SOP for TPS 2500
thermal conductivity
Doc. No: 2010-04-04-V01
Department of Energy Technology
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SOP for TPS 2500 thermal conductivity
Department of Energy Technology
Reference: e.g. KTH- XYz
Measure thermal conductivity of XYz in distilled water nanofluid
1. Purpose
1.1. Measure thermal conductivity in nanofluids.
2. Scope
This protocol is applicable to all members of NanoHex project and provides a descriptive
procedure to measure thermal conductivity with TPS 2500 instrument XYz in distilled water
nanofluid.
3. Principle
Transient Plane Source (TPS) method is used to measure thermal conductivity and thermal
diffusivity on various sample types such as liquids, pastes, solids and powders disregarding
they are electrically conducting or not. However the sensors to accommodate all of this
variety in samples are different in sizes and formats. The TPS probe comprises a sensor
(figure 1) acting both as heat source for increasing the temperature of the sample and a
resistance thermometer for recording the time dependent temperature increase of the
sensor. The TPS sensor element is made of a 10 μm thick electrically conducting Nickel foil
in the shape of a double spiral. The Nickel foil is sandwiched between two layers of (0.013 0.025 mm) polyimide (Kapton) in order to keep physical shape, increase mechanical
strength and supply electrical insulation.
For measurement the sensor is places between two pieces of the sample in contact with the
surfaces. Figure 2 shows the position of the sensor relative to the samples of which the
thermal conductivity is being measured. For liquids a special stainless steel liquid holder and
for solids a room-temperature solid sample holder both designed by Hot Disk AB are used.
(a) Hot Disk sensor 5501
(b) tip of the Hot Disk sensor 7281
Figure 1 - A typical TPS sensor
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SOP for TPS 2500 thermal conductivity
Department of Energy Technology
(a) Measurements for solids
(b) Special stainless steel liquid holder
for measurements in liquids
Figure 2 - A typical TPS sensor
An increase in temperature is created by passing a current through the Nickel foil during the
measurement. The time and output of power are adjusted manually depending on
characteristics of different materials. The generated heat is dissipated on both sides of the
sensor and the selected rate is dependent on the thermal transport characteristics of the
sample. The thermal characteristics are calculated from the recording of the temperature
increase versus time response in the sensor (figure 3). The graph (b) in figure 3 results from
200 resistance recordings taken during the pre-set time and at the pre-set output power in
the sensor.
(a) Current through the sensor
(b) Temperature increase of the sensor
Figure 3 - Measurement basis in TPS method
TPS is a fast, convenient and absolute method. The latter means that there is no
requirement to calibrate the sensor against a known thermal transport property material.
Table 1 shows the specifications for TPS 2500.
Table 1 - specifications for TPS 2500
Thermal Conductivity (TC):
Thermal Diffusivity:
Specific Heat Capacity:
Measurement Time:
Reproducibility for TC:
Accuracy for TC:
Temperature Range:
0.005 to 500 W/mK
0.1 to 100 mm²/s
Up to 5 MJ/m³K
1 to 1280 seconds
Typically better than 1%
Better than 5%
Standard; Ambient (Room Temp. only)
With Circulator; -50˚C to 150˚C
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SOP for TPS 2500 thermal conductivity
Department of Energy Technology
4. Nanofluids
The following samples delivered to Energy Department for NanoHex project:
• e.g. KTH- Xyz in distilled water
5. Safety procedures and precautions
5.1. Wear rubber gloves and safety glasses when working with nanofluids.
6. Procedure for liquids
6.1. Sensor 7577 with radius 2.001mm appropriate for measurement in liquids is selected.
The sensors with small radius (2-3 mm) are a good choice in order to keep the
measurements short.
6.2. Assemble the stainless steel liquid holder according to the instruction in the manual.
6.3. Fill the liquid holder with the test sample.
6.4. Insert the liquid holder into the thermostated bath and keep it there until the temperature
change during 5 minutes is less than 0,1 K.
6.5. Select appropriate value of power and time and measure thermal conductivity according
to the following:
6.5.1. To have good measurement accuracy with TPS 2500 the applied power and time
should be as high as possible. However for low viscosity liquids the power of the sensor
and the measurement time must be low to avoid convection.
6.5.2. The values for the power and time, is highly depending on the particular nanofluids
being tested, but should be in the following range:
• Power (0.01-0.05) W and time (2-10) seconds.
• Select the lowest power and keep it constant while you increase the time in a
couple of steps from the lowest value. Based on the stability in the results select
a time then increase the power in a number of steps while checking stability in
results. Thus the highest possible value for the power and time are selected
without causing convection.
6.5.3. Each measurement is repeated at least five times using the same settings of power
and time.
6.5.4. The temperature increase versus time includes a 200 recorded data points in the
selected power and time, which an example is shown in figure 4. Smoothly increasing
curve is the first step to have successful measurements otherwise it is recommended to
redo the measurements.
6.5.5. Select “Calculations” from the Analysis menu. The operator can exclude some of
the 200 recorded points. The shape of the plot of temperature difference versus the square
root of time,
can be a criteria to find out how many points should be excluded. The
points in this graph should follow a good random scatter without any tendency of curvature
Figure 5 and 6 indicates two examples for a bad and a good random scatter point. In most
of the cases some of the initial points must be deleted, which are on the influence from the
insulation layer of the sensor at the beginning of the transient time.
6.5.6. The shape of the plot of temperature difference versus the square root of time,
also can show the onset of convection graphically. In case convection happens the points
are not dispersed enough in time and the plot looks like a third degree polynomial.
6.5.7. The software also provides some checkpoints to evaluate the results:
• Total to Characteristic Time defined below should be ideally within 0.3 to 1.0.
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SOP for TPS 2500 thermal conductivity
Department of Energy Technology
Here, γ and r are thermal diffusivity for the sample and radius of sensor
respectively. When measuring low viscosity liquids this condition cannot be
satisfied however.
• The total temperature increase shall be less than one degree.
6.5.8. There is an option in the software to enter the value for specific heat as a known
parameter. The experience of measuring thermal conductivity in distilled water with TPS
2500 at KTH showed using this option has higher accuracy compared to standard
calculation. This option should therefore be used in the determination of the thermal
conductivity, and the specific heat of nanofluids should be calculated as:
•
In which nf, s, bf, and φ stands for nanofluids, solid, base fluid and volume concentration
respectively.
6.6. Change the temperature of the bath according to the test matrix and repeat the
measurements from 6.3.to 6.6
6.7. Disassemble the sensor from the stainless steel liquid holder. Wash the sensor and
inside of stainless steel liquid holder with ethanol, rinse with distilled water and dry it.
Wash the plastic tube connectors by a 3 Molar (diluted) hydrochloridric acid, rinse with
water and let dry.
6.8. Store the sensor in a safe place.
Important note: Never leave any liquid left in the stainless steel liquid holder to avoid any
risk of chemical reaction between the liquid and the metallic cell or the sensor.
Figure 4 - Temperature increase versus time
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SOP for TPS 2500 thermal conductivity
Department of Energy Technology
Figure 5 - temperature difference versus the square root of time - a bad random
scatter (points 1-200)
Figure 6 - temperature difference versus the square root of time - a good random
scatter (points 14-200)