Crossflow Fluid Research Articles

An experimental investigation of cross flow heat transfer and fluid flow of air over a longitudinally finned flat tubes bank

ABSTRACT This paper experimentally investigates the effect of transverse pitch on the heat transfer and fluid flow performance of the longitudinally finned flat tubes (LFFT) bank with staggered configurations. The studied Reynolds number (Re) was based on the hydraulic diameter of the flattened tube with a range of 223 ≤ Re ≤ 1114 . The tubes surfaces were maintained at constant temperature. Three dimensionless transverse pitches ( S T ˆ ) of LFFT were investigated, i.e. 3.0, 4.0, and 5.0, for dimensionless longitudinal pitch ( S L ˆ ) = 4.0, dimensionless upstream fin length ( L u ) ˆ = 0.8, dimensionless downstream fin length L d ˆ = 0.8, and dimensionless fin angle ( θ ˆ ) = 0.52, i.e. θ = 30°. The results showed that increasing S T ˆ from 3 to 5 slightly increased Nu at low Re, i.e. by 1.2% at Re = 223, At higher Re, i.e. 1114, Nu decreased by 20.8% for the same S T ˆ increase. Be decreased with increasing S T ˆ up to 60.7% at Re = 223. The thermal-hydraulic performance increased up to 153% at Re = 223.

Thermal Performance and Parametrical Analysis of Topologically-optimized Cross-flow Heat Sinks Integrated with Impact Jet

In this work, two novel cross-flow heat sink structures are firstly designed by means of topological optimization with the objective function which aims to achieve the minimum temperature difference and pressure drop or with the other objective function which aims to get the minimum mean temperature and pressure drop, namely, TOS1 and TOS2. By analyzing the effect of six channel heights Hch of TOS1 and TOS2 with the evaluation criterion j/f, we obtain that TOS2 with the Hch of 5 mm has the best ability of heat dissipation. A impact jet part is then implemented into the TOS2 to form a new integrated heat sink, that is, ITOS. Numerical results show that the ITOS exhibits much better thermal performance than TOS2 and TOS1. The in-depth parametric study on the flow and thermal behaviors of the ITOS shows that the average temperature of the bottom surface of the ITOS increases with the height of the channel of the bottom plate, while the temperature difference peaks at the Hch of 2 mm. The increase of the ratio of cross-flow fluid to total fluid leads to a reduction of the heat dissipation ability, implying that the high thermal performance of the impinging jet plays an important role in the heat transfer process of such ITOS. Finally, the convective heat transfer experiment of the ITOS with the Hch of 5 mm is conducted to testify the optimization and simulation results.

Investigations on the effect of graphene coating on thermophysical properties of aluminium and mild steel for cross flow heat exchanger

In a cross-flow heat exchanger, heat transfer and fluid dynamics studies were conducted to observe the performance of graphene coated pipes. The heat exchanger consists of a linear pipe made of Aluminum 6061-T6 and Mild Steel in separate studies carrying a heated fluid. The thermal interactions between the heated fluid having a laminar flow and the walls of the pipe have been studied under the influence of an external environment of water having a turbulent flow, in a direction normal to the pipe. A RANS model with a k-ε variant was used to model the behavior of different material pipes which were observed under the varying conditions of turbulence, velocity, pressure, and vorticity. When subjected to the same conditions, plots of the temperature gradient, isothermal contours, heat transfer coefficient against Reynolds number and thermal conductivity modelled against the various graphene coating thicknesses studied have shown that out of Aluminum 6061-T6 and Mild Steel, the former has shown a significant increase in thermal conductivity on the addition of a Graphene coating. Simulation results showed an increase in Aluminium 6061 T6′s conductivity by 6.8975% with a continuous decrease in the heat transfer coefficient, whereas Mild Steel showed an anomaly in the heat transfer coefficient value which peaked at 1.2 mm thickness of graphene coating with a value of 3858.862 W/m2K.

High-Speed Imaging of Forced Ignition Kernels in Nonuniform Jet Fuel/Air Mixtures

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates nonuniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel–air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel–air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low-aromatic/low-cetane-number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high-aromatic, more easily ignited fuel, shows the largest reaction region at early times.

Effect of crossflow velocity on underwater bubble swarms

We investigate the effect of crossflow velocity on submerged bubble plumes or swarms by employing the use of high-speed photography and an image-processing method to measure bubble rise velocities. Particle image velocimetry (PIV) was used to accurately determine the crossflow freestream velocity as well as boundary layer information. We varied the gas flow rates from 2 to 25 L/min. This range exceeds those of previous studies we could find in the open literature which were mostly less than 5 L/min and involved isolated bubbles. Combined with the crossflow velocities, this resulted in the investigation of a wide range of flow conditions providing a database of 36 experimental data points and constitutes a substantial addition to the bubble swarm/crossflow literature. Because our experiments involved larger gas flow rates than previously reported, we had to develop a digital image-processing algorithm using standard functions in Matlab to measure swarm rise velocities, and angles of inclination under crossflow. Results were validated against reported data at similar experimental conditions. It was established that increasing freestream velocity strongly suppressed bubble rise velocities and resulted in bubble breakup. Relationships for predicting rise velocity and inclination angle were derived as non-dimensional functions of the crossflow velocity, fluid properties and inlet gas flow rates. These showed good agreement with the current as well as reported experimental data.

Near-field dynamics of parallel twin jets in cross-flow

The present study examines the near-field flow developments and dynamics of parallel twin jets in cross-flow (TJICF) configured with jet-to-jet separation distances of 1.5 to 3 jet diameters (D) and velocity ratios of 2, 4, and 6. Both laser-induced fluorescence and particle-image velocimetry measurements were made along the streamwise and cross-stream planes in order to investigate the effects of the separation distance and velocity ratio upon the deflected jet and the formation of counter-rotating vortex-pairs (CVPs) within the near-field region. Results show that each jet in the parallel TJICF configuration attains higher cross-flow entrainment and produces greater jet half-widths than a single jet in cross-flow (SJICF). Moreover, as the separation distance decreases to 1.5D, the twin jets interact closer to the jet exit such that organized leading-edge and lee-side vortices are present along the symmetry plane. Cross-stream results indicate that the pair of inner vortices associated with the two resulting CVPs is being induced to move towards each other along the symmetry plane, where their opposite-signed vorticities annihilate with each other eventually. As such, the vorticity transition from two CVPs into a resulting single CVP takes place quickly within the near-field region when the separation distance is sufficiently small. Streamwise circulation decays determined for parallel TJICF show that their circulations increase moderately when the two CVPs begin to interact with each other. Further examination into the Reynolds shear stresses indicates that there exists substantial flow shear stress as the pair of inner vortices interacts, which yields higher entrainment level of the cross-flow fluid in regions adjacent to the symmetry plane. As a result, the near-field jet trajectories for each jet in the parallel TJICF are always lower than that of the corresponding SJICF when the separation distance is small, regardless of the velocity ratios.

Direct numerical simulation of a low momentum round jet in channel crossflow

Results of a direct numerical simulation of a jet in crossflow with passive scalar mixing are presented. The laminar jet issues from a circular exit into the channel crossflow with a low jet-to-crossflow velocity ratio of 1/6. The governing equations are solved by Incompact3d, an open-source code combining the high-order compact scheme and Poisson spectral solver. An internal recycling approach is used to generate the fully turbulent channel flow profile. Four main flow structures are identified: 1) a large recirculation seen immediately downstream of the jet-exit; 2) a contour-rotating vortex pair formed from the stretching and reorientation of the injection-flow vorticity; 3) a horseshoe vortex generated as a result of the stretching of the vorticity at the jet-exit windward side; 4) shear layer vortices coming from the lifted and shed crossflow boundary layer vorticity. Passive scalar profiles show the mixing are strong in the shear layer where the crossflow fluid encounters the jet fluid. The database is made available online for public access.

Large-eddy simulation of a pulsed jet into a supersonic crossflow

Abstract Numerical investigation of a pulsed jet injected into a supersonic crossflow was carried out using large-eddy simulation. The corresponding steady jet injection was also calculated for comparison with the pulsed jet injection and for validation against experimental data. Various fundamental mechanisms dictating the intricate flow characteristics, such as multi-scale vortical structures, complex shock systems, mixing properties and turbulence behaviors, have been studied. As the pulsed jet issuing transversely into the supersonic crossflow, the salient shock systems and vortical structures in terms of the instantaneous and phase-averaged flow field are analyzed. The large-scale jet shear vortices are formed along the interface of jet and crossflow due to the pulsation effect, which can promote the engulfing of the crossflow fluid and the mixing of the jet and crossflow fluids. Further we investigate turbulence properties of the jet and crossflow interaction and scalar statistics of the injectant mass fraction to reveal jet penetration enhancement and mixing property improvement for the pulsed jet. Results obtained in this study provide physical insight into the understanding the mechanisms for the interaction of pulsed jet and supersonic crossflow.

Liquid Fuel Composition Effects on Forced, Nonpremixed Ignition

The effects of jet fuel composition on ignition probability have been studied in a flowfield that is relevant to turbine engine combustors, but also fundamental and conducive to modeling. In the experiments, a spark kernel is ejected from a wall and propagates transversely into a crossflow. The kernel first encounters an air-only stream before transiting into a second, flammable (premixed) stream. The two streams have matched velocities, as verified by hot-wire measurements. The liquid fuels span a range of physical and chemical kinetic properties. To focus on their chemical differences, the fuels are prevaporized in a carrier air flow before being injected into the experimental facility. Ignition probabilities at atmospheric pressure and elevated crossflow temperature were determined from optical measurements of a large number of spark events, and high-speed imaging was used to characterize the kernel evolution. Eight fuel blends were tested experimentally; all exhibited increasing ignition probability as equivalence ratio increased, at least up to the maximum value studied (∼0.8). Statistically significant differences between fuels were measured that have some correlation with fuel properties. To elucidate these trends, the forced ignition process was also studied with a reduced-order numerical model of an entraining kernel. The simulations suggest ignition is successful if sufficient heat release occurs before entrainment of colder crossflow fluid quenches the exothermic oxidation reactions. As the kernel is initialized in air, it remains extremely lean during the initial entrainment of the fuel–air mixture; thus, richer crossflows lead to quicker and higher exothermicity.

A new archive of heat transfer coefficients from square and chamfered cylinders at angles of attack in crossflow

Calculations of convection heat transfer coefficients between a fluid in crossflow and two-dimensional square-cylindrical objects have been performed using numerical simulation. Some calculations included geometries with chamfered corners while others were sharp-edged. The numerical model allows a systematic study of various angles of attack and lengths of chamfer so that the entire range of angles and chamfers were investigated. It was found that the present results are in good agreement with previously published archival values for similar geometries and Reynolds numbers. In this regard, the present work significantly expands the upper bound of the Nusselt–Reynolds correlation.Comparison among the many investigated geometrical configurations reveals that more extensive chamfering results in a lowered dependence of the Nusselt number on the Reynolds number. In the lower range of the Reynolds numbers dealt with in this study, there was near parity in the Nusselt number values for square and octagonal chamfered cylinders; however, at the higher Reynolds number range (approximately 2,000,000), the octagon Nusselt numbers were ∼80% of those of the square for a zero-degree angle of attack. The largest angle of attack (45°) also exhibited Nusselt number values that were comparable for the square and octagonal shapes in the lower range of Reynolds numbers. However, at the higher Reynolds numbers, the results differed by approximately a factor of two (square cylinder Nusselt number is larger than the octagonal Nusselt number). The results calculated here for air are extended to other fluids by a simple calculation involving the ratio of Prandtl numbers.

Cross-flow effects on impingement array heat transfer with varying jet-to-target plate distance and hole spacing

New impingement heat transfer data are presented for experimental conditions and configurations employed have not been previously examined, which illustrate the effects of impingement cross-flows on local, line-averaged, and spatially-averaged Nusselt numbers, as both jet-to-target distance and jet hole spacing are altered. Data are given for a constant impingement jet Reynolds number of 8000. In general, the impingement passage cross-flows which accumulate are detrimental to local Nusselt number performance, especially for denser hole arrays with 5D and 8D hole spacing, where D is impingement hole diameter. This is illustrated by periodic variations of surface Nusselt numbers, which generally decrease with streamwise development, and by local Nusselt number peak values for hole spacings of 5D, 8D, and 12D which generally become smaller at successive x/D locations for each value of Z/D. Also considered are unique situations where significant accumulation of cross-flow fluid results in an opposite trend, with local Nusselt numbers which increase with streamwise development for dense hole spacing of 5D, and smaller jet-to-target plate distances of 1.5D and 3.0D.

Aerodynamic analysis and validation by using three turbulence models for narrow trench configuration

Three turbulence models SST Gamma Theta, k-ω and k-e which all found in ANSYS CFX were used. Velocity contours, pressure coefficient profiles and turbulence levels contours were discussed. Results indicate that three models calculated the cross flow boundary layer with different thicknesses. This leads to a difference in calculation each the momentum of the cross flow fluid closer to the jet exit and cooling performance. At M = 0.5 from range X/D = 5:40, the average centerline effectiveness values in case SST Gamma Theta model and k-ω model were 21 and 9.2 % larger than k-e model, respectively. While at high blowing ratios 1 and 1.4, the effectiveness values in case SST Gamma Theta model and k-ω model were 16, 24.4 % and 32, 46 % less than k-e model, respectively. k-ω model shows a larger backflow regions than others which a maximum negative value of u/u∞ = −0.198 is reached in zone 4.

Computational fluid dynamics modeling and experimental study of continuous and pulsatile flow in flat sheet microfiltration membranes

Due to the significance of fluid flow hydrodynamics on the membrane surface, pulsatile flow was investigated as a functional approach to promote membrane performance. As a turbulence promoter, pulsatile flow in the membrane channel and its effects on the membrane performance were experimentally and numerically studied. A three-dimensional computational fluid dynamics (CFD) model was used to simulate cross-flow microfiltration process and fluid flow, including porous media by solving Navier-Stocks equations coupled with the Darcy's law. Two different boundary conditions were imposed at the module entrance: simple continuous fluid flow and pulsatile flow. Permeate flux, resistances, and shear forces were calculated in different operating conditions in which the experimental and simulated data showed a good agreement. It was found that shear force was the highest at the entrance region and then decayed along the flow direction for both continuous and pulsatile flow. Besides, two different types of pulsatile flow were considered; sinusoidal pulse flow and step function flow in which the latter led to higher shear forces and consequently higher permeate flux was obtained.

The Interaction of Jets with Crossflow

It is common for jets of fluid to interact with crossflow. This article reviews our understanding of the physical behavior of this important class of flow in the incompressible and compressible regimes. Experiments have significantly increased in sophistication over the past few decades, and recent experiments provide data on turbulence quantities and scalar mixing. Quantitative data at high speeds are less common, and visualization still forms an important component in estimating penetration and mixing. Simulations have progressed from the Reynolds-averaged methodology to large-eddy and hybrid methodologies. There is a general consensus on the qualitative structure of the flow at low speeds; however, the flow structure at low-velocity ratios (jet speed/crossflow speed) might be fundamentally different from the common notion of shear-layer vortices, counter-rotating vortex pairs, wakes, and horseshoe vortices. Fluid in the near field is strongly accelerated, which affects the jet trajectory, entrainment, and mixing behavior. At low speeds, mixing depends more on Reynolds number than the jet trajectory or spatial extent does. Turbulence kinetic energy budgets are discussed that reveal the considerable nonequilibrium nature of the flow and the consequent challenges posed to time-averaged prediction methodologies. The parameter space at high speeds is fairly large, and even experimentally derived correlations for trajectories show significant scatter. Coherent motions in high-speed jets are seen to entrain large amounts of crossflow fluid but do not mix effectively in the near field.

EFFECT OF VARIABLE PROPERTIES ON HEAT TRANSFER IN A MICRO-CHANNEL WITH A SYNTHETIC JET

The effect of variable properties on thermal enhancement in a micro-channel due to synthetic jet and cross-flow fluid interaction is examined. Three-dimensional simulation is performed for low Reynolds number flow of water subjected to localized heating at the top surface of the micro-channel when a silicon wafer is etched. The complex conjugate heat transfer between the silicon substrate and water flow is analyzed. Axial conduction introduced by the thermal conductivity, density, and heat capacity temperature dependence of silicon is included. Computational results for the case of variable properties are compared against those of constant properties in both steady-state and transient conditions. The velocity field in the channel is found to be greatly influenced by the temperature distribution when the variable transport properties of water are taken into account. Numerical results of 30 full cycles of the actuator are simulated in order to track the development of the fluid flow and heat transfer. Quasi-steady results, which indicate the maximum cooling potential of a single synthetic jet actuator, are presented. The maximum, minimum, and average temperature profiles show a consistent reducing trend between the solutions of the variable and constant properties.

Study of Unforced and Modulated Film-Cooling Jets Using Proper Orthogonal Decomposition—Part II: Forced Jets

The effects of jet flow-rate modulation were investigated in the case of a 35 deg inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records, and large eddy simulations (LES). In forced experiments, average blowing ratios of 0.3 and 0.4 were investigated with a duty cycle of 50% and pulsing frequencies of St = 0.016 and 0.159. Time-resolved flow rate measurements during the experiments provided precise knowledge of the instantaneous jet blowing ratio and adequate inlet boundary conditions for large eddy simulations. The dynamics of the vortical structures generated during the transient parts of the forcing cycle as well as their impact on film cooling performance were investigated with respect of the forcing parameters. At the considered blowing ratios, a starting ring vortex was consistently generated at the transition from low to high blowing ratio. Ingestion of cross-flow fluid at the transition from high to low blowing ratio was also observed and had a negative impact on film cooling performance. All studied cases exhibited an overall decrease in coverage regardless of pulsing parameters over their corresponding steady jet cases at fixed mass flow rate. Comparisons between pulsed and steady jets at constant pressure supply (same high blowing ratio) did exhibit some film-cooling improvement with pulsing. 3D Proper orthogonal decomposition was performed on LES results at distinct forcing frequencies to provide an analysis of dominant modes in the velocity and temperature fields. Significantly different results were obtained depending on the forcing frequency.

Study of parameters and entrainment of a jet in cross-flow arrangement with transition at two low Reynolds numbers

Investigation of the mixing process is one of the main issues in chemical engineering and combustion and the configuration of a jet into a cross-flow (JCF) is often employed for this purpose. Experimental data are gained for the symmetry plane in a JCF-arrangement of an air flow using a combination of particle image velocimetry (PIV) with laser-induced fluorescence (LIF). The experimental data with thoroughly measured boundary conditions are complemented with direct numerical simulations, which are based on idealized boundary conditions. Two similar cases are studied with a fixed jet-to-cross-flow velocity ratio of 3.5 and variable cross-flow Reynolds numbers equal to 4,120 and 8,240; in both cases the jet issues from the pipe at laminar conditions. This leads to a laminar-to-turbulent transition, which depends on the Reynolds number and occurs quicker for the case with higher Reynolds number in both experiments and simulations as well. It was found that the Reynolds number only slightly affects the jet trajectory, which in the case with the higher Reynolds number is slightly deeper. It is attributed to the changed boundary layer shape of the cross-flow. Leeward streamlines bend toward the jet and are responsible for the strong entrainment of cross-flow fluid into the jet. Velocity components are compared for the two Reynolds numbers at the leeward side at positions where strongest entrainment is present and a pressure minimum near the jet trajectory is found. The numerical simulations showed that entrainment is higher for the case with the higher Reynolds number. The latter is attributed to the earlier transition in this case. Fluid entrainment of the jet in cross-flow is more than twice stronger than for a similar flow of a jet issuing into a co-flowing stream. This comparison is made along the trajectory of the two jets at a distance of 5.5 jet diameters downstream and is based on the results from the direct numerical simulations and recently published experiments of a straight jet into a co-flow. Mixing is further studied by means of second-order statistics of the passive scalar variance and the Reynolds fluxes. Windward and leeward sides of the jet exhibit different signs for the time-averaged streamwise Reynolds flux 〈vx′c′〉. The large coherent structures which contribute to this effect are investigated by means of timely correlated instantaneous PIV-LIF camera snapshots and their contribution to the average statistics of 〈vx′c′〉 are discussed. The discussion on mixing capabilities of the jet in cross-flow is supported by simulation results showing the instantaneous three-dimensional coherent structures defined in terms of the pressure fluctuations.

Direct numerical simulation of flame stabilization downstream of a transverse fuel jet in cross-flow

A reactive transverse fuel jet in cross-flow (JICF) configuration is studied using three-dimensional direct numerical simulation (DNS) with detailed chemical kinetics in order to investigate the mechanism of flame stabilization in the near field of a fuel jet nozzle. JICF configurations are used in practical applications where high mixing rates are desirable between the jet and the cross-flow fluids such as fuel injection nozzles and dilution holes in gas turbine combustors. This study examines a nitrogen-diluted hydrogen transverse jet exiting a square nozzle perpendicularly into a cross-flow of heated air. Improved understanding of the flame stabilization mechanism acting downstream of the transverse fuel jet will enable the formulation of more reliable guidelines for design of fuel injection nozzles which promote intrinsic flashback safety by reducing the likelihood of the flame anchoring at the injection site. The core of the heat release is located near the trailing edge of the fuel jet, at approximately 4 nozzle diameters away from the wall, and is characterized by the simultaneous occurrence of locally stoichiometric reactants and low flow velocities in the mean.The location where the most upstream tendrils of the flame are found is in the region where coherent vortical structures originating from the jet shear layer interaction are present. Instantaneously, upstream flame movement is observed through propagation into the outer layers of jet vortices.

Second law analysis and heat transfer in a cross-flow heat exchanger with a new winglet-type vortex generator

Abstract In this paper a second law analysis of a cross-flow heat exchanger (HX) is studied in the presence of a balance between the entropy generation due to heat transfer and fluid friction. The entropy generation in a cross-flow HX with a new winglet-type convergent–divergent longitudinal vortex generator (CDLVG) is investigated. Optimization of HX channel geometry and effect of design parameters regarding the overall system performance are presented. For the HX flow lengths and CDLVGs the optimization model was developed on the basis of the entropy generation minimization (EGM). It was found that increasing the cross-flow fluid velocity enhances the heat transfer rate and reduces the heat transfer irreversibility. The test results demonstrate that the CDLVGs are potential candidate procedure to improve the disorderly mixing in channel flows of the cross-flow type HX for large values of the Reynolds number.

Heat transfer enhancement in microchannels with cross-flow synthetic jets

This paper examines the effectiveness of using a pulsating cross-flow fluid jet for thermal enhancement in a microchannel. The proposed technique uses a novel flow pulsing mechanism termed “synthetic jet” that injects into the microchannel a high-frequency fluid jet with a zero-net-mass flow through the jet orifice. The microchannel flow interacted by the pulsed jet is modelled as a two-dimensional finite volume simulation with unsteady Reynolds-averaged Navier–Stokes equations while using the Shear-Stress-Transport (SST) k– ω turbulence model to account for fluid turbulence. For a range of conditions, the special characteristics of this periodically interrupted flow are identified while predicting the associated convective heat transfer rates. Results indicate that the pulsating jet leads to outstanding thermal performance in the microchannel increasing its heat dissipation by about 4.3 times compared to a channel without jet interaction within the tested parametric range. The degree of enhancement is first seen to grow gently and then rather rapidly beyond a certain flow condition to reach a steady value. The proposed strategy has the unique intrinsic ability to generate outstanding degree of thermal enhancement in a microchannel without increasing its flow pressure drop. The technique is envisaged to have application potential in miniature electronic devices where localised cooling is desired over a base heat dissipation load.