Periodic wetting phenomena

After venting of the elongated bubble, the region of liquid droplets begins. The vapor phase occupies most of the channel core. The distinctive feature of this region is the periodic dryout and wetting phenomenon. The duration of the two-phase period, i.e., the presence of a vapor phase and micro-droplet clusters on the heated wall, affects the wall temperature and heat transfer in micro-channels. As the heat flux increases, while other experimental conditions remain unchanged, the duration of the two-phase period decreases, and CHF is closer. 

Capillary forces offer a coherent explanation for the drying periods of many materials. If a tapered capillary is filled with water and exposed to a current of air, the meniscus at the smaller end remains stationary while the tube empties from the wider end. A similar situation exists in a wet particulate bed and the phenomenon is explained by the concept of suction potential. A negative pressure exists below the meniscus of a curved liquid surface which is proportional to the surface tension, X, and inversely proportional to the radius of curvature, r. (The meniscus is assumed to be a part of a hemisphere.) This negative pressure or suction potential may be expressed as the height of liquid, expressed by Eq. (25),... 

Initial adjustment period—is the stage at which the wet feed material heats up or cools down to the starting drying temperature which is basically referred to as the wet cake temperature. For example, the wet feed is introduced to the heated dryer at ambient temperature. During this period the material temperature will start to rise to the wet bulb temperature which may be different from the initial feed temperature. The reason the temperature of the wet cake remains low relative to the gas temperature is a phenomenon known as evaporative cooling. 

On the basis of a recently published article, however, it may be premature to conclude that the only potential performance benefit connected with the use of borate in this application is its hardness ion tolerance [119]. This article hints at another phenomenon as yet not fnUy nnderstood. In this work crude oil-laden thin limestone plates or short cores were contacted with aqueous solutions of sodium carbonate, sodium hydroxide, sodium metaborate, di-sodium tetraborate (borax), and sodium chloride. The spontaneous uptake of these very simple salt solutions by the limestone and the consequent expulsion/recovery of oil was then observed visually and analyzed over a period of several days. This phenomenon is known as capillarity-driven natural imbibition (CDNI), and is the spontaneous spreading of the water phase into the rock. In mixed-wet or oil-wet carbonate reservoirs, where high-dissolved salts cause incompatibilities with and prevent the use of many injected chemicals (ionic surfactants and common alkalis) CDNI is often the only mechanism available for oil recovery. What was surprising was that with solutions of sodium metaborate, greater than 50%... 

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