Mass loss rates

Anodes for boilers can be tested by such methods. Good-quality magnesium anodes have a mass loss rate per unit area < 30 g m d", corresponding to a current yield of >18% under galvanostatic anode loading of 50 /xA cm" in 10 M NaCl at 60°C. In 10 M NaCl at 60°C, the potential should not be more positive than t/jj = -0.9 V for the same polarization conditions [27],... 

Six iron anodes are required for corrosion protection of each condenser, each weighing 13 kg. Every outflow chamber contains 14 titanium rod anodes, with a platinum coating 5 /tm thick and weighing 0.73 g. The mass loss rate for the anodes is 10 kg A a for Fe (see Table 7-1) and 10 mg A a for Pt (see Table 7-3). A protection current density of 0.1 A m is assumed for the coated condenser surfaces and 1 A m for the copper alloy tubes. This corresponds to a protection current of 27 A. An automatic potential-control transformer-rectifier with a capacity of 125 A/10 V is installed for each main condenser. Potential control and monitoring are provided by fixed zinc reference electrodes. Figure 21-2 shows the anode arrangement in the inlet chamber [9]. 

FIRAC is a computer code designed to estimate radioactive and chemical source-terms as.sociaied with a fire and predict fire-induced flows and thermal and material transport within facilities, especially transport through a ventilation system. It includes a fire compartment module based on the FIRIN computer code, which calculates fuel mass loss rates and energy generation rates within the fire compartment. A second fire module, FIRAC2, based on the CFAST computer code, is in the code to model fire growth and smoke transport in multicompartment stmetures. 

Mass loss in rotating star is asymmetric. Very hot star have a dominant polar wind. Stars with Teff below about 24 000 K, due to their larger opacities, may have an equatorial ejection forming a disc. Polar ejection removes little angular momentum, while equatorial ejection removes a lot. ft is thus also important to consider the wind asymmetries in massive rotating stars. Also, rotation produces a general enhancement of the mass loss rates [7]. 

Thermogravimetric analysis (TGA) measures cellulose pyrolytic mass loss rates and activation parameters. The technique is relatively simple, straightforward and fast, but it does have disadvantages. One disadvantage is that determination of the kinetic rate constants from TGA data is dependent on the interpretation/analysis technique used. Another disadvantage of TGA is that the rate of mass loss is probably not equivalent to the cellulose pyrolysis rate. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

The objective of this research was to examine the effect of crystallinity, additives and data analysis technique on isothermally pyrolyzed cellulose. The Ea, activation enthalpy (AH+) and activation entropy (AS+) were determined from the mass loss rates. This data was used to develop an understanding of how cellulose pyrolysis is affected by crystallinity and additives and how the results obtained are dependent on the data analysis technique. 

Tables I, III, V, and VII give the kinetic mass loss rate constants. Tables II, IV, VI, and VIII present the activation parameters. In addition to the activation parameters, the rates were normalized to 300°C by the Arrhenius equation in order to eliminate any temperature effects. Table IX shows the char/residue (Mr), as measured at 550°C under N2.

The mass loss rates for the boric acid samples were comparable to the untreated samples, despite a higher char yield (Table IX) for the treated samples. This was unexpected since the role of a wood fire retardant is to increase the char by increasing the dehydration reaction (1,3,7). Thus, a fire retardant treated sample will actually pyrolyze at a lower temperature. Data from Table III suggests that boric acid may form more char by suppressing formation of flammable volatiles instead of by increasing the dehydration rate. 

Because heat of combustion of the volatile product is not the same as that of whole wood, one cannot estimate heat release rate based on mass loss rate as can be done with ideal fuels such as gases, liquids, and some noncharring solid materials. Thus, measuring heat release rate rather than mass loss rate is appropriate for wood and charring materials. Several bench-scale calorimeters have been developed to measure heat release rate of materials (1,11,12,13). 

Mass loss rate of product first ignited... 

Thus, smoke toxicity is often very closely associated simply with the mass loss rate, since the toxicity in a fire scenario will be primarily a function of the mass ofsmoke per unit volume and per unit time being emitted into the ambient atmosphere. 

Toxic potency of smoke data can be used as one of the inputs in fire hazard assessment. In particular, they can be combined with average mass loss rates and times to ignition to obtain a quick estimate of toxic fire hazard. 

This parameter, the smoke parameter, is based on continuous mass loss measurements, since the specific extinction area is a function of the mass loss rate. A normal OSU calorimeter cannot, thus, be used to measure smoke parameter. An alternative approach is to determine similar properties, based on the same concept, but using variables which can be measured in isolation from the sample mass. The product of the specific extinction area by the mass loss rate per unit area is the rate of smoke release. A smoke factor (SmkFct) can thus be defined as the product of the total smoke released (time integral of the rate of smoke release) by the maximum rate of heat release [19], In order to test the validity of this magnitude, it is important to verify its correlation with the smoke parameter measured in the Cone calorimeter. 

Furthermore, it has been shown that the time period until ignition occurs, in the Cone calorimeter, is proportional to the inverse of the flame spread rate [16]. The Cone calorimeter can also be used to provide the mass loss rate information required for the simplified classification into categories of toxic hazard [1] quick toxic hazard assessment. Thus, the NBS Cone calorimeter is a very useful tool to overcome some of the disadvantages associated with measuring a single property at a time. 

Mass Loss Rate as a Function of Temperature. The most commonly used technique is thermogravimetry (TG). The basic components of modern TG have existed since the early part of this century (22-2 4). 

Mass Loss Rate as a Function of External Heat Flux. The technique for the measurement of mass loss rate as a function of heat flux was developed in 1976 at FMRC using the Small-Scale Flammability Apparatus (8 ). Several other flammability apparatuses are now available for such measurements, such as OSU Heat Release Rate Apparatus (13) and NIST Cone Calorimeter (1 4). 

For the assessment of flame heat flux, expected in large-scale fires, 0.10 x 0.10 m samples with edges covered tightly with heavy duty aluminum foil, were burned in 40 oxygen concentration without the external heat flux. Mass loss rate was measured and Equation (1) was used to calculate flame heat flux. 

Describe measurements of mass loss rates of various electrical PVC products, by thermoanalytical experiments. 

The average rate of mass loss is calculated from the amount of mass lost and the corresponding time period. The calculations in Table I at 573 K represent the average mass loss of isothermal dehydrochlorination. Thus, the values in Table I (3.4 %/min for blue conduit, 2.9 %/min for grey conduit and 2.3 %/min for wire coating) represent a reasonable estimate of the mass loss rate of the PVC products in a fire, at a temperature not exceeding 563 K. 

Source Maeder (1992) for the case Z = 0.02, Y = 0.28, high mass-loss rates. 

The distribution function for field stars in the halo is reasonably well fitted by the Simple model equation (8.20) with a small remaining gas fraction, but with a very low effective yield p 10-11Z for oxygen (see earlier comments on dwarf galaxies). This was first noted (actually for globular clusters) by Hartwick (1976), who pointed out that it could be readily explained by continuous loss of gas from the halo in the form of a homogeneous wind with a mass loss rate from the system proportional to the rate of star formation. In this case,... 

A flat material of thickness is placed on a hot plate of controlled temperature Tb. The material is energetic and exothermic with a heat of combustion of Ahc and its reaction is governed by zeroth-order kinetics, Ae E RT the mass loss rate per unit volume. Notation is as used in the text. The differential equation governing the process to ignition is given as... 

Using the assumption of a minimum flame temperature needed for ignition of the mixture, determine the minimum fuel mass loss rate per unit surface area (m l) to cause flame propagation through the boundary layer. The heat of combustion that the volatile wood produces (Ahc) is 15 kJ/g. (Hint the adiabatic flame temperature at the lower flammable limit for the mixture in the boundary layer must be at least 1300 °C.)... 

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