Wall loss

Principle of Magnetic Flux Leakage for detection of wall loss... 

Wall losses through most refractory walls are ca 10% of the heat suppHed by the fuel. Losses increase with rising operating temperature. In special cases, eg, in glass tanks, losses can be as high as 30—35%. In these instances, very high values are requked to maintain the refractory at a temperature below which it does not melt or coUapse. 

Lr = dimensionless refractoiy-wall loss. m = mass flow rate. n = refractive index. 

L/A /(GSi)rOTf = Lr, refractory-wall loss number (dimensionless)... 

Particle bounce, wall losses labor intensive... 

Wall Loss of Oxidation Products. It is known that some classes of hydrocarbons (the higher terpenes, for instance) are prolific aerosol formers when subjected to atmospheric oxidation. Other classes, aromatic hydrocarbons for instance, although they do not form large amounts of suspended aerosol, have been shown to lose (at least under some conditions) large amounts of oxidation products to the reaction vessel walls. The fate of these oxidation products in the open atmosphere remains open to question, as does the extent to which they continue to participate in gas-phase chemistry (187). 

NP Vaughan. The Andersen Impactor calibration, wall losses and numerical simulation. J Aerosol Sci 20 67-90, 1989. 

Wall-loss factor. The wall-loss factor, xw, is given in terms of the compartment heat transfer surface area, A, and the overall heat transfer coefficient, h, as given by Equation (11.17) ... 

Fortunately, the kinetics of the wall loss, measured from the decay of the reactive species in the absence of added reactant, are generally observed to be first order, so that corrections for these processes can be readily incorporated into the kinetic analyses. When these wall losses are significant, the integrated form of the rate expression (T) for reaction (17) of A + B becomes... 

Ozone decomposes on surfaces, the rate depending on the nature of the particular surface and whether it has been previously conditioned by exposure to 03. While this heterogeneous decomposition is much slower than the wall loss of OH, the homogeneous gas-phase... 

Such experiments can also be carried out with 03 in great excess however, a technique must be available for following the concentration of the reactant X with time, and corrections may have to be made for changing ozone concentrations due to wall losses during the experiment. In addition, interferences from secondary reactions are more likely under these conditions. 

McMurry, P. H., and D. J. Rader, Aerosol Wall Losses in Electrically Charged Chambers, Aerosol Sci. Technol., 4, 249-268 (1985). 

Grosjean, D Wall Loss of Gaseous Pollutants in Outdoor Teflon Chambers, Environ. Sci. Technol., 19, 1059-1065 (1985). 

Figure 5 is a photograph of the parts of Harp s (23) cascade impactor. A special feature of this instrument is that wall loss of droplets in the sampling port and on the jets for the second and third stages is greatly reduced by passing air through the walls of these three parts which are made of porous metal. 

However, the intercept of the straightline d/dt (In [CIO]) = f ([DMS]) -, which was found to be (80 5)s indicates a substantial wall reactivity of ClO in the presence of DMS. Some dependence of CIO wall loss with DMS concentration can exist if the reactor wall is not saturated with DMS in the range of DMS concentration used to derive kj from the plots - d In [QO] /dt = f([DMS]). In such a case k2 is an upper limit of the rate constant of the homogeneous reaction. In the absence of any indication of the saturation degree of the reactor wall in this study, k should be considered as an upper limit for the rate constant. Such complications have not been observed for the reaction BrO + DMS —> products (3). For DMS and BrO concentrations ranging from 15 x 1014 to 7.9 x 1014 molecules cm 3 and from 1.33 x 1013 to 1.55 x 1013 molecules cm 3, respectively, die following rate constant was determined at 298 K and 1.4 Tom... 

The yields of SO2 and DMS02 were, on a molar basis, 60 10% and approximatly 30%, respectively. Because of a series of difficulties in calibration, wall loss, and aerosol formation it is not possible to indicate whether the observed yield of DMSO is being over- or underestimated. As stated above the observed products snow that both abstraction and addition reaction pathways are operative,... 

The experiments were performed by flushing NjO< from an external 201 bulb into the 420 1 reactor containing DMSO and isobutene in 500 Torr of synthetic air. The decays of DMSO and isobutene were monitored for a period of 5 min using FT-IR spectroscopy. Over the time period of the investigation the wall loss of DMSO was small (3%) compared to reaction with NO3. A typical plot of the results according to Equation (3) is shown in Figure 3. From a total of 6 experiments a rate constant ratio k (NO3 + DMSO) / k (NO3 +... 

As for the studies on OH + DMSO a correction had to be made for the wall loss of DMSO which contributed, in this case, approximately 40% to the DMSO decay. After correction for these wall losses rate constants ratios, k(Cl + DMSO)/k(Cl + propene), of 0.3 0.08 and 0.22 0.06 were obtained for the experiments performed in air and N2, respectively, from a total of five experiments in each diluent gas. Using the rate constant for Cl + propene quoted above values of (7.4 1.8)x 10-11 cm3 s 1 in air and (5.4 1.4)x 10-1 cm3 s 1 in N2 were obtained for the reaction of Cl with DMSO. The errors are 1 a and represent precision only. The rate constant obtained for the reaction of Cl with DMSO in N2 is approximately 40% lower than the rate constant obtained for the reaction in air. The results suggest a possible 02 dependence of the reaction rate. The rate constant for the reactions of OH with DMS (16.18) and CS2 and of Cl with CS2 (28) are known to be dependent on the oxygen concentration. However, in the present case further kinetic studies are needed... 

The principal problems in determining size distribution parameters with cascade impactors are wall losses, inefficient collection due to particle bounce, deposition of gas-phase species on impaction substrates, and deposition of fine particles from boundary layers. 

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