Stopped pressure dependent

Measurements of filtration rates should be repeated at different pressures or different vacuum levels. This gives information on the influence of pressure on the specific cake resistance. The specific resistance of cakes that are difficult to filter is often pressure-dependent. Thus, use of excessive pressure can result in blocking of the cake, causing filtration to stop. In the case of compressible cakes, information is needed over the whole range of pressures being considered for industrial filters since extrapolation of compressibility beyond the experimentally covered region is always risky. The larger the scale of an experimental filter, the less risky predictions based on the experimental data. 

Fig. 9. Pressure dependence of the proton stopping cross section in Si as obtained in this work.

The influence of temperature can be studied, and the activation parameters (e g. the activation enthalpies and entropies) can be calculated. If necessary, the high-pressure stopped-flow technique can be used to study the pressure dependence of reactions, and the corresponding volumes of activation may be calculated. 

To determine the activation parameters AH, A and Ay for the binding and release of NO, the kinetics was stndied at different temperatures (6-30 °C) and hydrostatic pressnres (0.1-170 MPa). The kon and kotr values determined from hnear dependences of kobs versus [NO] at each temperature and pressure allowed the construction of Eyring plots for the on and off reaction. Activation parameters can be calculated from the plots. Because of the small intercepts in the plots of kobs versus [NO] in the pressure-dependent study, the activation volume for the off reaction could not be determined accurately in this way. This value, however, could be measured in a stopped-flow experiment using the NO-trapping method. 

As osmosis proceeds, pressure builds up on the side of the membrane where volume has increased. Ultimately, the pressure prevents more water from entering, so osmosis stops. The osmotic pressure of a solution is the pressure needed to prevent osmosis into the solution. It is measured in comparison with pure solvent. The osmotic pressure is directly related to the different heights of the liquid on either side of the membrane when no more change in volume occurs. Osmotic pressure depends on the temperature and the original concentration of solute. Interestingly, it does not depend on what is dissolved. Two solutions of different solutes, for example alcohol and sugar, will each have the same osmotic pressure, provided they have the same concentration. Osmotic pressure is therefore a colligative property of solutions, one which depends only on the concentration of dissolved particles, not on their chemical identity. 

High pressure stopped-flow experiments upon the reaction of hexaaquairon(III) and promazine (R = CH3CH2CH2N(CH3)2, see reaction given below) yielded AV values of -6.3 and -12.5 cm mof for the forward and reverse reactions, respectively. [139] The derived reaction volume of 6.2 cm mof has been confirmed by calculation from the pressure dependence of the equilibrium constant obtained from the variation of the UV/Visible spectra as a function of pressure. The volume profile (see Figure 9) displays the fact of a compact transition state, and the positive reaction volume was suggested to arise from charge dilution in proceeding from the reactants to Fe(aq) and the promazine cation radical. 

Y and Lu (0001) surfaces with a sticking coefficient similar to that of oxygen. Surplice and Brearley (1978) have measured the work function change on an Er film exposed to CO. For small doses the work function was lowered by about 45-60 meV, whereas further exposure led to an increase and saturation at about 700 meV above the clean metal value. These results could be confirmed qualitatively by Strasser et al. (1982). In dynamic work function measurements a small but reproducible initial decrease of 5-10 meV was followed by an increase to +800-1000 meV after 250 L exposure (where still no saturation was observed). The slope seemed to be slightly pressure dependent. A slow decay of the work function after stopping CO admission indicated redistribution processes (Surplice and Brearley, 1978). Work function changes in the Yb/CO system (Strasser et al., 1982) showed similar trends. The initial decrease of -80meV was more pronounced. 

The Lewis-acid promoted [4 + 2] cycloadditions are the most extensively smdied. However, nitroalkenes can react as heterodienes without Lewis acid activation under high pressure as well [100]. For example, the cycloaddition of nitro-alkene 44 (Scheme 16.18) with ethyl vinyl ether is accelerated in a pressure-dependent manner but does not stop after the [4 + 2] step [101]. The intermediate nitronate 67a undergoes a further [3 + 2] cycloaddition to form nitroso acetal 68a as the major product (67a/68a l/6). Complete conversion is observed at pressures above 8 kbar after only 1 h. For comparison, the same reaction requires a large excess (90 equiv) of the dienophile to reach completion at ambient pressure in ethanol after 5 days. Nitronate 67a is formed with... 

The left-hand end of the activated monomer is sealed off by the OH terminator, but the right-hand end (with the star) is aggressively reactive and now attacks another ethylene molecule, as we illustrated earlier in Fig. 22.1. The process continues, forming a longer and longer molecule by a sort of chain reaction. The —OH used to start a chain will, of course, terminate one just as effectively, so excess initiator leads to short chains. As the monomer is exhausted the reaction slows down and finally stops. The DP depends not only on the amount of initiator, but on the pressure and temperature as well. 

A low-pressure cut-out switch is usually fitted to stop the compressor under these circumstances. Settings may be 0.6-1.0 bar below the design evaporator pressures, but depend very much on the type of system. The cut-out setting should be above atmospheric pressure if possible to avoid the ingress of air through any leaks. 

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