Titan C. Paul

Enhanced Thermal Performance of Ionic Liquid-Al2O3 Nanofluid as Heat Transfer Fluid for Solar Collector

Next generation Concentrating Solar Power (CSP) system requires high operating temperature and high heat storage capacity heat transfer fluid (HTF), which can significantly increase the overall system efficiency for power generation. In the last decade several research going on the efficacy of ionic liquids (ILs) as a HTF in CSP system. ILs possesses superior thermophysical properties compare to currently using HTF such as Therminol VP-1 (mixture of biphenyl and diphenyl oxide) and thermal oil. However, advanced thermophysical properties of ILs can be achieved by dispersing small volume percentage of nanoparticles forming nanofluids, which is called Nanoparticle Enhanced Ionic Liquids (NEILs). In the present study NEILs were prepared by dispersing 0.5% Al2O3 nanoparticles (spherical and whiskers) in N-butyl-N, N, N-trimetylammonium bis(trifluormethylsulfonyl)imide ([N4111][NTf2]) IL. Viscosity, heat capacity and thermal conductivity of NEILs were measured experimentally and compared with the existing theoretical models for liquid–solid suspensions. Additional, the convective heat transfer experiment was performed to investigate thermal performance. The thermal conductivity of NEILs enhanced by ∼5%, heat capacity enhanced by ∼20% compared to the base IL, which also gives 15% enhancement in heat transfer performance.Copyright

Heat Transfer and Flow Behavior of Nanoparticle Enhanced Ionic Liquids (NEILs)

Experimental investigations were carried out to characterize forced convection behavior of Nanoparticle Enhanced Ionic Liquids (NEILs). 1-butyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl} imide ([C4mim][NTf2]) was used as the base ionic liquid (IL) with 0.5% (weight%) loading of Al2O3 nanoparticles. Flow experiments were conducted in a circular tube in the laminar flow regime. Convection results from IL without nanoparticles were used as the base line data for comparison with convection results with NEIL. Viscosity and thermal conductivity of the NEIL and base IL were also measured. NEIL displayed superior thermal performance compared to the base IL. An average of 13% enhancement in heat transfer coefficient was found for the NEIL compared with that of the base IL. Probable reasons of these enhancements are discussed in the paper.Copyright

Effect of Cross Groove on Flow Boiling in a Microgap

Flow boiling performance of a microgap channel has been investigated experimentally. Experimental studies were carried out on a bottom surface heated single microgap channel having 5×0.372 mm cross sectional area using DI water as coolant. Four rectangular grooves were cut along the flow direction and surface morphology of the microgrooves was modified by depositing ZnO nanoparticles from a nanofluid using electrophoresis deposition technique. Flow boiling experiments were conducted for different mass flux. The results from the microgap channel having no cross grooves have been used as the baseline data. Cross grooves have been found effective in reducing boiling incipience temperature and enhancing heat transfer coefficient. Up to 50% enhancement in two-phase heat transfer coefficient was observed for the cross groove. Nanoparticles deposition reduces boiling incipient temperature but does not show any significant effect on two-phase heat transfer coefficient.Copyright

Natural Convection in Rectangular Cavity With Nanoparticle Enhanced Ionic Liquids (NEILs)

A systematic natural convection heat transfer experiment has been carried out of nanoparticle enhanced ionic liquids (NEILs) in rectangular enclosures (lengthxwidthxheight, 50×50×50mm and 50×50×75mm) heated from below condition. In the present experiment NEIL was made of N-butyl-N-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl} imide, ([C4mpyrr][NTf2]) ionic liquid with 0.5% (weight%) Al2O3 nanoparticles. In addition to characterize the natural convection behavior of NEIL, thermophysical properties such as thermal conductivity, heat capacity, and viscosity were also measured. The result shows that the thermal conductivity of NEIL enhanced ∼3% from the base ionic liquid (IL), heat capacity enhanced ∼12% over the measured temperature range. The natural convection experimental result shows consistent for two different enclosures based on the degrading natural convection heat transfer rate over the measured Rayleigh number range. Possible reasons of the degradation of natural convection heat transfer may be the relative change of the thermophysical properties of NEIL compare to the base ionic liquid.Copyright

Numerical investigation of natural convection of nanoparticle enhanced ionic liquids (NEILs) in enclosure heated from below

The paper presents the numerical simulation of natural convection heat transfer of Al2O3 nanoparticle enhanced N-butyl-N-methylpyrrolidinium bis{trifluoromethyl)sulfonyl} imide ([C4mpyrr][NTf2]) ionic liquid. The simulation was performed in three different enclosures (aspect ratio: 0.5, 1, and 1.5) with heated from below. The temperature dependent thermophysical properties of base ionic liquids (ILs) and nanoparticle enhanced ionic liquids (NEILs) were applied in the numerical simulation. The numerical results were compared with the experimental result. The numerical results show that at a certain Rayleigh number NEILs has a lower Nusselt number compared to the base IL which are consistent with the experimental results. But the percentage of degradation is much less on the numerical results compared to the experimental. However the numerical results match well with the predicted model of using thermophysical properties of NEILs. From these observations it can be concluded that the extra degradation in the...

Enhancement of Heat Transfer Performance in Nuclear Fuel Rod Using Nanofluids and Surface Roughness Technique

The experimental investigations were carried out of a pressurized water nuclear reactor (PWR) with enhanced surface using different concentration (0.5 and 2.0 vol%) of ZnO/DI-water based nanofluids as a coolant. The experimental setup consisted of a flow loop with a nuclear fuel rod section that was heated by electrical current. The fuel rod surfaces were termed as two-dimensional surface roughness (square transverse ribbed surface) and three-dimensional surface roughness (diamond shaped blocks). The variation in temperature of nuclear fuel rod was measured along the length of a specified section. Heat transfer coefficient was calculated by measuring heat flux and temperature differences between surface and bulk fluid. The experimental results of nanofluids were compared with the coolant as a DI-water data. The maximum heat transfer coefficient enhancement was achieved 33% at Re = 1.15 × 105 for fuel rod with three-dimensional surface roughness using 2.0 vol% nanofluids compared to DI-water.Copyright

Natural Convection of Heat Transfer Fluid (Therminol VP-1) in Square Cavity Heated From Below

Heat transfer fluid (HTF) plays an important role in the efficiency and cost effectiveness of solar thermal collector. From several choices, Therminol VP-1 (eutectic mixture of diphenyl oxide and biphenyl) are successfully used as heat transfer fluid in the collector field of parabolic trough plants. This paper experimentally analyzes the buoyancy driven heat transfer performance of Therminol VP-1 in a square enclosure with uniformed heating from below and for a Rayleigh number up to 1.11×108. Thermophysical properties such as density, viscosity, and thermal conductivity of Therminol VP-1 were also measured experimentally. The results show that the density, viscosity, and thermal conductivity decrease with temperature within the measured temperature range 10–60°C. The obtained convective heat transfer coefficient was lower than the De-Ionized (DI) water, whereas the dimensionless Nusselt number was observed higher than DI water, which is because of the low thermal conductivity (approximately 25% of DI water) of Therminol VP-1.Copyright

Numerical Investigation of Natural and Forced Convection of Ionic Liquids

The paper focused on the numerical simulation of natural and forced convection of N-butyl-N-methylpyrrolidinium bis{trifluoromethyl)sulfonyl} imide ([C4mpyrr][NTf2]), ionic liquids (ILs). For natural convection heated from below in a square enclosure and forced convection flow through a pipe with uniform heat flux condition was considered. In numerical simulation the dimensions of the natural convection enclosure and forced convection tube are considered same as the experimental setup. Both constant and temperature dependent thermophysical properties of ILs are applied in forced convection and only temperature dependent properties are applied in natural convection simulation. The temperature dependent thermophysical properties such as density, viscosity, thermal conductivity, and heat capacity of ILs are measured experimentally. Higher accuracy was observed for temperature dependent models. The numerical results were compared with the experimental data of natural and forced convection, reported reasonably good agreements between experimental and numerical results.Copyright

Flow Boiling Characteristics of Dilute Emulsion in Microchannel

Effect of dispersed low boiling point liquid on flow boiling performance of DI water in a microchannel has been investigated experimentally. Experiments were carried out in a single microchannel having hydraulic diameter 672 μm and also in a parallel microchannel having hydraulic diameter of each channel 500 μm. Emulsion was prepared by dispersing FC-72 in de-ionized (DI) water. Both single-phase and two-phase convective heat transfer experiments were performed at different flow rates for different volume fraction of the dispersing liquid. Results from the pure DI water were used as the base line data. It was found that presence of the dispersed low boiling point liquid doesn’t show any significant effect in two-phase convective flow, whereas in single-phase region HTC decreases marginally. Temperature gradient present along the axial direction of the microchannel was observed to reduce for the emulsion compared to the pure DI water.Copyright

Nanostructures Length Effect on Phase Transition Phenomena of Ultra-Thin Liquid Film From a Nanostructured Surface: A Molecular Dynamics Study

A molecular dynamics simulation has been employed to investigate the boiling phenomena of few molecular-layer thin liquid-film adsorbed on a nanoscale roughened solid surface. The molecular system comprises of three phase system: solid platinum wall, liquid argon and argon vapor. A few layer of liquid argon has been placed on the nanoposts decorated solid surface where nanoposts ensemble surface roughness. Nanoposts height has been varied keeping liquid film thickness constant to capture three scenario: (i) Liquid-film thickness is higher than the height of the nanoposts (ii) Liquid-film and nanoposts are of same height (iii) Liquid-film thickness is less than the height of the nanoposts. Rest of the simulation box space has been filled with argon vapor. The simulation starts from the equilibrium three phase system and then suddenly the wall is heated to a higher temperature which resembles an ultra fast laser heating. Two different jump temperatures has been selected: one is a few degrees above the boiling point to initiate normal evaporation and the other one is far above the critical point temperature to initiate explosive boiling. Simulation results indicate nanostructures play significant role in both the cases. Argon responds very quickly in the nanoposts decorated surface and evaporation rate increases with the nanoposts height. Different boiling behavior has been observed for the nanoposts decorated surface.Copyright