Faculty Publications

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Author: search.filters.author.Samuel, A.Subject: search.filters.subject.Inverse problems

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    Assessment of Heat Transfer Characteristics of Transesterified Waste Sunflower Cooking Oil Blends for Quench Hardening
    (Springer, 2022) Samuel, A.; Prabhu, K.N.
    Mineral oils used in the heat treatment industry are derivatives of non-renewable petroleum fuel and are toxic and non-biodegradable. Vegetable oils are an ideal substitute for mineral oil due to their superior heat transfer characteristics and eco-friendliness. However, the initial cost of vegetable oils is very high. In addition, the maintenance cost of vegetable oils would be higher due to their poor thermal and oxidative stability than mineral oil. In this context, recycling and reusing waste cooking oil could be a cheaper and eco-friendly alternative. In this study, the fatty acid methyl ester (FAME) produced from the waste sunflower cooking oil through transesterification was blended with sunflower and mineral oils at various proportions. The cooling characteristics of the FAME/oil blends were assessed using the cooling curve analysis according to ASTM D6200 and ISO9950 standards. A solution to the inverse heat conduction problem was used to estimate the spatiotemporal metal/quenchant interfacial heat flux. The uniformity of heat flux was analyzed. The results indicated that blending waste cooking oil-derived FAME in sunflower oil up to 60 vol.% and mineral oil up to 50 vol.% provided comparable cooling characteristics to pure oils. The estimated heat flux transients showed a marginal decrease in peak heat flux for FAME blends in sunflower oil, whereas an increased peak heat flux with mineral oil. The FAME blends less than 60 vol.% in sunflower oil showed higher cooling uniformity. With mineral oil, the blend proportion of up to 50 vol.% increased cooling uniformities compared to pure oil. The characteristic cooling time (t85) increased with the increase in FAME blends in oils. However, the distribution of t85 in the quench probe was uniform for FAME/oil blends. © 2022, ASM International.
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    Experimental investigation of heat transfer characteristics of polyethylene glycol (PEG) based quench media for industrial heat treatment
    (Elsevier Inc., 2023) Soni, A.; Samuel, A.; Prabhu, K.
    Aqueous polymer quenchants are now increasingly used in the quench hardening of steels. The inverse solubility property of polymer media leads to polymer film encapsulation of the quenched component, followed by an instantaneous rupture of the polymer film. The film boiling stage is absent, thus improving heat transfer uniformity. In the present investigation, the effect of molecular weight of Polyethylene glycol (PEG) on heat transfer characteristics of PEG/water quenchants with concentrations of 5, 10, and 20 vol% was studied. The cooling curve analysis is performed to assess the cooling characteristics. Spatially dependent surface heat flux transients are estimated using the inverse heat conduction method. The rewetting kinematics is analyzed by videography and acoustic analysis of polymer film rupture during quenching. The results indicated that an increase in the molecular weight of PEG from 200 to 6000 changed the rewetting kinematics from a local wetting front movement to an instantaneous rupture of the polymer film. The change in the rewetting kinematics is reflected in the surface heat flux, indicating an increased uniformity of heat transfer. The film rupture acoustics showed that the polymer film's instantaneous breakup had a higher sound intensity than the one showing wetting front motion. © 2023 Elsevier Inc.
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    A Phase Transformation Enthalpy Parameter for Modeling Quench Hardening of Steels
    (Springer, 2024) Samuel, A.; Pranesh Rao, K.M.P.; Prabhu, K.N.
    The effect of phase transformations on the steel/quenchant interfacial heat flux during quench hardening heat treatment is investigated in the present work. Experimental and modeling approaches comprising the inverse heat conduction problem (IHCP) were employed to analyze the thermal behavior of different steel grades with varying section thicknesses. The results revealed that phase transformation led to a distinctive pattern of the interfacial heat flux, characterized by a dip and subsequent rise. We observed that increasing the section thickness increases the surface heat flux for stainless steel probes without phase transformation. In contrast, the surface heat flux decreased with thicker sections in phase transformation. The increased heat evolved due to the latent heat liberation during phase transformation, and a reduction in thermal diffusivity due to increased specific heat caused a fall in the heat flow rates. Furthermore, the study proposed a phase transformation enthalpy parameter (ΔQ) to access the enthalpy change during quenching. ΔQ was consistent for a specific steel grade and independent of section thickness but varied with the cooling rate or quench media. The incorporation of phase transformation in the quenching heat transfer model is complex due to the required material data, including TTT/CCT diagrams and thermophysical properties that vary with steel grade. The study suggests directly incorporating the ΔQ values into the heat conduction equation or the IHCP model with phase transformation, simplifying the simulation process and minimizing data inputs. A database on ΔQ as a function of temperature and cooling rate would facilitate heat transfer modeling during quench hardening. © 2023, The Minerals, Metals & Materials Society and ASM International.
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    Effect of process variables on heat transfer and the product quality during layer deposition of Al4043 alloy by wire arc additive manufacturing
    (John Wiley and Sons Inc, 2025) Raghavendra Pai, K.; Vijayan, V.; Samuel, A.; Prabhu, K.N.
    In the present work, heat transfer dynamics between the substrate and the deposited metal is investigated to assess its effect on the evolution of defects and the quality of the product. A series of experiments involving the deposition of Al4043 wire were conducted on Al4043 aluminum alloy substrate at a voltage range of 13–19 V. A one-dimensional inverse computational model was adopted to estimate the heat flux transients. The metal/substrate interfacial heat flux was correlated with the microstructure evolution during the solidification of the metal. The experimental results clearly indicated that heat transfer plays a dominant role in the final finish and quality of the product and is controlled by variables, such as voltage, gas flow rate (GFR), wire feed rate (WFR), and forward traversal speed. At an integral heat flow (HF) in the range of 3000–5000 kJ/m2 corresponding to voltages between 13.8 and 14.5 V, argon GFR of 12–15 L/min, and a WFR of 4.1 mm/min, the porosity in the additively manufactured component was found to be minimum. The ultimate tensile strength was found to be 65 and 76 MPa, corresponding to the voltage of 13.5 and 14.5 V, respectively, and decreased to 25 MPa for a higher voltage of 19 V. At the GFR range of 8–10 L/min, the HF was in the range of 450–510 kJ/m2 with increased porosity (33%–42%). Porosity was found to decrease (15%–22%) with 12–15 L/min range of GFR and the corresponding HF was in the range of 700–950 kJ/m2. The specimens fabricated under these optimal parameters exhibited superior mechanical properties. © 2024 Wiley Periodicals LLC.