EXPERIMENTAL AND THEORETICAL ANALYSIS OF THE ADVECTION OF HEAT AND SOLUTE IN NON-REACTIVE POROUS MEDIA

One of the first objectives of this project was to design and build an experiment that could measure the advection rates of heat and solute in a non-reactive porous medium. The second objective was to examine the continuum theories that relate to the transport of heat and solute in a non-reactive porous medium. Specifically, to verify that the velocity of solute is faster than the thermal velocity when the Peclet number is below 1 at the pore scale and that their advection rates are similar when the Peclet number is above 1 at the pore scale. To simulate a non-reactive porous medium, sand, glass microspheres and expanded polystyrene were used. A liquid that contrasted the temperature and solute levels present in the cell, was supplied via a supply tank whose height was varied to create variable flow rates in a pressure-driven system. Changes in voltage, caused by changes in temperature and conductivity inside the porous medium, were recorded by a personal computer (PC) oscilloscope (a PicoScope); the sensors were electrodes and thermistors installed near the inlet and outlet of the cell containing the porous medium. The time between the inlet and outlet signals was used to determine the experimental velocity which was then compared to theoretical values. Experiments where the system was transitioned from a state of low to high resistivity were the most challenging in terms of obtaining good signal quality. A numerical model was introduced to assist in the analysis of the signal shape for these experiments. Results are given for pore-scale Peclet numbers (Pe_pore) of less than and greater than 1. In experiments for Pe_pore < 1, the advection rates of solute were observed to be greater than heat which agrees with the theory that assumes heat equilibrates with its surroundings as it is advected with the fluid causing it to lag the solute. When the pore-scale Peclet number is greater than 1, the expectation was that the advection rates of heat and solute would be similar. In some cases, their velocities were similar while in others, the solutal velocity was faster than the thermal velocity. The difference was due to significant roles that thermal conductivity and volumetric heat capacity play in the transport of heat