Begell House Inc.
Heat Transfer Research
HTR
1064-2285
49
15
2018
INCREASE IN CONVECTIVE HEAT TRANSFER OVER A BACKWARD-FACING STEP IMMERSED IN A WATER-BASED TiO2 NANOFLUID
1419-1429
C. S.
Oon
Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603
Kuala Lumpur, Malaysia; School of Built Environment, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF,
United Kingdom
Ahmad
Amiri
Department of Chemical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad,
Mashhad, Iran
B. T.
Chew
Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603
Kuala Lumpur, Malaysia
S. N.
Kazi
Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603
Kuala Lumpur, Malaysia
A.
Shaw
School of Built Environment, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, United Kingdom
A.
Al-Shamma'a
School of Built Environment, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, United Kingdom
Investigation of flow separation and reattachment of 0.2% water-based TiO2 nanofluid in an annular suddenly expanding pipe is presented in this paper. Such flows occur in various engineering and heat transfer applications. A computational fluid dynamics package (FLUENT) is used to study turbulent nanofluid flow in this research. Only a quarter of an annular pipe was investigated and simulated because of its symmetrical geometry. Standard k–ε second-order implicit, pressure based-solver equations are applied. Reynolds numbers between 17,050 and 44,545, step height ratio of 1.82, and a constant heat flux of 49,050 W/m2 were utilized in simulation. The numerical simulation results show that increase in the Reynolds number leads to an increase of the heat transfer coefficient and of the Nusselt number. Moreover, the surface temperature dropped to its lowest value after the expansion and then gradually increased along the pipe. Finally, the chaotic movement and high thermal conductivity of the TiO2 nanoparticles have contributed to the overall heat transfer enhancement of the nanofluid.
NUMERICAL STUDY OF THE INFLUENCE OF DESIGN PARAMETERS ON HEAT TRANSFER IN A HELICALLY COILED HEAT EXCHANGER
1431-1443
Shiva
Kumar
Department of Mechanical and Manufacturing Engineering, Manipal Institute of Technology,
Manipal Academy of Higher Education, Manipal — 576104, India
Pijakala
Dinesha
Department of Mechanical and Manufacturing Engineering, Manipal Institute of Technology,
Manipal Academy of Higher Education, Manipal — 576104, India
Heat exchangers play an important role in the industries comprising heat transfer applications like power plants, refineries, etc. Enhancing the heat transfer coefficient can be achieved by increasing the area of heat transfer per unit volume. This could be achieved by considering a helically coiled tube as a heat exchanger. The present paper investigates the effect of different design parameters like the tube diameter, pitch circle diameter, and pitch of the coil on heat transfer in a helical heat exchanger. A helically coiled heat exchanger was simulated for constant wall temperature boundary conditions. It was observed that the Nusselt number, heat transfer coefficients, and pressure drop were significantly affected by the change in the tube diameter and pitch circle diameter of the coil. For a mass flow rate of 0.05 kg/s, the average Nusselt number decreases by 8.8% when the pitch circle diameter is changed from 30 to 150 mm. When the tube diameter is increased from 8 to 12 mm, the Nusselt number was decreased by 62%. The influence of coil pitch on the heat transfer was not that significant.
MODELING THE NORMAL SPECTRAL EMISSIVITY OF BRASS H62 AT 800–1100 K DURING OXIDE LAYER GROWTH
1445-1458
Deheng
Shi
College of Physics and Material Science, Henan Normal University, Xinxiang 453007, China
Fenghui
Zou
College of Physics and Material Science, Henan Normal University, Xinxiang 453007, China
Zunlue
Zhu
College of Physics and Material Science, Henan Normal University, Xinxiang 453007, China
Jinfeng
Sun
College of Physics and Material Science, Henan Normal University, Xinxiang 453007, China
This work aims to model and predict the normal spectral emissivity of brass H62 at 800–1100 K during the growth of an oxide layer on the surface of specimens. During the experimental period, a specimen was completely exposed to air, so that the oxide layer could grow freely on its surface. The normal spectral emissivity was measured during a 6-h heating period at certain temperatures from 800 to 1100 K in steps of 20 K. The radiance from specimens was measured by an InGaAs detector, which worked at a wavelength of 1.5 μ;m with a bandwidth of 20 nm. The specimen temperature was measured by averaging the readings of two thermocouples. The observed strong oscillations of the normal spectral emissivity were examined and were confirmed to originate from the interference effect between the radiation from the oxide layer on the specimen surface and the radiation from the substrate. The uncertainties of the normal spectral emissivity and the temperature, to which only the surface oxidation contributed, range approximately from 3.3% to 15.9% and from 3.0 to 11.5 K, respectively. The variation of the normal spectral emissivity with the heating time was evaluated at a certain temperature. The variation of the normal spectral emissivity with the temperature for a given heating time is discussed. A simple functional form is derived which reproduces well the variation of the normal spectral emissivity with the heating time at a given temperature, including the strong oscillations occurring during the initial heating period.
CYLINDRICAL COORDINATE SYSTEM-BASED FORMULATION TO INVESTIGATE THERMAL RESPONSE OF LASER-IRRADIATED TISSUE PHANTOMS USING NON-FOURIER HEAT CONDUCTION MODELS
1459-1488
K. K.
Sravan
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai – 400076,
Mumbai, India
Atul
Srivastava
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai – 400076,
Mumbai, India
Phenomenon of heat transfer through the body of biological tissue phantoms has been numerically modelled in cylindrical coordinate system. The tissue phantom has been subjected to a train of short pulse laser irradiation. Time history of intensity distribution within the phantom has been determined through FVM-based solution of transient radiative transfer equation (RTE). The solution of RTE has been coupled with one of the most generalised non-Fourier heat conduction models, i.e. dual phase lag (DPL) model to determine the temperature field. The numerical methodology developed has been verified against the results reported in the literature. The DPL-based temperature predictions have been compared with those of Fourier and hyperbolic models. Effects of relaxation times associated with temperature gradient (τT) and heat flux (τq) have been investigated. Results reveal that non-Fourier models predict substantially higher temperature levels compared to that for the Fourier model. The studies performed to analyse the effects of τT and τq on temperature response show that τq induces wave nature to the thermal fronts propagating in the tissue medium. On the other hand, τT tends to smoothen the wave nature of sharp thermal wave fronts induced by τq. Effects of absorption inhomogeneity on temperature distributions have been captured quite well. To the best of our knowledge, the work presented is one of the first attempts to develop the cylindrical coordinate system-based numerical methodology for coupling the transient form of RTE to the most generalised non-Fourier model (dual phase lag model) and holds it importance in therapeutic applications of short pulse lasers.
CuO/WATER NANOFLUID FLOW OVER MICROSCALE BACKWARD-FACING STEP AND ANALYSIS OF HEAT TRANSFER PERFORMANCE
1489-1505
Recep
Ekiciler
Department of Mechanical Engineering, Gazi University, Ankara, Turkey
Kamil
Arslan
Department of Mechanical Engineering, Karabük University, Karabük, Turkey
Three-dimensional numerical simulation of steady-state laminar forced convection flow of a CuO/water nanofluid and heat transfer in a duct having a microscale backward-facing step (MBFS) are presented in this study. The study was conducted for determining the effects of nanoparticle volume fraction on the flow and heat transfer characteristics. The Reynolds number ranged from 100 to 1000. The step height and inlet height of the duct were 600 μ;m and 400 μ;m, respectively. The duct expansion ratio was 2.5. The downstream wall was subjected to a constant and uniform heat flux, whereas the other walls were insulated. The nanoparticle volume fraction varied from 1.0% to 4.0%. The Nusselt number and Darcy friction factor were obtained for each nanoparticle volume fraction. Plots of velocity streamlines were analyzed. It was found from
the results of numerical simulation that the Nusselt number increases with increasing nanoparticle volume fraction and
Reynolds number. The nanoparticle volume fraction does not exert any substantial effect on the Darcy friction factor and the length of the recirculation zone. Moreover, the performance evaluation criterion (PEC) was analyzed for nanoparticle volume fractions of 1.0%, 2.0%, 3.0%, and 4.0% of CuO. It was obtained that the volume fractions of 4.0% has the highest PEC in terms of heat transfer. It was obtained that while heat transfer for nanoparticle volume fraction of 30% and 4.0% the friction factor is superior for nanoparticle volume fraction of 1.0% and 2.0% due to the PEC number.
ENTROPY GENERATION DUE TO FRACTIONAL COUETTE FLOW IN A ROTATING CHANNEL WITH EXPONENTIAL HEATING OF WALLS
1507-1526
Waqas Ali
Azhar
Abdus Salam School of Mathematical Sciences, GC University, Lahore, Pakistan
Dumitru
Vieru
Department of Theoretical Mechanics, Technical University of Iasi 700050, Romania
Constantin
Fetecau
Academy of Romanian Scientists, Bucuresti 050094, Romania
The effect of the time-fractional Caputo-Fabrizio derivative on the entropy generation due to unsteady hydromagnetic fractional Couette flow in a rotating channel with the temperature of the channel walls varying exponentially is investigated analytically and numerically. Analytical solutions for primary and secondary velocity are obtained. These solutions are written as the sum of the post-transient solution (steady-state solution) and transient solution. Analytical and numerical solutions for the temperature filed, and local volumetric rate of entropy generation were obtained. Especially, we studied the influence of the fractional order parameter on the velocity components, temperature and entropy generation. It is found that the memory parameter influences only the transient parts of velocities. Therefore, after a critical time the velocity of fractional fluid will be close to that of the ordinary fluid. The fractional parameter significantly influences the temperature field and the local volumetric rate of entropy generation. The fluid temperature increases if the memory parameter decreases. The smallest value of temperature is obtained for ordinary fluids. Analyzing the influence of the fractional parameter on the dimensionless number of entropy generation and on the Bejan number, it is found that the entropy generation can be decreased by reducing the value of memory parameter.