Experimental investigation of pulsating flow structures and heat transfer characteristics in sinusoidal channels

In the present work, hydrodynamics and heat transfer characteristics in the sinusoidal channel are investigated experimentally for both steady and pulsating flow conditions. The experiments for heat transfer investigations were performed under a constant heat flux in the range of Strouhal number, St 0.11? St ?2.07for the Reynolds number, in the range of 4 × 103?Re?7 × 103. After seeing the improvement of heat transfer with employing pulsation to the working fluid the hydrodynamics of pulsating flow was analyzed by considering the pulsating flow characteristics such as the time-averaged streamlines topology, , streamwise velocity distribution, , cross-streamwise velocity distribution, , and turbulent Reynolds stress, u'v'¯/U2 using instantaneous flow data measured by the Particle image velocimetry (PIV) system. The results revealed that pulsating flow is highly effective for the lower turbulent flow case in the sinusoidal channel. As the Reynolds number increases, the effect of Strouhal number, St becomes less effective. There is an optimum Strouhal number,St value for different Reynolds numbers, Re to reach the maximum enhancement compared to steady flow cases. The entrainment between the core flow and recirculating flow enhances the heat transfer rates in a steady flow. But the pulsating flow forces the recirculating flow zones in the diverging-converging section of the channel wave to exchange the flud from the core flow region further and that is an additional mechanism to upgrade the rate of heat transfer comparing to the steady flow cases. © 2019Firat University Scientific Research Projects Management UnitThe authors wish to thank the office of Scientific Research Projects of Çukurova University for funding this project under Contract no. FDK-2016-6339

A review of hydrodynamics and heat transfer through corrugated channels

Ever-increasing consumption of limited energy sources forces researchers and engineers to produce more efficient energy systems in order to use energy sources effectively. Enhancing the heat transfer rate with an acceptable pressure drop is an important parameter to produce more compact heat exchangers which are used in air-conditioning systems, chemical reactors, thermal power plants and others. Nowadays many engineering techniques such as surface modifications, swirl flow creators, flow conditioners, additives, etc. are implemented to enhance the heat transfer performance of energy systems. Researchers are still interested in the implementation of these techniques to improve the performance of energy systems further although the current literature has many experimental and numerical research data. Even though the corrugated channel is a passive technique to augment heat transfer, researchers have been insisting on trying to get further improvement by implementing one or more passive/active techniques to corrugated channels. The objective of the present work is to gather available research data which particularly focus on the flow characteristics and heat transfer rates through the corrugated channels. The design parameters, practical limitations and conclusions of energy systems, obtained previously are presented in tabular forms and the necessary discussion is also provided. © 2019 Elsevier LtdFirat University Scientific Research Projects Management UnitThe authors wish to thank the office of Scientific Research Projects of Çukurova University for funding this project under Contract No. FDK-2016-6339

Heat transfer and flow characteristics in a sinusoidally curved converging-diverging channel

The objective of this work is to present the thermal performance characteristics and to examine the hydrodynamic structure of the fluid which improves the rate of heat transfer in parallel with the penalty of pressure drop by means of the time-averaged streamlines topology, <?>, streamwise velocity distribution, <u>, vorticity concentration, <?> and turbulent Reynolds stress, u'v'? /U2 for the sinusoidal wavy channel. A wide range of experiments were performed for Reynolds numbers, Re ranging from 4 × 103 to 1 × 104 in order to determine the heat transfer rate and the friction factor, f with varying the channel height expansion/contraction ratio, M = Hmin/Hmax such as 0.5, 0.35 and 0.28. The results revealed that a significant heat transfer enhancement was achieved with a considerable penalty of pressure drop. The highest thermal performance factor, TPF was obtained as 1.46 for M = 0.5. Numerical simulations were conducted to confirm the experimental results for the same parameters. The Shear Stress Transport k-w (SST k-w) turbulence model was used to perform numerical analyses. After ensuring the consistency of experimental thermal performance results with numerical predictions, the Particle image velocimetry (PIV) system was utilized for investigating the flow physics in the sinusoidally curved converging-diverging channel for all M values at Re = 4 × 103 where the TPF is maximum. © 2019 Elsevier Masson SASFirat University Scientific Research Projects Management UnitThe authors wish to thank the office of Scientific Research Projects of Çukurova University for funding this project under Contract No. FDK-2016-6339 . Appendix When conducting the numerical simulation, the equations for turbulence model were used in the section of 2.1. In equations (2)–(4) , the subscript t represents “turbulent.” Value of the Pr t is determined as 0.85 and the turbulent viscosity, µ t is defined by µ t = ? * ? k ? . Here k and ? represent turbulence kinetic energy and specific dissipation rate, respectively. The coefficient ?* has introduced by Wilcox [ 33 ] in order to define the boundary-layer transition that is defined by: (A.1) ? * = ? ? * ( ? 0 * + R e T / R k 1 + R e T / R k ) where Re T = ? k µ? , R k = 6 , ? 0 * = ß i 3 , ß i = 0.072 The transport equations for k and ? are as follows: (A.2) ? ? t ( ? k ) +   ? ? x i ( ? u ? i k ) =    ? ? x j   [ ( µ + µ t ? k ) ( ? k ? x j ) ] + G ˜ k - Y k (A.3) ? ? t ( ?? ) +   ? ? x i ( ? u ? i ? ) = ? ? x j   [ ( µ + µ t ? ? ) ( ? ? ? x j ) ] + G ? - Y ? + D ? ? k and ? ? correspond to the turbulent Prandtl numbers. Their definition is given as: (A.4) ? k = 1 F 1 ? k , 1 + ( 1 - F 1 ) ? k , 2 (A.5) ? ? = 1 F 1 ? ? , 1 + ( 1 - F 1 ) ? ? , 2 F 1 is called blending function and its definition is as follows: (A.6) F 1 = tan ( ? 1 4 ) where ? 1 is defined by: (A.7) ? 1 = min [ m a x ( k 0.09 ? y , 500 µ ? y 2 ? ) , 4 ? k ? ? , 2 D ? + y 2 ] D ? + denotes the positive portion of the cross-diffusion term. (A.8) D ? + = m a x [ 2 ? 1 ? ? , 2 1 ? ? k ? x j ? ? ? x j , 10 - 10 ] The production and dissipation terms in Eqs. (A.2, A.3) represented as ( G ˜ k G ? ) and ( Y k , Y ? ) respectively and they are expressed as (A.9) G ˜ k = m i n ( G k , 10 ? ß * k ? ) ; G ? = ? ? µ t G k G k = - ? u i ' u j '   ? ( ? u j ? x i ) is turbulence kinetic energy production caused by mean velocity gradients. (A.10) Y k = ? ß * k ? ; Y ? = ?ß ? 2 and D ? in eq. (A.3) is (A.11) D ? = 2 ( 1 - F 1 ) ? ? ? , 2 1 ? ? k ? x j ? ? ? x j where ß is a model constant and ? is thermal diffusivity which is defined by Eq. (A.11) . (A.12) ? = ? ? ( ? 0 * + R e ? 1 + R e T / R e ? ) Here R e ? = 2.95 , ? 0 * = ß i 3 and ? ? = F 1 ? ? , 1 + ( 1 - F ) ? ? , 2 , ß i = F 1 ß i , 1 + ( 1 - F ) ß i , 2 . The terms ? ? , 1 and ? ? , 2 are given as: (A.13) ? ? , 1 = ß i , 1 ß ? * - ? 2 ? ? , 1 ß ? * (A.14) ? ? , 2 = ß i , 2 ß ? * - ? 2 ? ? , 2 ß ? * where K?=?0.41. Model constants used in above equations are summarized in Table A.1 . Table A.1 Model constants. Table A.1 ? k , 1 = 1.176 ? k , 2 = 1.0 ? ? , 1 = 2.0 ? ? , 2 = 1.168 ? 0 * = 1 / 9 ? 1 = 0.31 ? ? = 0.52 ? ? * = 1.0 ß i , 1 = 0.075 ß i , 2 = 0.0828 ß i = 0.072 ß ? * = 0.09 R ß = 8.0 R k = 6 .0 R e ? = 2.95 ? * = 1.5 ? k = 2.0 ? ? = 2.0 a amplitude of a wavy (m) A area (m 2 ) c specific heat capacity (j/kgºC) D H hydraulic diameter, m E enhancement f friction factor f* relative friction factor H channel height (m) h convective heat transfer coefficient (W/m 2 ºC) k turbulent kinetic energy L Length of a wavy (m) P pressure Pr Prandlt number q ' heat flux (W/m 2 ) Q ' heat transfer rate (W), flow rate (kg/s) Re Reynolds number Nu Nusselt number T temperature t time TPF thermal performance factor u streamwise velocity (m/s) v transverse velocity (m/s) U free-stream velocity (m/s) u' streamwise velocity fluctuation v' transverse velocity fluctuation time-mean velocity distribution w width of channel (in z direction) (m) y+ dimensionless length of next-to-wall cel

Paediatric lateral humeral condyle fractures: internal oblique radiographs alter the course of conservative treatment

PubMed: 23959034Introduction: At first presentation of paediatric humeral lateral condyle fractures, radiological methods such as computerised tomography, ultrasonography, magnetic resonance imaging, arthrography, and internal oblique radiography are used to determine stability. Very few studies show which radiological method should be used to evaluate displacement at follow-up for conservatively treated patients. This study aimed to show that internal oblique radiography is a simple, effective method to determine the subsequent development of fracture displacement in patients with an initially non-displaced or minimally displaced fracture. Materials and methods: In this retrospective study, 27 paediatric patients with non-displaced or minimally displaced (2 mm as a result of the evaluation of the internal oblique radiography and underwent surgery. At follow-up, 2 of 11 patients were defined with displacement from anteroposterior and internal oblique radiographs and 4 from the internal oblique radiographs and underwent surgery. Conservative treatment was applied to 5 patients. Conclusions: Internal oblique radiography is the best imaging showing subsequent fracture displacement in initially non-displaced or minimally displaced humerus lateral condyle fractures. At the first week follow-up, anteroposterior and particularly internal oblique radiographs should be taken of conservatively treated patients. © 2013, Springer-Verlag France

3D resistivity imaging from an archaeological site in south-western Anatolia, Turkey: a case study

A large-scale resistivity imaging survey was performed in the acropolis area of Archaic Cnidos, south-western Turkey. This survey was a part of the geophysical studies conducted between 1999 and 2004. Two-dimensional resistivity data were acquired along a number of parallel lines using a pole-pole array. The data was processed using a 3D inversion algorithm based on a robust technique. We also applied shaded-relief processing to enhance the representation of the images of apparent-resistivity data and inversion results. In addition, the inverted resistivity data were visualized by a volumetric representation technique to display both the horizontal and the vertical extents of the archaeological structures. The inversion results revealed that a rectangular gridding pattern and a dense structuring existed in the depth range 0.35-1.5 m in the acropolis. Moreover, the bedrock was the base of the archaeological structures in the area. Based on the resistivity survey, four test excavations were carried out in various localities in the acropolis in 2004. These excavations yielded results supporting those obtained by the resistivity inversion. This indicated that large-scale 3D resistivity imaging can be a useful tool in archaeological prospection

Modified myocardial performance index is not affected in fetuses with an isolated echogenic focus in the left ventricle

Objectives: We prospectively investigated the efficacy of modified myocardial performance index (mod-MPI) in the assessment of cardiac functions in fetuses with and without an isolated hyperechogenic focus (IHF) in the left ventricle and compared with conventional fetal echocardiography