Thermal Aspects of

Cadmium Zinc Telluride (CZT) Imager

Presented By M.K. Hingar

Plan Configuration Design Inputs Design of the Detector Board Analysis Results Radiator & Heat Pipe Design Critical Elements Conclusions

CONFIGURATION

Thermal design Inputs for CZT-Imager Power generated by each channel of

CZT ASIC3 mW

Number of channels in each CZT Module

256

Power generated by each CZT Module 768 mW

Number of CZT in each quadrant 16

Power generated by each quadrant 12.3 W

Number of quadrants 4

Power generated by the CZT-Imager 49.2 W

Allowed temperature variation among CZTs of each quadrant

5o

Allowed temperature difference among quadrants

5o

Working temperature range of the Instrument

0o to – 20o

CZT DETECTOR CZT DETECTOR BOARD

WITHIN CZT DETECTOR BOARD

HEAT PIPERADIATOR

5 o 4 o

5o

5 o

TEMPERATURE DIFFERENCE BETWEEN DIFFERENT STAGES IN ONE QUADRANT

Thermal Analysis has five Steps:• Transfer of heat from CZT Detector to the CZT

Detector Board.• Transfer of heat within the CZT Detector Board. • Transfer of heat from CZT Detector Board to

the Heat pipes.• Transfer of heat from Heat pipes to Radiator.• Radiator design.

Transfer of heat from CZT Detector to the CZT Detector Board

q = k A ΔT

Where q = Power = 0.780 W,k = Thermal Conductivity of thermal epoxy = 0.08 W / cm2 oKA = Area = 4 cm2

ΔT = 0.78 / (0.08 * 4) = 2.42 o K

If we consider factor of safety 2, it may be about 5 o K.

Design of Detector Board

Cu-In-Cu Copper Coating

PROPERTIES OF CIC LAMINATE

Metal /Core/ Metal Density(g/cm3)

Coefficient of Thermal

Expansion(ppm/0c)

Thermal Conductance

W/m-0c

Modulus elasticity,

GPa

Tensile strength,MPa

x, y z x, y z

20Cu/60In/20Cu 8.45 6.0 7.7 164 22 135 310-412

12.5Cu/75In/12.5Cu 8.31 3.6 5.3 110 64 140 380-472

Transfer of heat within the CZT Detector Board

• The Detector Board of 20Cu/60In/20Cu.

• The thickness of Detector Board is 3mm.

• The preliminary analysis give the maximum temperature on the Detector Board of the quadrant is about 4o.

Boundary Conditions

Temperature at the edges of Detector Board is 0o

CZT Power (780 mW) distributed equally in 20mm X 20mm area

Analysis shows

Heat Drain from two opposite sides of the Detector Board is necessary.

Radiation losses not considered.

STEPS TEMPERATURE DIFFERENCE

Transfer of heat from CZT to the Detector

Board

5 o

Within Detector Board

4 o

Detector Board to heat pipe

5 o

Heat Pipe to Radiator 5 o

-60 -50 -40 -30 -20 -10 0 10 20 30 400

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000A

rea

(cm

2 )

Radiator temperature (0C)

Power (W) 5 10 15 20 25 30 35 40 45 50

Fig. 2 Radiator area for different power dissipation values

Implications of quadrants failures for thermal design

Suppose one of the quadrants fails then radiator will dissipate about 37 W (50 W ), the Radiator will have temperature of - 27o ( - 20o ).

Suppose two of the quadrants fail then radiator will dissipate about 25 W (50 W), the Radiator will have temperature of - 40o ( - 20o ).

Possible use of heaters to be considered after final simulation.

CONCLUSIONS

Total temperature difference is within 15 o to 20 o .

Procuring one Detector Board and measure temperature difference.

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