HEMS technique for heat-harm control and geo-thermal utilization in deep mines

With the increasing exploitation scope and intensity,the shallow resources would be exhausted in the future;and the deep mining will become an essential choice.In deep tunnel engineering,the heat-harm becomes one of the mainbariers.Investigations on high temperature coal mine have been done in Nothem China,with the construting of threemodels of high temperature mines suffering heat-harm,at the Jiahe mine,Sanhejian mine and Zhangshuanglou mine.Thedomestic and abroad cooling technologies of the mine respectively are also summarized after comparatively analyzing theadvantages and disadvantages of each technology.Finally,we find that the high temperature exchange machinery system(HEMS)technology that use mine discharge as the cold source,is excellent to heat-ham control in deep mines.Taking theJiahe coal mine as an example,we systematically introduce this teclnology by disposing three main workstations.HEMStechnology with its operations and functions in different exploitation levels are accomplished,including the extraction ofrefrigerating output,the transportation of chilled water by closed circulation line,the decompression of circulation linesand equipment by pressure transformation machine,and the heat exchange and cooling of workplace by heat exchangebetween wind stream and the chilled water.The exchanged heat source from the workplace is taken to ground heating bythe circulating water which acts as a carrier.It shows that the HEMS-technology benefit in environment protection andemission reduction.Results of this project illustrate that it is efficient in heat-ham control with the temperature decrease ofthe workplace down to 26-29℃,and being 4-6℃ lower than the original,and the relative humidity 5%-15%lowerthan before.It greatly improves the working environment of underground workplace suffering heat-ham of high tem-perature and high humidity.In addition,by the extracting of deep geothermal enery,ground fired boiler for heating hasbeen replaced,reducing environmental pollution.This technology is worth generalization in deep mines and related fields.

Risks of non-conservative design according to ASME B31.1 for high-temperature piping subjected to long-term operation in the creep range

This study investigates the risks of non-conservative piping design according to ASME B31.1 for hightemperature piping subjected to long-term operation at high temperature in a creep regime based on a sensitivity analysis of the hold time. Design evaluations of hightemperature piping were conducted over a range of hold times in the creep regime according to ASME B31.1,which implicitly considers the creep effects, and the French high-temperature design code of the RCC-MRx, which explicitly considers the creep effects. Conservatisms were quantified among the codes in terms of the hold times. In the case of B31.1, the design evaluation results do not change depending on the hold time at high temperature,whereas in the case of RCC-MRx, they do. It was shown that the design limits of RCC-MRx were exceeded when the hold time exceeded certain values, whereas those of B31.1 were satisfied regardless of the hold times. Thus, the design evaluations according to B31.1 did not consistently yield conservative results and might lead to non-conservative results in the case of long-term operations in the creep range.

LOW TEMPERATURE MAGNETIC FORCE MICROSCOPY STUDY OF VORTEX IN A YBa_2Cu_3O_(7-x) THIN FILM

A low temperature magnetic fore microscope for the study of high temperature superconductor is developed. It has been applied to spatially resolve single vortices at law temperature (77K) in a YBa2Cu3O7-x thin film deposited by laser ablation on a NdGaO3 substrate. The images of disordered vortex arrangements are obtained. The movement of single vortices after a contact mode scanning of the detecting tip over the thin film surface is observed. The reason for the movement is discussed.

Mechanism of thermoviscoelasticity driven solid-liquid interface reducing friction for polymer alloy coating

High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient supply of lubricating oil and grease.Traditional self-lubricating coatings prepared by inorganic,organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function,so that it is difficult to meet the engineering requirements of high-temperature lubrication.We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy.Polytetrafluoroethylene(PTFE,T_(m)=329℃)and polyphenylene sulfide(PPS,T_(g)=84℃,T_(m)=283℃)are used to prepare a PTFE/PPS polymer alloy coating.As the temperature increases from 25 to 300℃,the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state,which is owing to the thermodynamic transformation characteristic of the PPS component.Additionally the friction coefficient(μ)decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300℃.The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature(T),temperature–centrifugal force(T–F_(ω)),temperature–centrifugal force–shearing force(T–F_(ω)–F_(τ))were investigated.The physical model of“thermoviscoelasticity driven solid–liquid interface reducing friction”is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers.The high-temperature adjusts the viscosity(η)of the coating,increases interface slipping and intensifies shear deformation(τ),reducing the friction coefficient.The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.

Ultra-fast synthesis and thermodynamic analysis of MoAlB by self-propagating high-temperature combustion synthesis

MoAlB as a typical member of MAB phases has attracted much-growing attention due to its unique properties.However,the low production of MoAlB powders limits its further development and potential applications.In the present work,the ultra-fast preparation of high-purity MoAlB powders in a few seconds is achieved by self-propagating high-temperature synthesis(SHS)using a raw powder mixture at an atomic ratio of Mo:Al:B=1:1.3:1.SHS reaction mechanism is obtained by analyzing the corresponding composition changes of starting materials.Furthermore,the thermodynamic prediction for the SHS reaction is consistent with the present experiments,where the preparation of MoAlB also conforms to two common self-propagating conditions of the SHS.The enthalpy vs.temperature curve shows that the adiabatic temperature of the reaction decreases with the amount of excuse Al increasing but increases when pre-heating the reactants.Also,this thermodynamic calculation provides a new idea for the preparation of other MAB phases by the SHS.

High temperature oxidation behavior of Ni-based superalloy GH586 in air

In this paper, the isothermal oxidation kinetics and oxidation behavior of GH586 superalloy from 800 to 1000℃ were investigated. The oxide scale morphologies of the surfaces and the cross sections after oxidation were characterized by means of X-ray diffraction （XRD） and scanning electron microscope （SEM） equipped with energy-dispersive spectroscopy （EDS）. The results show that the growth of the oxide scales on the surface of superalloy GH586 obeys a parabolic law with the activa- tion energy of 241.4 kJ.mo1-1 from 800 to 1000℃ The dense oxide scale formed at 800℃ is mainly composed of Cr203, NiCr204 and a small amount of TiO2. At 900℃, the oxide scale is divided into two layers： the outer layer with multiple cracks is mainly composed of ＂Cr203 and TiO2, while the inner is a layer of dense Cr203. Under the oxide scale, aluminum-rich oxides along the grain bound- aries are generated by the internal oxidation. At 1000 ℃for 100 h, cracks throughout the whole oxide film accel- erate the oxidation rate of Ni-based superalloy GH586 and large blocks of TiO2 in the oxide scale are generated, resulting in the spallation of oxide scale.