Jerry K. Keska

Incorporation of Flow Pattern Phenomena Into the Study of Advanced Micro Cooling Modules

The need for high-performance thermal protection and fluid management techniques for systems ranging from cryogenic reactant storage devices to primary structures and propulsion systems exposed to extreme high temperatures, and other space systems such as cooling or environmental control for advanced space suits and integrated electronic circuits, requires an effective cooling system to accommodate the compact nature and high heat fluxes associated with these applications. A two-phase forced-convection, phase-transition system can accommodate such requirements through the use of the concept of Advanced Micro Cooling Modules (AMCMs), which are essentially compact two-phase heat exchangers constructed of microchannels and designed to remove large amounts of heat rapidly from critical systems by incorporating phase transition. Realizing the significance of research in this area, this paper presents the results of experimental research on two-phase flow in microchannels with verification and identification of data using concomitant measurement systems, where based on the experimental research conducted on air-water mixture flows in the entire range of concentration and flow patterns in a horizontal square microchannel, a mathematical model based on in situ parameters is developed and presented, which describes pressure losses in two-phase flow incorporating flow pattern phenomena. Validation of the model is accomplished. A hypothetical model for the two-phase heat transfer coefficient is also presented, which incorporates the flow patterns through the use of a flow pattern coefficient.Copyright

Progress in Analysis of Two‐Phase Flow

This paper presents the developed mathematical model of two‐phase flow in a minichannel incorporating flow pattern phenomena for applications in cooling modules. It is still recognized today that two‐phase flow is scientifically one of the most challenging fluid dynamic problems to be explored since the 1940s. Consequently, to successfully design, analyze, and control such systems, it is necessary to first obtain a fundamental understanding of the two‐phase flow and heat transfer in the mini and microchannels. This is accomplished through the development of a quantitative model incorporating in‐situ concentration/void fraction, velocities, and flow patterns. Based on the results of the experimental research conducted on air‐water mixture flows in the full range of concentration and flow patterns in a horizontal square minichannel, a mathematical model based on in situ parameters is developed and presented. The model describes pressure losses in two‐phase flow incorporating flow pattern phenomena. The pres...

An Application of Concomitant Measurements for Two-Phase Flow of Air-Water Mixture in Minichannels

The complex nature of two-phase flow itself creates obstacles in detecting, monitoring and description of flow patterns, which are directly related to spatial and temporal distributions of concentration in the mixture. In addition to this, difficulties in comparing results and noticed differences in reported results generated in different experiments require more extensive research toward finding a satisfactory explanation. Because of both high significance and difficulties in measurement of in-situ parameters including concentration measurements and existence of significant differences in the published results, one possible approach to reduce the differences is to conduct a comparative study of the measurement properties of the concomitant measurement systems for the same flow conditions (identical time and space). This reported experimental study focuses on the comparison of two different concentration measurement methods (capacitive and conductive system) including the determination of concomitancy for those two systems. In this investigation, a Computer Aided Experimentation System (CAES) is used to generate a broad range of flow conditions and flow patterns, where the in-situ concentrations are measured simultaneously in the same time and space for air-water heterogeneous mixture flow. Based on the in-situ concentration measurements (full range of concentration) from both capacitive and conductive systems, a direct comparison between the results is presented and the concomitancy between the two systems is determined.Copyright

Flow Pattern Phenomena in Two‐Phase Flow in Microchannels

Space transportation systems require high‐performance thermal protection and fluid management techniques for systems ranging from cryogenic fluid management devices to primary structures and propulsion systems exposed to extremely high temperatures, as well as for other space systems such as cooling or environment control for advanced space suits and integrated circuits. Although considerable developmental effort is being expended to bring potentially applicable technologies to a readiness level for practical use, new and innovative methods are still needed. One such method is the concept of Advanced Micro Cooling Modules (AMCMs), which are essentially compact two‐phase heat exchangers constructed of microchannels and designed to remove large amounts of heat rapidly from critical systems by incorporating phase transition. The development of AMCMs requires fundamental technological advancement in many areas, including: (1) development of measurement methods/systems for flow‐pattern measurement/identification for two‐phase mixtures in microchannels; (2) development of a phenomenological model for two‐phase flow which includes the quantitative measure of flow patterns; and (3) database development for multiphase heat transfer/fluid dynamics flows in microchannels. This paper focuses on the results of experimental research in the phenomena of two‐phase flow in microchannels. The work encompasses both an experimental and an analytical approach to incorporating flow patterns for air‐water mixtures flowing in a microchannel, which are necessary tools for the optimal design of AMCMs. Specifically, the following topics are addressed: (1) design and construction of a sensitive test system for two‐phase flow in microchannels, one which measures ac and dc components of in‐situ physical mixture parameters including spatial concentration using concomitant methods; (2) data acquisition and analysis in the amplitude, time, and frequency domains; and (3) analysis of results including evaluation of data acquisition techniques and their validity for application in flow pattern determination.

Mathematical Model of Two‐Phase Flow in Advanced Micro Cooling Modules Incorporating Flow Pattern Phenomena

This paper presents the results of experimental research on two‐phase flow in a microchannel with verification and identification of data using concomitant measurement systems. Based on the results of the experimental research conducted on air‐water mixture flows in the full range of concentration and flow patterns in a horizontal square microchannel, a mathematical model based on in situ parameters is developed and presented. The model describes pressure losses in two‐phase flow incorporating flow pattern phenomena. A relation for the two‐phase heat transfer coefficient is also presented, which incorporates the flow patterns using a flow pattern coefficient. This model significantly reduces the difference between the experimental and calculated values typically encountered in previous efforts.

Incorporated Flow Patterns Into a Model of Two-Phase Heterogeneous Mixture Flow in Microchannels

In the two-phase or multiphase flow of such heterogeneous mixture like gas-liquid many more independent parameters are involved, thereby making this process more complicated and less transparent for understanding, mathematical modeling and simulating or calculating of such parameter like the length pressure gradient. In two-phase flow, there is a very complicated and random phenomenon of flow patterns, which needs to be quantitatively and accurately incorporated. Unfortunately, nowadays, a method of how to measure flow patterns is not available. And, also there is a need for mathematical models with quantitatively incorporated flow patterns in full range of flow. It is understandable that in all such cases any reasonable attempt to define and incorporate quantitatively this phenomenon in mathematical model will be beneficial. Recognizing these challenges this paper will present an approach to incorporate flow pattern phenomenon into the two-phase flow model by (1) developing a mathematical model for pressure losses in two-phase flow based on in-situ parameters, (2) developing and defining a flow pattern coefficient, which incorporates the flow pattern phenomena, and (3) present the developed mathematical model with the incorporation of flow patterns, which demonstrated significant increase of accuracy of calculations based on conducted experimental research on air-water twophase mixture flow in a horizontal square microchannel.Copyright

An Application of a Flow Pattern Coefficient in Two-Phase Flow of Air-Water Mixture in Minichannels

Concerning the two-phase gas-liquid mixtures, the present understanding of even fully developed turbulent flow of a single-phase component in close channels is not completely satisfactory. In the two-phase or multiphase flow of such heterogeneous mixture like gas-liquid many more independent parameters are involved, thereby making this process more complicated and less transparent for understanding, mathematical modeling and simulating or calculating of such parameter like the length pressure gradient. In those mathematical models for calculations and simulations, as well as for interpretation of experimental results, there is a very complicated and random phenomenon of flow patterns, which needs to be quantitatively and accurately, incorporated producing higher accuracy in calculation and description. Unfortunately, nowadays, a method of how to measure flow patterns is not available. Recognizing these challenges this paper will present an approach to incorporate flow pattern phenomenon into the two-phase flow calculation model by (1) developing a mathematical model for pressure losses in two-phase flow based on in-situ parameters, (2) developing and defining a flow pattern coefficient, which incorporates the flow pattern phenomena, and (3) present the developed mathematical model with the incorporation of flow patterns, which demonstrated significant increase of accuracy of calculations based on conducted experimental research on air-water two-phase mixture flow in a horizontal small square channel.Copyright

Model of Two-Phase Heterogeneous Mixture Flow in a Microchannel With Incorporated Flow Patterns

In the two-phase or multiphase flow of such heterogeneous mixture like gas-liquid there is a very complicated and random phenomenon of flow patterns, which needs to be quantitatively and accurately, incorporated. Unfortunately, a model with quantitatively incorporated flow patterns in full range of concentration or method of how to measure flow patterns is not available. Recognizing these challenges this paper will present an approach to incorporate flow pattern phenomenon into the two-phase flow calculation model by (1) developing a mathematical model for pressure losses in two-phase flow based on in-situ parameters, (2) developing and defining a flow pattern coefficient, which incorporates the flow pattern phenomena, and (3) present the developed mathematical model with the incorporation of flow patterns, which demonstrated significant increase of accuracy of calculations based on conducted experimental research on air-water two-phase mixture flow in a horizontal square microchannel.Copyright