Suspensions sensitive to external electric and magnetic fields (Shulman et al., 1972) have a wider application in power plant seal systems, nuclear power plants, vacuum devices, heat exchangers, etc. The response of these suspensions to the external field effect exhibits itself in powerful structuring that noticeably changes their rheological and thermophysical properties.

A. Electrorheological disperse systems

These are suspensions of dielectric particles, primarily of silica in nonpolar, weakly electroconducting media. In the electric field, these suspensions sharply and reversely alter the yield stress and apparent viscosity. Most studied are four-component systems containing both the polar activator adsorbed on the particle surface that intensifies structuring and the surfactant that controls suspension consistency.

The growing electric field intensity markedly increases the thermal conductivity of suspensions. With increasing content of the activator there appears a set of stable bridges in these suspensions, and heat transfer occurs primarily along intimately contacting adsorptive shells of particles. Heat conduction along the bridges is enhanced due to decreasing thermal resistance of inter- particle contacts (Shulman et al., 1974). Figure 1 shows the effect of three main factors (particle concentration, activator content, and electric field intensity) on thermal conductivity of a typical aerosil suspension in cetane. It is found that the quantity λ is twice as much as in the electric field. The knee of the curve (c < 3%) is attributed to electric convection. The unique specific features of electrorheological suspensions are proposed to be useful in recuperative heat exchangers (Shulman et al., 1978a).

Figure 1 Effect of solid phase and activator content on thermal conductivity of electrorheological suspension