Variations of thermophysical properties and heat transfer performance of nanoparticle-enhanced ionic liquids

Abstract

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) was investigated as a promising absorbent for absorption refrigeration. To improve the thermal conductivity of pure [EMIm]Ac, IL-based nanofluids (ionanofluids, INFs) were prepared by adding graphene nanoplatelets (GNPs). The thermal stability of the IL and INFs was analysed. The variations of the thermal conductivity, viscosity and specific heat capacity resulting from the addition of the GNPs were then measured over a wide range of temperatures and mass fractions. The measured data were fitted with appropriate equations and compared with the corresponding classical models. The results revealed that the IL and INFs were thermally stable over the measurement range. The thermal conductivity greatly increased with increasing mass fraction, while only slightly changed with increasing temperature. A maximum enhancement in thermal conductivity of 43.2% was observed at a temperature of 373.15 K for the INF with a mass fraction of 5%. The numerical results revealed that the dispersion of the GNPs in the pure IL effectively improved the local heat transfer coefficient by up to 28.6%.

Remarkable Thermal Conductivity Enhancement in Carbon-Based Ionanofluids: Effect of Nanoparticle Morphology

“…The maximum enhancement for INFs with 1 wt % loading of in-house MWCNTs 7 h and 16 h was equal to 43.1% and 43.9%, respectively, which are remarkably higher values in comparison with the literature data. 13 , 23 , 24 The commonly quoted values for thermal conductivity of individual CNTs at room temperature are 3000 W·m –1 ·K –1 and 3500 W·m –1 ·K –1 for MWCNTs and SWCNTs, 50 respectively; hence, we have obtained synergetic and so far unrivaled enhancement in thermal conductivity of INFs in comparison with literature data.…”

“… 13 , 19 − 22 The highest thermal conductivity enhancement of 43.2% was found for an INF composed of 1-ethyl-3-methylimidazolium acetate [EMIM][OAc] + 5 wt % graphene nanoplatelets. 23 High enhancements of 35% and 32.3% were also reported for INFs composed of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTf 2 ] + 1 wt % MWCNTs in the temperature range from 20 to 80 °C, 24 and [EMIM][SCN] + 1 wt % MWCNTs at 70.5 °C, 13 respectively. Baytubes MWCNTs with an outer mean diameter of 13–16 nm and length of 1–10 μm were used in both cases.…”

“…For example, the aforementioned INF composed of [EMIM][OAc] + 5 wt % GNPs showed the highest thermal conductivity increase with a simultaneous isobaric heat capacity decrease. 23 Generally, the literature reports are not consistent, often contradictory, and indicate that the addition of nanoparticles to the base IL caused both an increase 4 , 35 − 38 and a decrease 39 , 40 or no influence on the isobaric heat capacity of INFs. 41 …”

Effect of ultrasonication time on microstructure, thermal conductivity, and viscosity of ionanofluids with originally ultra-long multi-walled carbon nanotubes

“…There is little literature on the influence of ultrasound treatment conditions on the microstructure as well as thermal and rheological properties of INFs. Most of the research in the field was carried out under constant sonication settings [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] . The notable exceptions were works of Wittmar et al [32] , [33] , who investigated rheological properties of INFs containing 0.5 wt% 95% anatase TiO 2 with average particle size 5 nm or 100% anatase TiO 2 with average particle size from 5 to 26.4 nm and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Emim][NTf 2 ], 1-ethyl-3-methylimidazolium tetrafluoroborate [Emim][BF 4 ], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF 4 ], or 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF 4 ], prepared with various sonication times up to 4 h. They concluded that the rheological behavior of nanodispersions was complex and depended on the type of IL.…”

Performance of Ionic Liquid-Water Mixtures in an Acetone Cooling Application

“…Minea [3] reported the properties of ionic liquids and noted that experimental studies are critical to establish a complete understanding of the behavior of ionic liquids. Zhang et al [4] considered ionic liquids as a potential absorbent in absorption refrigeration system. Thermal stability and thermal properties were all investigated at varying mass fractions.…”