Deposit direct weighing

The simplest method for assessing the extent of deposition on test surfaces in the laboratory is by direct weighing. The method requires an accurate balance so that relatively small changes in deposit mass may be detected. It may be necessary to use thin walled tube to reduce the tare mass so as to increase the accuracy of the method. Mott and Bott [1991] used the technique satisfactorily, to estimate the amount of biofouling that had accumulated on the inside of simulated heat exchanger tubes. The mean thickness of the biofilm over the whole inner surface of the tube may be made from a knowledge of the deposit density for biofilms the density may be assumed to be that of water since the biofilm is substantially made up of water [Patel 1981]. The inside surface area of the tube is given by... 

Besides the standard weighing methods, it has also been proposed to use the piezoelectric properties of quartz for mass determination. Changes in the amount of sample that has been deposited directly on a quartz surface cause a change in the oscillation frequency of the quartz crystal. Mass changes as small as 10 g can be determined by this method. The changes in frequency with temperature must be established by calibration, or the experimentation must be done isothermally. ... 

Directions for determining in Water the Nonvolatile Organic Matter—Silica, Iron, Alumina arid Phosphates Lime and Magnesia.—Evaporate slowly half a gallon of wator to about a pint, over a gas flame then transfer tire dish -to a sand-bath, and continue the evaporation till the bulk is reduced to about two fluid ounces. Now accurately weigh a dean platinum dish. Scrape the deposit carefully from the bottom of the porcelain basin, and rub off that which cannot be removed by the platinum knife with the middle finger rinse the whole into tire platinum dish, and then evaporate to dryness on a water-bath. Be careful to observe that every particle of the deposit is removed from the porcelain vessel, When the residuo Is dry place the dish in an air-hath, and heat it for half on hour or on hour at a temperature of 260°,... 

A quartz tube with diameter of 100 mm permits direct observation of the process with normal coal. The cyclone furnace produces steady combustion at gas temperature of 700 C but can also be extended to a temperature level of more than lOOO C. Combustion of salt coals is difficult to observe because the alkalines vaporize from the fuel and condense on the colder quartz tube wall to form an opaque layer. This problem is partially overcome by inserting a probe which measures gas and wall temperature and allows the slagging process to be determined as a function of temperature by weighing the deposit. Measurement of deposit hardness supplies additional information on the character of the clinker formed. The cyclone separator behind the reactor allows an analysis of structural changes which occur in the finest grain. The test results obtained indicate the cyclone reactor can be improved by automation (for easier operation) and by standardization to result in a piece of equipment capable of evaluating slagging tendencies. 

The only quantity in this equation that can be measured directly is the total current density. The partial current densities for each of the three reactions are obtained by weighing the deposit and analyzing its composition. Each of the current densities is calculated from the Butler-Volmer equation... 

Cordierite monoliths were coated with an alumina washcoat and stabilised at 550°C. Some of the samples were then immersed in either an aqueous solution of cerous or cobalt nitrate, dried and calcined in air at 550°C at which the metal nitrates decomposed into their oxides [11]. The samples were weighed and the procedure was repeated until 40 mg of the metal oxide had been deposited onto the alumina washcoated monolith samples. Pt and Pd were applied by direct impregnation using aqueous solutions of HaPtCla and PdCb followed by diying and calcination in air at 550°C [8]. The Pt and Pd loadings (2.0 and 1.09 mg, respectively) of the catalysts were equal on molar basis. The nominal composition of the eight catalysts prepared are listed in Table 1. 

Mass accumulation probes as the name suggests, are used to obtain a deposit that can be weighed, i.e. a direct measurement of the fouling per unit area of probe for given conditions. The technique has also been used to assess corrosion under the conditions within a combustion space. 

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