In the present study,hydraulic and thermal behavior of an automatic transmission nano-fluid(ATNF) inside a tube with a twisted tape has been investigated.The heat transfer improvement and pressure drop of transmission...In the present study,hydraulic and thermal behavior of an automatic transmission nano-fluid(ATNF) inside a tube with a twisted tape has been investigated.The heat transfer improvement and pressure drop of transmission oil for each of case of using twisted tape and nano-particles were also examined separately and compared with each other.The Cu O nano-particles were used to prepare the ATNF.The effects of different Reynolds numbers and different mass fractions of nano-particle were investigated.The results showed that applying nano-particles and twisted tape simultaneously increases both the pressure drop and Nusselt number,on average by about 53% and 76%,respectively.By using a parameter,namely thermal performance index η,the effect of increasing heat transfer and pressure drop was studied simultaneously.The heat transfer improvement predominates the pressure drop increment in all cases.It was observed that the highest thermal performance of 1.9 was obtained at Re=634 and Φ=2%.Furthermore,regarding the increment of the Nu number,it was shown that the use of twisted tapes individually could increase the average Nu number by 41%,while the max increment arising from individual use of 2% nano-particles is 13%,so using twisted tape is a more effective-technique for this case study.展开更多
There are three predominant aspects of the rheological requirements: maximum possible high temperature thickening,minimum possible low-temperature thickening,and high shear stability for automatic transmission fluids....There are three predominant aspects of the rheological requirements: maximum possible high temperature thickening,minimum possible low-temperature thickening,and high shear stability for automatic transmission fluids.High temperature thickening by VI improvers is largely a function of molecular size and high solubility to give extended polymer coil size.On the other hand,the desirable characteristic of minimum low-temperature thickening is a function of somewhat the opposite characteristic;namely relatively poor solubility leading to minimal polymer coil size and thus low viscosity contribution.In addition to not thickening fluids at cold temperatures VI improvers should also provide control of wax-gelation which,if unfettered,can lead to congealed fluids.Finally the third property of high shear stability is in direct conflict with the desirable characteristic of large molecular size for effective high temperature thickening.In this paper we shall attempt to sort out these conflicting properties and provide some insight into how we approach design of VI improvers for the highly demanding world of automatic transmission fluid rheology.展开更多
In this paper,the influence of oxidation of automatic transmission fluids(ATFs)and sliding distance on the friction coefficients of a wet clutch in approached running-in conditions was investigated.The ATFs were oxidi...In this paper,the influence of oxidation of automatic transmission fluids(ATFs)and sliding distance on the friction coefficients of a wet clutch in approached running-in conditions was investigated.The ATFs were oxidized by a laboratory process approaching oxidation occurred in actual ATFs.Oxidation was evaluated by means of increase in carbonyl compounds and depletion of zinc dialkyldithiophosphates(ZDDPs)additives.Also,the changes in kinematic viscosity and viscosity index were evaluated.Pin-ondisk tests were conducted to replicate the actual sliding contact in a wet clutch.The pin specimens were cut from friction material composite plates and the disks were actual steel separators both from an automotive wet clutch.Friction coefficient, μ,was measured at progressive sliding velocity,ν,to obtain μ–νcurves at 26 and 100°C.Three μ–νtests were consecutively run using the same pair of specimens and oil.The cumulative sliding distance for each μ–νtest generated surface flattening using the oils.The friction coefficients of the wet clutch increased due to the ATFs oxidation meanwhile the dm/dv values decreased in most cases.It suggests that ATF oxidation can enhance torque capacity of the wet clutch,but it could reduce anti-shudder property.Progressive sliding distance improved the slopes in the μ–νresults using fresh ATFs meanwhile it generated a slope decrease by using aged ATFs.展开更多
文摘In the present study,hydraulic and thermal behavior of an automatic transmission nano-fluid(ATNF) inside a tube with a twisted tape has been investigated.The heat transfer improvement and pressure drop of transmission oil for each of case of using twisted tape and nano-particles were also examined separately and compared with each other.The Cu O nano-particles were used to prepare the ATNF.The effects of different Reynolds numbers and different mass fractions of nano-particle were investigated.The results showed that applying nano-particles and twisted tape simultaneously increases both the pressure drop and Nusselt number,on average by about 53% and 76%,respectively.By using a parameter,namely thermal performance index η,the effect of increasing heat transfer and pressure drop was studied simultaneously.The heat transfer improvement predominates the pressure drop increment in all cases.It was observed that the highest thermal performance of 1.9 was obtained at Re=634 and Φ=2%.Furthermore,regarding the increment of the Nu number,it was shown that the use of twisted tapes individually could increase the average Nu number by 41%,while the max increment arising from individual use of 2% nano-particles is 13%,so using twisted tape is a more effective-technique for this case study.
文摘There are three predominant aspects of the rheological requirements: maximum possible high temperature thickening,minimum possible low-temperature thickening,and high shear stability for automatic transmission fluids.High temperature thickening by VI improvers is largely a function of molecular size and high solubility to give extended polymer coil size.On the other hand,the desirable characteristic of minimum low-temperature thickening is a function of somewhat the opposite characteristic;namely relatively poor solubility leading to minimal polymer coil size and thus low viscosity contribution.In addition to not thickening fluids at cold temperatures VI improvers should also provide control of wax-gelation which,if unfettered,can lead to congealed fluids.Finally the third property of high shear stability is in direct conflict with the desirable characteristic of large molecular size for effective high temperature thickening.In this paper we shall attempt to sort out these conflicting properties and provide some insight into how we approach design of VI improvers for the highly demanding world of automatic transmission fluid rheology.
基金The authors would like to acknowledge to CNMNIPN for the support in the spectroscopic analyses of our oil samplesWe also thank to“Laboratorio de Reología y Física de la Materia Blanda”from ESFM-Instituto Politécnico Nacional for the assistance and equipment support for the viscosity measurements of our oil samples.
文摘In this paper,the influence of oxidation of automatic transmission fluids(ATFs)and sliding distance on the friction coefficients of a wet clutch in approached running-in conditions was investigated.The ATFs were oxidized by a laboratory process approaching oxidation occurred in actual ATFs.Oxidation was evaluated by means of increase in carbonyl compounds and depletion of zinc dialkyldithiophosphates(ZDDPs)additives.Also,the changes in kinematic viscosity and viscosity index were evaluated.Pin-ondisk tests were conducted to replicate the actual sliding contact in a wet clutch.The pin specimens were cut from friction material composite plates and the disks were actual steel separators both from an automotive wet clutch.Friction coefficient, μ,was measured at progressive sliding velocity,ν,to obtain μ–νcurves at 26 and 100°C.Three μ–νtests were consecutively run using the same pair of specimens and oil.The cumulative sliding distance for each μ–νtest generated surface flattening using the oils.The friction coefficients of the wet clutch increased due to the ATFs oxidation meanwhile the dm/dv values decreased in most cases.It suggests that ATF oxidation can enhance torque capacity of the wet clutch,but it could reduce anti-shudder property.Progressive sliding distance improved the slopes in the μ–νresults using fresh ATFs meanwhile it generated a slope decrease by using aged ATFs.
