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A new microfluidic product for measuring fluid density, specific gravity and chemical concentration has been developed. At the core of this lab-on-a-chip sensor is a vacuum-sealed resonating silicon microtube. Measurements can be made with under a microliter of sample fluid, which is over 1000x less than is conventionally required. Since the product is MEMS-based the overall system size is a fraction of conventional density meters and it weighs much less than the traditional desk-top, temperature controlled, density meters. The syringe or pipette loaded system includes a dynamic temperature control system that operates between 0 degree C and 90 degree C with an accuracy of less than 0.01 degree C. Density measurement accuracies of 4 to 5 digits have been observed with aqueous solutions. Measurement examples and applications will be discussed.

A shortcut method is proposed for the design of columns separating homogeneous azeotropic mixtures. Azeotropes are treated as pseudocomponents, and a C-component system with A azeotropes is treated as an enlarged (C + A)-component system. This enlarged system is divided into compartments, where each compartment behaves like a nonazeotropic distillation region formed by the singular points that appear in it. The compartment boundary is linearly approximated. A procedure is proposed for transforming vapor−liquid equilibrium behavior in terms of pure components into that in terms of singular points, allowing relative volatilities to be characterized in terms of singular points. The classical Fenske−Underwood−Gilliland method can then be used to design columns separating azeotropic mixtures. This method is extremely computationally efficient and can be applied to homogeneous azeotropic mixtures with any number of components. The results of the shortcut design method are useful for initializing rigorous simulations using commercial software.

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