Mechanical similarity

Mechanical similarity in a SFPC system can only be achieved if both kinematic and dynamic similarity requirements are satisfied. In other words, kinematic similarity is achieved when corresponding particles trace out geometrically similar patterns in corresponding intervals of time. Times are measured from an arbitrary zero for each system, and corresponding times are defined as times such that t it = i is 

If two geometrically similar fluid systems are kinematically similar, then the flow patterns are geometrically similar, and heat- or mass-transfer rates in the two systems will bear a simple relation to one another. Kinematic similarity in fluids entails both geometrically similar eddy systems and geometrically similar streamline boundary films. Hence, if L is the linear scale ratio, heat- and mass-transfer coefBcients in the prototype will be 1/L times those in the model, fi om which the total quantities for heat or mass transferred can easily be calculated, 

Dynamic similarity is achieved when the forces retarding or accelerating the movement of mass within the system are correspondingly similar. These are the forces that define the dynamics of fluid systems in motion. In a supercritical fluids cleaning system, the forces of pressure, inertia, viscosity, and interfacial interactions are important for scaleup when it is desirable to predict either pressure drops or power consumption. For most cleaning systems, however, dynamic similarity is usually only of importance as an indirect means of establishing kinematic similarity. 

Mechanical similarity introduces the major element of motion. It basically deals with systems in motion. It can be divided into two major subclasses. 

1 Dynamic Similarity Geometrically similar moving systems are dynamically similar when the ratios of various forces affecting the motion are equal  

the parallelograms or polygons of forces for corresponding particles should be geomehically similar. A corollary of this definition is that the ratios of different forces in the same system shall be constant  

Ratio of buoyancy force and surface tension force 

Ratio of inertial force and gravitational force. For liquids undergoing rotational motion ratio of centripetal force and gravitational force Ratio of rate of mass transfer in the presence of a chemical reaction and that in the absence of a chemical reaction Ratio of viscous force and interfacial force 

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The oxidation of 3-substituted indole to oxindoles can also be done with a mixture of DMSO and cone, hydrochloric acid[6-9]. This reaction probably involves a mechanism similar to the halogenation with a protonated DMSO molecule serving as the electrophile[10]. 

These monomeis were mixed with nonfluoiinated acrylates and cured conventionally, such as by free-radical mechanism. Similar monomers and their... 

The reaction of 2iac and water is not a simple homogeneous one. Rather it is a heterogeneous electrochemical reaction, involving a mechanism similar to that of a battery. There are two steps to the reaction 2iac dissolves at some locations as shown ia equation 8 while hydrogen gas is generated at other sites. 

Azoleacetic acids with a carboxymethyl group also decarboxylate readily, e.g. all three thiazole isomers, by a mechanism similar to that for the decarboxylation of /3-keto acids cf. Section 4.02.3.1.2. The mechanism has been investigated in the oxazole case, (396) (397) (398) <72JCS(P2)1077). 

The suction gas which enters from the periphery is trapped by the scrolls. The closed volumes move radially inward until the discharge port is reached, when vapor is pressed out. The orbiting scroll is driven by a short-throw crank mechanism. Similar to screw compressors, internal leakage should be kept low, and is occurring in gaps between cylindrical surfaces and between the tips of the involute and the opposing scroll base plate. 

The commercial polymers are mechanically similar to PTFE but with a somewhat greater impact strength. They also have the same excellent electrical insulation properties and chemical inertness. Weathering tests in Florida showed no change in properties after four years. The material also shows exceptional non-adhesiveness. The coefficient of friction of the resin is low but somewhat higher than that of PTFE. Films up to 0.010 in thick show good transparency. 

In basic solution, a mechanism similar to the Bac2 mechanism for ester hydrolysis is believed to operate ... 

Breakdown of the amide dihydrate occurs by a mechanism similar to its formation. The ionized aspartate carboxyl (Asp in Figure 16.27) acts as a general base to accept a proton from one of the hydroxyl groups of the amide dihydrate, while the protonated carboxyl of the other asparate (Asp in this case) simultaneously acts as a general acid to donate a proton to the nitrogen atom of one of the departing peptide products. 

The structure of the product of the Reimer-Tiemann reaction of 1,2,3-trimethylindole (24) has been confirmed as 3-dichloromethyl-1,3-dimethyl-2-methyleneindoline (25) by spectroscopy and oxidation to the iV -methyloxindole when the dichlorocarbene was generated under neutral conditions a ring-expanded product, 3-chloro-1,4-dimethyl-2-methylene-1,2-dihydroquinoline (26) could be isolated and oxidized to the corresponding a-quinolone. These reactions presumably proceed by mechanisms similar to those discussed for 2,3-di-... 

By a mechanism similar to that discussed in relation to platinum coating, titanium can function as a conducting jig to support aluminium components and assemblies in conventional anodising baths. In this application the exposed titanium acquires the insulating film, but allows current to pass to the aluminium at the points of contact . 

Water adds to alkenes to yield alcohols, a process called hydration. The reaction takes place on treatment of the alkene with water and a strong acid catalyst (HA) by a mechanism similar to that of HX addition. Thus, protonation of an alkene double bond yields a carbocation intermediate, which reacts with water to yield a protonated alcohol product (ROH2+). Loss of H+ from this protonated alcohol gives the neutral alcohol and regenerates the acid catalyst (Figure 7.2). 

Figure 7.3 Mechanism of the oxymercuration of an alkene to yield an alcohol. The reaction involves a mercurinium ion intermediate and proceeds by a mechanism similar to that of halohydrin formation. The product of the reaction is the more highly substituted alcohol, corresponding to Markovnikov regiochemistry.

Iodine azide, 1N3, adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as 1-butene is used, only one product results ... 

Like the mitomycins, FR900482 (6), FR66979 (7), FK973 (8), and FK317 (9) have also been shown to crosslink DNA both in vivo [68-70], and in vitro after reductive activation [71-76] with selectivity for the 5 -CpG-3 sequence [77]. The mechanism outlined in Figure 11.2 was originally proposed by Goto and Fukuyama [78] and has been verified by the experimental work of Williams and Hopkins [71-77, 79]. Reduction of the N-O bond produces intermediate 27, which can lose a molecule of water to form 28, which reacts with DNA by a mechanism similar to that found... 

Acyloins (a-hydroxy ketones) are formed enzymatically by a mechanism similar to the classical benzoin condensation. The enzymes that can catalyze reactions of this type arc thiamine dependent. In this sense, the cofactor thiamine pyrophosphate may be regarded as a natural- equivalent of the cyanide catalyst needed for the umpolung step in benzoin condensations. Thus, a suitable carbonyl compound (a -synthon) reacts with thiamine pyrophosphate to form an enzyme-substrate complex that subsequently cleaves to the corresponding a-carbanion (d1-synthon). The latter adds to a carbonyl group resulting in an a-hydroxy ketone after elimination of thiamine pyrophosphate. Stereoselectivity of the addition step (i.e., addition to the Stand Re-face of the carbonyl group, respectively) is achieved by adjustment of a preferred active center conformation. A detailed discussion of the mechanisms involved in thiamine-dependent enzymes, as well as a comparison of the structural similarities, is found in references 1 -4. 

Since n bonding is believed to be more important in low oxidation states, as d orbitals contract with increasing oxidation state leading to poorer dw-pw overlap, this would not be expected on the basis of a 7r-bonding mechanism. Similarly, one can compare /(Pt-P) for pairs of isomers in the +2 and +4 states in a planar platinum(II) complex, the platinum 6s orbital is shared by four ligands whereas in an octahedral platinum(IV) complex it is shared by six ligands. Therefore, the 6s character is expected to be only 2/3 as much in the platinum(IV) complexes, correlating well with the 7(Pt-P) values, which can be taken to be a measure of the a-character in the bond. 

A linear mechanism similar to the accepted mechanisms for Ziegler-Natta polymerization, which has been proposed, e.g. by Marshall and Ridgewell (21), is also excluded by the tracer experiments. 

The efficiency of the halide- radical transformation is reported to be near quantitative. The yield of block or graft is then limited by the efficiency of the halide synthesis. Whether AB or ABA blocks are formed depends on the termination mechanism. Similar halo-compounds have been used to initiate A TRP (Section 9.4). 

Homeostasis, a mechanism similar to chemical equilibrium, allows living... 

The compound Rh2(02) may be regarded as the metal-metal-bonded dimer of the parent monomer RhCO ), presumably formed by a mechanism similar to that described for Ag2(CO) (118). The lower-stoichiom-... 

Esterases have a catalytic function and mechanism similar to those of lipases, but some structural aspects and the nature of substrates differ [4]. One can expect that the lessons learned from the directed evolution of lipases also apply to esterases. However, few efforts have been made in the directed evolution of enantioselective esterases, although previous work by Arnold had shown that the activity of esterases as catalysts in the hydrolysis of achiral esters can be enhanced [49]. An example regarding enantioselectivity involves the hydrolytic kinetic resolution of racemic esters catalyzed by Pseudomonasfluorescens esterase (PFE) [50]. Using a mutator strain and by screening very small libraries, low improvement in enantioselectivity was... 

There is much evidence for this mechanism, similar to that discussed for ester hydrolysis. A MO study on the mechanism of amide hydrolysis is available. In certain cases, kinetic studies have shown that the reaction is second order in OH , indicating that 107 can lose a proton to give 108. Depending on the nature... 

It must be emphasized once again that the rules apply only to cycloaddition reactions that take place by cyclic mechanisms, that is, where two s bonds are formed (or broken) at about the same time. The rule does not apply to cases where one bond is clearly formed (or broken) before the other. It must further be emphasized that the fact that the thermal Diels-Alder reaction (mechanism a) is allowed by the principle of conservation of orbital symmetry does not constitute proof that any given Diels-Alder reaction proceeds by this mechanism. The principle merely says the mechanism is allowed, not that it must go by this pathway. However, the principle does say that thermal 2 + 2 cycloadditions in which the molecules assume a face-to-face geometry cannot take place by a cyclic mechanism because their activation energies would be too high (however, see below). As we shall see (15-49), such reactions largely occur by two-step mechanisms. Similarly. 2 + 4 photochemical cycloadditions are also known, but the fact that they are not stereospecific indicates that they also take place by the two-step diradical mechanism (mechanism... 

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