Heat Transfer Phenomena Research Articles

Theoretical simulation of steady flowing manifold in hybrid pneumatic power system

Improving the energy efficiency of existing power systems is part of energy conservation and carbon reduction efforts. Internal combustion engines (ICEs) are currently the most commonly used power source in transportation, and they can be combined with gas power sources to form hybrid power systems for enhanced energy efficiency and potential commercialization. This study introduces hybrid pneumatic systems that integrate energy from ICEs and exhaust gas through a manifold to reuse waste heat. However, the turbulence caused by compressed air in the manifold can prevent the smooth transfer and mixing of thermal energy, leading to reduced power at the final outlet. We use ANSYS Fluent software to conduct heat flow streamline analysis of the three-dimensional flow field in the manifold structure, with key parameters including throttle valve opening, manifold geometry, pressure, and temperature. Through this analysis, we explore the flow situation and heat transfer phenomenon inside the pipe, observe the flow field changes in the pipe, and adjust the diameter of the compressed air end channel for effective thermal energy. A backflow with velocity magnitude up to 72 m/s in high pressure case can be solved by compressing pipe and temperature increases from 349.9 K to 682.5 K with more efficient heat transfer and gas mixing. Thermal power, enthalpy, and mass flow rate of the hybrid power system are also investigated, enabling the ICE to operate at its optimal point. The waste heat from the ICE can also be recycled and converted into effective mechanical energy through flow work.

Application of the fast 3D simplified simulation method for the large CAP1400 nuclear island evaporator based on the coupled source term method

As for the evaporator of the large CAP1400 nuclear power plant, it has a large volume with numerous tubes along with the complex flow heat transfer phenomenon. The traditional direct simulation method usually takes a lot of time and computing resources to obtain the flow heat transfer data. To solve the problem, a fast simulation method established on the porous medium source term was herein proposed. In this simplified simulation method, the complex evaporator model is replaced with the porous medium model, where the derived heat and momentum source terms are added into the governing equation to control the heat flows. Five kinds of simplified evaporator models with different numbers of pipes were set to be the research objects, the internal flows inside the evaporator were studied with the traditional direct simulation method and the newly proposed simplified simulation method. Via comparative analysis, it can be found that: 1) The newly proposed simplified simulation method accurately captures the distribution characteristics of pressure, temperature, and entropy production in the evaporator, serving as a viable alternative to traditional direct simulation methods. Specifically, the average simulation errors for inlet-outlet pressure difference and temperature difference are both less than 5 % and 7 %, respectively. 2) The newly proposed simplified simulation method can capture the mutual interference effects between the evaporator and the nuclear main pump. When the evaporator is connected in series with the main nuclear pump, the average head of the main pump increases by 0.34 m, while the efficiency decreases by an average of 0.34 %. The average simulation errors of the simplified simulation method are 0.06 m and 0.13 %, respectively. 3) The application of the simplified simulation method leads to a significant 85 % decrease in the average computational cost for evaporator calculations and a notable 36 % decrease for combined calculations of the evaporator and main pump. The study here is expected to provide technique support for the simulation and evaluation of the large nuclear island.

Experimental investigation of effects of convective heat transfer and thermal performance of impinging jet on a metal plate with porous media

This experimental investigation is aimed to evaluate the effects of convective heat transfer phenomena in an aluminium metal flat disc/plate placed below metal foam using a single round jet of air impinging in a confined region. The Jet impingement technique contains pressurized air, which is configured for certain specific application. It is designed to spray the fluid with the help of a nozzle on the surface of the disc or plate which is being heated or is being cooled. To understand the heat transfer phenomena in a metal plate with metal foams facing round air jet impingement; three metal foams of similar geometries but of different porosities and permeabilities are taken for study. Each experiment is performed with seven different flow rates and at two different heights with two different heat flux values. The recorded measurements are temperatures, pressure differences, flow rates, resistance voltages and currents, and time. The outcomes of the experimental data are analysed and compared results of all four distinct kinds of metal foams with different jet to plate height and at different heat fluxes. It is concluded that heat transfer efficiency may or may not increase depending upon the metal foam used. Overall, the conclusions are extremely useful in engineering.

Dynamics of Jeffrey fluid flow and heat transfer: A Prabhakar fractional operator approach

The primary goal of current study is to formulate a novel mathematical model employing the Prabhakar fractional operator, aimed at examining the dynamic behaviour of Jeffrey fluid flow and heat transfer phenomena under ramped wall temperature conditions. Our investigation entails a meticulous investigation of magnetohydrodynamic (MHD) natural convective flow within Jeffrey fluids, where we derive precise analytical solutions utilizing the Prabhakar fractional derivative, characterized by a non-singular type kernel. Furthermore, our study integrates fundamental principles such as Fick’s and Fourier’s laws into the model, leveraging a multi-parameter Mittag-Leffler kernel associated with the fractional operator. We delve into the intricacies of fluid flow near an infinitely vertical plate, considering characteristics such as velocity u0. To address the complexities of the problem, we express it in context the of partial differential equations along side generalized boundary conditions, employing a set of appropriate variables to transform these equations into a dimensionless form. Utilizing Laplace transform, we analyse the equations of fractional system, presenting outcomes both in the form of series and through specialized functions. We systematically explore the influence of key parameters α, Pr, β, Gm, Sc, γ, Gr on fluid flow dynamics, unveiling significant insights. Our comparative analysis reveals the superior performance of the Prabhakar-like non-integer approach over existing operators, substantiated by graphical representations of the results. Additionally, we extend our investigation to various limiting cases, including Newtonian fluids and second-grade, in both fractionalized and classical forms, thus highlighting the versatility and applicability of our proposed model within fluid dynamics research.

Numerical modelling of heat and mass transfer during cake baking

This article deals with the development of a numerical multiphysics model to study heat and mass transfer phenomena as well as the swelling during the baking of a cake contained in mold. The aim of this study is to provide an effective numerical tool, experimentally validated, for a better understanding of mechanisms leading to the desired end product. Based on the governing equations for heat and mass transport and under few assumptions (homogenous medium, local thermodynamic equilibrium, ideal gas mixture…), the problem consists in solving a system of five coupled partial derivative equations. Temperature, moisture content, total gas pressure, porosity and displacement are used as state variables in this study. The swelling of dough caused by the increase of total gas pressure is predicted by a viscoelastic model. This thermo-hydro-mechanical model is implemented in finite elements code. Moreover, an experimental laboratory set-up was developed in order to continually acquire temperatures, water losses, deformation and to correctly apprehend the boundaries conditions. The numerical results are then compared with experimental data. They are overall in good agreement. Various operating conditions are tested to check the robustness of predictions.

Critical Behavior of an Extreme Fire “Fire Junction”

In this paper the concept of extreme forest fire behavior denominated as Junction Fire is analyzed, this phenomenon consists of the interaction between two linear fire fronts which in their propagation intersect at a single point making a small angle between them. In their process of fusion, the phenomena of heat transfer by radiation and convection are extremely amplified due to the concentration of energy at the point of intersection. The concentration of energy and therefore the development of the powerful heat transfer mechanism induces an extremely high and sudden increase in the rate of spread until it reaches a maximum value after which begins to decrease. This behavior of the order parameter exhibits a non-universal phase transition. The analysis carried out in the ADIA-LEIF laboratories show that fires junction are a source of instability which leads to serious safety and management problems for those who are confronted with this type of forest fire. The results show that the fire junction spread exposed two main regimes; an initial acceleration phase characterized by a high rate of spread depends essentially on the initial angle between the fire fronts θ0 , which shifts during the evolution of the fire until the limit of creation of a single front of fire in a straight line explaining a decreasing phase. Nevertheless, the front fire dynamics depends both on the initial angle between the fire fronts θ0 and on the slope ground αJ exhibiting a non-universal phase transition known in the literature. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved.

Thermal stratification and heat generation/absorption impacts on stagnation point flow of MHD UCM fluid through a permeable medium

We investigated two dimensional magnetohydrodynamic (MHD) stagnation point upper-convected Maxwell (UCM) fluid flow through a stretch sheet in a porous medium having the effects of heat generation/absorption and thermal stratification. Utilizing suitable similarity transformations, the governing partial differential equations (PDEs) of the fluid flow and heat transfer phenomena are converted to nonlinear dimensionless ordinary differential equations (ODEs). We numerically solved these nonlinear ODEs and compared our results of skin friction and Nusselt number with previous work which demonstrated accuracy of the presented solutions. We also illustrated the graphical behavior of dependent variables that is of the velocity and temperature fields versus the key parameters involved. It showed that velocity field decreases for Deborah number, porosity and magnetic parameters. The temperature of the fluid showed an increasing behavior for Deborah number, magnetic, porosity, and heat source/sink parameters while declining for thermal stratification and velocity ratio parameters.

Towards a mechanistic understanding of the floating catalyst CVD of CNTs: Interplay between catalyst particle nucleation, growth and deactivation

The chemical vapor deposition (CVD) of carbon nanotubes (CNTs) with the floating catalyst technique, using ferrocene as catalyst, is computationally investigated from its mechanistic perspective. The present work presents a novel model dealing with the phenomena taking place in the bulk of a floating catalyst CVD reactor. The developed model incorporates the gas flow, heat transfer and species transport phenomena, coupled with reaction mechanisms and kinetics, as well as the catalyst particle formation and growth dynamics. The novelty of the approach lies on the inclusion of carbon species deposition on the catalyst particle surface, which have a crucial effect on the particle growth and catalyst deactivation, leading to the termination of CNT growth on the particles. The model predictions are directly compared with experimental results from the literature for the same process and for a range of process parameters, showing a very good agreement. The computational model not only successfully predicts the experimental behavior but also reveals the effect of individual mechanisms on the inhibition of particle growth, catalyst deactivation and CNT growth. In this way, the model provides an in-depth mechanistic understanding of the mechanisms in the reactor bulk, which is currently missing, thus paving the way towards the knowledge-based process design and optimization and the possibility of using more sustainable or environmentally-friendly precursors and catalysts which have not been studied experimentally in detail.

Influence of heat flux profile on two-phase flow instability in parallel channels of helical coil once-through steam generator

To enhance the heat transfer capability, the helical coil once-through steam generator (HCOTSG) has been widely utilized in the small modular reactor (SMR). There are hundreds of parallel helical channels in the HCOTSG, and the coolant undergoes the phase change from subcooled liquid to superheated vapor in the helical tube. The flow oscillation between parallel channels may be triggered during the phase change. In present study, the two-phase flow instability is investigated with different heat flux profiles under many operating conditions. The thermal–hydraulic model for parallel channels of HCOTSG is established based on our previous work, while the local heat transfer phenomenon such as subcooled boiling, critical heat flux, and wall conduction are considered in detail. The heat flux profile along the tube is ascertained by the steady-state analysis of HCOTSG under different operating conditions and applied to the outside surface of the helical channel. The heat flux value is increased step by step to trigger the out-of-phase oscillation between parallel helical channels. The thermal–hydraulic model and analysis method are validated against experimental results. The characteristics of flow instability in the helical channel are also analyzed. It is observed that the delay effect causing the flow instability is more obvious if the void fraction exceeds 0.7 in the starting stage. Then the boundary of flow instability is compared under different heat flux profiles for various operating conditions of HCOTSG. The results suggest that the distribution of heat flux in the two-phase region plays a more significant role in the occurrence of flow instability in the parallel helical channel system. The thermal–hydraulic characteristics during flow instability are governed by the combined effects of void propagation and delayed feedback in the system. In conclusion, the thermal–hydraulic condition of HCOTSG undergoes the unstable region to achieve the normal operating point, which can be avoided by adjusting the operating parameters.

Advances in Numerical Heat Transfer and Fluid Flow

Scientists continuously are looking for new methods that allow them to better understand the flow and heat transfer phenomena [...]

Reconstruction of internal heat source in biological tissue using parallel particle swarm optimization

With the rapid development of engineering thermophysics, researches on human biological heat transfer phenomena has gradually shifted from qualitative to quantitative. The heat distribution information of human lesions is of great value for disease analysis, diagnosis, and treatment. It is a typical inverse problem of heat conduction that deriving the distribution of internal heat sources from the temperature distribution on the body surface. Differing from traditional numerical methods for solving heat conduction, this paper transforms such an inverse problem of bio-heat transfer into a direct one, thereby avoiding complex boundary conditions and regularization processes. To noninvasively reconstruct the internal heat source and its corresponding 3D temperature field in biological tissue, the parallel particle swarm optimization (PPSO) is used in the simulation module, where the position P(x, y, z) of point heat source in biological tissue and its corresponding temperature T are set as the optimization variables. Under a certain optimized sample, one can obtain the simulated temperature distributing on the surface of the module, then subtract the simulated temperature from the measured temperature of the same surface which was measured using a thermal infrared imager. If the absolute value of the difference is smaller, it indicates that the current sample is closer to the true location and temperature of the heat source. When the values of optimization variables are determined, the corresponding 3D temperature field is also confirmed. The simulation results show the simulated position and temperature of the heat source are very approximate with those of the real experimental module. The method presented in this paper has enormous potential and promising prospects in clinical research and application, such as tumor hyperthermia, disease thermal diagnosis technology, etc.

Entropy generation analysis for magnetohydrodynamic flow of chemically reactive fluid due to an accelerated plate

BackgroundThe mixed convection flow of viscous fluid due to an oscillating plate is inspected. The external heating effects and chemical reaction assessment are predicted. Moreover, the flow applications of the entropy generation phenomenon are claimed.ResultsThe dimensionless system is expressed in partial differential forms, which are analytically treated with the Laplace scheme. The physical aspects of the flow model are graphically observed. The optimized phenomenon is focused on flow parameters. The results for the Bejan number are also presented. The dynamic of heat transfer and entropy generation phenomenon is observed with applications of Bejan number.ConclusionsIt is claimed that an enhancement of entropy generation phenomenon is noticed due to heat and mass Grashof coefficients. The Bejan number declined due to mass Grashof number. Furthermore, the velocity profile boosted due to Grashof constant.

EXERGOECONOMIC ANALYSIS OF A HYBRID SYSTEM OF WASTE INCINERATION AND ABSORPTION REFRIGERATION

The current global scenario presents a significant increase in energy demand for HVAC-R (Heating, Ventilation, Air Conditioning and Refrigeration) systems. Considering also that Brazil has the sixth most expensive energy in the world and that there is currently a greater scarcity of natural resources for energy generation, it is necessary to seek viable alternatives with lower energy consumption to the currently most used models, without any quality loss. On the other hand, absorption refrigeration and waste incineration systems can be lines of studies and research to be considered, considering that it is possible to reduce electrical energy consumption and also the environmental impacts that the usual compression refrigeration systems provide. . . In this context, one of the segments of Thermal Systems Engineering studied is the exergoeconomic analysis that comprises the concepts of Heat Transfer, Fluid Mechanics and Thermodynamics, based on the Second Law of Thermodynamics and which uses the notions of optimization and economic analysis. Therefore, this work aims to perform an exergoeconomic analysis of a hybrid system of waste incineration and absorption refrigeration, with the specific objective of developing an exergoeconomic model for the hybrid system. Absorption incinerator-refrigerator. This is an exploratory bibliographic research using an absorption refrigerator from the Center for Research and Development of Self-Sustainable Energy (NPDEAS) of the Federal University of Paraná, in which a model was made with a macroscopic approach of the mass and heat transfer phenomena of a absorption refrigeration cycle, applying the principles of conservation of mass and energy in steady state for each component of the cycle, that is, each component will be considered as a single control volume. It is expected that it will be possible to predict the behavior of the absorption refrigeration system and that it will be possible to develop a scientific analysis tool to design, control and optimize absorption refrigeration systems, using waste incineration. The highest exergy destroyed was verified in the desorber with about 0.9461 kW and through the exergoeconomic analysis of the incinerator, it was found that the cost rate associated with the product of the incineration gases was $ 39,926.31 per year.

Investigation of fluid flow during flow boiling inside a horizontal rectangular channel with single-sided heating using particle image velocimetry

Subcooled flow boiling is a highly efficient cooling systems for thermal management systems. This study explores the intricate dynamics of subcooled flow boiling within a horizontal channel, investigating the impact of vapor generation on liquid-phase velocity using Particle Image Velocimetry (PIV) and advanced image processing techniques. Four mass flow rates ranging from 5–20 g/s with subcooled inlet conditions are investigated in a rectangular channel with single-sided heating. Three regions of interest along the heated channel are investigated for instantaneous PIV analysis. The PIV system captures detailed velocity profiles, illustrating the impact of varying mass flow rates and heat flux levels on flow behavior. Vapor masking techniques are introduced to enhance the precision of PIV data by mitigating interference from the vapor phase. Results demonstrate the influence of vapor bubbles on flow resistance, revealing non-uniform velocity distributions and turbulence near the liquid–vapor interface. The study emphasizes the critical role of inertia and buoyancy forces in shaping the velocity profiles. Moreover, the investigation sheds light on the effects of flow rates on the interfacial behaviors, hinting at a transition point between 10 and 15 g/s. In summary, this research contributes valuable insights into the nuanced dynamics of flow boiling, laying the foundation for future studies on turbulence, heat transfer, and phase-change phenomena in two-phase thermal management systems.

A novel time-dependent analytical model for optimizing efficiency and valve timing in Ericsson engines

In this work, a novel analytical time-sensitive model for Ericsson engines was developed taking into account the heat transfer phenomena between the working gas and the cylinder walls in the compressor and the expander. For the calculation of the mass flow entering/exiting each cylinder, another dedicated flow model was developed to account for the pressure drop at the valves. From the energy equilibrium taking into consideration the time-dependent thermal response of the cylinder walls and the enthalpy entering/exiting each cylinder through the valves, an analytical solution of the working gas pressure and temperature can be obtained for every time step and consequently, the thermal efficiency of the engine can be calculated. A case study was performed where the thermal efficiency of an Ericsson engine was calculated for different rotational speeds and heat exchanger gas temperatures. It was observed that with higher temperatures thermal efficiency maintained a more stable behaviour with a weak dependence on rotational speed. The thermal efficiency of the engine in the performed case studies was found in the range of 10% to 14%. The valve timing of the Ericsson engine was optimized in order to achieve the highest thermal efficiency possible. The thermal efficiency of the engine could be increased up to 26% as a percentage after a thorough optimization of the valve timing. Finally, backflow phenomena accounting for thermal efficiency drop were studied. The developed model can also be applied to other types of external combustion engines such as Stirling engines.

Influence of variable viscosity and slip on heat and mass transfer of immiscible fluids in a vertical channel

This study examines the heat and mass transfer phenomena that take place in a vertical channel containing immiscible fluids, specifically micropolar and viscous fluids. The main objective is to explore the impact of variable viscosity, velocity slip, and other pertinent parameters on various properties, including velocity, angular velocity, temperature, and diffusion. This investigation reveals a significant correlation between these parameters and the observed effects. Also analyzes the transfer rates of heat, mass, and velocity on both boundaries of the channel. This comprehensive examination provides valuable insights into the intricate mechanisms governing these transfer processes. To solve the complex system of coupled equations, the Runge-Kutta sixth-order method, utilizing the ND Solve Mathematica software is used. This numerical technique offers accurate and reliable solutions for simulating the dynamics of heat and mass transfer in this system. As a result, the velocity slip parameter and thermal conductivity increases, the velocity,angular velocity and temperature decreases within the system, reverse effect is observed in diffusion. These findings further enhance our understanding of the complex behavior of the immiscible fluids in the vertical channel are depicted graphically.

Inclined surface mixed convection flow of viscous fluid with porous medium and Soret effects

Abstract The combined heat and mass transfer phenomenon is a significant aspect of engineering and industrial processes. This phenomenon finds applications in various areas such as air conditioning, cooling and heating control of electronic devices, reactors, chemical systems, and emission processes. This research model focuses on the analysis of mixed convection flow of a viscous fluid with heat and mass transfer on an inclined surface with porous medium characteristics. The study also considers external heat transfer effects, radiation, Soret influence, and chemical reactions. A perturbation solution is derived in closed form, and the impact of various parameters on the thermal behavior is investigated. A comparative analysis of the heating and cooling regimes in plate flow is conducted, revealing a reduction in velocity in the heated plate regime with changes in the permeability parameter and an increase in concentration phase due to the Soret number.

Fractional scaling analysis of cladding temperature in large break loss of coolant accident

In integral test facilities, some phenomena relevant in the separate effect test are usually neglected due to scaling limitations and design compromises. The typical heat transfer phenomenon in reactor core in large break loss of coolant accident (LBLOCA) scenario is analyzed with fractional scaling analysis (FSA) method in this work. A conservation form of cladding temperature is derived on the basis of energy conservation. Then the scaling criteria and their importance are evaluated. It is found that the similarities of the criteria for convection heat transfer and heat accumulation should be guaranteed since their priorities are high. The contribution of initial pressure and distribution of coolant inventory to cladding temperature in LBLOCA scenario is too slight. This work is encouraging and may shed a light on the coupling application of hierarchical two-tiered scaling (H2TS) and FSA method in engineering application.

Heat Transfer Performance Tests of a Circular-Fin Sodium-to-Air Heat Exchanger for Sodium-Cooled Fast Reactors

Shell and tube-type crossflow heat exchangers with circular fins are widely used in various industries, including nuclear power plants. This study focuses on the sodium-to-air heat exchanger, which is one of the key safety features in sodium-cooled fast reactors. Tube alignment inside the heat exchanger is important because it directly determines the performance. Although heat exchangers are generally designed to have staggered tube alignment, inevitable inline-aligned zones exist. Therefore, this paper proposes a hybrid tube alignment modeling approach that considers both staggered and inline tube heat transfer phenomena. The results of the hybrid model calculations are verified and validated with liquid sodium experiments. The hybrid approach to the tube arrangement reduced the temperature deviation between experimental and calculated values to a difference of 4.55% and 7.38% for both sodium and air sides, respectively, while for the heat transfer, the difference was 15.12% and 9.06% for sodium and air sides, respectively. The results of this study can also be used as a basis for the safety evaluation of nuclear reactors and licensing processes for sodium-cooled fast reactors. In addition, this study is limited not only to sodium heat exchangers but also to any serpentine tube arrangement or crossflow heat exchanger under high-temperature systems, such as concentrated solar power and thermal energy storage industries.

Self-supervised learning of shedding droplet dynamics during steam condensation

Knowledge of condensate shedding droplet dynamics provides important information for the characterization of two-phase heat and mass transfer phenomena. Detecting and segmenting the droplets during shedding requires considerable time and effort if performed manually. Here, we developed a self-supervised deep learning model for segmenting shedding droplets from a variety of dropwise and filmwise condensing surfaces. The model eliminates the need for image annotation by humans in the training step and, therefore, reduces labor significantly. The trained model achieved an average accuracy greater than 0.9 on a new unseen test dataset. After extracting the shedding droplet size and speed, we developed a data-driven model for shedding droplet dynamics based on condensation heat flux and surface properties such as wettability and tube diameter. Our results demonstrate that condensate droplet departure size is both heat flux and tube size dependent and follows different trends based on the condensation mode. The results of this work provide an annotation-free methodology for falling droplet segmentation as well as a statistical understanding of droplet dynamics during condensation.