Nanoparticle transport phenomena in confined flows.

Second-law analysis (SLA) is an important concept in thermodynamics, which basically assesses energy by its value in terms of its convertibility from one form to another.[...]

Nanoscale heat pipe using surface-diffusion-driven condensate return

Nanofluid is a kind of new engineering medium which is created by dispersing small quantity of nano-sized particles in the base fluid. The dispersion of solid nanoparticles in conventional fluids changes their transport properties remarkably. Molecular dynamics simulation (MDS) is an important approach to study the transport properties of nanofluids. However, the computation amount is huge, and it is very difficult to use the normal MDS to capture the transient flow and heat processes in Cu-H2O nanofluids if the regions in the simulation reach 149.6443 nm3 or 299.2883 nm3, and the number of Cu nano-particles reaches 6-64. Further study by means of simulation on the effects on effective transport properties of nanofluids is also difficult. In this paper, the water-based fluid region of 149.6443 nm3 or 299.2883 nm3 is assumed as continuum phase because of the very low Knudsen number of fluid, and the effects of water on nano-particles are fitted into the Cu-Cu potential parameters. Using the proposed method, the computation amount is significantly reduced. The effective thermal conductivity and dynamic viscosity coefficient of Cu-H2O nanofluids under the stationary condition are simulated and the results are verified with existing experimental data. The motion and aggregation processes of nano-particles in the water-based fluids at different velocity shear rate are simulated. Effects of velocity shear rate, fluid velocity, temperature gradient, and average temperature on the effective thermal conductivity and the dynamic viscosity of Cu-H2O nanofluids in the processes of flow and heat transfer are studied. Three conclusions can be drawn from the obtained results. Firstly, the proposed method is feasible to capture the transient flow and heat processes in Cu-H2O nanofluids, and is also capable to further study the transport properties of Cu-H2O nanofluids. Secondly, the velocity shear rate acting on a nanofluid can effectively prevent the aggregating process of nano-particles, and therefore reduce the diameter of particle-aggregations. Finally, the velocity shear rate and the average temperature of Cu-H2O nanofluids have much more effects on the transport properties, while the fluid velocity and temperature gradient have less effects; the velocity shear rate increases the effective thermal conductivity of a nanofluid but decreases its dynamic viscosity. A rise of average temperature increases the effective thermal conductivity but decreases the dynamic viscosity.

The present paper is focused on numerical investigations of the heat transfer and flow field development around a low pressure turbine blade (T106) with the use of computational fluid dynamics (CFD) tools and methods. The CFD computations were performed with OpenFoam open source CFD software with the use of the Shear Stress Transport (SST) low-Reynolds number turbulence model. At the first part of the present work, the CFD computations were validated in relation to available detailed isothermal experimental measurements and useful conclusions about the accuracy of the modelling approach and the flow field development were derived. At the next stage, additional CFD computations were performed for flow and thermal conditions adapted in order to reflect more closely the low-pressure turbine blade operation. In these CFD computations the interaction between the velocity and thermal boundary layers and their effect on the heat transfer was quantified through the derivation of the distribution of the local Nusselt number on the T106 surface, which was compared in relation to available correlations from open literature. Through the analysis of the CFD results it was possible to identify the regions on the low-pressure turbine surface in which decreased heat transfer performance was presented as a result of the non-optimum flow and thermal field development. Furthermore, through the CFD computations secondary flow effects resulting in operational efficiency decrease were identified. The elimination of these sources of operational decrease is planned to be the main target of future research efforts targeting the development of methodologies for the design of highly efficient turbomachinery components.

This review brings out those aspects of the development of proton exchange membrane (PEM) fuel cells over the last two to three decades that are of interest to the heat and mass transfer community. Because the heat transport and mass transport in proton exchange membrane fuel cells are very important from the efficiency point of view, an emphasis is given here to these transports and their influence on operating cell parameters. The works are classified as models with either isothermal or non-isothermal conditions of various assumed dimensionality and with either single-phase or two-phase flow. Along with modeling, a few experimental studies available are also reported here. Researchers in the area of PEM fuel cells are involved in activities such as development of new and low-cost materials, modeling the relevant physical processes, and electrochemical experimentation. These collective efforts may lead to making this technology viable to meet world needs for clean and cheap energy. This review brings out the fact that computational fluid dynamics (CFD) has become an inevitable tool in fuel cell analysis, as the detailed interactions between the flow structure geometry, fluid dynamics, multiphase flow, heat transfer, mass transfer, and electrochemical reaction can be modeled simultaneously, given the present state of the art in CFD. Through the predictive capability of CFD, it will be possible for fuel cell designers to better optimize the design and operating parameters of fuel cells before testing them in laboratory.

It is our great pleasure to present the Proceedings of the 41st UIT International Heat Transfer Conference, held from 19 to 21 June 2024 at the Congress Centre of the Università degli Studi di Napoli Federico II, organized by the Dipartimento di Ingegneria Industriale. This year, the conference held special significance as it took place within the events celebrating the eight hundredth anniversary of the foundation of the Università degli Studi di Napoli Federico II, a milestone underscoring the university’s long-standing tradition of excellence in education and research. The conference was attended by approximately 180 participants, including 85 members of the UIT community, 40 non-members, and 55 students. The sessions were dedicated to key topics such as Computational Fluid Dynamics, Conduction Radiation and Thermophysical Properties, Heat and Mass Transfer in Energy Systems and Nuclear Plants, Natural, Forced, and Mixed Convection, Micro and Nano-Scale Heat Transfer, and Multiphase Heat Transfer. The program featured three keynote lectures, during which distinguished speakers shared their insights on pressing issues and emerging challenges in the field. Additionally, the Program Manager of the European Innovation Council presented valuable opportunities for transferring research into innovation, bridging the gap between academia and industry. List of Conference Chairs, Scientific Committee, Organizing Committee, Sponsors and Editors contact details are available in this Pdf.

Nanofluids are heterogeneous suspensions of nanoparticles in common fluids (base fluids) and have been the subject of investigation for numerous research projects since 1995. A great deal of experimental data indicates that the addition of very small quantities of nanoparticles to base fluids has the following effects on the heat transfer characteristics of the mixture: (1) Increases significantly the effective thermal conductivity of the suspensions; (2) Increases by a higher amount the convective heat and mass transfer coefficients; (3) In general, decreases the pool boiling and convective boiling coefficients; and (4) Significantly enhances the critical heat flux. Several early experiments showed convective heat transfer coefficient enhancements higher than 100%, but more recent experimental studies show enhancements closer to 50%. Typical critical heat flux enhancements are more than 100%. Such experimental observations indicate that, appropriately designed engineering systems operating with suitable nanofluids will have heat and mass transfer characteristics that are far superior to the heat transfer media that are currently used.

All operations in process metallurgy involve complex phenomena comprising momentum, heat, and/or mass transport; iron- and steelmaking is not an exception. Transport phenomena, i.e. fluid flows, heat transfer and mass transfer, play a dominant role in process metallurgy since their respective laws govern the kinetics of the various physical phenomena occurring in ironmaking and in steelmaking. These phenomena include such events as three-phase reactions, entrainment of slag and gas in liquid steel, vacuum degassing, alloy melting and mixing, the movements and flotation of inclusions, melt temperature losses, residence times in a metallurgical reactor, erosion of refractory linings, etc. In all these aspects, the evolution in our techniques and abilities to model single and multiphase flows and their attendant heat and mass transfer processes has contributed significantly to our understanding and effectively operating these processes, to designing improvements, and to developing new processes. To be ignorant of these matters can doom a processing operation to the scrap heap of metallurgical failures. Computational fluid dynamics (CFD) and computational heat and mass transfer has been a very effective tool over the last three decades, for modelling iron- and steelmaking processes, starting from the blast furnace up to continuous casting and beyond. With the advent of commercial CFD packages and ever increasing computational power through parallel processing, CFD has now become the dominant approach for predicting various aspects in iron- and steelmaking processes. In Part 1 of this review paper, the applications of CFD in ironmaking processes are thoroughly reviewed, discussed and critiqued. In Part 2, fluid flows and CFD in steelmaking and steel casting processes are similarly reviewed and critiqued.

The petroleum and petrochemical industries continually seek mechanical methods to improve heat transfer in shell-and-tube heat exchangers. Tube bundle inserts are popular mechanical devices that help improve performance. The increase in the tubeside heat transfer coefficient by the insert allows for a decrease in required shellside flow length, assuming single tube pass. The flow length reduction allows for designing higher velocities and subsequent shellside shear rates, to help reduce crude oil fouling potential. This work presents some of HTRI’s ongoing experimental measurements and preliminary Computational Fluid Dynamics (CFD) simulations. CFD visualization of swirl flow dynamics and heat transfer inside the augmented tube provides insight on complex flow physics, which is misunderstood. Heat Transfer Research, Inc. (HTRI) collected experimental data for in-tube single-phase flow using twisted tape inserts in the Tubeside Single-Phase Unit (TSPU) situated in the Research and Technology Center (RTC). Our data will be used to calibrate ANSYS FLUENT CFD simulations of a tube with a twisted tape swirl insert. We first performed plain tube simulations and compared the heat transfer results with open literature measurements, for validation. We will modify the CFD tube model to have a swirl flow insert, and compare numerical results against open literature experimental data of diabatic single-phase swirl flow. In future, we will compute heat transfer (heating and cooling) and pressure drop for tube insert configurations at laminar and turbulent Reynolds numbers from 3000 to 500000. The range of tubeside Reynolds numbers required the use of the laminar, transition, and Realizable k-epsilon turbulence models with scalable wall functions. This study describes some of the mechanisms behind turbulent swirl flow augmentation inside a tube, as well as the limitations of conventional in-tube heat transfer correlations applied to swirl flow inserts.

A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one dimensional, viscous, and heat-conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. In successfully predicting the time-dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, biofluidics / bioengineering, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one dimensional and/or radial spherical coordinates with or without including energy generation / addition terms. No other solution exists for such applications.

A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one dimensional, viscous, and heat conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for tansport properties. In successfully predicting the time dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, biofluidics / bioengineering, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one dimensional and/or radial spherical coordinates with or without including energy generation / addition terms.

A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one dimensional, viscous, and heat conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. In successfully predicting the time dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one dimensional and/or radial spherical coordinates with or without including energy generation / addition terms. No other solution exists for such applications.

A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one-dimensional, viscous, and heat-conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. In successfully predicting the time-dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, biofluidics/bio-engineering, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one-dimensional and/or radial spherical coordinates with or without including energy generation/addition terms. No other solution exists for such applications.

A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one dimensional, viscous, and heat-conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. In successfully predicting the time-dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, biofluidics / bioengineering, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one dimensional and/or radial spherical coordinates with or without including energy generation / addition terms. No other solution exists for such applications.

This paper investigates the effects of turbulence flow, the heat, and phases transfer on thermal arrest time in the casting process. In this study, a computational fluid dynamic (CFD) package, Fluent, is used to investigate the phenomena of pure Pb going through the two-dimensional rectangular cavity. The simulation will describe the casting process by using volume of fluid (VOF) model integration with the solidification model in Fluent.The results of the simulation shown that the heat transfer is stable soon, the time of thermal arrest is short; the heat transfer is very low, it will produce imperfections in products; and a highly increasing in the heat alternation increases the solidification time. The result also found that the turbulence flow will reduce when the heat transfer is steady; the turbulence flow occurs strongly, the thermal arrest time will take a more long time. Moreover, the effects of the phases transfer on the thermal arrest time are almost seldom. Finally, both Vinlet = 0.15m/s and Tc= 500K are the most significant parameters for reducing the time of thermal arrest and turbulence flow.