Faculty Publications
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Item 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.Item Effect of modification melt treatment and chilling on eutectic arrest temperature and time during solidification of A357 alloy(2011) Prabhu, K.N.; Hegde, S.Thermal analysis technique has been recognised as an efficient non-destructive tool to assess the degree of modification in Al-Si alloys. Apart from chemical modification, chilling refines the microstructure. This is particularly significant as majority of Al-Si alloys are cast in metallic moulds. In the present study, the interaction between chilling and modification melt treatment is investigated to assess their effect on thermal analysis parameters using computer aided cooling curve analysis. For modified alloys, the depression of the eutectic arrest temperature was significant at higher cooling rates. The eutectic arrest temperature and time were correlated with the cooling rate using a power law. High cooling regime in thermal analysis plots was attributed to the combined effect of chilling and modification melt treatment on heat transfer. © 2011 Institute of Materials, Minerals and Mining.Item A dimensional parameter for prediction of cooling performance of quenchants(ASTM International, 2014) Prabhu, K.; Ramesh, G.Computer aided cooling curve analysis was carried out during immersion quenching of ISO/DIS 9950 quench probe. Water, brine solutions, polymer solutions, mineral oils, and vegetable oils were used as quench media. The results showed that the quench medium used had a significant effect on the quench probe cooling curve parameters. An empirical correlation was proposed to predict the average cooling rate from surface tension, wetting angle, thermal conductivity, and kinematic viscosity of the quench medium. © 2014 by ASTM International.Item A Computer Aided Cooling Curve Analysis method to study phase change materials for thermal energy storage applications(Elsevier Ltd, 2016) Sudheer, R.; Prabhu, K.N.The suitability of a simple Computer Aided Cooling Curve Analysis (CACCA) technique for characterizing thermal energy storage phase change materials (PCM) was proposed in the present work. Two modes of CACCA, namely, Newtonian and Fourier techniques were used to predict the phase transition temperatures, the latent heat of fusion and thermal diffusivities of PCMs. Solidification of potassium nitrate and zinc-8% aluminium alloy (ZA8) was studied using CACCA method. These PCMs were chosen to demonstrate the ability of the proposed technique to characterize PCMs freezing at a single temperature as well as over a range of temperatures. CACCA method showed that potassium nitrate and ZA8 are suitable candidate materials for TES applications operating at 300-350 °C and 350-450 °C respectively. © 2015 Elsevier Ltd.Item Cooling Curve Analysis of Micro- and Nanographite Particle-Embedded Salt-PCMs for Thermal Energy Storage Applications(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Sudheer, R.; Prabhu, K.N.In recent years, the focus of phase change materials (PCM) research was on the development of salt mixtures with particle additives to improve their thermal energy storage (TES) functionalities. The effect of addition of microsized (50 ?m) and nanosized (400 nm) graphite particles on TES parameters of potassium nitrate was analyzed in this work. A novel technique of computer-aided cooling curve analysis was employed here to study the suitability of large inhomogeneous PCM samples. The addition of graphite micro- and nanoparticles reduced the solidification time of the PCM significantly enhancing the heat removal rates, in the first thermal cycle. The benefits of dispersing nanoparticles diminished in successive 10 thermal cycles, and its performance was comparable to the microparticle-embedded PCM thereafter. The decay of TES functionalities on thermal cycling is attributed to the agglomeration of nanoparticles which was observed in SEM images. The thermal diffusivity property of the PCM decreased with addition of graphite particles. With no considerable change in the cooling rates and a simultaneous decrease in thermal diffusivity, it is concluded that the addition of graphite particles increased the specific heat capacity of the PCM. It is also suggested that the additive concentration should not be greater than 0.1% by weight of the PCM sample. © 2017, ASM International.Item Characterization of metals and salts-based thermal energy storage materials using energy balance method(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2019) Agarwala, S.; Prabhu, N.K.Thermal energy storage technologies minimize the imbalance between energy production and demand. In this context, latent heat storage materials are of great importance as they have a higher density of energy storage as compared with the sensible heat storage materials. The present study involves the characterization of energy storage materials using an energy balance cooling curve analysis method. The method estimates the convective heat transfer coefficient in the solidification range to characterize the phase change materials for applications in energy storage. The method is more beneficial than the Computer Aided Cooling Curve analysis methods as it eliminates baseline calculations and the associated fitting errors. Metals (Sn) and salts (KNO3 and NaNO 3) were used in the present work. Phase change characteristics like the rate of cooling, liquidus and solidus temperatures, time for solidification, and enthalpy of phase change were estimated for both metals and salts. It was observed that the energy balance cooling curve analysis method worked very well for metals but not well suited for low conductivity salts. Salts could not be characterized since the thermal gradient existing within the salt sample was not considered in this method. © 2019 Wiley Periodicals, Inc.Item An experimental approach based on inverse heat conduction analysis for thermal characterization of phase change materials(Elsevier B.V., 2020) Agarwala, S.; Prabhu, K.N.A new method based on solution to inverse heat conduction problem for the assessment of solidification parameters of PCM salts has been proposed. The method estimates the mold -salt interfacial heat flux and it is used to calculate the latent heat of salt PCMs using calorimetry based energy balance equations. This method is more accurate compared to Computer Aided Cooling Curve Analysis (CACCA) techniques as it eliminates the drawbacks involved with base line fitting calculations and errors introduced due to the improper selection of solidification points. Pure salt PCMs such as KNO3 and solar salt were used for the validation of this technique. Both air and furnace cooling were adopted to demonstrate the effect of cooling rate on solidification characteristics. The wettability of salt samples on mild steel surface was analyzed to account for the difference in the thermal behavior of salts. © 2020 Elsevier B.V.Item Understanding Solidification Behavior of Salt Phase Change Material with Added Carbon Nanoparticles Using Computer-Aided Cooling Curve Analysis(Springer, 2022) R, S.; K.n, P.In recent years, nanoparticle-dispersed salt-based phase change materials (PCMs) have emerged to be suitable for thermal energy storage applications. In this work, the carbon nanostructures of graphite, multiwall carbon nanotube (MWCNT) and graphene were separately dispersed in potassium nitrate. Solidification of these nanosalt-PCMs was analyzed using a computer-aided cooling curve analysis technique. The technique is much more effective in comparison with other alternatives such as differential scanning calorimetry, as it is simple and low cost and employs large sample sizes. In the present study, PCM sample size of 1kg was fixed with nanoparticle concentration varying from 0.1 to 0.5% by weight of the sample. The solidification time of the PCM was observed to decrease significantly on addition of nanoparticles indicating an enhancement in the heat removal rate. It is beneficial as the same amount of stored thermal energy can then be withdrawn at a much higher rate. Graphite and MWCNT additions decreased the thermal diffusivity property of the base PCM, while the graphene additions resulted in higher thermal diffusivity. However, the benefits of addition of nanoparticles to the salt-PCM reduced on thermal cycling. SEM images show that the deterioration in the observed enhancements occurred due to agglomeration of nanoparticles. This was observed in the initial 3-4 thermal cycles, and the nanosalt-PCM remained stable thereafter. The PCM developed here offers higher heat transfer rates with superior energy density. © 2021, ASM International.Item Review of thermal characterization techniques for salt-based phase change materials(Elsevier Ltd, 2022) Agarwala, S.; Prabhu, K.N.Phase change materials (PCM)-based energy storage system is a quite promising technology for the efficient usage of the excess solar energy produced and utilize it at the hour of high demand. The major challenge here is the selection of PCMs for energy storage applications. Inorganic PCMs possess higher thermal conductivity and energy storage capacity when compared to organic PCMs. Thus, inorganic PCMs have a great potential to be used in energy storage systems majorly in medium to high-temperature applications where organic PCMs cannot be used. An accurate and reliable data on the thermophysical properties of the PCMs is essential before its selection and installation of a energy storage system. In this study, various characterization methods based on calorimetry, temperature difference, cooling rate, and cooling curve used to date are described. Methods such as conventionally used differential scanning calorimetry (DSC), T-history method, and computer-aided cooling curve analysis (CACCA) are reviewed and discussed in this study. The two modes of CACCA, Newtonian, and Fourier techniques are explained. The advantages and limitations associated with all these methods are outlined. Inverse heat conduction problem (IHCP)-energy balance method based on CACCA which is devoid of the limitations associated with the conventional characterization methods is discussed. Thermal conductivity is the main characterization parameter of the PCMs and therefore methods to measure thermal conductivity are critically reviewed in this study. Thermal cycling stability is discussed in the context of the review. © 2021 Elsevier Ltd