1. MEMS 1043 SeniorDesignProject, Spring 2012
Final Report
1
Mechanism Enabling Retrofit for Cooling of Data Center Components
Matthew Kaminski, Naji Alibeji, Gregory Meyer, Chenell York
Department of Mechanical Engineering and Materials Science
University of Pittsburgh, Pittsburgh, PA 15261, USA
1. ABSTRACT
A data center is a facility used to house computer
system server boards and supporting infrastructure.
Increasing computing capabilities and demand are
resulting in greater room power densities and increases
in the need for cooling of the electronic components
within the server boards. Current cooling techniques
which use forced air convection with the aid of fans are
loud, inefficient, and expensive. This design focuses
on a mechanism that enables a retrofit for cooling of
data center components. The main features of this
design are cooling blocks, which consists of a
microchannel heat sinks and supporting housing. The
microchannels consist of an arrangement of channels
and fins whose purpose is to increase the area available
for heat transfer from the component to the water. A
separate cooling block is placed on each heat
generating component within the server board. As
water is pumped through the cooling blocks, it flows
through the microchannels where it removes the heat
generated from the component. The water travels
through a series of tubes where it enters each
successive cooling block. Ultimately, the water flows
through a radiator where the water is cooled and sent
back to the pump. Thermocouples were used during
testing of the design to obtain temperature readings of
the water and the heat generating components. These
measurements were used to compare the actual thermal
resistance of each cooling block to the calculated
theoretical values. The optimal design will yield the
minimum thermal resistance for each heat sink. This
design demonstrates the feasibility of retrofitting a data
center with a liquid-cooled thermal management
solution. Additional tests are needed to better quantify
the design’s effectiveness in removing the required
amount of heat from the heat generating components.
NOMENCLATURE
Ac = microchannel wetted area
Acx = microchannel cross-sectional area
As = base area of heat sink
Cp = specific heat
Dh = hydraulic diameter
f = Darcy friction factor constant
h = convection heat transfer coefficient
Hch = microchannel depth
k = thermal conductivity
L = length of heat sink
𝑚̇ = mass flow rate
N = number of microchannels
Nu = Nusselt number
P = pressure
Pm = microchannel perimeter
P0 = pump curve y-intercept
Q = thermal design power
Q0 = pump curve x-intercept
R = total thermal resistance
Re = Reynolds number
t = substrate thickness
Tch = temperature at base of channel
Tfl_avg = average fluid temperature
Tfl_in = fluid temperature at inlet of channel
Tfl_out = fluid temperature at outlet of channel
Tj = junction temperature
u = mean flow velocity
𝑉̇ = volumetric flow rate
W = width of heat sink
wch = microchannel width
wf = fin thickness
Greek symbols
μ = dynamic viscosity
ρ = density of fluid
ΔP = pressure drop
ΔT = temperature difference

2. 2
.
2. INTRODUCTION
DATA CENTER BACKGROUND
Data centers allow the storage of large amounts of
equipment connected to communication systems,
computers and electronics [1]. They house the highly
specialized equipment responsible for the support of
the computers, networks, data storage and security of a
company’s business intelligence and business process
[2]. The basic layout of a data center is shown in
Figure 1.
Figure 1: Typical layout of a data center
The most fundamental data center has a computer
network, contains backup power supplies, air
conditioning, and security procedures [1]. Data centers
are absolutely critical for companies as they act as the
brain for most companies.
Data centers consume a tremendous amount of energy.
According to a 2007 Scientific American Report, the
overall total energy usage of data centers was 61
billion kilowatt-hours [3]. This corresponds to roughly
1.5% of the country’s entire electricity consumption
[3]. Of the 61 billion kilowatt-hours consumed, as
much as 40% of a data center’s energy bill comes from
cooling equipment [4]. A breakdown of the power
distribution for data centers can be seen in Figure 2.
Figure 2: Data center power distribution
As shown in Figure 2, data center cooling is a
significant part of a data center’s total energy
consumption. Failure to adequately cool data center
components could result in irreversible damage to the
components.
This design focused on cooling three components of
the Foxconn G41MXE motherboard shown in Figure
3.
Figure 3: Foxconn G41MXE SeriesMotherboard with
Core 2 Duo Processor (1), North Bridge Chipset (2),
and South Bridge Chipset (3).
MOTIVATION FOR CURRENT WORK
The two main methods for cooling data center
equipment are air cooling and liquid cooling. As seen
in Figure 4, air cooling generally involves mounting a
heat sink and a fan to each heat generating component
of a server board [5]. Heat generated from the
component is transferred to a heat sink by conduction.
The fan blows air through the heat sink and removes
the heat through convection [6].

3. 3
Figure 4: Heat source/heat sink relationship for air
cooling of a CPU [5]
Liquid cooling may be more efficient at removing the
heat generated from server board components than air
due to its higher thermal conductivity and specific heat
capacity. When compared to traditional air-cooled
methods, liquid cooling devices have the capability of
reducing the power consumption of in-room cooling
devices by as much as 90% [6]. For a liquid cooled
system, liquid is pumped through a heat sink where it
absorbs the heat from the component. The liquid exits
the heat sink where it is then cooled by means of a
radiator [5]. An image of liquid cooled computer
component is shown in Figure 5.
Figure 5: Liquid cooled component
Air-cooled methods can create a very costly, complex,
and inefficient infrastructure [6]. On the contrary, by
allowing data centers to operate with higher-density
racks, rack-level liquid cooling can reduce the data
center IT footprint by as much as 80% [6].
Another advantage of liquid cooling is that it is much
quieter than air cooling. As computer systems are
constantly upgraded, this creates the need for
additional fans throughout the data center facility,
eliminating the need for high speed fans throughout a
data center. This design focuses on retrofitting data
center server trays with a liquid cooled system rather
than completely rebuilding the server trays.
Retrofitting a cooling device is a much cheaper
alternative than completely replacing data center server
trays.
MICROCHANNELS
A microchannel heat sink functions in the same
manner as conventional centimeter scale channel
designs with the exception that microchannels are on
the scale of hundreds of micrometers. Microchannel
heat sinks consist of an array of channels and fins
which are used to increase the area available for heat
transfer from the component to the fluid. Figure 6
depicts the layout of a microchannel heat sink.
FIGURE 6: Microchannel heat sink layout
The junction temperature is the temperature at the
interface between the base of the heat sink and the top
of the heat generating component. It is desired to keep
this junction temperature as low as possible in order
to ensure that the component remains below its
maximum operating temperature. The microchannel
heat sink is attached to the component of the server
tray via a thermal paste. Heat is first transferred by
𝐻
𝑊𝑐ℎ
𝐻𝑐ℎ
𝑊𝑓 𝑇𝑐ℎ
𝑇𝑗
L
W
t

4. 4
conduction up from the component through the base
of the heat sink and up through the fins. The fluid that
flows through the microchannels picks up this heat
and convects the heat away from the component.
Microchannels exhibit dramatically better heat
transfer performance than centimeter scale designs
due to a large increase in the convection heat transfer
coefficient. However, the better heat transfer
performance must be balanced with the fact that
microchannels also increase the pressure drop
experienced by the fluid as it travels through the
channels. Competition between these two parameters
will yield optimal channel dimensions. This is
explained in more detail in the thermal analysis
section.
3. DESIGN
THERMAL ANALYSIS
The goal of the thermal analysis was to determine the
number of channels, dimensions of the channels, and
the required flow rate through the channels that would
yield the lowest total thermal resistance for each heat
sink. The total thermal resistance is comprised of
caloric resistance, convective resistance, and
conduction resistance [7]. By minimizing the thermal
resistance, the maximum amount of heat will be
transferred from the component to the fluid. The
analysis was performed in a MATLAB file in order to
perform the iterative calculations. The final product of
the analysis was a graphical user interface (GUI) which
allows the user selects how many components need to
be cooled, the dimensions of the components, and the
maximum operating temperature and thermal design
power (TDP) of the component. The MATLAB GUI is
shown in Figure 7. Refer to Appendix B for the
MATLAB code used to generate the GUI.
Figure 7: GUI used to determine optimal number of
channels, dimensions of the channels, and the required
flow rate through the channels for each heat sink
The maximum operating temperature and TDP can be
gathered for each component from the manufacturer’s
data sheets. The main requirement in the thermal
analysis was to ensure that the junction temperature for
each component remained below its maximum
temperature while operating at TDP.
As discussed earlier, it was determined that the most
cost effective way to cool each component would be to
run the tubing in series from one component to the
next. Therefore, the fluid that exits the first
microchannel heat sink would be the same fluid that
enters the second microchannel heat sink. This reduces
the fluid’s ability to convect heat away since the fluid’s
temperature will increase each time it flows through a
heat sink. In addition, the pressure drops will
accumulate each time the fluid passes through each
additional heat sink.
In order to simplify the analysis and to ensure the
microchannels could be machined, certain dimensions
were fixed throughout the analysis. The dimensions of
the base of each heat sink were the same dimensions
used for the base of the heat generating component.
Thus, the user will specify these values. After
consulting the machine shop at the Swanson School of
Engineering, it was determined that a fin aspect ratio of
four would be the maximum value that would permit
machining of the microchannels. In addition, there
were also constraints on the minimum width of the
channels since there are only certain mill bit sizes
available in the machine shop. As discussed earlier,
water is superior to air for this particular heat removal
application. The higher density and specific heat of
water allow for more effective heat removal than air;
therefore, room temperature water was chosen as the
working fluid for this design. Another property
specified prior to beginning the analysis was the heat
sink material. It was concluded that copper would yield
the most desirable properties due to its high thermal
conductivity and ease of machinability. Table 1
summarizes the dimensions that were fixed at the
beginning of the analysis. Table 2 lists material
properties of water and copper.
Table 1: Summary of dimensions that were fixed prior
to beginning thermal analysis

5. 5
Base
thickness of
heat sink
Channel
depth
Fin width
Minimum
Channel
width
1 mm 0.8 mm 0.2 mm 0.5 mm
Table 2: Summary of the properties of the fluid and
material used for the heat sinks [7]
Specific
Heat
Density
Dynamic
viscosity
Thermal
conductivity
Water
4183
𝐽
𝑘𝑔𝐾
998.3
𝑘𝑔
𝑚3
1.002*
10−3 𝑘𝑔
𝑚∗𝑠
0.6
𝑊
𝑚∗𝐾
Copper N/A N/A N/A 400
𝑊
𝑚∗𝐾
For the purposes of this design, a Foxconn G41MXE
series motherboard was used as the basis for the design
of the three heat sinks. Table 3 lists the components in
the motherboard that require cooling. The PMP-300
Compact Pump from Koolance was chosen as the
pump for this system because it provides an adequate
head with low power consumption.
Table 3: Motherboard chip specifications [8, 9, 10]
Pentium
Core 2
Duo CPU
North
Bridge
Chipset:
Intel G41
South
Bridge
Chipset:
Intel ICH7
Length 30 mm 11.5 mm 25.5 mm
Width 30 mm 10 mm 25.5 mm
Thermal
Design Power
65 W 25 W 3.3 W
Maximum
Operating
Temperature
72 °C 102 °C 99 °C
The goal of this design is to achieve the lowest total
thermal resistance for each heat sink while also
minimizing the pressure drop through the heat sinks.
The optimal design of each heat sink would ensure that
the junction temperature of each component is
minimized. By varying the number of channels used in
each heat sink, a minimum junction temperature for
each component can be found. However, there is
competition between achieving the minimum junction
temperature and achieving a minimum pressure drop
through the channels. Equation 1 is used to calculate
the junction temperature of a component.
𝑇𝑗 =
𝑄
𝑁ℎ𝐴 𝑐
+
𝑄𝑡
𝑘𝐴 𝑠
+
𝑄
𝑚̇ 𝐶 𝑝
+ 𝑇𝑓𝑙_𝑖𝑛
In order to optimize heat transfer from the component
to the fluid, and thus minimize the junction
temperature, several factors were considered. A tall,
thin fin increases the number of channels and fins that
comprise the heat sink, and thus there is more area
available for heat transfer. As the number of channels
increases,the junction temperature decreases as seen in
Equation 1. This, however, must be balanced with the
fact that a taller fin increases the hydraulic diameter of
the channel which ultimately decreases the convection
heat transfer coefficient. A decrease in the convection
heat transfer coefficient will increase the junction
temperature as seen in Equation 1. Therefore, it was
desired for each channel to have the smallest hydraulic
diameter possible because this would increase the
convection heat transfer coefficient and lower the
junction temperature. As discussed earlier, the ratio of
the channel height to channel thickness must be below
four due to machinability constraints. The challenge
presented with using microchannel heat sinks is the
large pressure drop that accumulates as the fluid flows
through the channels. The pressure drop increases
dramatically as the hydraulic diameter of the channel
decreases. In addition, increasing the mass flow rate
through the channels to achieve a lower junction
temperature also increases the pressure drop.
Therefore, the increase in heat transfer performance
must be balanced with the increase in pressure drop. A
larger pressure drop requires a larger pump which is
not desired due to an increase in the cost of a pump and
electricity usage.
Equation 2 below is the system curve for the pressure
drop experienced by the water as it flows through three
heat sinks. Varying the number of channels in each
heat sink will yield a number of different system
curves.
𝛥𝑃 =
32𝑉̇ 𝜇
𝐻𝑐ℎ
(
𝐿1
𝑊 𝑐ℎ1 𝐷ℎ1
2 +
𝐿2
𝑊𝑐ℎ2 𝐷ℎ2
2 +
𝐿3
𝑊𝑐ℎ3 𝐷ℎ3
2 )
The equation that describes the PMP-300 pump curve
[11] is given below as Equation 3.
𝛥𝑃 = 𝑃0 −
𝑃0 𝑉̇
𝑄0
The intersections of the system curves and the pump
curve yield a range volumetric flow rates that will
ensure that the water from the pump can overcome the
pressure losses as it travels through the heat sinks.
These volumetric flow rates are easily converted into
(1)
(2)
(3)

6. 6
mass flow rates, 𝑚̇ , which can then be substituted into
Equation 1 to yield a range of values for 𝑇𝑗 . The
optimal number of channels, channel dimensions, and
flow rate are determined at the point where the junction
temperature is minimized for each heat sink. Equation
4 was used to calculate the total thermal resistance for
each heat sink.
𝑅 =
𝑇𝑗−𝑇 𝑓𝑙_𝑎𝑣𝑔
𝑇𝐷𝑃
Table 4 lists the calculated total thermal resistance for
each heat sink.
Table 4: Total thermal resistance for heat sinks
Heat Sink 1 Heat Sink 3 Heat Sink 3
Total
Thermal
Resistance
0.1905
℃
𝑊
0.8974
℃
𝑊
1.5603
℃
𝑊
Please refer to Appendix A for a complete derivation
of the above equations and for a more detailed
analysis.
DESIGN REQUIREMENTS
The main objective of this project was to design a
liquid cooled heat sink that can be used to retrofit
outdated data center air cooled systems. Since this
product is intended to be a retrofit, it must be capable
of being installed in any server board configuration.
Server trays come in many different variations, each
with their own internal dimensions, server board
layouts, and electrical components that require cooling.
In order to effectively cool the electrical components,
heats sinks apply a static load on the components with
a specific amount of pressure in order to ensure
effective thermal surface contact. This is typically done
by directly mounting the heat sinks to the server board
using bolts and standoffs. Other methods include
retention springs that also use fixtures that bolt onto the
server board to add support. The server boards have
holes in the electrical board to accommodate for these
options, but the bolt holes patterns and locations vary
with different server trays models.
Current liquid cooled retrofit heat sink options, such as
the products offered by Koolance, use adjustable
brackets and springs to mount the heat sinks to the
server tray board as seen in Figure 8 [12]. However,
these options are only compatible with a select few
server board trays. One of the main concentrations of
this project was to design a mounting mechanism that
is capable of accommodating any server board tray.
Therefore, the mounting mechanism must not depend
on the bolt hole patterns in the server boards. Thus it
was decided that using the weight of the server tray lid
would be the best option to hold the cooling block into
place.
Figure 8: Mounting cooling block fromKoolance with
either adapter bracket or retention springs [12]
Upon choosing the final design for the mounting
mechanism, many designs were considered. Design
one consisted of installing a network of tracks under
the lid. These tracks would allow the mounting of the
cooling block in any location in the server board.
However, this design was eliminated because of the
limited space inside of the board and the numerous
obstacles that would restrict the path of the tracks. The
second design involved drilling a grid of holes into the
lid and directly mounting the cooling block to the lid.
This design was also dismissed because it is preferred
to not have to modify the existing lids. The
consideration of using magnets to hold the cooling
blocks in place was also eliminated because it is
advised to not have magnets around the electrical
components.
Every time a data center is retrofitted with this product,
the design of the cooling block will need to adjust
depending on the size and specifications of the
electrical components requiring cooling. If a standard
solid model is used, the parts will have to be
redesigned for every electrical component. To avoid
this constant need for manually reconfiguring the parts,
iParts and iAssemblies were used. iParts and
iAssemblies use parametric tables which depend on
key variables or dimensions to easily reconfigure the
parts. Using iParts and iAssemblies make the inner
(4)

7. 7
workings of the models more complicated but in return
they eliminate the need for manually reconfiguring the
model. For further information about iParts and
iAssemblies refer to Appendix C.
The final design consisted of a cooling block, spring,
locator bracket, and adhesive. The cooling block sits
directly onto the electrical component and is comprised
of a microchannel base, headers, and a lid. Its purpose
is to dissipate the heat from the heat generating
component and keep the water contained within.
Figure 9 shows a solid model of the final design.
Please refer to Appendix E for the technical drawings
of each part.
Figure 9: Solid model of final design
The copper microchannel base will contain the
required number of channels indicated by the GUI. In
addition, the microchannel base will also have eight 2-
56 UNF threaded holes for the lid and headers to bolt
to.
The lid sits directly onto the sides of the microchannel
base and is bolted down. A recessed hole is located on
top of the lid to help hold the spring in place. On the
sides of the lid, tabs protrude out directly with a hole in
the center of them. These tabs/holes are used to mate
with the locator bracket and prevent the cooling block
from shifting side to side. The locator bracket is
attached to the lid using adhesive, and the pins mate
with the cooling block and hold it in place as
mentioned before. At first we planned to have a
mechanism snap into place with the lid to hold it in
place. After consideration we decided that a simple pin
would suffice. An added benefit of using a simple pin
is that the lid can be removed along with the locator
bracket without having to undo the cooling block
configuration.
The headers are designed to bolt onto both sides of the
microchannel base. Each header has a 10-28 UNF
threaded hole for the fittings on the top face of the
header. This hole intersects with a channel on the side.
This channel is just big enough to expose the
microchannels to the water flow. Through holes on the
header allow the header to be bolted to the
microchannel base.
The spring sits in the recessed hole of the lid and
expands past the locator bracket. When the lid is
closed, the spring will be forced to compress and apply
pressure to the cooling block. The stiffness of the
spring was chosen based on the static load required by
electrical component and the amount of compression
the spring will experience.
The fitting chosen to connect the tubes to the header is
an elbow to barb fitting. It was initially planned to use
luer fittings which are typically used in medical
applications. Figure 10 shows an assortment of
different luer fittings available. They are small,
reliable, and provide an easy quick release connection
feature. However, with the limited amount of space in
the server tray, it was difficult to find a combination of
luer fittings that would effectively distribute the flow
and provide the quick release connection. Therefore, it
was decided to use a single elbow thread to barb
fitting.
Figure 10: Luer fittings assortment
Spring
Headers
Microchannel
Base
Locator
Bracket
Elbow
Fitting
Lid
Dowel Pin

8. 8
To assemble the cooling block, 2-56 UNC bolts were
used to hold the microchannel base, headers, and lid
together. The dowel pins were press fitted into the
locator bracket. The cooling block was sealed using
silicon, and Teflon tape was used to maintain a seal
around the elbow fittings.
CONSTRUCTION
The materials used to construct the parts were
purchased from McMaster-Carr. The microchannel
base was made from a 6”x 6” slab of high ultra-
conductive copper. The material chosen to make the
headers, lids, and locator brackets was acrylic. Acrylic
is cheap, easy to machine, and serves as a good thermal
insulator. After some design reviews and iterations to
the design, the drawings were finalized. A CNC
machine was selected as the best method of machining
the parts. After converting the 15 parts into a format
compatible with the CNC machine, the code used to
machine the parts was written by the machinist.
The first step was to cut the copper and acrylic stock
into smaller work pieces and square them off. The
parts where then machined using the CNC machine
and the generated code. The microchannels in the base
were cut using a special ordered 0.026” mill bit. After
completing the parts, they were cleaned and the
threaded holes were tapped. Figures 11, 12, and 13
shows the three completed microchannels, headers,and
lids respectively.
Figure 11: Complete microchannel base
Figure 12: Completed headers
Figure 13: Completed lids
The dowel pins were purchased from McMaster-Carr
and grinded down to the correct length using a belt
sander. The dowel pins for the locator bracket were
press fitted using a precision vice. Each cooling block
assembly included a microchannel base, lid, two
headers, elbow fittings, locator bracket plate, two
dowel pins, adhesive, silicon, four 2-56 UNC x 0.125”
bolts, and four 2-56 UNC x 0.5” bolts. Figure 14 shows
the assortment of parts for each cooling block
assembly. For the smaller cooling blocks, the bolts
from the lid and header intersected at some points, so
the bolts from the header were shortened using a belt
sander to an appropriate length.

9. 9
Figure 14: Components included in one assembly
An important feature of the cooling block is that it
must be completely sealed to eliminate any leaks. This
was challenging to achieve since there were many
mating faces and small critical openings that had to be
unobstructed. The first attempt included using scotch
tape; the tape was layered onto the mating faces. The
adhesive helped keep the tape in place while the
openings for the channels and holes were cut using a
surgical scalpel.
To ensure the integrity of the seal, water was pumped
through the assembled cooling block for a few minutes.
The scotch tape gasket was unsuccessful. The next
attempt included a 1 mm gasket film from McMaster-
Carr. However, it proved difficult to cut the rubbery
gasket into a usable shape. The final attempt included
the use of silicon. This was the last option considered
because it was feared that the silicon would ooze into
the header channel when compressed. This would have
obstructed the flow and hindered the performance of
the cooling block. To prevent the silicon from oozing,
the mating faces were only wetted with the silicon
leaving no excess to ooze into the channels. To further
strengthen the seal, silicon was smeared on each seam.
After testing this option, the seal proved to be reliable.
4. EXPERIMENT AND TESTING
As previously mentioned, the optimal design of each
cooling block will minimize the thermal resistance
between the heat generating component and the
environment. Achieving this minimum thermal
resistance will optimize the heat transfer performance
of each cooling block. Due to excessive leakage in the
North Bridge cooling block design, this cooling block
was not tested. A bill of materials is shown below in
Table 5.
Table 5: Bill of Materials
Part Description Vendor
Unit
Price
($)
QTY
Copper Slat McMaster 62.94 1
Acrylic Slat McMaster 7.04 1
.026" End Mill McMaster 23.61 3
Compression Spring McMaster 7.36
1 pack
(5)
Elbow Fitting
Value
Plastics
Sample
2 packs
(5)
Dowel Pin McMaster 4.77
2 packs
(5)
Flexible PVC Tubing McMaster 0.25 1ft
Double-Sided Tape McMaster 15.44 1
Adapterfitting,Tube
to male threaded
pipe
McMaster 5.26
1 pack
(10)
Threading Adapter,
NPT
1"
8
M to G
1"
4
F
Koolance 2.17 5
TOTAL: $195.51
EXPERIMENTAL SET-UP
Figure 15 is a schematic of the experimental setup used
to test the CPU cooling block and the South Bridge
cooling block.
Figure 15: Schematic of testing set-up
A thermofoil heater was used in conjunction with a
power supply to simulate the heat generated from the

10. 10
data center components. Wires were soldered to the
leads in the thermofoil heater, shown in Figure 16.
Figure 16: Thermofoil heaterwith connected wires
Banana clips were used to connect these wires to the
power source. In order to ensure the heat was evenly
dissipated, a copper spreader was machined and then
placed on top of the thermofoil heater. Prior to
mounting the cooling block to the spreader, a groove
was milled into the center of the spreader to allow a
thermocouple to be placed at the junction of the
spreader and the cooling block. This thermocouple was
used to measure the junction temperature. A complete
setup of the cooling block assembly and heating
element is shown in Figure 17. Refer to Appendix D
for complete cooling block assembly instructions.
Figure 17: Complete set-up of cooling block and
heating component
TESTING
Experimental testing began by applying a known
power input to each cooling block. This power input
was used to simulate the heat that would be generated
from a server board component. The power input to
each cooling block was increased in increments of two
watts, ranging from three to fifteen watts. The pump
was then turned on and water from the reservoir tank
was pumped through the system. The pump supplied
the water with the necessary head to overcome the
pressure losses experienced in the system. The flow
from the pump was measured by the volumetric flow
sensor as seen below in Figure 18.
Figure 18: Pump (left) with flow sensor (center) and
reservoir tank (right)
The system was allowed to reach steady state before
any true measurements were taken. Steady state was
defined as the point of operation where every
temperature in the system remained at a constant value.
Once the system was operating at steady state, the true
temperature measurements were recorded.
Thermocouples were used at different points along
system to gather temperature readings. The first
thermocouple was placed after the flow sensor to
record the temperature of the water before it entered
the cooling block. Figure 19 shows the thermocouple
used to measure the inlet temperature of the water.

11. 11
Figure 19: Thermcouple used to measure inlet water
temperature
After the inlet temperature of the fluid was measured,
the fluid traveled into the cooling block, where a
second thermocouple was used to measure the junction
temperature. The thermocouple used to measure the
junction temperature is located between the two wires
in Figure 17. A third thermocouple, Figure 20, was
used to collect temperature data at the outlet of the
cooling block.
Figure 20: Thermcouple used to measure outlet water
temperature
After the water exits the cooling block, it travels into a
radiator which then cools the water and recycles it to
the reservoir tank where it can be used again to
continue the process. The reservoir tank and radiator
are shown in Figure 21.
Figure 21: Reservoir (front) and radiator (back)
Temperature and flow measurements were collected
for the CPU and South Bridge cooling block using a
data acquisition unit and MATLAB code. However, as
previously mentioned, data was not collected for the
North Bridge cooling block due to excessive leakage.
The goal was to determine the junction temperature as
well as the inlet and outlet water temperatures for each
cooling block at each power level. These values were
used to calculate the convection heat transfer
coefficient and the total thermal resistance of each
cooling block.
5. RESULTS AND DISCUSSION
Based on the channel dimensions, material properties,
and temperature measurements for each cooling block,
the convection heat transfer coefficient was calculated
for each cooling block. Figure 22 is a plot of the
convection heat transfer coefficient at each power level
for the CPU cooling block and South Bridge cooling
block.

12. 12
Figure 22: Convection Coefficient vs.Power
Theoretically, the convection heat transfer coefficient
should have remained constant at each power level
since it is only a function of the channel dimensions. It
was anticipated that the convection heat transfer
coefficient would be around 2917
𝑊
𝑚2
and 1455
𝑊
𝑚2
for
CPU cooling block and South Bridge cooling block
respectively. As seen in Figure 22, not only was the
convection heat transfer coefficient an order of
magnitude less than the predicted value for each
cooling block, but the convection heat transfer
coefficient is larger for the South Bridge cooling block
than the CPU cooling block. It is possible that the flow
in the either cooling block may not have been fully
hydrodynamically or thermally developed. If this were
the case, then not all of the channels in the CPU
cooling block may have had water running through
them. This would result in a much lower convection
heat transfer coefficient than expected.
The convection resistance accounts for nearly 90% of
the overall thermal resistance. A plot of the total
thermal resistance versus heat input was created for the
CPU cooling block and the South Bridge cooling block
as seen in Figures 23 and 24.
Figure 23: Thermal Resistance vs. Power for CPU
Cooling Block
Figure 24: Thermal Resistance vs. Power forSouth
Bridge Cooling Block
As a result of the low convection heat transfer
coefficients, the thermal resistance values obtained for
both cooling blocks were much higher than the
calculated values in Table 4. Theoretically, the total
thermal resistance should be independent of the heat
input. However, since the convection heat transfer
coefficient varied for each cooling block, this resulted
in a fluctuating total thermal resistance.
Uncertainty bars are represented by vertical bars on
each plot. The flow rate was assumed to be constant in
the GUI program; however, during the testing, it was
found that the flow rate was steadily rising with the
power input, which caused some discrepancies in the
reported results.
-50
0
50
100
150
200
250
300
350
0 5 10 15 20
ConvectionCoefficient(W/m2)
Heater Power Input(W)
Convection Coefficient vs Power Input
CPU Cooling
Block
South
Bridge
Cooling
Block
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20
ThermalResistance(°C/W)
Heater Power Input(W)
CPU Cooling Block
Conduction
Convection
Caloric
Total
0
2
4
6
8
10
12
14
16
18
20
0 5 10 15 20
ThermalResistance(°C/W)
Heater Power Input(W)
South Bridge Cooling Block
Conduction
Convection
Caloric
Total

13. 13
As seen in Figures 22, 23, and 24, there exists an
inverse relationship between the power input and the
uncertainty. As the power into each cooling block was
increased, the error was decreased. This can be
accounted for by the relationship between the
temperature difference and the uncertainty. As the
value for ΔT grew, the uncertainty for the
thermocouples lessened.
Due to the inability to seal the North Bridge cooling
block, no testing was done and therefore no data was
collected.
6. CONCLUSIONS
The current method of air cooling data center server
tray components is noisy and inefficient. The goal of
this project was to design a mechanism that enables a
retrofit for cooling of data center components. The
design was successful in that it provided a solution for
retrofitting current air cooled server boards with a
universal water cooled mechanism. However,
preliminary testing of the CPU cooling block and
South Bridge cooling block yielded insufficient
results. Although two of the three cooling blocks
proved to be functional with water as the working
fluid, the total thermal resistance for each cooling
block was much higher than expected.
7. RECOMMENDATIONS FOR FUTURE WORK
Recommendations for future work include redesigning
the cooling block to limit the amount of mating faces
in the assembly. This can be accomplished by
machining the headers and the microchannels as one
part with a lid designed to fit snugly against the
microchannel base. Less hardware would result in less
machining time, and the lower amount of mating faces
in the assembly will reduce the risk of leakage.
A second recommendation would be to improve the
mounting mechanism to something more stable and
consistent. The current mounting mechanism of
double-sided tape could be improved by using
something more stable and more user-friendly for the
installer.
The GUI could also be improved to accommodate for
more than three cooling components. A link could also
be made between the GUI results and the solid model.
Therefore, the GUI would not only calculate the
necessary heat sink dimensions, but it would also
transfer those dimensions into iParts and iAssemblies
to create an accurate solid model.
Finally, additional testing of the three cooling blocks is
needed to better quantify their effectiveness in
removing the required amount of heat.
8. GLOBAL IMPACT OF THE WORK
The heat generated from data centers is a critical
concern both economically and environmentally. If
components within a data center overheat, this can
create an expensive problem as many of these
components are no longer usable. As a result, cooling
is a very important and necessary feature of data
centers. Data center electricity consumption will
continue to grow with the increasing demand for
computing power. To put things into perspective, in
2003 there were 5.6 million servers used in US data
centers, and in 2007 there were 11.8 million [13]. A
graphical representation of how power and cooling
costs are increasing as the volume of business data
continues to increase is shown in Figure 25 [14].
Figure 25: Trend in various costs involved in data
centers with time
Servers and their accompanying cooling components
now consume more power than all of the televisions in
the US [13]. One large 50,000 square foot data center
consumes around 5 MW of power which is equivalent
to the power it would take to power 5,000 homes [13].

14. 14
Currently, data centers servers use the equivalent of
one full year’s output from five 1,000 MW power
plants [13]. This is equivalent to powering five million
houses [13]. If energy efficiency could improve just 20
percent, that would be a power saving equivalent to the
output from an entire 1,000 megawatt power plant,
which would be enough to power one million homes
[13]. With the growing demand for computing power,
these numbers will most definitely grow.
Water cooling is environmentally friendly because the
water is recycled after each pass through the system.
This would have environmental benefits in decreasing
pollution and decreasing the diversion of water from
sensitive ecosystems [14]. All in all, using water as a
coolant in data centers can provide numerous
environmental and economic benefits to society. With
the growing need for computing power in the future,
the need for more energy efficient designs and cooling
mechanisms for data centers has never been greater.
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[11] "Pump, PMP-300 [no Nozzles] - Water Cooling
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[12]Cooling Block, CHC-120-VO6. Koolance.com.
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[13] PingdomBlog. Pingdom AB, 25 July 2008. Web.
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[14] NEC: Powered by Innovation. N.p.,1994-2012.
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ACKNOWLEDGEMENTS
Dr. Mark Kimber, Ph.D.,Department of Mechanical
Engineering

15. 15
Dr. Anne Robertson, Ph.D.,Department of Mechanical
Engineering
Andrew Holmes, Swanson School of Engineering
Machine Shop
Ricardo Rivera-Lopez, Graduate Student, Department
of Mechanical Engineering