Faculty Publications

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Subject: search.filters.subject.Nanofluids

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    Severity of quenching and kinetics of wetting of nanofluids and vegetable oils
    (ASTM International, 2010) Jagannath, V.; Prabhu, K.N.
    In the present work, the suitability of vegetable oil blends with mineral oil and alumina based nanofluids as quench media for industrial heat treatment was investigated. Sunflower oil, palm oil, and mineral oil were used for preparing the blends. Alumina based nanofluids of varying concentrations ranging from 0.01-4 % were used. The size of alumina particles was about 50 nm. The severity of quenching and heat transfer coefficients were estimated during quenching of copper probes. Heat transfer coefficients were estimated using a lumped heat capacitance model. The static contact angle was measured on copper substrates having a surface texture similar to the probes used for estimation of heat transfer coefficients. A dynamic contact angle analyzer was used for this purpose. The measured contact angles of nanofluids on copper were high compared to oils, indicating poor wetting by quench media that are polar in nature. Wetting characteristics had a significant effect on heat transfer coefficients estimated during quenching. Copyright © 2009 by ASTM International.
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    Replacement of heat sink fan by nanocoolants for enhancement of CPU efficiency
    (Institution of Engineering and Technology journals@theiet.org, 2013) Siddique, A.B.; Prabhu, K.N.
    The highest temperature under which a CPU can operate without interruption is 90°C. Heat sink fans generally provided for removal of heat produced by the processor are proved to be inadequate when CPU usage is 100%. The objective of this work is to exploit the enhanced thermal properties of nanofluid for dissipation of heat from the Intel (R) Core (TM) i5- 2310 CPU @ 2.9GHz quad-core processor for cooling it to a suitable operating temperature. Nanocoolants were prepared with two types of nanoparticles, titania and copper. The volume percentage of nanoparticles in nanocoolants were 0.01 and 0.1. It was observed that nanofluids are more efficient coolants than the base fluid and found to be significantly better than the traditional heat sink fan, as indicated by the CPU temperature, under the same loading condition. The average CPU temperatures were 90°C, 58°C, 56.6°C and 54.5°C with heat sink fan, deionized water, 0.1 vol% TiO2 and 0.1 vol% Cu nanofluids respectively at the flow rate of 700ml/min and CPU usage of 100%. The lowest CPU operating temperature (54.5°C) was obtained with 0.1 vol% Cu at the flow rate of 700ml/min. The cooling of CPU was also affected by the flow rate and the volume fraction of nanoparticles in the nanocoolant.
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    Experimental and numerical investigation on conjugate effects in deep parallel microchannel using tio2 nanofluid for electronic cooling
    (Dalian University of Technology, 2018) Narendran, G.; Gnanasekaran, N.; Arumuga Perumal, D.A.
    The present study reports the numerical investigation of laminar forced convection based on TiO2 nanofluid in a rectangular copper microchannel surrounded by Aluminium block to examine the cooling effects for increased flow rates and particle concentration. The analysis involves the use of pure fluid and TiO2 nanofluid with the volume fractions of 0.01, 0.15, 0.20 and 0.25% for different flow rates. The study also examines the influence of conjugate heat transfer behavior of the microchannel using commercially available software FLUENT-15. © 2018 by the authors of the abstracts.
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    A review on recent advances in microchannel heat sink configurations
    (Bentham Science Publishers, 2018) Narendran, G.; Gnanasekaran, N.; Arumuga Perumal, D.A.
    A qualitative observation has been undergone to review the various geometries of a microchannel that has been reported for the last two decades in literature majorly for the application of high power devices. Recent research on microchannel is more focused on numerical and experimental work with various configurations of the heat sink. In this paper, a comparative work on different flow geometries used in the microchannel and their influence on heat transfer and pressure drop is investigated with the brief representation of different working fluids used in microchannel heat sink for the purpose of electronic cooling and their associated performance characteristics with various examined parameters. Background: The microchannel cooling is an established cooling technique for high power electronic components which effectively enhances the performance of the high power devices. Objective: This article presents a general overview of microchannels with novel constructional bifurcations structures with related patents. Further, the influential parameter on thermal and flow characteristics with greater depth is also reviewed by authors. Methods: This review directs by presenting standard and benchmark investigation in the microchannel and different working parameters continued with recent studies. Further, it is addressed with the application of electronic cooling with latest patents using bifurcations and fractal microchannels. Result: The current situation of 3D cooling requires a robust cooling system to accommodate increased heat flux without compromising the packaging. Moreover, the recently developed patents also evolved with improved thermal load handling under constrained packaging. Conclusion: The advanced microchannel cooling with an optimized fluid handling system with effective packaging results in a highly effective heat dissipation system. © 2018 Bentham Science Publishers.
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    Severity of quenching and kinetics of wetting of nanofluids and vegetable oils
    (2009) Jagannath, V.; Prabhu, K.N.
    In the present work, the suitability of vegetable oil blends with mineral oil and alumina based nanofluids as quench media for industrial heat treatment was investigated. Sunflower oil, palm oil, and mineral oil were used for preparing the blends. Alumina based nanofluids of varying concentrations ranging from 0.01-4 % were used. The size of alumina particles was about 50 nm. The severity of quenching and heat transfer coefficients were estimated during quenching of copper probes. Heat transfer coefficients were estimated using a lumped heat capacitance model. The static contact angle was measured on copper substrates having a surface texture similar to the probes used for estimation of heat transfer coefficients. A dynamic contact angle analyzer was used for this purpose. The measured contact angles of nanofluids on copper were high compared to oils, indicating poor wetting by quench media that are polar in nature. Wetting characteristics had a significant effect on heat transfer coefficients estimated during quenching. Copyright © 2009 by ASTM International.
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    Critical heat flux enhancement in pool boiling using alumina nanofluids
    (2010) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
    The pool boiling characteristics of dilute dispersions of alumina nanoparticles in water were studied. Consistent with other nanofluid studies, it was found that a significant enhancement in critical heat flux (CHF) can be achieved at modest nanoparticle concentrations (<0.1% by volume). During experimentation and subsequent inspection, formation of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly changes surface texture of the heater wire surface which could be the reason for improvement in the CHF value. © 2010 Wiley Periodicals, Inc.
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    Role of surface roughness in pool boiling with Alumina-water nanofluid on a horizontal wire surface
    (International Information and Engineering Technology Association, 2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
    Boiling heat transfer is one of the major phenomenon which of late, has drawn the attention of many researchers and scientists throughout the world. With nanofluids, further boost is given in heat transfer enhancement. This research paper is the study of heat transfer enhancement using Alumina nanofluid in different volume concentrations ranging from 1 to 9%. The role of surface roughness on critical heat flux enhancement (CHF) in pool boiling with nanofluids was experimentally studied using a 36 gauge NiCr wire at atmospheric pressure. Experimentation included i) investigations on boiling heat transfer subjecting the wire surface to Alumina nanofluid at higher volume concentrations and ii) investigations on surface roughness due to surface coating, subjecting the wire surface to a single heating cycle with different volume concentrations of Alumina nanofluid. Boiling of nanofluid resulted in nanoparticle deposition and subsequent roughning of the wire surface. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by studying the surface roughness and SEM images of the wire surface. The experimental results show the evidence of nanoparticle deposition on the wire surface and its effect on CHF enhancement and deterioration in pool boiling heat transfer.
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    Enhancement of heat transfer characteristics of transformer oil by addition of aluminium nanoparticles
    (2011) Rajesh, E.; Prabhu, K.N.
    A two step approach involving the synthesis of Al nanoparticles by mechanical milling followed by dispersion of the nanoparticles in the base fluid is adopted in the present work to prepare transformer oil based nanofluids. Stainless steel (AISI 304) probes of diameter 15 mm and height 70 mm were used to determine the cooling rate intensities of nanofluids. Heat transfer coefficients were determined using Kobasko's method. A dynamic contact angle analyzer was used to determine the contact angle of the droplet on the substrate. The addition of Al nanoparticles to the base fluid decreases the wettability and improves its heat transfer capability. The vapour phase stage existed for a longer period of time for transformer oil than for Al-transformer oil based nanofluids. The dispersion of nanoparticles in the base fluid is believed to disrupt the vapour blanket stage in the early stage of the cooling process. The peak heat transfer coefficient increases with an increase in the Al nanoparticle content in the oil. The addition of 0.5 vol % nanoparticles enhances the peak heat transfer coefficient by about 70 %. Copyright © 2011 by ASTM International.
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    Comparison of Grossmann and lumped heat capacitance methods for assessment of heat transfer characteristics of quench media
    (2011) Prabhu, K.N.; Ali, I.
    The suitability of Grossmann and lumped heat capacitance (LHC) methods for estimation of quench severity of nanofluids, brine solutions and a laboratory detergent based medium was investigated. The study involved the assessment of the effect of section thickness of the probe on heat transfer coefficients for different quench media. Computer aided cooling curve analysis during quenching of type 304 stainless steel probes was carried out. The measured thermal history data were used to estimate heat transfer coefficients by Grossmann and LHC methods. The LHC method based on a 10 mm diameter stainless steel probe was found to be applicable for characterising media having quench severity less than 20 m-1. Although Grossmann method is based on the concept of average heat transfer coefficient, it can be used for quench media having varying severity of quenching. Grossmann method is found to be more sensitive to the effect of section thickness on heat transfer. © 2011 IHTSE Partnership.
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    Behavioral study of alumina nanoparticles in pool boiling heat transfer on a vertical surface
    (2011) Hegde, R.N.; Reddy, R.P.; Rao, S.S.
    Experiments were carried out to investigate the pool boiling of alumina-water nanofluid at 0.1 g/l to 0.5 g/l of distilled water, and the nucleate pool boiling heat transfer of pure water and nanofluid at different mass concentrations were compared at and above the atmospheric pressure. At atmospheric pressure, different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer. The effect of pressure and concentration of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. The heat transfer coefficient of 0.5 g/l alumina-water nanofluid was compared with pure water and clearly indicates deterioration. At all pressures the heat transfer coefficients of the nanofluid were lower than those of pure water. Experimental observation revealed particles coating over the heater surface and subsequent SEM inspection of the heater surface showed nanoparticles coating on the surface forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, investigation was done by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, surface roughness of the heater surface confirmed it. Based on the experimental investigations it can be concluded that an optimum thickness of nanoparticles coating favors an increase in heat flux. Higher surface temperature due to the presence of nanoparticles coating results in the deterioration of boiling heat transfer. © 2011 Wiley Periodicals, Inc.