Thermal performance investigation of LiBr solution–based nanofluids in plate heat exchangers

Abstract

ABSTRACT The poor heat transfer performance of LiBr solution is one of the main obstacles to improving the performance of absorption cooling systems. In this study, the combined effects of the heat transfer enhancement and pressure loss increment of LiBr solution-based nanofluids in plate heat exchangers are investigated theoretically. First, a correlation for predicting the Nusselt number of the LiBr solution in a chevron plate heat exchanger with different chevron angles is developed based on the experimental data, and the prediction error is in the range of−3.8% to 6.0%. Second, the heat transfer coefficients and friction factors of Al2O3 nanofluid and MWCNT nanofluid are numerically calculated. The nanofluids have higher heat transfer rates than the LiBr solution. The heat transfer enhancement of the nanofluid in the 30°Chevron type plate heat exchanger is similar to that in the 60°Chevron type plate heat exchanger. The Nusselt number and heat transfer coefficient of the Al2O3 nanofluid with a 2.5% volume fraction are about 2.2% and 9% higher than those of the LiBr solution. The Nusselt number and heat transfer coefficient of the MWCNT nanofluid with 0.05% volume fraction are about 7.8% and 8.1% higher than those of the LiBr solution. The friction factor increases with the rising nanofluid volume fraction because the viscosity increases. When the nanofluid volume fractions are one-third and two-thirds of the equivalent value, the performance coefficient improvement of MWCNT nanofluid is about two to four times higher than that of the Al2O3 nanofluid. When the volume fraction is one-third of the equivalent value, the performance coefficient improvement of Al2O3 is about 30% to 40% higher than that of the MWCNT nanofluid. When the volume fraction of MWCNT nanofluid is between 0.01% vol. and 0.02% vol. and that of Al2O3 nanofluid is between 1% vol. and 1.5% vol. the heat transfer performance and economic performance of the two nanofluids can be regarded as equivalent. Finally, the appropriate selections of LiBr-solution based nanofluids for different application requirements are presented.