Experimental Investigation of CaSO_4 Crystallization on a Flat Plate

摘要

The scaling of calcium sulfate was studied by performing laboratory experiments under controlled conditions. The experiments were aimed at measuring the rate of deposition at different positions on a heated surface. The overall thermal resistance was determined from temperatures measured using thermocouples positioned in the bulk fluid and the wall of the heated plate. Calcium sulfate was used as the experimental fluid. It was observed that nucleates started forming on the downstream side. A nucleation front was formed, and it was seen to move from the downstream to the upstream side. The rate of growth as a function of position was observed to increase with the initial wall temperature distribution, resulting in a final thickness of the scale layer that increases accordingly. While the rate of growth was found to be independent of flow velocity for Reynolds numbers of 11,000 and 23,000, the results showed that the rate of growth decreased by about 20% for Re = 34,000. Further, the induction period is reduced by increasing the flow velocity. An increase in the degree of supersaturation also reduces the induction period. It is concluded that scaling due to CaSO_4 results in a non-uniform porous scale layer with a profile that mimics the initial surface temperature.