Heat Transfer Considerations Research Articles

Two-phase magnetohydrodynamic blood flow through curved porous artery

Blood arteries are important part of our cardiovascular system. A comprehensive study of shape and anatomy of blood arteries allows to elucidate the dynamics of blood flow in these arteries. Typically, the arteries are a curved-tube like structure, with arterial walls exhibiting a composition of various porous layers. The current study embarks on a theoretical exploration of a two-fluid model of blood flow and heat transfer through the curved artery under an influence of a magnetic field. The artery walls are composed of Brinkman and Darcy layers. The blood flows through a curved artery exerts centrifugal forces on the arterial walls that leads to change the blood flow patterns. The significant effects of curvature along with the intensity of an applied magnetic field on the blood flow patterns, heat transfer, and resistance impedance in curved artery have been investigated in the present work. The mathematical model of the proposed work is tackled by the homotopy analysis method using physically relevant boundary and interface conditions. The significant outcome of the present work is that the heat transfer rate increases with the increase in the curvature parameter, and it reduces on raising the couple stress parameter and Hartmann number. The novelty of this work lies in the consideration blood flow and heat transfer in inner endothelial layers of curved porous artery. The result presented in this work is vital to assess the condition of atherosclerosis, aneurysms, vasculties, blood clot, etc.; beyond this, the present model can be extended for medical diagnostics, treatment planning, medical device design, drug delivery optimization, and biomedical engineering research. This study can ultimately contribute for improved patient care and outcomes in cardiovascular medicine.

Numerical study of the particle-scale heat transfer in the HTR-PM pebble bed based on GPU-DEM

An essential aspect of the design of a pebble bed high-temperature gas-cooled reactor (HTGR) is the consideration of heat transfer. A particle-scale heat transfer model was developed based on the previous GPU-DEM numerical model. This model includes the heat conduction of the particles in contact, the radiative heat transfer among particles, and unidirectional convection heat transfer in the flow field. The comparison of the predicted results with the results of the TF-PBEC experiment demonstrates the accuracy of the conduction and radiation modules within the current model. Based on the current model and the porous media model, a numerical study of the natural convection heat transfer in the High-Temperature gas-cooled Reactor-Pebble-bed Module (HTR-PM) after reactor shutdown is performed. This paper systematically introduces the model design, pebble bed generation, flow field calculation, and heat transfer simulation. The results indicate that natural convection contributes to removing residual heat in the reactor core, and a higher pressure leads to better convection heat transfer. At extremely low Reynolds numbers (Re < 10), convection heat transfer is comparable to conduction and radiation, while for pressurized pebble beds (Re = 50–500), convection heat transfer dominates. Furthermore, the influence of different models used to calculate the Nusselt number of the results is compared and analyzed. For most cases, the differences in the temperature distribution of the pebble bed obtained from the different correlations are minor. However, the impact of porosity on the local Nusselt number cannot be ignored in the extremely low Reynolds numbers flows. Overall, the particle-scale heat transfer model can provide more effective reference information for the design and construction of an HTGR.

Thermal design of a non-isothermal microfluidic channel for measuring thermophoresis

Thermophoresis describes mass transport in a non-isothermal temperature field and thus provides a fundamental understanding of the behavior of colloidal particles. Various methods have been proposed for measuring the Soret coefficient, a representative value of thermophoresis. In particular, microscopic channels are an emerging method as they shorten the equilibrium time and allow direct observation of the particles. However, little emphasis has been placed on the simultaneous consideration of fluid dynamics, heat transfer, and mass transfer characteristics within the microfluidic channel, despite the simultaneous presence of natural convection and thermodiffusion phenomena. In this study, we present a novel approach to address this gap by introducing a figure of merit, which incorporates essential parameters to accurately characterize a specific cell configuration. This figure of merit allows for the identification of a reliable measurement range in a microfluidic channel with a temperature gradient, while accounting for fluid dynamics, heat transfer, and mass transfer characteristics. The proposed approach is validated through rigorous simulations and experiments, enabling an evaluation of the impact of figure of merit-derived parameters on the measurement channel. The findings from our study demonstrate that the figure of merit serves as a representative measure for stable thermophoretic measurements in a microfluidic channel. Moreover, we propose a threshold value that signifies the transition from a diffusion-dominant to a convection-dominant field.

Morphological changes and color development during cookie baking-Kinetic, heat, and mass transfer considerations.

Color and shape are important quality attributes in baked goods, particularly cookies. Composition and processing conditions determine and influence color development and morphological changes in these baked goods. The objective of this study was to systematically evaluate the evolution of color and shape during baking to determine useful correlations that can be implemented during the assessment and modeling of the baking process. Cookies (AACC-I standard protocol 10-53.01) were baked at 185, 205, and 225°C. Moisture content, water activity, surface temperature, characteristic dimensions (radius and thickness), and color indexes (lightness, redness, blueness, and browning index [BI]) were monitored at different locations on the cookie surface and baking times. Relationships among the tested conditions were explored using correlation analysis. The cookies' dimensions and color indexes were strongly correlated with changes in moisture content over time, and those relationships were characterized using empirical models. The temperature dependence of the kinetic parameters of the changes in lightness and BI was also described and deemed independent of the location on the cookie surface. This study provides insights into the influence of heat and mass transfer on the physical and physicochemical changes of cookies during baking. The kinetic and secondary models developed in this study can serve as important components for establishing a comprehensive approach for coupling heat transfer, mass transfer, and reaction kinetics to estimate and optimize cookie-baking processes. PRACTICAL APPLICATION: The findings from this study provide valuable information for better understanding the morphological changes and color developments during the cookie-baking process. The quantitative data and models generated in this study will allow identifying baking conditions for better quality development.

Large-scale PANDA facility – radiation experiments and CFD calculations

Abstract CFD modelling of the thermo-hydraulic phenomena in the containment during the various phases of a severe accident necessarily requires consideration of radiative heat transfer – in the presence of steam. These radiative phenomena include (i) energy transfer within the gas mixture and (ii) between the gas and surrounding structures. Preliminary calculations carried out for these types of experiments within the OECD/NEA HYMERES-2 project with the CFD code containmentFOAM using a Monte Carlo solver for thermal radiation, demonstrated that the radiative heat transfer is significant even for very small amounts of vapour in the range of ≈0.1 % to ≈2 %. For this reason, the test matrix was tailored to the two opposite extremes: either gas compositions with a low vapour/steam content, where radiative heat transfer can be neglected, or gas mixtures with higher vapour contents, so that radiative heat transfer plays a dominant role. For the selected experiments of the H2P2 series and the corresponding CFD calculations, a vessel with a diameter of 4 m and a height of 8 m was preconditioned with different air-vapour mixtures (a) at room temperature and (b) elevated temperatures. A stable helium layer was then built-up in the upper part of the vessel. The gas was then compressed by injecting helium from above which resembles with best efforts a compression with a piston in a cylinder. This results in a height-dependent and transient increase of the gas temperature. These experiments and the associated CFD calculations were developed to isolate the phenomena of thermal radiation as good as possible from convective and diffusive effects – within the always present experimental limitations. For the reference experiment with ‘dry conditions’ corresponding to the lowest experimentally possible humidity of ≈0.1 %, we show that the use of a model without radiation provides the best agreement between the experimental and numerical results. For the much higher steam content of ≈60 %, the statistical narrow band correlated-k model (SNBCK), non-gray gas model, is the best candidate for future calculations – with computationally forgivable additional effort. We also provide with the Filtered Rayleigh Scattering technique (FRS) an outlook for a possible future instrumentation approach to better meet the requirements of the CFD community.

6-Stroke water injection engine literature review with an introduction of heat transfer and thermodynamic analysis

AbstractInternal combustion engines have played a crucial role in the advancement of society. Consequently, there has been a persistent need to enhance their efficiency and performance. The water-injected six-stroke engine is based on conventional four-stroke engines, producing additional power by injecting water into the hot combustion products during the expansion stroke, thereby increasing the overall engine efficiency. However, a comprehensive review that consolidates existing knowledge and identifies future research opportunities in six-stroke engine technology is lacking. This study addresses this gap by thoroughly examining the thermodynamic operation of six-stroke engines and analyzing the impact of water injection on engine performance. The review covers literature from 1994 to 2023, categorizing studies based on the modeling approach, working fluid, thermodynamic cycle, and consideration of heat transfer. Among the 18 analyzed articles, predominantly published from 2015 to 2019, half utilize analytical models, while the rest employ experimental models addressing heat transfer losses. Notably, water injection exhibits a substantial influence, manifesting as a 5.18% increase in brake power and a 1.55% enhancement in thermal efficiency, particularly with acetylene as the working fluid. Finally, a literature overview of water injection in hot gas environments within the engine cylinder was conducted in addition to a preliminary thermodynamic analysis of the Otto and Diesel cycles to compare different configurations outlined in the literature. The lack of studies, experimental setups, and non-idealized models that consider factors such as heat transfer or water evaporation during injection is evident. By critically synthesizing the available literature, this study offers valuable insights into the potential advantages, limitations, and prospects of six-stroke engine studies.

Effect of aspect ratio on mechanical anisotropy of lattice structures

Triply periodic minimal surface (TPMS) lattice structures with controllable mechanical properties and porous architecture are promising candidates for lightweight and energy-absorbing applications. In parametric structural design, the research on structural geometric characteristics, such as aspect ratio (R) and surface curvature, has mainly focused on fluid and heat transfer considerations. However, their impact on multi-directional mechanical properties has yet to be thoroughly investigated. This study, combining representative volume elements (RVE) based on periodic boundary conditions and theoretical surface morphological characteristics, investigates the mechanical properties and deformation behavior of lattice structures with different aspect ratios in multiple directions. The results indicate that the aspect ratio highly influences the deformation behavior of the lattice structure in different directions. The local curvature and force state of the lattice structure can be adjusted by aspect ratio to reduce local stresses and deformations in different loading directions. Compared with the simulation results of representative volume elements, the structural stress concentration and failure position can be predicted by the Gaussian curvature distribution. In addition, the elastic modulus of the structures in the [100] and [001] directions can also be adjusted by aspect ratio. Through experimental verification in the [001] direction, the structure with an aspect ratio of 2 can greatly enhance the elastic modulus (121%∼440%), maximum stress (10%∼183%), and energy absorption (33%∼85%). The significance of this work is to improve the understanding of the influence of geometric features on the mechanical properties and deformation behavior of lattice structures, which provides a new design approach for triply periodic minimal surface lattice structures in applications of impact protection and bone scaffold.

Three-dimensional analysis of thermoelastic damping in couple stress-based rectangular plates with nonlocal dual-phase-lag heat conduction

Since thermoelastic damping (TED) plays a decisive role in the functioning of micro/nanoresonators, accurate assessment of its magnitude in these tiny systems is imperative. Successfully simulating the thermomechanical behavior of various mechanical elements requires consideration of heat transfer in all three principal directions. Furthermore, there is no denying the impact of size on the mechanical and thermal domains. In light of these reasons, the current study strives to create a three-dimensional (3D) size-dependent TED model for rectangular micro/nanoplates via the use of the modified couple stress theory (MCST) and nonlocal dual-phase-lag (NDPL) heat transfer model concurrently for the first time. To accomplish this, by applying the Galerkin method to the 3D NDPL-based heat equation, the relation of temperature field is derived. Moreover, the coupled thermoelastic constitutive relations are extracted by including the couple stress effect. Lastly, by exploiting the obtained relations in the energy dissipation approach, an analytical TED formula in the form of infinite trigonometric series is attained. To appraise the rightness of derived formulation, the method of model reduction is applied. Moreover, an elaborate convergence analysis is implemented to realize the number of sufficient terms of the provided solution that result in well-grounded outcomes. A rigorous simulation study is also accomplished on the role of 3D heat conduction, scale parameters of MCST and NDPL model, boundary constraints, geometry and material in the variations of TED. Findings imply the definite impact of heat conduction dimension on TED value in rectangular plates with a large ratio of thickness to length and width.

A Consideration of Heat Transfer between the Head and the Media in HAMR

A Consideration of Heat Transfer between the Head and the Media in HAMR

Thermomechanical modeling of the shearing process during fine blanking of quenched and tempered steel

In order to develop an alloy design for fine blanking of deformation mechanism-based sheet metal materials such as high manganese steel, knowledge of the temperature during the shearing process is required. Thermomechanical modeling of shear zone temperature requires consideration of contact heat transfer, which depends on stress state as well as temperature. This paper deals with a methodology for calibrating the contact heat transfer coefficient during fine blanking using indirect temperature measurements. For this purpose, a thermomechanically coupled finite element (FE) model was designed considering thermoviscoplasticity, temperature-dependent physical and thermophysical parameters as well as a steady-state calibrated contact heat transfer coefficient. Experimental fine blanking tests were carried out to validate the model using force, die roll and thermography measurements based on varied blanking velocities. The thermomechanically coupled FE modeling showed a sufficiently accurate correspondence regarding the experimentally determined blanking force, die roll as well as sheared surface temperature. Thermographically determined sheared surface temperatures allowed calibration of locally different contact heat transfer coefficients as a simplified approach under steady-state conditions.

Review on nanofluid preparation, stability analysis, and heat enhancement by nanofluids in pipe with passive elements

Heat enhancement applications such as heat exchangers, heating, ventilation, and air-conditioning systems, nuclear and chemical plants, etc., help to increase the thermal rating and performance of the system in addition to decreasing the cost, and size of the system. The heat exchanger design is very complex compared to other designing procedures, which requires proper heat transfer value and consideration of pressure drop, performance of the system, reliability, and durability of the system. The major drawback of the conventional fluid is its low thermal conductivity, which creates a negative impact on heat transfer, the nanofluids need to overcome this limitation. This paper reviews the preparation of nanofluid, stability analysis of nanoparticles, typical nanoparticles, and base fluids in heat transfer augmentation. Passive element heat enhancement techniques like twisted tapes showed positive results in laminar flow compared to turbulent flow, and ribs on the geometry, conical nozzles, and rings are better for turbulent flows than laminar flows. This article highlighted the main gaps and challenges for future research.

Water/ice mixture- and freezing-front motion in a non-isothermal liquid bridge

We experimentally investigate the water/ice mixture- and freezing-front behavior in a water liquid bridge under isothermal and non-isothermal conditions. We find rapid propagation, temporary suspension, and regression of the water/ice mixture front, and finally, it merges with the freezing front when part of the liquid bridge is higher than the freezing temperature. However, freezing-front propagation follows dendritic ice formation, and a protrusion forms at the middle of the liquid bridge as long as the whole liquid bridge is lower than the freezing temperature. We explain those phenomena by quasi-stationary heat-transfer considerations.

Numerical modelling for design of microchannel reactors: Application to hydrogen production from methanol by steam reforming

Microchannel reactors involve chemical-reaction engineering problems in their design and operation, with heat and mass transfer considerations dominating their practicability and efficiency. Study of the fundamental transport phenomena necessitates their description in sophisticated mathematical form. The present study seeks to address this particular problem by investigating the effects of various factors on the transport processes in a heterogeneously catalysed microchannel steam reforming reactor. Numerical modelling for reactor design was performed using a model that accounted for complex catalyst dynamics. Dimensionless number analyses were conducted to understand the nature of the transport processes. The reactor performance was evaluated by means of various parameters, and design recommendations were made. Different operating limit lines were mapped out, and various definitions of energy efficiency were distinguished. The results indicated that the use of microchannel technology enables the achievement of unusually favourable conversion. While mass-transfer limitations are dominant, the reaction is practically feasible at millisecond contact times. A maximum output power in excess of 70 watts per channel can be reached, and energy efficiencies up to about 70 percent are available. The operating limit line can be changed as desirable to maintain the desired product yield throughout the range of conditions. While an optimum velocity for maximum efficiency exists, the flow rate and catalyst loading must be carefully adjusted to simultaneously control the conversion and maximum power within certain needed limits.

Explicit–implicit schemes for non-isothermal filtration problem: Single-temperature model

In this paper, we consider a non-isothermal filtration model for a two-phase immiscible incompressible fluid, for the numerical implementation of which an explicit–implicit algorithm is proposed. The problem is presented in a mixed generalized formulation, and an explicit–implicit method of the IMPES type is used to calculate the pressure, full velocity and water saturation, and an explicit–implicit scheme is built to calculate the temperature and heat flux with explicit consideration of convective heat transfer. At the beginning of the article, the mechanism of temperature homogenization of according to temperature heterogeneous system is considered. In computational experiments, special attention is paid to the comparison of the non-isothermal model with the isothermal one, including the discussion of fingering instability.

Exploring Propagating Soliton Solutions for the Fractional Kudryashov–Sinelshchikov Equation in a Mixture of Liquid–Gas Bubbles under the Consideration of Heat Transfer and Viscosity

In this research work, we investigate the complex structure of soliton in the Fractional Kudryashov–Sinelshchikov Equation (FKSE) using conformable fractional derivatives. Our study involves the development of soliton solutions using the modified Extended Direct Algebraic Method (mEDAM). This approach involves a key variable transformation, which successfully transforms the model into a Nonlinear Ordinary Differential Equation (NODE). Following that, by using a series form solution, the NODE is turned into a system of algebraic equations, allowing us to construct soliton solutions methodically. The FKSE is the governing equation, allowing for heat transmission and viscosity effects while capturing the behaviour of pressure waves in liquid–gas bubble mixtures. The solutions we discover include generalised trigonometric, hyperbolic, and rational functions with kinks, singular kinks, multi-kinks, lumps, shocks, and periodic waves. We depict two-dimensional, three-dimensional, and contour graphs to aid comprehension. These newly created soliton solutions have far-reaching ramifications not just in mathematical physics, but also in a wide range of subjects such as optical fibre research, plasma physics, and a variety of applied sciences.

Theoretical and experimental validation of critical thermal properties of advanced vacuum bagging for composite manufacturing

The vacuum bagging is a common but critical step of various manufacturing process chains for Carbon/Glass Fibre reinforced polymers (C/GFRP). Whilst developing a new generation of vacuum bagging, significant efforts have been made to deeply understand the relevant physics fields, process variables involved and to provide predictive approaches to support dimensioning and scaling exercises prior to implementation into real production process. Main features of the new bagging system are, (1) the reduction of material diversity through merging of various properties within one single layer and, (2) the suppression of critical folding steps by using thermoforming for pre-shaping purposes. This paper will mainly focus on considerations of heat transfer during the pre-shaping of the film, directly on the CFRP part short before the curing step. For the better risk assessment of the short time exposition of an uncured composite part to the heat flow, a problem of transient coupled field analysis involving heat transfer via conduction, convection and radiation is formulated and solved by using Finite Element Analysis in COMSOL under consideration of realistic process conditions. Further a section dedicated to the comparison of the obtained results with measurements performed on a system including an IR-emitter, the bagging material, a ground plate and in some studies as well a CFRP sample is included. During the study the influence of time, power output of the emitter, distance between emitter and surface as well as irradiation angle has been assessed including a comparison of simulated results and performed measurements.

A comparative analysis of integrating thermochemical oxygen pumping in water-splitting redox cycles for hydrogen production

Solar thermochemical hydrogen (STCH) is a promising route for renewable fuel production, but efficiency and cost concerns must be addressed before it can contribute meaningfully to decarbonization efforts. The oxygen removal (reduction) step of two-step STCH redox cycles needs high temperature (1300–1500 °C) and low oxygen partial pressure (10-5-10-3 bar). This consumes significant energy by way of redox reheating, re-radiation losses and pumping work. Thermochemical oxygen pumping (TcOP) has been shown to be more efficient than mechanical pumps in the medium vacuum range, enabling higher heat-to-fuel efficiency and potentially lower reduction temperatures. We have previously proposed a novel Reactor Train System for STCH and reported significant efficiency and productivity improvements by replacing mechanical pumps with TcOP. The current work is a comparative analysis of different implementations of TcOP and its hybridization with conventional oxygen removal schemes like mechanical vacuum pumps and inert gas sweep. The integration of these hybrid TcOP systems with different STCH reactor systems using redox monoliths or particles is analyzed in terms of energy use along with mass and heat transfer considerations. Our results show that direct oxygen transfer between STCH and TcOP reactors results in the best performance for reduction oxygen partial pressures below 10 Pa. Furthermore, we show that achieving reduction pressures of 1 Pa and lower is challenging with existing reactor systems due to a combination of low gas density and relatively high molar flowrates. This challenge also applies to other oxygen removal systems like vacuum pumps and inert sweep.

Importance, influence and limits of CFD radiation modeling for containment atmosphere simulations

In the appearance of steam, the CFD modeling of thermal-hydraulic phenomena in reactor containments during various phases of an accident necessarily requires consideration of radiative heat transfer. These radiation phenomena involve (i) energy transfer within the gas mixture and (ii) between the gas and the surrounding structures which have a much higher thermal inertia. Preliminary calculations performed for the present experiments in the OECD/NEA HYMERES-2 project with the CFD code containmentFoam using a Monte Carlo thermal radiation solver with non-gray gas modeling of steam absorption, showed that radiant heat transfer is important even with a very low amount of steam (≈ 2%). Therefore, the test matrix was tailored to the two opposite extremes: Either gas compositions with low steam content, where radiative heat transfer can be neglected, or gas mixtures containing larger amounts of steam, so that radiative heat transfer plays a dominant role. For the two selected experiments within the H2P2 series and the corresponding CFD calculations, a vessel with a diameter of 4 m and a height of 8 m was preconditioned with different mixtures of air/steam at room and elevated temperatures. This was followed by the build-up of a stable helium stratification in the upper part of the vessel. Helium was then injected from the top at a higher mass flow rate, which (a) compresses the gas atmosphere, (b) resembles piston compression and (c) leads to a height-dependent and transient increase in gas temperature below this helium stratification, influenced by thermal radiation effects — or their absence. These experiments and the associated CFD calculations were developed to isolate the thermal radiation phenomena as much as possible from convective and diffusive effects. They are the first of their kind to be conducted in a large-scale thermal-hydraulic facility. It is demonstrated (a) that neglecting thermal radiation for the high steam content case, the temperature rise is significantly over-predicted by a factor of two compared to the application of the suggested Monte Carlo thermal radiation solver with non-gray gas modeling, (b) the computational effort considering CFD and non-gray gas radiation is feasible with the suggested tailored Monte Carlo solver and (c) that the suggested radiation model outperforms the widespread used P1 radiation model.

Assessing the performance of the non-hydrostatic RegCM4 with the improved urban parameterization over southeastern China

This study evaluates the performance of the non-hydrostatic RegCM4 model (RegCM4-NH) incorporating the building energy model (BEM) in simulating urban climate over the Pearl River Delta (PRD) and Yangtze River Delta (YRD) regions. Specifically, it focuses on examining how the inclusion of BEM can ameliorate the severe warm bias in urban grids observed in high-resolution RegCM4 simulations by improving the surface energy balance. The prognostic calculation of interior building temperature and the consideration of ventilation and heat transfer between the building and the environment can collectively lead to a better estimate of anthropogenic heat flux (AHF). The effect of BEM does not appear to be uniform, showing spatial and temporal variations. While the magnitude of AHF reduction is roughly proportional to the urban density, the maximum reduction occurs at nighttime, which results in an asymmetric response to the minimum and maximum temperatures. Although the degree of lowering temperature is not sufficient to remove the systematic warm bias, adding physical realism to the model is helpful to make further improvements. The performance evaluation of RegCM4-NH with BEM targeted in vast urban agglomerations for the first time will be a valuable reference to facilitate the wider use of RegCM4-NH in the study of urban surface impacts.

Heat Transfer Model of Curtain Wall Facade Systems under Insolation

This paper deals with the problem of creating the basis of microclimate regulations and increasing the energy efficiency of various types of curtain walls in relation to the building thermal air envelope. The aim of the study is to distribute the heat flux flowing through the experimental envelope and determine the minimum temperature on the inner surface of the facade to develop a heat transfer model and increase the energy efficiency of curtain walls. The research methods are known scientific and technical results analytical generalization, the processes under study physical and mathematical modelling, the provisions theory of probability and mathematical statistics implementation, and fullscale experimental research. A computational model of heat transfer through curtain walls of various types is developed in relation to multiple reflections (absorption) of their surfaces in hot climatic conditions when the heat flux of beam and diffuse solar radiation passes through. Optimization of curtain wall with modern shading systems is considered. Comparison of the characteristics of similar experimental setup with traditional translucent curtain walls confirms the simulation. The proposed curtain wall with shading systems significantly improves the energy performance in the warm season compared to traditional curtain walls. A methodology based on modern computational methods that allow more accurate consideration of heat transfer through curtain walls in relation to the insolation of thermal building air envelope was developed. The methodology improves the quality of building design and microclimate and energy savings for indoor air conditioning.