Effect Of Porous Material Research Articles

Heat transfer of phase change materials (PCMs) and thermochemical heat storage in porous materials

Thermal energy storage plays an important role in energy conservation and reducing CO2 emissions. Thermal energy storage involves sensible heat storage, latent heat storage and thermochemical heat storage. Compared with sensible heat storage, latent heat storage and thermochemical heat storage benefits of their high energy storage densities, which helps to reduce the initial cost of the construction of heat storage systems. However, the thermal conductivities of the phase change and thermochemical reaction materials are usually lower than 1 W m - 1 K - 1, which impedes the development and further applications of the corresponding energy storage systems. Porous materials, e.g. metal foams and expanded graphite, combining with other materials to form composites is an effective method for heat transfer enhancement. In this paper, the feasibility of using metal foams to enhance the heat transfer characteristics of heat storage materials in thermal energy storage systems was assessed. Heat transfer in solid/liquid phase change and thermochemical reaction of porous materials (metal foams and expanded graphite) was investigated. Organic commercial paraffin wax and inorganic calcium chloride hydrate were employed as the low-temperature materials, whereas sodium nitrate was used as the high- temperature materials in the experiment. Heat transfer characteristics of these PCMs embedded with open-cell metal foams and expanded graphite were studied. Composites of paraffin and expanded graphite with a graphite mass ratio of 3%, 6%, and 9% were prepared. The heat transfer performances of these composites were tested and compared with the results using metal foams. It is shown that heat transfer can be enhanced by adding these porous materials. Metal foams have better heat transfer performance due to their continuous inter-connected structures than expanded graphite. However, porous materials can suppress the effects of natural convection in liquid zone, particularly for PCMs with low viscosities, thereby leading to different heat transfer performances at different regimes (solid, solid/liquid, and liquid regions). This implies that porous materials do not always enhance heat transfer in every regime; thereby an optimal metal foam structure or expanded graphite fraction can be developed using PCMs for the overal thermal energy storage performance. For thermochemical heat storage systems, the feasibility of using metal foams to enhance the heat transfer capability of heat storage materials was assessed. Reversible reaction MgH2↔Mg+H2 was used as thermochemical heat storage reaction. The effective thermal conductivities of metal foams with various porosities (0.88–0.98) were estimated with Boomsma & Poulikakos model. A two dimensional mathematical model for the Mg/MgH2 system was estabilished to study the transient heat and mass transfer process. Heat release characteristics of chemical reaction in fixed beds with/without metal foams were compared to illustrate the effects of metal foams. Various factors influencing the reaction time for fixed reaction beds with metal foams were analyzed. The results show that metal foams shorten the reaction time and increase the output power by decreasing the average temperatures of the fixed beds. After adding metal foams with a porosity of 0.92, a 40% reduction of the reaction time and 60% promotion of the exothermic power can be achieved. The parametric study shows that there exists an optimal porosity of metal foams for the highest output power under a certain reaction condition. The cooling fluid temperature and hydrogen pressure are confirmed to have a more significant impact on the reaction rate when metal foams are embeded in fixed beds. In general, as heat transfer is coupled to phase change and chemical reaction processes in latent heat storage and thermochemical heat storage, the effects of porous materials on these heat storage systems are complex. The porous materials need to be carefully selected in order to optimizing the performance of heat storage systems.

Homogenization of a thermo-diffusion system with Smoluchowski interactions

We study the solvability and homogenization of a thermal-diffusion reaction problem posed in a periodically perforated domain. The system describes the motion of populations of hot colloidal particles interacting together via Smoluchowski production terms. The upscaled system, obtained via two-scale convergence techniques, allows the investigation of deposition effects in porous materials in the presence of thermal gradients.

609 気流中の静止二次元翼から発生する空力音に及ぼす表面性状の影響(流体力学3)

609 気流中の静止二次元翼から発生する空力音に及ぼす表面性状の影響(流体力学3)

Effects of porous materials in an insert earphone on its frequency response -experiments and simulations

This article presents a promising approach to customize the sound-pressure response of an insert earphone by delicately tuning the acoustic impedance of porous materials in it. The effects of applying porous materials on and in various parts in the insert earphone were tested experimentally to determine the resulting sound pressure responses. An equivalent circuit model (ECM) is also presented to simulate the sound-pressure-level (SPL) response of the insert earphone. For each part of the earphone, the effect of applying porous materials was simulated using the ECM approach. For porous elements, modified formulae with correction factors are proposed to determine the acoustic impedance. Comparisons of the simulated responses with experimental data have verified the veracity of the ECM simulations. The present work has verified the feasibility of adjusting the aeration of the porous materials to customize the resulting SPL response of an earphone.

How does confinement affect the catalytic activity of mesoporous materials?

So-called confinement effects in porous materials are known to strongly affect diffusion, phase transformations, catalytic properties, etc. In the field of catalysis, it is generally admitted that antagonistic effects at the mesoscale result in the existence of an optimal catalytic efficiency depending on pore size. Herein we highlight some recent examples of pore size effects and their proposed mechanisms. Confinement studies on periodically organised mesoporous materials must be developed because they should provide a certain clearness of arguments and understanding.

A novel in vitro hydroponic culture system for potato (Solanum tuberosum L.) microtuber production

An innovative in vitro hydroponic culture system used in potato (Solanum tuberosum L.) microtuber production is described in this paper. In vitro potato plantlets, 6–8 cm in height, derived from meristems of potato tubers cultured on 1/2 Murashige and Skoog (MS) nutrient medium after 30 days culture were cut into 1.5 cm stem node segments and used as explants. These stem nodes were cultured in a novel system called in vitro hydroponic culture system containing 1/2 MS medium supplemented with 0.5 μM naphthaleneacetic acid (NAA), 0.3 μM gibberellic acid (GA3), 3.7 μM adenine sulfate, 10% coconut water, 0.5 g/l activated charcoal, 80 g/l sucrose with or without 8 g l−1 agar. Liquid medium was distributed to the carrier substrates in each storey of the system with the aid of capillary robes. In the present paper, the effects of porous material used as substrate carrier and the number of storeys involved in the culture system on microtuber formation and their morphological characteristics are reported. Cotton layer substrate is more stable for organogenesis of potato microtubers. Microtubers, 3.19 mm in diameter and 49.82 mg in weight, could be harvested from a one-storey in vitro hydroponic culture system containing filter paper as substrate. However, microtubers cropped from three-storey in vitro hydroponic culture system with cotton layer were bigger and weightier than those from three-storey system containing filter paper. The above results of the in vitro hydroponic system examined in this study might open up a new approach in producing potato and other hygrophilous microtuber.

Modeling of ice formation in porous solids with regard to the description of frost damage

The freezing and thawing of liquid in porous media in connection with the question concerning the frost durability of solid materials is an important subject for discussion in civil engineering. Each construction or body which is in contact with liquid and frozen water is criticized by its resistance to the environment. The durability concerning frost attacks of a building material is affected by its porosity and the pore size distribution. The ice formation is a phenomenon of coupled heat and mass transport in freezing porous media, and is primarily caused by the expansion of ice in connection with hydraulic pressure. The volume increases due to the freezing front inside the porous solid. Taking into account the aforementioned effects in porous materials, a simplified macroscopic model within the framework of the Theory of Porous Media (TPM) for the numerical simulation of initial and boundary value problems of freezing and thawing processes of super saturated porous solids will be presented. The phase change between the ice and the liquid phase is modeled by different real densities of the phases.

Numerical decoupling analysis of a resonator with absorbent material

The purpose of this paper is to analyze the acoustic performance of resonators with porous material inside the expansion chamber. Sound wave propagation in the porous media is an extremely complicated phenomenon. In the present study the dynamic density and bulk modulus of air in the porous media are used to describe the viscous effects and the thermal effects in an air-saturated rigid frame porous material. With this assumption the absorbent material in the expansion chamber can be equivalent to a fluid with complex sound speed and wave number. Then the coupled equations for sound wave propagation in air (in straight tube) and the equivalent fluid (in expansion chamber) are solved by the numerical decoupling method. Finally, the effects of porous material on the performance of a resonator are discussed. ©

Strain Rate Effects in Porous Materials

ABSTRACTThe behavior of metal foams under rapid loading conditions is assessed. Dynamic loading experiments were conducted in our laboratory using a split Hopkinson pressure bar apparatus and a drop weight tester; strain rates ranged from 45 s−1 to 1200 s−1. The implications of these experiments on open-cell, porous metals, and closed- and open-cell polymer foams are described. It is shown that there are two possible strain-rate dependent contributors to the impact resistance of cellular metals: (i) elastic-plastic resistance of the cellular metal “skeleton,” and (ii) the gas pressure generated by gas flow within distorted open cells. A theoretical basis for these implications is presented.

Hygroscopic Properties and Effect of Porous Materials

Hygroscopic Properties and Effect of Porous Materials

A numerical investigation of phase change effects in porous materials

In this paper, a numerical study of heat and mass transfer with phase change in porous materials is performed. The problem is modelled by a system of transient inter-coupled equations governing the two-dimensional multiphase transport process in porous media. The solution algorithm allows full simulation without any significant simplifications. The variations and the interrelationship between the temperature, vapor density, condensation rate, liquid content and the fluid velocity fields are demonstrated and discussed in detail. It is found that the aspect ratio of the porous matrix does not have a significant effect on the Nusselt number results. Furthermore, it is found that the one-dimensional model is not valid when the boundaries of the porous matrix are subjected to a small or zero pressure difference and that the constant pressure simplification would generate significant errors under some circumstances. The present analysis, which presents a full simulation of the problem for the first time, can be applied to a class of problems on heat and mass transport with phase change through a porous medium.