This column deals with the thermal conductivity and melting points of liquid metals. Thinking about liquid metals, many people associate them with high temperatures. It is not widely known that some metallic alloys are liquid below 0�C, with the exception of course of mercury which was already known in ancient times. China's first emperor is said to have been buried in rivers … [Read more...]
Thermal Effusivity
The Technical Data column of the previous issue discussed the concept of thermal diffusivity. It makes sense to discuss in this issue a related topic: thermal effusivity. While thermal diffusivity, a, is defined as the ratio between the thermal conductivity, k, and the volumetric thermal capacity, ρcp, the effusivity, e, is related to their product, as follows: It is … [Read more...]
About viscosity
Table 1. Dynamic Viscosity Values for Various Gases and Liquids When we look at a fluid parcel subject to a velocity gradient in the direction perpendicular to the direction of the flow, we observe that this fluid parcel deforms. This type of deformation is called shear. The ability to withstand shear is a material property called the dynamic viscosity m. The viscosity … [Read more...]
The Seebeck Coefficient
In this issue, we address the Seebeck coefficient, a property that determines the performance of thermocouples and Peltier elements. Basically, the Seebeck coefficient is related to the fact that electrons are both carriers of electricity and heat. If a temperature gradient exists over a piece of electrically conductive wire, there is a net diffusion of electrons from the hot … [Read more...]
Thermal Conductivity of Doped, Porous and Isotopically Pure Silicon
Earlier issues of ElectronicsCooling showed the thermal conductivity for pure Si (May '98), SiO2 (Aug '04) and III-V semiconductors (Feb '06). This column focuses on doped Si, porous Si and isotopically pure Si. Table 1. Thermal Conductivity Data at Room Temperature The first seven rows of Table 1 show thermal conductivity data for natural and isotopically pure Si as … [Read more...]
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