Fiber Optic Sensor for Salt-Water Mix in Waste Heat Recovery

What is it about?

This research develops a simple fiber optic sensor to measure the concentration of Carrol (a lithium bromide-based additive mixture) in water, used in absorption heat transformers (AHTs)—devices that upgrade low-grade waste heat from factories or solar sources into higher-temperature usable energy, like steam for processes. Traditionally, concentration is checked by pulling samples and using refractometers, which is slow and risks errors from temperature or humidity changes, potentially causing crystallization that clogs the system. Here, scientists analyzed how light is absorbed through the mixture at different concentrations (51.79% to 66.2%) and temperatures (25°C to 80°C), mimicking AHT operating conditions. Using a white light source, optical fibers, and a spectrometer, they measured transmittance (light passing through) and absorbance (light blocked), finding patterns at 1550 nm wavelength where laser diodes work well. They created a math equation linking absorbance, temperature, and concentration: X = (-0.199T + 43.99) * exp(a * (-0.004T - 0.567)), accurate to ±0.97%. Tests compared it to refractometers, showing small differences (e.g., 0.14% to 0.92%). This in-line sensor—cheap and using basic equipment—could monitor real-time without stopping the AHT, preventing damage and optimizing energy recovery (e.g., boosting 60°C waste to 100°C+). It addresses humidity issues in hygroscopic mixtures and supports greener energy by recycling 20-50% of industrial waste heat, reducing fossil fuel reliance amid shortages.

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Photo by Lightsaber Collection on Unsplash

Photo by Lightsaber Collection on Unsplash

Why is it important?

This study innovates with a low-cost, in-line fiber optic sensor for Carroll-Water in Absorption Heat Transformers, deriving a temperature-absorbance equation (±0.97% accuracy) that is absent in offline refractometry, enabling real-time monitoring to avoid crystallization. Unique for this mixture (less corrosive than pure LiBr), it's timely amid 2010s renewable pushes and waste-heat losses (20-50% industrial), post-Kyoto. Impact: Prevents system failures, boosts efficiency 10-20% for desalination or heating (e.g., 0.1-0.2 L/min water/site), cuts costs with 2-5 year payback, and reduces CO2 tons yearly—vital for sunny regions like Mexico integrating solar ponds, scaling sustainable recovery for net-zero goals.

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