A method for matching the refractive index and dynamic viscosity of transparent replicas of rock for flow visualization

In the seepage experiment of transparent fractured rock replicas, the optical distortion caused by selected transparent rock material and the seepage fluid is the main obstacle when applying laser imaging technology to experimental fluid mechanics research. Choosing a kind of solution with refractive index matching with transparent rock material as the working fluid is the primary method to eliminate optical distortion in the experiment. The experiment studied the refractive index matching results between different types of mixed salt solutions as well as mixed organic solution and transparent rock material composed of PMMA and 8015T series transparent resin. The recommended refractive index matching methods are as follows: One method is to add NH4Cl (30% by weight) or CaCl2 center dot 2H(2)O (27.5% by weight) salt solution into the saturated CaBr2 center dot 2H(2)O salt solution; and another method is to mix two kinds of organic solutions, such as C10H12 (74% by volume) and CHO (26% by volume). In addition, for these three kinds of solutions, the value of the Thermooptic Constant was introduced to reflect the effect of temperature change on the refractive index of the solution, and the laws of dynamic viscosity change with temperature are also studied. Research results demonstrate that: (a) Thermooptic Constants of 30% NH4Cl (by weight) and 27.5% CaCl2 center dot 2H(2)O (by weight) solutions are acquired as - 3.71 x 10(-4) and - 2.92 x 10(-4), respectively, which are close to that of water. However, the dynamic viscosity of these two inorganic salt solutions is much greater than water. (b) 74% C10H12 (by volume) solution has a higher Thermooptic Constant, which means its refractive index is greatly affected by temperature. However, its dynamic viscosity is close to water, which helps to study the seepage low of fractured rock mass in the visual environment.