The photochemical reaction applied to a multiply hybridized water-splitting system

The photochemical reaction expressed by

$\text{2Fe}{}^{\mathrm{2+}}\text{+ I}{}^{\mathrm{?}}{}_3\text{+ light →2FE}{}^3\text{+ 3I}{}^{\mathrm{?}}$

is applied to the water-splitting cycles hybridized by photochemical and electrochemical reactions (Yokohama Mark 5), and by photochemical, electrochemical, and thermochemical reactions (Yokohama Mark 6).The theoretical expression for the conversion efficiency of light energy to chemical energy is derived using the reaction dynamics, and the factor which maximizes it and the Gibbs free energy change ΔG are studied.The magnitude of stored energy depends on the intensity of light, the concentration of the reactants, and the kind of anions existing in the solution.Considering the reactivity of the photochemical process and the retardation of the back reaction, the SO₄^2? system yields a large value of ΔG.A value of 15–20% is finally obtained for the efficiency of the photochemical conversion process.     

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.     

Thermochemical hydrogen preparation—Part V. A feasibility study of the sulfur iodine cycle

A sulfur-iodine cycle consists of the following three reactions:

$\text{2H}{}_2\text{O + SO}{}_2\text{+ I}{}_2\text{→ H}{}_2\text{SO}{}_4\text{+ 2HI,}$

$\text{H}{}_2\text{SO}{}_4\text{→ H}{}_2\text{O + SO}{}_2\text{+}\text{1}\text{2O}{}_2\text{,}$

$\text{2 HI → H}{}_2\text{+ I}{}_2\text{.}$

It was found that the first reaction can be performed as a cell reaction without the addition of external energy. The sulfuric acid and the hydriodic acid are produced separately in the anode and cathode compartments, respectively. The second and third reactions can be carried out as catalytic thermal decompositions. A process flow sheet of this cycle and its mass balance was based on experimental results, and the heat balance for this cycle was made. It was found that internal heat exchange for this cycle was very large (about 2600 kcal/mol H₂), due mainly to the low yield of the decomposition reaction of hydrogen iodide. Theoretical and experimental studies were made to improve the yield of this reaction. The following three methods seem to be promising for this purpose: (1) continuous removal of the hydrogen produced in the reaction zone; (2) performance of the reaction at low temperature (185–250°C) and high pressure (100 atml; and (3) substitution of the benzene-cyclohexane cycle (6HI ? C₆H₆ → C₆H₁₂ + 3I₂; C₆H₁₂ → C₆H₆ ? 3H₂) for the hydrogen iodide decomposition step.     

Thermal analysis of pyrotechnic compositions containing potassium chlorate and lactose

Thermal analysis of a mixture containing potassium chlorate and lactose 50:50, which is commonly used in vaporizing pyrotechnic compositions, has revealed that there are two principal exothermic reactions in the absence of air. The first, coinciding with the fusion of lactose at approximately 200°C, is the oxidation of the lactose by the chlorate and may be represented by the stoichiometric reaction (1).

$\text{8}\text{KC}\text{10}{}_3\text{+}\text{C}{}_{12}\text{H}{}_{22}\text{O}{}_{11}\text{?}\text{H}{}_2\text{O→8}\text{KC}\text{1+12}\text{CO}{}_3\text{+12}\text{H}{}_2\text{O}$

, It is postulated that this reaction is initiated by the partial solution of the potassium chlorate in the lactose, and terminates when there is no liquid lactose in the mixture. This is followed immediately by the dehydration of lactose, represented by Eq. (2)

$\text{C}{}_{12}\text{H}{}_{22}\text{O}{}_{11}\text{?}\text{H}{}_2\text{O→12}\text{C}\text{+12}\text{H}{}_2\text{O}$

. This reaction terminates when approximately half the maximum possible amount of water is evolved, and does not contribute to the exothermicity at this stage. The second exothermic reaction occurs at about 340°C and is probably initiated by the fusion of the potassium chlorate. This reaction is the oxidation of the carbonaceous organic residues by the remaining potassium chlorate. Since there is an excess of fuel in this mixture other slow exothermic reactions occur in the presence of air due to further oxidation of the fuel. These reactions will not occur during combustion, when the ingress of air is prevented. An application of thermal analysis to a practical pyrotechnic composition is presented and discussed.     

A nickel-iodine-sulfur process for hydrogen production

A thermochemical hydrogen production process which consists of the following reactions containing nickel, iodine and sulfur (NIS process) was studied.

(1.1)$\text{So}{}_2\text{(aq.)+I}{}_2\text{(aq.)+2H}{}_2\text{O(1)→2H}{}_2\text{SO}{}_4\text{(aq.)}$

(1.2)$\text{2HI(aq.)+H}{}_2\text{SO}{}_4\text{(aq.)+2Ni(c)→NiI}{}_2\text{+NiSO}{}_4\text{(aq.)+2H}{}_2\text{(g)}$

(2)$\text{NiI}{}_2\text{(c)→NI(c)+I}{}_2\text{(g)}$

(3.1)$\text{NiSO}{}_4\text{(c)→NiO(c)+SO}{}_3\text{(g)}$

(3.2)$\text{SO}{}_3\text{(g)→SO}{}_2\text{(g)+}\text{1}\text{2}\text{O}{}_2\text{(g)}$

(4)$\text{NiO(c)+H}{}_2\text{(g)→Ni(c)+H}{}_2\text{O(g)}$

This process is an improved iodine-sulfur process, and is characterized by the separation of the products of reaction (1.2) by solvent extraction, and by the absence of hydrogen or water in the high temperature reactions (3.2), (3.1) and (2). Experimental results of the main unit operations are described. The energy balance of the process is estimated, based on a simplified flow-sheet. A conceptual plant flow-sheet is discussed in connection with a VHTR.     

Optimizing energy transition paths in CO2 emission reduction strategies

In the consideration of energy use scenarios designed to avoid excessive build-up of atmospheric carbon dioxide and the effects of the associated climatic changes it can be anticipated that difficulties will ensue if needed rates of increased deployment of non-fossil fuel burning energy plants become very large. This may result if allowable maximum CO₂ concentrations are set sufficiently low, or if acceleration of non-fossil fuel energy use is sufficiently delayed.In a broad ranging numerical investigation of this problem, Perry et al.¹ have suggested that difficulty will be experienced in the transition to a non-fossil based economy, not only if the rate of growth of non-fossil fuel energy use rate, $\text{E}\text{?}{}_{\mathrm{N}}$ is excessive, but also if the second derivative, $\text{E}\text{?}{}_{\mathrm{N}}$, becomes too large. This observation has important ramifications, since $\text{E}\text{?}{}_{\mathrm{N}}$ may exceed tolerable limits, whilst $\text{E}\text{?}{}_{\mathrm{N}}$ still remain modest in size. In making the estimates an empirical method for joining early and asymptotic energy use rates was employed. In order to make sure that the conclusions reached were not sensitive to the ad hoc nature of this technique, we have introduced a more rigorous approach by using a variational interpolation approach that minimizes the peak value of $\text{E}\text{?}{}_{\mathrm{N}}$ (or a combination of $\text{E}\text{?}{}_{\mathrm{N}}$ and $\text{E}\text{?}{}_{\mathrm{N}}$.$\text{E}\text{?}{}_{\mathrm{N}}$ We find that such an optimization procedure can reduce the maximum values of $\text{E}\text{?}{}_{\mathrm{N}}$ by as much as 50% from those calculated by Perry et al. This indicates that the energy transition process should be easier that concluded by them, at least as far as a criterion based upon $\text{E}\text{?}{}_{\mathrm{N}}$ variation is concerned, but can still create difficulties, especially if a 500 ppmv CO₂ ceiling is considered hazardous and if actions to reduce fossil fuel use are delayed too long.     

A tutorial on reversed NH3H2O absorption cycles for solar applications

The $\text{NH}{}_3\text{H}{}_2\text{O}$ absorption refrigeration cycle is already used in solar applications. The solar heat is either used to operate the vapor generator of the refrigeration units or, in the case of heat pumps, to load the evaporator. In the first case the solar heat is added to the high-temperature part of the unit; in the second, to the low-temperature part. In both cases the absorption unit is rejecting heat to the ambient at a mean temperature level. The present paper considers the addition of solar heat at the mean temperature level and the operation of a reversed absorption $\text{NH}{}_3\text{H}{}_2\text{O}$ cycle splitting the solar heat into two parts. One part is rejected at a lower temperature level, and the other part, the output, is delivered for use at higher temperature levels. The thermodynamics of the reversed cycle is examined, and its theoretical behaviour is described.     

Reactor design for the UT-3 thermochemical hydrogen production process

The UT-3 thermochemical cycle for hydrogen production previously proposed consists of four reactions given by:

(1)$\text{CaBr}{}_2\text{+H}{}_2\text{O→CaO +2HBr}$

(2)$\text{CaO+Br}{}_2\text{→CaBr}{}_2\text{+}\text{1}\text{2}\text{O}{}_2$

(3)$\text{Fe}{}_3\text{O}{}_4\text{+8HBr→3FeBr}{}_2\text{+4H}{}_2\text{O+Br}{}_2$

(4)$\text{3FeBr}{}_2\text{+4H}{}_2\text{O→Fe}{}_3\text{O}{}_4\text{+6HBr+H}{}_2$

.At present, a series of both theoretical and experimental studies aiming at the industrialization of this process have been conducted. In this paper the measurements of the kinetic study for reaction (3) were first described. Based on experimental data and conceptual design of the whole process, then the simulation of the performance for the reactor using a honeycomb-shaped solid reactant was conducted. The result gives information on the reactor design.     

Water splitting reaction on a polynaphthoquinone catalyst a polynaphthoquinone-SO2-I2 system for H2O decomposition

The water splitting reaction in a polynaphthoquinone-SO₂-I₂ system under mild conditions is reported. One mole H₂O was decomposed to form 2 moles HI and 1 mole H₂SO₄ by the following two successive hydrogen transfer reactions in conjunction with the redox cycle of quinones(Q)-hydroquinones(QH₂) in the polynaphthoquinone catalyst:

$\text{2H}{}_2\text{O +SO}{}_2\text{+ Q ? QH}{}_2\text{+ H}{}_2\text{SO}{}_4\text{, QH}{}_2\text{+ I}{}_2\text{? 2HI + Q}$

The hydrogen transfer reaction from H₂O to Q was accelerated by a factor of 3–5 by light irradiation and hence this system could work also as a hybrid thermochemical cycle. When the catalytic hydrogen transfer reactions on the polynaphthoquinone are combined with the thermal decompositions of HI(2 HI ? H₂ + I₂) and H₂SO₄ ($\text{H}{}_2\text{SO}{}_4\text{? H}{}_2\text{O + SO}{}_2\text{+}\text{1}\text{2}\text{O}{}_2$), a closed water splitting cycle for the hydrogen production could be constructed. The reaction mechanism is also discussed.     

Kinetics of the reaction between Mg2Ni and hydrogen

The reaction between Mg₂Ni and hydrogen was investigated by volumetric method. The reaction was divided into two stages; the initial stage was a very rapid reaction whose rate could not be measured, the later stage was the slower step whose rate was expressed by the equation

$\text{dn/DT}\text{=}\text{K′}\text{(}\text{P}\text{?}\text{P}{}_{\mathrm{eq}}\text{/}\text{t}$

where k′ is the constant, P_eq and P are hydrogen pressures at equilibrium and at time t. The reaction rate of the later stage did not depend upon temperature, content of hydrogen in the alloy, and directions of the reaction, desorption and absorption. The amount of reacted hydrogen, Δn, in the initial stage was expressed by

$\text{Δ}\text{n}\text{=k(}\text{P}{}_{\mathrm{o}}\text{?}\text{P}{}_{\mathrm{eq}}\text{)(}\text{n}{}_{\mathrm{s}}\text{?}\text{n}{}_{\mathrm{o}}$

where P₀ is the initial hydrogen pressure, n_s is a constant around 4, n₀ is a ratio of H to Mg₂Ni at the initiation of the run, and k is a constant. The apparent activation energy of the reaction was nearly zero. It is considered that the reaction between the alloy and gaseous hydrogen takes place on metallic Mg₂Ni in the initial stage and in the later stage reaction proceeds on the deactivated site.     

Development and design of a continuous laboratory-scale plant for hydrogen production by the Mark-13 cycle

The Mark-13 cycle, invented by Schütz and Fiebelmann in 1974, consists of the following three reactions:

$\text{SO}{}_2\text{+}\text{Br}{}_2\text{+2}\text{H}{}_2\text{O}\text{→}\text{H}{}_2\text{SO}{}_4\text{+2}\text{HBr}\text{,}\text{(320–370 K)}$

$\text{2}\text{HBr}\text{→}\text{H}{}_2\text{+}\text{Br}{}_2\text{,}\text{(electrochemical)}$

$\text{H}{}_2\text{SO}{}_4\text{→}\text{H}{}_2\text{O}\text{+}\text{SO}{}_2\text{+0.50}{}_2\text{.}\text{(1000–1100 K)}$

In the present paper the state of the art of the experimental development work carried out at JRC-Ispra is given. The results obtained have been considered a sound basis for the design and construction of a complete laboratory-scale cycle.The expected net hydrogen production rate of this plant is 4.0 gmol/h, i.e. about 100 l/h S.T.P.The aim of the work is the construction of a reliable small scale model of the process which should yield indispensable information for further scale-up. Therefore we applied design and/or simulation rules in the design calculations for the process.It is believed that this installation is the first demonstration of a complete thermochemical hydrogen production process.     

Heats of reaction of pyrotechnic compositions containing potassium chlorate

The heats of reaction of a number of mixtures containing potassium chlorate and lactose have been determined. It has been shown that when there is excess potassium chlorate in the mixture these results can be explained theoretically using Eqs. (1) and (2).

$\text{KC}\text{10}{}_3\text{+}\text{C}{}_{12}\text{H}{}_{22}\text{O}{}_{13}\text{?}\text{H}{}_2\text{O→8}\text{KC}\text{1+12}\text{CO}{}_2\text{+12}\text{H}{}_2\text{O,}$

$\text{KC}\text{10}{}_3\text{→}\text{KC}\text{1+}\text{3}\text{20}{}_2$

. When there is excess lactose present, the results can be correlated with theory using Eqs. (1), (3), and (4)

$\text{C}{}_{12}\text{H}{}_{22}\text{O}{}_{11}\text{·}\text{H}{}_2\text{O→12}\text{C}\text{+12}\text{H}{}_2\text{O}$

,

$\text{C}\text{+}\text{H}{}_2\text{O→}\text{CO}\text{+}\text{H}{}_2$

. Reaction (4) does not go to completion when there is less than 55% potassium chlorate in the mixture. The heats of reaction of mixtures of potassium chlorate with various organic compounds which can be used as fuels were also determined. It was found that, with two exceptions, there was little variation in the heat of reaction, so that this property cannot be the sole criterion when selecting a fuel. The heats of reaction of a few typical vaporizing compositions are given.     

Results of a dynamic analysis of crack propagation and arrest data in the modified compact tension geometry

Crack arrest toughness is of relevance to the integrity assessment of nuclear pressure vessels. Hence a detailed analysis has been performed on the dynamic behaviour of two proposed crack arrest specimen geometries. A one-dimensional finite difference computer program has been used to determine the instantaneous dynamic stress intensity factor, $\text{K}{}_{\mathrm{<mtext>ID</mtext>}}$, during fast crack growth. Experimental data used as input were in the form of crack length/time pairs determined in specimens of the compact tension geometry. An analysis of the errors involved in this technique suggests that they are part systematic and part random and each typically at the 5% level.Values of $\text{K}{}_{\mathrm{<mtext>ID</mtext>}}$ showed similar trends to those observed by previous workers using different experimental techniques. Within the first few millimetres of growth $\text{K}{}_{\mathrm{<mtext>ID</mtext>}}$ dropped to about 0·7 times the nominal stress intensity at initiation from a blunt notch and decayed further to about half of the value. Average values of $\text{K}{}_{\mathrm{<mtext>ID</mtext>}}$ and crack speed were much less than values predicted from an analysis using the assumption of a velocity-independent fracture toughness.Load line displacements and specimen energy were also calculated in the present analysis. This indicated that there were repeated exchanges between potential and kinetic energy during crack growth. These data taken together with those obtained by previous workers allow a more complete understanding of the dynamic behaviour of the crack arrest specimen geometry.     

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.     

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.     

The maximum power,heat demand and efficiency of a heat engine operating in steady state at less than Carnot efficiency

An imperfect, Carnot-like engine operating in steady state and receiving heat through conductance k₁ from a source at T₁ and discharging heat only through a conductance k₂ to a sink at T₄ has an efficiency at maximum net power output of $\text{η}{}_{\mathrm{m}}\text{= (}\text{?}\text{g9}\text{){1 ? √(1 ? ?(1 ?}\text{T}{}_4\text{T}{}_1$)}, where ? is a non-Carnot efficiency and $\text{? =}\text{(?k}{}_1\text{+ k}{}_2\text{)}\text{(k}{}_1\text{+ k}{}_2\text{)}$.     

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.     

An R curve approach to COD and J for an austenitic steel

This paper describes investigations of the fracture toughness of a type 316 stainless steel by means of $\text{δ}{}_{\mathrm{R}}$ and $\text{J}{}_{\mathrm{R}}$ curves. Both COD (δ) and $\text{J}$ values rise dramatically after crack initiation and reach plateau values after some crack extension. These plateaux are much higher than the value of δ and $\text{J}$ at maximum load and are considered to represent the maximum fracture toughness of the material.A load/crack mouth opening record is shown to be sufficient to obtain a $\text{J}{}_{\mathrm{R}}$ as well as a $\text{δ}{}_{\mathrm{R}}$ curve. The maximum plateau value can be obtained only in specimens with sufficient ligament depth. It is shown that this is achieved for a specimen whose depth, $\text{W}$, is four times the thickness, $\text{B}$, with a ligament length of $\text{2·8B}$.The relationship between the $\text{δ}{}_{\mathrm{R}}$ concept and the model of crack tip behaviour proposed by Green & Knott¹³ for an extending ductile tear is also investigated.     

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,

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