Faculty Publications

Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736

Publications by NITK Faculty

Browse

Author: search.filters.author.Sathyabhama, A.Subject: search.filters.subject.Experimental investigations

Search Results

Now showing 1 - 8 of 8
  • No Thumbnail Available
    Item
    Experimental investigation in pool boiling heat transfer of ammonia/water mixture and heat transfer correlations
    (2011) Sathyabhama, A.; Ashok Babu, T.P.A.
    The nucleate pool boiling heat transfer coefficient of ammonia/water mixture was investigated on a cylindrical heated surface at low pressure of 4-8bar and at low mass fraction of 0NH3<0.3 and at different heat flux. The effect of mass fraction, heat flux and pressure on boiling heat transfer coefficient was studied. The results indicate that the heat transfer coefficient in the mixture decreases with increase in ammonia mass fraction, increases with increase in heat flux and pressure in the investigated range. The measured heat transfer coefficient was compared with existing correlations. The experimental data were predicted with an accuracy of ±20% by the correlation of Calus&Rice, correlation of Stephan-Koorner and Inoue-Monde correlation for ammonia/water mixture in the investigated range of low ammonia mass fraction. The empirical constant of the first two correlations is modified by fitting the correlation to the present experimental data. The modified Calus&Rice correlation predicts the present experimental data with an accuracy of ±18% and the modified Stephan-Koorner correlation with an accuracy of ±16%. © 2011 Elsevier Inc.
  • No Thumbnail Available
    Item
    Experimental investigation of pool boiling heat transfer in ammonia-water-lithium nitrate solution
    (2012) Sathyabhama, A.; Ashok Babu, T.P.
    The nucleate pool boiling heat transfer coefficient of an NH 3-H 2O-LiNO 3 mixture was investigated on a cylindrical heated surface at low pressure of 4 to 8 bar, low ammonia mass fraction of 0 < xNH 3 < 0.3, and different heat fluxes. The lithium nitrate concentration of the solution was chosen in the range of 10-50% of mass ratio of lithium nitrate in pure water. The effects of concentrations, heat flux, and pressure on boiling heat transfer coefficient was studied. The results indicate that the heat transfer coefficient in the mixture decreases with increase in ammonia mass fraction, increases with the addition of lithium nitrate, and increases with an increase in heat flux and pressure in the investigated range. © 2012 Copyright Taylor and Francis Group, LLC.
  • No Thumbnail Available
    Item
    Effect of surface vibration on boiling heat transfer froma copper flat circular disc
    (Begell House Inc. orders@begellhouse.com, 2016) Sathyabhama, A.; Pandiyan, P.S.
    This paper presents the experimental investigation of the effect of surface vibration on pool boiling heat transfer from a copper flat circular surface immersed in saturated water at atmospheric pressure. The forced vertical vibrations were induced on this copper test surface with the help of a mechanical vibrator. The frequency was varied in the range 0-25 Hz and the amplitude of vibration was varied in the range 0-5 mm. The results indicate that the heat transfer coefficient increases at low frequency and amplitudes; at higher amplitude and frequency, heat transfer deteriorates in the investigated range. Rohsenow-type correlation was developed, which predicts the present experimental data with an average absolute error of 30%. © 2018 by Begell House, Inc.
  • No Thumbnail Available
    Item
    Effect of boiling surface vibration on heat transfer
    (Springer Verlag service@springer.de, 2017) Sathyabhama, A.
    Experimental investigation of effect of forced vertical surface vibration on nucleate pool boiling heat transfer of saturated water at atmospheric pressure is presented in this paper. Vertical vibration was induced externally to the circular copper test surface on which boiling took place, using a vibration exciter. Frequency was varied in the range 0–25 Hz and amplitude of vibration was varied in the range 0–5 mm. Boiling takes place at much lower superheats for the same heat flux, slope of boiling curve decreases remarkably, when the surface is given external excitation. High frequency and high amplitude oscillations lead to more intensive heat transfer. There are some combinations of frequency and vibration amplitude, which cause up to two times increase in heat transfer coefficients. © 2016, Springer-Verlag Berlin Heidelberg.
  • No Thumbnail Available
    Item
    Enhancement of Boiling Heat Transfer Using Surface Vibration
    (John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2017) Sathyabhama, A.; Pandiyan, S.P.
    An experimental investigation of the effect of mechanical vibrations of a copper flat circular surface on the pool boiling heat transfer coefficient of water at atmospheric pressure are presented in this paper. A vibration exciter was used to vibrate this copper test surface vertically. Effect of frequency and amplitude of vibration on the boiling heat transfer coefficient was studied. An increase in the heat transfer coefficient was observed at low frequency and amplitudes, at higher amplitude and frequency heat transfer deteriorates. Heat transfer coefficient increases up to 26% with vibration intensity, represented by vibrational Reynolds number. © 2015 Wiley Periodicals, Inc.
  • No Thumbnail Available
    Item
    Transient CHF enhancement in high pressure pool boiling on rough surface
    (Elsevier B.V., 2018) Walunj, A.; Sathyabhama, A.
    Experimental investigation of transient pool boiling heat transfer (PBHT) to saturated water from thick, non-lumped 20 mm diameter copper sample is carried at 1 bar, 5 bar and 10 bar pressure. The time constant (?) of exponential heat supply is varied from 1 to 6. The unidirectional scratches are made on the surface to obtain wide range of surface roughness varying from Ra = 0.106 ?m to Ra = 4.03 ?m. The effect of surface roughness, pressure and time constant on transient critical heat flux (CHF) is extensively studied. Transient CHF enhancement for Ra = 4.03 ?m when ? = 1 is found to be 98.88%, 76.55% and 53.21% at pressures P = 1 bar, P = 5 bar and P = 10 bar, respectively, however it is found to be lower by 9.38%, 21.40% and 9.73%, compared to steady state CHF enhancement for Ra = 4.03 ?m, at respective pressures. The Gorenflo correlation is modified by including the additional parameter ? and it predicts the present transient HTC values with mean absolute error (MAE) of 14.91%. The CHF model is developed by considering the effect of capillary wicking in the narrow unidirectional scratches and the bubble angle. This model predicts the present transient CHF values with MAE of 11.89%. © 2018 Elsevier B.V.
  • No Thumbnail Available
    Item
    Experimental investigation on transient pool boiling heat transfer from rough surface and heat transfer correlations
    (International Information and Engineering Technology Association info@iieta.org, 2019) Walunj, A.; Sathyabhama, A.
    This paper presents the study of transient boiling characteristics on rough copper sample with surface roughness value (Ra) ranging from 0.106 ?m to 4.03 ?m. The effect of roughness and time constant of exponential heat supply on transient critical heat flux (CHF), maximum heat transfer coefficient (HTC) and onset of nucleate boiling (ONB) is extensively studied. The mechanism of heat transfer in unidirectional scratches of rough sample is discussed. High speed visualization is carried to observe the stages of boiling and bubble dynamics. The HTC correlation developed in this study predicts the present experimental values of HTC with a mean absolute error (MAE) of 9.62 %. © 2019 International Information and Engineering Technology Association. All rights reserved.
  • No Thumbnail Available
    Item
    NUMERICAL AND EXPERIMENTAL INVESTIGATION INTO THE EFFECT OF LEADING-EDGE PROTUBERANCES ON THE AERODYNAMIC PERFORMANCE OF WIND TURBINE
    (Begell House Inc., 2025) Sathyabhama, A.; Sinha, R.K.; Reddy, C.J.
    In this paper, the numerical and experimental analysis of the effect of leading-edge protuberances on the performance of small horizontal axis wind turbines (SHAWT) at low Reynolds number was carried out. The wind turbine blades were designed using the blade element momentum theory (BEMT) with wake rotation. The E216 profile was chosen over other airfoils because, in low Reynolds number flow conditions, it gives a high lift-to-drag ratio. The tubercle shapes employed for the study are slot, triangular, and sinusoidal, and their effects on the performance of wind turbine were compared with baseline turbine as well as among themselves. The flow behavior and the influence of pitch angle on the performance of baseline wind turbine were investigated. The numerical simulations were conducted in ANSYS FLUENT R2021, and the experiments carried out in a low-speed wind tunnel were used to validate the results. The numerical equations were solved using a three-dimensional Reynolds-averaged Navier-Stokes equation with a shear stress turbulence (SST) k-? turbulence model. The output power, torque, and coefficient of power (CP) values for the baseline turbine increased up to 25° pitch angle and afterwards, a decline was seen. The optimum tip-speed ratio (TSR) was also investigated and found to be 2.67. The pitch angle 25° provides the greatest improvement among all pitch angles examined for the same blade profile. Hence, for the study of different-shaped tubercles (triangular, sinusoidal, and rectangular slot) pitch angle of 25° was considered. Sinusoidal tubercles show a greater lift-to-drag (CL /CD) ratio than baseline wind turbines, although there is no substantial difference in CP. Furthermore, the CL /CD for triangular and slotted tubercles is more significant than that of the baseline wind turbine, as is the CP. When all three tubercles are compared, the slot has the highest CP, while the sinusoidal wind turbine has the highest CL /CD. © 2025 by Begell House, Inc.