Flame quenching and spontaneous combustion suppression during high pressure hydrogen leakage by metal porous medium

A remountable high-temperature superconducting magnet, whose segments can be mounted and demounted repeatedly, has been proposed for construction and maintenance of superconducting magnet and inner reactor components of a fusion reactor. One of the issues in this design is that the performance of the magnet deteriorates by a local temperature rise due to Joule heating in jointing regions. In order to prevent local temperature rise, a cooling system using a cryogenic coolant and metal porous media was proposed and experimental studies have been carried out using liquid nitrogen. In this study, flow and heat transfer characteristics of cooling system using subcooled liquid nitrogen and bronze particle sintered porous media are evaluated through experiments in which the inlet degree of subcooling and flow rate of the liquid nitrogen. The flow characteristics without heat input were coincided with Ergun’s equation expressing single-phase flow in porous materials. The obtained boiling curve was categorized into three conditions; convection region, nucleate boiling region and mixed region with nucleate and film boiling. Wall superheat did not increase drastically with porous media after departure from nucleate boiling point, which is different from a situation of usual boiling curve in a smooth tube. The fact is important characteristic to cooling superconducting magnet to avoid its quench. Heat transfer coefficient with bronze particle sintered porous media was at least twice larger than that without the porous media. It was also indicated qualitatively that departure from nucleate boiling point and heat transfer coefficient depends on degree of subcooling and mass flow rate. The quantitative evaluation of them and further discussion for the cooling system will be performed as future tasks.

Mixed convection heat transfer in a vertical concentric annulus packed with a metallic porous media and heated at a constant heat flux is experimentally investigated with water as the working fluid. A series of experiments have been carried out with a Rayleigh number range from Ra=122418.92 to 372579.31 and Reynolds number that based on the particles diameter of Red=14.62, 19.48 and 24.36. Under steady state condition, the measured data were collected and analyzed. Results show that the wall surface temperatures are affected by the imposed heat flux variation and Reynolds number variation. The variation of the local heat transfer coefficient and the mean Nusselt number are presented and analyzed. An empirical correlation has been proposed for computing the Nusselt number for the geometry and boundary conditions under investigation. 

Photovoltaic system is one of the promising electricity generation devices due to its direct solar energy conversion, safe power transmission and practicability. However, its performance is very sensitive to higher temperatures. Photovoltaic/Thermal systems were presented for enhancing the electrical efficiency and making use of the lost thermal energy. In this research, a combined usage of Paraffin as a phase change material and a stainless-steel porous media was used to decrease its temperature and make use of it. Two different systems were used for comparison. One contains Stainless steel wool with paraffin, and the other with only Paraffin. Three flow rates of 0.2, 0.3, and 0.4 LPM were used of water as a circulating and cooling fluid. It was found that, for all the flow rates, the system with a porous metallic media achieved lower surface temperature, higher electrical efficiency, and higher overall efficiency. The temperature of the PV cell decreased by from 5 to 25⁰ C. The enhancement achieved was from 10% to 28% in the overall efficiency, and 1% to 4% in the electrical efficiency. This proves the importance of the porous metallic media in enhancing properties of the phase change materials when using with the Photovoltaic modules cooling.

In a fusion reactor, almost 30% of fusion energy is deposited on plasma facing components. In the divertor region, it is, however, difficult to utilize this energy with conventional cooling techniques based on high velocity flow with highly subcooled cooling. From this viewpoint, the authors have been developing a cooling technique with metal porous media. In this study, in order to attain both the higher cooling performance and the acquisition of high density energy, high heat removal experiments are performed by using homogeneous and functionally graded porous media to estimate their fundamental heat transfer performances. From the experiments with the homogeneous porous media, it is clarified that the cooling performance is not always improved by using finer pore size media. The functionally graded porous media can reduce a pressure loss. Additionally, in case of the functionally graded porous media with the finer pore, the heat transfer coefficient is higher than that obtained in the homogeneous case. As for the optimal design, it is important to consider the degree of vapor development near a heated surface in the porous media and an effective discharge of vapor from the heated region.

In the case of using rare-earth barium copper oxide (REBCO) tape as a current-limiting element, there are three requirements: high normal state resistance, high thermal stability, and quick recovery to the superconducting state. In this study, a new type of REBCO tape with a metal porous medium as a stabilizer (a porous-stabilized REBCO tape) was proposed, which has high resistance compared to bulk material and prevents film boiling due to its strong capillary force. First, a numerical simulation was performed to evaluate the current-limiting performance of the porous-stabilized REBCO tape with a Ni–Cr porous medium. The results showed that the current-limiting performance was dramatically improved by placing indium partially on the REBCO tape to join the porous medium compared to placing indium wholly. Then, the porous-stabilized REBCO tapes with various arrays of indium were manufactured, and tested to confirm its recovery characteristics. The experimental results indicated that the partially-joined Ni–Cr porous-stabilized REBCO tape reduced the recovery time by 69% compared to that of the stabilizer-free REBCO tape.

Using porous media to extend the heat transfer area, improve effective thermal conductivity, mix fluid flow and thus enhance heat transfer is an enduring theme in the field of thermal fluid science. According to the internal connection of neighbouring pore elements, porous media can be classified as the consolidated and the unconsolidated. For thermal purposes, the consolidated porous medium is more attractive as its thermal contact resistance is considerably lower. Especially with the development of co-sintering technique, the consolidated porous medium made of metal, particularly the metallic porous medium, gradually exhibits excellent thermal performance because of many unique advantages such as low relative density, high strength, high surface area per unit volume, high solid thermal conductivity, and good flow-mixing capability (Xu et al., 2011b). It may be used in many practical applications for heat transfer enhancement, such as catalyst supports, filters, biomedical implants, heat shield devices for space vehicles, novel compact heat exchangers, and heat sinks, et al. (Banhart, 2011; Xu et al., 2011a, 2011b, 2011c). The metallic porous medium to be introduced in this chapter is metallic foam with cellular micro-structure (porosity greater than 85%). It shows great potential in the areas of acoustics, mechanics, electricity, fluid dynamics and thermal science, especially as an important porous material for thermal aspect. Principally, metallic foam is classified into open-cell foam and close-cell foam according to the morphology of pore element. Close-cell metallic foams are suitable for thermal insulation, whereas open-cell metallic foams are often used for heat transfer enhancement. Open-cell metallic foam is only discussed for thermal performance. Figure 1(a) and 1(b) show the real structure of copper metallic foam

Numerical study on the influence mechanism of different types of burst disc on high pressure hydrogen spontaneous combustion in tube

A study on a numerical simulation of the leakage and diffusion of hydrogen in a fuel cell ship

Heat transfer enhancement by filling metal porous medium in central area of tubes

Commercial solar water heating collectors are usually oversized in order to satisfy a heat demand and this increases their manufacturing cost. It is possible to reduce the size of collectors if heat transfer from the channel walls to the working fluid is increased. To enhance the heat transfer to the working fluid a metal porous medium placed inside pipes. The presence of a metal porous medium made of aluminium or stainless steel results in the increase of the interface between the fluid and absorber, diffusion in the near wall flow and increases in the heat transfer rate. The aim of this study is to experimentally investigate the effect of heat transfer inside the channels, partially filled with porous medium, of a simplified flat plate solar water collector for application in the Southern Europe.

This study evaluates heat transfer characteristics of a sub-channels-inserted (SCI) porous heat removal device for divertor cooling. It is clarified that increasing the total volume of the sub-channels strongly contributes to the enhancement of phase-change of coolant as well as the vapor discharge. A high heat flux of approximately 25 MW/m2 is removed at a wall superheat less than 70 K by increasing the number of the sub-channels installed under low flow rate conditions. The results also suggest that the SCI porous heat removal device could be applicable for the divertor cooling by optimizing the sub-channel design. Furthermore, especially for an enlarged heating area, optimizing the location of the sub-channel inlet, that is the interval of each sub-channel inlet, could be essential in order to smoothly discharge the generated vapor outside the porous medium.

This study evaluates convective and boiling heat transfer characteristics of a water impinging jet flow in porous media in order to remove the heat flux of 10 MW/m2 imposed to fusion divertors. The metal porous media with complicated microchannels have large heat transfer surface due to fin effect and superior mixing effect of fluid, which enhances not only the convective heat transfer but also the boiling heat transfer by improving the evaporation rate of the cooling liquid. In a proposed heat removal device called EVAPORON-3-Type3, the cooling water is supplied as an impinging jet flow into the porous medium, which is a two-layered copper particle bed, and the generated vapor is discharged through high porosity gaps on the heat transfer surface. As a result, the convective heat transfer coefficient is improved by 1.6 times compared with that of an impinging jet flow without the copper particle bed. In the boiling heat transfer regime, the critical heat flux is increased by 1.5 times and the heat flux of 8.4 MW/m2 is achieved under low velocity and highly subcooled conditions though it’s not maximum.

This study presents a new concept for the use of non-Darcy flow characteristics in reservoir characterization, development, and well performance. More than 1,000 core samples are analyzed under unsteady-state flow conditions. A universal scale turbulent factor vs. permeability is developed on the basis of the reference base-line of turbulent flow through metallic porous media. This new scale is used to:Classify reservoirs in terms of permeability heterogeneity; and,Establish an iso-turbulence map for reservoir development by selecting adequate zones to drill new wells. In this paper, different applications for Algerian reservoirs are outlined and a new concept for the use of a turbulence factor is highlighted. Introduction This study develops characteristics related to fluid flow through porous media for a turbulent flow regime (high Reynolds number). It involves laboratory experimental analysis followed by numerical and analytical simulations. Six reservoirs are selected: the Upper Trias Shally Sand (TAGS/UTSS) of Hassi R'Mel; the Lower Trias Shally Sand (TAGI/LTSS) of Ourhoud and Rhourd el Khrouf; the Ordovicien of TFT; the Cenomanian Carbonate of Guerguet El Kihal South; and, the Cambrian of both Gassi and Agreb. Data related to these reservoirs include production and core description. The flow of helium under pressure blowdown conditions is performed on 1,600 core samples selected from the above defined reservoirs. In addition, artificial and homogeneous metallic porous media, used for permeameter and porosimeter calibrations, are analyzed in order to establish a base-line for turbulent flow through natural cores. Turbulence factor vs. permeability relationship is developed for each reservoir. A universal scale of these properties is established for improving reservoir characterization in terms of reservoir heterogeneity. Ini tially, analysis is done on the Hassi R'Mel (HR) and Rhourd El Khrouf (RKF) reservoirs(1). The analysis is then extended to additional reservoirs (Sandstone and Carbonates). Layers of the same reservoir are also characterized in order to validate the universal scale. The results show that this developed scale can be considered as a reliable tool for reservoir characterization. The universal scale was also used in the development of the TFT reservoir and to assist with well performance of the Hassi R'Mel field. Literature Review In this section, some ideas that have been developed in the area of non-Darcy flow characteristics are briefly presented. Darcy's pioneering experimental work(2) is well recognized as the key factor in predicting production performance of porous and permeable flow systems. However, in certain circumstances such as the turbulent flow, this law may lead to erroneous results. Forchheimer(3) demonstrated that the pressure gradient to sustain a high flow rate through a porous medium is higher than the one Darcy's equation would predict. As the flow rate increases, the deviation between pressure gradient and flow rate increases. Forchheimer attributed the excess gradient required to inertial flow resistance. As a result, he developed a quadratic form to relate the pressure gradient and fluid flow velocity.

Flow-pattern-based experimental analysis of convective boiling heat transfer in a rectangular channel filled with open-cell metallic random porous media

Critical heat flux enhancement on a downward face using porous honeycomb plate in saturated flow boiling