Transient-state Method Research Articles

Thermal properties of beef cattle manure

The thermal conductivity of beef cattle manure was measured by a transient state method, while its specific heat was measured by a classical method of mixtures. The specific heat of beef cattle manure was found to decrease as Total Solids concentration (TS) increased, ranging from 4·13 kJkg −1 °C −1 at 1·42% TS to 1·400 kJkg −1 °C −1 at 99·4% TS. The thermal conductivity of beef cattle manure was found to range from 630mW m −1 °C −1 at 2·8% TS to 60· 4mW m −1 °C −1 at 95% TS. At low TS, the manure slurry's thermal conductivity was directly proportional to slurry density and decreased as TS increased. At a TS greater than 51%, the thermal conductivity was directly related to the manure's bulk density and was independent of the manure's TS. An equation relating the thermal conductivity of beef cattle manure to the volume fraction of void space in manure with TS greater than 51% is also given. In addition, results concerning the thermal diffusivity of beef cattle manure are presented.

Sub-units of citrate oxaloacetate-lyase.

Citrate lyase has been shown to have values for S°20,W and D°20,W of 17.6 S and 3.02 × 10−7 cm2 sec−1, respectively. Using the Svedberg equation a value of 533000 was assigned for the molecular weight of the active preparation. The meniscus depletion sedimentation equilibrium method led to a value of 550000 while the transient state method gave a value of 566000. The partial specific volume was determined by the 2H2O method of Edelstein and Schachman to be 0.73 ml g−1.The enzyme was also studied in a variety of denaturing solvents. Molecular weights were measured in the analytical ultracentrifuge and also using dodecylsulphate‐polyacrylamide‐gel electrophoresis with marker proteins of known molecular weight. A range of particles resulted suggesting that there could be 16 sub‐units in the active enzyme preparation.

Specific polarization resistance in linear sweep voltammetry on hydrogen electrodes

The theory of specific polarization resistance R pt in linear sweep voltammetry round the equilibrium potential of hydrogen electrodes is presented. R pt is calculated with the relation ▪ where S is the true surface of the test electrode, v the sweep rate of the applied voltage, I( t) the recorded current, R Σ = ( R S + R I), with R S the solution resistance and R I the internal resistance of the measuring circuit. THe R pt values obtained in transient state are compared with the steady state ones, R ps, on Pt, H 2 and (Pd — H), H 2 electrodes in 1 M H 3PO 4 solution bubbled with 2 l/h hydrogen, at 25°C. R pt ≈ R ps, within ± 10 per cent. The ratio R pt/ S depends on the true surface area of the electrodes and on this basis one calculates the roughness factor of a palladized palladium electrode as 10 3, in agreement with values given in literature for the platinized platinum. The advantage of the transient-state method is exemplified by the time variation of R pt/ S during the poisoning of a (Pd − H), H 2 electrode with Hg 2Cl 2.

Self‐Diffusion Coefficients of Phosphorus in Soil Measured by Transient and Steady‐State Methods

AbstractSelf‐diffusion coefficients of P in soil were measured by two independent methods and by calculating Dp from chloride diffusion. All three methods yielded similar values for Dp at low moisture suctions. On Apishapa silty clay loam, values of Dp ranged from 0.4 × 10‐7 to 15.5 × 10‐7 cm2/sec as the volumetric moisture content increased from 0.22 to 0.55, or as the soil moisture suction decreased from 6 to < 0.1 bar. From these values of Dp a self‐diffusion coefficient for P in bulk solution was calculated, which agreed closely with the experimentally measured value. The transient state method required a separate evaluation of a capacity factor which varied between 100 to 300. If this capacity factor had been omitted, the apparent Dp would have been smaller by 100‐ to 300‐fold. These results demonstrate the necessity of measuring a capacity factor when Dp is to be determined by a transient state method.

Sorption and surface diffusion in porous glass

Sorption, gas-phase diffusion in the region of molecular streaming, and surface diffusion in very dilute adsorbed films have been studied quantitatively for a number of gases in membranes of porous glass. The sorption of oxygen, nitrogen, argon, sulphur dioxide and ammonia near their liquefying temperatures resulted in type IV isotherms with very characteristic hysteresis loops. From the isotherms porosity, surface area and mean pore radius were evaluated. Heats of sorption, Δ H , have been obtained in very dilute adsorbed films and in films where v/v m approaches or exceeds one. These heats showed the porous glass to be an energetically non-uniform sorbing surface. The Henry’s law region of sorption was studied and Henry’s law sorption constants evaluated at 273, 290, 323 and 343° K for the most dilute adsorbed films of oxygen, nitrogen, argon, krypton, methane and ethane. Nearly all this information is essential for measurements of surface diffusion by the transient state method of Barrer & Grove (1951). The micropore structure was so fine that non-sorbed gases diffused within the porous glass only by molecular streaming at pressures up to half an atmosphere or more. Effects of sorption upon this diffusion were inappreciable for helium, neon and possibly hydrogen; for oxygen, nitrogen, argon, krypton, methane and ethane the influence of sorption upon timelags and diffusion coefficients became progressively more marked. In the steady state of flow there was little evidence of surface diffusion when, in the most dilute adsorbed films, Henry’s law is obeyed. On the other hand, in the transient state of flow, surface diffusion makes a substantial contribution to flow. Reasons are given for the difference in the extent to which surface mobility can be detected in the two states of flow. Consistent values of the surface diffusion coefficients, D 8 , were obtained for oxygen, nitrogen, argon, krypton, methane and ethane. These values of D 8 were compatible with the Arrheniusequation D 8 = D 0 exp ( – E / RT ) over the temperature range of 273 to 343° K investigated. The ratio of E to Δ H for very dilute adsorbed films lay between 0·5 and 0·6, and should in order of magnitude be characteristic of a heterogeneous sorbing surface. The numerical values of D 8 have been compared with D for liquids, and analyzed in terms of entropy and energy of activation.