scholarly journals Numerical investigation on the convective heat transfer in a spiral coil with radiant heating

2016 ◽  
Vol 20 (suppl. 5) ◽  
pp. 1215-1226
Author(s):  
Milan Djordjevic ◽  
Velimir Stefanovic ◽  
Mica Vukic ◽  
Marko Mancic
Keyword(s):  
Heat Transfer ◽  
Axial Direction ◽  
Outer Wall ◽  
Secondary Flows ◽  
Temperature Fields ◽  
Heat Transfer Fluid ◽  
Radiant Heating ◽  
Mean Flow ◽  
Archimedean Spiral ◽  
Spiral Coil

The objective of this study was to numerically investigate the heat transfer in spiral coil tube in the laminar, transitional, and turbulent flow regimes. The Archimedean spiral coil was exposed to radiant heating and should represent heat absorber of parabolic dish solar concentrator. Specific boundary conditions represent the uniqueness of this study, since the heat flux upon the tube external surfaces varies not only in the circumferential direction, but also in the axial direction. The curvature ratio of spiral coil varies from 0.029 at the flow inlet to 0.234 at the flow outlet, while the heat transfer fluid is water. The 3-D steady-state transport equations were solved using the Reynolds stress turbulence model. Results showed that secondary flows strongly affect the flow and that the heat transfer is strongly asymmetric, with higher values near the outer wall of spiral. Although overall turbulence levels were lower than in a straight pipe, heat transfer rates were larger due to the curvature-induced modifications of the mean flow and temperature fields.

scholarly journals EXPERIMENTAL INVESTIGATION OF THE CONVECTIVE HEAT TRANSFER IN A SPIRALLY COILED CORRUGATED TUBE WITH RADIANT HEATING

2017 ◽  
Vol 15 (3) ◽  
pp. 495 ◽  
Author(s):  
Milan Đorđević ◽  
Velimir Stefanović ◽  
Mića Vukić ◽  
Marko Mančić
Keyword(s):  
Heat Transfer ◽  
Radiation Field ◽  
Design Solution ◽  
Laboratory Model ◽  
Fluid Temperature ◽  
Radiant Heating ◽  
Archimedean Spiral ◽  
Spiral Coil ◽  
Corrugated Tube ◽  
Heat Absorber

The Archimedean spiral coil made of a transversely corrugated tube was exposed to radiant heating in order to represent a heat absorber of the parabolic dish solar concentrator. The main advantage of the considered innovative design solution is a coupling effect of the two passive methods for heat transfer enhancement - coiling of the flow channel and changes in surface roughness. The curvature ratio of the spiral coil varies from 0.029 to 0.234, while water and a mixture of propylene glycol and water are used as heat transfer fluids. The unique focus of this study is on specific boundary conditions since the heat flux upon the tube external surfaces varies not only in the circumferential direction, but in the axial direction as well. Instrumentation of the laboratory model of the heat absorber mounted in the radiation field includes measurement of inlet fluid flow rate, pressure drop, inlet and outlet fluid temperature and 35 type K thermocouples welded to the coil surface. A thermal analysis of the experimentally obtained data implies taking into consideration the externally applied radiation field, convective and radiative heat losses, conduction through the tube wall and convection to the internal fluid. The experimental results have shown significant enhancement of the heat transfer rate compared to spirally coiled smooth tubes, up to 240% in the turbulent flow regime.

A Comparative Study of DES and URANS in a Two-Pass Internal Cooling Duct With Normal Ribs

2005 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Detached Eddy Simulation ◽  
Mean Flow ◽  
Streamline Curvature ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Developing Flow

The capabilities of the Detached Eddy Simulation (DES) and the Unsteady Reynolds Averaged Navier-Stokes (URANS) versions of the 1988 κ-ω model in predicting the turbulent flow field and the heat transfer in a two-pass internal cooling duct with normal ribs is presented. The flow is dominated by the separation and reattachment of shear layers; unsteady vorticity induced secondary flows and strong streamline curvature. The techniques are evaluated in predicting the developing flow at the entrance to the duct and downstream of the 180° bend, fully-developed regime in the first pass, and in the 180° bend. Results of mean flow quantities, secondary flows, friction and heat transfer are compared to experiments and Large-Eddy Simulations (LES). DES predicts a slower flow development than LES, while URANS predicts it much earlier than LES computations and experiments. However it is observed that as fully developed conditions are established, the capability of the base model in predicting the flow and heat transfer is enhanced by switching to the DES formulation. DES accurately predicts the flow and heat transfer both in the fully-developed region as well as the 180° bend of the duct. URANS fails to predict the secondary flows in the fully-developed region of the duct and is clearly inferior to DES in the 180° bend.

Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Yunfei Xing ◽  
Fengquan Zhong ◽  
Xinyu Zhang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Outer Wall ◽  
Centrifugal Effect

Three-dimensional turbulent forced convective heat transfer and its flow characteristics in helical rectangular ducts are simulated using SST k–ω turbulence model. The velocity field and temperature field at different axial locations along the axial direction are analyzed for different inlet Reynolds numbers, different curvatures, and torsions. The causes of heat transfer differences between the inner and outer wall of the helical rectangular ducts are discussed as well as the differences between helical and straight duct. A secondary flow is generated due to the centrifugal effect between the inner and outer walls. For the present study, the flow and thermal field become periodic after the first turn. It is found that Reynolds number can enhance the overall heat transfer. Instead, torsion and curvature change the overall heat transfer slightly. But the aspect ratio of the rectangular cross section can significantly affect heat transfer coefficient.

Numerical Investigation of Flow and Heat Transfer Performance of Nano-Encapsulated Phase Change Material Slurry in Microchannels

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Sarada Kuravi ◽  
Krishna M. Kota ◽  
Jianhua Du ◽  
Louis C. Chow
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Numerical Investigation ◽  
Phase Change Material ◽  
Temperature Fields ◽  
Heat Transfer Fluid ◽  
Inlet Temperature ◽  
Bulk Fluid ◽  
Encapsulated Phase Change Material ◽  
Change Material

Microchannels are used in applications where large amount of heat is produced. Phase change material (PCM) slurries can be used as a heat transfer fluid in microchannels as they provide increased heat capacity during the melting of phase change material. For the present numerical investigation, performance of a nano-encapsulated phase change material slurry in a manifold microchannel heat sink was analyzed. The slurry was modeled as a bulk fluid with varying specific heat. The temperature field inside the channel wall is solved three dimensionally and is coupled with the three dimensional velocity and temperature fields of the fluid. The model includes the microchannel fin or wall effect, axial conduction along the length of the channel, developing flow of the fluid and not all these features were included in previous numerical investigations. Influence of parameters such as particle concentration, inlet temperature, melting range of the PCM, and heat flux is investigated, and the results are compared with the pure single phase fluid.

Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pipe Flow ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Pitch Ratio ◽  
The Mean

In the current investigation, we performed large eddy simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow in order to study the effects of periodically mounted square ribs on heat transfer characteristics. The ribs were implemented on a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models were used to model Reynolds stresses and turbulent heat flux terms. A constant and uniform wall heat flux was imposed on all the solid boundaries. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number is fixed at Pr = 0.71. The blockage ratio (BR) based on the pipe diameter and rib height is fixed with 0.0625, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology, we focus on its effects on the characteristics of turbulent heat transfer. Mean flow and temperature fields are presented in the form of streamlines and contours. How the surface roughness, manifested by the wall-mounted ribs, affects the mean streamwise-velocity profile was investigated by comparing the roughness function. Local heat transfer distributions between two neighboring ribs were obtained for the pitch ratios under consideration. The flow structures related to heat transfer enhancement were identified. Friction factors and mean heat transfer enhancement factors were calculated from the mean flow and temperature fields, respectively. Furthermore, the friction and heat-transfer correlations currently available in the literature for turbulent pipe flow with surface roughness were revisited and evaluated with the LES data. A simple Nusselt number correlation is also proposed for turbulent heat transfer in ribbed pipe flow.

Stable channel flow with spanwise heterogeneous surface temperature

2022 ◽  
Vol 933 ◽  
Author(s):  
T. Bon ◽  
J. Meyers
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Friction Coefficient ◽  
Surface Temperature ◽  
Channel Flow ◽  
Secondary Flows ◽  
Heterogeneous Surface ◽  
Length Scale ◽  
Mean Flow ◽  
The Impact

Recent studies have demonstrated that large secondary motions are excited by surface roughness with dominant spanwise length scales of the order of the flow's outer length scale. Inspired by this, we explore the effect of spanwise heterogeneous surface temperature in weakly to strongly stratified closed channel flow (at $Ri_\tau =120$ , 960; $Re_\tau = 180$ , 550) with direct numerical simulations. The configuration consists of equally sized strips of high and low temperature at the lower and upper boundaries, while an overall stable stratification is induced by imposing an average temperature difference between the top and bottom. We consider the influence of the width of the strips ( ${\rm \pi} /8 \leq \lambda /h \leq 4{\rm \pi} $ ), Reynolds number, stability and upper boundary condition on the mean flow structure, skin friction and heat transfer. Results indicate that secondary flows are excited, with alternating high- and low-momentum pathways and vortices, similar to the patterns induced by spanwise heterogeneous surface roughness. We find that the impact of the surface heterogeneity on the outer layer depends strongly on the spanwise heterogeneity length scale of the surface temperature. Comparison to stable channel flow with uniform temperature reveals that the heterogeneous surface temperature increases the global friction coefficient and reduces the global Nusselt number in most cases. However, for the high-Reynolds cases with $\lambda /h \geq {\rm \pi} /2$ , we find a reduction of the friction coefficient. At stronger stability, the vertical extent of the vortices is reduced and the impact of the heterogeneous temperature on momentum and heat transfer is smaller.

Heat Transfer Enhancement by EHD-Induced Oscillatory Flows

2005 ◽  
Author(s):  
F. C. Lai ◽  
J. Mathew
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Heat Transfer Enhancement ◽  
Numerical Solutions ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Temperature Fields ◽  
Transfer Enhancement ◽  
Periodic Flows ◽  
Small Reynolds Numbers

Prior numerical solutions of electrohydrodynamic (EHD) gas flows in a horizontal channel with a positive-corona discharged wire have revealed the existence of steady-periodic flows. It is speculated that heat transfer by forced convection may be greatly enhanced by taking advantage of this oscillatory flow phenomenon induced by electric field. To verify this speculation, computations have been performed for flows with Reynolds numbers varying from 0 to 4800 and the dimensionless EHD number (which signifies the effect of electric field) ranging from 0.06 to ∞. The results show that heat transfer enhancement increases with the applied voltage. For a given electric field, oscillation in the flow and temperature fields occurs at small Reynolds numbers. Due to the presence of oscillatory secondary flows, there is a significant enhancement in heat transfer.

scholarly journals Thermal Modernization of the Panel Buildings External Walls

2018 ◽  
Vol 7 (3.2) ◽  
pp. 116
Author(s):  
Olena Filonenko ◽  
Oleg Yurin ◽  
Olga Kodak
Keyword(s):  
Heat Transfer ◽  
Thermal Protection ◽  
Residential Buildings ◽  
Outer Wall ◽  
Temperature Fields ◽  
Heat Conducting ◽  
Protection Level ◽  
Protective Properties ◽  
Wall Panels ◽  
Before And After

The thermal protection level of the first mass series panel buildings (series 111-94) is the lowest among residential buildings in Poltava. The problems of these buildings’ thermal modernization, is consideration of heat-conducting inclusions effect on the reduced resistance to heat transfer. In the studies such heat-conducting inclusions as the panel joints’ design, the window slope and the external wall geometry (the external corner) were taken into account. Studies were performed for the four pattern sections of the outer wall. Panels of two thickness variants with two joint designs were under consideration.To analyze the thermal protection level, the results of the two-dimensional temperature fields’ calculations were used. The analysis of the wall panels’ thermal protection level before the thermal modernization was performed. The magnitude of the heat conducting inclusions effect on reduced resistance of the walling to the heat transfer before and after the thermal modernization is determined. Possible ways of improving the wall panels’ heat-protective properties to the level of the standards in Ukraine are considered. The optimal variant of insulation for each pattern was chosen.  

The Characteristics of Spiral Vortex Flow at High Taylor Numbers

1979 ◽  
Vol 21 (2) ◽  
pp. 65-71 ◽  
Author(s):  
M. M. Sorour ◽  
J. E. R. Coney
Keyword(s):  
Vortex Flow ◽  
Hydrodynamic Instability ◽  
Wave Length ◽  
Axial Direction ◽  
Outer Wall ◽  
Mean Flow ◽  
Annular Gap ◽  
Spiral Vortex ◽  
The Mean ◽  
Made In

This experimental investigation is devoted to the study of combined axial and rotational flow in a concentric annular gap, of radius ratio 0.8, formed by a stationary outer and a rotatable inner cylinder. Taylor numbers varying from the critical to an order of 106 will be considered. The investigation is divided into three parts, illustrating different aspects of spiral vortex flow. Firstly, the evolution of the flow with increasing Taylor number at a constant axial Reynolds number is studied by the analysis of the spectrum of the signal from a hot-wire anemometer. Secondly, the wave length and drift velocity of the spiral vortices are determined for the axial direction. Thirdly, the effects of hydrodynamic instability on the mean flow are investigated. It should be noted that the first and second parts are under adiabatic conditions, while the third is both adiabatic and diabatic, heat being transferred isothermally through the outer wall of the annular gap. Also, all of the measurements were made in the fully-developed region of the flow.

The Experimental and Computational Study of a New Cooling Strategy for Turbomachinery Rotational Components

2005 ◽  
Author(s):  
N. I. Elhabeshi ◽  
S. M. Guo
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Closed Loop ◽  
Imaging System ◽  
Computational Study ◽  
Turbine Blades ◽  
Temperature Fields ◽  
Heat Transfer Fluid ◽  
Rotational Components

Many cooling methods have been developed for gas turbine rotational components. Film cooling is one of the most commonly used technique, which introduces cold air through film cooling holes onto the outer surfaces of gas turbine components to protect them from hot mainstreams. Although film cooling is very effective, it is well known that film cooling could reduce the engine power rating and introduce losses, mainly due to the direct coolant/mainstream interactions. In this paper, a preliminary study of a new closed-loop rotor cooling technique is reported. Filled with suitable heat transfer fluid, this closed loop design is applicable to turbomachinery rotors. Due to the combined buoyancy-centrifugal forces under turbine working conditions, the heat transfer fluid could transport the heat effectively from the outer surface of the blade to the internal cooling air. Instead of relying on the temperature gradient inside the blade walls for heat absorption from the high temperature mainstream side to the low temperature cooling airside, these closed loops act as heat transport superhighways. With proper insulation, the center part of the blade walls could be kept at a lower temperature, comparing to the conventional cooling designs. This would potentially provide vital important extra mechanical strength to the highly loaded turbine blades. Preliminary experimental work and CFD predictions have been conducted to prove this novel design. The tests were conducted using a rotational disk at a speed up to 1500 rpm. A liquid crystal based imaging system was employed to measure the surface temperature under transient conditions. Steady/unsteady 2D/3D CFD predictions were carried out to provide detailed information about the flow and temperature fields inside the proposed cooling configuration. Both experimental and computational work proved that this new design would work, providing the mechanical and manufacturing requirements could be met.

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