The percolation model of relative conductivities and phase permeabilities

The universal mathematical model of relative conductivities of percolation clusters and phase permeabilities of oil-water-saturated rocks is presented. It is obtained on the basis of percolation theory, porous body physics and statistics. The model takes into account the influence of change in pore space surface properties and the nature of fluid flow on the studied characteristics and may be applied for comprehensive analysis and modeling of technological processes of oil production.

Numerical Modelling of Heat Transport in Freezing Mortars with an External Liquid Reservoir

Several studies indicate that the temperature distribution in concrete may affect the extent of frost scaling. This study presents a numerical model that describes the thermal response of freezing mortars in the presence of an external liquid reservoir, where the external liquid is either pure water or 3% sodium chloride solution. The phase transformation of supercooled external liquid is modelled in two stages: quick freezing, when the supercooled liquid starts to form crystals and slow freezing. The model is developed in two parts. In part I, the focus is the modelling of external liquid, and therefore a non-porous body with an external liquid reservoir is modelled and validated. In part II, the model developed in part I is developed further for a porous body containing different phases, i.e., unfrozen liquid and ice, in the pores. A comparison of simulated and experimentally measured temperature distributions shows a good agreement.

Method and device for the control of surface properties of porous solids at the boundary of their contact with liquids and gases

The article indicates the relevance of the problem of controlling the surface properties of solids, analyzes the features of interaction between porous solids in direct contact with liquids. The process of adhesive interaction of the system “liquid – porous solid” at the interface of these phases is analyzed and the dependence of the degree of wetting by a liquid of the surface of a solid on the structure of the porous body and the surface properties of the liquid is established. The dependence of the contact angle hysteresis of the solid with liquid on the porosity and roughness of the sample of the controlled body is substantiated. A method of complex express control of the wetting process, which consists in determining the hysteresis of fluid flowing in and out from the surface of a solid body, has been proposed. The method consists in determining the rate of liquid outflow from a tilted sample of a solid. At the same time, the liquid is applied with the same speed to the surface of a porous body sample. The design of device for realization of the method has been developed.

Subcooled Flow Boiling Heat Flux Enhancement Using High Porosity Sintered Fiber

Passive methods to increase the heat flux on the subcooled flow boiling are extremely needed on modern cooling systems. Many methods, including treated surfaces and extended surfaces, have been investigated. Experimental research to enhance the subcooled flow boiling using high sintered fiber attached to the surface was conducted. One bare surface (0 mm) and four porous thickness (0.2, 0.5, 1.0, 2.0 mm) were compared under three different mass fluxes (200, 400, and 600 kg·m−2·s−1) and three different inlet subcooling temperature (70, 50, 30). Deionized water under atmospheric pressure was used as the working fluid. The results confirmed that the porous body can enhance the heat flux and reduce the wall superheat temperature. However, higher porous thickness presented a reduction in the heat flux in comparison with the bare surface. Bubble formation and pattern flow were recorded using a high-speed camera. The bubble size and formation are generally smaller at higher inlet subcooling temperatures. The enhancement in the heat flux and the reduction on the wall superheat is attributed to the increment on the nucleation sites, the increment on the heating surface area, water supply ability through the porous body, and the vapor trap ability.

On the Disappearance of the Steady Wake Region Behind Porous Objects Under Free Stream Flow At Low Reynolds Numbers

A solid bluff object produces a recirculating wake region immediately behind it when subjected to flow separation under a steady flow condition. Similar phenomena can also be observed for a porous body. However, unlike the solid object the porous body allows some part of the flow to go through it. A consequence of this flow penetration in porous objects is, the wake behind the body may get reduced in size and detach from the body. The wake even may disappear at some value of the porosity parameter (Darcy number). In this brief article, we compute the critical values of the porosity parameter for complete disappearance of the wake region behind two-dimensional porous bodies of circular and square shapes. A regime diagram is constructed to show the regions of wake formation, its detachment and finally its disappearance around circular and square shaped porous bodies. The critical value of the porosity parameter increases with increasing Reynolds number, and it is found greater for the square body in comparison to the circular one. The study provides a quantitative estimation of how the porosity plays a significant role in demarcating the flow characteristics around porous objects.

EFFECTIVE THERMOPHYSICAL PROPERTIES OF POWDER MATERIALS DURING SINTERING UNDER ELECTRONBEAM HEATING

Background. Development of the consolidation processes of powder products using highly concentrated energy sources is impossible without a detailed analysis of the processes of thermal conditions arising in these products. Objective. The aim of the study is to select a method for calculating the thermal conductivity of a porous body, which will be established under various conditions of electron-beam sintering of molybdenum compacts, and to study the effect of the parameters of the porous structure on the thermal conductivity. Methods. An analysis of the sintering process in finite element calculations, in problems of thermal conductivity for two-dimensional and three-dimensional domains, simulating the real porous structure of molybdenum compaction and a regular porous structure with dense packing of spheres is proposed. Results. Mathematical analysis of the contribution of re-radiation to the total thermal conductivity of the porous material is performed. The obtained dependences of the relative thermal conductivity on the porosity of the material and the relative radius of contacts between its particles are presented. Conclusions. According to the results of the mathematical analysis of the conditions of heat transfer in a porous compact of molybdenum for the case of electron-beam heating, it was found that the radiant component of the thermal conductivity of a porous body with pores of the order of 2.5 μm is four orders of magnitude less than the conductive component of its thermal conductivity. Based on the results of finite element modeling of two-dimensional and three-dimensional porous objects, a significant effect of the contact area between particles on their integral thermal conductivity has been established, especially at small sizes of these contacts. At the same time, almost linear effect of porosity on thermal conductivity was established at contact radii between particles > 0.1 Rparticles. A significant influence of the uniformity of the distribution of contacts in aporous material on the uniformity of the temperature field in it is shown.