Heat Transfer and Thermal Energy Storage Enhancement by Foams and Nanoparticles

The use of innovative methods for the design of heating, cooling, and heat storage devices has been mainly oriented in the last decade toward the use of nanofluids, metal foams coupled with working fluids, or phase change materials (PCMs). A network of nine Italian universities achieved significant results and innovative ideas on these topics by developing a collaborative project in the last four years, where different approaches and investigation techniques were synergically employed. They evaluated the quantitative extent of the enhancement in the heat transfer and thermal performance of a heat exchanger or thermal energy storage system with the combined use of nanofluids, metal foams, and PCMs. The different facets of this broad research program are surveyed in this article. Special focus is given to the comparison between the mesoscopic to macroscopic modeling of heat transfer in metal foams and nanofluids, as well as to the experimental data collected and processed in the development of the research

Deterrence in Cyberspace: An Interdisciplinary Review of the Empirical Literature

The popularity of the deterrence perspective across multiple scientific disciplines has sparked a lively debate regarding its relevance in influencing both offenders and targets in cyberspace. Unfortunately, due to the invisible borders between academic disciplines, most of the published literature on deterrence in cyberspace is confined within unique scientific disciplines. This chapter therefore provides an interdisciplinary review of the issue of deterrence in cyberspace. It begins with a short overview of the deterrence perspective, presenting the ongoing debates concerning the relevance of deterrence pillars in influencing cybercriminals’ and cyberattackers’ operations in cyberspace. It then reviews the existing scientific evidence assessing various aspects of deterrence in the context of several disciplines: criminology, law, information systems, and political science. This chapter ends with a few policy implications and proposed directions for future interdisciplinary academic research

A novel porous media-based approach to outflow boundary resistances of 1D arterial blood flow models

In this paper we introduce a novel method for prescribing terminal boundary conditions in one-dimensional arterial flow networks. This is carried out by coupling the terminal arterial vessel with a poro-elastic tube, representing the flow resistance offered by microcirculation. The performance of the proposed porous media-based model has been investigated through several different numerical examples. First, we investigate model parameters that have a profound influence on the flow and pressure distributions of the system. The simulation results have been compared against the waveforms generated by three elements (RCR) Windkessel model. The proposed model is also integrated into a realistic arterial tree, and the results obtained have been compared against experimental data at different locations of the network. The accuracy and simplicity of the proposed model demonstrates that it can be an excellent alternative for the existing models

Numerical investigation of a phase change material including natural convection effects

Nowadays, Organic Rankine Cycle (ORC) is one of the most promising technologies analyzed for electrical power generation from low-temperature heat such as renewable energy sources (RES), especially solar energy. Because of the solar source variation throughout the day, additional Thermal Energy Storage (TES) systems can be employed to store the energy surplus saved during the daytime, in order to use it at nighttime or when meteorological conditions are adverse. In this context, latent heat stored in phase-change transition by Phase Change Materials (PCM) allows them to stock larger amounts of energy because of the larger latent energy values as compared to the specific heat capacity. In this study, a thermal analysis of a square PCM for a solar ORC is carried out, considering four different boundary conditions that refer to different situations. Furthermore, differences in including or not natural convection effects in the model are shown. Governing equations for the PCM are written with references to the heat capacity method and solved with a finite element scheme. Experimental data from literature are employed to simulate the solar source using a time-variable temperature boundary condition. Results are presented in terms of temperature profiles, stored energy, velocity fields and melting fraction, showing that natural convection effects are remarkable on the temperature values and consequently on the stored energy achieved

A thermoporoelastic model for fluid transport in tumour tissues

In this paper, the effect of coupled thermal dilation and stress on interstitial fluid transport in tumour tissues is evaluated. The tumour is modelled as a spherical deformable poroelastic medium embedded with interstitial fluid, while the transvascular fluid flow is modelled as a uniform distribution of fluid sink and source points. A hyperbolic-decay radial function is used to model the heat source generation along with a rapid decay of tumour blood flow. Governing equations for displacement, fluid flow and temperature are first scaled and then solved with a finite-element scheme. Results are compared with analytical solutions from the literature, while results are presented for different scaling parameters to analyse the various physical phenomena. Results show that temperature affects pressure and velocity fields through the deformable medium. Finally, simulations are performed by assuming that the heat source is periodic, in order to assess the extent to which this condition affects the velocity field. It is reported that in some cases, especially for periodic heating, the combination of thermoelastic and poroelastic deformation led to no monotonic pressure distribution, which can be interesting for applications such as macromolecule drug delivery, in which the advective contribution is very important owing to the low diffusivity

Effects of pulsating heat source on interstitial fluid transport in tumour tissues

Macromolecules and drug delivery to solid tumours is strongly influenced by fluid flow through interstitium, and pressure-induced tissue deformations can have a role in this. Recently, it has been shown that temperature-induced tissue deformation can influence interstitial fluid velocity and pressure fields, too. In this paper, the effect of modulating-heat strategies to influence interstitial fluid transport in tissues is analysed. The whole tumour tissue is modelled as a deformable porous material, where the solid phase is made up of the extracellular matrix and cells, while the fluid phase is the interstitial fluid that moves through the solid matrix driven by the fluid pressure gradient and vascular capillaries that are modelled as a uniformly interspersed fluid point-source. Pulsating-heat generation is modelled with a time-variable cosine function starting from a direct current approach to solve the voltage equation, for different pulsations. From the steady-state solution, a step-variation of vascular pressure included in the model equation as a mass source term via the Starling equation is simulated. Dimensionless 1D radial equations are numerically solved with a finite-element scheme. Results are presented in terms of temperature, volumetric strain, pressure and velocity profiles under different conditions. It is shown that a modulating-heat procedure influences velocity fields, that might have a consequence in terms of mass transport for macromolecules or drug delivery

Hypo-and hyperthermia effects on macroscopic fluid transport in tumors

Combining the effects of transvascular and interstitial fluid movement with the structural mechanics of a tissue is necessary to properly analyze processes such as nutrient transport in a tumor cell. Furthermore, externally induced heat loads can play a role: for example, cryoablation can be performed by means of hypothermia and hyperthermia can be induced in order to treat some kinds of tumors such as liver tumor. Recently, the study of the effects of hypo-and hyperthermia on fluid flow and mass transport in biological systems by considering the fluid–structure interaction has gained researchers’ attention. In this paper, fluid flow in a tumor mass is analyzed at the macroscopic scale by considering the effects of both solid tissue deformation and temperature via hypo-and hyperthermia. Governing equations are averaged over a representative elementary volume of the living tissue, and written by means of the thermo-poroelasticity theory. Darcy’s law is used to describe fluid flow through the interstitial space, while transvascular transport is described with a generalized Starling’s law. The effects of hypo-and hyperthermia on the living tissue are included with a source term in the tissue momentum equation that considers thermal expansion. This term can be either negative or positive, i.e., hypo-or hyperthermia is herein considered. Governing equations with the appropriate boundary conditions are solved with the finite-element commercial code COMSOL Multiphysics in the steady-state regime. The numerical model is validated with analytical results from previously published results for an isothermal case. Results are presented in terms of pressure, velocity, and temperature fields for various thermal loads and the effects of hypo-and hyperthermia on various physical parameters are analyzed

Enhancing PCMs thermal conductivity: A comparison among porous metal foams, nanoparticles and finned surfaces in triplex tube heat exchangers

Increasing latent heat thermal energy storage system thermal conductivity is of primary importance to take advantage of their capability of storing large amount of thermal energy. For this task, various solutions have been proposed through the years and a throughout comparison depending on the final application is still lacking. In this paper, the melting process of PCMs embedded in a Triplex-Tube Heat Exchanger (TTHX) is investigated numerically by considering three different methods that include separately or together metal foams, nanoparticles addition and finned surfaces. Organic PCMs with different melting points are used as PCMs in the middle shell of the 3D (TTHX) to maximize latent heat depending on local temperatures. Water across inner and outer tubes is considered too as the heat transfer fluid. Results are presented in terms of liquid fraction, temperature evolution as well as charging the energy storage rate. The results show that a composite of PCM/Metal Foam with porosities that vary from 0.98 to 0.92 engenders shorter melting comparing to pure PCM. By inserting metallic foam with different porosities and nanoparticles with 5% volume fraction in the TTHX (Case A), the melting time decrease can achieve a 69.52% when compared with Pure-PCM. Regarding the melting process in pure Multilayer-PCM (Case B), for all metal foam porosities the foam/nano-PCM device shows a shorter melting time even if nanoparticles have minor impact compared to metal foams, reaching a 83.48% in terms of reduction if nanoparticles and metal foams are employed. Finally, for the Case C, melting times are smaller when comparisons are done with Cases A and B for pure PCM. Furthermore, in the finned surfaces of TTHX (Case C), the inclusion of nanoparticles with foam reduced the melting durations by 53.17% compared to the TTHX (Case A) with pure PCM