Vortex Heat Transfer Enhancement Research Articles

Study on the efficient heat transfer mechanism of microchannel pin-fin arrays under low pumping power

The efficient heat transfer with low pressure loss has long been a critical challenge in the microchannel heat sinks (MCHS) design. Further study is required for the quantitative analysis of the longitudinal vortex heat transfer enhancement mechanism. In this research, a microchannel heat transfer experiment and corresponding simulations are conducted. Based on the common Reynolds number range in engineering applications of MCHS, the underlying causes of heat transfer enhancement and pressure loss increase in MCHS with respect to Reynolds numbers is clarified. The results show that when the Reynolds number is 400, the cylindrical wake reduces the synergistic angle between the velocity and the temperature gradient at the streamwise gap, which greatly enhances the heat transfer performance of MCHS. In addition, when the Reynolds number is 900, the early separation of the cylindrical wake vortex leads to a significant reflux near the center of the spanwise gap, which significantly increases the pressure loss. A Different Reynolds number Efficiency Evaluation Criterion (DEEC) is proposed for evaluating the performance of MCHS. It is found that the flow state of cylindrical wake with Reynolds number of 400 has the best heat transfer efficiency. The concept of introducing longitudinal vortices into the pin–fin array can serve as a key guideline in the heat transfer enhancement optimization design of MCHS.

Vortex heat transfer enhancement by energy-efficient structured plates with zigzag grooves for micro- and macro-scale energy and electronic devices

An energy-efficient flat surface is formed when applying single-row cross-flow zigzag grooves (VVVVVV) in a dense arrangement. Convective heat transfer is considered in turbulent flow around a longitudinal fragment of a plate with a length of 40 and a width of 4 with a package of 14 singlerow inclined backslash(\\)-shaped grooves with symmetry conditions at the lateral boundaries. The width of the grooves is 1, the depth is 0.25, the edge rounding radius is 0.2, the angles of inclination are 30°, 45°, 50° and 60°, the pitch is 2.4, the Reynolds number is 104, and the thickness of the incoming boundary layer is 0.175. The phenomenon of anomalous enhancement of the separation flow and heat transfer in zigzag grooves and acceleration of the wall flow discovered in inclined oval-trench dimples has been confirmed.

Vortex heat transfer enhancement on energy-efficient surfaces structured by inclined trench dimples

Experimental measurements and numerical predictions of the longitudinal component of the air velocity in a narrow channel with two rows of 26 densely packed oval trenches at angles of ±45° and ±135° in laminar (Re=103) and turbulent (Re=4×103) regimes have been compared. The acceptability of the RANS approach using the modified SST turbulence model within the Rodi–Leschziner–Isaev approach has been substantiated. The flow acceleration in the dimpled channel up to the longitudinal velocity maxima of 1.85 and 1.55 of the average bulk velocity for laminar and turbulent air flows has been experimentally confirmed.

Vortex heat transfer enhancement in the separated flow near structured dimpled surfaces

The numerically discovered phenomena of abnormal enhancement of the separated flow in the inclined oval-trench dimple (OTD) and the flow acceleration in the dimpled narrow channel are substantiated experimentally. The analysis of turbulent flow around a deep OTD on the plate and on the channel wall show that within the inclination angle range from 25° to 85°, the pressure drop is seen between the zones of stagnation on the windward slope and of rarefaction in the place where a tornado-like vortex is generated. The velocity field measurements in the narrow channel with two rows of inclined OTDs at the inclination angles of ±45° and ±135° reveal that the shear flow with a maximum velocity in front of the dimple entrance is formed in the flow core. This maximum shear flow velocity exceeds the maximum velocity in the plane-parallel channel.

Simulation of Vortex Heat Transfer Enhancement in the Turbulent Water Flow in the Narrow Plane-Parallel Channel with an Inclined Oval-trench Dimple of Fixed Depth and Spot Area

This article is devoted to the development of the multiblock technique for numerical simulation of vortex heat transfer enhancement (VHTE) by inclined oval-trench dimples. Special attention is paid both to the analysis of numerical predictions of different-type boundary conditions at the wall: T = const and q = const and to the comparison of the standard and modified shear stress transport models. The article discusses the mechanism of change in the flow structure and secondary flow augmentation due to an increase in a relative length of an oval-trench dimple (at its fixed spot area, depth and orientation) where a long spiral vortex is formed.

Vortex heat transfer enhancement in the narrow plane-parallel channel with the oval-trench dimple of fixed depth and spot area

The article is devoted to the analysis of vortex heat transfer enhancement due to the use of oval-trench dimples. The main role in the understanding of this process is associated with the application of the technologies developed in engineering practice thanks to design decisions. As a result, prevailing interest has been paid to a spherical dimple when a spot diameter is chosen as a characteristic size, whereas hydraulic losses depend on the dimple-to-device size ratio. Progress in vortex heat transfer enhancement due to the use of oval dimples is connected with the explanation of the mechanism of generation of both vortex structures in dimples and spiral vortices behind them. An abrupt increase of heat transfer in the vicinity of the spherical dimple due to the restructuring of the flow structure in the dimple with two vortices to that in the dimple with one spiral vortex made it possible to propose a new shape of a surface vortex generator – an oval dimple located at an angle of inclination to the incoming flow and consisting of two spherical dimple halves separated by a cylindrical insert. The generation of vortex structure in this case is rather stable and intense in comparison to spherical dimple. The numerical results for vortex heat transfer enhancement in the turbulent water flow in the rectangular narrow channel with spherical, 10°-truncated conical and oval dimples of the same spot area and depth at the heated wall are presented. In the article, central attention is given to the mechanism of secondary flow restructuring and heat transfer enhancement due to increase in a relative length and width of an oval dimple followed by the formation of a long spiral vortex in it. The change in the length of the oval dimple (in terms of its width) from 1 to 6.78 allowed one to rationally mount spiral vortex surface generators in the narrow channel with high thermal and thermal-hydraulic efficiencies, significantly exceeding the identical characteristics of channels with spherical and conical dimples. In this case, moderate hydraulic losses in the channel with an oval-trench dimple, when its length is increased to 6.78, are comparable to those in the channel with a basic spherical dimple.

Numerical simulation of the turbulent air flow in the narrow channel with a heated wall and a spherical dimple placed on it for vortex heat transfer enhancement depending on the dimple depth

Numerical study is made of heat transfer enhancement in the narrow channel with insulated walls in air steady flow around a heated spherical dimple, when its relative depth is varied from 0 to 0.26 (in terms of spot diameter) at a defined Reynolds number 4×104 based on bulk velocity and dimple spot diameter. The applicability of multiblock computational technologies for solution of Reynolds and energy equations with the implication of an implicit factorized finite-volume algorithm and overlapping different-scale structured grids of different topology, as well as the verification of the shear stress transfer model (SST model) modified with regard to the streamline curvature within the framework of Leschziner–Rodi–Isaev’s approach is assessed from the comparison of numerical predictions obtained by different SSTM versions. Flow regimes in a spherical dimple, as its depth is increased, are classified on the basis of the analysis of change in the jet–vortex flow structure in the dimple and its wake in the channel. In what follows, special attention is paid to asymmetric flow around a dimple with the greatest vortex heat transfer enhancement.

Numerical Simulation of Vortex Heat Transfer Enhancement in Transformer Oil Flow in a Channel with One-Row Spherical Dimples

Numerical Simulation of Vortex Heat Transfer Enhancement in Transformer Oil Flow in a Channel with One-Row Spherical Dimples

Experimental study of vortex heat-transfer enhancement mechanisms

In this paper comparative analysis of various heat transfer enhancement method effects and the experimental study results of vortex heat transfer enhancement physical mechanisms are presented. Experimental investigations were made of friction and heat transfer on surfaces shaped by systems of spherical cavities streamlined by a turbulent flow. Also flow structure in single, two- and three -dimensional cavities is investigated. The experiments were run on a special aerodynamic test bed using a traditional procedure for diagnosing a turbulent boundary layer. Obtained results allow to conclude that such a shaping of a heating surface has no appreciable effect on the hydrodynamics of a flow with considerable (up to 30–40%) heat transfer enhancement. Experimental data on heat transfer are generalized, and a relationship suitable for engineering estimation of heat transfer on surfaces shaped by a regular relief of spherical cavities and valid for the investigated geometric parameters of shaping and flow regimes has been obtained. Also, obtained results allow to formulate the physical flow model in the single cavity dependent on the geometric parameters and flow regime. Besides, the vortex technology problems, practical application of heat transfer enhancement by vortex method and progress prospectives are elucidated.