Effect of temperature gradient on crack initiation

Compact tension (CT) specimens of pressure vessel steel A533B have been subjected to linear distributions of temperature along the crack line. The temperature dependence of fracture toughness for the A533B steel creates a fracture toughness gradient in such a specimen. The specimens simulated an irradiated pressure vessel wall and a functionally gradient material. The CT specimens subjected to linear distributions of temperature were tested to evaluate the fracture toughness for crack initiation. In all tests, the temperature at the crack tip was kept at −10°C or −55°C. If the value of the temperature gradient ahead of the crack tip exceeded a critical value, the fracture toughness deviated from the toughness obtained under a uniform temperature of −10°C or −55°C.     

Effect of a booster mirror on the performance of a ‘built-in’ storage solar water heater

In this paper, the performance of a ‘built-in’ storage solar water heater-flat mirror system has been presented. Numerical calculations have been made for a typical cold day (viz. 28 Jan. 1980) at Delhi. The booster mirror causes a minimum temperature rise during the moring and a temperature difference of 7°C excess with respect to the reference panel occurred. The reflectance of the mirror is taken as 0·88.     

The role of reverse temper embrittlement on some low and high temperature crack extension processes in low carbon, low alloy steels: A review

The present paper attempts to review the influence or role that reverse temper embrittlement (RTE) plays on the low temperature (<400°C) environmentally assisted cracking (EAC) processes in aqueous environments and the high temperature ( > 400°C) creep dominated crack growth processes prevalent in low carbon, low alloy steels. RTE is a generic problem in iron based alloys and causes a marked reduction in the cohesion strength of grain boundaries due to the segregation of impurity solute atoms.

It has been shown that there is a strong possibility that RTE can promote or enhance EAC in low alloy steels (the heat affected zone in weldments being the most susceptible) subjected to aqueous environments at temperatures below about 350°C.

At higher operational temperatures, viz. above 400°C, the characteristics of creep embrittlement are discussed and three microstructural features which contributed to this phenomena are highlighted. Proposals aimed at mitigating creep embrittlement processes in low alloy steels are forwarded.

In certain steels it was recorded that two embrittlement processes were prevalent at operational temperatures in the range 450–550°C, viz. RTE and an irreversible creep embrittlement which was prevalent when large deformation occurred in service. Indeed both 2·25 Cr1Mo and Cr-Mo-V steels were severely temper embrittled at service temperatures of 430°C while the Cr-Mo-V steels did not exhibit evidence of RTE at higher service temperatures of around 530°C. However, the effects of RTE in promoting creep embrittlement are, as yet, unclear.     

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%).     

Effect of sub-freezing temperatures on a PEM fuel cell performance, startup and fuel cell components

The cold-start behavior and the effect of sub-zero temperatures on fuel cell performance were studied using a 25-cm² proton exchange membrane fuel cell (PEMFC). The fuel cell system was housed in an environmental chamber that allowed the system to be subjected to temperatures ranging from sub-freezing to those encountered during normal operation. Fuel cell cold-start was investigated under a wide range of operating conditions. The cold-start measurements showed that the cell was capable of starting operation at −5 °C without irreversible performance loss when the cell was initially dry. The fuel cell was also able to operate at low environmental temperatures, down to −15 °C. However, irreversible performance losses were found if the cell cathode temperature fell below −5 °C during operation. Freezing of the water generated by fuel cell operation damaged fuel cell internal components. Several low temperature failure cases were investigated in PEM fuel cells that underwent sub-zero start and operation from −20 °C. Cell components were removed from the fuel cells and analyzed with scanning electron microscopy (SEM). Significant damage to the membrane electrode assembly (MEA) and backing layer was observed in these components after operation below −5 °C. Catalyst layer delamination from both the membrane and the gas diffusion layer (GDL) was observed, as were cracks in the membrane, leading to hydrogen crossover. The membrane surface became rough and cracked and pinhole formation was observed in the membrane after operation at sub-zero temperatures. Some minor damage was observed to the backing layer coating Teflon and binder structure due to ice formation during operation.     

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.     

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.     

Design and performance study of a solar energy powered vaccine cabinet

An insulated steel sheet cabinet of 0.6 × 0.3 m face area and 0.5 m depth was designed. The cabinet was intended to store vaccine in remote desert areas, away from the electrical national grid. World Health Organization regulations limit the inside temperature of such vaccine storage cabinets to the range of 0–8°C. A solar energy powered absorption refrigeration cycle using Aqua-Ammonia solution was designed to keep this cabinet temperature in the range of required temperatures, away from the outside temperature, which reaches about 45°C in August. A computer simulation procedure was developed to study the performance and characteristics of the cooling cycle. The simulation included MATLAB computer programs for calculating the absorption cycle, thermodynamic properties and quantities as subroutines for the main program, and a detailed mathematical model using EXCEL for the solar side of the unit. A year round work was predicted. Refrigeration cycle coefficient of performance ranged between 0.5 and 0.65; cylindrical solar concentrator extended the daily operating time to about 7 h and increased the output temperature up to >200°C, while the temperature which gives optimum condition (of COP = 0.65) was 120°C.     

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.     

Investigation of lithium intercalation materials with organic solvents and molten salts as electrolytes at temperatures between 60 and 175 °C

Lithium intercalation in TiS₂ and vanadium oxides (V₂O₅, V₂O₄, V₂O₃) has been investigated in two kinds of electrolytes: (i) molten chloroaluminates (butylpyridinium chloride-AlCl₃-LiCl) at 60 °C, and LiAlCl₄-LiCl (saturated) at 175 °C; and (ii) dimethylsulfone (DMSO₂) + LiClO₄ or LiAsF₆ at 130 – 150 °C. The intercalation process has been studied by cyclic voltammetry, galvanostatic discharge/charge and open-circuit voltage measurements.

In chloroaluminates, TiS₂ appears to be stable in both media, with a one-step intercalation at 0.40 V (60 °C) or 0.65 V (175 °C) (versus Al reference). V₂O₅ can only be cycled at a low temperature (60 °C) and two steps are observed at 1 V and 0.45 V.

In DMSO₂, V₂O₅ intercalates 2.5 Li⁺ per unit V₂O₅, with four steps, as observed in propylene carbonate (PC).

OCV measurements at different intercalation steps indicate that the effect of temperature increases the kinetics of the processes.

A comparison of the OCV variations with Li⁺ concentration in DMSO₂ and PC suggests that the intercalation process differs in both solvents. The difference can be correlated with changes in the Li⁺ solvation effects of the solvents.     

Year round performance of a cylindrical solar water heater

A cylindrical collector-cum-storage type solar water heater has been designed, developed and tested. Its year round performance has been carried out and reported in this paper. The heater can provide 50 litres of hot water at 50–60°C in the afternoon and a temperature of 35°C can be retained till the next day for early morning use. The heater receives approximately 30% more radiation as compared to a flat surface. The economics of the heater has been worked out and it has been found that the cost can be recovered within one year.     

Low temperature μc-Si film growth using a CaF2 seed layer

This paper describes low temperature thin film Si growth by remote plasma chemical vapor deposition system for photovoltaic device applications. Using CaF₂/glass substrate, we were able to achieve an improved μc-Si film at a low process temperature of 300°C. The μc-Si film on CaF₂/glass substrate shows that a crystalline volume fraction of 65% and dark conductivity of 1.65×10⁻⁸ S/cm with the growth conditions of 50 W, 300°C, 88 mTorr, and SiH₄/H₂=1.2%. XRD analysis on μc-Si/CaF₂/glass showed crystalline film growth in (1 1 1) and (2 2 0) planes. Grain size was enlarged as large as 700 Å for a μc-Si/CaF₂/glass structure. Activation energy of μc-Si film was given as 0.49 eV. The μc-Si films exhibited dark- and photo-conductivity ratio of 124.     

Bin weather data for 38 Greek cities

Ambient temperature bin data are used for estimating the energy consumption for heating and cooling of buildings. This well-known method is a steady-state approach and the energy requirements are determined at various outdoor temperatures, in order to account for the effect of outside temperature on the HVAC equipment efficiency. The application of the method requires detailed bin data. In this paper, the dry-bulb temperature bin data for 38 Greek cities are determined by using a reliable estimating methodology, based on monthly-average outdoor temperatures and solar clearness index. The data are calculated from −18 °C to 42 °C with 2 °C increments in six daily 4-h shifts, and are presented in tabular form.     

Synthesis of LiCoO2 from cobalt—organic acid complexes and its electrode behaviour in a lithium secondary battery

Well-crystallized, layered LiCoO₂ has been prepared by heating cobalt—organic acid complexes (such as malic acid and succinic acid) at 900 °C in air after preheating at 400 °C (2 h) and at 650 °C (6 h). LiCoO₂ obtained by this method shows a high (003) peak intensity and low (104) or (101) intensities in X-ray diffraction (XRD). The first discharge capacity of LiCoO₂ obtained from this method in ester-based electrolyte is 132 mA h g⁻¹ on cycling between 4.3 and 3.7 V. The value is larger than that obtained by the conventional method. X-ray diffraction studies and open-circuit voltage curves show the presence of at least two types of reaction. A two-phase reaction occurs in the region of 0.71<χ <1.0 in Li_xCoO₂. The lithiation proceeds as a homogeneous reaction together with expansion of the c-axis in the region of 0.47<χ<0.71. The expansion of the c-axis againstΔχ at x=0.56 corresponds well with the voltage jump observed in the charge/discharge curves.     

Thermal insulation provided by dry, single-layer clothing materials

At 20 ± 2°C for a wide range of clothing fabrics, which usually have high air-volume voidages, the thermal resistance to ‘dry’ heat transfers (apart from boundary layer contributions on their faces) is proportional to the fabric thickness. This resistance exhibits a maximum at a fabric density of approximately 90 kg m⁻³.     

Thermal design of a roof as an inexpensive solar collector/storage system

This paper presents the thermal performance of a roof as a solar collector/storage system which is important for the thermal design of buildings. The system consists of a mass of concrete or concrete insulation, one face of which is blackened/glazed and exposed to solar radiation and ambient air, while the other is in contact with room air at constant temperature. The heat can be extracted by the passage of water through the network of tubes in this block. It is seen that, by increasing the depth of the tubes, the rise in water temperature decreases but the time difference between the maxima of the solair temperature and that of the outlet water temperature increases. At a tube depth of 0·10 m, the maximum temperature rise of the water is 33·5°C. The corresponding efficiency of the system is 28·0% while the flow rate of water is 5·0 litre/h m²; the heat flux entering the room is also reduced considerably.     

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.     

Bismuth oxide doped scandia-stabilized zirconia electrolyte for the intermediate temperature solid oxide fuel cells

Electrical and structural properties of bismuth oxide doped scandia-stabilized zirconia (ScSZ) electrolyte for solid oxide fuel cells (SOFCs) have been evaluated by means of XRD, TGA, DTA, and impedance spectroscopy. The amount of Bi₂O₃ in the ScSZ was varied in the range of 0.25–2.0 mol%. The original ScSZ samples indicated a rhombohedral crystalline structure that in general has lower conductivity than the cubic phase. However, the addition of Bi₂O₃ to ScSZ electrolyte was found to stabilize the cubic crystalline phase as detected by XRD. Impedance spectroscopy measurements in the temperature range between 350 and 900 °C indicated a sharp increase in conductivity for the system containing 2 mol% of Bi₂O₃ that is attributed to the presence of the cubic phase. In addition, impedance spectroscopy measurements revealed significant decrease of both the grain bulk and grain boundary resistances with respect to the temperature change from 600 to 900 °C and concentration of Bi₂O₃ from 0.5 to 2 mol%. The electrical conductivity at 600 °C obtained for 2 mol% Bi₂O₃ doped ScSZ was 0.18 S cm⁻¹.     

Performance analysis of a solar-powered/fuel-assisted Rankine cycle with a novel 30 hp turbine

The subject of this analysis is a novel hybrid steam Rankine cycle, which was designed to drive a conventional open-compressor chiller, but is equally applicable to power generation. Steam is to be generated by the use of solar energy collected at about 100°C, and is then to be superheated to about 600°C in a fossil-fuel fired superheater. The steam is to drive a novel counter-rotating turbine, and most of its exhaust heat is regenerated. A comprehensive computer program developed to analyze the operation and performance of the basic power cycle is described. Each component was defined by a separate subroutine which computes its realistic off-design performance from basic principles. Detailed predicted performance maps of the turbine and the basic power cycle were obtained as a function of turbine speed, inlet pressure, inlet temperature, condensing temperature, steam mass flow rate, and the superheater's fuel consumption rate. Some of the major conclusions are: (1) the turbine's efficiency is quite constant, varying in the range of 68.5–76.5 per cent (75 per cent at design) for all conditions, (2) the efficiency of the basic power cycle is 18.3 per cent at design, more than double as compared to organic fluid cycles operating at similar solar input temperatures, at the expense of adding only 20 per cent non-solar energy. This, combined with the fact that actual organic Rankine cycles operate typically at temperatures above 140°C, predicts that this system would be economically superior by using less than half of the collector area and by also using less expensive collectors.