Department of Mechanical engineering

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Start date: 2000Subject: search.filters.subject.Heat Transfer

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Now showing 1 - 10 of 77
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    Thermal conductivity enhancement of magnetic nanofluids for energy applications
    (Elsevier, 2023) Parameshwaran, R.
    Nanofluids are a class of fascinating energy transfer fluids that are gaining impetus in many heat transfer applications due to their tremendous potential in augmenting the thermal properties of the base fluids such as water, ethylene glycol, engine oil and so on. From this perspective, this study was aimed at investigating the enhancement of thermal conductivity of distilled water (base fluid) using magnetic nanoparticles. The magnetic nanoparticles were experimented for understanding their surface morphology, crystal structure, chemical stability, thermal conductivity and viscosity using the respective characterization techniques. The scanning electron microscopy results infer that the average size of the agglomerated spherically shaped magnetic nanoparticles was 600.8 nm, however the size of individual particles was observed to be well within 100 nm. The X-ray diffraction pattern showed prominent intense peaks at 29.87°, 35.61° and 63° which have justified the crystalline nature of the nanoparticles. The as-prepared magnetic nanofluids (MNF) when tested for its surface structure has revealed good chemical stability between the base fluid and the magnetic nanoparticles. It is noteworthy that, the thermal conductivity of the MNF was ranging from 0.7666 W/m K to 0.9666 W/m K for the volume fraction of nanoparticles ranging from 0.01 % to 0.1 % and temperature ranging from 35° C to 55 °C. The significance of this work has been justified in terms of achieving enhanced thermal conductivity ranging from 21.3 % to 53.1 % for such low volume fractions of the nanoparticles. Furthermore, the MNF exhibited only marginal variations in viscosity for the specified volume fractions of the nanoparticles. In summary, the as-prepared MNF with these enhanced attributes can be considered to be viable and beneficial for the energy applications.
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    Analytical and experimental investigations of nanoparticles embedded phase change materials for cooling application in modern buildings
    (Elsevier, 2012-03) Parameshwaran, R.
    his paper presents the analytical and experimental investigations of the phase change heat transfer characteristics and thermodynamic behavior of spherically enclosed phase change material (PCM) with dispersion of nanoparticles for latent thermal energy storage (LTES) system in buildings. In this study, the heat transfer characteristics in terms of the transient temperature variations, moving interface positions, complete rate of solidification and melting were analyzed for the six different PCMs considered in pure form and with dispersed nanoparticles as well. The heat transfer characteristics of the PCMs considered were analytically modeled and experimentally evaluated for the steady state and transient conditions for various heat generation parameters during freezing and melting cycles of the LTES system. The experimental results infer that for the same thermal load conditions the rate of solidification for the PCMs decreased with the increased mass fractions of nanoparticles while compared to the pure PCMs. For the same operating conditions of the LTES system, similar heat transfer characteristics were observed for the six PCMs considered. In this paper, the analytical model solutions and experimental results for the 60% n-tetradecane: 40% n-hexadecane PCM are presented. The solidification time for the 60% n-tetradecane: 40% n-hexadecane PCM embedded with the aluminium and alumina nanoparticles were expected to reduce by 12.97% and 4.97% than at its pure form respectively. Besides, the test results indicate that by increasing the mass fraction of the nanoparticles beyond the limiting value of 0.07 the rate of solidification was not significant further. Furthermore, the rate of melting was improved significantly for the PCMs embedded with the dispersed nanoparticles than the pure PCMs. The analytical solutions obtained for the pure and dispersed nanoparticles based PCMs were validated using the experimental results. The deviations observed between the analytical solutions and the experimental results were in the range of 10%–13%. Based on the analytical and experimental results the present nanoencapsulated LTES system can be regarded as a potential substitute for the conventional LTES system in buildings for achieving enhanced heat transfer characteristics and energy efficiency.
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    Experimental investigation on convective heat transfer and rheological characteristics of Cu–TiO2 hybrid nanofluids
    (Elsevier, 2014-01) Parameshwaran, R.
    An experimental study has been carried out to investigate the heat transfer potential and rheological characteristics of copper–titania hybrid nanofluids (HyNF) using a tube in the tube type counter flow heat exchanger. The nanofluids were prepared by dispersing the surface functionalized and crystalline copper–titania hybrid nanocomposite (HyNC) in the base fluid, with volume concentrations ranging from 0.1% to 2.0%. The Heat transfer and rheological characteristics of nanofluids containing HyNC of an averaged size of 55 nm were experimentally investigated. The test results reveal that the convective heat transfer coefficient, Nusselt number and overall heat transfer coefficient were increased by 52%, 49% and 68% respectively, up to 1.0% volume concentration of HyNC. Beyond the volume concentration of 1.0% and up to 2.0%, the reduction in the convective heat transfer potential and the Nusselt number were marginal, which signified the effective thermal conductivity enhancement in HyNF. The functionalized structure and crystalline nature of HyNC acted as extended surfaces within the fluid medium, thereby creating more thermal interfaces for achieving improved thermal conductivity and the heat transfer potential of HyNF. The friction factor and pressure drop of HyNF for 2.0% volume concentration were expected to be 1.7% and 14.9% respectively, which implies a penalty in the pumping capacity. However, the enhancement in the heat transfer characteristics and acceptable variations in rheological aspects of HyNF, would help to reduce the consumption of higher volume concentration of metallic or metal oxide nanostructures, to be dispersed in the fluid medium. In order to validate the experimental measurements, a new correlation was developed, which predicted the experimental data with a maximum deviation of +7% and −4% for all the volume concentrations of HyNF. The present correlation was in good agreement with the experiments and can be helpful in predicting the heat transfer potential of HyNF.
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    Heat transfer from horizontal tubes in pool boiling: influence of three-dimensional heat conduction in the wall of the evaporator tube—a finite element analysis
    (Springer, 2005-10) Ranganayakulu, Chennu
    In pool boiling, the electrically heated tube releases the energy non-uniformly to the liquid, due to different surface roughness and flowing liquid. The heat transfer coefficient therefore varies with axial and azimuthal position on the tube. Hence a finite element analysis has been carried out on a horizontal 1in. copper tube for evaporation in pool boiling for three-dimensional conduction heat transfer. A test tube has been made with different surface structures, tested and analysed for heat conduction effects. It has been observed that significant amount of heat flows in azimuthal and axial directions in addition to the heat flow in radial direction.
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    Condensation heat transfer and pressure drop of R-134a saturated vapour inside a brazed compact plate fin heat exchanger with serrated fin
    (Springer, 2016-05) Ranganayakulu, Chennu
    This paper presents the experimental heat transfer coefficient and pressure drop measured during R-134a saturated vapour condensation inside a small brazed compact plate fin heat exchanger with serrated fin surface. The effects of saturation temperature (pressure), refrigerant mass flux, refrigerant heat flux, effect of fin surface characteristics and fluid properties are investigated. The average condensation heat transfer coefficients and frictional pressure drops were determined experimentally for refrigerant R-134a at five different saturated temperatures (34, 38, 40, 42 and 44 °C). A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 22 kg/m2s. In the forced convection condensation region, the heat transfer coefficients show a three times increase and 1.5 times increase in frictional pressure drop for a doubling of the refrigerant mass flux. The heat transfer coefficients show weak sensitivity to saturation temperature (Pressure) and great sensitivity to refrigerant mass flux and fluid properties. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. Correlations are provided for the measured heat transfer coefficients and frictional pressure drops.
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    Flow boiling heat transfer and pressure drop analysis of R134a in a brazed heat exchanger with offset strip fins
    (Springer, 2017-05) Ranganayakulu, Chennu
    The saturated flow boiling heat transfer and friction analysis of R 134a were experimentally analyzed in a brazed plate fin heat exchanger with offset strip fins. Experiments were performed at mass flux range of 50–82 kg/m2 s, heat flux range of 14–22 kW/m2 and quality of 0.32–0.75. The test section consists of three fins, one refrigerant side fin in which the boiling heat transfer was estimated and two water side fins. These three fins are stacked, held together and vacuum brazed to form a plate fin heat exchanger. The refrigerant R134a flowing in middle of the test section was heated using hot water from upper and bottom sides of the test section. The temperature and mass flow rates of water circuit is controlled to get the outlet conditions of refrigerant R134a. Two-phase flow boiling heat transfer and frictional coefficient was estimated based on experimental data for offset strip fin geometry and presented in this paper. The effects of mass flux, heat flux and vapour quality on heat transfer coefficient and pressure drop were investigated. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier ϕ f , and Martinelli parameter X.
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    Investigation of flow boiling heat transfer and pressure drop of R134a in a rectangular channel with wavy fin
    (Elsevier, 2020-01) Ranganayakulu, Chennu
    The saturated flow boiling heat transfer and pressure drop studies of R134a were experimentally investigated in a rectangular channel with wavy fin. Experiments were performed at mass flux range 30–50 kg m−2 s−1, heat flux range 11–18 kW m−2 and quality 0.26–0.8. The experimental data were obtained in a brazed test section. In preliminary step, single phase experiments were conducted to find out the j and f data of the wavy fin. In second step, two-phase flow boiling experiments were conducted to estimate the heat transfer and frictional coefficient based on experimental data. The trends of heat transfer and pressure drop with respect to mass flux, heat flux and quality were studied. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier, and Martinelli parameter, X.
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    Development of heat transfer coefficient and friction factor correlations for offset fins using CFD
    (Emerald, 2011-11) Ranganayakulu, Chennu
    In aerospace applications, due to the severe limitations on the weight and space envelope, it is mandatory to use high performance compact heat exchangers (CHEs) for enhancing the heat transfer rate. The most popularly used ones in CHEs are the plain fins, offset strip fins (OSFs), louvered fins and wavy fins. Amongst these fin types, wavy and offset fins assume a lot of importance due to their enhanced thermo‐hydraulic performance. The purpose of this paper is to investigate the influence of geometrical fin parameters, in addition to Reynolds number, on the thermo‐hydraulic performance of OSFs.
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    Studies on pumping power in terms of pressure drop and heat transfer characteristics of compact plate-fin heat exchangers—A review
    (Elsevier, 2010-01) Ranganayakulu, Chennu
    Renewable energy sources like solar energy, wind energy, etc. are profusely available without any limitation. Heat exchanger is a device to transfer the energy from one fluid to other fluid for many applications in buildings, industries and automotives. The optimum design of heat exchanger for minimum pumping power (i.e., minimum pressure drop) and efficient heat transfer is a great challenge in terms of energy savings point of view. This review focuses on the research and developments of compact offset and wavy plate-fin heat exchangers. The review is summarized under three major sections. They are offset fin characteristics, wavy fin characteristics and non-uniformity of the inlet fluid flow. The various research aspects relating to internal single phase flow studied in offset and wavy fins by the researchers are compared and summarized. Further, the works done on the non-uniformity of this fluid flow at the inlet of the compact heat exchangers are addressed and the methods available to minimize these effects are compared.
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    Numerical simulation of Laminar flow heat transfer Enhancement in a three-dimensional Channel flow with Inclined ribs
    (Cyber Times International Journal of Technology & Management, 2014-09) Bhattacharyya, Suvanjan
    Effects of ribs on forced convection heat transfer and friction loss behaviors for laminar airflow through a constant heat flux channel are numerically investigated in the present work. Ribs are known to enhance the heat transfer between the energy-carrying fluid and the heat transfer surfaces. A numerical investigation on the laminar flow and heat transfer behavior in the circular channel with inclined ribs for three different. The computations based on the finite volume method with the SIMPLE algorithm have been carried out with Reynolds number ranging from 100 to 1000. The numerical results show that the heat transfer of the inclined ribbed channel are improved about 90-110% compared with smooth duct because co-rotating vortices are generated on the cross section of channel. In addition, the effects of geometric parameters for ribs on the heat transfer, such as rib height, rib pitch, were analyzed. The heat transfer, pressure loss and thermal performance of the inclined ribs with different attack angles (θ) of 0o, 10o, 15o, 20o, 25o, and 90oare examined.