Which Fluids and Designs Work Best for Turning Waste Heat into Useful Energy?

What is it about?

Many industrial processes produce large amounts of low-temperature waste heat that is usually lost. Absorption heat transformers are systems that capture waste heat and upgrade it to higher temperatures for reuse. This study compares different designs of these systems—single-stage, two-stage, and double-absorption heat transformers—to understand which configurations perform best. The research also compares two working fluid mixtures: the commonly used water–lithium bromide and an alternative, water–Carrol (which includes lithium bromide and ethylene glycol). Using mathematical models, we evaluated key performance indicators, including efficiency (coefficient of performance), temperature rise (gross temperature lift), and operational limits. The results show that while both mixtures perform similarly at lower temperatures, the water–Carrol mixture performs better at higher temperatures. It allows the system to reach higher temperature increases and operate over a wider range without problems like crystallisation, which can limit the performance of water–lithium bromide systems.

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Photo by National Cancer Institute on Unsplash

Photo by National Cancer Institute on Unsplash

Why is it important?

Improving how we recover and reuse waste heat is essential for reducing industrial energy consumption and emissions. This study is important because it provides a systematic theoretical comparison of both system designs and working fluids, helping identify the most efficient combinations. The key contribution is demonstrating that alternative mixtures, such as water–Carrol, can extend the operating range and improve performance, especially at higher temperatures where conventional systems fail. These insights can guide engineers in selecting better designs and fluids, leading to more efficient and reliable heat recovery systems in real-world applications.

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