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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.
Nomenclature
| A | = | total area, m2 |
| A0 | = | free flow area, m2 |
| AD | = | average deviation, % |
| AlN | = | LiBr solution based Al2O3nanofluid |
| a | = | constant |
| b | = | corrugation depth, m |
| CPHE | = | chevron type plate heat exchanger |
| cp | = | specific heat capacity, kJ/kg K |
| Dh | = | hydraulic diameter, m |
| f | = | friction factor |
| G | = | mass velocity, kg/m2 s |
| h, HTC | = | heat transfer coefficient, W/m2 K |
| k | = | conductivity, W/m K |
| LMTD | = | log-mean temperature difference, °C |
| MN | = | LiBr solution based MWCNT nanofluid |
| m | = | flow rate, kg/s |
| Np | = | channel number |
| Nu | = | Nusselt number |
| P | = | price, $ |
| PER | = | properties of enhancement ratio |
| PPI | = | price performance index |
| Pr | = | Prandtl number |
| Q | = | heat transfer rate, kW |
| RD | = | relative deviation, % |
| Re | = | Reynolds number |
| SD | = | standard deviation, % |
| T | = | Temperature, °C |
| U | = | overall heat transfer coefficient, W/m2 K |
| W | = | width, m |
| wf | = | LiBr solution concentration, wt% |
| Greek symbols | = | |
| ΔΦ | = | performance coefficient improvement |
| δ | = | thickness, m |
| λ | = | corrugation length, m |
| θ | = | chevron angle, ° |
| μ | = | viscosity, kg/m s |
| ρ | = | density, kg/m3 |
| Subscripts | = | |
| c | = | cold side |
| E | = | experiment |
| h | = | hot side |
| i | = | Inlet |
| lb | = | LiBr solution |
| nf | = | Nanofluid |
| np | = | nanoparticle |
| o | = | Outlet |
| S | = | simulation |
| wf | = | working fluid |
Acknowledgements
This study was financially supported by the Scientific Research Fund of Zhejiang Provincial Education Department (No. Y202147944), Special support for the marine economic development of Guangdong Province (GDNRC[2022]28), and Scientific Research Foundation of Zhejiang University City College (No.J-202115). We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.
Disclosure statement
No potential conflict of interest was reported by the author(s).