Thermal Analysis and Design

1
Thermal Analysis and Design of ACOP-T for PDR
A.- S. Wu and M.- C. Yu
January 10, 2005
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Outline

• Content
  
  Page
• 1. Introduction
  3
  
• 2. System Description
  4
• 3. Thermal Control Concept and Thermal Design
  Description 6
• 4. Thermal Requirements
  8
• 5. Boundary conditions
  9
• 6. Thermal Loads
  10
• 7. Model Description and thermal Analysis
  13
• 8. Analysis Results
  17
• 9. Conclusions
  
  26
• Reference
  
  29

3
1. Introduction

• Since the existed acoustic noise of the ISS cabin
  is beyond the specifications, and fortunately
  ducted cooling air is provided by the Express
  Rack locker to cool the installed ACOP, the
  cooling system for ACOP will discard the cooling
  fans to meet the requirements of no noise.
• The sketch of ACOP is shown as in Figure 1.

Figure 1 The current design of cooling system for
ACOP .
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2. SYSTEM DESCRIPTION

• The size of two square ports of the inlet and the
  outlet for the ducted cooling air is 110 x 110 mm
  at the back side of ACOP.
• The ports are fitted with screens with an open
  area ratio of 60.02.
• The friction coefficient of pressure loss for the
  screens
• is calculated conservatively to be around
  2.0.
• A minimum flow rate, 12 cfm, of the cooling air
  with a conserved pressure of 10.2 psia is
  compressed into the inlet of ACOP.
• Two ducts are designed to connect the ports of
  the inlet and the outlet with the fin channels as
  heat sinks in order to reduce the pressure loss.

5
2. SYSTEM DESCRIPTION

• At both sides of ACOP chassis extrude 56 fins
  respectively to be the heat sinks in order to
  increase both of the heat transfer area and the
  heat transfer coefficient.
• The thickness of the aluminum alloy fins is 1.5mm
  with height and length of 60mm by 162mm as listed
  in Table 1.
• The gap between two neighboring fins is 2.5mm.
• The cooling air comes into the inlet, by the
  ducts, through the fins to take away the power
  dissipation, generated on the boards and in the
  hard disk drivers and conducted to the chassis
  and the extruded fins, and comes out to the front
  chamber to cool the LCD panel, and then goes
  through the fins of the opposite side, by the
  opposite conduit and finally goes out to the Rack
  locker via the outlet port.

6
3. THERMAL CONTROL CONCEPT AND THERMAL DESIGN
DESCRIPTION

• In ACOP, there are three main subsystems to
  consume power rate.
• Four hard disk drivers, installed in the upper
  chassis of ACOP, are used to record the data
  collected by AMS-02.
• One single board computer, three compact-PCI 6U
  PMC carrier boards, and one power distribution
  board consisted of the controlling module of
  ACOP, are arranged in the bottom of ACOP.
• One LCD monitor is fixed on the front panel of
  ACOP to show the required information.

7
3. THERMAL CONTROL CONCEPT AND THERMAL DESIGN
DESCRIPTION

• The power dissipation of parts on the boards is
  nearly conducted through the copper layers of
  power planes and of ground planes to the board
  edge via the spacer ,fixed to the chassis by a
  card-locker, to the chassis and spreads to the
  fins, and finally transfers to the cooling air.
• The commercial hard disk driver has a control
  board and a driver. Both of them will consume
  power. The board power dissipation also conduct
  to the edge of the HDD edge through the board.
  The driver uses spreader to conduct the heat to
  the HDD edge.

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4. THERMAL REQUIREMENTS

• According to the thermal management design of
  J-crate of AMS-02, the worst condition for the
  crate wall temperature can reach 50 ?. Under this
  condition, the thermal modelling results and the
  TVT measurements show that the part temperature
  is under the specification of the data sheet.
• Currently the electronics designers cannot
  provide the temperature requirements without
  further information of the board and of the
  parts. However, the crate wall temperature of
  AMS-02 can be the temporary temperature
  requirement for the chassis of ACOP.

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5. Boundary conditions

• The cooling air temperature supplied by the AAA
  will be in the range of 18.3 to 29.4?, cited in
  5.3.1.3.2 of reference 1.
• Here the cooling air temperature is assumed to be
  30 ? for a conserved calculation of the model.
• The back-plate, top-plate, two side-plate, and
  bottom-plate of ACOP are assumed to insult from
  the cabin air.
• The tip plate to enclose the fin channels is also
  considered to insult from the surrounding air.
• Only the front-plate, seeing the open space of
  the cabin, has a natural convection with the
  cabin by 0.965 W/m2 ? , referred to 5.3.1.1.3 of
  reference1.

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6. THERMAL LOADS

• Table 2 shows the power dissipation of boards
  and HDDs of ACOP.
• The total typical power dissipation of ACOP is
  estimated to be around 62.41W.
• One approach is that the power dissipation is
  allocated evenly and uniformly on the slots. The
  other is that 80 of the thermal load allocated
  on the cold fins and 20 on the hot fins.
• The power consumption of the LCD monitor is
  uniformly put on the surface of the square panel.
• The analyzed cases for different thermal load
  allocations and flow models are shown in Figures
  24.

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Figure 2 Thermal load for cases 1 and 2.
Figure 3 Thermal load for cases 3 and 4.
Figure 4 Thermal load for case 5
12
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13
7. MODEL DESCRIPTION AND THERMAL ANALYSIS

• I-DEASTMGESC code is applied to solve the
  computation task.
• The analyzed domain is meshed into around 224
  thousand elements by mapping method.
• For the solid and the fluid, 67,045 hexagonal
  elements and 157,671 trihedral elements are
  meshed respectively.
• Based on the electrical analogy, thermal model of
  the solid domain is established to construct a
  resistance-capacitance thermal network.
• A hybrid approach is developed in the code by
  utilizing the element based finite difference
  method to simulate conduction, and surface
  convection.
• The thermal code is coupled with the element
  based finite volume method flow solver, which
  models air flow, turbulence, fluid conduction,
  and advection.

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7. MODEL DESCRIPTION AND THERMAL ANALYSIS

• The Reynolds number of the fin channel flow is
  calculated to be around 142 to recommend a
  laminar flow model here.
• The turbulence model of the fixed turbulent
  viscosity model is adopted in the code to
  calculate the heat transfer coefficient of the
  ducts and the front panel to compare the
  calculated value of h via semi-empirical
  correlations.
• Where denotes the dynamic viscosity,
  denotes the density, Vm is a mean flow velocity
  scale, and Lt is a turbulent eddy length
  scale.

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7.MODEL DESCRIPTION AND THERMAL ANALYSIS

• Both the thermal and momentum wall functions
  utilized to calculate the heat transfer
  coefficient for the solid surface and the cooling
  air, described by B.A. Kader in 19812.
• The front plate is also treated as the aluminum
  alloy to conduct the power dissipation of the LCD
  monitor effectively.
• The thermal conductivity of aluminum alloy
  7075T-7351 is given by a constant value of 151
  W/m? , neglecting the insignificant variation
  with temperature in the domain.
• The thermal conductivity of air is calculated by
  the internally established data-base in ESC code.
  

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7. MODEL DESCRIPTION AND THERMAL ANALYSIS

• System pressure loss of ACOP is calculated via
  semi-empirical correlations for three flow rates
  of the cooling air with 12, 15, and 18cfm
  respectively.
• The inlet cooling air temperature is fixed to be
  30 ? with a conserved consideration.
• Inlet air pressure is fixed as 10.2psia. However,
  for a limited condition, the pressure 15.2psia is
  adopted to see the possible value of the system
  pressure loss.

17
8. Analysis Results

• The cooling air velocity field is shown in Figure
  5. The predicted maximum velocity is around
  1m/sec in the fin channel. At the outlet of the
  fin channels produces turbulent eddies due to an
  abrupt expansion.
• A low Reynolds number produces a laminar flow.

Figure 5 The predicted velocity field of the
cooling air
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8. Analysis Results

• The calculated heat transfer coefficient h is
  around 42.1 W/m2 ? at the fin channels via the
  laminar flow model with two meshed elements, as
  shown in Figure 6.
• According to the semi-empirical equation for the
  Nusselt number(Nu) of the fully developed flow in
  channels, the calculated heat transfer
  coefficient by hands is around 40. W/m2 ?with an
  aspect ratio of 24.

Figure 6 Heat transfer coefficient on the ACOP
chassis and fins.
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8. Analysis Results

• At the inlet of the cold fin channels, 35.7? ,
  and the outlet of the hot, 43? for case 1, as
  shown in Figure7.
• The maximum temperature at the central chassis,
  44.1 ?.
• The high k value of the chassis and fins leads to
  a significant reduction of the working
  temperature.

Figure 7 Predicted temperature of the ACOP
chassis and fins.

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8. Analysis Results

• Figure 8 shows the predicted temperature of the
  front panel.
• Power dissipation of LCD 6.3 W
• Heat transfer coefficient h 8 W/m2 ?
• Predicted maximum temperature41.4 ?

Figure 8 The predicted temperature profile of the
ACOP front plate.
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8. Analysis Results

• Figure 9 shows the predicted temperature of the
  cooling air.
• The predicted maximum temperature44 ?
• Figures 1013 show the predicted chassis and fin
  temperature for cases 13 and 5 respectively.

Figure 9 the predicted temperature profile of the
cooling air
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Fig. 11 Predicted temperature of the chassis and
fins for case 2
Fig. 10 Predicted temperature of the chassis and
fins for case 3
Fig. 12 Predicted temperature of the chassis and
fins for case 4
Fig. 13 Predicted temperature of the chassis and
fins for case 5
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Table 1. Geometry of the fin channels of ACOP and
the applied heat transfer coefficient h
Table 3. Boundary conditions of ACOP
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Table 4. Predicted maximum Temperature for the
analyzed cases
Table 5. Fin channel pressure loss of one side
with different flow rates and
pressures of cooling air via the semi-empirical
correlations
25
8. Analysis Results

• The laminar flow model under-estimates the
  pressure loss of the fin channels significantly.
• Without the pressure loss of the screens, the
  predicted value of the laminar flow model is
  around 3.7 Pa via the ESC code.
• System pressure loss 10.865/20.61Pa for the
  flow rate 12/18cfm and the inlet air pressure
  10.2/15.2psia respectively via semi-empirical
  correlations.

26
9. Conclusions

• The introduction of fin channels extruded out
  from ACOP chassis can provide two enhancing
  effects on the heat transfer rate from chassis to
  the cooling air.
• The apparently significant effect is due to a
  large increase of the area value for forced
  convection of the cooling air.
• The other enhancing effect of heat transfer
  results from a reduction of the channel gap,
  leading to an increase of the heat transfer
  coefficient.
• Both effects make the effective thermal
  resistance between the cooling air and ACOP be
  low enough, leading to a maximum increase
  temperature by around 15 ? at the chassis center
  for mounting the HDDs for cases 3 and 4.

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9. Conclusions

• Including the uncertainty due to the numerical
  convergence, to the allocations of the thermal
  load, and to the flow model for h value, the
  maximum temperature of ACOP is predicted around
  45?for the conserved condition of the cooling air
  flow rate 12cfm, pressure10.2psia and temperature
  30?.
• The predicted value of the maximum working
  temperature of ACOP chassis 45? is below the
  temporary requirement, the crate wall temperature
  of AMS-02 J-crate 50?.
• For the analysed cases, the maximum difference of
  the predicted temperature is around 1.7? among
  these five cases, which is much less than the
  increase of the working temperature by 15?.  

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9. Conclusions

• The currently thermal management design is
  appropriate for ACOP to dissipate the power
  consumption effectively without any installed
  fans and needs a maximum pressure loss around
  10.865/20.61 Pa for the flow rate 12/18cfm, and
  pressure 10.2/15.2psia respectively which are
  below the recommended value 0f 25 Pa.

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Reference

• 1. Expedite the Processing of Experiments to
  Space Station (EXPRESS) Rack Payloads Interface
  Definition Document , SSP 52000-IDD-ERP
• 2. B.A. Kader, Temperature and Concentration
  Profiles in Fully Turbulent Boundary Layers,
  Int. J. Heat Mass Transfer, V.24, No.9,
  PP.15411544,1981