Experimental study of interzonal natural convection through an aperture

The work was concerned with measuring natural convection through an aperture between two zones in an environmental chamber. Airflow rates between the two zones were measured using a tracer-gas decay technique, and the temperature at the centre of each zone was measured using thermocouples. Zone 1 was heated to various temperatures in the range 18–38°C using thermostatically controlled heaters. Zone 2 was unheated. A multipoint sampling unit was used to collect a tracer-gas sample from each zone. The concentration of SF₆ tracer was measured using an infra-red gas analyzer. The heat and mass flow rates between the two zones were calculated from the tracer-gas concentrations and temperature differences. Results were compared with values predicted by existing algorithms for two-zone enclosures. The mass flow rate through the aperture was found to be a function of the temperature difference between the two zones.     

Monitoring hydrofluorocarbon refrigerant leakage from air-conditioning systems in buildings

Hydrofluorocarbons (HFCs) are now widely used in refrigeration and air-conditioning systems. These systems lose refrigerants through leaks and during servicing. This paper discusses the possibility of determining the emission rate of HFCs in buildings by applying tracer-gas techniques. The measurement of the emission rate of an HFC refrigerant (R134a) using the concentration-decay technique was carried out in a single-zone chamber. The results were compared with measurements made using an SF₆ tracer and the Pitot-tube traverse method.     

Some aspects of fluidized bed combustion of paddy husk

Some agricultural wastes—for example, bagasse, paddy husk, etc.—are frequently used as fuels, paddy husk appearing, in particular, to be quite suitable for fluidized bed combustion. The conventional method of combustion of paddy husk in grate-type furnaces is slow and inefficient.

This paper reports certain aspects of the fluidized bed combustion of paddy husk. Fluidized bed combustion was carried out by feeding husk in a bed of sand particles. The unexpanded bed height was 10 cm and the size of the sand particles, 351–420 μm. The superficial velocity of the ambient fluidization air through the bed ranged from 11·1 to 22·2 m/min.

A combustion intensity of about 530 kg/h/m² of distributor area could be achieved. This is about 7·5 times higher than the maximum combustion intensity possible in a grate-type furnace per unit grate area. The efficiency of combustion, which ranged from 81 to 98 per cent was found to increase with the air flow rate. There was significant carry-over of inert sand particles from the bed under conditions of high air flow rate.

Combustion intensity increased as the bed height rose from 10 cm to 15 cm, but increased sand entrainment also occurred.     

Membranes based on phosphotungstic acid and polybenzimidazole for fuel cell application

Composite membranes based on phosphotungstic acid (PWA) adsorbed on silica (SiO₂) and polybenzimidazole (PBI) have been prepared and their physico-chemical properties have been studied. The membranes with high tensile strength and thickness of less than 30 μm can be cast. They are chemically stable in boiling water and thermally stable in air up to 400°C. Proton conductivity is influenced by the temperature (range: 30–100°C), relative humidity and PWA loading in the membrane. Maximum conductivity of 3.0×10⁻³ S/cm is obtained at 100% relative humidity and 100°C with membrane containing 60 wt.% PWA/SiO₂ in PBI. Conductivity measurements performed at higher temperatures, in the range from 90°C to 150°C, give almost stable values of 1.4–1.5×10⁻³ S/cm at 100% relative humidity.     

Forced-convective internal cooling of a horizontal equilateral-triangle cross-sectioned duct

An experimental determination of the steady-state forced convection from the internal surfaces of a horizontal, uniformly heated electrically, equilateral-triangle cross-sectioned duct with sharp corners has been undertaken. The average Nusselt number _D, using the hydraulic diameter as the characteristic physical dimension, is a constant if the flow in the duct is laminar, but a function of the air's Reynolds number, when the flow is turbulent. Non-dimensional correlations, which can be used for predicting the value of the steady-state rate of convective heat transfer from such a triangular duct into the airflow, have been deduced, viz. _D = 3·25 for laminar flows, i.e. Re_D < 1450; and _D = 0·012 Re_D^0·83 for turbulent flows, i.e. Re_D ≥ 1450.     

Monitoring the global climatic impact of direct heat addition associated with escalating energy use

Using Budyko's overall heat-balance equation, we estimate that direct heat addition associated with worldwide energy use in the year 2050 will be responsible for a mean global temperature rise of 0.27 °C at a 20 kw_t per capita energy consumption for a world population of ten billion people. The corresponding temperature rise between 15 and 60 °N is estimated to be 0.44 °C. If per capita energy consumption during the year 2050 is reduced to 5 kw, (i.e. about one half of U.S. consumption in the year 1970), the estimated temperature rise for the 15–60 °N latitudinal belt will be about 0.11 °C and therefore still not negligibly small.

A program for monitoring the global climatic impact of escalating energy use involves precise monitoring of the following quantities:

1. (a) the solar constant

2. (b) the effective earth-atmosphere albedo

3. (c) the net (long-wavelength) radiant energy emitted from the earth-atmosphere system.

Both the effective albedo and the (long-wavelength) radiant energy emitted from the earth-atmosphere system will depend on the nature and size of particulate concentrations in the atmosphere, on molecular emitters (especially CO₂ and H₂O), cloud cover, and on the radiative-convective circulation pattern. A satellite observation program that is closely integrated with ground-based and atmospheric measurements and with a detailed program of theoretical analysis will be needed for more precise predictions of inadvertent climate changes and for developing the means to effect desirable global climate controls.     

A human-powered hydrofoil racing-boat: Design and development

A human-powered, hydrofoil-supported, racing boat has been designed, built, tested and developed. At relatively high speeds (4ms⁻¹), this craft provides a more energy efficient means of transport than a conventional displacement hull. An athlete should be capable of powering such a hydrofoil boat through its ‘take-off’ speed of approximately 3·6 ms⁻¹, and then in its ‘foil-borne’ mode of operation, be able to achieve record speeds exceeding 6·0 ms⁻¹. The prototype hydrofoil-supported craft, built for this investigation, required about 287 W of effective power to ‘take-off’, i.e. for the weight of boat plus driver to be entirely hydrofoil-borne, so that the hull was lifted completely out of the water. Due to employing an inappropriate propeller (of only 57% efficiency) and at least 16% excess weight for the boat plus chosen human driver, he could power the craft only to 3·5 ms⁻¹, at which speed the hull had risen so that all but the lowest 5 cm depth of it was above the water. With further developments human-powered hydrofoil craft will fully take off.     

Fermentative biohydrogen production by a new chemoheterotrophic bacterium Citrobacter sp. Y19

A newly isolated Citrobacter sp. Y19 for CO-dependent H₂ production was studied for its capability of fermentative H₂ production in batch cultivation. When glucose was used as carbon source, the pH of the culture medium significantly decreased as fermentation proceeded and H₂ production was seriously inhibited. The use of fortified phosphate at 60–180 mM alleviated this inhibition. By increasing culture temperatures (25–36°C), faster cell growth and higher initial H₂ production rates were observed but final H₂ production and yield were almost constant irrespective of temperature. Optimal specific H₂ production activity was observed at 36°C and pH 6–7. The increase of glucose concentration (1–20 g/l) in the culture medium resulted in higher H₂ production, but the yield of H₂ production (mol H₂/mol glucose) gradually decreased with increasing glucose concentration. Carbon mass balance showed that, in addition to cell mass, ethanol, acetate and CO₂ were the major fermentation products and comprised more than 70% of the carbon consumed. The maximal H₂ yield and H₂ production rate were estimated to be 2.49 molH₂/mol glucose and 32.3 mmolH₂/gcellh, respectively. The overall performance of Y19 in fermentative H₂ production is quite similar to that of most H₂-producing bacteria previously studied, especially to that of Rhodopseudomonas palustris P4, and this indicates that the attempt to find an outstanding bacterial strain for fermentative H₂ production might be very difficult if not impossible.     

Spatially continuous mapping of solar resources in a complex high latitude topography

The annual number of hours with low sun is highest at 60–70° latitude, making the scope for horizon screening effects particularly wide there. The present paper presents a technique for spatially continuous mapping of local screening effects. The method requires a digital topographical map, and radiation data from a site with free horizon. Screening effects are found to introduce local spatial variations in the solar radiation field, amounting to a factor of more than two within a 10 × 10 km area around Bergen (69°24′N, 5°19′E).     

Creep deformation of induction pressure welded 2·25Cr-1Mo steel

In this paper, experimental results involving the effect of stress and temperature on creep behaviour of induction pressure welded (IPW) 2·25Cr-1Mo steel are presented. Creep rupture tests were conducted at 550–700°C in steps of 50°C over a stress range of 112·5–180 MPa. Above 650°C failure of the specimen was enhanced due to the microstructural instability. Failure in the specimens occurred invariably in the heat affected zones (HAZ), and the fracture surfaces indicated ductile failure.     

Creep strain growth behaviour of Hastelloy X above 800°C under thermal-stress cyclings

Actual structural components at high temperature are usually not only subjected to steady mechanical and cyclic loads but also accompanied by temperature variation. Creep ratcheting due to cyclic thermal stress is one of the typical examples. The creep strain growth behaviours of Hastelloy X above 800°C under thermal stress cyclings have been discussed. (1) Cycle dependent creep ratchet strain growth can be estimated to be ΔT, where is the thermal expansion coefficient and ΔT is temperature difference across a body. (2) Time dependent strain growth with temperature variation can be derived by time fraction, virtual activation energy and creep strain of the base temperature. (3) Decreasing creep rate will appear in the neighbourhood of 15–20% of rupture time and increasing creep rate will occur after this, which is almost linear on a logarithmic time scale and Hastelloy X shows softening behaviour on creep after exposure at the higher temperature.     

Atmospheric methane: Its contribution to global warming

Methane, a significant atmospheric trace-gas, controls numerous chemical processes and species in the troposphere and stratosphere. Its concentration in the Earth's atmosphere has been increasing at a rate of about 1% per year during the last century, and reached 1·72 ppmv in 1990. Methane is a strong greenhouse gas with significantly adverse environmental impacts. On a molecule-for-molecule basis, it is more than 20 times as potent a greenhouse gas as carbon dioxide. The contribution of methane to global warming between 1880 and 1980 has been estimated to be about 15%, with an increasing share, 18%, during the 1980s. In this paper methods for estimating the change in atmospheric concentration of methane, and for predicting its global-warming effect, are described. Influences of some of the suggested emission-control policies are also discussed. Methane concentration in the atmosphere might reach a value of more than 4 ppmv by the end of the next century with no control policies implemented. This could produce an unavoidable long-term mean rise in the surface temperature of the Earth of more than 0·5°C.     

Stability of some ternary and quaternary CeNi5-based and PrNi5-based hydride systems

The Ce_1−xR_xNi_2.5Cu_2.5 (R = La,Pr; 0.8 x 0.3) and PrNi_5−xM_x (M = Cu, Fe; 0.5 x 2.5) alloys were investigated for their hydriding characteristics in the temperature range 0–70°C and hydrogen pressure range 0.01–50 atm. The nonlinear behaviour of unit cell volume vs x in Ce_1–xLa_xNi_2.5Cu_2.5 suggests that both size and electronic effects are involved. The partial replacement of Ce by La and Ni by Cu in CeNi₅ causes a substantial reduction in the hydrogen sorption pressures without significantly impairing its hydrogen capacity. It was observed that Fe is more effective than Cu in stabilizing PrNi₅-H₂. The high values of the molar entropy of hydrogen of the β-hydrides studied, S^β_H, are attributed to extensive hydrogen disorder in the interstitial sites of the host lattice. A linear correlation between the hydride decomposition pressures (or free energy) and the unit cell volume. V_c, of the host alloys was observed. This behavior is helpful in predicting the stabilities of new hydrides in a given substitutional alloy series.     

Soil carbon sequestration beneath hybrid poplar plantations in the North Central United States

Hybrid poplar plantations grown on tilled agricultural lands previously in prairie, sequester significant quantities of soil carbon. Comparisons are made between hybrid poplar plantations and adjacent row crops or mowed grass. Establishing and tending plantations often results in early soil carbon loss, but soil carbon is significantly related (positive) to tree age. Increasing tree age eventually results in a net addition of soil carbon from plantations older than about 6 to 12 years of age. Soil carbon loss under trees occurred most frequently from the surface 30 cm early in the plantation history—evidence that the loss was due to mineralization. Soil carbon gain was most significant in the 30–50 cm layer and was attributed to tree root growth. Soil carbon accretion rate beneath 12- to 18-year-old poplar plantations exceeded that of adjacent agricultural crops by l.63 ± 0.16 Mg ha⁻¹ yr⁻¹. There was a significant crop × soil depth interaction for bulk density with bulk density lower beneath trees in the 0–30 cm layer and higher in the 30–50 cm layer. There was little evidence of carbon trapping of wind-blown organic detritus by tree plantations in the prairie environment.     

Measurement of crack propagation velocity in nuclear pressure vessel steel (SA516 gr. 70)

An attempt has been made to develop a simple, reliable and cost-effective device for measuring the dynamic crack propagation velocity in a nuclear pressure vessel steel (SA516 gr. 70). The experimental method is described and a simple digital approach is proposed. The experimentally determined dynamic crack velocity has been utilized to obtain elastic dynamic stress intensity factors by INSAMCR (a two-dimensional dynamic finite element code which is a modified version of SAMCR developed by Dr Schwartz at the University of Maryland). A relationship between instantaneous crack tip velocities and dynamic stress intensity factors for pressure vessel steels is estimated using dynamic crack propagation velocities determined by a proposed measuring device. The relationship between the dynamic stress intensity factor and time history and the dynamic arrest toughness for each test are obtained using the generation mode dynamic finite element analysis. A function ƒ(å) = 1·356 − 2·672å + 6·494å² − 4·539å³ + 1·461å⁴ is suggested which may be useful to predict the relationship between the dynamic fracture toughness (K(å)) and the dynamic crack arrest toughness (K_Ia) for SA516 gr. 70 steel (say K(å) = K_Ia ƒ(å) where å is the dynamic crack propagation velocity).     

Data sampling speed versus energetic measurement errors of irradiation monitoring in photovoltaic systems

To measure solar irradiation and photovoltaic array output energy a measuring accuracy cannot be guaranteed unless the data sampling interval is appropriately selected. From this viewpoint, actual irradiance has been measured by comparatively high speed sampling of 1–4 s for 44 months and the daily errors of the numerical integral have been estimated for various step sizes. Approximation formulae of the error versus the step size have been statistically obtained as well as their probability density function covering ±4σ. Finally, a nomograph is presented to decide an appropriate sampling interval. A concluding example shows that the deviating component of the error exceeding ±1% can happen once for every 1 month or 6 months if the step size is selected as 105 or 65.5 s, in each of which the total error becomes −0.0485±1% or −0.0336±1% including an average error component according to the data measured at Tsukuba.     

The thermal conductivity of toluene. New determinations and an appraisal of recent experimental work

New, absolute determinations of the thermal conductivity of toluene in the temperature range −20° to +112°C are reported. These results were compared with the best data published during the last 10 years, and as a result of a subsequent analysis a linear relation between the thermal conductivity and temperature is proposed, which predicts the thermal conductivity of toluene within better than 1 per cent between −20° and +112°C. In the absence of comprehensive experimental evidence from −20°C to the f.p. At −95°C, it is tentatively suggested to use this equation for extrapolations which will probably fall within 2–3 per cent of the real values.

The accuracy and consistency of the results of the various investigations from which the above relation was derived, and the favourable physical and chemical properties of toluene justify making a strong recommendation for using this substance for calibration purposes in relative determinations, or for control measurements in absolute measurements of the thermal conductivity of fluids.     

Catalytic conversion of fast pyrolysis oil to hydrocarbon fuels over HZSM-5 in a dual reactor system

The catalytic conversion of fast pyrolysis bio-oil to hydrocarbon fuels was studied over HZSM-5 at atmospheric pressure. Experiments were conducted in a dual reactor system having two reactors in series. The temperatures in these reactors were in the range 340–400°C (first reactor) and 350–450°C (second reactor). The bio-oil was co-processed with tetralin in all the runs. The objective was to maximize the organic distillate product with a high concentration of aromatic hydrocarbons. The maximum amount of organic distillate in the effluent from the second reactor was 21 wt% of the bio-oil feed and the highest concentration of aromatic hydrocarbons was 76 wt% of the distillate. The dual reactor system was particularly beneficial when the temperature in the first reactor was low. Thus, with the first reactor at 340°C, the yields of organic distillate and aromatic hydrocarbons were 15–16 wt% and 8–11 wt% of wood, respectively, which are nearly two-fold compared to those from a single reactor system operated at 340°C (7.8 wt% and 4.8 wt%). Under the above conditions, the coke plus char yields were 25–26 wt% of wood which are up to 10 wt% lower than from the single reactor system at 340°C (29 wt%).     

Battery performances and thermal stability of polyacrylonitrile nano-fiber-based nonwoven separators for Li-ion battery

The microporous polyacrylonitrile (PAN) nonwoven separators have been developed by using electrospun nano-fibers with homogeneous diameter of 380 and 250 nm. The physical, electrochemical and thermal properties of the PAN nonwovens were characterized. The PAN nonwovens possessed homogeneous pore size distribution with similar pore size to the conventional microporous membrane separator. Moreover, the PAN nonwovens showed higher porosities, lower gurley values and better wettabilities than the conventional polyolefin microporous separator. Cells with the PAN nonwovens showed better cycle lives and higher rate capabilities than that of a cell with conventional one. Any internal short circuit was not observed for the cells with the PAN nonwovens during charge–discharge test. Hot oven tests for the charged cells up to 4.2 V have revealed that the PAN nonwoven was thermally stable at 120 °C, but showed shrinkage of about 26% isotropically after the test at 150 °C for 1 h. The Celgard membrane showed uniaxial shrinkage of about 30% along the machine direction at 150 °C for 1 h.     

Characteristics of oxygen-blown gasification for combustible waste in a fixed-bed gasifier

With increasing environmental considerations and stricter regulations, gasification of waste is considered to be a more attractive technology than conventional incineration for energy recovery as well as material recycling. The experiment for combustible waste mixed with plastic and cellulosic materials was performed in a fixed-bed gasifier to investigate the gasification behaviour with the operating conditions. Waste pelletized to a diameter of 2–3 cm and 5 cm length, was gasified in the temperature range 1100–1450 °C. The composition of H₂ was in the range 30–40% and CO 15–30% depending upon the oxygen/waste ratio. Gasification of waste due to the thermoplastic property of the mixed-plastic melting and thermal cracking shows a prominent difference from that of coal or coke. It was desirable to maintain the top temperature at 400 °C to ensure the mass transfer and uniform reaction throughout the packed bed. As the bed height was increased, the formation of H₂ and CO was increased, whilst the CO₂ decreased by the char-CO₂ reaction and plastic cracking. From the experimental results, the cold gas efficiency was around 61% and the heating values of product the gases were in the range of 2800–3200 kcal/Nm³.