Croell, A.

Ostrogorsky, A. G.

Riabov, V.

Volz, M. P.

NASA Technical Reports Server

Heat transfer model of the SUBSA furnace
V. Riabov 1, A. G. Ostrogorsky1, M. P. Volz2 and A. Croell3    
1Illinois Institute of Technology, Chicago, IL 60616, AOstrogo@IIT.edu
2NASA Marshall Space Flight Center, Huntsville, AL35812
3University of Alabama in Huntsville, Huntsville, AL35899
• The SUBSA (Solidification Using a Baffle in Sealed 
Ampoules) furnace was designed in 2002 for growth 
of indium antimonide in the Microgravity Science 
Glovebox at the International Space Station.
• The furnace features a transparent section, which 
allows a side view of the melt and growing crystal. 
• At present, the SUBSA furnace is being used to grow 
the radiation detector materials InI and Cs2LiYCl6:Ce 
(CLYC) 
• Heat transfer models of the SUBSA furnace have 
been developed using the modelling programs 
CrysMAS to help optimize the design of the 
experiments for these new materials.
1996 - 2002
2016 - present
https://ntrs.nasa.gov/search.jsp?R=20180007885 2019-08-31T17:13:36+00:00Z
SUBSA Furnace (left) and Microgravity 
Science Glovebox (MSG) Unit (right)
Original Experiments WITH InSb: 
A schematic of the furnace and a sample 
ampoule assembly (SAA)
Temperatures measured by the sample 
thermocouples during growth of InSb
• Transparent section was feasible, because of the low melting point (512 C) 
and high thermal conductivity of InSb  (10 𝑊𝑊/𝑚𝑚 − 𝐾𝐾 for liquid and 18 𝑊𝑊/𝑚𝑚 −𝐾𝐾 for solid InSb)
• During “seeding” i.e. peak temperature, 𝑇𝑇𝑇𝑇𝑇𝑇𝑇 − 𝑇𝑇𝑇𝑇𝑇𝑇𝐶 = 120𝐾𝐾. 𝑇𝑇𝑇𝑇𝑇𝑇𝐶 − 𝑇𝑇𝑇𝑇𝑇𝑇𝐶 =100𝐾𝐾.  Thus,  𝒅𝒅𝒅𝒅/𝒅𝒅𝒅𝒅 > 𝟏𝟏𝟏𝟏𝟏𝟏 𝑲𝑲/𝒄𝒄𝒄𝒄
Heat transfer in the transparent zone
Radiation shields
The radiation shields are effective if they:
• reflect radiation back towards the ampoule (are cylindrical and coaxial)
• have high reflectivity and low emissivity
• Are small and close to the heat source to be relatively “hot” (to reduce Δ T4). 
• Are not transparent, τ=0 (except in the visible range).
The radiation shield geometry used in the SUBSA furnace uses the radiation 
reflectors that are flat and far from the ampoule (Fig. 2 b),and the conditions  i, 
and iii are not satisfied.  Only a small fraction of radiation is reflected back to the 
ampoule.  Instead, it is absorbed in the shields after multiple reflections.   As a 
result dT/dr and dT/dx are high.
Convection and Radiation heat transfer 
coefficient in the transparent zone on Earth 
in microgravity (ISS)
g Gr_D Gr_L h_Hori h_Vert h_rad h_Total
W/m2-K W/m2-K W/m2-K W/m2-K
9.81E-06 0.01585 0.2477 1.306 1.221 18.16 19.46
9.81E-05 0.1585 2.477 1.57 1.493 18.16 19.73
9.81E-04 1.585 24.77 2.04 1.943 18.16 20.2
9.81E-03 15.85 247.7 2.876 2.709 18.16 21.03
9.81E-02 158.5 2477 4.363 4.065 18.16 22.52
9.81E-01 1585 24771 7.006 6.551 18.16 25.16
9.81E+00 15853 247710 11.71 11.27 18.16 29.86
Conclusions:
•On Earth, hconvection =11 W/m-K  and hrad ~ 18 W/m-K. hTotal ~ 30 W/m-K.
• At 10-6g0, ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = 1.𝐶𝑊𝑊𝑚𝑚 − 𝐾𝐾, hTotal ~ 20 W/m-K.
•Heat transfer is dominated by radiation
𝑞𝑞𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑇𝑇 − 𝑇𝑇𝑓𝑓𝑓𝑓𝑓𝑓𝑐𝑐𝑓𝑓 ; 𝑞𝑞𝑟𝑟𝑟𝑟𝑓𝑓 = ℎ𝑟𝑟𝑟𝑟𝑓𝑓 ∗ 𝑇𝑇 − 𝑇𝑇𝑠𝑠𝑓𝑓𝑟𝑟
ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − 𝑒𝑒𝑚𝑚𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑚𝑚𝑚𝑚𝑚𝑚𝑒𝑒𝑒𝑒 Type equation here.
Experiments with InI and CLYC in 2016-
present
• At present, the SUBSA furnace is being used to grow the radiation 
detector material InI and scintillator Cs2LiYCl6:Ce (CLYC) both of 
which have low thermal conductivity, k~ 0.5 W/m-K (~10x lower than 
the thermal conductivity of InSb).
InI detector CLYC crystal
Image source: 
https://www.nasa.gov/sites/
default/files/thumbnails/ima
ge/imclyc.jpg
• Both salts have low thermal conductivity, k~ 0.5 W/m-K (~10x lower than 
the thermal conductivity of InSb).
• At the ISS in 2002, one experiment failed, because 0.503 g of molten salt 
LiCl-KCl eutectic was present. LiCl-KCl has similar properties as InI or 
CLYC (k~ 1 W/m-K) 
Axial temperature gradient dT/dx as a 
function of melt thermal conductivity 
Using the “fin” model we show that the resulting the temperature profile T(x) 
and gradient dT/dx, depend on the the thermal conductivity of the charge in 
the ampoule.
• dT1/dx ~ 100 K/cm, is in excellent agreement with the data from InSb-
SUBSA experiments
• dT2/dx ~ 300 K/cm. One  must overheat the melt by 300 C, for 1 cm  to be 
visible in the transparent zone
0
100
200
300
400
500
600
700
0 0.01 0.02 0.03 0.04
T_1
T_2
Axial profile in SUBSA SAA. T_1 for InSb, k1=10 
W/m-K and T_2 for a salt, k2=1 W/m-K, 
Modeling for optimization
• Using CrysMas software package, Axi-
Symmetric Heat conduction and radiation 
model was developed to explore the application 
of highly conductive sleeve on SAA to help 
supply heat from the heater core into the 
transparent zone and to reduce dT/dx
0100
200
300
400
500
600
700
800
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
T,C NO SLEEVE
T,C, WITH SLEEVE
Axial temperature profile and field in the model 
• CrysMass calculations show significant reduction of dT(x)/dx when 15  cm long,  
OD=17.6 mm, ID=16  mm sapphire pipe is used 
0
100
200
300
400
500
600
700
800
0 0.05 0.1 0.15 0.2
Te
m
pe
ra
tu
re
, d
eg
re
es
 C
Distance from cartridge head outer surface, m
Computed, C No sleeve
Computed, C, With sleeve
Experimental, C
Comparison of temperatures measured by 
sample TC's in experimental run InI-G1 with 
values obtained by simulation
Conclusion
• The step change in temperature, between the heated and the 
unheated zone, causes large temperature gradients, dT/dx, which are 
(a) undesirable for single crystal growth
(b) may cause convective interference with diffusion in 
microgravity experiments. 
(c) For InI, CLYC and there non-metallic melts, ~1 cm of 
melt is visible. 
• temperature gradient in the SAA should be reduced to a value of 20 to 
50 K/cm in order to: 
- reduce overheating the melt
- reduce thermal stresses and stress induced dislocations.
- reduce convection on Earth and in microgravity.
- allow 3 to 4 cm of the melt to be visible (as this was the 
case with InSb). 
• Using a sapphire (or other highly conductive material) tube will 
significantly reduce the step change in the boundary conditions 
Flight samples – Melt growth
• The design of SAA featuring highly conductive silver and sapphire 
sleeves was implemented in the flight experiment samples
• Four melt growth samples of InI were delivered to the ISS in March 
2017 
Vapor growth of InI
Over the course of this investigation a bulk crystals of 
InI were produced by physical vapor transport for the 
first time
Flight samples – vapor growth
Two vapor growth samples of InI were delivered to the ISS in March 2017
Acknowledgement
• This work was supported by CASIS under Grant Number GA-2015-207/NASA 
NNH11CD70A, the National Science Foundation under Grant Number CMMI-
1853512, and by the National Aeronautics and Space Administration Space Life 
and Physical Sciences Research and Applications Division under cooperative 
agreement NNM11AA01A.


Heat Transfer Model of the SUBSA Furnace

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