Begell House Inc.
Heat Transfer Research
HTR
1064-2285
50
6
2019
NUMERICAL STUDY OF THERMAL ENHANCEMENT IN MODIFIED RACCOON MICROCHANNELS
519-543
Nishant
Tiwari
Department of Mechanical Engineering, National Institute of Technology Rourkela, Rourkela
769008 (Odisha), India
Manoj Kumar
Moharana
Department of Mechanical Engineering, National Institute of Technology Rourkela, Rourkela
769008 (Odisha), India
An improved design of raccoon microchannel heat sink with a combined change in wave amplitude and wavelength along the channel length is proposed in this work. A three-dimensional conjugate heat transfer model studies the characteristics of fluid flow and heat transfer numerically. The total channel length is divided into three zones of equal length where the channel expansion factor (α) and waviness (γ) are varied in each zone to create six sets of modified raccoon microchannels (MRMC). The results indicate that changing the waviness (γ) along an equally divided length of the channel in MRMC contributed to disturbance of the core fluid region and intensified the mixing of laminar boundary layer that enhances the thermal performance of the microchannel. The assessment of MRMC is based on the thermal performance factor (η), and the results indicate that there exists an optimal combination of wave amplitude and wavelength arrangement along the channel length, which has an additive effect on the thermal performance. The Nusselt number and friction factor of the new heat-sink design is well demonstrated by comparison with the simple raccoon microchannel (SRMC). In addition, a wide range of parametric variations is also considered to indicate the axial wall conduction effect in raccoon microchannels.
THERMAL PERFORMANCE OF MULTITUBE LATENT HEAT STORAGE USING A METAL MATRIX FOR SOLAR APPLICATIONS: NUMERICAL STUDY
545-564
Shah
Rauf
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai,
400 076, India
Sandip Kumar
Saha
Department of Mechanical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai – 400 076. Maharashtra, India
This study presents an analysis of multitube shell and tube latent heat thermal energy storage system (LHTES) for medium-temperature solar applications (~ 200°C) to evaluate its thermal performance during discharging operation. As the present commercially available organic PCM possesses very low thermal conductivity, a metal matrix, acting as a thermal conductivity enhancer, is embedded in the annular space saturated with PCM. A numerical model, consisting of momentum and two-temperature nonequilibrium energy equations coupled with enthalpy technique for phase change of PCM, is developed and validated with experimental results. Further, parametric studies are conducted by varying the porosity and pore diameter of the metal matrix for estimating entropy generation, second law efficiency, and thermal performance index (TPI). The study finds that the second law efficiency increases with the decrease in the porosity and pore diameter. However, the TPI decreases with increase in porosity, while the pore diameter has no significant effect on it.
STUDY OF LAMINAR NATURAL CONVECTION OF AN ISOTHERMAL VERTICAL PLATE USING SCHLIEREN PHOTOGRAPHY AND NUMERICAL METHODS
565-580
Christopher
Hampel
University of Portland, Portland, OR, USA
Hollis
Crowder
University of Portland, Portland, OR, USA
Heather
Dillon
University of Portland, Portland, OR, USA
The objective of this research has been to build the foundation for developing more advanced mathematical models for heat transfer research by understanding, with various techniques, the commonly accepted solution of laminar flow due to natural convection on an isothermal vertical plate. To form this foundation, a numerical solution to the Navier-Stokes equations was solved using traditional numerical methods, and schlieren photography was applied to a physical experiment of the plate to allow flow visualization. Schlieren images illustrated laminar boundary layer formation that was expected due to the temperature difference applied. Boundary layer thickness measurements taken from schlieren images were compared well with a theoretical correlation. In addition, the Boussinesq approximation for density was graphed for comparison to linearly interpolated density values associated with schlieren image color scale to approximate density values. Results showed that the image interpolation technique was in good agreement with the Boussinesq approximation. Furthermore, theoretical velocity and temperature profiles were solved with the similarity solution of the governing Navier-Stokes equations.
SIMULTANEOUS SOLUTIONS FOR MHD FLOW OF WILLIAMSON FLUID OVER A CURVED SHEET WITH NONUNIFORM HEAT SOURCE/SINK
581-603
Anantha Kumar
Kempannagari
Sri Venkateswara University
J. V. Ramana
Reddy
Department of Mathematics, Sri Venkateswara University, Tirupati-517502, India
Vangala
Sugunamma
Department of Mathematics, Sri Venkateswara University, Tirupati-517502, India
N.
Sandeep
Department of Mathematics, Central University of Karnataka, Kalaburagi-585 367, India
Heat and mass transfer effects on both time-dependent and time-independent MHD flow of Williamson fluid due to a curved surface are discussed. This analysis is carried out subject to thermal radiation and chemical reaction. The solutal and convective boundary conditions are considered. To seek the solution of the problem, a system of proper transmutations is appraised to convert the flow equations into ODE. The solution of the transformed equations is attained by the consecutive application of the Fehlberg and shooting techniques. Graphs are plotted to emphasize the impact of sundry physical parameters on flow fields. Further, we evaluated the friction factor, as well as heat and mass transport rates. It is noted that the curvature parameter enhances the velocity field while the reverse trend is detected due to the Williamson fluid and magnetic field parameters. Also, it is worth mentioning that the temperature profiles of steady flow are fruitfully affected when compared to the unsteady flow for all the parameters involved in the flow.
EFFECTS OF SINUSOIDAL STRIP ELEMENT WITH DIFFERENT AMPLITUDES ON HEAT TRANSFER AND FLOW CHARACTERISTICS OF CIRCULAR CHANNELS
605-616
Aziz Hakan
Altun
Department of Airframe and Powerplant Maintenance, Selcuk University, 42031 Konya, Turkey
Mehmet
Gürdal
Department of Mechanical Engineering, Karabuk University, 78050 Karabuk, Turkey
Adnan
Berber
Department of Mechanical Engineering, Necmettin Erbakan University, 42370 Konya, Turkey
In this study, the effect of Reynolds number in turbulent flow on heat transfer and flow characteristics for different sinusoidal decoupled strip elements placed separately from the pipe was investigated experimentally. Experiments were carried out under forced convection and constant heat flux conditions. Corrugated strip elements were positioned axially at the pipe center, which draws a sinusoid used as a turbulator. Experiments were repeated for three different amplitudes of sinusoidal strip elements with 3D/4 width, D/8, 3D/16, and D/4. Experiments showed that although the strip elements enhanced heat transfer at different rates, they also caused a considerable pressure drop. As a result, it was seen that the heat transfer ratio, i.e., the Nusselt number, increased with the amplitude value. This ratio is 47% to 80% at the D/8 amplitude, 44% to 100% at the 3D/16 amplitude, and 75% to 174% at the D/4 amplitude in a straight pipe. It was determined that the friction coefficient is significantly affected by a sinusoidal corrugated strip element. It was determined that the value of friction coefficient is around 0.02 in a smooth pipe, 0.17 to 0.25 at n = D/8, 0.35 to 0.42 at n =3D/16, and 0.43 to 0.45 at n = D/4