In this paper, a novel method of cryogenically cooled (low-temperature nitrogen gas) wire tool is used during the oxygen-mist near-dry wire-cut electrical discharge machining (NDWEDM) process to cut ...Inconel 718 alloy material. The current, pulse-width, pulse-interval, and flow rate are the controllable variables for response characteristics, such as the material removal rate (MRR) and wire wear ratio (WWR). The Box-Behnken method is applied to design the experiments to collect the observations from experiments. The mathematical models for each response were developed using significant individual, interaction, and quadratic terms by the sequential sum of the square test. The response surfaces were developed. It was revealed from the analysis that 52.92 % of current, 24.63 % of Pulse-width, 12.81 % of pulse- interval and 5.75 % of flow rate contributed to MRR, while 14.89 % of current, 9.75 % of pulse-width, 62.20 % of pulse-interval, and 5.44 % of flow rate contributed to WWR. The pulse-width has more contribution on MRR due to the long period of spark between the wire and work materials. It was also observed that the pulse-interval has more effect on WWR due to the more ideal period (high spark-pause-time) between two consecutive high-temperature sparks in the wire tool. The wear of the wire tool has been analysed using scanning electron microscopy (SEM) photographs. The desirability principles were first applied to obtain multi-objective solutions with a combination of process parameters to achieve the optimal values of both responses. The predicted combination of results has been validated by data that were collected from confirmation experiments.
The elastocaloric cooling, utilizing latent heat associated with martensitic transformation in shape-memory alloys, is being considered in the recent years as one of the most promising alternatives ...to vapour compression cooling technology. It can be more efficient and completely harmless to the environment and people. In the first part of this work, the basics of the elastocaloric effect (eCE) and the state-of-the-art in the field of elastocaloric materials and devices are presented. In the second part, we are addressing crucial challenges in designing active elastocaloric regenerators, which are currently showing the largest potential for utilization of eCE in practical devices. Another key component of elastocaloric technology is a driver mechanism that needs to provide loading for active elastocaloric regenerators in an efficient way and recover the released energy during their unloading. Different driver mechanisms are reviewed and the work recovery potential is discussed in the third part of this work.
Additive manufacturing technologies are nowadays used in various industries. In most cases, however, the surface texture of the produced models is unsatisfactory and requires further processing, ...aiming to reduce surface roughness and waviness. The quality of the surface layer in many cases plays not only an aesthetic role but also affects, for example, the process of wear and tribological properties. In the presented work, samples prepared by fused deposition modelling technology from polylactic acid (PLA) material were subjected to tests. The samples were subjected to heat or chemical treatment through the use of acetone. The quality of the surface texture was tested both before and after the treatments. In addition, tests were carried out to determine the effect of the presented finishing treatment on the tensile strength of the tested sample models. The test results showed that both thermal treatment and acetone treatment influence the surface texture quality, especially the waviness, and that the acetone treatment can improve some mechanical properties. Keywords: 3D printing, finishing treatment, fused deposition modelling, surface texture, mechanical properties
To study the failure of conventional packers in the fracturing and stimulation of low-porosity and low-permeability reservoirs and reduce the failure accidents of packers in the fracturing process, a ...suitable integrated string packers was selected in the process of fracturing and stimulation in an oilfield in the Middle East as a case study. Three different well types have been established. The wellbore temperature distribution and the axial force of the string can be calculated under the conditions of various wellhead pressures and different displacement, and it is found that the temperature at the bottom of the well can reach 130 °C, and the maximum axial force at the wellhead is 500 kN. At the same time, the applicability of retrievable tubing testing squeeze (RTTS) and hydraulic-set retrievable (RH) packer in different working conditions was evaluated, and it was found that only RTTS packers can meet the needs of the oil field. According to the calculated temperature field and axial force distribution, the stress on different components of the packer under different working conditions is established during the fracturing-stimulation operation. In the worst working conditions, the maximum stress of the packer occurs at the lower part of the central pipe, reaching 303.83 MPa, which is in a safe state. The contact stress on rubber rings can reach 30 MPa, indicating that the sealing performance can meet the requirements of on-site use. The temperature and axial force data calculated by the model provide a theoretical basis for safe well control. Through model evaluation, it was found that the RTTS packer can be suitable for the fracturing and stimulation needs of the oilfield. The research methods and achievements in the article provide theoretical guidance for evaluating the applicability of packers in the fracturing and stimulation process of low porosity and low permeability reservoirs.
The investigation of the domestic application of heat flux dissemination is in high demand. The best strategy to obtain a coolant with an ideal execution is by including particular sorts of ...nanoparticles in the base fluid. The utilization of nanofluids escalates the heat transfer coefficient through the enhancement of the base fluid's thermal conductivity. An advanced coolant (hybrid nanofluid) was delivered by blending two or more different types of nano-sized particles with conventional fluid. This article mainly aims to cover the recent publications on hybrid nanofluids on different aspects, such as preparation, thermophysical properties, and heat transfer enhancement. In general, the combination of different nanoparticle properties results in excellent thermal conductivity: improvement in heat transfer coefficient was up to 148 % compared to the base fluid. Moreover, a moderate increase on pressure drop has been detected due to the presence of composite nanoparticles. In any case, the anticipated results for both thermal conductivity and viscosity values utilizing conventional relationships were distinctive from the experimental results. Keywords: hybrid nanofluids, Nusselt number, thermal conductivity, viscosity, thermal applications Highlights * Hybrid nanofluids are produced by mixing two or more nanoparticles types with a base fluid, via physical or chemical processes. * Using hybrid nanofluids provides an enormous enhancement in thermophysical and rheological properties. * A significant enhancement in the heat transfer coefficient for hybrid nanofluid compared to water base fluid is presented. * The effect of hybrid nanofluids in reducing the pressure drop is observed.
This experimental work aims to devise and establish quadratic regression equations, including various input criteria of a friction stir welding (FSW) technique to predict and determine the responses ...during the fabrication of AZ91C Mg alloy joints. The input process parameters taken into consideration include the traversing speed of the tool, the speed of rotation of the tool, its pin profile (geometry) and the axial force. A five-level, 4 four-factor composite design (of central nature) was applied, and response surface methodology (RSM) was used to formulate quadratic regression models, to develop 3D response surface charts, and to anticipate the responses for various mechanical properties. The generated quadratic mathematical model was tested and validated using the technique of analysis of variance. Validation experimental trial results outlined in the form of scatter diagrams revealed precedented coincidence with that of the generated models. The AZ91C Mg alloy joints obtained using the tool having taper cylindrical pin geometry employed at 1045 rpm, 1.5 mm/s traversing speed, under the exertion of an axial load of 4.87 kN was found to exhibit improved mechanical properties.
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