THISYS Apparatus for thermal conductivity measurement of thin samples
THISYS offers an accurate, fast and
uncomplicated measurement of the thermal conductivity of thin samples of high
thermal conductivity materials. Typical samples are sheet materials of metals,
alloys and high conductivity plastics with various filler materials. Metal
samples are ideally in the thickness range of 0.1 mm and less, plastic samples
typically in the thickness range of 6 mm, composites in between. THISYS is a
combination of a Thin Sample Instrument (THI01) and a Measurement and Control
Unit (MCU). The measurement essentially determines the temperature gradient
across the sample when it is heated, in the plane of the sample itself.
Employing a specially designed high accuracy thermopile sensor THI01 can handle
thin sample materials (less than 0.01 to 6 mm) usually in the thermal
conductivity range to 200 W/mK. Following this method, problems with contact
resistance are avoided. The method is a good alternative
when procedures according to ASTM D5470 are failing. Using a climate chamber
a large temperature range can be covered, performing measurements at regular
intervals. THISYS is fully PC controlled. For use with low thermal conductivity
materials a different model, type THASYS, is available.
Figure 1
THISYS consists of the Thin Sample Instrument (THI01), (1) and a
Measurement and Control Unit (MCU), (2). It is PC controlled though RS232 (4, 5). The PC is not
included. The measurement result appears on screen automatically. The THI01
housing contains two heat sinks in a bath of glycerol. It has a slot on top
through which the sample is inserted. The sample is heated on two sides. One
heater also contains the hot joints of the thermopile sensor. The sample plus
heater are then pressed together with the heat sinks using a screw on the
side, creating a perfectly symmetrical setup. The glycerol fluid eliminates
the problem of contact resistance.
Free: For a nice clear print of the
original product brochure (PDF) click here.
INTRODUCTION
The measurement of thin materials with
relatively high thermal conductivity is a classic problem. Commonly used methods
like ASTM D 5470 – 01 (Standard Test Method for Thermal Transmission Properties
of Thin Thermally Conductive Solid Electrical Insulation Materials) have shown
to be highly sensitive to contact resistance, and not applicable with high
conductivity materials. THISYS offers a solution to this problem.
THISYS essentially measures the
temperature gradient from centre to side across the sample when mounted across a
well insulated cavity, and heated with a known uniform flux.
By measuring the flux φ (derived from
heater power), the differential temperature across the samples, ∆Tamp,
and the sample thickness, H, it is straightforward to calculate the relative
thermal conductivity λrel:
λrel ~ φ / H ∆Tamp
The measurement is performed relative to
a known reference material.
Figure 2 THI01 geometry: heat sinks
(7, 9). sample material (8), air filled
cavities (17), heaters (4). Heat generated by the heaters first flows in the
plane of the sample and only after that into the heatsinks (14).
THI01 DESIGN
The Hukseflux THI01 employs two
aluminium "heat sinks”. Each of these contains a heater that is mounted over
an air-filled, insulating cavity. The sample is installed over the cavities.
The resulting temperature gradient
(centre-edge) is measured. Apart from the new design, the technological
novelties are a thin thermocouple thermopile (proprietary Hukseflux design)
performing an accurate and ultra-sensitive differential ∆T measurement, and the
fact that the measurement is performed in a bath of glycerol.
The THI01 can handle samples of less
than 0.01 to 6 mm thickness. Samples typically are sheet materials with a size
of 70 by 100 mm.
The reference material is 5 mm Pyrex
7740 material. The thermal conductivity in the sheet plane, H.λ, is around 4 10-3
m2K/W. Samples ideally have values of
H.λ close to that.
The measurement essentially is done at
the temperature of the THI01. If necessary the temperature can be changed by
putting the whole THI01 in a climate chamber, performing measurements while the
instrument temperature changes across the required range. In a simplified
description, the measurement consists of a heating cycle and a measurement to
establish ∆T. The THI01 temperature is monitored by a Pt100 temperature sensor
to correct for the temperature dependence of the thermopile sensitivity.
Figure 3.
Analysis of several samples of filled plastics using the THISYS. The graphs
represent the signals when putting the heater on. The signal amplitude is
inversely proportional to the thermal conductivity
λ
multiplied by the thickness H.
MCU01 DESIGN
The MCU performs the functions of
measurement and control as well as data storage. It is PC operated. Software in
a Windows environment is part of the delivery. The parameters cycle time, sample
thickness and heater area are entered and the experiment is started from the
screen.
CALIBRATION
Depending on the samples to be analysed,
various reference samples can be offered. Typically Pyrex 7740 is used. The
Pyrex sample thermal conductivity is traceable to NPL. THISYS is suitable for
use by ISO certified laboratories.
SUGGESTED USE
MORE INFORMATION / OPTIONS
Please consult the manual for a full
list of THI01 specifications. This manual is available free of charge as a PDF
file via e-mail. For use with low thermal conductivity materials the model
THASYS is available.
THI01 SPECIFICATIONS
- Test method: Thin sample analysis
- Temperature range: -30 to +120 °C
- Accuracy (λref) (depending on
samples): depending on reference, typically +/- 6% @ 20 °C with H. λ around
4 10-3 m2K/W
- Repeatability (λref): +/- 2% @
20 °C
- Total measurement time: 3000 s (typical)
- Power requirements (switched): 15 V, 0.8
Watt (typical)
- Heater (resistance, diameter): 50 Ohm,
80mm
- Sample requirements: H = up to 6 mm, A
around 70 x 50 mm, H.λ = 1 to 5 10-3 m2K/W
- Sample surface A: preferred: 70x110 mm,
always >50x50 mm
- Temperature sensing Pt100: Class B, IEC
751:1983
- Traceability: NPL National Physical
Laboratory UK
MCU01 SPECIFICATIONS
-
Differential temperature readout: 0.5 µV
@ 0 - 30 °C
-
Pt100 readout: +/- 0.2
°C @ 20 °C
-
Voltage input/output: 220-110 VAC / 15
VDC
-
Further functionality: Relay function,
heater power measurement,
temporary data storage
-
Communication: RS232
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