The effective thermal conductivity of glass bubbles or microspheres depends on several factors such as the size of the bubbles, the composition of the glass, the presence of any fillers or coatings, and the method of their arrangement within a material. Glass bubbles are often used as additives to enhance the properties of materials like polymers, coatings, or composites.

Generally, glass bubbles have low thermal conductivity due to the presence of air or gas within the hollow spheres, which hinders the transfer of heat compared to solid materials like glass or metals.

The effective thermal conductivity of a composite material containing glass bubbles can be estimated using different models such as:

  1. Maxwell’s Model: This model assumes that the heat transfer occurs through the solid material and the gas within the bubbles independently. The effective thermal conductivity is calculated based on the volume fractions and thermal conductivities of the two phases (solid matrix and gas in the bubbles).
  2. Lewis and Nielsen Model: This model considers the geometry of the microspheres and their arrangement within the composite material. It takes into account factors like the size, shape, and packing arrangement of the bubbles to estimate the effective thermal conductivity.
  3. Experimental Measurements: Actual measurements using techniques like laser flash analysis or transient plane source (TPS) methods can directly determine the effective thermal conductivity of materials containing glass bubbles.

The effective thermal conductivity of glass bubbles typically ranges from very low values (comparable to insulating materials) to moderately higher values, depending on their size, concentration, and the material they are incorporated into. It’s important to note that the effective thermal conductivity may vary significantly based on the specific composition and manufacturing process of the glass bubbles and the composite material they’re added to.