Limits...
Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment.

Ramesh G, Prabhu NK - Nanoscale Res Lett (2011)

Bottom Line: Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics.Further water-based nanofluids are environment friendly as compared to mineral oil quench media.These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Srinivasnagar, Mangalore, India. prabhukn_2002@yahoo.co.in.

ABSTRACT
The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment.

No MeSH data available.


Related in: MedlinePlus

Surface hardness profile calculated from the measured wetting time tB and the specific calibration curve for the material related to the distance from the lower end of the sample and compared to the measured hardness profile. Sample: 100Cr6 dia 25 mm × 100 mm, bath: (a) distilled water, (b) polymer solution.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211422&req=5

Figure 5: Surface hardness profile calculated from the measured wetting time tB and the specific calibration curve for the material related to the distance from the lower end of the sample and compared to the measured hardness profile. Sample: 100Cr6 dia 25 mm × 100 mm, bath: (a) distilled water, (b) polymer solution.

Mentions: During quenching, the local boiling phenomenon of quenchant leads to occurrence of a wetting front which ascends the cooling surface with a significant velocity during nucleate boiling and descends in the fluid direction during film boiling. A wetting process that occurs over a long time period of time is called non-Newtonian wetting, whereas a wetting process that occurs in a short time period or an explosion-like wetting process is termed as Newtonian wetting. A Newtonian type of wetting usually promotes uniform heat transfer and minimizes the distortion and residual stress development. In extreme cases of non-Newtonian wetting, because of large temperature differences, considerable variations in the microstructure and residual stresses are expected, resulting in distortion and the presence of soft spots [1]. Tensi has shown that the measured values indicate congruent curves for calculated hardness sample quenched in the distilled water and the total wetting time measured at the top of the sample was more than 60 s, whereas the measured hardness profile shows a continuous line in the case of sample quenched in the polymer solution having total wetting time of 1.5 s (Figure 5) [2]. Thus, the type of the wetting process significantly affects the cooling behaviour of the quenchant and hardness profile of the quenched samples. Vafaei et al. measured the contact angle of nanofluid sessile droplets and showed that the contact angle depends strongly on nanoparticle concentration and for the same mass concentration smaller size nanoparticles lead to larger changes in contact angle [110]. Sefiane et al. observed that advancing contact line velocity increases to a maximum as the concentration increases up to 1% and then decreases as the concentration is increased further. They explained that the enhanced wetting is attributed to a pressure gradient within the nanofluid which is created due to the nanoparticles forming a solid-like ordering in the fluid 'wedge' in the vicinity of the three-phase contact line and agglomeration of nanoparticles at higher concentration reduces the degree of enhanced wetting [106]. The surface wettability study by Kim et al. measured the static contact angle of sessile droplets for pure water and nanofluids on clean surfaces and nanoparticle-fouled surfaces. They found dramatic decrease of the contact angle on the fouled surfaces and concluded that the wettability was enhanced by the porous layer on the surface, not the nanoparticles in the fluid [111]. Another study by Mehta and Khandekar measured static contact angles of sessile droplets showed that the wettability of laponite nanofluid on copper substrate was indeed much better than both alumina nanofluid and pure water [112]. These studies imply that the use of nanoparticles in the conventional quenching media would result in enhancement of wettability. The enhanced wetting characteristics of nanofluids can be adopted to promote the Newtonian wetting and improve the spreading process during quench heat treatment of components.


Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment.

Ramesh G, Prabhu NK - Nanoscale Res Lett (2011)

Surface hardness profile calculated from the measured wetting time tB and the specific calibration curve for the material related to the distance from the lower end of the sample and compared to the measured hardness profile. Sample: 100Cr6 dia 25 mm × 100 mm, bath: (a) distilled water, (b) polymer solution.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211422&req=5

Figure 5: Surface hardness profile calculated from the measured wetting time tB and the specific calibration curve for the material related to the distance from the lower end of the sample and compared to the measured hardness profile. Sample: 100Cr6 dia 25 mm × 100 mm, bath: (a) distilled water, (b) polymer solution.
Mentions: During quenching, the local boiling phenomenon of quenchant leads to occurrence of a wetting front which ascends the cooling surface with a significant velocity during nucleate boiling and descends in the fluid direction during film boiling. A wetting process that occurs over a long time period of time is called non-Newtonian wetting, whereas a wetting process that occurs in a short time period or an explosion-like wetting process is termed as Newtonian wetting. A Newtonian type of wetting usually promotes uniform heat transfer and minimizes the distortion and residual stress development. In extreme cases of non-Newtonian wetting, because of large temperature differences, considerable variations in the microstructure and residual stresses are expected, resulting in distortion and the presence of soft spots [1]. Tensi has shown that the measured values indicate congruent curves for calculated hardness sample quenched in the distilled water and the total wetting time measured at the top of the sample was more than 60 s, whereas the measured hardness profile shows a continuous line in the case of sample quenched in the polymer solution having total wetting time of 1.5 s (Figure 5) [2]. Thus, the type of the wetting process significantly affects the cooling behaviour of the quenchant and hardness profile of the quenched samples. Vafaei et al. measured the contact angle of nanofluid sessile droplets and showed that the contact angle depends strongly on nanoparticle concentration and for the same mass concentration smaller size nanoparticles lead to larger changes in contact angle [110]. Sefiane et al. observed that advancing contact line velocity increases to a maximum as the concentration increases up to 1% and then decreases as the concentration is increased further. They explained that the enhanced wetting is attributed to a pressure gradient within the nanofluid which is created due to the nanoparticles forming a solid-like ordering in the fluid 'wedge' in the vicinity of the three-phase contact line and agglomeration of nanoparticles at higher concentration reduces the degree of enhanced wetting [106]. The surface wettability study by Kim et al. measured the static contact angle of sessile droplets for pure water and nanofluids on clean surfaces and nanoparticle-fouled surfaces. They found dramatic decrease of the contact angle on the fouled surfaces and concluded that the wettability was enhanced by the porous layer on the surface, not the nanoparticles in the fluid [111]. Another study by Mehta and Khandekar measured static contact angles of sessile droplets showed that the wettability of laponite nanofluid on copper substrate was indeed much better than both alumina nanofluid and pure water [112]. These studies imply that the use of nanoparticles in the conventional quenching media would result in enhancement of wettability. The enhanced wetting characteristics of nanofluids can be adopted to promote the Newtonian wetting and improve the spreading process during quench heat treatment of components.

Bottom Line: Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics.Further water-based nanofluids are environment friendly as compared to mineral oil quench media.These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Srinivasnagar, Mangalore, India. prabhukn_2002@yahoo.co.in.

ABSTRACT
The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment.

No MeSH data available.


Related in: MedlinePlus