Force water, mean

The term "hydrophobic interaction" unfortunately implies some form of molecular repulsion, which, outside the van der Waals radii of a molecule, is quite impossible. The term "hydrophobic force" literally means "fear of water" force. The term hydrophobic has been introduced as an alternative to dispersive but means the same. It is not clear from the literature how the word hydrophobic originated, but it may have been provoked by the immiscibility of a dispersive solvent such as n-heptane with a very polar solvent such as water. 

The term "hydrophilic force", literally meaning "love of water" force, was introduced as a complement to "hydrophobic force". Hydrophilic forces are equivalent to polar forces, and polar solvents that interact strongly with water are called hydrophilic solvents. 

Waste-heat boilers are often used to recover heat from furnace flue gases and the process gas streams from high-temperature reactors. The pressure, and superheat temperature, of the stream generated will depend on the temperature of the hot stream and the approach temperature permissible at the boiler exit (see Chapter 12). As with any heat-transfer equipment, the area required will increase as the mean temperature driving force (log mean AT) is reduced. The permissible exit temperature may also be limited by process considerations. If the gas stream contains water vapour and soluble corrosive gases, such as HC1 or S02, the exit gases temperature must be kept above the dew point. 

In order to understand the basis for the prevention of bubble coalescence and hence the formation of foams, let us examine the mechanical process involved in the initial stage of bubble coalescence. The relatively low Laplace pressure inside bubbles of reasonable size, say over 1 mm for air bubbles in water, means that the force required to drain the water between the approaching bubbles is sufficient to deform the bubbles as illustrated in Figure 8.2. The process which now occurs in the thin draining film is interesting and has been carefully studied. In water, it appears that the film ruptures, joining the two bubbles, when the film is still relatively thick, at about lOOnm thickness. However, van der Waals forces, which are attractive in this system (i.e. of air/water/air), are effectively insignificant at these film thicknesses. 

By forcing water through narrow openings or capillaries, work is also converted by friction into heat. Joule forced water through small holes in a cylinder by means of a piston, and obtained by this method J = 424-6 kgm. 

A wooden sphere is held by a string in a water stream (Fig. 5P-8). Determine the string force by means of a dimensional analysis. 

ULTRA FILTRATION - A process that forces water through a filtering membrane by means of pressure gradients in order to obtain ultra pure water. 

At the top feed liquid flows downward as a thin film by gravitational force, by means of a highspeed rotor film thickness is equalized and the surface is constantly renewed. Z 0.5-0.6 m (heated length), d = 0.15-1.7 m (outer diameter), heating area A 0.1-25 m, operating pressure down to ca 1 mbar, mean solution residence time 10-60 s, rotor speed ca. 1000 revolutions/min, film thickness 0.1-1 mm, final solution viscosity ca. 20-200 Pa-s, k = 500-1800 W/(m k) at concentration of aqueous solutions, evaporation rate ca. 80-1000 kg/h water, to calculate heat transfer see [7.21]... 

The dissolving of ionic substances in water means that the ionic molecules split up to give separate ions or stay as the solvated entities. Students often reason that ionic substances consist of discrete molecules made from uni-directional bonded ion-pairs. In the case of solvated ionic molecules, they reason that the weaker bonds (often seen as Van der Waals forces) between ionic molecules have been broken. 

But Joule had already, in a postscript to this paper, transferred his attention from the electrical generation of heat to the purely frictional. By forcing water through tiny holes in a perforated cylinder, he had been able to evolve a detectable amount of heat, which compared with the work expended yielded a mechanical value for a unit of heat of 770 ft.lbs. This was in tolerable if not good agreement with the value obtained by means of the electrical experiments."... 

Viscosity is measured in poise. If a force of one dyne, acting on one cm, maintains a velocity of 1 cm/s over a distance of 1 cm, then the fluid viscosity is one poise. For practical purposes, the centipoise (cP) is commonly used. The typical range of gas viscosity in the reservoir is 0.01 - 0.05 cP. By comparison, a typical water viscosity is 0.5 -I.OcP. Lower viscosities imply higher velocity for a given pressure drop, meaning that gas in the reservoir moves fast relative to oils and water, and is said to have a high mobility. This is further discussed in Section 7. 

The concept of the potential of mean force can be extended to mixtures and solutions. Consider two ions in a sea of water molecules at fixed temperature T and solvent density p. The potential of mean force w r) is the direct interaction between the ions u.j r) = plus the interaction between the ions tln-ough water... 

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