Faculty Publications
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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 A quantitative approach for thermal characterization of phase change materials(ASTM International, 2021) Agarwala, S.; Prabhu, K.N.A quantitative method for the calculation of phase change parameters of salt-based phase change materials (PCMs) has been proposed. This technique involves the estimation of mold-salt interfacial heat flux by solving Fourier's law of heat conduction within the salt and using it for the calculation of phase change enthalpy of salt PCMs. Radial heat transfer was ensured by keeping the length to diameter (L/D) ratio of the mold equal to 5. The proposed method eliminates any drawbacks involved with sample size, reference material, the baseline fitting calculations, and the errors introduced due to the selection of solidification points. Pure salt PCMs such as potassium nitrate (KNO3), sodium nitrate (NaNO3), and solar salt mixture (60 wt. % NaNO3 + 40 wt. % KNO3) were used for validation of this technique. The thermal behaviors of the salt and the mold during solidification of the salt sample were analyzed, and solidification characteristics such as cooling rate, solidification time, and phase change enthalpy of PCMs were determined. © © 2021 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959Item 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