A TRANSIENT SPHERICAL SOURCE METHOD TO DETERMINE THERMAL-CONDUCTIVITYOF LIQUIDS AND GELS

A method developed for the measurement of tissue blood flow is modifie d to measure the thermal conductivity of liquids and silica gels. The method controls a thermistor temperature at a set point above the base line and determines conductivity from the power as a function of time. Natural convection in the liquids is suppressed by reducing the measu rement time to 10 s and by reducing the temperature step, thus decreas ing the magnitude of buoyancy. Conductivities were measured in six aqu eous liquids and in gels constituted from these liquids with various a mounts of silica. The technique determined the conductivity with a 95% confidence interval to less than 1% in nearly all cases. It was found that conductivity varied 0.3% per 1% silica for gels made from a CuSO 4 solution and 1% per 1% silica for gels made from a Cu(BF4)(2) soluti on.