thermal processes were simulated at three temperatures (80, 90 and 100 °C). Numerical results revealed that the process at 100 °C provided the best retention of quality compared to the 80 and 90 °C processes. For the three quality parameters evaluated, color ( a* value), lycopene and ascorbic acid, for 100 °C, retention values of 92.25, 74.76 and 83.68% were obtained, while for the 80 °C treatment, the retentions were 65.60, 18.35 and 36.13%, respectively. • A multiphysics model was built to study crushed tomato in glass bottle pasteurization. • The microbial inactivation during cooling was greater than 50% of the total P-value . • Coldest point was located on axial axis at 38.5% of the total height for all cases. • The best retention of quality was provided by the treatment at 100 °C. • The developed model can be used to design and optimize protocols for pasteurization.

Nanofluids (CuO &amp; TiO2) - water as heat transfer fluid in a thermal energy storage system for applications of solar heating: An experimental study

The present work aims to exploit the thermal performance of a packed bed of combined sensible and latent heat of storage unit with an integrated solar heat source. A cylindrical insulated storage tank in the thermal energy storage (TES) unit is filled with spherical capsules separately which contains PCM as paraffin wax and stearic acid. The PCM usage has the benefits that it can be used as a thermal management tool and it reduces the cost and size of the system as it offers higher isothermal behavior and thermal storage capacity. The thermal conductivity of heat transfer fluid (HTF) can be enhanced by using nanoparticles mixed in water. Nanofluids are the more efficient fluids for the applications of heat-transfer. The water based nanofluids are used to transfer heat between the solar collector and storage tank which is a sensible heat storage material. The HTF materials are varied and experimental trials have been conducted separately. Experimentation was carried out first by considering only water as HTF and is extended by adding water with one of the nanomaterials i.e. The TiO2 and CuO, each in 3 HTF vol.% as 0.2, 0.5, and 0.8. The variable source of heat supply considered is solar flat plate collector. The study was transpired by varying the flow-rates of nanofluids as 2.0, 4.0, and 6.0 Lpm. The novelty of this work is to envisage the enhancement of heat transfer and to study the effects on the melting time of the PCM of these fluids which were carried out. The performance parameters like charging time and system efficiency, instantaneous stored heat, cumulative stored heat were studied for the different HTF and for the PCM-paraffin and stearic acid. The batch wise process experiments for discharging were carried out to recover the heat stored, and the results are presented.

HEAT-TRANSFER ENHANCEMENT OF MONO ETHYLENE GLYCOL-WATER-BASED SOLAR THERMIC FLUIDS DISPERSED WITH MULTIWALLED CARBON NANOTUBES IN A COILED TUBE HEAT EXCHANGER

The current research focuses on how the inclusion of multiwalled carbon nanotubes (MWCNTs) in mono ethylene glycol-water mixtures affects thermal conductivity, heat transfer, and dynamic viscosity for solar thermal applications. To achieve high stability in mono ethylene glycol-water mixtures, MWCNTs were oxidized and then dispersed at concentrations of 0.5, 0.25, and 0.125 wt.&amp;#37;. Zeta potential analysis was used to track the stability of the nanofluids over a two-month period. With the dispersion of MWCNTs in the base fluids, there is a remarkable increase in thermal conductivity from 15 to 24&amp;#37;. The dynamic viscosity variation is found to be minimal at high temperatures. Heat-transfer studies conducted on a specially designed test rig consisting of a coiled heat exchanger show that ethylene glycol-water mixtures dispersed with MWCNTs exhibit excellent performance under laminar conditions. Correlations for thermal conductivity, dynamic viscosity, and Nusselt number were obtained for all temperature conditions, mass fractions, and percentages of ethylene glycol. In the case of 100&amp;#37; mono ethylene glycol and mono ethylene glycol-water mixtures (90:10 and 80:20) as base fluids, the increase in heat-transfer coefficients of the corresponding nanofluids is up to 30, 26, and 25&amp;#37;, respectively.

Effects of shape-stabilized phase change materials in cementitious composites on thermal-mechanical properties and economic benefits

• The effects of PCMs to save building energy consumption was investigated. • Physical-thermal-mechanical testing and cost analysis were conducted. • Energy saving efficiency was calculated via computational modeling. • Findings infer the potential application of coconut oil as an engineered PCM. Phase change materials (PCMs) have been utilized to improve the thermal properties of cementitious composites by using their latent heat capacity. Applying them to building components can reduce their heating and cooling loads through energy absorption during the phase change period. The shape-stabilized method using porous lightweight aggregates can prevent PCM leakage during the phase transition process. While many attempts have been made to develop and improve shape-stabilized PCM composites to achieve a high level of energy savings, their economic benefits have not been fully investigated, as most analyses are based on initial material costs with a limited linkage of their thermal-mechanical properties. This study used an integrated experimental-computational method to evaluate the effects of different PCMs in building components by considering the core thermal-mechanical properties with an economic benefit analysis. Toward that end, two different PCMs (PureTemp® and coconut oil) were selected to fabricate Thermal Energy Storage Aggregates (TESA) using the vacuum impregnated method: TESA-P (with PureTemp®) and TESA-C (with coconut oil). The thermal-mechanical properties were experimentally determined and used for building energy simulation for a typical small office in Houston, Texas. The cementitious composites incorporated with PCM showed lower thermal conductivity and heat transfer than the non-PCM specimens. The TESA-P specimens showed a more prolonged time lag and better energy-saving performance than the TESA-C specimens due to better thermal properties of PCM itself. In contrast, the costs of TESA-C applications could be less with a shorter pay-back time. The findings of this study infer the potential application of coconut oil as an engineered PCM in building construction.

Revisiting “Non-Thermal” Batch Microwave Oven Inactivation of Microorganisms

Over the last few decades there has been active discussion concerning the mechanisms involved in “non-thermal” microwave-assisted inactivation of microorganisms. This work presents a novel non-invasive acoustic measurement of a domestic microwave oven cavity-magnetron operating at fo = 2.45 ± 0.05 GHz (λo ~ 12.2 cm) that is modulated in the time-domain (0 to 2 minutes). The measurements reveal the cavity-magnetron cathode filament cold-start warm-up period and the pulse width modulation periods (time-on time-off and base-time period, where time-on minus base-time = duty cycle). The waveform information is used to reconstruct historical microwave “non-thermal” homogeneous microorganism inactivation experiments: where tap-water is used to mimic the microorganism suspension; and ice, crushed ice, and ice slurry mixture are used as the cooling media. The experiments are described using text, diagrams, and photographs. Four key experimental parameters are indentified that influence the suspension time-dependent temperature profile. First, where the selected process time > the time-base, the cavity-magnetron continuous wave rated power should be used for each second of microwave illumination. Second, external crushed ice and ice slurry baths induce different cooling profiles due to difference in their heat absorption rates. In addition external baths may shield the suspension resulting in a retarding of the time-dependent heating profile. Third, internal cooling systems dictate that the suspension is directly exposed to microwave illumination due to the absence of surrounding ice volume. Fourth, four separated water dummy-loads isolate and control thermal heat transfer (conduction) to and from the suspension, thereby diverting a portion of the microwave power away from the suspension. Energy phase-space projections were used to compare the “non-thermal” energy densities of 0.03 to 0.1 kJ·m-1 at 800 W with reported thermal microwave-assisted microorganism inactivation energy densities of 0.5 to 5 kJ·m-1 at 1050 ± 50 W. Estimations of the “non-thermal” microwave-assisted root mean square of the electric field strength are found to be in the range of 22 to 41.2 V·m-1 for 800 W.

Thermal safety of solid rocket motor with complex charge structure

This present work is focused to study thermal safety and heat transfer characteristics of large-scale solid rocket motor (SRM) with complex star-charged structure. Here, we have used three-dimensional unsteady heat transfer model coupled with a two-step global reaction mechanism of ammonium perchlorate/hydroxyl terminated polyether (AP/HTPE) propellant. Comparisons of the ignition delay time and temperature of computational results are done with experimental studies, and a reasonable match has been obtained in these comparisons. It is found that the heats transferred from the thermal environment and released from the exothermic reaction of the propellant jointly intensify the occurrence of the cook-off response of the SRM. The propellant at the bottom of the SRM can reach to a higher temperature over the time and thus the exothermic reaction is rapidly intensified with an increase of the propellant temperature, releasing more reaction heat simultaneously. The heat energy is gradually accumulated in the SRM and the propellant is eventually ignited under this high-heat environment. The ignition temperature of the SRM basically linearly increases with the AP content at 10.8% HTPE and the ignition temperature curve under different AP contents is closer to the quadratic curve at 7.8% HTPE. Also, the content of HTPE mainly has a certain effect on the ignition time that is 288 s and 283 s with its content of 7.8% and 10.8%, respectively. The heat transfer rate and the case temperature of the SRM are all increasing with an increase of environmental temperature, while the depth of the heat transfer is decreasing. Further, the ignition delay time can be expressed on environmental temperature as: ti = 2.073263exp11 × Te-2.89.