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Abstract Steady-state free and forced convective cooling of vertical, rectangular, 3 mm thick, 250 mm long fins, uniformly separated and protruding vertically upwards from a 250 mm × 190 mm isothermal horizontal base was investigated. For each combination of specified fin protrusion, horizontal forced air flow-rate in the direction along the fins and fin base temperature, the optimal fin spacing—corresponding to the maximum rate of heat loss—has been deduced. As the fin protrusion of the heat exchanger increases, this optimal value rises significantly in forced convection conditions, but declines slightly in the presence of free convection alone. The temperature distributions over the fins' surfaces were also studied, when the fin base was maintained at constant temperatures of either 40°C, 60°C or 80°C above that of the ambient environment. Large temperature depressions occurred near the leading edges and tips of the fins in forced convection, whereas much nearer isothermal temperature distributions were present under free convection conditions.

Abstract Algae have been considered as a promising biodiesel feedstock. One of the major factors affecting large-scale algae technology application is poor wintering cultivation performance. In this study, an integrated approach is investigated combining freshwater microalgae Chlorella zofingiensis wintering cultivation in pilot-scale photobioreactors with artificial wastewater treatment. Mixotrophic culture with the addition of acetic acid (pH-regulation group) and autotrophic culture (control group) were designed, and the characteristics of algal growth, lipid and biodiesel production, and nitrogen and phosphate removal were examined. The results showed that, by using acetic acid three times per day to regulate pH at between 6.8 and 7.2, the total nitrogen (TN) and total phosphate (TP) removal could be increased from 45.2% to 73.5% and from 92.2% to 100%, respectively. Higher biomass productivity of 66.94 mg L−1 day−1 with specific growth rate of 0.260 day−1 was achieved in the pH-regulation group. The lipid content was much higher when using acetic acid to regulate pH, and the relative lipid productivity reached 37.48 mg L−1 day−1. The biodiesel yield in the pH-regulated group was 19.44% of dry weight, with 16–18 carbons as the most abundant composition for fatty acid methyl esters. The findings of the study prove that pH adjustment using acetic acid is efficient in cultivating C. zofingiensis in wastewater in winter for biodiesel production and nutrient reduction.

Feature-based machine learning models for capacity and internal resistance (IR) curve prediction have been researched extensively in literature due to their high accuracy and generalization power. Most such models work within the high frequency of data availability regime, e.g., voltage response recorded every 1–4 s. Outside premium fee cloud monitoring solutions, data may be recorded once every 3, 5 or 10 min. In this low-data regime, there are little to no models available. This literature gap is addressed here via a novel methodology, underpinned by strong mathematical guarantees, called ‘path signature’. This work presents a feature-based predictive model for capacity fade and IR rise curves from only constant-current (CC) discharge voltage corresponding to the first 100 cycles. Included is a comprehensive feature analysis for the model via a relevance, redundancy, and complementarity feature trade-off mechanism. The ability to predict from subsampled ‘CC voltage at discharge’ data is investigated using different time steps ranging from 4 s to 4 min. It was discovered that voltage measurements taken at the end of every 4 min are enough to generate features for curve prediction with End of Life (EOL) and its corresponding IR values predicted with a mean absolute percentage error (MAPE) of approximately 13.2% and 2.1%, respectively. Our model under higher frequency (4 s) produces an improved accuracy with EOL predicted with an MAPE of 10%. Full implementation code publicly available.

Abstract The pressure-loss coefficient for a duct junction of square cross-section was determined using computational fluid dynamics (CFD). The predicted junction pressure-loss coefficient for combining flows was generally in good agreement with experimental data from the literature. The junction pressure-loss coefficient was associated with the flow from the side branch to the duct carrying the total flow.

Waste biomass is generated during the conservation management of semi-natural habitats, and represents an unused resource and potential bioenergy feedstock that does not compete with food production. Thermogravimetric analysis was used to characterise a representative range of biomass generated during conservation management in Wales. Of the biomass types assessed, those dominated by rush (Juncus effuses) and bracken (Pteridium aquilinum) exhibited the highest and lowest volatile compositions respectively and were selected for bench scale conversion via fast pyrolysis. Each biomass type was ensiled and a sub-sample of silage was washed and pressed. Demineralization of conservation biomass through washing and pressing was associated with higher oil yields following fast pyrolysis. The oil yields were within the published range established for the dedicated energy crops miscanthus and willow. In order to examine the potential a multiple output energy system was developed with gross power production estimates following valorisation of the press fluid, char and oil. If used in multi fuel industrial burners the char and oil alone would displace 3.9 × 105 tonnes per year of No. 2 light oil using Welsh biomass from conservation management. Bioenergy and product development using these feedstocks could simultaneously support biodiversity management and displace fossil fuels, thereby reducing GHG emissions. Gross power generation predictions show good potential.

The photosynthetic capacity of algae as a primary producer in nature and the relative ease of its cultivation on a large scale make it attractive to explore opportunities and develop algal technology for simultaneous sequestration of industrial and atmospheric CO2 (to mitigate climate change), whilst developing sustainable processes for manufacturing renewable fuels alongside biochemicals of value. The development of strategies that maximise algal product yield while optimising the CO2 gas supply is needed for the appropriate scale-up of algal technology. One of the main targets of this technology is the potential exploitation of flue gases, an inexpensive and carbon-rich source. So far, the growth of microalgae has predominantly been investigated using relatively low CO2 concentrations that are far from the levels offered by flue gas (6–25%), which are more useful for energy generation with concomitant development of carbon neutral processes. Here, we tested a series of gas supply strategies to investigate microalgal growth at high CO2 levels with the aim to improve algal CO2 fixation and lipid accumulation. Optimal growth of Nannochloropsis salina (a marine algae) occurred at 6% CO2, whilst few cells grew under 20% CO2. Excess CO2 resulted in medium acidification, pigment reduction, and growth inhibition. However, the fixation capacity of CO2 and the production of specific lipids were improved by O2 removal from the inlet gas by up to 4.8-fold and 4.4-fold, respectively. These parameters were further improved by 72% and 25%, respectively, via a gradual increase in CO2 concentration. Extremely high CO2 levels (100%) completely inhibited cell growth, but this effect was reversed when air containing atmospheric CO2 levels was introduced in place of 100% CO2. These findings will allow for the future development of more effective strategies using algal biotechnology for producing biofuel while mitigating carbon emissions.

Single-phase ‘shaded-pole’ induction motors, which are commonly employed for driving small (i.e. <0·25-m diameter) tube-axial fans, are characterised by end-use efficiencies of less than 20%. However, electronically commutated (i.e. ‘brushless’) permanent-magnet, low voltage, DC motors achieve significantly greater efficiencies (e.g., typically exceeding 40%) when used for the same purpose. Although for air-moving applications, the popularity of brushless DC motors has been limited by their high manufacturing costs, the ready availability of monolithic, specific-purpose, integrated circuits now permits the development of designs which offer cost-effective alternatives to conventional low power-output (<100-W) AC, as well as DC, motive systems. In particular, a dsign of a low-cost brushless motor for driving a standard tube-axial fan, of 0·115-m diameter, is described: it is optimised so that the least cost per unit of mass production ensues. This fan unit achieves an 80% reduction in the rate of energy consumption and a 52% saving in weight, when compared with its AC counterpart of nominally identical performance. Further improvements in its efficiency (e.g. from 44% to 53%) are attainable, for relatively small increases in manufacturing cost (e.g. <5%).

Abstract Flow patterns and temperature profiles, as well as local and overall heat transfer coefficients, were measured for a horizontal, annular cavity, containing air at atmospheric pressure. The radius ratio of the bounding surfaces of the cavity was 1·5, the inner cylinder being heated. The insertion of two horizontal, radial, co-planar spacers bridging the 18·9 mm cavity along its whole length, reduced the convective rate of heat transfer from the surface of the inner cylinder whereas the same co-planar spacers, if vertical, led to an increased rate of convective heat transfer. Flow instabilities, encountered in the plain cavity, were also eliminated by the insertion of the horizontal spacers.