The air oxidation of super-heavy oil at low temperature was studied in laboratory and its influences on oil viscosity, component and steam sweep efficiency before and after air-injection were analyzed. The feasibility...The air oxidation of super-heavy oil at low temperature was studied in laboratory and its influences on oil viscosity, component and steam sweep efficiency before and after air-injection were analyzed. The feasibility, operation mode and air flooding effect at the late stage of steam assisted gravity drainage(SAGD) were investigated by numerical simulation. The experimental results show for vertical-horizontal well pair SAGD test area of Xing VI Formation in Block Du 84 of Liaohe Oilfield, the low temperature oxidation occurred between 150-250 ?C(steam chamber temperature), the oil viscosity increased greatly after low temperature oxidation, consequently, the oil displacement efficiency dropped sharply. Three development methods in the late stage of SAGD were simulated, i.e., steam + air low temperature oxidation, only air low temperature oxidation and only air high temperature oxidation. By comparing production dynamic curves and residual oil distribution etc., high temperature oxidation reduced the heat loss in late stage of SAGD, recovered the residual oil effectively, and prolonged reservoir development time.展开更多
This study investigated the effects of gaseous emissions from crude storage tank and gas flaring on air and rainwater quality in Bonny Industrial Island. Ambient air quality parameters, rainwater and weather parameter...This study investigated the effects of gaseous emissions from crude storage tank and gas flaring on air and rainwater quality in Bonny Industrial Island. Ambient air quality parameters, rainwater and weather parameters were collected at 60 m, 80 m, 100 m, 200 m and control plot for 4 weeks at the Bonny. Rainwater parameters were investigated using standard laboratory tests. Data analyses were done using Analysis of variance, pairwise t-test and Pearson’s correlation statistical tools. Results show that emission rates, volatile organic compound (VOC) noise and flare temperature decreased with increasing distance from flare points and crude oil storage tanks. Findings further revealed the emission rates varied significantly with distance away from the gas flaring point (F = 6.196;p = 0.004). The mean concentration of pollutants between gas flare site and crude oil storage tank showed that CO (0.02 ± 0.001 - 0.002 ±0.001), SPM (0.011 ± 0.001 - 0.01 ± 0.001), VOC (0.005 ± 0.001 - 0.01 ± 0.001) and NO<sub>2</sub> (0.04 ± 0.001 - 0.005 ± 0.000) had significant variations (p > 0.05) with CO, O<sub>3</sub> and NO<sub>2</sub> having higher concentrations at the gas flare site while SPM, and VOC were higher around the crude oil storage tank site. Wind turbulence was higher around the gas flaring point (4.93 TKE) than the crude oil storage tank (4.55 TKE). Similarly, there was significant variation in the sun radiation, precipitation, and wind speed caused by gas flaring (1582.25 w/m<sup>2</sup>, 436.25 mm, 0.53 m/s) and crude oil storage tank (1536.25 w/m<sup>2</sup>, 3.91.41 mm, 0.51 m/s). There were also significant variations in flared temperature (F = 22.144;p = 0.001);NO<sub>2</sub> (F = 8.250;p = 0.001), CO (F = 6.000;p = 0.004) and VOC (F = 5.574;p = 0.006) with distance from the gas flaring point. The variation in the rainwater parameters with distance from the gas flaring indicated significant variations in pH (F = 5.594;p = 0.006). The study showed that the concentration of VOC and particulates were high in the supposedly control area which is perceived to be safe for human habitation. Significant variations exist in emission rate (p = 0.015), flare temperature (p = 0.001), NO<sub>2</sub> (p = 0.003), VOC (p = 0.001), noise (p = 0.041), hydrogen carbonate (p = 0.037) and chromium (p = 0.032) between the gas flaring and crude oil storage tank. Regular monitoring is advocated to mitigate the harmful effects of the pollutants.展开更多
In the present work, the performance of oil-air two-phase flow under different lubricant oils was investigated. The simulation method was applied to study the influence of the oil viscosity on the flow pattern, veloci...In the present work, the performance of oil-air two-phase flow under different lubricant oils was investigated. The simulation method was applied to study the influence of the oil viscosity on the flow pattern, velocity distribution and Re number in oil-air lubrication by FLUENT software with VOF model to acquire the working performance of oil-air lubrication for high-speed ball bearing. This method was used to obtain the optimum lubrication conditions of high-speed ball bearing. The optimum operating conditions that produce the optimum flow pattern were provided. The optimum annular flow was obtained by PAO6 oil with the low viscosity. Reynolds number influences the fluid shape and distribution of oil and air in pipe. The annular flow can be formed when Reynolds number is an appropriate value. The velocity distribution of oil-air two-phase flow at outlet was also discussed by different oil viscosities. The simulating results show that due to the effect of the oil viscosity and flow pattern the velocity decreased and expanded gradually close to the pipe wall, and the velocity increased close to the central pipe. The simulation results provide the proposal for the design and operation of oil-air two-phase flow lubrication experiments in the present work. This work provides a useful method in designing oil-air lubrication with the optimum flow pattern and the optimum operating conditions.展开更多
Air emissions during palm oil processing by smallholders are issues of public health concern demanding urgent intervention by environmentalist. In this study, six smallholder oil palm processing mills were studied inE...Air emissions during palm oil processing by smallholders are issues of public health concern demanding urgent intervention by environmentalist. In this study, six smallholder oil palm processing mills were studied inElele,Nigeria. Air emission parameters (NO2, NH3, CO, H2S, SO2, VOC), noise and meteorology (wind speed, temperature, relative humidity and pressure) were determined at three distances (10 ft,25 ftand50 ft) in both wind ward and lee ward directions from the mills covering boiling and digestion activities. The emissions from biomass were found to be significantly higher than that from fossil diesel, while noise was higher during digestion. The health implications of air emissions were discussed. The study concluded by directing attentions of regulatory agencies to monitor the activities of smallholder oil palm processing to ensure the environmental sustainability of their operations. In summary, evidence during boiling activity revealed that: · H2S ranged from - 2.400 ppm at10 ft, - 2.067 ppm at25 ftand - 0.833 ppm at50 ftfrom the mills in the wind ward direction, and - 1.167 ppm at10 ft, - 0.567 ppm at25 ftand - 0.367 ppm at50ftdistance from the mills in lee ward direction and was significantly lower during digestion. · SPM ranged from 1634 - 7853 μg/m3 at10 ft, 657 - 1110 μg/m3 at25 ftand 81 - 854 μg/m3 at50 ftfrom the mills in the wind ward direction, and 46 - 236 μg/m3 at10 ft, 44 - 120 μg/m3 at25 ftand 30 - 58 μg/m3 at50 ftfrom the mills in lee ward direction. SPM was significantly lower during digestion. · VOC ranged from 67 - 13.933 ppm at10 ft, 1.033 - 13.133 ppm at25ftand 0.500 -展开更多
The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow ...The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow state. The analyses of oil droplet movement, mass and momentum transfer during the impingement of droplet/wall, as well as wall oil film thickness and flow velocity are very important for the bearing chamber lubrication and heat transfer calculation. An integrated model in combination with droplet movement, droplet/wall impact and film flow analysis is put forward initially based on the consideration of droplet size distribution. The model makes a contribution to provide more practical and feasible technical approach, which is not only for the study of droplet-film interaction and physical behavior in bearing chambers with oil/air two-phase flow phenomena, but also useful for an insight into the essence of physical course through droplet movement and deposition, film formation and flow. The influences of chamber geometries and operating conditions on droplet deposition mass and momentum transfer, and wall film thickness and velocity distribution are discussed. The feasibility of the method by theoretical analysis is also verified by the ex- isting experimental data. The current work is conducive to expose the physical behavior of wall oil film configuration and flow in bearing chamber, and also significant for bearing chamber lubrication and heat transfer study under oil/air two-phase flow conditions.展开更多
Beating chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Consid- eri...Beating chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Consid- ering the pressure of sealing air is an important operating condition that affects the oil droplet and oil film mo- tions, the effect of sealing air pressure on airflow in bearing chamber is investigated in this paper firstly ; and then based on the air velocity and air/wall shear force, the oil droplet moving in core air, deposition of oil droplet im- pact on wall as well as velocity and thickness of oil film are analyzed secondly; the effect of sealing air pressure on oil droplet velocity and trajectory, deposition mass and momentum, as well as oil film velocity and thickness is discussed. The work presented in this paper is conducive to expose the oil/air two phase lubrication mechanism and has certain reference value to guide design of secondary air/oil system.展开更多
The permafrost along the China-Russia Crude Oil Pipeline(CRCOP) is degrading since the pipeline operation in 2011. Heat dissipated from the pipeline, climate warming and anthropogenic activities leads to permafrost wa...The permafrost along the China-Russia Crude Oil Pipeline(CRCOP) is degrading since the pipeline operation in 2011. Heat dissipated from the pipeline, climate warming and anthropogenic activities leads to permafrost warming. The processes of permafrost warming along the CRCOP were studied based on the monitoring of air and soil temperatures, and electrical resistivity tomography(ERT) surveys. Results show that:(1) the mean annual air temperature(MAAT) in permafrost regions along the CRCOP increased with a rate of 0.21°C/10a–0.40°C/10 a during the past five decades;(2) the mean annual ground temperature(MAGT, at-15 m depth) of undisturbed permafrost increased by 0.2°C and the natural permafrost table remained unchanged due to the zero-curtain effect;(3) permafrost surrounding the uninsulated pipeline right-of-way warmed significantly compared with that in a natural site. During 2012–2017, the MAGT and the artificial permafrost table, 2 m away from the pipeline centerline, increased at rates of 0.063°C/a and 1.0 m/a. The thaw bulb developed around the pipe and exhibits a faster lateral expansion;(4) 80-mm-thick insulation could reduce the heat exchange between the pipeline and underlying permafrost and then keep the permafrost and pipe stable. The MAGT and the artificial permafrost table, 4.8 m away from the center line of the pipeline, increased by 0.3°C/a and 0.43 m/a, respectively. Due to the heat disturbance caused by warm oil, the degradation of wetland, controlled burn each autumn and climate warming, the permafrost extent reduced and warmed significantly along the CRCOP route. Field observations provide basic data to clarify the interactions between CRCOP and permafrost degradation and environmental effects in the context of climate change.展开更多
Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are a...Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.展开更多
There are certification and airworthiness requirements relevant to the provision of clean breathing air in the crew and passenger compartments. There have been continuing reports and studies over the years regarding o...There are certification and airworthiness requirements relevant to the provision of clean breathing air in the crew and passenger compartments. There have been continuing reports and studies over the years regarding oil fumes in aircraft, including impaired crew performance. Oil fumes are viewed in varying ways ranging from rare seal bearing failures, to low level leakage in normal flight. A Masters of Science (MSc) research degree was undertaken to assess whether there is any gap between the certification requirements for the provision of clean air in crew and passenger compartments, and the theoretical and practical implementation of the requirements using the bleed air system. A comprehensive literature search reviewed applicable certification standards, documented and theoretical understanding of oil leakage. Two types of interviews were conducted to address the research questions. Key aviation regulators were questioned about the process by which they certify and ensure compliance with the clean air requirements. Aerospace engineers and sealing professionals were interviewed about their understanding of how oil may leak past compressor oil bearing seals, and into the air supply under various flight conditions. The outcome of the research showed that there is a gap between the clean air certification requirements, and the theoretical and practical implementation of the requirements using the bleed air system. Low level oil leakage into the aircraft cabin in normal flight operations is a function of the design of the engine lubricating system and bleed air systems, both utilising pressurised air. The use of the bleed air system to supply the regulatory required air quality standards is not being met or being enforced as required.展开更多
The latest available data for mean annual air temperature at sites away from the Arctic coast in both Alaska and the Yukon Territory show no significant warming in the last 30-50 years. However, around the Arctic coas...The latest available data for mean annual air temperature at sites away from the Arctic coast in both Alaska and the Yukon Territory show no significant warming in the last 30-50 years. However, around the Arctic coast of northwest North America centered on Prudhoe Bay, the weather stations show significant warming of both the air and the ocean water, resulting in substantial losses in sea ice west of Prudhoe Bay. These changes appeared shortly after the commencement of shipment of oil through the Trans-Alaska Pipeline in 1977, but have now reached a quasi-stable thermal state. Since more than 17 trillion barrels of oil have passed through the pipeline after being cooled by the adjacent air, which in turn, can then result in the melting of the adjacent sea ice, there appears to be a very strong relationship between these events, and a marked lack of correlation with the changes of the content of greenhouse gases in the atmosphere. This contrasts with the IPCC interpretation of the available climatic data, which assumes that the maximum climatic warming at Prudhoe Bay is typical of the entire region and is the result of increasing greenhouse gases. Engineers need to consider heat advection by oil or gas from underground when designing pipeline facilities, and to take account of the potential environmental con-sequences that they may cause.展开更多
基金Supported by the China National Oil and Gas Major Project(2016ZX05012-002)
文摘The air oxidation of super-heavy oil at low temperature was studied in laboratory and its influences on oil viscosity, component and steam sweep efficiency before and after air-injection were analyzed. The feasibility, operation mode and air flooding effect at the late stage of steam assisted gravity drainage(SAGD) were investigated by numerical simulation. The experimental results show for vertical-horizontal well pair SAGD test area of Xing VI Formation in Block Du 84 of Liaohe Oilfield, the low temperature oxidation occurred between 150-250 ?C(steam chamber temperature), the oil viscosity increased greatly after low temperature oxidation, consequently, the oil displacement efficiency dropped sharply. Three development methods in the late stage of SAGD were simulated, i.e., steam + air low temperature oxidation, only air low temperature oxidation and only air high temperature oxidation. By comparing production dynamic curves and residual oil distribution etc., high temperature oxidation reduced the heat loss in late stage of SAGD, recovered the residual oil effectively, and prolonged reservoir development time.
文摘This study investigated the effects of gaseous emissions from crude storage tank and gas flaring on air and rainwater quality in Bonny Industrial Island. Ambient air quality parameters, rainwater and weather parameters were collected at 60 m, 80 m, 100 m, 200 m and control plot for 4 weeks at the Bonny. Rainwater parameters were investigated using standard laboratory tests. Data analyses were done using Analysis of variance, pairwise t-test and Pearson’s correlation statistical tools. Results show that emission rates, volatile organic compound (VOC) noise and flare temperature decreased with increasing distance from flare points and crude oil storage tanks. Findings further revealed the emission rates varied significantly with distance away from the gas flaring point (F = 6.196;p = 0.004). The mean concentration of pollutants between gas flare site and crude oil storage tank showed that CO (0.02 ± 0.001 - 0.002 ±0.001), SPM (0.011 ± 0.001 - 0.01 ± 0.001), VOC (0.005 ± 0.001 - 0.01 ± 0.001) and NO<sub>2</sub> (0.04 ± 0.001 - 0.005 ± 0.000) had significant variations (p > 0.05) with CO, O<sub>3</sub> and NO<sub>2</sub> having higher concentrations at the gas flare site while SPM, and VOC were higher around the crude oil storage tank site. Wind turbulence was higher around the gas flaring point (4.93 TKE) than the crude oil storage tank (4.55 TKE). Similarly, there was significant variation in the sun radiation, precipitation, and wind speed caused by gas flaring (1582.25 w/m<sup>2</sup>, 436.25 mm, 0.53 m/s) and crude oil storage tank (1536.25 w/m<sup>2</sup>, 3.91.41 mm, 0.51 m/s). There were also significant variations in flared temperature (F = 22.144;p = 0.001);NO<sub>2</sub> (F = 8.250;p = 0.001), CO (F = 6.000;p = 0.004) and VOC (F = 5.574;p = 0.006) with distance from the gas flaring point. The variation in the rainwater parameters with distance from the gas flaring indicated significant variations in pH (F = 5.594;p = 0.006). The study showed that the concentration of VOC and particulates were high in the supposedly control area which is perceived to be safe for human habitation. Significant variations exist in emission rate (p = 0.015), flare temperature (p = 0.001), NO<sub>2</sub> (p = 0.003), VOC (p = 0.001), noise (p = 0.041), hydrogen carbonate (p = 0.037) and chromium (p = 0.032) between the gas flaring and crude oil storage tank. Regular monitoring is advocated to mitigate the harmful effects of the pollutants.
文摘In the present work, the performance of oil-air two-phase flow under different lubricant oils was investigated. The simulation method was applied to study the influence of the oil viscosity on the flow pattern, velocity distribution and Re number in oil-air lubrication by FLUENT software with VOF model to acquire the working performance of oil-air lubrication for high-speed ball bearing. This method was used to obtain the optimum lubrication conditions of high-speed ball bearing. The optimum operating conditions that produce the optimum flow pattern were provided. The optimum annular flow was obtained by PAO6 oil with the low viscosity. Reynolds number influences the fluid shape and distribution of oil and air in pipe. The annular flow can be formed when Reynolds number is an appropriate value. The velocity distribution of oil-air two-phase flow at outlet was also discussed by different oil viscosities. The simulating results show that due to the effect of the oil viscosity and flow pattern the velocity decreased and expanded gradually close to the pipe wall, and the velocity increased close to the central pipe. The simulation results provide the proposal for the design and operation of oil-air two-phase flow lubrication experiments in the present work. This work provides a useful method in designing oil-air lubrication with the optimum flow pattern and the optimum operating conditions.
文摘Air emissions during palm oil processing by smallholders are issues of public health concern demanding urgent intervention by environmentalist. In this study, six smallholder oil palm processing mills were studied inElele,Nigeria. Air emission parameters (NO2, NH3, CO, H2S, SO2, VOC), noise and meteorology (wind speed, temperature, relative humidity and pressure) were determined at three distances (10 ft,25 ftand50 ft) in both wind ward and lee ward directions from the mills covering boiling and digestion activities. The emissions from biomass were found to be significantly higher than that from fossil diesel, while noise was higher during digestion. The health implications of air emissions were discussed. The study concluded by directing attentions of regulatory agencies to monitor the activities of smallholder oil palm processing to ensure the environmental sustainability of their operations. In summary, evidence during boiling activity revealed that: · H2S ranged from - 2.400 ppm at10 ft, - 2.067 ppm at25 ftand - 0.833 ppm at50 ftfrom the mills in the wind ward direction, and - 1.167 ppm at10 ft, - 0.567 ppm at25 ftand - 0.367 ppm at50ftdistance from the mills in lee ward direction and was significantly lower during digestion. · SPM ranged from 1634 - 7853 μg/m3 at10 ft, 657 - 1110 μg/m3 at25 ftand 81 - 854 μg/m3 at50 ftfrom the mills in the wind ward direction, and 46 - 236 μg/m3 at10 ft, 44 - 120 μg/m3 at25 ftand 30 - 58 μg/m3 at50 ftfrom the mills in lee ward direction. SPM was significantly lower during digestion. · VOC ranged from 67 - 13.933 ppm at10 ft, 1.033 - 13.133 ppm at25ftand 0.500 -
基金National Natural Science Foundation of China (50975233)
文摘The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow state. The analyses of oil droplet movement, mass and momentum transfer during the impingement of droplet/wall, as well as wall oil film thickness and flow velocity are very important for the bearing chamber lubrication and heat transfer calculation. An integrated model in combination with droplet movement, droplet/wall impact and film flow analysis is put forward initially based on the consideration of droplet size distribution. The model makes a contribution to provide more practical and feasible technical approach, which is not only for the study of droplet-film interaction and physical behavior in bearing chambers with oil/air two-phase flow phenomena, but also useful for an insight into the essence of physical course through droplet movement and deposition, film formation and flow. The influences of chamber geometries and operating conditions on droplet deposition mass and momentum transfer, and wall film thickness and velocity distribution are discussed. The feasibility of the method by theoretical analysis is also verified by the ex- isting experimental data. The current work is conducive to expose the physical behavior of wall oil film configuration and flow in bearing chamber, and also significant for bearing chamber lubrication and heat transfer study under oil/air two-phase flow conditions.
基金supported by the Natural Science Foundation of China under Grant No.51275411
文摘Beating chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Consid- ering the pressure of sealing air is an important operating condition that affects the oil droplet and oil film mo- tions, the effect of sealing air pressure on airflow in bearing chamber is investigated in this paper firstly ; and then based on the air velocity and air/wall shear force, the oil droplet moving in core air, deposition of oil droplet im- pact on wall as well as velocity and thickness of oil film are analyzed secondly; the effect of sealing air pressure on oil droplet velocity and trajectory, deposition mass and momentum, as well as oil film velocity and thickness is discussed. The work presented in this paper is conducive to expose the oil/air two phase lubrication mechanism and has certain reference value to guide design of secondary air/oil system.
基金funded by the National Key Research and Development Program(2016YFC0802103)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA2003020102)+3 种基金National Natural Science Foundation of China(Grants Nos.U1703244,41672310,41630636 and 41702333)the Research Project of the State Key Laboratory of Frozen Soils Engineering(Grant No.SKLFSE-ZY-16)the Major Program of Bureau of International Cooperation of CAS(131B62KYSB20170012)the STS research project of CAS(HHS-TSS-STS-1502)
文摘The permafrost along the China-Russia Crude Oil Pipeline(CRCOP) is degrading since the pipeline operation in 2011. Heat dissipated from the pipeline, climate warming and anthropogenic activities leads to permafrost warming. The processes of permafrost warming along the CRCOP were studied based on the monitoring of air and soil temperatures, and electrical resistivity tomography(ERT) surveys. Results show that:(1) the mean annual air temperature(MAAT) in permafrost regions along the CRCOP increased with a rate of 0.21°C/10a–0.40°C/10 a during the past five decades;(2) the mean annual ground temperature(MAGT, at-15 m depth) of undisturbed permafrost increased by 0.2°C and the natural permafrost table remained unchanged due to the zero-curtain effect;(3) permafrost surrounding the uninsulated pipeline right-of-way warmed significantly compared with that in a natural site. During 2012–2017, the MAGT and the artificial permafrost table, 2 m away from the pipeline centerline, increased at rates of 0.063°C/a and 1.0 m/a. The thaw bulb developed around the pipe and exhibits a faster lateral expansion;(4) 80-mm-thick insulation could reduce the heat exchange between the pipeline and underlying permafrost and then keep the permafrost and pipe stable. The MAGT and the artificial permafrost table, 4.8 m away from the center line of the pipeline, increased by 0.3°C/a and 0.43 m/a, respectively. Due to the heat disturbance caused by warm oil, the degradation of wetland, controlled burn each autumn and climate warming, the permafrost extent reduced and warmed significantly along the CRCOP route. Field observations provide basic data to clarify the interactions between CRCOP and permafrost degradation and environmental effects in the context of climate change.
文摘Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.
文摘There are certification and airworthiness requirements relevant to the provision of clean breathing air in the crew and passenger compartments. There have been continuing reports and studies over the years regarding oil fumes in aircraft, including impaired crew performance. Oil fumes are viewed in varying ways ranging from rare seal bearing failures, to low level leakage in normal flight. A Masters of Science (MSc) research degree was undertaken to assess whether there is any gap between the certification requirements for the provision of clean air in crew and passenger compartments, and the theoretical and practical implementation of the requirements using the bleed air system. A comprehensive literature search reviewed applicable certification standards, documented and theoretical understanding of oil leakage. Two types of interviews were conducted to address the research questions. Key aviation regulators were questioned about the process by which they certify and ensure compliance with the clean air requirements. Aerospace engineers and sealing professionals were interviewed about their understanding of how oil may leak past compressor oil bearing seals, and into the air supply under various flight conditions. The outcome of the research showed that there is a gap between the clean air certification requirements, and the theoretical and practical implementation of the requirements using the bleed air system. Low level oil leakage into the aircraft cabin in normal flight operations is a function of the design of the engine lubricating system and bleed air systems, both utilising pressurised air. The use of the bleed air system to supply the regulatory required air quality standards is not being met or being enforced as required.
文摘The latest available data for mean annual air temperature at sites away from the Arctic coast in both Alaska and the Yukon Territory show no significant warming in the last 30-50 years. However, around the Arctic coast of northwest North America centered on Prudhoe Bay, the weather stations show significant warming of both the air and the ocean water, resulting in substantial losses in sea ice west of Prudhoe Bay. These changes appeared shortly after the commencement of shipment of oil through the Trans-Alaska Pipeline in 1977, but have now reached a quasi-stable thermal state. Since more than 17 trillion barrels of oil have passed through the pipeline after being cooled by the adjacent air, which in turn, can then result in the melting of the adjacent sea ice, there appears to be a very strong relationship between these events, and a marked lack of correlation with the changes of the content of greenhouse gases in the atmosphere. This contrasts with the IPCC interpretation of the available climatic data, which assumes that the maximum climatic warming at Prudhoe Bay is typical of the entire region and is the result of increasing greenhouse gases. Engineers need to consider heat advection by oil or gas from underground when designing pipeline facilities, and to take account of the potential environmental con-sequences that they may cause.
