Abstract
Porous medium are products of processing in food, agricultural, chemical and many other industries. Calculations of processes with wet porous medium are based on capillary properties of the liquid in a pore space. The capillary properties of liquids in porous media are established in pore models in the form of thin tubes of circular or slit transverse sections. The intensity of the processes occurring in it depends on the nature of the filling of the pore space with liquid. Filling with liquid and the formation of a capillary layer is possible only in small pores. However, there is no analytical justification for the transverse pore size, more than which it cannot be filled with liquid by capillary forces. With this in mind, the concept of the limiting transverse size of a capillary for a liquid under conditions of complete wetting is introduced. The limiting size calculation is based on two conditions: the shape of the axial section of the meniscus surface has the appearance of a semicircle and its extremum point is located at the level of the free surface of the fluid supplying the capillary. A capillary column cannot form in larger pores. The absence of formulas for calculating capillaries of the limiting sizes can introduce a significant error into the analytical calculation of the moisture content in the capillary layer of a liquid in porous media and moisture transfer processes. The aim of the study was to obtain formulas for calculating the limiting (largest) sizes of capillaries of a circular, flat slit section and annular transverse sections with complete wetting of their walls. For the conditions above, it was identified that the limiting distance between the walls was independent from annular capillary diameter. The formulas for the limiting transverse sizes of the flat slit and annular capillaries turned out to be the same under the assumptions above. This indicates a weak dependence of the limiting size of a slit capillary on the curvature of its transverse section. Examples of calculations of capillaries of the limiting sizes are performed.
Highlights
FOOD SYSTEMS | Volume 3 No 2 | 2020There is a wide variety of practical problems where the capillary properties of po medium are shown [1,2,3,4]
A quantitative concept of the limiting transverse size of a capillary is introduced. It is based on the fulfillment of two conditions: the axial sectional shape of the meniscus surface in the form of an arc of a circle and the position of its extremum point at the level of the free surface of the liquid supplying the capillary
Considering the mutual influence of the properties of both the liquid and the wall material in contact with the formation of the meniscus, the limiting size of the capillary will vary for different wetting liquids and unchanged other factors
Summary
FOOD SYSTEMS | Volume 3 No 2 | 2020There is a wide variety of practical problems where the capillary properties of po medium are shown [1,2,3,4]. Calculations of the processes associated with wetness po UDC 664–4: 631.434.12. The effect of a drastic decrease in moisture in the capillary layer ca Porous medium are products of processing in food, agricultural, chemical and many other industries. The limiting size calculation is based on two conditions: the shape ofotfhethaexicaolnsceecptitonofoaf tchaepmilleanriyscauss asutrufbaceeinhaws hthicehapapceaaprailnlcaeryofcoalsuemmnicoirfclleiqaunidd imtsay appea ecaxntrneomtufomrmpoiinntlaisrgleorcaptoertdhesias.tTtrhheeegalaerbvdse,elntohcfeethoaefnffaorlerymetisuculaarlfsasfcooerloucftaitlohcnuelfatlotuiindtghsecuapppprilolylbainrleigemsthoeoffctahopebilltliaamirniyti.inAnggcasthipzeiellsaccrayalcncuoilnlauttmrioon-n formula duce a significant error instuocthhecaapnialllyatriiceasl icsalrceulelavtaionnt.of the moisture content in the capillary layer of a liquid in porous media and moisture transfer processes. The aim of the study was to obtain formulas for calculating the limiting (largest) sizes of capTihllearaiensaolyftaiccairlcpurloarp,eflratitessliot fsepcotiroonusanmdeadninuumlaarntrdanmsoveisrtsuerseectrtaionnssfewripthroccoemsspelesteare consid wetting of their walls. For a capillar circular transverse section and zero contact angle of liquid wetting, corresponding to
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