Modeling of LHP Temperature Control in EcosimPro

1. F.Romera, R.Pérez, C.Gregori, E.Turrion, D.Mishkinis, A. Torres Modeling of LHP Temperature Control in EcosimPro

2. Introduction • The main objective of a thermal control system is to maintain some components within some appropriate temperature limits. For many applications there is also the need to keep it above a temperature lower bound. This temperature control can be performed by several ways: • To introduce extra thermal power in the equipment (survival heaters) • To interrupt partially or totally the heat pumping towards the heat sink (thermal switch). • To control the LHP evaporator operating temperature by suitably heating the CC or the liquid line (temperature control loops) • This paper presents the capability of a general purpose simulation tool, EcosimPro for LHP modeling. This modeling encompasses all the typical tasks: • Design • Test results prediction • Test analysis • Performance prediction under non easily testable conditions International Conference "Heat Pipes for Space Application"

3. EcosimPro • is an object-oriented simulation tool with a user-friendly environment for modeling simple and complex physical processes that can be expressed in terms of differential-algebraic equations or ordinary-differential equations and discrete events, such as: • • Fluid flow in pipe networks • • Heat transmission • • Chemical reactions • • Mechanical components • • Electrical circuits • • Control devices • • Etc. • http://www.ecosimpro.com/ • EcosimPro also provides links to the external world: • Already existing functions in FORTRAN, C or C++ • External C++ classes (optimizers, solvers, etc.) • External Tools MATLAB/SIMULINK, EXCEL • Company Specific Tools. International Conference "Heat Pipes for Space Application"

4. LHP LIBRARY OF ECOSIMPRO I • A dedicated EcosimPro library has been created for LHP modeling. The component of this library can be coupled with other components as controllers, electrical, mechanical, etc. coming from other libraries in a multidisciplinary simulation environment. Example of LHP EcosimPro model International Conference "Heat Pipes for Space Application"

5. LHP LIBRARY OF ECOSIMPRO II • The model of a LHP has modular architecture generated by connection of standard LHP components: Ev, CC, transport lines and Cond. • Modular feature of EcosimPro allows quickly introduce new elements (radiators, cold plates, etc.) or upgrade existing ones and analyze complex two-phase systems including multi-evaporator and multi-condenser schemes. • Following main assumptions have been made for the LHP components modeling: • The 1D fluid flow model is a homogeneous equilibrium model. • The calculated thermodynamic properties correspond to the two-phase mixture. They are obtained by interpolation using the NIST tables. • LHP components can exchange heat with the environment by convection and radiation, and with other external components (such as saddles) by conduction. • Fluid model is based on the one-dimensional fundamental conservation equations (mass, momentum and energy) applied to control volumes. The fluid part of each LHP component is sub-divided into individual control volumes. International Conference "Heat Pipes for Space Application"

6. LHP LIBRARY OF ECOSIMPRO III • Compressibility and Transient effects are taken into account. Viscous effects are taken into account through the pressure drop calculations, which include correlations for the pressure drop in a porous media. • The gravity effects due to the different orientations of the LHP have been taken into account. • Full explanation of the general mathematical model and the main hypothesis made for the capillary pump and the LHP lines can be found in references: • Gregori C., Torres A., Perez R., and Kaya T., LHP Modeling with EcosimPro and Experimental Validation // SAE Paper No. 2005-01-2934, 2005. • Gregori, C., Torres, A., Pérez, R., Kaya, T., Mathematical modeling of multiple evaporator/ multiple condenser LHPs using EcosimPro, SAE Paper 2006-01-2174, 2006 • The components of LHP library can be coupled with other components as controllers, electrical, mechanical, etc. coming from other libraries in a multidisciplinary simulation environment. International Conference "Heat Pipes for Space Application"

7. MODEL OF THERMAL SWITCH • The “switch” capacity of the LHP is provided by the valve, which passively splits the evaporator flow to the bypass line or the condenser in accordance with the working fluid pressure. Example of Thermal Switch application is the TCS for a Mars rover. DETAILS: D. Mishkinis, C. Gregori, F. Romera and A. Torres. Development of Propylene LHP for European Mars rover applications. Heat pipes, heat pumps, refrigerators and power sources; VII Minsk International Seminar, 8-11 Sept-2008. model of LHP with PRV developed for Mars rover applications International Conference "Heat Pipes for Space Application"

8. MODEL OF THERMAL SWITCH • To compare the model and test results, it is selected a test in which the sink temperature and the applied power are varying continuously (transient case) in order to represent a hot case Mars scenario: International Conference "Heat Pipes for Space Application"

9. MODEL OF THERMAL SWITCH • Test/model temperature comparison for the Mars hot case scenario: International Conference "Heat Pipes for Space Application"

10. MODEL OF CC TEMPERATURE CONTROL LOOP • Another technique to control the LHP evaporator temperature is increasing the saturation temperature of the CC chamber by active control with heater. Model of LHP with T-control by heating CC Model of LHP with T-control by heating LL International Conference "Heat Pipes for Space Application"

11. MODEL OF CC TEMPERATURE CONTROL LOOP • Simulation results (heater on CC) with and without heat application to the compensation chamber and for a hot case where the valve is not regulating (no flow is bypassed). The desired compensation chamber set point is 29.8 ºC. With temperature control, the CC temperature remains constant at the setpoint up to 30W. Then, the regular CC temperature is above the desired set point and the control can not regulate it since power is above the range where regulation can be realized International Conference "Heat Pipes for Space Application"

12. MODEL OF CC TEMPERATURE CONTROL LOOP • Second example of the LHP temperature control. Temperature of evaporator (34±0.5 from time 1700 s) is controlled by heater on CC. Good agreement was obtained between test and modeling results: International Conference "Heat Pipes for Space Application"

13. MODEL OF CC TEMPERATURE CONTROL LOOP • Video International Conference "Heat Pipes for Space Application"

14. CONCLUSIONS • EcosimPro simulation tool allows the multidisciplinary modeling of LHP temperature control system, for which thermo-hydraulic, electrical, control and mechanical elements are present in the same system. • LHP temperature controls based on pressure regulating valves or control loops of the compensation chamber temperature (by heating the compensation chamber itself or the liquid line) have been modeled. • The model results are compared to experimental with good agreement, which prove the high capacity of EcosimPro and related LHP library to reproduce real systems. International Conference "Heat Pipes for Space Application"

15. Несовместимо! Совместимо! Compatible! • Thank you! • Спасибо! International Conference "Heat Pipes for Space Applications"