| Two types of experiment have been done to study the effects of polymer additives in nucleate boiling for plates and wires. Here, boiling on a flat surface is simulated by placing a flat unheated surface immediately underneath an electrically heated platinum wire. Saturated nucleate pool boiling curves have been measured for water and solutions of six different polymers at various concentrations. For a bare wire and a simulated flat surface, the nucleate boiling curves are qualitatively similar. For equal heat fluxes, the temperature difference increases as the relative viscosity increases, although the temperature difference for the simulated flat surface is less than that for the bare wire. The observed changes in the nucleate boiling curves for polymer solutions are in qualitative agreement with those predicted using the Rohsenow correlation to account for change in the solution viscosity. These results show that for both wires and simulated flat surfaces, drag-reducing additives will reduce the heat transfer rate in nucleate boiling.;Bubble dynamics on the heated wire and simulated flat surface have also been measured using a high speed movie camera for water and Separan AP-30 at a relative viscosity of 1.16. The number density of bubbles, the bubble diameter, and the bubble departure frequency are obtained. The data has been used to determine the relative contribution to the boiling heat flux of latent heat transport by bubbles, natural convection heat transfer, and "enhanced" convection heat transfer. At high heat flux, a large portion of the boiling heat flux is transported by latent heat removal. The data show that while nucleate boiling is retarded by polymeric additives, the critical heat flux increases with increasing viscosity for Separan AP-30 in both boiling surfaces. By changing the boiling surface setup from a bare wire to a simulated flat surfaces, the critical heat flux is decreased for both water and Separan AP-30. |
