The Microelectronics Heat Transfer Laboratory has experimental facilities and extensive experience in a wide variety of convection and thermal contact resistance measurements.

Natural and Forced Convection

• 12 in. Open Circuit Wind Tunnel with Variable Test Section Orientation
• 18 in. Open Circuit Vertical Wind Tunnel
• Natural Convection Test Enclosure

Thermal Conductivity

• Thermal Conductivity Measurements

Thermal Contact Resistance

• Thermal Contact Resistance Measurements
• Surface Microhardness Testing
• Surface Roughness Testing

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This unique, multi-purpose wind tunnel is designed for mixed and forced convection testing for horizontal, vertical and inclined geometries. By rotating the test section and duct assemble about a pivot axis coincident with the center line of the blower, the test section can be set to any angle between vertical and horizontal. The contraction section in the inlet plenum has a 9:1 contraction ratio and a 10 cm (4 in.) thick honeycomb flow straightener that reduces non-uniformities in the mean flow field and produces a relatively uniform velocity profile at the entrance of the test section. The removable, 30 cm x 30 cm x 60 cm (12 in. x 12 in. x 24 in.) test section is generally large enough to accomodate most common test specimens. Airflow velocities of 0 - 15 m/s (0 - 50 fpm) are controlled using a Danfoss VLT frequency-based speed regulator.

Temperature measurements and control of power dissipation by resistive heater elements are controlled controlled using a Fluke Helios data logger connected to an IBM PC compatible computer. This data logger is capable of monitoring up to 40 channels on a continuous basis and through the use of data aquisition software, this system can be programmed to automatically perform a series of tests at a variety of power settings.

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A recent addition to laboratory equipment at the MHTL, this vertical wind tunnel has a large 45 cm x 45 cm x 60 cm (18 in. x 18 in. x 24 in.) test section and is capable of airflow velocities from 3 m/s (10 fps) to 20 m/s (66 fps). The contraction has a 6.25:1 area ratio, with a symmetric cross section and analytical developed contours. The primary diffuser section expands with a total included angle of 6 degrees. The inlet section includes an aluminum honeycomb section and graduated mesh, high porosity screens and velocity variation in the test section is less than 1% variation from the mean, free stream velocity. Airflow velocity is controlled by a transistor invertor type variable frequency controller and velocity measurements are made using an anemometer.

Thermocouple temperature reading and resistive heater power levels are measured, recorded and controlled using a Fluke Helios data logger connected to an IBM PC compatible computer.

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The MHTL Natural Convection Test Enclosure is a vertical flowthrough apparatus designed specifically for use in natural convection experiments, where air flow is due soley to buoyancy effects. Ambient and heated air freely enters and exits the enclosure through inlet and outlet plenums, while the test section is protected from unwanted ambient air movements by honeycomb sections at the inlet and outlet. The vertically-oriented 45 cm x 30 cm x 45 cm test section is sufficiently large to hold full-size circuits boards and systems of boards for natural convection measurements.

Process control and data acquisition are controlled using a Fluke Helios data logger connected to an IBM PC compatible computer, capable of continuously monitoring up to 40 channels and automatically varying the resistive heater's power settings.

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Thermal conductivity measurements are performed in the thermal contact resistance rig, a test apparatus enclosed in a Pyrex bell jar connected to a vacuum system which combines a mechanical pump connected in series with an oil diffusion pump. Using this system, a vacuum lower than 1E-07 torr is attained under ideal conditions, which stops any heat transfer from the test apparatus due to convection. The test column used for thermal conductivity measurements consists of two ARMCO iron heat meters placed in contact with the upper and lower surface of the test specimen.

This column is located between a heater block, consisting of pencil-type resistive heaters embedded in a brass block, and a closed-loop constant temperature bath cooled cold plate. A load is applied to the test column using a diaphragm-type air cylinder and the contact pressure is measured by a calibrated load cell. The mechanical loads, heater power and temperature readings of the heat meters are measured and controlled using a data acquisition system connected to an IBM PC compatible computer. By varying the power dissipated by the heater block, the thermal conductivity of the test sample can be determined as a function of its mean temperature. This measurement technique has been used successfully for a wide variety of materials, including various aluminum alloys and other metals and silicon-based rubbers.

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Two experimental rigs are available at the MHTL for measuring the thermal resistance between contacting surfaces. Available test conditions include contact pressures from 0.4 to 9.0 MPa, interface temperatures between 50 C and 250 C, and evacuated, helium or argon environments. Data acquisition and control over the experiment are performed using either an ACRO or a Fluke Helios data logger connected to an IBM PC compatible computer.

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The Leitz Durimet Bench-Type Microhardness Tester is a manually-operated device with nine-present indenter loads between 15 and 2000 g. The test bed also allows heated specimens, up to 200 C, to be tested

The Shimadzu Bench-Type Microhardness Tester is a semi-automatic hardness tester fitted with a Vickers pyramidal indenter with 11 present indenter loads between 5 and 2000 g. The loading is fully automatic and the loads can be placed on the indenter for a period ranging from 5 to 60 s.

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Talysurf 5 is a surface texture measurement device that determines surface roughness, waviness and profile for flat or circular surfaces. Test conditions can include a wide range of magnification settings, from 100X to 100,000X, and a range of traverse lengths from 0.56 mm to 56 mm. Cut-off lengths between 0.08 mm and 8 mm are available. A seperate analog-to-digital converter connected to the measuring device can recored digitized height readings at uniformly spaced intervals. This information is analyzed by the device to predict the CLA, the RMS roughness and the RMS surface slope for the surface being examined.

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