Mini-design Project (Third year) Designed and fabricated cooling solution to dissipate 140 W of heat generated form the electrically heated block.

1. DESIGN REPORT CPU
COOLING SOLUTION
BY: ABHIMANYU SEHRAWAT ,VIRRUJAN SRIBASKARAN
PAUL HAMO AND CHUKWUBUIKEM OMEZIRI
MARCH 3, 2017
Team: Alpha (α)
1

2. Project Description
Advanced manufacturing technologies enable increased amount of transistors which
develops heat in CPU.
Provide a new cooling solution for CPU cooling to maintain the performance of
multiple built-in cores.
The current CPU design uses a cooling solution via conduction and convection. The
heated air is removed using an integral fan.
2

3. Main Design Considerations
The maximum allowed CPU block temperature is 70 degree C.
Design must dissipate 140 W from a 4cm by 4 cm heated copper
block
The ambient air temperature is 21 degree C
The mounting holes for the heat sinks limited to a total of 4 holes .
This limitation necessitate the sub-frame implementation to allow
for proper heatsink retention and heatsink-to cpu pressure.
3

4. Main design considerations contd.
Secondary objectives:
Maximize performance
 Must be able to handle a CPU emitting 180 W of Heat
Minimize sound
Under 40 dBA
4

5. Cooling Strategy
Heat Absorption Strategy
Water block will absorb the heat from the copper
Heat Removal Strategy
Pumped water will cool the block by dissipating the heat through radiator
Overall, the mechanism is based on liquid cooling and additional heat is removed via
forced convection.
The fans and radiator are coupled together and mounted on board for proper retention
5

6. Initial prototype CAD Model
Heat sink 1
(water block)
Heat sink 2
(radiator)
Fan (forced convection)
6

7. Initial Prototype
7
Iteration 3Iteration 2

8. Physical Model
The solution consists of two heat-sinks, a heat sink mounting frame and two fans to remove the
heated air from the water passing through the radiator.
 A pump regulates the water between the reservoir and the rest.
A relief valve provides safety feature and controls the flow coming out of the water block .
Oriented in such a manner that air flow from one side of the fan is ejected out from the other side.
Fabrication: Water block is fabricated using CNC in two separate parts and fastened together
using screws.
Radiator was bought.
8

9. Other components:
The heatsink fans are 12 cm x 2.5 cm x 12 cm thick,
rated @ 2000 rpm, 0.35 A, 4.2 W) fans capable of 90
cfm .
However, these are 12 VDC fans. This allows us to
control the voltage and make them run slowly. The
air flow rates may be reduced to lower fan capacity.
System becomes quieter as well.
The fiber-glass pump rated at 13.2 W, 12VDC, 1.1A
having max. flow-rate: 8.3LPM
Dimensions: 80 mm x 64.4mm x 48 mm.
9

10. Mechanical
Components
10

11. Water Block Mounting Block and Gasket
Clamping mechanism: Gasket:
11

12. Thermal Solution Final Assembly: Video
12

13. Thermal simulation: Copper base
The thermal model will closely follow the mechanical model.
The copper channel of the water block is meshed using coarse fineness.
Thermal entrance length = 150 mm
Boundary conditions applied:
a. Convection heat transfer co-efficient ℎ 𝑤𝑎𝑡𝑒𝑟 = 2938
𝑊
𝑚2.𝑘
b. Inlet reference temperature = 303 K
c. Base was supplied with heat flux of 24.11 KW/m2
13

14. Temperature results
Heat-sink (water block maximum case
temperature): 50.5 𝑜 𝐶
This also complies with base temperature from
initial calculation i.e. 49.5 𝑜
𝐶
Real-case measurement : 55 𝑜 𝐶
Maximum allowable temperature: 70 𝑜
𝐶
14

15. Final Design
FanReservoir
Pressure valve
Radiator
Clamping
mechanism
Water block
Pump
15

16. Final results
Steady-state temperatures:
o(Q= 140W): 𝑇𝑎𝑐𝑡𝑢𝑎𝑙 = 48.1 𝑜
𝐶, 𝑇𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 = 49.62 𝑜
𝐶
o(Q= 180W): 𝑇𝑎𝑐𝑡𝑢𝑎𝑙 = 55 𝑜
𝐶, 𝑇𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 = 49.5 𝑜
𝐶
oThe agreement in both the cases is similar due to lower thermal resistance of copper.
Maximum overall system resistance:
𝑅𝑡𝑜𝑡𝑎𝑙 = ∆
𝑇
𝑄
= 𝑇𝑠𝑢𝑟𝑓 − 𝑇𝑎𝑚𝑏.÷ 𝑄 = 55 𝑜 𝐶 − 24 𝑜 𝐶 ÷ 180 = 0.172 𝐾/𝑊 <<0.32 K/W
16

17. Final temperatures
17

18. Conclusions and lessons learned
1. Do not attempt to fabricate components when it is already available in the
market.
2. Buy better sealing material. Plumbers putty not adequate for high flow.
3. CAD design does not guarantee a functioning final design.
4. Contact resistance plays a crucial role for heat transfer.
5. Team work and communication is necessary for success of the design.
18