Water Membrane Evaporator Research Articles

Experimental study of heat rejection performance of water membrane evaporator in vacuum environment

The water membrane evaporator (WME) is a kind of consumable heat sink proposed for application in spacecraft thermal control systems. It has great potential to be applied as a primary or auxiliary heat sink in the thermal control systems of spacecraft such as the Mars extravehicular spacesuit, the near space vehicle and others. In the space high vacuum pressure atmosphere, the water evaporates to the environment and absorbs the latent heat of vaporization to achieve the purpose of cooling the fluid. The heat rejection of WME is a very complex physical process of heat and mass transfer, and its performance is affected by the coupling of several parameters. However, the influence laws of various operating and structural parameters of the WME on its performance have not been adequately investigated in previous studies. Thus leading to the considerable challenge of optimizing design of WME and its usage strategies. In this paper, five groups of tests were conducted on three WME prototypes with different structures and the effect laws of temperature, backpressure, circulating water flow rate, and hollow fiber (HoFi) tube distance on their heat rejection and water consumption rate were obtained. The WME based on porous HoFi membranes has a very considerable heat rejection capacity. Several WME prototypes tested in this study obtained a maximum heat rejection of 589 W/m2 at the inlet water temperature of 45 °C. The structure of HoFi membrane tubes and parameters such as inlet flow rate have a significant effect on its performance. The heat rejection per unit area for Case 1 is about 3.76 times that of Case 4 at the inlet water temperature of about 45 °C and the backpressure of about 700 Pa. In addition, the dimensionless analysis was also carried out, and the correlations that can be used to predict the heat rejection performance were obtained. These results are of guiding significance for optimizing the structural design, heat rejection performance and operating strategy of WME.

Discrete time adaptive neural network control for WME and compression refrigeration systems

In this paper, we study the discrete-time control problem for the refrigeration system with unmodeled dynamics. This paper proposes discrete adaptive neural network controllers for two refrigeration systems, including the water membrane evaporator cooling and compression refrigeration systems. The influence of model uncertainty on system performance can be eliminated effectively by designing the neural network and the corresponding discrete-time adaptive updating strategy. Thus, the model parameters in the refrigeration system are not required in our control algorithms. Simulation results show that the proposed strategy can effectively adjust the refrigeration system temperatures. Compared with the traditional PID control strategy, the system response overshoot under our method can be reduced by 0.3%, and the system settling time is reduced by at least 94.3%.

Performance evaluation and model of spacesuit cooling by hydrophobic hollow fiber-membrane based water evaporation through pores

A comprehensive mathematical model is presented that accurately estimates and predicts failure modes through the computations of heat rejection, temperature drop and lumen side pressure drop of the hollow fiber (HF) membrane-based NASA Spacesuit Water Membrane Evaporator (SWME). The model is based on mass and energy balances in terms of the physical properties of water and membrane transport properties. The mass flux of water vapor through the pores is calculated based on Knudsen diffusion with a membrane structure parameter that accounts for effective mean pore diameter, porosity, thickness, and tortuosity. Lumen-side convective heat transfer coefficients are calculated from laminar flow boundary layer theory using the Nusselt correlation. Lumen side pressure drop is estimated using the Hagen-Poiseuille equation. The coupled ordinary differential equations for mass flow rate, water temperature and lumen side pressure are solved simultaneously with the equations for mass flux and convective heat transfer to determine overall heat rejection, water temperature and lumen side pressure drop. A sensitivity analysis is performed to quantify the effect of input variability on SWME response and identify critical failure modes. The analysis includes the potential effect of organic and/or inorganic contaminants and foulants, partial pore entry due to hydrophilization, and other unexpected operational failures such as bursting or fiber damage. The model can be applied to other hollow fiber membrane-based applications such as low temperature separation and concentration of valuable biomolecules from solution.

A Model-based Design of the Water Membrane Evaporator for the Advanced Spacesuit

A Model-based Design of the Water Membrane Evaporator for the Advanced Spacesuit

Theoretical Analysis and Model-Based Design of the Water Membrane Evaporator for the Advanced Spacesuit

Theoretical Analysis and Model-Based Design of the Water Membrane Evaporator for the Advanced Spacesuit

A fuzzy coordination control of a water membrane evaporator cooling system for aerospace electronics

A safe and reliable thermal control strategy is of great significance for the cooling of aerospace electronics in deep space exploration. How to run efficiently and reliably when a thermal control system is faced with increasingly complex thermal conditions and limited cooling capacity makes the optimization of control strategy more and more important. This paper presents a new fuzzy coordination control (FCC) strategy for the water membrane evaporator (WME) cooling system composed of the liquid cooling and ventilation garment (LCVG), the cold plate, and the WME. A 3-node thermodynamic model of the WME cooling system was established, in which the WME thermal model considered heat and mass transfer across the membrane. The FCC is proposed to coordinate two separate controllers to balance the two inputs, one regulating the flow of the pump and the other regulating the opening of the three-way valve. Numerical results suggest that the FCC can avoid the reliability reduction caused by only using valve control, due to the limited valve opening range. When the step of the cold plate thermal load increases by 40%, the FCC's setting time is 75.4% of the control pump alone, but the FCC only needs 92.2% of the pump flow; The FCC's overshoot is 50% of the control valve alone, but the FCC only needs 76% of the valve opening. Thus, the FCC has the advantages of less overshoot, less oscillation period, and save energy.

An investigation on fuzzy incremental control strategy of water membrane evaporator cooling loop for mars spacesuit

The safe and robust temperature control strategy is important for Mars spacesuit's thermal control subsystem. This paper presents a fuzzy incremental control strategy using a fuzzy logic for the spacesuit water membrane evaporator (SWME) cooling loop composed of the liquid cooling and ventilation garment (LCVG), the cold plate and the SWME. A thermodynamic model of the SWME cooling loop is developed, in which the SWME model considers the heat and mass transfer of water transmembrane transport. A detailed analysis of the open-loop response under the variation of water flow, Mars' atmospheric pressure and the opening of the backpressure valve in the SWME provides a basis for developing the fuzzy incremental control strategy. This paper also compares the control effect of a fuzzy incremental controller and the optimized proportional-integral-derivative (PID) controller. Numerical simulation results suggest that the proposed control strategy has the advantages of the small overshoot, short response time, and less oscillation period, which will benefit the adaptability of complex systems and expand the application field of fuzzy incremental control.

An approach to mixed-fidelity system simulation of extravehicular activities

The National Aeronautics and Space Administration (NASA) is currently developing the next generation of spacesuits for use in future exploration missions. This effort, referred to as the Exploration Extravehicular Mobility Unit (xEMU), has been underway since 2015 with the goal of demonstrating the new technologies during a mission to the International Space Station (ISS).Due to the complexity of the xEMU system, and particularly its portable life support system (PLSS), computer simulations are heavily relied on in the development process, from dynamic loads analysis to software verification. The models of the physical systems that are currently being used for system-level simulations are mostly empirical, where the underlying formulas are mathematical fits to test or simulation data. An advantage of this approach is the fact that these models are very performant and can be used in real-time applications such as user interface testing and operator training.The research presented in this paper describes a different approach to modeling and simulation. A simulation tool focused on life support systems for human spaceflight in general and PLSSs in particular has been under development at the Technical University of Munich (TUM) since 2006. The spacesuit specific variant of this tool is called The Virtual Spacesuit (V-SUIT) and is now being utilized in the current spacesuit development process at the NASA Johnson Space Center (JSC). In contrast to the previously mentioned empirical models, V-SUIT uses a first-principles-based, bottom up modeling approach, where basic physical, chemical or biological effects are modeled at the lowest level and the component and system models are created using these fundamental building blocks. This enables the simulation to account for effects, and especially off-nominal situations, that may not be within the range of validity of the empirical models.This paper presents the structure of and the rationale behind V-SUIT itself as well as a status report on the ongoing effort to integrate it with the existing simulation systems in use at JSC, which is based on Trick/GUNNS. As a proof of concept, a single component model from V-SUIT, that of the spacesuit water membrane evaporator (SWME), has been integrated with NASA's simulation tool.Results include comparisons of the performance of the two simulation systems and a description of challenges that were encountered during implementation. The paper closes with an outlook towards the future developments that are planned for V-SUIT within the xEMU development program.

Thermal Performance Model for Spacesuit Waste Heat Rejection Using Water Membrane Evaporators

Hydrophobic, micropore membrane evaporators are studied for use in waste heat rejection in new generation spacesuits developed by the U.S. National Aeronautics and Space Administration (NASA). The waste heat rejection is accomplished via evaporation of liquid water through membrane pores, whereby the hydrophobic membrane allows only water vapor to pass through and retains the liquid phase inside the membrane water channel, allowing the waste heat rejection through the proposed spacesuit water membrane evaporator (SWME) system to be significantly less sensitive to contamination while improving the overall contaminant and system control. Although SWME uses the same heat transport loop as used in current NASA sublimator systems, thus eliminating the need for a separate feedwater system, it permits the system configuration to be simpler and more compact while also eliminating corrosion problems and reducing system freeze-up potential. An improved thermal performance model based on membrane segment energy balances is presented, which is a spacesuit water membrane evaporator for a single circular annulus water channel bounded by two annular vapor channels. The model allows for the investigation of the local heat transfer characteristics along the annulus including temperature gradients in the membrane wall and the water channel using a steady-state approach. The model also accounts for the effects of thermal and hydraulic entry lengths, far field radiation, and energy carried away by the mass of water evaporation. The local heat transfer analysis enables the straightforward calculation of the overall magnitude of heat transfer from the SWME. A model validation is presented via the sum of the squares error analyses between the model predictions and the experimental results.

Hollow Fiber Space Suit Water Membrane Evaporator Development for Lunar Missions

The Space Suit Water Membrane Evaporator (SWME) is the baseline heat rejection technology selected for development for the Constellation lunar suit. The Hollow Fiber (HoFi) SWME is being considered for service in the Constellation Space Suit Element (CSSE) Portable Life Support Subsystem (PLSS) to provide cooling to the thermal loop through water evaporation to the vacuum of space. Previous work described the test methodology and planning to compare the test performance of three commercially available hollow fiber materials as alternatives to the sheet membrane prototype for SWME: 1) porous hydrophobic polypropylene, 2) porous hydrophobic polysulfone, and 3) ion exchange through nonporous hydrophilic modified Nafion. Contamination tests were performed to probe for sensitivities of the candidate SWME elements to organics and non-volative inorganics expected to be found in the target feedwater source, i.e., potable water provided by the vehicle. The resulting presence of precipitate in the coolant water could plug pores and tube channels and affect the SWME performance. From this prior work, a commercial porous hydrophobic hollow fiber was selected to satisfy both the sensitivity question and the need to provide 800 W of heat rejection. This paper describes the trade studies, the design methodology, and the hollow fiber test data used to design a full