Sealing Shielding

Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials?

Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials? - THERM-A-GAP Gel 30 - Parker ChomericsA common question often asked by our customers is the reason why flow rate is reported on datasheets of liquid-dispensed thermal interface materials instead of viscosity. And it’s a fair question; viscosity is a fundamental property of fluids such as thermally conductive pastes. But measuring viscosity, however, is more complicated than meets the eye.

Parker Chomerics THERM-A-GAP Thermally Conductive GELs belong to a class of fluids referred to as “thixotropic.” In case you’re not familiar, thixotropy is a time-dependent decrease in viscosity as shear stress is applied.

This shear stress may be introduced during mixing, pumping, or dispensing of the product. The extent of the viscosity decrease depends of the duration and magnitude of the agitation, and viscosity recovers gradually over time after the stress is removed. The act of measuring viscosity introduces shear stress, so gathering repeatable data requires carefully controlling the duration of the test and the relaxation time between trials.

Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials? - Viscosity vs. Flow Rate Chart - Parker Chomerics

 

 

 

 

 

 

 

 

 

 

 

 

To complicate the measurement further, viscosity is strongly influenced by sample temperature. A warmer dispensable thermal paste flows more quickly than one at room temperature, a characteristic that is particularly relevant in thermal interface materials.

Therefore, a viscosity measurement is only accurate for a given shear stress, duration, and temperature. The resulting value of viscosity is difficult to generalize, so it is more convenient to use flow rate, as it is a measurement that is more representative of actual end-use conditions.

Automated dispensing is one of the primary advantages of dispensable thermal pastes, such as Parker Chomerics THERM-A-GAP GELs. Publishing flow rate data provides a framework with which to compare different gels based on their dispensability.

Additionally, measuring flow rate instead of viscosity controls the critical parameters described above, such as:

  • Shear stress, which is controlled by dispensing from a specified container at a constant pressure
  • Test duration
  • Ambient temperature

Measuring flow rate is repeatable and more representative of actual dispensing situations than a viscosity value.

So, the next time you’re reading a datasheet, you’ll be armed with the knowledge that flow rate is a more accurate representation of real-world conditions.

Download Thermal Interface Materials

 

 

 

 

 

 

Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials? -Jon Appert, R&D Engineer - Parker Chomerics

 

This blog post was contributed by Jon Appert, R&D engineer, Chomerics Division.

 

 

 

 

Related content:

The Difference Between Thermal Conductivity and Thermal Impedance

The Four Best Thermal Interface Materials For Cooling Electronics

New Thermal Gel Benefits Consumer and Automotive Applications

Categories
Recent Posts by Author

Why is Outgassing Critical in Optics and Electronics Applications?

For some applications, a critical component of selecting a seal material is a phenomenon known as “outgassing”. However, even within the elastomer community, outgassing is not something that...

Semiconductor Fab Processes Benefit From Retention Ribbed EZ-Lok Seals

When it comes to semiconductor fabrication processes, reducing the cost of ownership is a multi-faceted goal approached from a variety of angles. Tool engineers and equipment technicians take pride...

Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials?

A common question often asked by our customers is the reason why flow rate is reported on datasheets of liquid-dispensed thermal interface materials instead of viscosity. And it’s a fair...
Comments

Have a question about Parker products or services? We can help: Contact Us!

Comments for Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials?


Please note that, in an effort to combat spam, comments with hyperlinks will not be published.

Leave a comment





Captcha