THE LOOP HEAT PIPE FOR AMS02 Stefano Zinna

THE LOOP HEAT PIPE FOR AMS-02 Stefano Zinna Marco Marengo LSRM, Faculty of Engineering, University of Bergamo, viale Marconi 5, 24044 Dalmine, Italy

Inside ANTASME OBTAINED RESULTS 8. 1 The LHP for AMS is built and run for orbital conditions 8. 2 The ground LHP for AMS is built and stationary results are compared with LHP model in microgravity 8. 3 The construction of thermal chamber in China is delayed (cancelled) 8. 4 A simplified model of the LHP is carried out in order to be implemented in multidisciplinary codes 9. 3 The LHP model has been run by including the FEM results about valve

INDEX 1. 2. 3. Simulation of the LHP prototype in thermal chamber (ground test) (deliverable 8. 2) Definition of data input and output structures for future implementation in general multidisciplinary codes (deliverable 8. 4) Implementation of the FEM data in the SINDA/FLUINT network scheme (deliverable 9. 3)

Deliverable - 8. 2 Simulation of the LHP prototype in thermal chamber (ground test)

Ground LHP results l l The ground propylene LHP has been implemeted: The model has different correlation for pressure drop and condensation in the two-phase part (condenser) The reservoir temperature (TCC) and subcooling temperature (TS) are compared with microgravity model TCC TS CONDENSER l l l Stationary mode is run with power from 30 W to 90 W The 1 G results have temperature lower than m. G while the power is increasing The temperature difference is about 2° for 90 W

m-G/1 G PRESSURE DROP m-G l Bubbly/Slug flow: Mc. Adam’s formulation for homogeneous flow l The annular regime: Lockhart-Martinelli correlation (Zhao L. Rezkallah K. S. , 1995. Pressure drop in gas-liquid flow at microgravity conditions. Int. J. Multiphase Flow 21, 837 -849) 1 G l The predicted pressure drops is based on the Muller-Steinhagen and Heck correlation (John R. Thome, Wolverine Engineering Data Book III, 2006) The factors A and B are the frictional pressure gradients for all the flow liquid and all the flow vapour

1 G Model SLIP FLOW l The Tabular connector device allows users to specify flow rate versus head (or pressure drop) relationships in tabular (array) formats l The gravitational forces are independent of the velocity while the friction and the acceleration forces are function of the square of the flow rate l These coefficient are inserted in the equation for the fluid path while the vapour path is set in order to satisfy the slip flow model chosen

m-G/1 G pressure drop differences l The Clausius–Clapeyron correlation is used to calculate the temperature difference in the two-phase part of the condenser Q [W] l MICROGRAVITY NORMAL GRAVITY DT DP (Pa) 30 0. 008 69. 3 0. 012 97. 2 60 0. 076 701. 7 0. 095 874 90 0. 16 1815. 7 0. 16 1791 THE TEMPERATURE DIFFERENCE IS WEAKLY RELATED TO THE PRESSURE DROP

m-G/1 G CONDENSATION m-G The condensation heat transfer coefficient for two-phase flow is based on Shah’s correlation (Po-Ya Abel Chuang, An improved steady-state model of loop heat pipes on experimental and theoretical analyses. 2003, Phd Thesis) l 1 G The correlation is based on Dobson and Chato method. (Soliman transition criterion) (John R. Thome, Wolverine Engineering Data Book III, 2006) l l The annular correlation: l The stratified-wavy correlation:

GRAVITY FLOW PATTERN l The Soliman transition criterion for predicting the transition from annular flow to stratified-wavy flow was used l The G is always lower than 500: G (30 W)=9. 3; G (60 W)=18. 7; G (90 W)=28 l The transition from stratified to annular is with quality between 0. 6 and 0. 8 depending on the temperature ANNULAR STRATIFIED

m-G/1 G condensation differences l l l Stratified-wavy Dobson & Chato heat transfer compared with Shah heat transfer High quality The heat transfer coefficient difference is higher with higher power incoming the evaporator Annular Dobson & Chato heat transfer compared with Shah heat transfer Low quality The heat transfer for D&C is always higher

CONCLUSIONS l The gravity model temperatures are lower than the microgravity model and the difference is increasing while the power incoming in the evaporator is increasing l The pressure drop has a negligible influence on the temperature drop in the two-phase condenser l Wider two-phase lenght for high power l Higher difference in the heat transfer for high power

Deliverable - 8. 4 Definition of data input and uotput structures for future implementation in general multidisciplinary codes

ANALYTICAL MODEL (Evaporator balance) • To test the SINDA/FLUINT results and to understand which are the most important parameters that influence the LHP in order to set the input/output structures • The heat absorbed from the cryoocooler crosses from the evaporator wall to the solid wick and it is shared between Fluid wick and Reservoir: • The pressure in the end of the liquid line is close to the saturation pressure & the liquid flow rate depends on the power and the evaporation enthalpy at saturation temperature (Tsat): UW Gback

ANALYTICAL MODEL (Radiator balance) • The temperature changes depends only on the axial conductances with the evaporator wall and can be considered negligible while the pressure drop has a small influence on the enthalpy: • The power rejected from the radiator (Qout) is due to the radiation towards the external environmental

ALGEBRAIC SYSTEM • The algebraic system has now 5 parameters: UWB, QCRYO, Qflux, Grad, Tsink: • The results are shown in the graphic for the steady state operating temperature: (a) Qflux=70 [W], Uwb=25/3 (b) Qflux=0 [W], Uwb =25/3 (c ) Qflux=70 [W], Uwb=25/6. For all the cases the radiative conductance Grad is 5. 0 10 -9 [W/T^4] and the Tsink is 170 K.

CONDENSER TEMPERATURE l The initial part of the pipe is near the end. The high temperature of the incoming two-phase fluid causes a important heat transfer to the outgoing fluid, the TS increases and consequently the TCC is higher. l Another heat flux is exchanged between two parts of the same condenser in the middle of the radiator and leads to the first maximum in figure.

Input/output structures l Where Lo is a system operator, t is time, x(t) is the state of the system, u(t) is its input, w(t) is some external or internal disturbance, and l is a parameter that defines the system. Each one of these quantities belongs to a suitable set or vector space and there a large number of possibilities l y: the steady state operating temperature and subcooling temperature; u: the power coming in the evaporator; w: the boundary conditions (the external fluxes in the radiator, the radiative conductance and the sink temperature for the radiator); l : the ratio between the conductance inside the wick and the conductance from the wick to the reservoir, and the radiator area. INPUT OUTPUT SYSTEM BOUNDARY

CONCLUSIONS l l An analytical model is carried out in order to achieve a simplified model: good approximation of the SINDA results for high power The input/output structures are defined: the solver Lo could be by the analytical model (Lo -> an algebraic operator ) or the sinda model SINDA ANALYTICAL MODEL

Deliverable - 9. 3 Implementation of the FEM data in the SINDA/FLUINT network scheme

LHP-VALVE l Temperature requirements: Q Min. turn-on and operational temperature of the Cryocooler 263 K Max. operational temperature of the Cryo-cooler 313 K WORST CONDITIONS (Coldest environment, nominal working (2 LHP), minimum power (61 W)) : 226 K< TCRYO <230 K TCRYO EVAPORATOR VALVE l CRYOCOOLER TCC OPEN CLOSE MODE L H RADIATOR TRAD EXTERNAL AMBIENT P

Implementation of the FEM data l l l The information about the valve come from FEM ANALYSIS (Speetjens M. & Rindt, C. 2006 Numerical analysis of the bypass valve in aloop heat pipe, INTERREG IIIC MATEO-ANTASME Deliverable 9. 2. ) The solver is only sinda (NO analytical model) The pressure drop : VALVE SINDA

1 set point l l OPEN MODE: TCRYO<263 CLOSE MODE: TCRYO>263 The temperature in the cryo react quickly to the open mode The temperature in the cryo reachs 262. 7 CC CC

2 set point l l l OPEN MODE: TCRYO<263 CLOSE MODE: TCRYO>265 Valve between the open and the close mode: 263<TCRYO<265 The temperature requirements are satisfied The temperature is 2° higher than 1 set point CC

CONCLUSIONS l l The FEM data are inserted in the sinda model and two cases are run depending on 1/2 set points There is a little inertia between the compensation chamber and the cryo l l a higher set point should be chosen 2 set point should be definied