Trajectory optimisation in electrical discharge machining of three-dimensional curved and twisted channels

Numerical control electrical discharge machining(NC EDM) is one of the most widely used machining technologies for manufacturing a closed blisk flow path, particularly for three-dimensional(3D) curved and twisted flow channels. In this process, tool electrode design and machining trajectory planning are the key factors affecting machining accessibility and efficiency. Herein, to reduce the difficulty in designing the electrode and its motion path in the closed curved and twisted channels, a heuristic search hybrid optimisation strategy based on channel grids is adopted to realise the initial electrode trajectory design search and optimised size reduction. By transferring the trajectory optimisation constraints from the complex free-form surface to numbered grids, the search is found to be more orderly and accurate. The two trajectory indicators, namely argument angle and minimum distance, are analysed separately for the optimised results of the adaptive learning particle swarm optimisation algorithm, demonstrating that they can meet the actual processing requirements.Experimental results of NC EDM indicate that the motion path generated by this design method can meet the machining requirements of 3D curved and twisted flow channels.

Effect of DC electric field on moisture migration characteristics in oil-pressboard

The moisture content has a great influence on the electric insulation strength of oil-pressboard.Therefore,it is very important to assess the moisture content in power transformers.There is lack of research about the effect of DC electric field on moisture migration.Here,the authors analyse the moisture migration characteristics of oil-press-board under DC electric field.The DC electric field has a greater influence on the moisture content in the oil.Compared with no DC electric field,the moisture content in oil is reduced by 22.91 mg/L at 50℃,while it is reduced by 17.63 mg/L at 70℃.Under the same moisture content in the oil,the moisture content in the pressboard which affected by the DC electric field is higher than the Oommen curve,the maximum dif-ference is 0.88%at 50℃,and 0.05%at 70℃.This result can provide a reference for the revision of existing moisture assessment methods.

High yield bio-oil production by hydrothermal liquefaction of a hydrocarbon-rich microalgae and biocrude upgrading

A green colonial microalgae Botryococcus braunii was hydrothermally processed under subcritical water conditions without the addition of catalysts,obtaining an oil yield as high as 68%.The higher heating value of liquefaction products is close to that of petroleum crude oil.The oil fraction from Botryococcus braunii liquefaction was specified for the first time,and the liquefaction mechanism was proposed.Due to the high lipid content of Botryococcus braunii,the liquefaction product distribution is quite distinct from other microalgae.The produced biocrudes contain
9%oxygen,with oleic acid as the main source.Amides derived from oleic acid and proteins are the major nitrogenates in the biocrudes.The biocrude was processed using catalytic cracking and hydrotreating.Catalytic cracking mostly produces aromatics,while the majority of hydrotreating products are straight and branched hydrocarbons.The oxygen content in the catalytic cracking products was very low.The presence of amides in the hydrotreating feed changes the reaction pathway from hydrodecarboxylation to hydrodeoxygenation as a result of the competitive adsorption of amides on the active sites for hydrodecarboxylation.Both processes show satisfactory denitrogenation performance.Catalytic cracking displays superior ability than hydrotreating with regards to the removal of oxygen.