Rate Of Heat Evolution Research Articles

Chemistry of Belousov-type oscillating reactions

The heat output and the accumulation of monobromomalonic acid during chemical oscillation in the bromate, malonic acid, sulphuric acid and catalyst [Ce(III), Mn(II), Fe(phen)2+3, Ru(dipy)2+3] systems were measured and the results interpreted. The behaviour of the reacting oscillating systems depends to a certain extent on the catalyst applied. Both the rate of heat evolution and the rate of accumulation of monobromomalonic acid are periodic. The heat of the cerium-catalysed Belousov oscillating reaction is 130 ± 5 kJ mol–1 bromate.

Periodicity in the rate of heat evolution during the temporal oscillation in the 2,4-pentanedione-bromate-catalyst system

Periodicity in the rate of heat evolution during the temporal oscillation in the 2,4-pentanedione-bromate-catalyst system

BIOENERGETIC APPROACH TO ETHANOL-LIMITED CULTURE OF SACCHAROMYCES CEREVISIAE

Kinetic equations dealing with rates of substrate consumption, cell growth, respiration, product formation and heat evolution have been derived for Saccharonzyces cerevisiae growing on ethanol as the sole carbonaceous material. These equations which could all be shown as functions of ethanol and dissolved oxygen concentrations will be of help to simplify the approach from microbial kinetics to an attempt of optimization in the fermentation industry.

Adsorption and Calorimetric Investigations on Carbon Black Surfaces. III. Immersion Heats in Model Elastomers and Isosteric Heats of Adsorption of C-4 Hydrocarbons

Abstract The heats of immersion of U-1 channel and SAF, SPF, HAF-HS, and HAF furnace blacks have been measured at 25° C in three isoprenoid olefins and four liquid elastomers of the polybutadiene, polyisoprene, and SBR types. An extensive microcalorimeter redesign was necessary because of the high viscosity of these latter fluids. The immersion heats observed with the liquid elastomers were similar to n-decane immersion heats and there was little evidence for specific interactions between these liquids and any of the blacks. The possibility that the very high structure SPF black gives slightly enhanced immersion heats should be further investigated. Since only integral immersion heats could be measured with the non-volatile liquid elastomers, the possibility is not ruled out that specific, relatively high-energy interactions may occur between the adsorbate and a very small fraction of the black surface. The similarities between the immersion heats with n-decane and the liquid elastomers indicate that almost all of the carbon black surface is accessible to the polymer segments. It appears that the rate of heat evolution may be considered a measure of the rate of attainment of intimate molecular contact between the liquid and carbon substrate. The enhancement in heat of wetting with increasing chain length over the C6 to C16 n-alkane series reported by others with a highly uniform, graphitized black was not observed with HAF. Isosteric heats of adsorption of n-butane and butene-1 at low surface coverages on several carbon blacks were calculated from adsorption isotherms obtained with a precision microgravimetric system. The isosteric heats as a function of coverage curves were typical of those expected for heterogeneous surfaces and reflected the presence of high energy physical adsorption sites at low coverages (θ<0.1).

Influence of SO<sub>3</sub> on the Hydration of Aluminous Cement

The authors investigated the hydration of aluminous cement manufactured by the burning process, especially investigated the relationship between the process of heat evolution of the aerated cement and the including SO3.SO3 in the burned aluminous cement clinker remains in the form of calcium sulfoaluminate [3(CaO⋅Al2O3)⋅CaSO4], and it influences the rate of hydration when the cement is aerated.The results obtained are summerized as follows;(1) Both aluminous cement A which contains 0.7% of SO3 and B which contains 0.2% equally had the heat of hydration value 77cal/g, but the time of exothermic peak of A cement delays about 30 to 60 mins. in comparison with B and the pattern on the rate of heat evolution of A changed after aeration, too.(2) Investigating chemical contents of the solution extracted from neat paste mixed for 5 mins., the solubility of A cement changed by aeration from 1, 690 to 990mg/l in Al2O3, 1, 140 to 950mg/l in CaO, 0 to 20mg/l in SO3. In addition, the X-ray figure of the precipitated material changed from β-2CaO⋅Al2O3⋅8H2O plus 3CaO⋅Al2O3⋅CaSO4⋅12H2O to 3CaO⋅Al2O3⋅CaSO4⋅12H2O plus 3CaO⋅Al2O3⋅3CaSO4⋅32H2O.(3) In the case of synthesized 3(CaO⋅Al2O3)⋅CaSO4 the rate of heat evolution is also influenced like A cement by aeration.

Cool-flame oxidation of ketones

The cool flames of three ketones (acetone, methyl ethyl ketone, and diethyl ketone) have been studied in a static system. The pressure, light emission, and temperature of the reacting gases have been measured and recorded simultaneously. The light emission appears as a pale-blue glow to the naked eye, and occurs not only in the cool flame, but also in the slow reaction before and after the passage of the flame. The maximum intensity of light occurs just after the rate of pressure change has reached its maximum value. Even in the slow reaction there are significant temperature increases. In the cool-flame region, the self-heating is even more marked-temperature rises of 20°C before the cool flame, and 120°C in the flame itself frequently being observed. The temperature rise begins at the center of the reaction vessel, and spreads out to the walls. The temperature changes observed in the flames at the critical condition are just sufficient to take the system into the region of negative temperature coefficient. Chemical analysis has shown that there is a considerable build-up of organic peroxides in the cool flame, followed by a very sharp fall as the flame temperature reaches its maximum. These facts combine to support the theory of cool flames put forward by Knox and Norrish and others. In this theory, the cool flame is regarded simply as a “low-temperature” slow reaction in which the rate of heat evolution is greater than the maximum rate of heat loss. Consequently, the reaction accelerates, but when the temperature reaches the negative temperature coefficient region this ceases. At the high temperatures reached, the low-temperature branching intermediate is rapidly destroyed, and so the rate falls. This sequence may be repeated a number of times thus leading to the phenomenon of multiple cool flames.

Calorimetric measurement of free energy utilization by Nitrosomonas and Nitrobacter.

Calorimetric estimates of the utilization efficiency of the free-energy derived from substrate oxidation by cell suspensions of two nitrifying bacteria, Nitrosomonas and Nitrobacter, provided two ranges of values: 11 to 27% and 15 to 51%, respectively. About 15 to 30% of the utilized free-energy is used for driving endergonic reactions other than CO2 fixation, probably the synthesis of polyphosphates. The molar heat of substrate oxidation does not seem to be influenced by the age of cells harvested during growth or by the length of the incubation period during which cells have been kept in a buffer suspension in a starved condition. The loss of respiratory activity measured either by oxygen uptake or heat evolution in the presence of the specific substrate, nitrite or ammonium, decreases according to kinetics which are influenced by the aerobiosis of the suspension. The viability of the starved cells decreases in a way which is similar to that of the respiratory activity. It seemed impossible to obtain cells which had lost their viability but kept the ability to oxidize their substrate. Two inhibitors of the respiratory chain, quinacrine and cyanide, are without effect on the molar heat of substrate oxidation and consequently on the free-energy utilization efficiency. 2.4 dinitrophenol did decrease the rate of heat evolution during substrate oxidation at concentrations at which the rate of oxygen uptake was not depressed, with the consequences that free-energy efficiency was apparently increased.

Radical recombination and heat evolution in H 2-O 2 flames

Fuel-lean H 2 -O 2 -Ar-N 2 O flames were probed: their rates of heat evolution h ˙ were deduced from the temperature traverses; and their concentrations of H atoms deduced on the assumption that −d [N 2 O]/ dt =(known rate constant)×[H][N 2 O]. The h ˙ were corrected for the contribution from nitrous oxide combustion, the corrections averaging 40%, and fitted to h ˙ − c o r r e c t i o n = k Q [ H ] [ O 2 ] [ H 2 O ] , where k is the rate constant for H+O 2 +H 2 O→HO 2 +H 2 O, and Q =heat evolved per mole of HO 2 formed. The reasonable k obtained in this way, 1×10 17 cm 6 mole −2 sec −1 , shows that the heat of H 2 −O 2 combustion is probably evolved at the rate of formation of HO 2 . The dependence of [H] on pressure and mass flow is also consistent with a recombination of radicals via HO 2 . In fuel-rich flames, the rate of heat evolution may be controlled by HO 2 formation far enough upstream where [O 2 ] is considerable and the temperature is relatively low. Later in the reaction zone of rich flames, HO 2 is a less important species.

Heat Evolution Tests with Calcium Aluminate Binders and Castables

A simple device is described for the determination of the rate of temperature increase during the hydration of calcium aluminate binders and castables under semiadiabatic conditions. Automatically recorded time-temperature curves are shown for commercial binders of various compositions. The complex relations between the rate of heat evolution and other properties of commercial and synthetic binders were studied by varying such factors as composition, crystal development, and fineness of the binder. The effect of additions of polyelectrolytes was also explored. It was found that, for a given binder composition, the thermal history of the binder and the amount of admixtures influenced the rate of hydration most markedly. Some correlation between heat evolution and strength development was indicated.

Kinetics of Isoprenepolymerization Initiated with TiCl4—Trialkyl Aluminum

Abstract For the study of the mechanism of polymerization by means of complexes of aluminum organic compounds with titanium chlorides, data on the kinetics of polymerization is of great interest. Up to the present time, the rate of polymerization of propylene has been studied but the interpretation of the kinetic data is difficult because the polymer, which is practically insoluble in the reaction medium, entraps the catalyst resulting in a rate of reaction which is dependent on the diffusion of monomer through the polymer to the active sites. In this work the polymerization of isoprene, which yields polymers soluble in the monomer, in saturated hydrocarbons and in benzene, was studied. The rate of the polymerization reaction was measured by the thermal effect in a calorimeter consisting of a 3.5 1. Dewar flask, with a lid, immersed in a thermostated air bath maintained at approximately the temperature of the reaction. Low viscosity spindle oil, heated to the temperature of the reaction (about 32°), served as the calorimeter fluid. The ampoule holder extended outside of the calorimeter and was connected to a shaking apparatus. The ampoule was divided by a thin partition into two sections each holding 45–50 cc. Into one section previously purified monomers and solvent were distilled. The other section was filled with catalyst components from a Shlenk container. The change in temperature of the calorimeter was determined with a Beckman thermometer with an accuracy of 0.01 °. When the temperature of the calorimeter containing the ampoule remained constant to within 0.01–0.02° for 30–40 minutes, the shaking apparatus was connected and the partition was broken with a striker. Intensive shaking was continued during the entire experiment resulting in mixing of the reaction mixture and of the calorimeter fluid. The rate of reaction was determined by the rate of heat evolution ; in other words, by the temperature rise in the calorimeter. For a rise of 0.1–0.5° the reaction conditions remained practically isothermal. This rise permits the kinetics of the reaction to be observed with sufficient accuracy. Adiabaticity of the calorimeter and the effect of mechanical heat were controlled in separate experiments.

Hot-flame propagation by chain mechanisms

1. The process of chain-thermal flame propagation with a simplified chain decomposition scheme was investigated and a principle for determining the flame velocity from the greatest possible rate of heat evolution was proposed. 2. Approximate formulas were deduced to calculate flame velocity and these gave values which practically coincided with the results of numerical integration of the initial system of equations. The formulas obtained were used for numerical calculations on examples of flame decomposition of hydrazine.

Determining Maximum Heat Load in Equipment Design. Determination of Heat Evolution Rates.

Determining Maximum Heat Load in Equipment Design. Determination of Heat Evolution Rates.

An isothermal calorimeter for measuring low rates of heat evolution over long periods

An isothermal calorimeter for measuring low rates of heat evolution over long periods

Temperature rise in a heat-evolving medium

Among the many problems of heat flow which are of importance to the physicist and the engineer, the question of a heat-evolving medium, i.e ., a medium evolving heat everywhere in its mass, has only recently found a place, and consequently it has as yet been but little considered from the theoretical standpoint. As exceptions to this general statement may be cited the astrophysical problem of heat generation in the interior of a star which has been considered by EDDINGTON, MILNE, and others, and the geophysical problem, treated by JEFFREYS and others, of the effect on the earth ’s cooling of the heat generated by radioactive substances in the earth ’s crust. The increasing use, in engineering construction, of rapid hardening cement with its accompanying rapid heat evolution has caused the temperature rise due to heat of reaction to be no longer a negligible quantity, and it has thus become of considerable practical importance to obtain some means of estimating the magnitude of the temperature rise in large masses of concrete. The theoretical problem thus presented of heat conduction in a chemically reacting mass in which the rate of heat evolution is a function of time, forms the subject of the present paper and, so far as the author is aware, no systematic treatment of this problem has hitherto been published.

A Note on the Experimental Measurement of the High-Frequency Resistance of Wires

The Author refers to a Paper read by him in December, 1909, before the Institution of Electrical Engineers on Quantitative Measurements in Connection with Radio-Telegraphy ( Journal, Inst. Elec. Eng., Vol. XLIV., p. 349, 1910), in which he described an apparatus consisting of a differential air thermometer having tubular bulbs into which similar wires could be placed, and by means of which a comparison could be made of the high-frequency (H.F.) resistance R' of a straight wire and its steady or ohmic resistance R. If two equal wires have passed through one, a steady current A and through the other a H.F. current A1, then if these currents are adjusted until the rate of heat evolution in each case is the same we have A 2R = A1 2R'. Certain precautions are described in the Paper for eliminating in-equalities, but by means of correct reading H.F. ammeters as devised by the Author, the ratio of the resistances R'/R can be determined from the ratio of the mean square currents A2/A12. The H.F. currents used were obtained by condenser discharges and the equiheating steady current determined by means of the differential thermometer arrangement having two equal wires in the two tubular bulbs. It is then shown that the results for straight wires agree very well with the formulae given by Lord Kelvin and by Dr. A. Russell for the ratio R'/R for wires of different sizes and for different frequency. It is pointed out that the correction to be applied for damped oscillations as compared with persistent oscillations is at most 1 per cent. in the cases measured and that the correction for the heating effect of the condenser charging current is negligible. The case of spiral wires is then discussed. The resistance Rdouble prime of a spiral is greater than that of the same wire R' stretched out straight. In the cases examined the ratio Rdouble prime/R exceeds R'/R by about 50 to 80 per cent. A formula given by Dr. Nicholson for Rdouble prime/R is then discussed, and it is shown that it does not agree with the results of observation. Experiments are also described on the H.F. resistance of wires of magnetic metals, and it is shown that in this case the observed value of R'/R can be used to determine the permeability for small H.F. magnetising forces.