Inner surface area

One of the main reasons for a lower specific activity resides in the fact that electrodes with disperse catalysts have a porous structure. In the electrolyte filling the pores, ohmic potential gradients develop and because of slow difiusion, concentration gradients of the reachng species also develop. In the disperse catalysts, additional ohmic losses will occur at the points of contact between the individual crystallites and at their points of contact with the substrate. These effects produce a nonuniform current distribution over the inner surface area of the electrode and a lower overall reaction rate. 

Another factor producing an apparent decrease in the activity of disperse catalysts is steric hindrance. In reactions involving relatively large molecules, not aU of the inner surface area of the catalyst may by accessible for these molecules, so that the true working surface area is smaller than that measured by BET or hydrogen adsorption. 

Porous-layer- open tubular (PLOT) and support-coated open tubular (SCOT) columns are prepared by extending the inner surface area of the capillary tube. A layer of particles can be deposited on the surface or the column wall can be chemically treated to create a porous adsorbent layer. Obviously some of the wall-modified open tubular columns discussed in section 2.3.3 could be... 

Molecular models indicate that cavitand (259) has a tall, vase-shaped architecture in which the four benzene rings and four nine-membered rings combine to form a concave cavity to which is attached the four diazanaphthalenes (Moran, Karbach Cram, 1982). The latter groups resemble flaps which may occupy either equatorial or axial positions. In the former arrangement, the inner surface area of the cavity is quite reduced and hence a considerable decrease in the inclusion ability of this form is expected. 

Capillary Modification. The capillary was etched with a fluoride compound at high temperature to prepare a whisker column with a 1000-fold increased inner surface area as compared to an unmodified capillary... 

Example 1 A given chamber has a volume of 70 m and an inner surface area of 100 m a subsfanfial gas evolution of 2 10 mbar I s" m is assumed. The first question is to decide whether a pump with a nominal pumping speed of 1300 m /h is generally suitable in this case. The coordinates for the surface area concerned of 100 m and a gas evolution of 2 10 mbar I s" m result in an intersection point A, which is joined to point B by an upward sloping line and then... 

In the case of heat transfer equipment using metal tubes, one problem is which surface area - the inner surface area Aj or the outer surface area - should be taken in defining LI. Although this is arbitrary, the values of LI will depend on which surface area is taken. Clearly, the following relationship holds ... 

By Equation 5.7 (A ) [J = (110 - 35)/ln (110/35) = 65.6 °C Thus, heat to be transferred Q = 2000 X 1030 X 0.946 (85 — 10) = 146 200 kcal h . In calculating the required heat transfer surface area A of a tube, it is rational to take the area of the surface where h is smaller that is, where the heat transfer resistance is larger and controlling - which is the milk-side inner surface area in this case. Thus,... 

Consider two closed air-sampling vessels made out of (a) teflon and (b) glass (assume like quartz) with an air volume Fa = 10 3m3 (1 L) and an inner surface area of ASUTf = 6 x 10" 2m2. In these vessels you capture air samples that you want to analyze for phenanthrene. Calculate the fraction of the total phenanthrene present in the air in the two vessels after adsorption equilibrium between the gas phase and the walls of the vessel has been established at 15°C (288 K) and 50% relative humidity. Assume that only adsorption at the surface of the walls is important. (Note that in the case of teflon, absorption could also be important.)... 

For the liquid phase kinetic studies of esterification, with a few exceptions [402,435—437] only the standard (non-porous, see Sect. 1.2.5) ion exchangers were used. The macroreticular (porous) ion exchangers with a large inner surface area are prefered for vapour phase reactions, especially in more recent studies [436—443]. The authors claimed that diffusion was not the limiting process under their conditions. This observation cannot be generalised, however, and even with vapour phase reactions and macroreticular polymers, the possibility of transport limitations through the pores or the polymer mass cannot be excluded a priori. 

The cement mortar samples, in contrast to the lime mortar samples, exhibit a higher cyanide concentration by a factor of two. The higher iron content of the cement mortar samples may be the reason for this, since the cyanide content increases proportionally to the iron content (see the last column of Table 19). In addition, hydrogen cyanide adsorption was certainly favored by the higher inner surface area of the cement mortar as compared to lime mortar. 

Fig. 20 SEM (sample preparation critical point drying) of inner surface areas. 1 - BASYC in the middle region of the interposition four weeks after implantation in the carotid artery of the rat with endothelial cells, 2 - BASYC before incorporation. Reprinted with permission from [65]...

The surface of an adsorbent is not smooth but shows a roughness of molecular or higher dimensions. Many catalysts used in practice are deliberately prepared to contain a great number of capillaries of submicro-scopic dimensions. There are many places on the highly developed inner surface areas of such microporous adsorbents where the adsorbed molecules come into direct contact with many more atoms of the adsorbent than would be possible if the surface were an ideally smooth plane. Such places where an increased number of atoms of the adsorbent are in direct contact with the adsorbed molecules form active places or active spots for van der Waals adsorption (28-30). 

The highly efficient separations afforded by capillary electrophoresis (CE) are a direct result of employing extremely narrow separation channels. Effective dissipation of heat generated by the passage of electrical current through the separation medium occurs only when the ratio of capillary Inner surface area to Internal volume is sufficiently large (typically 104 to 10s m 1). 

In this polymerization, the biofunctional component (enzyme) can be concentrated in an interfacial area between the frozen ice crystal and the supercooled monomer phase, and immobilized by molecular entanglement between the enzyme and polymer molecules. This is a different procedure for fixation from the usual entrapping method with a crosslinked structure in a gel. Therefore, we may call this procedure the adhesion-method to distinguish it from the usual entrapping. This term was extended to cover the use of the usual synthetic polymers including hydrophobic polymers as the supports. One of the characteristic properties of products obtained in this way was that there is a maximum activity at a certain monomer concentration. The maximum activity is observed when the increased inner surface area is balanced by the increased leakage of enzyme and these occur with a decrease of monomer concentration. Immobilization by physical entrapping was also studied by Rosiak [26], Carenza [27] and Ha [28]. 

Picture inflating a basketball. As you add more and more air to it, more molecules collide against the inside wall of the basketball. Each collision exerts a force on the basketball s inner surface area. The collective number of collisions as well as the strength of the force form the net or overall gas pressure. Since the molecules move in all directions, the net pressure exerted will be equal throughout. (Figure 11.8 illustrates this.)... 

Ai - inner surface area of the pipe, m2 d0 and di - outside and inside diameters of the pipe, m t - thickness of the insulation, m kp - thermal conductivity of pipe (usually steel), W/m.°C... 

To calculate the reduction in the concentration of surfactant in the fluid by adsorption it is necessary to have an estimation of the inner surface area of the reservoir. This parameter is related to the porosity of the medium and to its permeability. Attempts have been made to correlate these two quantities but the results have been unsuccessful, because there are parameters characteristic of each particular porous medium involved in the description of the problem (14). For our analysis we adopted the approach of Kozeny and Carman (15). These authors defined a parameter called the "equivalent hydraulic radius of the porous medium" which represents the surface area exposed to the fluid per unit volume of rock. They obtained the following relationship between the permeability, k, and the porosity, 0 ... 

Polymer Cross-linking agent Comonomer Percentage of cross-linking (%) Inner surface area (m /g) Splitting percentage (%) Swellability Separation factor (a)... 

As regards the outer and inner surface areas of the amphiphiles, the results indicate that these should be about the same, and close (within 1 %) to the area in lamellar bilayers, as observed. - ... 

A test is conducted to determine the overall heat transfer coefficient in an automotive radiator that is a compact cross-flow water-to-air heat exchanger with both fluids (air and water) unmixed (Fig, 11-22). The radiator has 40 tubes of internal diameter 0.5 cm and length 65 cm in a closely spaced plate-finned matrix. Hot v ter enters the tubes at 90°C at a rate of 0.5 kg/s and leaves at 65°C. Air flows across the radiator through the interfin spaces and is heated from 20 C to 40°C. Determine the overall heat transfer coefficient (7,-of this ra- w c diator based on the inner surface area of the tubes. 

SOLUTION During an experiment involving an automotive radiator, the inlet and exit temperatures of water and air and the mass flow rate of water are measured. The overall heat transfer coefficient based on the inner surface area is to be determined. 

Water a( an average temperature of 110°C and an average velocity of 3.5 m/s flows tlirough a 5-m-long stainless steel lube (k = 14.2 W/m °C) in a boiler. The inner and outer diameters of the lube are 0, = 1.0 era and 1.4 Cm, respectively. If the convection heat transfer coefficient at the outer surface of the tube where boiling is taking place is /i = 8400 W/m C, determine the overaU heat transfer coefficient //, of this boiler based on the inner surface area of the tube. 

A tesi is conducted lo detennine the overaU heal transfer coefficient in a shell-and-Cube oil-to-watcr heat exchanger that has 24 tubes of internal diameter 1.2 cm and length 2 m in a single. shell. Cold water (c, = 4180 J/kg - "C) enters the tubes at 20°C at a rate of 3 kg/s and leaves at 55°C. Oil Cp = 2150 J/kg C) flows through the shell and is cooled from 120 C to 45 C. Detennine the overall heal transfer coefficient Ui of this heat exchanger based on the inner surface area of the tubes, /tnsiver 8.31 kW/m C... 

A double-pipe counter-flow heat exchanger is to cool ethylene glycol (cp = 2560 J/kg °C) flowing at a rate of 3.5 kg/s from 80 C to 40°C by water (c, = 4180 J/kg C) that enters at 20°C and leaves at 55 C. The overall heat transfer coefficient based on the inner surface area of the lube is 250 V/m "C. Determine (o) the rate of heat transfer, (A) the mass flow rate of water, and (c) the heat transfer surface area on the inner side of the tube. 

Hot water coming from the engine is to be cooled by ambient air In a car radiator. The aluminum tubes in which the water flows have a diameter of 4 cm and negligible thickness. Firs are attached on the outer surface of the lubes in order to increase Ihe lieat transfer surface area on the air side. The heat transfer coefficients on the inner and outer surfaces are 2000 and 150 W/m °C, respectively. If the effective surface area on the finned side is 10 limes the inner surface area, the overall heat transfer coefficient of this lieat exchanger based on the inner surface area is... 

In other ways, a zeolite is like a fluid solvent. A zeolite may host a broad range of guests, and solution (sorption) may occur only slightly or to a great degree. The opportunities for interaction on the extensive inner surface areas of zeolites (extent of sorption) are comparable to those offered by conventional solvents (solubility). Even stronger interaction opportunities, comparable in energy to ordinary chemical bonds, more like those offered by clean surfaces, may be available. 

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