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

2. 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 the 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
Unitil now the results are the modelization of the LHP both numerical and physical. In particular in microgravity the heat transfer is 50% less than in normal gravity hence a parameter that cut 50% heat transfer coefficient’s value is imposed.

3. INDEX
Simulation of the LHP prototype in the 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)

4. Simulation of the LHP prototype in the thermal chamber (ground test)
Deliverable - 8.2
Simulation of the LHP prototype in the thermal chamber (ground test)

5. Ground LHP results TCC TS
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
Stationary mode is run with power from 30 W to 90 W
The 1G results have temperature lower than mG while the power is increasing
The temperature difference is about 2° for 90W TS
CONDENSER

6. m-G/1G PRESSURE DROP m-G 1G
Bubbly/Slug flow: McAdam’s formulation for homogeneous flow
The annular regime: Lockhart-Martinelli correlation
(Zhao L. Rezkallah K.S., Pressure drop in gas-liquid flow at microgravity conditions. Int. J. Multiphase Flow 21, ) 1G
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

7. 1G Model SLIP FLOW
The Tabular connector device allows users to specify flow rate versus head (or pressure drop) relationships in tabular (array) formats
The gravitational forces are independent of the velocity while the friction and the acceleration forces are function of the square of the flow rate
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

8. m-G/1G pressure drop differences
The Clausius–Clapeyron correlation is used to calculate the temperature difference in the two-phase part of the condenser
THE TEMPERATURE DIFFERENCE IS WEAKLY RELATED TO THE PRESSURE DROP
MICROGRAVITY
NORMAL GRAVITY DT
DP (Pa)
Q [W] 30
0.008
69.3
0.012
97.2 60
0.076
701.7
0.095
874 90
0.16
1815.7
1791

9. m-G/1G 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) 1G
The correlation is based on Dobson and Chato method. (Soliman transition criterion) (John R. Thome, Wolverine Engineering Data Book III, 2006)
The annular correlation:
The stratified-wavy correlation:

10. GRAVITY FLOW PATTERN
The Soliman transition criterion for predicting the transition from annular flow to stratified-wavy flow was used
The G is always lower than 500: G (30W)=9.3; G (60W)=18.7; G (90W)=28
The transition from stratified to annular is with quality between 0.6 and 0.8 depending on the temperature
ANNULAR
Il numero di Froude confronta le forze di inerzia con le forze gravitazionali
Il numero di Reynolds= forze di inerzia/forze viscose
Il numero di Galileo= forze gravitazionali con le forze viscose
Ja= c (DT)/Hlg
Bond number= forze gravitazionali alle forze della tensione superficiale Bo=rho*a*r^2/sigma
Pr=v/alfa
STRATIFIED

11. m-G/1G condensation differences
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

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

13. Deliverable - 8.4
Definition of data input and uotput structures for future implementation in general multidisciplinary codes

14. 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 cryoo-cooler 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
Il modello numerico realizzato con Sinda può essere approssimato tramite una forma analitica chiusa
Il calore assorbito dalla parte solida deve bilanciare l’entalpia che entra e che esce dal volume di controllo fluido
The liquid flow rate depends on the power and the evaporation enthalpy at saturation temperature (Tsat). Besides the pressure in the end of the liquid line (PL) is close to the saturation pressure (Psat) because the possible difference is due only to the pressure losses at the entrance in the reservoir from the liquid line.
By using the previous simplifications the Eq. (3.3) becomes …..dove sono state introdotte le conduttanze nell’evaporatore per tenere in conto delle potenze scambiate e si sono considerate trascurabili le potenze destinate alla reservoir & per superheat the groove

15. 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

16. 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 170K.

17. CONDENSER TEMPERATURE
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.
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.

18. Input/output structures
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 are a large number of possibilities
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

19. CONCLUSIONS
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

20. Implementation of the FEM data in the SINDA/FLUINT network scheme
Deliverable - 9.3
Implementation of the FEM data in the SINDA/FLUINT network scheme

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

22. Implementation of the FEM data
The information about the valve come from FEM ANALYSIS (Speetjens M. & Rindt, C 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

23. 1 set point OPEN MODE: TCRYO<263 CLOSE MODE: TCRYO>263CC
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

24. 2 set point OPEN MODE: TCRYO<263 CLOSE MODE: TCRYO>265CC
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

25. CONCLUSIONS
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
a higher set point should be chosen
2 set point should be definied

28. WORST CASES
Coldest environment and minimum dissipation 63W the cryocooler temperature is much lower than -10℃, reaching -45.7℃. Freezing problem will not occur in the condenser of LHP even in -90℃, because of the low freezing point of propylene.