Study and development of a technique for measuring concentration and mass flow rate for saline solutions

Abstract

The purpose of this work is the design and construction of a non-invasive meter for concentration in saline solutions and the proposal of a low-cost mass flow meter for absorption refrigeration systems with LiBr/H2O. The proposed meter makes use of a capacitive sensor relating the electrical capacitance of the LiBr/H2O mixture to the mass fraction of LiBr in the solution. Thus, an experimental apparatus composed of a capacitive sensor with cylindrical geometry, high-frequency oscillators, and a temperature control system was built. Tests involving samples of the solution at concentrations from 50 to 64% LiBr were conducted to reproduce the typical operating conditions of the absorption chiller, establishing correlations between concentration, voltage, and temperature. The matches of these correlations between concentration and density were very good with maximum relative errors of less than 2.5%. The same procedure was performed for the density measurement, achieving a density, voltage, and temperature relationship with errors of less than 0.27%. For the determination of the volumetric flow rates, a turbine-type meter, equipped with a Hall effect sensor W1305347 and an Arduino microcontroller (MEDY FLOW), was adopted, which proved to be effective when dealing with the LiBr/H2O salt solution and good accuracy when compared to conventional meters, showing statistically proven relative errors of less than 4%. The results showed a satisfactory level of repeatability and accuracy with errors of 0.4% and 2.5%, for the range of operation evaluated.