Basin-type solar distillation with air flow through the still

The energy balances for basin-type solar distillation with air flowing through the still have been derived. The effects of G and (t_w ? t_o) on the modified factor F have been investigated experimentally and a correlation equation derived. Considerable improvement in productivity may be obtained if the water vapor is carried away directly by the flowing air.     

Hydrogen and sulfur from hydrogen sulfide—IV. Quenching the effluent from a solar furnace

Solar thermochemical production of H₂ and sulfur from H₂S were studied, using a 4.2 m solar furnace as a source of process heat. We used two reactor configurations. The independent variables were temperature, feed rate and pressure. Hydrogen production rate, yield, and the quench fraction (fractional yield) were measured. High yields (of the order 0.5) and quench fractions (of the order 0.7) were obtained over a range of temperatures and feed rates. Yields were a monotonically increasing, almost linear, function of the temperature.The observations are rationalized by a kinetic model that concludes that gas phase reaction rates are too low to account for the observed yields; a good reactor should embody the heating of the feed stream in contact with a surface to facilitate decomposition of H₂S, and the product stream should be quenched in such a way as to minimize surface reactions.The reactors are described. Mullite, Al₂O₃, Fiberfrax and ZrO₂ are suitable materials of construction from a chemical standpoint. Mullite underwent some sintering, deformation and thinning in the hottest parts of the reactor, where it may have been exposed to high temperature excursions and some cracking, apparently due to thermal stress, where it came in contact with a separator.     

Flux and temperature distribution in the receiver of parabolic solar furnaces

In this study, a mathematical analysis is presented on the complete interface problem between solar concentration systems and high temperature thermochemical processes. This includes the thermal process starting from the incoming solar radiation up to the heat transfer to a heat carrier fluid or reactants in a given reactor. The system considered comprises a heliostat, a parabolic concentrator and a receiver. The hourly incoming radiation, the hourly reflection and absorption losses on the heliostat and concentrator systems, the radiation flux density distribution in the receiver space, the solar and IR bands radiation exchange and the useful heat transfer are all considered in the analysis. The parameters such as temperature distribution in the receiver as well as thermal efficiency can be calculated for a given case. The model has been verified using the experimental results obtained in two different systems. In addition, a parametric study has been carried out on the global receiver efficiency with respect to temperature.     

Solar energy storage using chemical potential changes associated with drying of zeolites

Compact solar storage systems depend upon identification of systems which can store energy as chemical potential. Simple, noncorrosive, systems that operate at reasonably low temperatures are rare. The use of the heat of adsorption of moisture on zeolite molecular sieves is discussed here. The advantages of zeolites are high heats of adsorption (as much as 80 kJ mol⁻¹), large maximum adsorption capacity (0.2–0.3 kg H₂O/kg adsorbent) and easy control of the store following from control of heat output by regulations of flows of moist air. The disadvantages are the relatively high upper temperature required to utilize maximal storage capacities (up to 250°C) and cost. There is reason to project falling cost.

Zeolite storage is compared favourably with respect to capacity to water, stone, and heat of phase change systems. Compared to salt hydrates, acid solution, and salt solutions any capacity advantage is supplemented by low corrosion and opportunity for long term storage. Zeolites are compared favourably to alternative absorbent materials; alumina, charcoal, and silica gel.

The warm dry air output from a zeolite storage bed can be utilized not only in space heating but also in the drying of agricultural timber and fish products.     

Dewpoints of flue gases for energy-recovery system design and operation

Low temperature corrosion from flue gases is a common problem in energy recovery systems. We present a simple computation procedure to estimate the dewpoint of combustion gases, which is the limiting design temperature to prevent corrosion. If the composition of fuel oil and the percentage of CO₂ or O₂ in the flue gases are known, the air ratio, percentage of H₂O, p.p.m. of SO₃ in the flue gas, and the dewpoint can be estimated with an error of 1.9%. The results indicate that the dewpoint is high because the combustion conditions are not appropriately adjusted, even if low sulfur fuel oil is used. We conclude that both the fuel quality and the combustion conditions are controlling variables in the design and operation of energy recovery systems.     

The delayed action of magnesium anodes in primary batteries Part I. Experimental studies

Magnesium exhibits a delayed dissolution on anodic polarisation owing to a slow, field-induced breakdown of the passive film on its surface. The phenomenon depends on several factors such as the pretreatment of the anode, the composition of the solution, etc. In order to clarify the mechanism of the field-induced film-breakdown process, a detailed experimental study of the delayed action and its dependence on several experimental variables such as ageing of the anode in contact with the solution, the nature of the surfactant-coating on the magnesium anode, the anodic current density, etc., has been carried out. The results of the single electrode studies have been verified with improved MgMnO₂ dry cells. Finally, a probable mechanism based on a ‘metal dissolution — film dilatation — film breakdown’ model has been proposed in order to explain the delayed action under various experimental conditions.     

Evaporation of a volatile-liquid lens floating on the surface of a stagnant immiscible liquid

The paper presents experimental results of evaporation of isolated lenses on n-pentane or R 113 (C₂C?₃F₃) at a horizontal interface between a hot water and the common vapors of the two fluid substances. n-Pentane lenses often became unstable and even split into smaller lenses during evaporation process, while R 113 lenses were always stable. Corresponding to this fact, the evaporation rate of n-pentane lenses was typically 10 times higher than that of R 113 lenses under the same temperature driving force. A variation in the water layer thickness exhibited no appreciable effect on the evaporation rate. These findings indicate that the primary factor for enhancing the heat transfer from the water to lenses is such an interfacial turbulence, with an unidentified mechanism, as to give lenses the unstable behavior rather than a buoyancy-driven convection in the water bulk.     

Hydrogen and sulfur from H2S-III. The economics of a quench process

The capital cost, operating costs, revenues, and payback period of a 100 gm-mole/s solar-thermochemical plant which converts H₂S to H₂ and S_x by quenching the effluent from a solar furnace are presented. Payback times are compared with those of alternatives which use energy from other sources. The process compares favorably with current technology and appears to be economically attractive.     

Application of non-aqueous solvents to batteries part I. Physicochemical properties of propionitrile/water two-phase solvent relevant to zinc—bromine

The properties of bromine/propionitrile solution are investigated with a view to its use as an electrolyte in zinc—bromine batteries which use circul     

The delayed action of magnesium anodes in primary batteries: Part II. Theoretical studies

A physical model for the field-induced breakdown of the passive film on magnesium anodes has been developed based on experimental data on the delayed action of magnesium anodes. The model essentially involves, successively, metal dissolution at the metal-film interface, film-dilatation, and film breakdown. A theoretical analysis of the model has been carried out to obtain an explicit expression for the time dependence of the electrode potential during the delayed action phenomenon. The delay-time curves obtained are compared with experimental data, especially with regard to the effects of film thickness, ageing of the anode in solution, current density, temperature, etc. Finally, possible means of reducing the delayed action of magnesium anodes are predicted from the ‘metal dissolution-film dilatation-film breakdown’ model.     

The un-utilizability design method for collector-storage walls

The monthly-average auxiliary energy requirement of a building with a collector-storage (Trombe) wall is estimated using upper and lower theoretical limits to system performance. These two limits on the building auxiliary energy requirements result from considering the building and collector-storage wall to have either zero thermal capacity or infinite thermal capacity. With zero thermal capacity, all solar gain in excess of the load, on an instantaneous basis, is not useful and must be dumped. With infinite thermal capacity, the house is able to store any gain in excess of the instantaneous load and use it at some later time. Auxiliary energy use by real systems will fall between these two theoretical bounds. An empirical correlation is presented for the fraction of the load met by the collector-storage wall, F, for systems with finite capacity. The correlation is based on the solar radiation statistic, utilizability. The correlation is compared to yearly TRNSYS simulation results for a wide variety of system types. The root-mean-square difference between F found from the un-utilizability method and from TRNSYS simulations is less than 4 per cent. One advantage of this method over other simplified design methods is that this method covers a much larger range of design parameters.     

Electrochemical determination of the anode film resistance and double layer capacitance in magnesium—manganese dioxide dry cells

The transient and steady-state analysis of the galvanostatic discharge response of MgMnO₂ cells — in the absence of a dielectric breakdown of the passive film on Mg — yields valuable information on the resistance and capacitance of the protective film on the Mg anode. Theoretical analysis of the response curves has been completed, and a simple, reliable technique has been evolved to obtain, experimentally, the response data. Experimental data have been found to be in good agreement with theoretical analysis. The technique can be easily applied as a non-destructive tool for examining the stability of the film on Mg anodes and can be extended to anodes of other battery systems that involve reactive metals (e.g., Li, Al, etc.) covered by a protective film. Several modes of failure of such cells may be predicted by applying the method proposed.     

LiAsF6 in propylene carbonate—acetonitrile for primary lithium batteries

1M LiAsF₆ in 50% v/v propylene carbonate—acetonitrile (PC-AN) is an electrolyte solution which offers improved cathode utilization, improved energy efficiency and more stable discharge voltages when used in primary lithium batteries with MnO₂, TiS₂, Cu₂S, CuS, MoO₃, V₂O₅, V₆O₁₃ and NbSe₃ cathodes. Incorporation of solvated Li⁺ into the cathodic material may be part of the cathodic process, and the lower viscosity and lower molar volume of acetonitrile, which is a solvator of Li⁺ in PC/AN mixtures, are thought to be responsible for the major improvement over LiAsF₆ in PC as electrolyte solution for these cells.     

Studies on photogalvanic effect in systems containing toluidine blue

The photovoltages and photocurrents in photogalvanic cells containing a dye toluidine blue (Tb⁺) and reducing agents, Fe(II), EDTA, triethanolamine and triethylamine have been determined. The photo-outputs with EDTA or amines as reducing agents are higher than when Fe(II) is the reducing agent. The efficiency of the EDTA-Tb⁺ photogalvanic cell has been estimated to be 0.0022%. The electrochemical behaviour of toluidine blue in presence of all the reducing agents has been examined by cyclic voltametry. Plausible mechanisms of photogalvanic action have been discussed.     

Room temperature hydrogen production from aliphatic alcohols over uv-illuminated powder Ni/TiO2 catalysts

The dependence of the room temperature H₂ production from liquid methanol or propan-1-ol on the degree of reduction of Ni and on the Ni content (0.03–13.8 wt%) of UV (λ ? 297 nm) illuminated Ni/TiO₂ catalysts has been studied. A complete reduction of Ni was found beneficial and an optimum rate of H₂ production from methanol (quantum yield ～0.05) was observed for ～5 wt% Ni. Magnetic measurements indicated that the mean Ni crystallite size varied with the content and was in the 6.5–18 nm range, as compared with ～2 nm for Pt particles on the same support. At least the highest Ni percentages induced a decrease in the anatase photoconductance under vacuum, which can be attributed to an electron transfer from the semiconductor grains (～25 nm dia.) to the Ni particles. The optimum in the photocatalytic H₂ production was considered as resulting from a compromise between the Ni catalytic properties and this electron transfer either because of a decrease in the number or strength of the TiO₂ basic sites or an increase in the electron-hole recombination at the Ni particles. Finally, the difference in the optimum metal content for Ni and Pt(0.1–1 wt%) was attributed mainly to the distinct particle sizes.     

Battery lifetime prediction by pattern recognition. Application to lead-acid battery life-cycling test data

A novel approach to battery lifetime prediction has been evaluated by application to life-cycling data collected for 108 ESB EV-106 6-V. golf cart batteries (tests conducted by TRW for NASA-Lewis). This approach utilized computerized pattern recognition methods to examine initial cycling measurements and classify each battery into one of two classes: “long-lived” or “short-lived”. The classifier program was based on either a linear discriminant or nearest neighbor analysis of a training set consisting of: each member of the EV battery set which had failed; the relative lifetime of each member — normalized with respect to test conditions; and a set of “features” based on measurements of the initial behavior.The raw data set included capacity trends over the first 8 or 9 cycles and records of specific gravity and water-added for each cell after initial cycling. Features defined from these raw data included the individual data items as well as transformations and combinations of these data. All features were represented as standardized variables. It was shown that lifetime prediction of batteries within the two categories defined could be made with about 87% accuracy. It is concluded that for a similarly-manufactured battery set, relative lifetime prediction could be based on initial measurements of the same type examined here.     

Wood waste fuel in the secondary wood products industries

The secondary wood products industry is a suitable candidate for energy recovery from waste. As a whole, the industry consumes about 150 × 10⁹ Btu of purchased fuels and electricity. The wood scrap generated by this industry is sufficient to displace the purchased fuels and electricity if its energy were recovered. The major hurdle inhibiting widespread application of energy recovery technology is the extremely high share of small firms within the industry. The best choice for a smaller manufacturer is direct combustion in a boiler for process and space heat. A straightforward procedure is developed to provide an assessment of the economic feasibility of such boilers for individual firms within the industry. The procedure is used to estimate the amount of wood waste required and the quantity of heat produced in order to achieve rapid payback. These are compared with actual conditions to provide a first estimate of economic feasibility.     

Comment on ‘laminar film condensation in a tube with upward vapour flow’ by Seban and Hodgson

In this paper analytical solution is presented for condensation when the friction factor augmentation factor (F) [1] is negligible. For the cases where F is significant an alternative route involving the solution of cubic equation in is shown. It is demonstrated that the results satisfactorily represent the numerically computed values of Seban and Hodgson.