Thermohydraulic, Exergetic, and Environmental Assessment of Water-Based Nanofluids in Plate Heat Exchangers

Abstract

Nanofluid-cooled plate heat exchangers (PHEs) have strong potential to improve thermal system performance, but they often incur substantial pressure-drop penalties and are affected by uncertainties in the underlying correlations. I built a steady-state numerical model of a counter-current PHE in an ammonia heat-pump application to assess water-based mono- and hybrid nanofluids using an integrated thermohydraulic, exergetic, and operational–environmental perspective. The model was validated using my own experimental thermal conductivity measurements. While purely theoretical predictions suggest an 8.0% thermal improvement and a reduction in required plates (32 to 31) for 3 wt.% graphene, experiments show the graphene thermal conductivity is overpredicted by 35.10% because of nanoplatelet agglomeration. When the measured (realistic) conductivity is used, graphene’s heat-transfer benefit falls to only 1.2%, eliminating the plate-count advantage. As a result, dilute oxide nanofluids (1 wt.% TiO2 and SiO2) appear to be the most practical and sustainable choices, with Performance Evaluation Criterion (PEC) values of 0.994. In addition, the sensitivity study reveals a large 167–181% spread between the Pietrzak- and Kumar-type Nusselt-number correlations. Overall, the results show that physical constraints significantly limit the practical gains of concentrated carbon-based nanofluids, whereas low-loading metal oxides provide the most dependable route for sustainable PHE design.