Representative stresses for creep deformation and failure of pressurised tubes and pipes

Results of a series of tube and uniaxial tests on two casts of $\text{1}\text{2}\text{CrMoV}$ pipe steel are examined to determine the representative stress which must be applied to uniaxial data in order to predict the strain rates and lives of pressurised tubes and pipes. The stress criterion for deformation is shown to correlate with the analytically derived reference stress ($\text{σ}{}_{\mathrm{<mtext>R</mtext>}}$) at low pressure while at high pressures a modified reference stress ($\text{> σ}{}_{\mathrm{<mtext>R</mtext>}}$) must be used. The rupture life exhibits a similar correlation such that the representative stress for rupture is given by $\text{σ}{}_{\mathrm{<mtext>R</mtext>}}$ at low stresses yet, at high stresses, it is greater than $\text{σ}{}_{\mathrm{<mtext>R</mtext>}}$ and attains a value comparable with the mean diameter hoop stress. The latter thus describes the rupture life at high pressures but significantly underestimates the life at low pressures approaching those in service. Consideration is given to the multiaxial stress rupture criterion and the effect of geometry in constant load tests.     

Surface renewal theory for turbulent mixed convection in vertical ducts

A heat transfer correlation for opposing mixed turbulent convection in vertical ducts was obtained utilizing surface renewal theory. The correlation was found to be Nu_Db = 0.0115Re_Dh^0.8Pr^0.5 The correlation fit data to within 7% over a parameter range of 0.7 < Pr < 7, 1 × 10⁴ < Re_Dh < 2 × 10⁴, and 1 × 10⁶ < Gr_Dh < 2 × 10⁹. The mean residence time, characterizing the time a clump of fluid resides on the wall, was found to decrease as both and Re_Dh increase. This explains the enhanced heat transfer due to buoyancy in opposing mixed turbulent flows. This heat transfer enhancement was also reflected in a decreasing thermal boundary layer thickness with increasing Re_Dh, Gr_Dh or Pr.     

A theoretical elastic analysis of spherical thin shell segments in pressure vessels with a circular hole under transverse load P0 and Moment M0

In this paper, according to the theory of thin shells, the uniformly valid asymptotic homogeneous solution and the exact particular solution are derived for spherical thin shell segments with a circular hole under transverse load $\text{P}{}_0$ and moment $\text{M}{}_0$.     

Droplet evaporation: Effects of transients and variable properties

A numerical study of the effects of transients and variable properties on single droplet evaporation into an infinite stagnant gas is presented. Sample calculations are reported for octane droplets, initially at 300°K with R_o = 0·1, 0·5, 2·5 × 10^?4m, evaporating into air at temperatures and pressures in the ranges 600–2000°K and 1–10 atm, respectively. It is found that initial size R_o is eliminated from the problem on scaling time with respect to R²₀ and that the evaporative process becomes quasi-steady with ($\text{R}\text{R}{}_0\text{)}{}^2\text{= (}\text{R1}{}_0\text{R}{}_0\text{)}{}^2\text{?}\text{βt}\text{R}{}^2{}_0$, as suggested by experiment. Comparisons of solutions using various reference property schemes with those for variable properties show that best agreement obtains using a simple $\text{1}\text{3}$ rule wherein properties are evaluated at $\text{T}{}_{\mathrm{r}}\text{= T}{}_{\mathrm{s}}\text{+}\text{(T}{}_{\mathrm{e}}\text{?T}{}_{\mathrm{s}}\text{)}\text{3}$ and $\text{m}{}_{\mathrm{1,r}}\text{= m}{}_{\mathrm{1,s}}\text{+}\text{(m}{}_{\mathrm{1,e}}\text{? m}{}_{\mathrm{1,s}}\text{)}\text{3}$. The effects of temporal storage of mass species, energy, etc. and radial pressure variations in the vapor phase prove to be negligible, the early transient behavior being solely due to sensible heat effects within the droplet and related variations in vapor-side driving forces.     

Influence de la variation de la viscosite avec la temperature sur le frottement avec transfert de chaleur en regime turbulent etabli

Experimental research about measurement of local friction pressure drop in fully developed turbulent flow of water in a smooth and uniformly heated circular tube has been investigated.The effect of variable viscosity with temperature in the laminar boundary layer is isolated by varying the heat flux at constant values of the local bulk Reynolds and Prandtl numbers. This severe method shows that the usual dependence of friction ratio $\text{f}{}_{\mathrm{H}}\text{f}{}_{\mathrm{iso}}$ on viscosity ratio $\text{μ}{}_{\mathrm{p}}\text{μ}{}_{\mathrm{b}}$ is more complex than the simple power law appearing in the familiar empirical results. It has been found that the exponent is a complicated function of Reynolds number and the viscosity ratio and is independent of the Prandtl number in our experimental range.We propose a new relationship for the friction coefficient ratio in which the viscosity ratio is changed by the more accurate parameter: $\text{x}\text{\$}\text{?}\text{= (-μ}{}_{\mathrm{b}}\text{-1/μ}{}_{\mathrm{p}}\text{)(μ}{}_{\mathrm{b}}\text{/μ}{}_{\mathrm{b}}\text{/μ}{}_{\mathrm{p}}\text{)}{}^{0.17}$ which is directly proportional to the heat flux when the Reynolds and the Prandtl numbers are fixed. The dispersion is caracterised by a standard deviation σ = ±0·7%, 98% of the points are within 2σ = ±1·4%. The agreement between prediction and the previously existing results can be considered satisfactory for Reynolds number from 2 × 10⁴ to 30 × 104 and Prandtl number from 2 to 6.     

Blackbody radiation functions

The present paper reports an exact solution of the fractional function of blackbody radiation. The new equation is expressed as

$\text{F}{}_{\mathrm{0?\lambda T}}\text{=}\text{∫}\text{λT}\text{0}\text{E}{}_{\mathrm{b\lambda }}{}^{\mathrm{(T)}}\text{σT}{}^5\text{d (λT)=}\text{15}\text{π}{}^4\text{∑}\text{n=1}\text{∞}\text{e}{}^{\mathrm{?nx}}\text{n}\text{(x}{}^3\text{+}\text{3x}{}^2\text{n}\text{+}\text{6x}\text{n}{}^2\text{+}\text{6}\text{n}{}^3\text{)}$

     

High temperature kinetics of NCO

Mixtures of cyanogen and nitrous oxide diluted in argon were shock heated to measure the ratio of the rate constants for

(3)$\text{NCO}\text{+}\text{O}\text{→}\text{CO}\text{+}\text{NO}$

and

(4)$\text{NCO}\text{+}\text{M}\text{→}\text{N}\text{+}\text{CO}\text{+}\text{M}\text{.}$

The diagnostic was narrow-line absorption of NCO at 440.479 nm using a remotely located cw ring dye laser source. By varying the mole fraction of nitrous oxide in the initial mixture and conducting otherwise identical experiments, we inferred at 2240°K

$\text{k}{}_3\text{k}{}_4\text{=10}{}^{\mathrm{3.54(+0.34,\; ?0.37)}}\text{.}$

Utilizing a recent determination of k₃ and previous measurements of the ratio $\text{k}{}_3\text{k}{}_4$, we recommend over the temperature range 2150 ? T ? 2400°K

$\text{k}{}_4\text{=10}{}^{16.8}\text{T}{}^{\mathrm{?0.5}}\text{exp}\text{[?24000/T] cm}{}^3\text{/mole/s [×2.3, ×0.4].}$

An additional mixture of cyanogen, oxygen, hydrogen, and nitrous oxide diluted in argon was shock heated and NCO was monitored to infer the rate constant for

(5)$\text{NCO}\text{+}\text{H}\text{→}\text{CO}\text{+}\text{NH}$

and the ratio $\text{k}{}_6\text{k}{}_7$:

(6)$\text{C}{}_2\text{N}{}_2\text{+}\text{H}\text{→}\text{CN}\text{+}\text{HCN}\text{,}$

(7)$\text{CN}\text{+}\text{H}{}_2\text{→}\text{HCN}\text{+}\text{H}\text{.}$

We found near 1490°K

$\text{k}{}_5\text{=10}{}^{\mathrm{13.73(+0.42,?0.27)}}\text{cm}{}^3\text{/mole/s,}$

and

$\text{k}{}_6\text{k}{}_7\text{=0.81(+0.89, ?0.47).}$

These experiments also led to an estimate of the rate constant for

(8)$\text{NCO}\text{+}\text{H}{}_2\text{→}\text{HNCO}\text{+}\text{H}\text{,}$

with the result, near 1490°K,

$\text{k}{}_8\text{?10}{}^{\mathrm{12.1(+0.4,?0.7)}}\text{cm}{}^3\text{/mole/s.}$

     

Effects of suction and injection on self-similar solutions of second-order boundary-layer equations

Effects of suction and injection on self-similar boundary-layer flows at moderately large Reynolds numbers are studied. The general form of normal velocity at the wall is assumed to be $\text{v}{}_{\mathrm{w}}\text{= R}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{v}{}_{\mathrm{w1}}\text{+ R}{}^{\mathrm{?1}}\text{v}{}_{\mathrm{w2}}\text{+…}$ In addition to the usual five second-order effects (due to longitudinal curvature, transverse curvature, displacement speed, external vorticity, temperature gradient) an additional sixth effect due to $\text{v}{}_{\mathrm{w2}}$ is linearly separated. Both the cases of the momentum and heat transfer are studied. For heat transfer two cases of prescribed wall temperature and that of insulated wall with full similarity with viscous dissipation considered. Numerical solutions are displayed graphically and critically discussed.     

A kinetic model of hydrogen absorption in CeMg12

Comparing kinetic equations derived from a theoretical model with experimental data published, the kinetic mechanism of hydriding reaction of CeMg₁₂ was analysed.At the initial stage the reaction is controlled by chemisorption of hydrogen on the metal surface and the reacted fraction (F) is expressed as a function of time (t) and temperature (T)

$\text{F=(1.19 × 10}{}^2\text{)}\text{(P}{}_{\mathrm{o}}\text{? P}{}_{\mathrm{eq}}\text{)}\text{T}\text{1}\text{2}\text{exp}\text{(?3560}\text{cal/RT}\text{)t}$

in the range of 0 ? F ? 0.4. The later stage of the reaction is controlled by another mechanism of metal/hydride interface chemical reaction or hydrogen diffusion in the hydride phase which cannot be clearly distinguished at the moment.     

Hydrogen production through microheterogeneous photocatalysis of hydrogen sulfide cleavage. The thiosulfate cycle

Cleavage of hydrogen sulfide into hydrogen and sulfur occurs in alkaline aqueous CdS dispersions under visible light illumination (?400 nm). Small quantities of a noble metal catalyst (RuO₂) loaded onto ‘naked’ CdS particles markedly improve the yield of hydrogen formation. The effect of RuO₂ is ascribed to catalysis of electron transfer to proton. Simultaneous and efficient photogeneration of hydrogen and thiosulfate occurs in CdS dispersions containing both sulfite and bisulfide (or sulfide) ions. Electron transfer from the conduction band of CdS to that of TiO₂ particles occurs in alkaline suspensions containing these HS^? ions and has been exploited to improve the performance of a system achieving decomposition of H₂S by visible light. Equally important is a recent finding that the performance of a system containing ‘naked’ CdS in combination with RuO₂-loaded TiO₂ particles is far better than that of CdS/RuO₂ alone. Additionally, conduction band electrons produced by bandgap excitation of TiO₂ particles efficiently reduce thiosulfate to sulfide and sulfite. The valence band process in alkaline TiO₂ dispersions is thought to involve oxidation of S₂ O₃^2? to tetrathionate, S₄O₆^2?, which quantitatively dismutates into sulfite and thiosulfate, the net reaction being

$\text{2h}{}_{\mathrm{vb}}{}^{\mathrm{+}}\text{(}\text{TiO}{}_2\text{)+0.5S}{}_2\text{O}{}_3{}^{\mathrm{2?}}\text{+1.5}\text{H}{}_2\text{O}\text{→}\text{SO}{}_3{}^{\mathrm{2?}}\text{+3}\text{H}{}^{\mathrm{+}}\text{.}$

The photodriven disproportionation of thiosulfate into sulfide and sulfite is of great interest in systems that photochemically cleave hydrogen sulfide into hydrogen and sulfur

$\text{1.5}\text{H}{}_2\text{O}\text{+1.5S}{}_2\text{O}{}_3{}^{\mathrm{2?}}\textcolor{red}{}\text{+2}\text{SO}{}_3{}^{\mathrm{2?}}\text{+}\text{SO}{}^{\mathrm{2?}}\text{+3}\text{H}{}^{\mathrm{+}}\text{.}$

     

Water-vapour diffusion through fibrous thermal insulants

The variation of water-vapour permeability $\text{k}{}^1$ with changes in bulk density has been measured for various fibrous insulants and the results compared with those obtained using the British Standard dry-cup and wet-cup methods. An exponential relationship of the form $\text{k}{}^1\text{exp}\text{(}\text{1}\text{V}{}_{\mathrm{\nu }}\text{)}$ was obtained, where V_ν is the volume voidage.     

Thermal insulation provided by plain,horizontal annular cavities containing atmospheric pressure air

For the range 3 × 10³ ≤ Gr_di ≤ 10⁸ and $\text{1·3 ≤}\text{r}{}_0\text{r}{}_{\mathrm{<mtext>i</mtext>}}\text{≤ 7·5}$, it is suggested that for the steady-state rate of heat transfer outwards by combined laminar, free convection and conduction through the atmospheric pressure air contained within horizontal concentric annuli. This simple correlation, evolved from an analysis of published, as well as new, experimental information, will enable designers to predict the combined convective/conductive resistance provided by the contained air for the range of concentric pipes likely to be encountered in practice.An optimal eccentricity of 0·24 (the inner cylinder being moved vertically upwards relative to the outer cylinder from the concentric position) corresponds to the maximum combined convective/conductive resistance configuration. For the systems tested in the temperature range 18°C ≤ T ≤ 150°C, this optimal eccentricity is not significantly affected by changes in the surface emissivities.