Investigation of lubricant transfer and distribution at head/disk interface in air-helium gas mixtures

Lubricant transfer and distribution at the head/disk interface in air-helium gas mixtures is investigated using a developed model that combines an air-bearing model with a molecular dynamics model. The pressure distribution is calculated by the air-bearing model at the head/disk interface with respect to the helium content and the pressure obtained is then input to the molecular dynamics model to understand the lubricant transfer mechanism. Finally, the effects of pressure at the boundary condition and disk velocity on lubricant transfer are discussed in relation to the helium fraction within the air-helium gas mixtures. Results show there is a decrease in the pressure difference with an increase in the helium percentage, which leads to a decrease in the volume of the lubricant transferred. The results also suggest that the lubricant is not easily to transfer in gas mixtures with a high percentage of helium, even when both higher disk velocities and pressure boundary conditions are applied.

The first extra-large helium-rich gas field identified in a tight sandstone of the Dongsheng Gas Field,Ordos Basin,China

Helium gas is a scarce but important strategic resource,which is usually associated with natural gas.Presently,only one extra-large helium-rich gas field has been found in China:the Hetianhe Gas Field in the Tarim Basin.This paper reports a new example,the Dongsheng Gas Field(DGF)in the Ordos Basin.In this study,92 natural gas samples from the DGF were analyzed for helium content and isotope composition using isotope mass spectrometry.The natural gas samples were found to have an average helium content of 0.133%,with 65(70.7%)of the samples having a helium content of 0.1%or more.Based on the proven natural gas reserves of the DGF,the proven geological helium reserves were calculated to be 1.96×10^(8)m^(3),suggesting that it represents the first extra-large helium-rich natural gas reservoir to be hosted in tight sandstone in China.The ^(3)He/^(4)He ratios of 5 natural gas samples from the DGF are within the range of 3.03×10^(−8)–3.44×10^(−8).Therefore,the helium in the gas field is thought to be of typical crustal origin and to have formed in the granitic basement that is rich in uranium and thorium.The accumulation of helium-rich natural gas was controlled by regional tectonic activities.Activity along the fault connecting the reservoir with the basement caused release of the helium gas,which entered the overlying strata along the fault and accumulated with conventional hydrocarbon gas.Based on the structural background and the distribution of helium source rocks in the Ordos Basin,the main helium source rocks with high exploration potential are located in deep strata within the north and middle parts of the basin.

Unsteady numerical simulation on helium cooldown process for the 650 MHz two-cell superconducting cavity

Background Superconducting cavity is usually needed to be gradually cooled from room temperature to the superconducting temperature zone(4.2 K and below)in the testing and sophisticated operation process of superconducting cavity.Purpose The purpose of this paper is to study the cooling law on the helium cooldown process for the 650 MHz two-cell superconducting cavity with the unsteady numerical simulation.Method A three-dimensional coupled heat-flow model of 650 MHz two-cell superconducting cavity was established.The unsteady numerical simulation of different inlet temperatures,flow rates and pressure conditions was carried out.The equiva-lent convective heat transfer coefficient and temperature distribution of 650 MHz two-cell superconducting cavity during cooldown process were obtained.The effects of cooling time and entrance parameters on the cooldown process were analyzed.Results The temperature distribution of the lower intersection lines has a large drop in the initial stage of cooldown process(120 s),while the temperature near the flanges at the both ends is still higher(remaining at the initial temperature of 300 K).With the passage of time,the temperature of the upper and lower intersection lines decreases.The maximum temperature difference on the lower intersections is within 2 K in the final stage of cooldown process(3600 s).The maximum temperature difference increases by 180%,and the difference between the maximum temperature and the minimum temperature(dT)at the end of a cooldown stage increases by 130%after 1 h,respectively,when the inlet temperature drops from 290 to 270 K(under the condition of the initial temperature of 300 K).Conclusions The maximum temperature difference and the dT at the end of a cooldown stage increase with the decrease in the inlet temperature.The maximum temperature difference increases with the increase in the inlet flow rate,while the dT at the end of a cooldown stage decreases with the increase in the inlet flow rate.The effect of changing the inlet flow rate on the cooling rate is not as obvious as changing the inlet temperature.Once there is a certain flow rate,the advantage of further increasing the flow rate to reduce the temperature of the superconducting cavity is not so great.

Accumulation mechanism of mantle-derived helium resources in petroliferous basins, eastern China

A series of marginal-sea basins and fault-depression basins were formed in eastern China under the background of subduction of the West Pacific plate.Different types of helium-rich natural gas reservoirs(He>1000 ppm,1 ppm=1μmol mol^(-1))have been found in these basins:helium-rich CO_(2)gas reservoirs,helium-rich N_(2)gas reservoirs,and helium-rich hydrocarbon gas reservoirs.Based on the analysis of gas geochemical data,the source and accumulation mechanism of helium in these heliumrich natural gas reservoirs were discussed.Helium-rich natural gas has relatively high 3He/4He ratios(0.88-4.91 Ra,average 2.82 Ra).The ^(3)He/^(4)He ratio characteristics of mantle xenoliths and mantle-derived CO_(2)gas reservoirs indicate that the helium in these helium-rich natural gas reservoirs is mainly mantle-derived(>70%).The original mantle volatile is mainly CO_(2)with a low helium concentration(He<200 ppm),and the enrichment of mantle-derived helium in the gas reservoir is mainly related to the dissolution and mineralization of CO_(2).During this process,the CO_(2)/3He ratio decreases from 2×10^(9)to approximately 2×10^(6).As CO_(2)dissolves and mineralizes,the concentration of conservative gases(He and N_(2))increases in the remaining CO_(2)gas proportionally to the loss of CO_(2).Large amounts of carbonate minerals,such as dawsonite,which are relatively enriched in 13C,are found in CO_(2)reservoirs in eastern China.The relative enrichment of^(12)C in residual CO_(2)gas is important evidence of the dissolution and mineralization of CO_(2).The relative abundance of mantle-derived helium and N_(2)gas increases thousands of times during the dissolution and mineralization of CO_(2),which is the main accumulation mechanism of mantle-derived helium-rich CO_(2)gas reservoirs and helium-rich N_(2)gas reservoirs.Helium-rich gas from the mantle is mixed with alkane gas generated by organic matter in the sedimentary basin to form helium-rich hydrocarbon gas reservoirs.