The Experts below are selected from a list of 24390 Experts worldwide ranked by ideXlab platform
Jizhao Liang - One of the best experts on this subject based on the ideXlab platform.
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predictions of normal stress difference during circular duct flow of polymer melts
Polymer Testing, 2002Co-Authors: Jizhao LiangAbstract:Abstract Obvious viscoelastic behaviour appears during die extrusion flow of viscoelastic fluids, such as die-swell, end Pressure losses, and unsteady flow or melt fracture. The first normal stress difference (N1), die-swell ratio (B) and Exit Pressure drop (ΔPex) are very important parameters for characterization of the elastic behavior for viscoelastic fluids in die flow. There should be, therefore, some interior correlation between them. In the present paper, the relationship between the first normal stress difference, die-swell ratio and Exit Pressure drop is discussed. On the basis of previous work, some expressions for describing the relationship of B and N1, B and ΔPex, and ΔPex, and N1 during long circular die flow of viscoelastic fluids are proposed. The predictions of N1 by using the measured data for ΔPex were compared with the calculations from the die-swell ratio data and the measured N1 during capillary die extrusion of a high-density polyethylene (HDPE) melt and two low-density polyethylene melts (LDPE) published in the literature. Good agreement was shown among these theoretical calculations of N1 at high shear stress level, and was consistent with the predictions by using the Bagley–Duffey equation.
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estimation of die swell ratio for polymer melts from Exit Pressure drop data
Polymer Testing, 2000Co-Authors: Jizhao LiangAbstract:Abstract The extrudate swell and Exit Pressure losses are very important characteristics of the elastic behaviour of viscoelastic fluids in die flow. Die-swell ratio (B) is usually used to describe the swell degree of the extrudate. In the present paper, a relationship between the Exit Pressure losses and extrudate swell is discussed and an expression for description of the B and Exit Pressure drop (ΔPExit) relationship during long die flow of viscoelastic fluids is proposed on the basis of previous work. This equation was preliminarily verified by using the measured data of ΔPExit during capillary die extrusion of a high density polyethylene melt published in the literature. Good agreement was shown between the theoretical calculations and the experimentally measured data for B.
Michael Toomas Kivisalu - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of shear driven internal condensing flows to Pressure fluctuations and its utilization for heat flux enhancements
International Journal of Heat and Mass Transfer, 2013Co-Authors: Michael Toomas Kivisalu, Ranjeeth R Naik, Amitabh Narain, Patcharapol Gorgitrattanagul, Mohammed HasanAbstract:Abstract The reported experimental results are for annular zones of fully condensing flows of pure FC-72 (perfluorohexane) vapor. The flow condenses on the bottom surface (316 stainless steel) of a horizontal, rectangular cross-section duct. The sides and top of the duct are made of clear plastic. The annular portion of the flow in the test-section is driven, under negligible to zero gravity effects along the flow direction, by Pressure-difference and cooling conditions. Since the annular regime condensate motion is primarily driven by an effective interfacial shear stress, all such flows are termed shear-driven flows. The experimental system in which this condenser is used is able to control quasi-steady (termed quasi-steady) values of inlet mass flow rate, inlet (or Exit) Pressure, and wall cooling conditions. For the experimental results reported here, the mean (time-averaged) inlet mass flow rate, mean inlet Pressure, and condensing-surface cooling conditions were held fixed at their quasi-steady values. Under these conditions, it was found that the imposition of small inlet Pressure fluctuations (relative to the mean inlet Pressure) induces significant mass flow rate fluctuations at the condenser inlet, and that there is a change in the very nature of the quasi-steady annular condensing flow regime. The resulting phenomena change the mean local heat flux values with significant (>200%) enhancements. There are accompanying time-varying changes in the liquid–vapor configurations within the annular and the non-annular regimes. This changes the mean and fluctuation amplitude values (with induced harmonics) in the Pressure at any interior location within the annular regime. It is shown here that the heat flux enhancement phenomenon is real and occurs regardless of the method of cooling for a suitable range of fluctuation frequencies and amplitudes. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of Pressure or mass flow rate fluctuations imposed at the inlet of the condenser. Associated theory and rudimentary experiments (not reported here) suggest that similar enhancement may be observed in annular flows which do not completely condense before the Exit, provided that suitable arrangements at the condenser Exit allow similar or equivalent liquid–vapor interfacial wave structures with the help of similar acoustic wave reflections in the vapor phase.
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Prediction and Control of Internal Condensing Flows in the Experimental Context of their Inlet Condition Sensitivities
Microgravity Science and Technology, 2012Co-Authors: Michael Toomas Kivisalu, Ranjeeth R Naik, Patcharapol Gorgitrattanagul, Soumya Mitra, Amitabh NarainAbstract:The reported experimental results involve fully condensing flows of pure FC-72 vapor on a horizontal condensing surface (316 stainless steel) which is the bottom surface (wall) of a rectangular cross-section duct of 2 mm height, 15 mm width, and 1 m length. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) mass flow rate, Exit Pressure, and wall cooling conditions. It has been found that, with the condenser mean (time averaged) inlet mass flow rate, Exit Pressure, and wall cooling condition held fixed at steady values, there is a very strong sensitivity to high amplitude Pressure fluctuations and flow rate pulsations at the condenser inlet. This sensitivity often significantly alters the condenser mean inlet Pressure, Pressure drop, local heat transfer rates (>200% increase at certain locations), and the condensing flow morphology. These effects are representative of fluctuations/pulsations that are typically encountered in applications but are either not accounted for or are not detected. The effects of imposed fluctuations/pulsations, as opposed to cases involving negligible imposed fluctuations/pulsations, are dependent on the amplitude and the frequency content of the imposed fluctuations and this is discussed in a separate paper. A significant upstream annular regime portion of the reported shear/Pressure driven fully condensing flows operate under conditions where the laboratory’s transverse gravity effects are negligible and, therefore, the identified sensitivity phenomenon is highly relevant to zero- or micro-gravity conditions. The micro-gravity relevance of this sensitivity for the annular regime phenomenon is currently also being demonstrated with the help of computations and simulations.
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shear Pressure driven internal condensing flows and their sensitivity to inlet Pressure fluctuations
ASME 2011 International Mechanical Engineering Congress and Exposition, 2011Co-Authors: Michael Toomas Kivisalu, N Gorgitrattanagul, Soumya Asimkumar Mitra, Ranjeeth R Naik, Amitabh NarainAbstract:The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the horizontal condensing surface (316 stainless steel) which is the bottom surface (wall) of a rectangular cross-section duct of 2 mm height, 15 mm width, and 1 m length. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or Exit) Pressure, and wall cooling conditions. Earlier it has been reported that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or Exit) Pressure, and wall cooling condition held at steady values, there is a very strong sensitivity to certain impositions of Pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these certain impositions, it was found that the mean Exit (or inlet) Pressure changes to significantly affect mean test-section Pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of Pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet Pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).
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computational and ground based experimental investigations of the effects of specified and unspecified free Pressure conditions at the condenser Exit for condensing flows in terrestrial and microgravity environments
Annals of the New York Academy of Sciences, 2009Co-Authors: Amitabh Narain, Soumya Asimkumar Mitra, Shantanu Kulkarni, Jorge H Kurita, Michael Toomas KivisaluAbstract:Reported experimental and computational results confirm that both the flow features and heat transfer rates inside a condenser depend on the specification of inlet, wall, and Exit conditions. The theoretical and experimental results presented in this paper allow us to propose important Exit condition based categorization of these flows. Of these, category II flows are defined to be cases for which Exit Pressures are left unspecified. However it is shown here that steady flows under specified Exit Pressure conditions (category I flows) are more stable and can be more easily achieved under all conditions (normal or zero-gravity). Existence of self-selected Exit Pressure conditions for unspecified Exit condition cases (category II flows) are more difficult to achieve and are often limited to gravity driven flows. In practice, however, special hardware arrangements are required for repeatable realization of both these categories of flow. If this is not so, one often has an inadvertent category I flow (flows with specified Exit Pressure) without the explicit knowledge of the Exit Pressure value. For microgravity situations, the remedy is to run condensers under suitably specified inlet and Exit Pressures (category I conditions) as well as a proper cooling strategy (i.e., proper wall temperature variations).
Zhouping Xin - One of the best experts on this subject based on the ideXlab platform.
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on admissible locations of transonic shock fronts for steady euler flows in an almost flat finite nozzle with prescribed receiver Pressure
arXiv: Analysis of PDEs, 2019Co-Authors: Beixiang Fang, Zhouping XinAbstract:This paper concerns the existence of transonic shock solutions to the 2-D steady compressible Euler system in an almost flat finite nozzle ( in the sense that it is a generic small perturbation of a flat one ), under physical boundary conditions proposed by Courant-Friedrichs in \cite{CourantFriedrichs1948}, in which the receiver Pressure is prescribed at the Exit of the nozzle. In the resulting free boundary problem, the location of the shock-front is one of the most desirable information one would like to determine. However, the location of the normal shock-front in a flat nozzle can be anywhere in the nozzle so that it provides little information on the possible location of the shock-front when the nozzle's boundary is perturbed. So one of the key difficulties in looking for transonic shock solutions is to determine the shock-front. To this end, a free boundary problem for the linearized Euler system will be proposed, whose solution will be taken as an initial approximation for the transonic shock solution. In this paper, a sufficient condition in terms of the geometry of the nozzle and the given Exit Pressure is derived which yields the existence of the solutions to the proposed free boundary problem. Once an initial approximation is obtained, a further nonlinear iteration could be constructed and proved to lead to a transonic shock solution.
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the existence and monotonicity of a three dimensional transonic shock in a finite nozzle with axisymmetric Exit Pressure
Pacific Journal of Mathematics, 2010Co-Authors: Zhouping Xin, Huicheng YinAbstract:We establish the existence of a multidimensional transonic shock solution in a class of slowly varying nozzles for the three dimensional steady full Euler system with axially symmetric Exit Pressure in the diverging part lying in an appropriate scope. We also show that the shock position depends monotonically on the Exit Pressure.
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on transonic shocks in a conic divergent nozzle with axi symmetric Exit Pressures
Journal of Differential Equations, 2010Co-Authors: Zhouping Xin, Huicheng YinAbstract:Abstract In this paper, we establish the existence and stability of a 3-D transonic shock solution to the full steady compressible Euler system in a class of de Laval nozzles with a conic divergent part when a given variable axi-symmetric Exit Pressure lies in a suitable scope. Thus, for this class of nozzles, we have solved such a transonic shock problem in the axi-symmetric case described by Courant and Friedrichs (1948) in Section 147 of [8] : Given the appropriately large Exit Pressure p e ( x ) , if the upstream flow is still supersonic behind the throat of the nozzle, then at a certain place in the diverging part of the nozzle a shock front intervenes and the gas is compressed and slowed down to subsonic speed so that the position and the strength of the shock front are automatically adjusted such that the end Pressure at the Exit becomes p e ( x ) .
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on transonic shocks in a nozzle with variable end Pressures
Communications in Mathematical Physics, 2009Co-Authors: Zhouping Xin, Huicheng YinAbstract:In the book, Courant and Friedrichs (Supersonic Flow and Shock Waves. New York: Interscience Publishers, 1948) described the following transonic shock phenomena in a de Laval nozzle: Given the appropriately large receiver Pressure pr, if the upstream flow is still supersonic behind the throat of the nozzle, then at a certain place in the diverging part of the nozzle a shock front intervenes and the gas is compressed and slowed down to subsonic speed. The position and the strength of the shock front are automatically adjusted so that the end Pressure at the Exit becomes pr. When the end Pressure pr varies and lies in an appropriate scope, in general, it is expected that a curved transonic shock is still formed in a nozzle. In this paper, we solve this problem for the two-dimensional steady Euler system with a variable Exit Pressure in a nozzle whose divergent part is an angular sector. Both existence and uniqueness are established.
Amitabh Narain - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of shear driven internal condensing flows to Pressure fluctuations and its utilization for heat flux enhancements
International Journal of Heat and Mass Transfer, 2013Co-Authors: Michael Toomas Kivisalu, Ranjeeth R Naik, Amitabh Narain, Patcharapol Gorgitrattanagul, Mohammed HasanAbstract:Abstract The reported experimental results are for annular zones of fully condensing flows of pure FC-72 (perfluorohexane) vapor. The flow condenses on the bottom surface (316 stainless steel) of a horizontal, rectangular cross-section duct. The sides and top of the duct are made of clear plastic. The annular portion of the flow in the test-section is driven, under negligible to zero gravity effects along the flow direction, by Pressure-difference and cooling conditions. Since the annular regime condensate motion is primarily driven by an effective interfacial shear stress, all such flows are termed shear-driven flows. The experimental system in which this condenser is used is able to control quasi-steady (termed quasi-steady) values of inlet mass flow rate, inlet (or Exit) Pressure, and wall cooling conditions. For the experimental results reported here, the mean (time-averaged) inlet mass flow rate, mean inlet Pressure, and condensing-surface cooling conditions were held fixed at their quasi-steady values. Under these conditions, it was found that the imposition of small inlet Pressure fluctuations (relative to the mean inlet Pressure) induces significant mass flow rate fluctuations at the condenser inlet, and that there is a change in the very nature of the quasi-steady annular condensing flow regime. The resulting phenomena change the mean local heat flux values with significant (>200%) enhancements. There are accompanying time-varying changes in the liquid–vapor configurations within the annular and the non-annular regimes. This changes the mean and fluctuation amplitude values (with induced harmonics) in the Pressure at any interior location within the annular regime. It is shown here that the heat flux enhancement phenomenon is real and occurs regardless of the method of cooling for a suitable range of fluctuation frequencies and amplitudes. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of Pressure or mass flow rate fluctuations imposed at the inlet of the condenser. Associated theory and rudimentary experiments (not reported here) suggest that similar enhancement may be observed in annular flows which do not completely condense before the Exit, provided that suitable arrangements at the condenser Exit allow similar or equivalent liquid–vapor interfacial wave structures with the help of similar acoustic wave reflections in the vapor phase.
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Prediction and Control of Internal Condensing Flows in the Experimental Context of their Inlet Condition Sensitivities
Microgravity Science and Technology, 2012Co-Authors: Michael Toomas Kivisalu, Ranjeeth R Naik, Patcharapol Gorgitrattanagul, Soumya Mitra, Amitabh NarainAbstract:The reported experimental results involve fully condensing flows of pure FC-72 vapor on a horizontal condensing surface (316 stainless steel) which is the bottom surface (wall) of a rectangular cross-section duct of 2 mm height, 15 mm width, and 1 m length. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) mass flow rate, Exit Pressure, and wall cooling conditions. It has been found that, with the condenser mean (time averaged) inlet mass flow rate, Exit Pressure, and wall cooling condition held fixed at steady values, there is a very strong sensitivity to high amplitude Pressure fluctuations and flow rate pulsations at the condenser inlet. This sensitivity often significantly alters the condenser mean inlet Pressure, Pressure drop, local heat transfer rates (>200% increase at certain locations), and the condensing flow morphology. These effects are representative of fluctuations/pulsations that are typically encountered in applications but are either not accounted for or are not detected. The effects of imposed fluctuations/pulsations, as opposed to cases involving negligible imposed fluctuations/pulsations, are dependent on the amplitude and the frequency content of the imposed fluctuations and this is discussed in a separate paper. A significant upstream annular regime portion of the reported shear/Pressure driven fully condensing flows operate under conditions where the laboratory’s transverse gravity effects are negligible and, therefore, the identified sensitivity phenomenon is highly relevant to zero- or micro-gravity conditions. The micro-gravity relevance of this sensitivity for the annular regime phenomenon is currently also being demonstrated with the help of computations and simulations.
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shear Pressure driven internal condensing flows and their sensitivity to inlet Pressure fluctuations
ASME 2011 International Mechanical Engineering Congress and Exposition, 2011Co-Authors: Michael Toomas Kivisalu, N Gorgitrattanagul, Soumya Asimkumar Mitra, Ranjeeth R Naik, Amitabh NarainAbstract:The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the horizontal condensing surface (316 stainless steel) which is the bottom surface (wall) of a rectangular cross-section duct of 2 mm height, 15 mm width, and 1 m length. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or Exit) Pressure, and wall cooling conditions. Earlier it has been reported that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or Exit) Pressure, and wall cooling condition held at steady values, there is a very strong sensitivity to certain impositions of Pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these certain impositions, it was found that the mean Exit (or inlet) Pressure changes to significantly affect mean test-section Pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of Pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet Pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).
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computational and ground based experimental investigations of the effects of specified and unspecified free Pressure conditions at the condenser Exit for condensing flows in terrestrial and microgravity environments
Annals of the New York Academy of Sciences, 2009Co-Authors: Amitabh Narain, Soumya Asimkumar Mitra, Shantanu Kulkarni, Jorge H Kurita, Michael Toomas KivisaluAbstract:Reported experimental and computational results confirm that both the flow features and heat transfer rates inside a condenser depend on the specification of inlet, wall, and Exit conditions. The theoretical and experimental results presented in this paper allow us to propose important Exit condition based categorization of these flows. Of these, category II flows are defined to be cases for which Exit Pressures are left unspecified. However it is shown here that steady flows under specified Exit Pressure conditions (category I flows) are more stable and can be more easily achieved under all conditions (normal or zero-gravity). Existence of self-selected Exit Pressure conditions for unspecified Exit condition cases (category II flows) are more difficult to achieve and are often limited to gravity driven flows. In practice, however, special hardware arrangements are required for repeatable realization of both these categories of flow. If this is not so, one often has an inadvertent category I flow (flows with specified Exit Pressure) without the explicit knowledge of the Exit Pressure value. For microgravity situations, the remedy is to run condensers under suitably specified inlet and Exit Pressures (category I conditions) as well as a proper cooling strategy (i.e., proper wall temperature variations).
Huicheng Yin - One of the best experts on this subject based on the ideXlab platform.
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the existence and monotonicity of a three dimensional transonic shock in a finite nozzle with axisymmetric Exit Pressure
Pacific Journal of Mathematics, 2010Co-Authors: Zhouping Xin, Huicheng YinAbstract:We establish the existence of a multidimensional transonic shock solution in a class of slowly varying nozzles for the three dimensional steady full Euler system with axially symmetric Exit Pressure in the diverging part lying in an appropriate scope. We also show that the shock position depends monotonically on the Exit Pressure.
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on transonic shocks in a conic divergent nozzle with axi symmetric Exit Pressures
Journal of Differential Equations, 2010Co-Authors: Zhouping Xin, Huicheng YinAbstract:Abstract In this paper, we establish the existence and stability of a 3-D transonic shock solution to the full steady compressible Euler system in a class of de Laval nozzles with a conic divergent part when a given variable axi-symmetric Exit Pressure lies in a suitable scope. Thus, for this class of nozzles, we have solved such a transonic shock problem in the axi-symmetric case described by Courant and Friedrichs (1948) in Section 147 of [8] : Given the appropriately large Exit Pressure p e ( x ) , if the upstream flow is still supersonic behind the throat of the nozzle, then at a certain place in the diverging part of the nozzle a shock front intervenes and the gas is compressed and slowed down to subsonic speed so that the position and the strength of the shock front are automatically adjusted such that the end Pressure at the Exit becomes p e ( x ) .
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on transonic shocks in a nozzle with variable end Pressures
Communications in Mathematical Physics, 2009Co-Authors: Zhouping Xin, Huicheng YinAbstract:In the book, Courant and Friedrichs (Supersonic Flow and Shock Waves. New York: Interscience Publishers, 1948) described the following transonic shock phenomena in a de Laval nozzle: Given the appropriately large receiver Pressure pr, if the upstream flow is still supersonic behind the throat of the nozzle, then at a certain place in the diverging part of the nozzle a shock front intervenes and the gas is compressed and slowed down to subsonic speed. The position and the strength of the shock front are automatically adjusted so that the end Pressure at the Exit becomes pr. When the end Pressure pr varies and lies in an appropriate scope, in general, it is expected that a curved transonic shock is still formed in a nozzle. In this paper, we solve this problem for the two-dimensional steady Euler system with a variable Exit Pressure in a nozzle whose divergent part is an angular sector. Both existence and uniqueness are established.