Papers by Keyword: Liquid Nitrogen

Abstract: Nitrogen cooling has been identified as a powerful industrial solution for the hot extrusion process to remove heat in the die and in the profile. The complexity involved in the design of cooling channels depends on many factors, including the cooling path, its position with respect to the hottest zones as well as the nitrogen phase change that strongly affects the heat removal capacity. However, the industrial approach is still stuck in the empirical and based-experience practices that too often strongly limit the possibilities of obtaining a performing cooling solution. In this context, this work intends to summarize and discuss the advanced recent trends in the design of cooling channels for extrusion dies proposed by the authors based on the numerical approaches, with the final aim to propose possible solutions to fill the current gaps of the suboptimal industrial approaches.

Abstract: AlN nanopowders are successfully synthesized via electrical Al wire explosion in liquid nitrogen. After pickling in 15 % HCl-ethanel, the purified AlN nanopowders are characterized by various techniques. It is observed that the synthesized AlN nanoparticles are hexagonal AlN (h-AlN) exhibiting various shapes, including sphere, spheroidicity, polygon and hexagon. The results show that the charging voltage affects on the AlN content and the morphology of samples, significantly. Further more, it is observed that synthesized AlN particles in the size of 100-300 nm are coated by an amorphous layer mostly resulted from the high cooling rate in liquid nitrogen.

Abstract: Machining of titanium alloys generates enormous amount of heat at the chip-tool interface leading to poor machinability. Use of coolants in the form of gas based lubricants is another approach for controlling the temperature at the cutting zone. The current research investigates the effect of gaseous cooling using CO₂ and cryogenic cooling using LN₂ at the tool rake face during machining of Ti6Al4V. The effect of both the cutting environments was analyzed at low and high level of cutting conditions through FE Model highlighting on thermal softening and through the experimental output responses emphasizing on cutting forces, surface finish and chip microstructure, etc.

Abstract: Titanium alloy is becoming increasingly employed in the aerospace industries due to its good mechanical and chemical properties. As a typical difficult-to-machine material, there are problems of fast tool wear and poor stability of the processing quality in the machining process. Therefore, experiments of high feed milling of TB2 titanium alloy in liquid nitrogen cooling were carried out to measure the cutting force and the cutting temperature. The experimental results showed that under some parameters, liquid nitrogen could decrease the cutting force and cutting temperature in comparison with dry cutting. What’s more, the tool life as well as the surface quality was improved.

Abstract: The MP800’s main frame be completed of spindle assembly during the manufacturing process, Processing to the spindle for a new benchmark for the rest of the dimension chain. The frame size is very large, heavier, material for iron, brittleness, uneven heating not easy to bear the impact and tensile force; flange hole on the frame, the size of parts relatively small, small weight, materials for low alloy steel; hole and shaft with high precision, large amount of interference, Relying on the cooperation between the surface to overcome the friction torque and axial force during working, belong to a large part of large interference not detachable fixed connection; the spindle assembly using liquid nitrogen cold fitting technology

Abstract: Liquid nitrogen cryotherapy is an effective treatment method for skin disease. However, due to the manual operation in the therapeutic process, the treatment effect is difficult to reach. Aimed this problem, the process of freezing in liquid nitrogen was explored. Firstly, the experiment of liquid nitrogen cryotherapy on pork with skin tissue is conducted to investigate the temperatures variation with time. Secondly, three-dimensional numerical simulation of liquid nitrogen cryotherapy was performed. According to the difference in the results of the simulation and experiment, the causes of differences are analyzed and related parameters are optimized. At last, the optimized parameters make the simulation results closer to the experimental results, and provide a reference for the simulation of human skin.

Abstract: The issue of damage to data distribution mechanisms is an overlooked theme today. However, it is very important to devote attention to this problem, since data distribution mechanisms are important carriers of diverse information. It is necessary to protect data distribution mechanisms, and armoured tubes are used for this purpose. Armoured tubes are used in particular where there is a danger of damage to data distribution mechanisms caused by mechanical strain. However, their use is not restricted only to protection against mechanical strain, but also includes protection of conductors against potential sabotage. They can very often be seen in massive or level crossing contacts. Testing of armoured tubes was performed due to the detection of potential deficiencies of such protection.

Abstract: A spatial cold-shield system with cryogenic phase change refrigeration was studied to decrease the surface temperature of spacecraft under 100 K and surface infrared intensity under 0.5 W/m² within 30 minutes in space. A 3-D unit and systematic model were established to simulate the real structures and the variation regularities of the major parameters under different flying periods. A simplified unit model and a systematic model were established to simulate the heat-transfer and flow-field of cold shield in cryogenic, vacuum and micro-gravitational conditions. The unit and systematic experiments were carried out to study the cryogenic phase change refrigeration in cold shield on the ground. The results indicated the simulated and experimented parameters of cold-shield were consistent with the designing conditions of spacecraft. The systematic model could make the LN₂ touching the surface easily and causing the surface temperature distributed more uniformly. The cold-shield could meet the requirement of cryogenic infrared intensity by phase change refrigeration in space.

Abstract: With the rapid development of superconducting technology, electrical properties of insulating materials in the low temperature have recently gained more and more attention. In this paper, the Alternating Current (AC) and negative Direct Current (DC) breakdown strength of polyimide (PI), polyester (PET) and polytetrafluoroethylene (PTFE) have been tested in room temperature and liquid nitrogen environment respectively by using different electrode system. The results show that the negative DC breakdown strength of these three kinds of material in the liquid nitrogen is lower than that in room temperature, and the AC breakdown strength of PTFE and PI in liquid nitrogen has a little increase than that in room temperature,but PET slightly decreases.

Abstract: Introduce the basic concepts of the superconducting and superconducting magnetic separation, the species and properties of superconducting material. Through the current use situation of superconducting magnetic separation machine to explain the advantages and disadvantages about superconducting magnetic separation machine than conventional magnetic separation machine. The paper analyzes the main problems of the superconducting magnetic separation. With a clear direction of superconducting magnetic separation research, improve the superconducting magnet of the critical temperature, especially in liquid nitrogen temperature, even at room temperature, which is a very important research subject.