The proposal directly addresses the critical need in Fluid Physics for NASA’s future missions where reduced-gravity multiphase flows, cryogenics, and heat transfer are identified as areas of particular interest. The research will lead to the generation of a large database of chilldown tests under terrestrial and microgravity environments, and closure theoretical and computational models to aid NASA engineers in future mission planning.

Development and Testing of a Closed Loop Two-Phase Flow Chill-down Test Module for Integration with the Flow Boiling and Condensation Experiment (FBCE) Module at the ISS:

Terrestrial chilldown experiments are performed on a 0.375'' OD, 0.065'' thickness SS-316 tube in a horizontal closed loop flow configuration with PF-5060 as the working fluid. The present experiments mimic the cryogenic transfer line chilldown process and captured the entire chilldown curve, including the film, transition, and nucleate boiling regimes along with the single phase liquid convective regimes. The experiments are performed at different inlet mass fluxes and inlet liquid subcooling. The results of the tests yielded useful data for temperature transition points, critical heat flux, regime specific heat flux and heat transfer coefficients as a function of inlet mass flux and inlet liquid subcooling. The heat transfer experiments will be extended to pulsed inlet flows and the obtained results will be compared with the continuous flow tests. Preliminary flow visualization experiments are performed in a Nichrome winded pyrex tube and the high speed imaging data revealed different flow boiling regimes – such as the inverted annular film boiling, transition boiling, and nucleate boiling typical of a cryogenic chilldown process. Further, high quality flow visualization experiments will be performed in an Indium-Tin-Oxide (ITO) coated quartz tube and outer wall temperature profiles will be recorded using an infrared (IR) camera.

CFD Studies on Flow Boiling during the Cryogenic Transfer Line Chill-down Process under Terrestrial and Microgravity Conditions:

3-D mixture computational fluid dynamics (CFD) simulations were performed for 3 low inlet mass flux test cases for 1-ge Liquid Nitrogen (LN2) vertical upflow chilldown experiments and the predictions seem to improve in the transition and nucleate boiling regimes. A subgrid nucleate boiling user-defined function (UDF) has been developed and testing is in progress for different configurations. 2-D axisymmetric CFD simulations are performed to validate the microgravity chilldown results with LN2 as the working fluid. The preliminary results are promising, and the simulation methodology is being extended to predict chilldown curves at different axial locations along the tube. In addition, attempts are made to predict the chilldown process using the sharp interface volume of fluid (VOF) formulation as well as Eulerian two-fluid model with Rensselaer Polytechnic Institute (RPI) wall heat flux partitioning during different flow boiling regimes.

Development of a 1-D Nodal Model for Line Chill-down Process:

No progress this year. The nodal model is being improved now to include more parametric effects. The experimental results obtained from the terrestrial chilldown tests will be used to develop correlations for use in the 1-D nodal model next year.

In addition, the Systems Requirements Review (SRR) for the project was held in January 2024 and received the science panel comments, which have been addressed. The Science Requirements Document (SRD), as well as the Integrated Science Requirements Document (ISRD), are being updated based on discussions with the University of Illinois, Urbana-Champaign (UIUC) and NASA Glenn Research Center (GRC) teams. The GRC Engineering team fabricated the heat transfer test section based on science requirements and testing will start soon to obtain high quality chilldown heat transfer data at different points in the proposed ISS test matrix.

The proposal directly addresses the critical need in Fluid Physics for NASA’s future missions where reduced-gravity multiphase flows, cryogenics, and heat transfer are identified as areas of particular interest. The research will lead to the generation of a large database of chilldown tests under terrestrial and microgravity environments, and closure theoretical and computational models to aid NASA engineers in future mission planning.

Development and Testing of a Closed Loop Two-Phase Flow Chill-down Test Module for Integration with the Flow Boiling and Condensation Experiment (FBCE) Module at the International Space Station (ISS):

Terrestrial chilldown experiments are performed on a 0.375'' OD, 0.065'' thickness SS-316 tube in a horizontal closed loop flow configuration with PF-5060 as the working fluid. The experiments are performed for a wide range of inlet mass fluxes ranging from 132.83-1303.96 kg/m2s, corresponding to inlet Reynolds numbers of 1,291-12,679 covering the entire regime of laminar to transition to turbulent inlet flows. With the help of a bypass loop and preheating of the test section, the present experiments mimic the cryogenic transfer line chilldown process and capture the entire chilldown curve including the film, transition, and nucleate boiling regimes, along with the single phase liquid convective regimes. The results of the tests yielded useful data for temperature transition points, critical heat flux, regime-specific heat flux, and heat transfer coefficients. Further, the effect of inlet subcooling was investigated by carrying out an elaborate set of 99 experimental tests, and the data is being processed now. Transparent Pyrex test sections for flow visualization during the chilldown process are also ready and will be tested next year.

CFD Studies on Flow Boiling during the Cryogenic Transfer Line Chill-down Process under Terrestrial and Microgravity Conditions:

2-D axisymmetric computational fluid dynamics (CFD) simulations were validated for the 1-ge LN2 vertical upflow chilldown experiments in the film boiling regime at 4 different inlet mass fluxes. The chilldown curves deviated from the experimental data in the transition and nucleate boiling regimes. 3-D CFD simulations were performed for 3 low inlet mass flux test cases for 1-ge LN2 vertical upflow chilldown experiments and the predictions seem to improve in the transition and nucleate boiling regimes, though a user-defined function (UDF) for sub-grid nucleate boiling is being developed to validate these regimes. 2-D axisymmetric CFD simulations are being performed to validate the microgravity chilldown results with LN2 as the working fluid. The preliminary results are promising, and the simulation methodology is being extended to predict chilldown curves at different axial locations along the tube. Finally, 2-D axisymmetric CFD simulations are performed to predict the LH2 chilldown process in a vertical upflow configuration. The initial results are encouraging and are being extended to different test cases.

Development of a 1-D Nodal Model for Line Chill-down Process:

No progress this year. The experimental results obtained from the terrestrial chilldown tests will be used to develop correlations for use in the 1-D nodal model next year. In addition, the Science Requirements Document (SRD) and Integrated Science Requirements Document (ISRD) for the project have been submitted in collaboration with the University of Illinois, Urbana-Champaign (UIUC), along with the Experiment Data and Management Plan (EDMP) and Mission (Level -1) Requirements Documents, for the Science Requirement Review (SRR) planned for January 2024.

The proposal directly addresses the critical need in Fluid Physics for NASA’s future missions where reduced-gravity multiphase flows, cryogenics, and heat transfer are identified as areas of particular interest. The research will lead to the generation of a large database of chilldown tests under terrestrial and microgravity environments, and closure theoretical and computational models to aid NASA engineers in future mission planning.

Development and Testing of a Two-Phase Flow Chill-down Test Module for Integration with the FBCE Module at ISS:

The new experimental test concept for the two-phase chilldown tests has been tested in the flow conditioning loop at Case Western Reserve University (CWRU), which is very similar to the actual Flow Boiling and Condensation Experiments (FBCE) module onboard the ISS. This will ensure that the new flow boiling module can replace the current module in the FBCE which will fit in the existing space and can be utilized to obtain both terrestrial and long-duration microgravity data for the line chilldown and transfer process. The main technological challenge for the new design is the pre-heating phase, where the test section walls should be heated to the desired temperature before starting the chilldown tests. The use of a simple check valve near the test section outlet along with a charged accumulator in the flow loop resolved this issue. Also, it has been experimentally shown that the fluid temperature is always at saturation vapor conditions, never superheated, after the heated test section due to the continuous presence of some liquid in the test section, which eliminates the need for additional cooling of the fluid before entering the FBCE loop. Initial chilldown data for a 3/8’’ stainless steel tube is now available with the new experimental concept which will be further extended for the entire test matrix conditions. The transparent Pyrex test section for the flow visualization test section during the chilldown process is also ready and will be tested by the end of this year.

CFD Studies on Liquid Nitrogen Flow Boiling During the Cryogenic Transfer Line Chill-down Process:

The prediction of the transfer line chill-down curve possesses unique challenges due to the presence of different flow boiling regimes, viz. film, transition and nucleate boiling; and hence, implementing a single computational fluid dynamics (CFD) modeling approach may not be adequate. Initial validations for the film boiling using a 3D mixture model for the liquid nitrogen chilldown data available in the literature is in a matured phase and will be applied for other operating conditions for robust predictions. A user-defined function in Fluent for predicting transition and nucleate boiling is in the development phase and will be implemented along with the 3D mixture model to predict the entire chilldown curve.

Development of a 1-D Theoretical Model for Line Chill-down Process:

A 1-D MATLAB code has been developed based on the published literature and has been tested for the different test matrix conditions for both stainless steel and Pyrex. This helped in fixing the limits for different flow and operating parameters in the test matrix and will be further refined based on the chilldown test data from the present project.

In addition, the Science Requirements Document (SRD) for the project is being completed and is progressing in collaboration with the University of Illinois, Urbana-Champaign (UIUC), and is due in January, 2023.

The proposal directly addresses the critical need in Fluid Physics for NASA’s future missions where reduced-gravity multiphase flows, cryogenics, and heat transfer are identified as areas of particular interest. The research will lead to the generation of a large database of chilldown tests under terrestrial and microgravity environments, and closure theoretical and computational models to aid NASA engineers in future mission planning.