Search

In this study, we present an exact derivation of a meso-scale mathematical model for analyzing heat transfer in nanofluids through variational convergence, targeting the reduction of discrepancies between theoretical predictions and experimental data. The model derives distinct sets of partial differential equations for microscale, mesoscale, and macroscale simulations, taking into account several influencing factors across different scales. By employing the weak convergence of distributions and the theory of distributions, we establish variational convergence between the PDEs at different scales. Significantly, the mesoscale model leads to a derivation of the quadratic dependence of thermal conductivity on the particle volume fraction. Our numerical evaluations reveal a marked improvement in prediction accuracy, with the proposed model reducing prediction error in some cases by as much as 92% compared to some existing linear models. Additionally, when tested against available experimental data, the model shows a closer alignment reinforcing its potential for enhancing the prediction and understanding of nanofluid heat transfer. Hence, this paper represents a valuable contribution to nanofluid heat transfer research, providing a promising direction for future advancements in the field. [ABSTRACT FROM AUTHOR]

Abstract: In this work we present a mathematical model describing the coupled heat and moisture transport in paper. The model is solved numerically and the numerical solution is used to study the interdependency of the moisture and temperature distribution in paper. The results show that variation with temperature of the saturated water vapor concentration and the sorption isotherm parameters are both important for inducing moisture desorption. It is also found that for steep relative humidity ramps moisture sorption generates temperature increments that slow down the sorption process itself. The model is also used to study the moisture gradients in a paper sheet inside a printer from Océ Technologies, which contains a warm print surface. The results predict changes in moisture content of only 0.2%, which suggests that no deformations are induced on the printed sheet. [Copyright &y& Elsevier]

Final dewatering in the production of dry creped tissue is performed by Yankee drying, which includes hot pressing followed by simultaneous contact and impingement drying. The present study models Yankee drying and compares simulation results to the data obtained from trials on a pilot tissue machine. It advances models published previously by the representations developed for the transport of heat in the pressing stage and for the heat transfer involved in the dehydration of the cylinder coating spray. The model predicts an average specific drying rate within 4% in the range of the experimental data used. [ABSTRACT FROM PUBLISHER]

In this paper, a method has been developed for heat treatment of details with a complex surface profile with a rapidly oscillating laser beam with modulated radiation power. This method is an alternative method for the dynamic formation of the distribution of the intensity of the laser spot. A mathematical model for calculating the distribution of the intensity of the oscillating beam and temperature fields induced by laser treatment is created. An algorithm for optimizing the parameters of high-frequency oscillations of the beam based on the solution of the inverse problem of thermal conductivity to obtain uniform heating of the near-surface layer of the material is developed. [ABSTRACT FROM AUTHOR]

The presented work is a continuation of the development of a computational and experimental method for determining the thermophysical characteristics (TPC) of the stator coils of a generator operating with the use of the phenomenon of high-temperature superconductivity (HTSC). The paper considers algorithms for identifying heat transfer models in the composite material of the stator coil winding. Using the discovered thermophysical properties, it is planned to study the electrothermal interaction in a high-temperature superconductor before its transition to a superconducting state. There is a significant variety of methods for solving the problems of identifying mathematical models of heat transfer, in particular, of determining the thermophysical characteristics of composite materials. As a result of the analysis of alternative methods for solving the identification problem, the iterative regularization method is used in this work. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of a procedure for the calculation and experimental determination of the thermophysical characteristics of the stator coils of a generator operating using the phenomenon of high-temperature superconductivity. To realize the conditions close to operational ones, temperature regimes of cooling down the coil from 300 to 78 K with subsequent heating to 300 K were implemented during the experiment. The values of the thermophysical characteristics were calculated from the data of temperature measurements at the internal points of the samples. The paper presents a description of the experimental technique. [ABSTRACT FROM AUTHOR]

This paper describes the study of a problem of thermocapillary convection in a flat bounded region filled with liquid and gas in contact along the interfacial interface under weak evaporation. It is proposed to investigate the heat and mass transfer processes and the parameters of phase transitions during local heating using a two-sided mathematical model based on the Oberbeck–Boussinesq equations. The characteristics of mass transfer through a thermocapillary interface due to evaporation and vapor content in the gas layer are analyzed with account for the influence of the Soret and Dufour effects. The results of a numerical study of the evolution of the interface and unsteady flows in a cell are presented. The calculation of the main characteristics of the liquid — gas system and the position of the interface at each time is carried out using a specially developed numerical algorithm. The model presented in this study makes it possible to describe the formation of characteristic thermal and concentration structures and the transition modes of cellular convection with a complex configuration of flows in layers. [ABSTRACT FROM AUTHOR]

Drying is a complex process of simultaneous heat, mass, and momentum transport phenomena with continuous phase changes. Numerical modelling is one of the most effective tools to mechanistically express the different physics of drying processes for accurately predicting the drying kinetics and understanding the morphological changes during drying. However, the mathematical modelling of drying processes is complex and computationally very expensive due to multiphysics and the multiscale nature of heat and mass transfer during drying. Physics-informed machine learning (PIML)-based modelling has the potential to overcome these drawbacks and could be an exciting new addition to drying research for describing drying processes by embedding fundamental transport laws and constraints in machine learning models. To develop such a novel PIML-based model for drying applications, it is necessary to have a fundamental understanding of heat, mass, and momentum transfer processes and their mathematical formulation of drying processes, in addition to data-driven modelling knowledge. Based on a comprehensive literature review, this paper presents two types of information: fundamental physics-based information about drying processes and data-driven modelling strategies to develop PIML-based models for drying applications. The current status of physics-based models and PIML-based models and their limitations are discussed. A sample PIML-based modelling framework for drying application is presented. Finally, the challenges of addressing simultaneous heat, mass, and momentum transport phenomena in PIML modelling for optimizing the drying process are presented at the end of this paper. It is expected that the information in this manuscript will be beneficial for further advancing the field. [ABSTRACT FROM AUTHOR]

This paper describes an accurate model of the Electrical Power Subsystem (EPS) of the Thermal Analysis Support and Environment Characterization Laboratory (TASEC-Lab), a university experiment developed for using in high-altitude balloon missions to measure and analyze the convection heat transfer. A Li-ion battery and two high efficient DC–DC converters have been characterized through laboratory tests and fitting to the experimental results. The developed mathematical models described in this paper are used to carry out accurate EPS simulations and are validated by comparison with the experimental data. • Design and modeling of the electrical power subsystem of a stratospheric balloon experiment. • New Li-lion battery discharging model that describes the three main parts: initial decay, linear, and exponential decay. • Formulation of a new DC/DC converter efficiency model. • Simulation and model validation of the electrical power subsystem. [ABSTRACT FROM AUTHOR]

In this paper, the analytical and numerical solutions of a non-steady state mathematical model are developed and analyzed. The mathematical model development of a non-steady state heat transport for a one-dimensional system is shown, and the analytical solution of the model is presented. The numerical solution of the model, using the finite element method (FEM), is compared to its analytical solution, proving its consistency. One of the advantages of using numerical tools is that more complex solutions can be obtained, even if the corresponding analytical solution does not exist or is not known, which is useful for engineering students. To demonstrate the applications and possibilities of this work, it is shown that changing the boundary conditions, geometry, or dimension in the system and the mathematical model, it can be solved through a numerical solution method. This is easier and more comprehensive for students rather than facing the complexity of the analytical solutions. The paper shows that it is possible to use the FEM in a university teaching context to complementarily explain the underlying physical phenomena of an engineering problem, here applied to a heat transfer problem in a vegetable. [ABSTRACT FROM AUTHOR]

Absorption machines are frequently used for cooling and heating. However, they must be improved to achieve high performance at a lower cost. Being a key component of these machines, this paper focuses on the absorber and specifically on falling film absorber configuration due to its compactness and simple geometry. This paper reviews the different analytical and numerical approaches used to analyze the thermal, mass and hydrodynamic phenomena occurring in falling films for both smooth and wavy-laminar regimes. It shows the significant progress made since 2000 in terms of mathematical models developed and coupling effect resolution. Research using thermodynamics to identify, locate and quantify the entropy generation sources in falling film absorbers is also presented. [ABSTRACT FROM AUTHOR]

Investments in the development of the district heating system require a thorough analysis of the technical, economic, and legal aspects. Regarding the technical and economic context, a mathematical model of the district heating system has been proposed. It optimizes both the technical and economic aspects of the function and development of a district heating system. To deal with non-linearities, the developed linear programming model is divided into three phases: flow, thermal, and pressure. Therein, non-linear dependencies are calculated between the linear optimization phases. This paper presents the main assumptions and equations that were used to calculate the parameters of the heating system, along with the optimal level of heat production, the flow rate of the heating medium in the heat nodes and edges of the network graph, the heat, power, and temperature losses at each edge, and the purchase costs of heat and its transmission. The operation of the model was tested on a real-world district heating system. The case study results confirm that the model is effective and can be used in decision support. The economic results of the model, before the calibration process, were 3.6% different from historical values. After the calibration process, they were very similar to the real data—all percentage deviations were within 1%. [ABSTRACT FROM AUTHOR]

In this paper, we construct a highly simplified mathematical model for studying the problem of conjugate heat transfer in gas turbine blades and their cooling ducts. Our simple model focuses on the relevant coupling structures and aims to reduce the unrelated complexity as much as possible. Then, we apply the port-Hamiltonian formalism to this model and its subsystems and investigate the interconnections. Finally, we apply a simple spatial discretization to the system to investigate the properties of the resulting finite-dimensional port-Hamiltonian system and to determine whether the order of coupling and discretization affect the resulting semi-discrete system. [ABSTRACT FROM AUTHOR]

Cerebrospinal fluid (CSF) is a symmetric flow transport that surrounds brain and central nervous system (CNS). Hydrocephalus is an asymmetric and unusual cerebrospinal fluid flow in the lateral ventricular portions. This dumping impact enhances the elasticity over the ventricle wall. Henceforth, compression change influences the force of brain tissues. Mathematical models of transport in the hydrocephalus, which constitutes an excess of fluid in the cavities deep within the brain, enable a better perspective of how this condition contributes to disturbances of the CSF flow in the hollow places of the brain. Recent approaches to brain phase spaces reinforce the foremost role of symmetries and energy requirements in the assessment of nervous activity. Thermophysical and mass transfer effects are therefore addressed in this paper to quantify the transport phenomena in pulsatile hydrocephalus CSF transport with oscillating pressure variations that characterize general neurological activity and transitions from one functional state to another. A new mathematical model is developed which includes porous media drag for brain tissue and solutal diffusion (concentration) effects. A classical Laplace transform method is deployed to solve the dimensionless model derived with appropriate boundary conditions. The analysis reveals that with increasing permeability of the subarachnoid space, the CSF velocity is increased, and a significant fluid flux enhancement arises through the brain parenchyma as the pressure of the fluid escalates drastically due to hydrocephalus disorder. Stronger thermal buoyancy (Grashof number) also results in deceleration in the flow. CSF temperature is reduced with progression in time. Particle (e.g. ion) concentration is suppressed with increasing Schmidt number. As heat conduction parameter increases, there is a substantial depletion in CSF velocity with respect to time. Increasing Womersley parameter displaces the CSF velocity peaks and troughs. The present effects are beneficial in determining the thermo-fluidic transport mechanism of the pathological disorder hydrocephalus. Also, the present results are compared with those clinical studies for some cases. We have confirmed that our validity provides a decent justification with the neurological studies. [ABSTRACT FROM AUTHOR]

An amplitude demodulator, using an on-line MEMS power sensor is studied in this paper. The model of the equivalent circuit of on-line structure is solved, and the heat transfer model related to the thermopile is proposed and also simulated to verify the feasibility of AM demodulation. Experiments are also performed to verify the proposed models. The microwave performance shows that the device has a return loss that is better than 20 dB, and an insertion loss of less than 0.5 dB up to 10 GHz. Both the model and the experimental results show that the MEMS device can perform demodulation of an AM signal with carrier frequency of 0.01–10 GHz and signal frequency of under 1kHz. [2021-0261] [ABSTRACT FROM AUTHOR]

This paper explores the hyperbolic heat transfer effects in processes involving high heating rates. The behavior of the model is analyzed in detail under different boundary conditions and the circumstances under which a non-Fourier law could be used to describe thermal conduction processes established from physical mathematical analysis. Finally, the model developed here is coupled to a previous population balance framework to predict the bubbling phenomenon that occurs during the fast pyrolysis of biomass. We found that a transient overheating occurs in the central zone of the generated liquid phase due to the high heating rates that take place during that process. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model of heat pump exchangers and their thermal interaction with a fan for an air dryer. The calculation algorithm developed for the finned heat exchangers is based on the ε-NTU method, allowing the determination of air side and refrigerant side heat transfer coefficients, evaporator and condenser heat capacity and air parameters at the dehumidifier outlet with known exchanger geometries, initial air parameters and mass flow rate. The model was verified on an industrial dehumidifier test bench. This enabled the heat transfer coefficients for the exchanger to be calculated as a function of the speed and, therefore, the power of the fan's drive motor. An increase in fan performance on the one hand results in an increase in the heat transfer rate, but, on the other hand, it causes an increase in the total energy consumption of the motor. Thus, while it causes an increase in drying capacity, it also causes an increase in the energy consumption of the dehumidifier. In order to optimise the unit in terms of energy consumption, it is therefore necessary to determine a function that relates the amount of heat exchanged to the efficiency of the fan. [ABSTRACT FROM AUTHOR]

This paper investigates the heat transfer of two-phase nanofluid flow between horizontal plates in a rotating system with a magnetic field and external forces. The basic continuity and momentum equations are considered to formulate the governing mathematical model of the problem. Furthermore, certain similarity transformations are used to reduce a governing system of non-linear partial differential equations (PDEs) into a non-linear system of ordinary differential equations. Moreover, an efficient stochastic technique based on feed-forward neural networks (FFNNs) with a back-propagated Levenberg–Marquardt (BLM) algorithm is developed to examine the effect of variations in various parameters on velocity, gravitational acceleration, temperature, and concentration profiles of the nanofluid. To validate the accuracy, efficiency, and computational complexity of the FFNN–BLM algorithm, different performance functions are defined based on mean absolute deviations (MAD), error in Nash–Sutcliffe efficiency (ENSE), and Theil's inequality coefficient (TIC). The approximate solutions achieved by the proposed technique are validated by comparing with the least square method (LSM), machine learning algorithms such as NARX-LM, and numerical solutions by the Runge–Kutta–Fehlberg method (RKFM). The results demonstrate that the mean percentage error in our solutions and values of ENSE, TIC, and MAD is almost zero, showing the design algorithm's robustness and correctness. [ABSTRACT FROM AUTHOR]

The present study investigates two models—two limiting cases—for the internal heat and mass transfer in a multicylinder dryer: the first model assumes that complete redistribution of heat and moisture in the thickness direction occurs instantaneously. The second model assumes that moisture transfer occurs only by vapor diffusion and that heat transfer takes place by conduction and condensation. The two models are written in dimensionless form, and applied for the same set of standard paper machine data. For basis weights below approximately 0.05 kg d.s./m2 the results are so close that the first, simple model is sufficient. A higher limiting basis weight—approximately 0.16 kg d.s./m2—was previously indicated by comparison of model predictions, assuming the simple model, to extensive sets of machine data from four different paper machines. [Copyright &y& Elsevier]

A mathematical model describing the heat and mass transfer in the dryer section of a paper machine has been applied to the production data from four paper machines. Model predictions for the machine speed are compared to actual machine speeds for a total of 163 data sets. The mathematical model assumes that the temperature and moisture content remain homogeneous in the thickness direction of the sheet. For three paper machines producing paper with basis weights ranging from 0.056 to 0.159 kg d.s./m2 the model predictions are adequate. For the paper machine producing the heaviest grades with basis weights ranging from 0.189 to 0.390 kg d.s./m2 the model predictions are flawed by a systematic error. For low machine velocities/high basis weights the machine velocity is over-predicted and for high machine velocities/low basis weights the machine velocity is under-predicted. This systematic error is caused by the assumption of homogeneous moisture content and temperature within the sheet being severely in error for thick sheets. [Copyright &y& Elsevier]

This study presents an integrated approach to assess energy performance during hood retrofitting from a semi-closed hood to a closed hood. According to the principle of heat and mass transfer, a simulation program was established by a mathematical model and some necessary model parameters. It could be used to simulate the paper-drying process and calculate steam and power consumption during paper drying. The method was applied to a corrugated paper machine. After a fundamental field test and observation, the simulation program determined appropriate model parameters. Finally, we found a 13.2% steam consumption reduction and a 13.5% total energy consumption reduction. [ABSTRACT FROM PUBLISHER]

Eddy current pulsed thermography (ECPT) applies induction heating and a thermal camera for non-destructive testing and evaluation (NDT&E). Because of the variation in resultant surface heat distribution, the physical mechanism that corresponds to the general behavior of ECPT can be divided into an accumulation of Joule heating via eddy current and heat diffusion. However, throughout the literature, the heating mechanisms of ECPT are not given in detail in the above two thermal phenomena and they are difficult to be separated. Nevertheless, once these two physical parameters are separated, they can be directly used to detect anomalies and predict the variation in material properties such as electrical conductivity, magnetic permeability and microstructure. This paper reports physical interpretation of these two physical phenomena that can be found in different time responses given the ECPT image sequences. Based on the phenomenon and their behaviors, the paper proposes a statistical method based on single channel blind source separation to decompose the two physical phenomena using different stages of eddy current and thermal propagation from the ECPT images. Links between mathematical models and physical models have been discussed and verified. This fundamental understanding of transient eddy current distribution and heating propagation can be applied to the development of feature extraction and pattern recognition for the quantitative analysis of ECPT measurement images and defect characterization. [ABSTRACT FROM AUTHOR]

Grate boilers are widely applied in biomass combustion for heat and energy generation. However, grate-firing systems often suffer from low efficiency and high emission. Computational fluid dynamic (CFD) becomes increasingly popular as a flexible method to obtain the detailed combustion behaviors in the furnace, and to optimize the performance of existing grate boilers. This paper presents efforts toward a reliable baseline CFD model for an industrial biomass-fired grate boiler, where the structure of the fuel-bed was sufficiently considered. The combustion performances in the furnace were investigated experimentally and numerically by coupling the fuel bed and freeboard, to clarify the impact of bed structure on the simulation accuracy. Results show that when the bed structure has been taken into account, the predictions are in better agreement with the various measurements, as the deviations between them are all within 10 %. Moreover, the flame center drops, the total heat transferred to the water-cooled walls increases, and the residence time of flue gas is greatly prolonged from 2.76 s to 3.90 s, resulting in a distinct difference of the temperature and species patterns in the freeboard. The simulations will provide valuable theoretical guidance for the accurate modeling of grate-fired boiler. [Display omitted] • A baseline model is proposed for accurate modeling of biomass-fired grate boiler. • Effect of fuel-bed structure on the simulation of grate boiler is clarified in detail. • Bed structure greatly affects the predicted temperature and species patterns. • Flue gas residence time and heat transfer are also highly impacted by bed structure. [ABSTRACT FROM AUTHOR]

The paper presents the mathematical model of the heat transfer processes for a single screw ash cooler (SSAC) working with a circulating fluidized bed (CFB) boiler. The validation of the model is based on experimental measurements made on a 230 MWe power unit. The analysis of measurement data from two bottom ash coolers showed that the correct prediction of the outlet temperatures of ash and cooling water requires the determination of their individual ash filling characteristics (i.e. coolers). The numerical results confirm that the mixing model proposed by Schlünder correctly predicts the heat transfer coefficient for ash. The described mathematical model can monitor the operating conditions of the single screw ash cooler. It enables the determination of the optimal volumetric flow rates of the cooling water in order to get its highest possible outlet temperature, and then for this water to be used, e.g. for sanitary purposes. [Display omitted] • Mathematical model of ash cooler is successfully verified with experimental data. • Schlünder model of particle mixing is used to calculate heat transfer coefficient. • Characteristic of filling ash cooler with ash is a key part of mathematical model. [ABSTRACT FROM AUTHOR]

This paper deals with a mathematical model of a fluid flowing between two parallel plates in a porous medium under the influence of electromagnetic forces (EMF). The continuity, momentum, and energy equations were utilized to describe the flow. These equations were stated in their nondimensional forms and then processed numerically using the method of lines. Dimensionless velocity and temperature profiles were also investigated due to the impacts of assumed parameters in the relevant problem. Moreover, we investigated the effects of Reynolds number, Hartmann number M, magnetic Reynolds number, Prandtl number, Brinkman number ℱ, and Bouger number 𝜔, beside those of new physical quantities (N, ). We solved this system by creating a computer program using MATLAB. [ABSTRACT FROM AUTHOR]

In this paper, the physical parameters of the absorber pipe of a linear parabolic collector have been investigated. The types of solar collectors, specifically the linear parabolic collector, have been comprehensively studied. Then, the mathematical model of heat transfer in the absorber pipe of the collector has been presented based on valid references. Numerical solutions of the equations related to the absorber pipe were performed by MATLAB software, and the effects of the physical parameters of the absorber pipe on its efficiency were investigated. The results show that increasing the length of the absorber pipe causes a nonlinear decrease in the efficiency of the absorber pipe. One of the important results is the increase in fluid temperature due to the increase in the diameter of the adsorbent tube, which increases the diameter of the fluid temperature by 60 K, in which the parameter increases the efficiency by 0.38%. [ABSTRACT FROM AUTHOR]

Summary: In this paper, development and preliminary validation of an in‐house code LETHAC (lead‐based fast reactor thermal‐hydraulic analysis code) is introduced. LETHAC is developed for predicting the thermal‐hydraulic transient performance of a lead‐bismuth reactor. The mathematical models and module relations of LETHAC are presented in detail. The most‐used LBE (lead‐bismuth eutectic) flow and heat transfer correlations are compared against data from KYLIN‐II 61‐rod wire‐wrapped bundle experiments. Results show little difference between the chosen heat transfer correlations as the relative error of these correlations is all within 2%. Novendstern correlation is recommended for wire‐wrapped bundle frictional resistance coefficient calculation as it fits the experimental data best. Besides, the transient calculation capability of LETHAC is also preliminarily evidenced by TALL transient tests. Good agreements are shown between the calculated temperatures and the experiment ones. Relative errors between calculation results and experimental data are almost within 10% during the whole transient process, which indicates LETHAC can be used for predicting the transient behavior of lead/lead‐bismuth cooled systems. [ABSTRACT FROM AUTHOR]

Energy efficiency of hydrostatic transmissions, and especially efficiencies of drives with motor speed controlled by throttle, as well as efficiency of hydraulic servomechanisms can in fact be higher than the efficiency values most frequently given by the respective literature in this field. With the progress achieved in recent years in the development of hydraulic systems it is becoming necessary to develop methods for precise energy efficiency calculation of such systems. It is difficult to imagine that more and more, better and better machines and control elements could be used without the possibility of a mathematical tool at our disposal to enable an accurate analysis and assessment of behavior of the system in which such machines and control elements have been applied. The paper discusses energy savings using mathematical model of losses in elements, the energy efficiency of the system. There are possibilities to reduce energy losses in proportional control systems (in the pump, in the throttle control unit, especially in the cylinder), and thus to improve the energy efficiency of the throttling manifold. The considerations allow for comparison of the loss power resulting from the applied hydraulic control structure of the hydraulic cylinder and the power consumed by the pump from the electric motor that drives it, the power necessary to provide pump-driven hydraulic cylinder. The article shows the impact on the output (useful) power consumed in the considered systems, and the impact on the power consumed of the loss power in the individual elements. The paper presents also formulas of loss power, formulas of energy efficiency connected with investigated hydrostatic drives, two schematic diagrams of hydraulic systems, their principle of operation and problems of studying losses in elements and energy efficiency characteristics of systems consisting of a feed assembly, control set and cylinder. It also includes a subject matter connected with an energy loss power of hydrostatic systems with hydraulic cylinder controlled by proportional directional control valve. Diagrams of loss power of two hydraulic systems worked at the same parameters of speed and load of a cylinder, which were different due to structure and ability of energy saving, were presented and compared. [ABSTRACT FROM AUTHOR]

The standard engineer's model for heat transfer between the fluid flowing through the pipe and the exterior medium neglects the effects of the pipe's wall. The goal of this paper is to prove that they are not always negligible. Comparing the ratio between diffusivities of the fluid and the wall with the wall's thickness, using rigorous asymptotic analysis, we find five different models for effective description of the heat exchange process. [ABSTRACT FROM AUTHOR]

The strong coupling heat transfer between subassemblies and inter-wrapper gaps is closely related to the safety of the sodium-cooled fast reactor (SFR). Therefore, it is very important to carry out a detailed thermal hydraulic analysis of the core. In this paper, the inter-wrapper channel is modeled using the subchannel analysis method. A core thermal-hydraulic analysis code SACOS-Na (Subchannel Analysis Code Of Safety for SFR) is developed by using SIMPLE algorithm. For the subassembly module, a total of three experiments, including ORNL 19-pin experiment, TOSHIBA 37-pin experiment and KNS 37-pin experiment, are adopted to demonstrate the feasibility of the mathematical and physical models and numerical algorithms of the SACOS-Na as well as the rationality of the selected auxiliary models. For the inter-wrapper gap module, WEISS 2-subassembly experiment and CCTL-CFR 3-subassembly experiment are used to verify not only the simulation capability for backflow and strong inter-subassembly heat transfer, but also the heat structure model and the subchannel modeling approach on inter-wrapper gaps. In addition, the prediction accuracy of SACOS-Na has reached the advanced international level by comparing with the worldwide well-known core thermal hydraulic analysis codes. • The subchannel modeling method is adopted to build the mesh for inter-wrapper channels. • The SIMPLE algorithm is used to solve the problems of the reverse flow and inter-subassembly heat transfer occurred in SFRs. • The universal core thermal-hydraulic analysis code SACOS-Na for SFRs is developed. • The accuracy and reliability of the SACOS-Na are discussed from all aspects. [ABSTRACT FROM AUTHOR]

Solid autogenous pyrolysis plugging technology is an innovative technology which is suitable for relieving hydrate plugging in wellbore. A mathematical model of phase equilibrium, decomposition rate and decomposition heat transfer of hydrate was established to solve the problems of heat release diffusion and loss during the reaction of autogenic pyrolysis plugging agent. The study of heat diffusion simulation was carried out at different concentrations and diameters, and the distribution cloud maps of wellbore temperature, water volume fraction, natural gas volume fraction and hydrate volume fraction were obtained under different conditions. The research shows that with the increase of concentration of autogenous pyrolytic plugging agent, the rate of heat release accelerates, the heat transfer to the surrounding area increases, and the heat diffusion is irregular. with the increase of wellbore diameter, the time of pyrolysis plugging increases, and the amount of autogenous pyrolysis plugging agent also increases. In this paper, the fitness of simulated calculation value and actual value is more than 85%, which provides a theoretical guidance for on-site plugging remove operation. [ABSTRACT FROM AUTHOR]

In order to make full use of the advantages of superheated steam (SHS), SHS injection in multi-point injection wells (MPIW) is proposed in this paper. Firstly, a mathematical model comprised of SHS flow model in inner tubing (IT) or long tubing (LT) and annulus, transient heat transfer model in oil layer is established. Secondly, type curves of SHS flow in MPIW is obtained by finite difference method on space and the iteration technique. Then, the effect of injection temperature on distributions of thermophysical properties of SHS in MPIW is discussed in detail. Results show that: (a) When the heat exchange between IT and annulus is taken into consideration. SHS temperature in IT has a decrease while SHS temperature in annulus has an increase. (b) With the help of MPIW, heating effect at both heel and toe points of the horizontal wellbores can be enhanced. (c) While the increase of SHS temperature certainly benefits the formation heating effect through the increase of both SHS temperature and superheat degree, the following decrease of SHS pressure in annulus will lead to the decrease of SHS absorption rate. This paper unravels some intrinsic flow characteristics of SHS in MPIW, which has a significant impact on the optimization of SHS injection parameters and analysis of heat transfer law in MPIW. [ABSTRACT FROM AUTHOR]

Fast estimation of thermal transmittance based on temperature measurements is uncertain, and the obtained results can be burdened with a large error. Nevertheless, such attempts should be undertaken merely due to the fact that a precise measurement by means of heat flux measurements is not always possible in field conditions (resentment of the residents during the measurements carried out inside their living quarters), and the calculation methods do not allow for the nonlinearity of thermal insulation, heat bridges or other fragments of building envelope of diversified thermal conductivity. The present paper offers the estimation of thermal transmittance and internal surface resistance with the use of temperature measurements (in particular with the use of thermovision). The proposed method has been verified through tests carried out on a laboratory test stand built in the open space, subjected to the influence of real meteorological conditions. The present elaboration involves the estimation of thermal transmittance by means of temperature measurements. Basing on the mentioned estimation, the authors present correction coefficients which have impact on the estimation accuracy. Furthermore, in the final part of the paper, various types of disturbance were allowed for using perturbation numbers, and the introduced by the authors “credibility area of thermal transmittance estimation” was determined. [ABSTRACT FROM AUTHOR]

The numerical modelling of the internal heat generation in passenger vehicle tyres using finite element analysis is a well-known numerical approach. However, this application is rather uncommon for earthmover tyres. This paper describes the development of a finite element model of a 23.5R25 earthmover tyre for the numerical modelling of the temperature distribution in the tyre cross-section at steady-state heat transfer conditions using an uncoupled analysis procedure. Considering the non-linear behaviour of the rubber compounds used for the manufacturing of these tyres, as well as the complexity associated with the composite structural aspects of the tyre, the material properties used for the proposed numerical model were established experimentally. In the analyses completed, the tyre behaviour was studied by simulations at various inflation pressures, loads and rolling velocities. The numerical tyre defection was within an 8% deviation from the actual tyre behaviour. Thermal simulation results were used to derive an equation that can be used to predict the maximum temperature that would occur in the tyre’s cross-section as a function of its vertical deflection, its forward rolling velocity and the ambient temperature of the surroundings. The numerical models and simulations presented in this paper were completed using MSC.Marc/Mentat. [ABSTRACT FROM AUTHOR]

Abstract: The paper summarizes the findings of a study on mathematical modeling of heat transfer in glass melts using the commonly employed diffusion or Rosseland approximation (R) for optically thick media and the more general, spectral discrete ordinates (DO) approach. The systems considered were the melting of an ultra‐clear glass in a furnace (optical thickness ~ 10) and heat transfer in 2 glass melts with different levels of iron oxide flowing through a delivery channel (optical thicknesses of ~17 and ~80). The results showed that the use of the R approach for modeling heat transfer in the ultra‐clear glass will lead to serious errors in the prediction of important practical parameters such as the refractory temperature, energy efficiency, and the quality of glass melt. The results for the channels showed that differences between the 2 thermal radiation models began to narrow as the optical thickness value approached 17. The paper also presents brief reviews of high‐temperature absorption spectra of commercial glass melts and the theoretical background on thermal radiation in participating media. In addition, a relatively simple system involving 1‐dimensional radiation heat transfer in a participating medium is used to illustrate the implications of using the diffusion approximation. [ABSTRACT FROM AUTHOR]

Specific heat is a property of foods materials needed for analysis and design processes involving heat transfer. The specific heat of edible-wild mushrooms as affected by moisture content, temperature and mushroom variety was investigated in this paper. The ranges of moisture content and temperature studied in this paper were 0.05-0.80 kg water/kg sample and 10-90°C. The significant of the studying factors was analyzed and the regression analysis was then performed to determine the best model for predicting specific heat. The statistical analysis and software were performed and used for the judgment of the degree of accuracy of the fitted models. A linear function of specific heat with moisture content and temperature was proposed and model efficiency was evaluated statistically. The obtained model obviously outperformed the other conventional models and was found to be successful in much better specific heat prediction of mushroom varieties which will be very useful in practical use of mushrooms in industry. [ABSTRACT FROM AUTHOR]

Numerous metrics and indices have been proposed for the assessment of thermal perception and comfort. Commonly used indices based on the estimate of the heat flow between the human and its environment includes the well-known Fanger's method, also known as the PMV-PPD thermal comfort model. Recently this thermodynamic approach has been expanded with the application of the second law of thermodynamics. In this paper, an exergy-based analysis of the relation between the human and its environment is presented. Heat and mass flow rate due to convection, radiation, evaporation and respiration are calculated and expressed in terms of exergy loss. This value is used in the modified Fanger's thermal comfort model, where the heat balance equation is replaced by the exergy loss. The paper builds upon prior studies on determination of internal and external exergy losses by revised and newly defined formulas taking into account clothing and indoor conditions. The results quantitatively show that thermal energy load in the original Fanger's PMV model could be substituted by exergy loss and it corresponds to a certain level of subjective assessed thermal comfort level. [ABSTRACT FROM AUTHOR]

The paper deals with heat transfer processes during pre-launch chilldown of consumption lines of the upper stage propulsion systems (PS) by a cryogenic component. Propulsion systems operating on high-efficiency cryogenic propellant components may be used at the first as well as at the upper stages of launch vehicles to deliver spacecrafts into final orbits. Cryogenic PS produce high specific impulse being environmentally friendly, which may provide a growing interest towards their application. Low temperature of cryogenic propellant components may pose considerable challenges when chilling down, fueling and storing components as well as draining fuel tanks and starting PS, especially under zero gravity conditions in long-term space flights. Complex experimental facilities (EF) along with test methods as well as physical and mathematical models for calculating nonsteady multiple-phase heat transfer processes with intense phase transformations are being developed to overcome these challenges. The methods for mathematical modelling of the chilldown and cryogenic component flow processes have been proposed considering mass - and energy-conservation equations in relation to supply lines, tank gas blanket and tank volume filled with cryogen liquid. Closing dependency ratios have been specified according to results of bench and flight testing of PS to solve equations for heat transfer and friction in the cryogenic supply system components of test stand (TS) and PS. Also, the paper studies heat transfer processes during pre-launch chilldown of consumption lines (CL) of 12KRB LV PS with the lox/liquid hydrogen engine KVD-1 considering results of bench and flight testing of the block. Findings on chilldown and fueling of the 12KRB upper stage may be used to verify calculation models while designing and developing the KVTK advanced upper stage with the lox/liquid hydrogen engine RD0146 of the Angara-A5V heavy class launch vehicle. [ABSTRACT FROM AUTHOR]

The article presents a review of works on mathematical modelling of biomass pyrolysis process. Models types, number of dimensions, captured phenomena, type and dimensions of the reactors and biomass particles as well as models validation methods were analysed. Particular attention was paid to descriptions of chemical reactions, which are the essence of biomass thermal decomposition simulation. The article briefly describes the most important issues related to biomass pyrolysis and provides a review of commonly used methods of modelling this process with emphasis on solutions "ready to employ" in CFD modelling. A summary of other review papers on this topic is also provided. The problem of mathematical modelling in the context of "model - an engineering tool" was also discussed. Mathematical model for an engineering applications must be prepared with consideration of necessary consensus between the calculations accuracy, calculation time, preparation efforts and analysis requirements. Therefore, in pyrolysis modelling context, the inclusion of chemical reactions and changes of heat transport conditions were considered as priority, while taking into account moisture evaporation and bed shrinkage should be conditioned by their actual contribution in the calculations accuracy and by their influence on the calculations time. • A review of research on mathematical modelling of biomass pyrolysis is presented. • Captured phenomena, kinetic models, properties change, reactor types are summarized. • Compromise between model precision and calculations costs is discussed. [ABSTRACT FROM AUTHOR]

Thermally activated building systems (TABS) constitute an energy efficient building conditioning solution through the combination of low‐exergy space heating and cooling and thermal energy storage (TES) features. Their implementation is, however, complex, due to the number of factors involved in their design and operation. Mathematical models are useful to overcome this, but require validation, while experimental setups to study sensible TES can be bulky and difficult to handle. In this work, a homogeneous concrete slab and a multilayer concrete‐sand‐gravel slab are built and activated with constant heat flow. Both slabs are experimentally tested and their thermal behaviour is modelled through a 1D finite difference method (FDM). Results demonstrate that materials such as sand and gravel can be used to provide relevant experimental data for TABS heat transfer model validation through a versatile lab test rig. A 1D FDM proves to be a simple, accurate method to predict the thermal behaviour of the slabs during transient peaks in charging and discharging processes as well as during steady‐state operation, given that most of the time absolute errors remain below the measurement uncertainty thresholds. Finally, this paper sets a basis to support future experimental work on sensible TES and provides data for further model validation. [ABSTRACT FROM AUTHOR]

The paper presents a physico-mathematical model for determining the heat transfer parameters between viscous gasdynamic flotations and cooled gas turbine blades made using the technology of composite permeable membranes (CPM). The mathematical model includes equations of dynamic and thermal boundary layers taking into account injection, three-dimensional transient heat conduction in CPM cooled frames, complex hydraulic flow and cooling inside the channels of a cooled blade with air taken from the power plant compressor. A complex problem was solved to determine the thermal state of microrocket engines, where a method was proposed for immersing a multiply-connected domain in a region of the simplest form. A new economical, absolutely stable method is proposed for numerically solving of spatial nonstationary heat transfer problems in multiply-connected domains. The results obtained showed greater cooling efficiency at lower cooling medium costs. [ABSTRACT FROM AUTHOR]

In this paper, we contemplate a comparison of results between constant and variable fluid properties while considering magnetohydrodynamics (MHD) flow and heat transfer for steady, two dimensional and laminar viscous fluid over a nonlinearly stretching sheet. The governing mathematical model for the underlying problem is drafted in its most general setup, i.e. we consider the the representative partial differential equations(PDEs) for viscous compressible fluid. Similarity transformation is exercised to transform governing nonlinear PDEs into a nonlinear ODEs. The set of two coupled ODEs are solved numerically by shooting technique and bvp4c (builtin MATLAB solver). Besides, we also present and execute a new numerical method for solving coupled nonlinear ODEs, the Simplified Finite Difference Method (SFDM). When comparing with bvp4c and shooting technique, the efficiency of SFDM for the above system has also been shown. Various governing parameters and their effect on temperature and velocity profiles are studied in detail. We have shown that there is a significant difference of results when its comparison is drawn between for constant and varying fluid properties. Skin friction coefficient shows increment in its values while rate of heat transfer shows decrement for variable viscosity when compared with constant viscosity. [ABSTRACT FROM AUTHOR]

This paper is the first part of a two‐part study, and it presented numerical research of double‐diffusive natural convection within an annulus area, situated in two horizontal confocal elliptic solids charged by a Newtonian fluid. The elliptical coordinates were used to transform the physical domain into a rectangular one. To resolve the governing equations and the boundary layer conditions, a calculator code based on the finite volume approach was developed. The details of the influences of thermal Rayleigh number on heat and mass transfer were investigated. Results obtained were compared with those existing in other reasearch works. [ABSTRACT FROM AUTHOR]

Cast-tape drying (CTD) process was evaluated by an experimental approach, obtaining drying curves, convective coefficients of heat (hh) and mass (hm) transfer, time-temperature, and pulp shrinkage kinetics for tomato pulp at 2, 3, and 4 mm thick. A heat and mass transfer model with moving border described CTD. Pulp thickness was reduced by 90%, under hh and hm of 55 W m−2 K−1 and 0.05 m s−1, respectively. Evaporative capacity ranged between 8 and 15 kg m−2 h−1, and drying time between 8 and 24 min for 2 and 4 mm thick, respectively. Coupled experimental and theoretical analysis of CTD clarified the relative importance of different phenomena controlling the process. [ABSTRACT FROM AUTHOR]

Combi-steamer condensation hoods are widely used in modern gastronomy. They condense steam produced by the combi-steamer and also filter solid particles, moisture, grease and smells. All these factors negatively affect the staff and dishes, so efficient work of the condensation hoods becomes important. A mathematical and experimental analysis of such a device is described in this paper. First a measurement methodology was designed and measurements of air humidity, temperature and mass flow rates were performed. The measurement procedure concerned dedicated a steam generator and combi-steamer. Next a mathematical model was developed. It was based on mass and energy balances of the condensation hood. The condensate flow rate turned out to be insufficient to fulfill the energy balance while measured directly. Hence, it was calculated from heater's power of the steam generator and the balance model was validated. The combisteamer had an unknown output, so the condensate flow rate was provided by the balance model after its validation. A preliminary diagnosis of the device was carried out as well. [ABSTRACT FROM AUTHOR]

This paper solves the problem of the identification of a complex of heterogeneous, thermophysical properties that are part of a system of ordinary differential equations of a mathematical model with lumped parameters. The previously developed iterative-variational method is used to regularize an unstable solution of the inverse heat-transfer problem. The results confirm the efficiency of this regularization method and make it possible to study the temperature dependences of the emissivity and thermal resistance of screen-vacuum thermal insulation. [ABSTRACT FROM AUTHOR]

In recent years, numerous studies have been done on the rheological behavior and heat transfer of nanofluids. In this paper, an experimental study on the rheological behavior of hybrid WO 3 -MWCNTs/Engine Oil hybrid Newtonian nanofluid has been carried out. Tungsten oxide (WO 3) nanoparticles have diameter of 23–65 nm and MWCNTs nanoparticles have diameter of 20–30 nm. Experiments were carried out at 6 vol fraction of nanoparticles of φ = 0, 0.05, 0.1, 0.2, 0.4 and 0.6% at the temperatures of 20, 30, 40, 50 and 60 °C. The results show that the relationship between the shear rate and shear stress of the base fluid and the hybrid nanofluid of WO 3 -MWCNTs/Engine Oil is linear at all temperatures and volume fraction of nanoparticles. So, the base fluid and the hybrid nanofluids are Newtonian. Also, with increasing temperature, the viscosity of nanofluid decreases and with increasing volume fraction of nanoparticles, the viscosity increases. Finally, a mathematical model has been proposed to estimate the nanofluid viscosity. The results obtained from the model show good compatibility with experimental values. Image 10478 • Experimental investigation for developing a new model for rheological behavior of nanofluid. • Tungsten oxide-MWCNTs/motor Oil hybrid Newtonian nanofluid was prepared. • Experiments were repeated at different shear rates. • The viscosity at different solid volume fractions was measured. [ABSTRACT FROM AUTHOR]

Mathematical model of the drying process for particles of capillary-porous materials in the apparatus with a suspended-swirled flow of heat-carrying medium and its numerical solution with the help of Euler's method was presented in this article. The sequence of the problem solution was developed by the authors. The movement path of the particle of the capillary-porous material in the vortex chamber during the drying process, the change in the mass and temperature of the particle on time, the change in the relative air velocity and the heat transfer coefficient on time are represented graphically in the paper. [ABSTRACT FROM AUTHOR]

Ogbono (lrvingia spp.) kernel is a popular soup condiment in West Africa. Drying is an important step in the processing of Ogbono (lrvingia spp.). This paper is geared towards developing a better understanding of the different factors involved in the heat transfer during the open-sun drying of Ogbono (lrvingia spp.) seeds. For this purpose, a mathematical model was developed for the heat transfer to and out of the seeds. This model served as the framework for factor effects and interaction studies. Ambient temperature, seed size, air velocity and the thermal conductivity of the drying surface showed a direct relationship with the internal temperature of the seeds albeit at varying levels. Moisture content showed an inverse relationship. An analysis of variance showed that ambient temperature, seed size and air velocity were observed to be the most significant factors affecting the heat transport. The interactions between the different factors as it affects heat transport were also elucidated. [ABSTRACT FROM AUTHOR]

Heat transfer between two plates of polar materials at nanoscale distance is known to be enhanced by several orders of magnitude as compared with its far-field value. In this article, we derive accurate analytical expressions to quantitatively predict heat fluxes in the near-field. These analytical expressions reveal the physical mechanisms responsible for the enhancement. For two dielectric polar materials and for gaps smaller than 75 nm at room temperature the heat transfer is dominated by the surface phonon polariton contribution. Between 75 nm and 500 nm, the enhancement is mostly due to frustrated total internal reflection. The paper reports accurate analytical expressions for both contributions. Our analytical results highlight two differences between radiation flux at the nanoscale and in the far field: i)the heat flux spectrum depends on the gap distance, ii) the temperature dependence of the heat transfer coefficient deviates strongly from the T3 law valid for gray bodies in the far-field. [ABSTRACT FROM AUTHOR]