Experimental evaluation of a thermosyphon-based waste-heat recovery and reintegration device: A case study on low-temperature process heat from a microbrewery plant

I. Carvajal-Mariscal, J. E. De León-Ruíz, J. M. Belman-Flores, A. Salazar-Huerta

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Abstract

An experimental study was conducted to design, build and test the performance of a waste-heat recovery device. Its feasibility and performance were evaluated, based on its implementation within a brewing process; recovering unallocated residual energy from wort cooling water (40 °C to 80 °C) and using it to heat cool air for barley drying (32 °C to 48 °C). Given the quality associated to the low-temperature source, thermosyphons were selected as heat conveyance device. The proposed heat recuperator design uses 18 carbon-steel thermosyphon tubes filled with a mixture of distilled water and hydrazine hydrate, as corrosion inhibitor, at 20% of the total inner volume. Given the passive nature of the device, the length ratio between the evaporation and condensation zones was also analysed, ranging from 50:50, 40:60 and 30:70. The results showed that the 50:50 length ratio was the most disadvantageous configuration available, with the lowest efficiency and heat conveyance, ascribed to a higher radial heat flux into the evaporator, thus, reducing the operation range considerably. Meanwhile, increasing condenser length, 40:60 and 30:70 length ratios, yields a higher maximum condensation heat flow, with 4.15 KW and 4.22 KW, respectively, a 31% increase. However, given the 1.2% difference between them, said increase is comparatively negligible, entailing that, for this thermosyphon setup, peak heat transfer available is reached with the 40:60 length ratio. Regarding efficiencies, it was found that the 50:50 length ratio is particularly susceptible to the thermosyphon inherent operation limits, specifically, the boiling limit. Nonetheless, all configurations have efficiencies above 50% with heat flows above 1.5 KW. Additionally, it was found that the lowest air flow velocities yield the highest achievable efficiencies, with 84%, 98% and 94%, for the 50:50, 40:60 and 30:70 length ratios respectively. Similarly, when evaluating through the thermal capacity framework, it was found that the 50:50 length ratio only possess a 8% accomplishment rate, whilst the remaining configurations, increase said rate by 20%. However, it also shows that the 30:70 length ratio yields a more dispersed dataset, which reveals that the imbalance after surpassing peak heat transfer, renders the device more susceptible to both inherent and environmental effects. From the findings it was found that the proposed device, with a 40:60 length ratio is capable of successful recover and reintegration of residual energy, without modifying existing brewhouse installation or requiring additional energy input. Therefore, the general assessment conducted proposes thermosyphon-based heat exchangers as viable alternatives for low-temperature heat recuperation beyond the case study here discussed.

Original languageEnglish
Article number101760
JournalSustainable Energy Technologies and Assessments
Volume49
DOIs
StatePublished - Feb 2022

Keywords

  • Heat recovery device
  • Low-temperature waste-heat
  • Process heat reintegration
  • Thermal capacity
  • Thermosyphons

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