Faculty Publications
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Publications by NITK Faculty
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Item Assessment of latent heat and solid fraction of Al-22Si alloy using Newtonian and Fourier analysis techniques(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Vijayan, V.; Prabhu, K.Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination of solidification characteristics of metals or alloys. The results of CACCA can be used to accurately determine latent heat and solid fraction needed for modeling of the solidification process. Newtonian and Fourier analysis techniques adopt a data base line fitting technique to the first derivative curve for calculation of the solid fraction and latent heat of solidification. This paper describes the theoretical and experimental procedures involved Newtonian and Fourier analysis techniques with reference to an Al-22% Si alloy. The correlations between the solid fraction and temperature/time for the alloy were determined. © (2015) Trans Tech Publications, Switzerland.Item Influence of Incorporating Phase Change Materials on Cementitious System—A Review(Springer Science and Business Media Deutschland GmbH, 2021) Snehal, K.; Das, B.B.Phase change materials (PCMs) are gaining more attention in achieving the sustainability and are being widely adopted as a green building material because of their exclusive ability to store latent heat of thermal energy. PCMs have a capacity to minimize the energy loads and to provide thermal comforts in building infrastructures by its iterative cycle of absorbing and releasing the heat energy. The potential need for manipulating the heating and cooling effect in buildings is significantly increasing especially in temperature fluctuating and varied climatic regions. It is for this one of the significant reasons, PCMs are getting pronounced interest by the research fraternity in the development of a thermally effective PCM-based construction material. In this paper, attempts were made to compile the data reported by the previous researchers on the influence of incorporating PCMs in the engineering properties of cementitious system such as slump, compressive strength, flexural strength, density, porosity, water absorption, shrinkage, durability, heat of hydration, specific heat capacity and thermal conductivity. This paper also discusses the most favorable content of PCM addition and effective methods of incorporating PCMs in the cementitious system. © 2021, Springer Nature Singapore Pte Ltd.Item Latent heat flux estimation using trapezoidal relationship between MODIS land surface temperature and fraction of vegetation-application and validation in a humid tropical region(Taylor and Francis Ltd., 2014) Laxmi, K.; Nandagiri, L.The present study was taken up with the objective of developing a methodology for estimation of actual evapotranspiration (AET) using only satellite data. Accordingly, an algorithm based on the popular Priestley-Taylor method was developed. While previous studies have assumed a triangular relationship between land surface temperature (LST) and fraction of vegetation (FV) to calculate the Priestley-Taylor parameter (?), a trapezoidal relationship was adopted in the present study to enable applications in forested regions in the humid tropics. The developed algorithm was applied to the humid tropical Mae Klong region, Thailand, and latent heat flux (ET) estimates were validated with measurements made at a flux tower located at the centre of the region. Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing satellite data products corresponding to the study area were used to derive various inputs required by the algorithm. Comparison of estimated and measured fluxes on five cloud-free days in 2003 yielded root mean square error (RMSE) of 64.73 W m-2 which reduced to 18.65 W m-2 when one day was treated as an outlier. The methodology developed in this study derived inputs only from satellite imagery and provided reasonably accurate estimates of latent heat flux at a humid tropical location. © 2014 Taylor & Francis.Item The effect of Sr modification on thermal diffusivity of Al–8Si alloy(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2018) Vijayan, V.; Prabhu, K.N.Newtonian and Fourier analysis techniques were used to calculate the solid fraction and latent heat during the solidification of Al–8Si alloy and the subsequent results were used to study the effect of Sr modification on thermal diffusivity of the solidifying melt. The results indicate that the thermal diffusivity increased significantly with increase in Sr content. The increase in the thermal diffusivity was attributed to the increase in the electronic conduction of the modified alloy due to the decreased activity of the bifilm. The results also indicate that the latent heat evolved during solidification increased with increase in Sr concentration and was associated with the increase in the solidification range that occurred during the modification process. © 2017 Informa UK Limited, trading as Taylor & Francis Group.Item Influence of Integration of Phase Change Materials on Hydration and Microstructure Properties of Nanosilica Admixed Cementitious Mortar(American Society of Civil Engineers (ASCE) onlinejls@asce.org 1801 Alexander Bell DriveGEO Reston VA 20191 Alabama, 2020) Snehal, K.; Das, B.B.; Kumar, S.The present study demonstrates the influence of integrating phase change materials (PCMs) on hydration and microstructure properties of nanosilica admixed cementitious mortar. First, the optimized dosage of nanosilica in correspondence to compressive strength was determined. Subsequently, the desired proportion of PCMs was identified pertaining to a designated compressive strength of 35 MPa at the curing age of 28 days. The hydration and microstructure studies were carried out through thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Further, thermal properties were determined by means of differential scanning calorimetry (DSC). Incorporation of nanosilica into the cementitious mortar was found to have a positive influence on early strength development and durability, however, there was found to be an increase in chemical shrinkage as compared to the control mixture. PCMs integrated cementitious mortar improved the thermal efficiency as well as reduced the chemical shrinkage, but adversely affected the mechanical, hydration, and durability properties. With respect to development of compressive strength of the cementitious mortar, it is found that n-octadecane PCMs performed better amidst other PCMs, such as paraffin and sodium carbonate hydrates. Further, studies were carried out on cementitious mortar having both nanosilica (optimized proportion) and PCMs (the best performing). From the results, it is found that cementitious mortar comprising of both nanosilica and PCMs have compensated the drawbacks of one another. Blended mortar (having both nanosilica and PCMs) showed superior strength gain at early age, better durability resistance, low chemical shrinkage, and superior thermal performance. © 2020 American Society of Civil Engineers.Item Thermo-physical analysis of natural shellac wax as novel bio-phase change material for thermal energy storage applications(Elsevier Ltd, 2020) B.V., B.V.; Gumtapure, V.The high energy density of latent heat storage makes it more competent than other types of thermal energy storage (TES) systems. Studying thermophysical and rheological properties of phase change material (PCM) is required for effective storage design, simulation, and applications. Bio-based PCM (BPCM) is a renewable and eco-friendly option for commercial paraffin-based PCMs. This study intends to characterize the shellac wax using the conventional and non-conventional approach as novel BPCM. Analysis of Fourier transforms infrared spectrophotometer (FTIR) indicates that shellac wax has aliphatic hydrocarbons, carboxylic acid, alcohol, and esters functional group. Thermogravimetric analysis (TGA) shows shellac wax has no mass change for operating temperature range (50–85 °C). Differential scanning calorimetry (DSC) analysis reported enthalpy of melting and crystallization as 148 kJ/kg and 161 kJ/kg, respectively. The crystallization enthalpy measured in the T-history method (THM) is 210.5 kJ/kg. However, DSC analysis of sample undergone 0,100,200 and 300 thermal cycle shows no significant change in thermal properties. Other properties like thermal conductivity, density, specific heat and viscosity are comparable to the present PCM used in storage applications. The overall study outcome that shellac wax is thermally stable and is potential BPCM for the TES application like solar desalination, district heating, waste heat recovery and solar cooking. © 2020 Elsevier LtdItem Performance assessment of composite phase change materials for thermal energy storage-characterization and simulation studies(Bentham Science Publishers, 2021) Chavan, S.; Gumtapure, V.; Arumuga Perumal, D.Background: The present study mainly focuses on the development of new Thermal Storage Materials (TSM) and compare the performance for thermal energy storage capacity. Linear Low-Density Polyethylene (LLDPE) based Composite Phase Change Materials (CPCMs) is prepared, and its properties are analyzed using characterization, analytical calculations, and numerical simulation meth-ods. The composites are prepared by blending the functionalized graphene nanoparticles (1, 3 & 5%) with three different concentrations into LLDPE. All three CPCMs show enhanced thermal performance compared to the base material, but it is noticed that higher concentrations of nanoparticles increase the dynamic viscosity and produce an adverse effect on thermal performance. Thermal characterization shows improved latent heat capacity with nanoparticle concentration, analytical and numerical results also compared, which shown a difference of 10 to 25%. Objective: The purpose of this study is the development and evaluation of the thermal storage capacity of different thermal storage materials and enlighten the techniques used for characterizing the storage materials. Methods: Composite material preparation is carried out by using twin-screw extruders, characterization of developed material is done through FTIR, SEM, and DSC analysis. For complete analysis character-ization, analytical calculations and numerical simulation methods are used. Results: Linear low-density polyethylene-based composite materials can be successfully developed using a twin-screw extruder. This extrusion provided proper dispersion of nanoparticles into the base material, and it is validated by SEM analysis. DSC analysis confirmed the enhancement in the thermo-physical properties of composite materials. Conclusion: The latent heat capacity increased around 20% during the heating cycle and reduced ap-proximately 23% during the cooling cycle for base material and 5% addition of nanoparticle, respec-tively. The comprehensive study accomplishes that the optimum concentration of nanoparticle provides better thermal performance for thermal energy storage applications. © 2021 Bentham Science Publishers.Item Performance evaluation of novel tapered shell and tube cascaded latent heat thermal energy storage(Elsevier Ltd, 2021) B.V., B.V.; Nidhul, K.; Gumtapure, V.Geometric design of the storage system plays a vital role in the enhancement of heat transfer rate and thereby in the advancement of latent heat thermal energy storage (LHTES) technology. The present study numerically compares the heat transfer performance of tapered type shell and tube cascaded latent heat storage (CLHS) model with that of the conventional cylindrical CLHS model with special emphasis on melting rate at the slowest melting portions (bottom) of the shell and tube unit. Thermal properties like transition temperature, latent, and specific heat of the three organic PCMs OM 42, OM 46, and OM 48 have been obtained using differential scanning calorimetry (DSC), and the same is employed in the 2-D numerical simulation carried out using enthalpy-porosity method. Tapered CLHS unit exhibited superior performance owing to stronger natural convective currents demonstrated via streamlines, velocity, temperature and mass fraction contours. In tapered unit, 17.6% higher mean power is obtained for same volume of PCMs in cylindrical unit. In contrast, the mean power of the discharging process for a tapered type is 2.4% lesser than cylindrical type CLHS. The outcomes highlight that the tapered type CLHS model utilizes convective heat transfer, effectively enhancing the melting rate of PCM without any additional structural configurations such as fins. Hence is also economically justifiable for higher energy storage for the same volume compared to conventional cylindrical CLHS units. © 2020 International Solar Energy SocietyItem Experimental investigation of shellac wax as potential bio-phase change material for medium temperature solar thermal energy storage applications(Elsevier Ltd, 2022) B.V., B.V.; Thanaiah, K.; Gumtapure, V.Thermal performance of shellac wax as a novel bio-phase change material (BPCM) and Therminol®-55 as heat transfer fluid (HTF) in a vertical shell and tube latent heat thermal energy storage (LHTES) unit is analyzed experimentally. Operational parameters considered, namely HTF flow rate and inlet temperature in the range of 2–5 LPM and 100–120 °C, respectively. The comprehensive study of contours and plots reveals the impact of natural convection and the progress of the melting and solidification front in the charging and discharging process. As the HTF flow rate increases, the charging rate improves considerably, and a maximum reduction in melting time is obtained as 43.6% for 4 LPM. The maximum reduction in melting time and storage efficiency are 42.2% and 73.4%, respectively, at 120 °C and 4 LPM. However, the discharging process's increased flow rate has no significant effect on solidification and discharge efficiency, which attributes the dominant mode of heat transfer is conduction during the solidification. Shellac wax storage efficiency is comparable to existing paraffin wax, stearic acid and palmitic acid-based LHTES unit. In this regard, shellac wax can be a potential Bio-PCM for medium temperature range (60–80 °C) solar thermal applications such as domestic water heating and food drying. © 2021 International Solar Energy SocietyItem Design of thermal energy storage system for solar cooker: a review(Springer, 2025) Anilkumar, B.C.; Maniyeri, R.Solar cooking has been a research focus worldwide over the last few decades due to its numerous advantages, such as no running costs, non-polluting nature and ample availability. Solar cookers incorporate thermal energy storage (TES) units to enable cooking during off-sunshine hours. Within solar thermal applications, latent heat storage materials (LHSMs), particularly phase change materials (PCMs) are increasingly vital due to their superior energy storage density and isothermal working properties. The present review aims to provide a comprehensive overview of various TES unit designs integrated with cooking vessels for solar cookers. We discuss different types of solar cookers, various TES unit configurations, and the thermo-physical properties of heat storage materials. A key aspect of this work involves comparing the sizes of various TES units, derived from our previously developed computational scheme, with existing research. Prior studies often lacked specifics on the duration of off-sunshine cooking. However, determining the optimal PCM mass is crucial for designing efficient LHS units that maximize heat storage and release for sustained cooking. To address this gap, we employed a computational procedure to determine the duration for which various LHS units, integrated with box-type solar cookers, can maintain a constant cooking temperature. We also identified and compared the dimensions of containers needed to hold the optimum PCM mass. Our computational findings for the outer vessel diameter of LHS units align closely with previous studies. This computational approach offers a robust methodology for developing TES units that optimize PCM latent heat utilization, significantly enhancing solar cooker performance during sundown hours. Ultimately, we propose a pathway for improving future TES unit designs and present a strategy for marketing solar cookers. This review will be an invaluable resource for researchers, stimulating further advancements in solar cookers integrated with TES systems. © Indian Academy of Sciences 2025.