Wax Deposit Thermal Conductivity Measurements under Flowing Conditions

Thermal conductivities of wax deposits formed on the cooled wall of a channel were measured under flowing conditions, for different values of the Reynolds number (Re) in laminar flow. To this end, a laboratory-scale experiment was especially designed, employing a rectangular channel flow loop. The thermal conductivities were directly measured for steady-state conditions in deposits formed after 7 h of deposition. The cooled wall on which the deposits were formed was equipped with embedded heat flux and thermocouple sensors. A micrometer-driven temperature probe of small dimensions was installed at the opposite channel wall and could be traversed across the channel, yielding the temperature profile of the deposited wax layer, as well as the liquid/deposit interface temperature. Deposit compositions were obtained by high-temperature gas chromatography. Thickness-averaged deposit thermal conductivities were obtained from the deposit thickness, heat flux, and interface-to-wall temperature measurements. The thermal conductivity results obtained for these well consolidate deposits did not display any sensitivity to the Re values tested, although the deposit wax content was seen to increase with Re. This finding was related to the nonhomogeneous character of the thick deposits studied. Temperature profiles within the wax deposit measured with the traversing temperature probe revealed small deviations from the linear profile expected for a one-dimensional, steady-state solution, considering a constant value for the thermal conductivity across an homogeneous deposit. These deviations were attributed to transverse variations of the deposit thermal conductivity. Local values of the thermal conductivity across the deposit were measured, revealing higher values closer to the deposit/liquid interface region, compared to those observed in the near-wall region. This variation was associated with the higher liquid fraction present in the deposit near the cold wall. The sensitive of the deposit thermal conductivity to the deposit liquid fraction was used as the basis for a novel technique developed to estimate the liquid and solid fraction distribution across the deposit. The technique was able to capture the increase in liquid fraction close to the cold wall, compared to the near-interface region, for the experimental conditions tested.