Development of a two-phase mechanically pumped loop (2ΦMPL) for the thermal dissipation management of spacecraft : Simulation and test results

Transcription

1 44th July 2014, Tucson, Arizona ICES Development of a two-phase mechanically pumped loop (2ΦMPL) for the thermal dissipation management of spacecraft : Simulation and test results Alain Chaix 1, Julien Hugon 1, Patrick Hugonnot 1, Anthony Delmas 2 1 Thales Alenia Space, 100 Boulevard du Midi, Cannes, France 2 Altran, Région Sud-Est, SPACE CAMP Bat. Y02, 4 allée des cormorans, Cannes, France To face the thermal control challenges of future powerful telecommunication satellites, THALES ALENIA SPACE FRANCE (TAS-F), through several ESA and CNES contracts, is currently developing a two-phase mechanically pumped loop (2ΦMPL) to transport the heat dissipation from telecom payload dissipative equipment (antenna, repeater) to dedicated large deployable or fixed radiators. After introducing the general context of the development and thermal management operated through twophase mechanically pumped loop (2ΦMPL), this paper gives firstly an overview of this thermal control solution and its advantages with respect to more classical solutions : Simplified payload accommodation, 3D units accommodation possibility, use of DPR and East & West panels if required to reject the power, centralized heating, cost reduction, RF harness mass reduction, RF performance improvement, AIV simplification, thermal performance improvement in terms of temperature gradient reduction between equipment and radiator, and isothermicity if required. In this first part, main challenges of this development will be presented as well. In a second part, a presentation of the current prototype, which is the central part of this development will be presented, with its different evolutions. Then, simulations (through dedicated fluidic tools and methodologies), which have allowed flight control laws definition and test predictions are presented, followed by test (done on a prototype) results and corresponding comparison between test and simulation results. At the end, perspectives and conclusions of this technology and its promising applications will be given in the paper. Nomenclature AA = Active Antenna AIT = Assembly Integration & Test AIV = Assembly Integration & Validation AATDM = Active Antenna Thermal Dissipation Management ARTES = Advanced Research in Telecommunication Systems BBM = BreadBoard Model CNES = Centre National d Etudes Spatiales DDVP = Detailed Development & Validation Plan DPR = Deployable Panel Radiator DRA = Direct Radiating Antenna EGSE = Electrical Ground Support Equipment EM = Engineering Model ESA = European Space Agency

2 HCA = Heat Controlled Accumulator HP = heat-pipe KhAI = Kharkov Aviation Institute MGSE = Mechanical Ground Support Equipment OMUX = Output Multiplexer PI = Proportional Integral PID = Proportional Integral Derivative RF = Radiofrecuency RPM = Revolutions Per Minute R&T = Research & Technology S/C = Spacecraft TAS-F = Thales Alenia Space France TCS = Thermal Control System TVT = Thermal Vacuum Test TWT = Traveling Wave Tube w.r.t = with respect to 2ΦMPL = Two-phase Mechanically Pumped Loop I. Introduction Thales Alenia Space France has developed a prototype for a two-phase mechanically pumped loop (2ΦMPL) together with the Kharkov Aviation Institute (KhAI). A 6kW prototype was designed, manufactured and tested in TAS-F premises. This prototype is fully functioning and can transport very efficiently 6 kw from more than 200 units accommodated on two shelves to reject the dissipation to two deployable radiators 1, 2. In the frame of an ESA ARTES 5 project (AATDM), the 6kW prototype has been adapted to test the thermal control of an active antenna (AA) mock-up. The aim of this development was to demonstrate the feasibility of Direct Radiating Antenna (DRA) architecture and its thermal control. The use of highly efficient and integrated thermal control system in order to transport high power (up to 4 kw) on a long distances, to reduce the thermal gradient between the antenna and the radiators and to guarantee at best the quasi-isothermal requirement on the amplifier chain (less than 5 C at TWT s level), was a major issue in AATDM design and implementation. This has been demonstrated through a complete test campaign and associated results. 3, 4 Currently, TAS-F is leading internally system analysis to investigate the possibility using such a thermal control sub-system to replace or to complete standard heat-pipe networks for its future platform. Concerning the follow-on of the TAS-F MPL development plan, the following key steps have been defined : - Optimization of hydraulic scheme - Selection of adapted thermo-hydraulic tool, both for sizing and test / flight predictions - Determination of appropriate control laws, taking into account component characteristics, such as pump, Heat Controlled Accumulator (HCA) and heaters of the MPL. Concerning the last point, following paragraphs present the methodologies and corresponding steps of this investigation. II. Advantages and challenges of MPL for telecom S/C MPL presents several advantages compared to current TCS with a heat pipe network: Simplified payload accommodation: generic layout & basic panel, uniform temperature areas, embedded evaporator profiles 3D units accommodation possibility (use of shelves, condenser and evaporator uncoupling) Use of Deployable Panel Radiator (DPR) and East & West panels if required (with the same loop and the same system architecture) to reject the power Centralized heating (simplified analysis & AIT) Simplification of thermal analysis Use of conductive (cheaper) TWT instead of radiative, by increasing power rejection RF harness simplification and mass reduction 2

3 RF performance improvement AIV simplification (TVT duration decrease and no gravity constraints) Isothermicity if required However, several challenges have to be solved in order to reach mature design and valid justification for flight application: Development and qualification of building blocks : o Pump assembly o HCA o Evaporators and condensers Development of methodologies and associated tools for MPL thermal analysis : o At sub-system level o At system level AIV constraints : o Integration of tubing, evaporators and condensers in the S/C structure, in consistency with S/C AIT sequence o Type of fluid o Filling and proof pressure test of the loop o MGSE & EGSE developments for MPL operations Flight constraints : o Reliability o Redundancy o Control laws Face to these challenges, TAS-F has elaborated a DDVP and associated risk mitigation plan. In this frame, through R&T CNES contract, TAS-F and CNES have investigated and defined control laws within an activity including test predictions, test campaign, correlation, and flight predictions for typical telecom application. III. MPL prototype presentation - Evolutions MPL prototype based in TAS-F Cannes, has been elaborated and improved through different co-funded projects : - A 1 st CNES R&T so called Technological evaluation of a MPL ukrainian prototype for future telecom spacecraft, led between 2005 and 2009, with collaboration of Kharkov Aviation Institute (KhAI, Ukraine), in order to size, manufacture and test a 6 KW prototype, allowing to transport heat power from 3 internal shelves supporting mock-up representative of dissipative units (TWT and OMUX), to 2 deployable radiators. - A 2 nd CNES R&T so called Characterization and optimization of a MPL evaporator, led in 2010, with collaboration of Kharkov Aviation Institute (KhAI, Ukraine), in order to accurately characterize 6 KW evaporators and test their limits. - An ARTES5.2 contract, so called AATDM, started in 2008 and completed in 2013, in order to evaluate an efficient TCS with a MPL for future powerful active antenna, by modifying the MPL prototype with a 4 KW PL representative of the active antenna. - A 3rd CNES R&T, presented in this paper, in order to define and validate control laws, and to determine flight predictions of a telecom spacecraft TCS based on MPL technology. To achieve these different activities, MPL prototype has been improved and updated. In particular, evaporator architecture, which has to be representative of the investigated payload, has been modified. In addition, the fluid has been changed for safety reason : R245fa has been identified as a promising alternative to ammonia. So, results presented in this paper deal only with R245fa. 3

4 2ΦMPL installation is composed of 4 main parts : - The evaporator with two parallel tubing branches - Two parallel radiators - A two-phase accumulator (HCA) - One centrifugal pump Apart from these 4 components, there are also 2 electrical heaters and 5 throttles. An electrical heater is installed in the bottom part of the two-phase accumulator used for the control of the loop saturation level. The other heater is installed at the evaporator inlet, and helps the subcooled fluid coming from the pump to achieve saturation temperature. Throttles in the evaporator, the radiator lines and in the HCA bypass are needed to regulate mass flow rate sharing in the system. Heat pipes Radiator A Liquid state Two-phase state Throttle Heater Evaporator : Evaporator : TWTB TWTA Dissipation per Unit - 50 W. 1,800 W 3,000 W HT HO Evaporator : OMUXB 540 W Evaporator : OMUXA 660 W Pump Accumulator HA Radiator B Figure 1. ΦMPL installation global scheme A. Evaporators The evaporator duct design is inspired by an axial groove heat-pipe profile (trapezoidal shape) for TWT branches, and by smooth cylindrical tubing for OMUX branch. These profiles have been optimized with respect to each power density and are shown in figure 2. Profiles with fins have been selected in order to enhance wall / fluid thermal exchanges. 4

5 Figure 2. Evaporator profiles for TWTA collector branch B. Radiators simulators Heat rejection at radiator level is possible thanks to a cooling system installed close to the 2ΦMPL prototype. External space environment is simulated via this cooling system with ethylene glycol as working fluid. The compressor temperature can be controlled within the range [-15 C, -1 C]. Hot fluid coming from the evaporator passes through 27 condensers in series and the fluid exchanges the energy with glycol flowing inside each condenser. Fluid flows out of the radiator with enough subcooling to avoid cavitation in the pump. In order to achieve this subcooling level even during critical transients, there is a single-phase fluid derivation line, which connects the pump outlet with the first condenser subcooling cavity of the radiators (see Figure 1). Each radiator ground prototype is equivalent to 3,95 m² of DPR radiating surface required to dissipate the heat load. C. Two-phase accumulator (HCA) The accumulator has two main roles: - Compensation of the volume fluid variation in the loop due to different environments and heat loads. - Control of the saturation temperature/pressure level of the loop. An electrical heater has been installed in the external wall of the HCA bottom. It allows controlling the saturation level of the loop. It s a PID controller with a limitation of 250 W. Thermal control is made as a function of the HCA internal temperature. 5

6 Figure 3. Heat Control Accumulator D. Pump Installed centrifugal pump corresponds to the BBM pump supplied by Realtechnology AG company. Table 1. Pump limitations Figure 4. Centrifugal pump E. Throttles and HCA bypass Three throttles (variable diameter) are used to create artificial pressure losses and to regulate the mass flow through the different branches (see details given in ref 4 ): - Evaporator lines inlet (collector and gun) - HCA bypass HCA bypass is a smooth tube (10 mm internal diameter) that goes inside the upper side of the HCA to decrease the vapor temperature and to avoid overheating during critical transients. Flow rate through this line, so heat exchange with R245fa inside the accumulator, can be modified via this dedicated throttle. 6

7 IV. Thermo-hydraulic simulations: flight control laws definition and test predictions The main task of the investigation is the validation of the control laws. The aim of this part is the prediction of the TCS behavior in steady states and transients. The study includes the following stages : 1. Use of AMESim tool to create the MPL thermo-hydraulic numerical model. 2. Numerical test predictions for typical TCS flight conditions: i. Steady states with heat load ON and OFF for hot and cold conditions; ii. Transients with abrupt heat load changing for hot and cold conditions. A. MPL thermo-hydraulic model The MPL model can be divided into six general groups, all connected via hydraulic lines: 1. Two parallel TWT evaporators with the heat load unit dummies (TWTA and TWTB) 2. OMUX evaporator with the heat load unit dummies 3. Two parallel ethylene glycol cooled radiators 4. Heat controlled accumulator with the electrical heater, bypass line and corresponding hydraulic lines 5. Continuous electrical heaters. The first electrical heater is located before TWTs and the second heater before the OMUX 6. Centrifugal pump with inverter Each group is represented by standard AMESim elements from the Thermal, Two-phase and Signal and Control libraries. An Omegacon element is also used from the Mechanical library in the pump model. Based on the model, investigations have been carried out to define the control laws, e.g. to determine the control parameters. Then test predictions, based on these parameters, have been performed. B. Control laws definition Based on simulations, following control parameters have been raised: - HCA heater ON/OFF regulation, total power of 250W (60W+190W): The first stage (60W) of the HCA heater is used during steady state. The second stage (190W) is used during transient. - Evaporator heater (installed in order to obtain saturation at inlet evaporator level) ON/OFF regulation, total power is 1000W (100W+200W+700W): Power of first stage of inlet heater (100W) depends on the steady state GEO orbit. The second stage (200W) is used during transient in hot case. The third stage (700W) is used during transient cold case. In safe mode only two stages (100W+200W) are used. - Evaporator PI heater control has been investigated in addition to ON/OFF control. Due to generation of oscillations in that case, ON/OFF control law is found to be more robust and has been preferred. - To reduce fluctuation amplitude in ON/OFF mode, it is required to reduce the heater regulation period. - Pump RPM can be reduced by 30% in the safe mode. This allows to prevent coolant freezing and devices overcooling with maximum heater power. - Maximum total power consumptions of the TCS (pump + heaters) are: for the steady state in hot case with 2800W payload: < 100W; for the steady state in hot case without payload: < 170W; for the steady state in cold case with 2800W payload: < 200W; for the steady state in cold case without payload: < 1100W; for the transient in hot case: < 320W; for the transient in cold case: < 1300W; in the safe mode: < 370W. 7

8 C. Test prediction cases Steady states 4 different steady states have been simulated and tested. In terms of input data, each case is characterized at evaporator level by a heat load power and an environmental temperature (heat-pipe, HP, temperature). The 4 steady state are: o Heat load 500W/ Hot orbit case, HP temperature = 7.5 C o Heat load 2800W/ Hot orbit case, HP temperature = 50 C o Heat load 2500W / Cold orbit case, HP temperature = -1 C o Heat load 2800W / Cold orbit case, HP temperature = 7 C For transient, 2 cases have been simulated : One hot and one cold case. For these transient cases, HP temperatures are the same than the corresponding steady state cases (same associations heat load / HP temperature). Both for steady state and transient cases, environment / HP temperature was limited at minimum around 0 C, due to limitation of the cooling system. This limitation has been taken into account on input data for test simulations. Transient Hot orbit Only this hot case among the 2 simulated configurations is shown, concerning obtained output parameters. The following MPL inputs have been defined: - TWTA dissipated power: W (see figure 5.); Figure 5. TWTA and TWTB dissipated power evolutions. TWTB dissipated power: W (see Figure 5.); Subcooling lines of the radiators are closed; HCA heater power: 250 W; Inlet heater power: 300 W; The following control laws have been set: HCA set point is Tpump inlet+8 C with a minimum set-point of 0 C; Evaporator inlet set point is +10 C; The obtained parameters during this hot orbit case simulation are represented on following figures : 8

9 Figure 6. Maximum unit temperature evolution. Figure 7. Pump inlet subcooling evolution. Figure 8. HCA pressure and HCA temperature evolutions. 9

10 Figure 9. Condensers block outlet temperature evolution. Figure 10. Pump head evolution Transient cold orbit The following MPL parameters must be set: Pump rotation speed: rpm; TWTA dissipated power is 1500 W (see Figure 11); TWTB dissipated power: W (see Figure 11); Subcooling lines of radiators are closed; HCA heater power: 250 W; Inlet heater power: 300 W. Control laws will be set according to the next conditions : HCA set point is Tpump inlet+8 C with a minimum set-point of 0 C; Evaporator inlet temperature set point is 6 C. 10

11 Figure 11. TWTA and TWTB dissipated power evolutions. The output parameters obtained for this cold case simulation are not presented in this paper, the same type of physical data have been obtained than the ones shown for the hot case (unit temperature, pump inlet subcooling, HCA pressure and temperature, condenser block outlet temperature, pump head). For better understanding and synthesis of the discussion, results both showed in this section (simulated results) and showed in section V-B are discussed only at the end of section V-B (see discussion). V. Test results and comparison with numerical predictions A. Tested cases Experimental steady state and transient cases have been carried out with the test set-up described before. The input data (heat load and HP temperature) are obviously the same than the one taken into account for test simulation (see IV-C). B. Steady state The first step of experiments is a verification of parameters during steady state on hot and cold orbit. Hot orbit : Two levels of heat load dissipation were tested: High heat load dissipation: 2800 W Low heat load dissipation: 500 W Cold orbit : Two levels of heat load dissipation were tested: High heat load dissipation: 2800 W Low heat load dissipation: 2500 W These dissipation ranges depend on the refrigeration unit and condenser s restrictions. C. Transients The second step of experiments is a verification of parameters during transients on hot and cold orbit with increase and decrease of heat load dissipation. Hot orbit : Two transients were tested : Heat load dissipation change from 2800W to 500W. Heat load dissipation change from 500W to 2800W. 11

12 Cold orbit : Two transients were tested: Heat load dissipation change from 2800W to 2500W. Heat load dissipation change from 2500W to 2800W. The results shown above led to the following conclusions: - Temperatures of unit dummies are not exceeding +74 C for the most dissipating unit. But in general, temperatures are below +70 C on Hot case. There are no problems with equipment temperatures on Cold case. - Balances of flow rates are very good. The discrepancy between test and model is less than 0.5 ml/sec. The order of magnitude of the volumetric flow rate is between 10 and 12 ml/sec. - Existing radiators are oversized. Adjusting of flow rates to set the heat transfer coefficient according to the calculated data is not possible. Temperature of refrigerant after the condensers depends on the temperature of coolant and have only a little dependence from the inlet parameters of refrigerant. - Radiators are not working with temperature level less than zero degrees. Flow rate through radiators leads to zero very quickly in this case. Due to this problem and according to the cooling system restrictions all experiments were provided with controlling of radiators outlet temperature after the junction of flows. There are no independent set points for each radiator. Regulated temperature was set with the changing of coolant temperatures and by the additional heater. - All obtained data (steady states and transients) have a good physical correlation with test predictions and can be used for detailed correlation. - Control laws for HCA heater and inlet heater are working properly even with fixed power of heaters. Temperature after the inlet heater was stabilized on required level (+6 and +10 C). Heat losses on EH1 heater (Electrical heater at the output of the pump, before evaporator branches, in order to compensate subcooling) have no influences on result of experiments.. D. Comparison between test and simulation results Steady state Table 2 presents steady state correlation results, i.e discrepancies between simulation and test results. The unit of physical data are given in addition. 12

13 Parameter Unit 1st hot case discrepancy, % 2nd hot case discrepancy, % 1st cold case discrepancy, % 2nd cold case discrepancy, % Maximal unit temperature Pump inlet subcooling HCA temperature o C o C o C HCA pressure bar Condenser block outlet temperature o C Pump head kpa TWTA volumetric flow rate ml/s Summary volumetric flow rate ml/s Evaporator pressure drop kpa Evaporator inlet temperature o C Table 2. Steady state cases discrepancies between simulation and test results Transients The second step of experiments is a verification of parameters during transients on hot and cold orbit with increasing and decreasing of heat load. Only the 1 st hot transient is detailed (heat load dissipation change from 2800W to 500W). The results of experiment parameters compared to the simulation are represented in figures 12 to 19. The evolution of TWT dissipation is the one shown in figure 5. Figure 12. Unit temperatures evolutions. 13

14 Figure 13. Pump inlet subcooling evolution. Figure 14. HCA pressure and HCA temperature evolutions. Figure 15. Condensers block outlet temperature evolution. 14

15 Figure 16. Pump head evolution. Figure 17. Flow rates evolutions. Figure 18. Pressure drop evolutions. 15

16 Figure 19. Evaporator inlet temperature evolution. E. Discussion According to the results showed above the following conclusions will be made: Temperatures of units (figure 12) : The discrepancy is due to a simplification of the heat load distribution all around the evaporator tubing. Pump inlet subcooling, HCA temperature and HCA pressure (figures 13-14) : Discrepancies are due to no heat losses at HCA level in simulation. Condensers (figure 15) : good agreement between numerical and experimental results. Pump head (figure 16) and pressure drops (figure 18) : big discrepancy between simulation and experiment. The cause is the model of pump in the AMESim software. Current pump model is a volumetric pump model instead of centrifugal one. Pump model modification is in progress. Flow rate (figure 17) are described by AMESim model correctly. Evaporators (figure 19) : good agreement between numerical and experimental results. The simulation has a good physical and numerical correlation with the test results. Existing discrepancies are explained by the AMESim pump model limitations and by the MPL prototype functioning state. New centrifugal pump model is necessary for better results in future. AMESim software can be used for design, adjustment and investigation of thermal control system for the NeoSat platform in future. VI. Perspectives In the frame of overall MPL development plan up to qualification prior to flight application, the following steps are foreseen : - Update of cooling system in order to reach typical cold GEO temperature (- 60 C) with power rejection capabilities up to 10 KW - Update of condenser and evaporator blocks, in order to be representative of a current and future telecom payload - Update of HCA hardware (EM level) with more representative capillary structure - Update of MPL architecture, in terms of number of branches for condenser and evaporator 16

17 These improvements will allow to integrate an MPL EM and to perform more representative tests in In parallel, the development of building blocks continues, in particular to reach qualification status of each component. In the same way, AIT and system modeling activities have been initiated. VII. Conclusion In the frame of the development of a two-phase mechanically pumped loop (2ΦMPL) for S/C telecom application, this study focuses on control laws definition and validation. First, main advantages and challenges of the MPL technology for telecom applications are presented. Based on thermo-hydraulic numerical simulations performed with AMEsim software, the control laws have been defined and simulated. After hardware evolutions of the MPL prototype (modification of evaporator, fluid change), a test campaign has been carried out to reproduce typical flight operational cases (both steady state / transient, and hot / cold cases), to be compared with numerical simulations. The validation of thermo-hydraulic models has been successfully performed, with globally good accordance between test and prediction results, representative of typical operational flight cases. Finally, perspectives and next steps of the continued overall MPL development are given. Acknowledgements The main author thanks the Centre National d Etudes Spatiales, for their support and their expertise for thermal point of view: Amaury Larue de Tournemine (CNES). The main author thanks also the Kharkov Aviation Institute for their support and valuable discussions: Pavlo Gakal, Vasyl Ruzaykin, Rustem Turna and Dmitry Chayka. References 1 Hugon, J. & al, Development of a two-phase mechanically pumped loop (2ΦMPL) for the thermal control of telecommunication satellites, Two Phase Workshop, ESTEC, Hugon, J. & al, Development of a two-phase mechanically pumped loop (2ΦMPL) for the thermal control of telecommunication satellites: experimental test results of a 6kW prototype, Two Phase Workshop, Aerospace Corporation, Merino, A-S., Hugon, J., Development of a two-phase mechanically pumped loop (2ΦMPDL) for the thermal dissipation management of an active antenna, ICES Soto Armananzas, I., Hugon, J., Ravasso, N., Rousseau, J.J., Schwaller, D., Larue de Tournemine, A. Development of a two-phase mechanically pumped loop (2ΦMPDL) for the thermal dissipation management of an active antenna: experimental on-ground results, ICES