Faculty Publications
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Item Heat transfer during immersion quenching in MWCNT nanofluids(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Nayak, U.; Prabhu, K.Quench heat treatment consists of rapid cooling of steel alloys after austenetization by subjecting them to cooling in a suitable cooling medium. At the heart of quench treatment is the transient heat transfer that occurs between the metal surface and the quenchant at their interface. This governs the quality of the component as it influences phase transformation, residual quench stresses and mechanical properties developed. In the present research work, spatially dependent transient heat flux in the axial direction was estimated using cooling curve analyses coupled with inverse heat conduction technique. A standard Inconel 600 probe instrumented with multiple thermocouples and heated to 865°C was quenched in distilled water (DW) and DW based multi walled carbon nanotubes (MWCNT) quench media. For evaluating the cooling performance, nanoquenchants with concentrations of 0.01, 0.1 and 1.0g/lt. were prepared. The cooling rate curve calculated from the measured temperature at the geometric center of the probe and the estimation of spatially dependent heat fluxes showed that the heat extraction during quenching with MWCNT nanoquenchant (0.1g/lt.) was higher than the other quenchants. The measured values of thermal conductivity and viscosities of quenchants did not show any significant variation. © (2015) Trans Tech Publications, Switzerland.Item Heat transfer during quenching of modified and unmodified gravity die-cast A357 cylindrical bars(2006) Prabhu, K.; Hemanna, P.Heat transfer during quenching of chill-cast modified and unmodified A357 Al-Si alloy was examined using a computer-aided cooling curve analysis. Water at 60°C and a vegetable oil (palm oil) were used as quench media. The measured temperatures inside cylindrical probes of the A357 alloy were used as inputs in an inverse heat-conduction model to estimate heat flux transients at the probe/quenchant interface and the surface temperature of the probe in contact with the quench medium. It was observed that modified alloy probes yielded higher cooling rates and heat flux transients. The investigation clearly showed that the heat transfer during quenching depends on the casting history. The increase in the cooling rate and peak heat flux was attributed to the increase in the thermal conductivity of the material on modification melt treatment owing to the change in silicon morphology. Fine and fibrous silicon particles in modified A357 probes increase the conductance of the probe resulting in higher heat transfer rates. This was confirmed by measuring the electrical conductivity of modified samples, which were found to be higher than those of unmodified samples. The ultrasound velocity in the probes decreased on modification. ©ASM International.Item Dimensionless cooling performance parameter for characterization of quench media(2013) Ramesh, G.; Prabhu, K.The effect of varying thermal properties and boundary heat transfer coefficients on temperature profiles inside cylindrical quench probes was simulated during immersion cooling. The results of simulation indicated that, for assessment of the cooling performance of the quench media, the ratio of the quench probe diameter to its thermal conductivity should be less than 0.0005 m2K/W. A simple dimensionless cooling parameter (D 2CR/??T) was proposed to assess the cooling performance of quench media. © 2013 The Minerals, Metals & Materials Society and ASM International.Item Effect of thermal conductivity and viscosity on cooling performance of liquid quench media(Maney Publishing Suite 1C, Joseph's Well, Hanover Walk Leeds LS3 1AB, 2014) Ramesh, G.; Prabhu, K.In this present work, the effect of the thermophysical properties of quenchants on its cooling performance was investigated. Water, brine solutions, polymer solutions and mineral oils were chosen to have quench media with varying thermophysical properties. Cooling curve analyses were carried out by using standard ISO/DIS 9950 quench probe. Grossmann H quench severity of the quench media was determined from the relation of H and cooling rate. Cooling curve analysis results showed that the change in thermophysical properties of the quench media had significant effect on the cooling history of the quench probe. The viscosity of the quenchant used for immersion quenching is the most important factor that controls the cooling performance of the quenchant compared to thermal conductivity of the quench medium. © 2014 IHTSE Partnership.Item Cooling performance of select mineral oil and polymer quenchants(ASTM International, 2014) Tiwary, V.; Prabhu, K.In the present investigation, quench severity was determined for industrial oil quenchants and varying concentrations of PAG polymer. Viscosity, thermal conductivity, density, flash point, and fire point were measured for all quenchants. Cooling curve parameters were determined based on cooling curve analysis ISO/DIS 9950 technique. An Inconel 600 probe was used for this purpose. Severity of quenching was determined based on the Grossmann technique. Viscosity and thermal conductivity had a significant effect on quench severity. Heat flux and HTC at the metal/quenchant interface were computed by both lumped capacitance and Inverse modeling techniques. The effect of ultrasonic and Tensi agitation on cooling curve parameters was assessed. Polymer quenchants of lower concentrations showed marginally higher heat transfer rates compared to water particularly during unagitated condition. © © 2014 by ASTM International.Item Heat transfer and quench performance of aqueous CuO nanofluids during immersion quenching(Inderscience Publishers, 2016) Nayak, U.; Prabhu, K.The present work involves the assessment of quench performance of aqueous-copper oxide nanofluids. Distilled water-based copper oxide nanofluids of concentrations 0.01, 0.05, 0.1 and 1.0 vol.% were prepared by a two-step process. Cooling curves analysis was carried out using an inconel probe that was instrumented with thermocouples. The recorded temperature data during experiments was used to estimate spatiotemporal heat flux transients by solving inverse heat conduction problem. Quenching of probe in nanofluids resulted in longer vapour phase stage duration compared to distilled water. The addition of nanoparticles altered the peak flux and the time of its occurrence. Rewetting temperatures were found to be lower for nanofluids. The measured thermal conductivities and viscosities showed similar values for all quench media. © 2016 Inderscience Enterprises Ltd.