Heat Transfer In Channel Research Articles

Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Swirl Multi-Pass Channel With Convergent Jet Slots

Abstract This paper presents a comparative experimental and numerical study of the heat transfer and pressure loss in a swirl multi-pass channel with tangential jet slots, and another baseline multi-pass channel with 180-deg U-bends as a comparison baseline has also been investigated. The tangential jets can induce large-scale swirling flows and significantly enhance the connective heat transfer. The swirl multi-pass channel can be considered as an effective internal cooling strategy for the gas turbine blades. Transient liquid crystal thermography is used to obtain the detailed heat transfer distribution on the internal surfaces of the multi-pass serpentine channels. The heat transfer patterns in the swirl multi-pass channel are quite different from those of the baseline multi-pass channel. Circumferentially, the three heat transfer surfaces, i.e., the bottom, top and side surfaces of the two multi-pass serpentine channels, have roughly similar trend along the flow direction and reach the peak values after the U-bends and jet injections, respectively. Compared with the baseline multi-pass channel, the experimental globally averaged Nusselt number ratios of the last two passes in the swirl multi-pass channel can be increased by up to 82.9%, 104.8%, and 124.6% for the Reynolds numbers 20,000, 40,000, and 60,000, respectively. The differences of globally averaged Nusselt number ratios between the two kinds of multi-pass serpentine channels gradually increase with the Reynolds numbers, which means that the swirl multi-pass channel has higher heat transfer enhancement capability at a higher Reynolds number. The circumferentially uniform heat transfer characteristic of swirling flow also performs well in this study. The high and circumferentially uniform heat transfer is mainly due to the large-scale swirling flow induced by the tangential slots. In more detail, the large-scale swirling flow impinges onto the surface and further induces high tangential velocity near the wall, which destroys the boundary layer flow and thus improves the heat transfer rates at the wall. However, the notable pressure loss of the swirl multi-pass channel should be further controlled reasonably, which is about 5.4 times that of the baseline multi-pass channel. As supplements to the experiments, three-dimensional numerical computations provide more insights into the turbulent flow structure in the two kinds of multi-pass serpentine channels.

Experimental and Numerical Study of the Turbulent Flow and Heat Transfer in a Wedge-Shaped Channel With Guiding Pin Fin Arrays Under Rotating Conditions

Abstract Experiments and numerical simulations under stationary and rotating conditions have been conducted to investigate turbulent flow and heat transfer characteristics of innovative guiding pin fin arrays in a wedge-shaped channel, which models the internal cooling passages for modern gas turbine blade trailing edge. The Reynolds number range is 10,000–80,000, and the inlet rotation number range is 0–0.46. With the increase of Reynolds number, the enhancement of heat transfer performance of the channel with guiding pin fin arrays is significantly higher than that of the channel with conventional circular pin fin arrays. At the highest Reynolds number of Re = 80,000, the overall Nusselt number of the channel with guiding pin fin arrays is about 33.7% higher than that of the channel with circular pin fin arrays under the stationary condition and is about 23.0% higher than the latter under the rotating conditions. At the highest inlet rotation number of Ro = 0.46, the heat transfer difference between the trailing side and leading side of the channel is significantly lower with the guiding pin fin arrays than with the circular pin fin arrays. Through both the experiments and numerical simulations, it is found that the heat transfer uniformity of the endwall is significantly improved by the guiding pin fin arrays, and the rotation presents appreciably less influence on the heat transfer distribution with the guiding pin fin arrays than with the circular pin fin arrays. Moreover, the novel guiding pin fins provide more reasonable flow distribution in the wedge-shaped channel and produce obviously higher heat transfer performance in the tip region of the channel, which is significantly advantageous for a better design of gas turbine blade trailing edge internal cooling.

Heat Transfer and Fluid Flow Characteristics in a Long Offset Strip Fin Channel by Using TiO2-Water Nanofluid

Heat Transfer and Fluid Flow Characteristics in a Long Offset Strip Fin Channel by Using TiO2-Water Nanofluid

Constructal design for tree-shaped compound heat transfer channel in a disc heat generation body

In this basic theoretical research paper, structure design of a tree-shaped compound heat transfer channel (CHTC) model in a disc heat generation body (HGB) is performed based on constructal theory. A complex function consisting of maximum temperature difference and pumping power consumption is minimized first based on the exhaustive method and Nelder-Mead optimization algorithm, and the optimal structure of the CHTC model is gained. The multi-objective optimization is further performed based on the non-dominated sorted genetic algorithm-II to obtain the Pareto optimal set, and the optimal results gained by the decision making approaches (DMAs) of LINMAP, TOPSIS and Shannon Entropy are compared. It reveals that the complex function of the HGB can approach its minimum when the reasonable radius, volume ratio and length ratio of the fluid channel in the CHTC are equal to 1.33 mm, 0.55 and 0.2, respectively. The thermal and fluid flow performances are increased by 11.6% and 30.3%, and the complex function is decreased by 21.0% after constructal design, which illustrates that the optimization effect is obvious. The thermal and fluid flow performances gained by the first two DMAs are increased by 29.60% and 5.10% after constructal design, and their deviation indexes are the same and the smallest one. Therefore, the optimal structure gained by the first two DMAs is recommended in the optimal design of the CHTC for disc HGB. Different optimal design schemes for different design requirements of the electronic devices can be offered by this paper, which aims to improve the thermal and fluid flow performances and theoretically solve the heat dissipation problem of the electronic devices. The contribution of this paper is to establish a tree-shaped CHTC model in a disc HGB, and introduce constructal theory into its structure design to obviously elevate the performance of the disc HGB.

Investigation on flow and heat transfer in rectangular cross-section sinusoidal channels

In this paper, the flow and heat transfer characteristics in a sinusoidal rectangular channel are numerically probed. It's found that Dean vortex can be induced in sinusoidal rectangular channel, and the intensity of Dean vortex varies regularly with channel curvature. The intensity of Dean vortex in sinusoidal channels with various cross-sectional ratios, and the local Nusselt number at different locations are further investigated to reveal the variation pattern of Dean vortex and the corresponding variation in heat transfer capacity. In addition, it's found that the Dean vortex becomes unstable when the Reynolds number exceeds a critical value. The Dean instability balances the spatial inhomogeneity of wall heat transfer by means of fluctuations with the time. The critical Reynolds number corresponding to sinusoidal rectangular channels with various cross-sectional ratios is obtained by the helicity method, and the relationship between the cross-sectional ratio and critical Reynolds number is obtained as well.

Enhancing Thermal Stability of Laser-Driven Phosphor Converter by Utilizing Copper Powder Sintering Framework/Paraffin

Laser-driven white light illumination is considered as the next generation of high brightness white light source. The most common way to achieve laser-based white light is using a blue laser to excite phosphor/ silicone converter (reference converter). However, the relatively low thermal conductivity of phosphor limits most of the heat to its surface and cannot be dissipated effectively. In this work, a converter with copper sintering powder framework/paraffin (CPSF/P) embedded into the phosphor/silicone is proposed. As an internal heat transfer channel, copper powder sintering framework (CPSF) transfers heat to paraffin coated in porous skeleton, and then paraffin absorbs the generated heat through solid–liquid phase transition, which effectively dissipates the heat concentrated on the phosphor surface and improves its thermal stability. Under high-power laser excitation of 7.74 W, the surface temperature of the reference converter is up to 660 °C, while the maximum temperature of the CPSF/P converter is only 139 °C, which is reduced by 521 °C (78.9%). The results show that the proposed CPSF/P converter can withstand higher excitation power and show better thermal stability than the reference converter, which is helpful to obtain higher color stability. This provides an efficient heat dissipation scheme for high-power laser-driven lighting.

Effect of channel orientation on heat transfer in a rotating impingement cooling channel

The jet impingement cooling technology is usually applied in the turbine blade leading edge which suffers high thermal loads. In a high-speed rotating turbine blade, however, the channel orientation (β, the angle between the direction of the jet and the rotating plane) could alter the jets and heat transfer. Therefore, the effects of channel orientation (from 90∘ to 180∘) on heat transfer of confined jet impingement cooling are experimentally studied under an iso-thermal boundary. Both the jet-to-target surface distance and the jet-to-jet spacing are 3 times of the jet diameter. The jet Reynolds number varies from 5000 to 15,000, and the maximum jet rotation number reaches 0.24. The results show that the rotational effect on heat transfer is different in each channel orientation. In the cases of 90∘≤β≤ 135∘, a large vortex generated by the Coriolis force in the supply channel significantly changes the mass-flowrate distribution in each jet orifice. Hence, the heat transfer in the middle part decreases with the rotation number whereas the heat transfer at both ends increases, resulting in a “U-shape” pattern of heat transfer in the impingement channel. In the cases of 135∘<β≤ 180∘, however, the heat transfer throughout the stagnation zone decreases with the rotation number. The rotation-induced jet diversion is the primary factor that weakens the heat transfer, and jets are driven away from the target surface at high rotation numbers. Moreover, the heat transfer correlation on the stagnant zone is developed, which considers the effects of channel orientation and rotation number.

Experimental Study on Convection Heat Transfer Enhancement of Channel-Flow with Piezoelectric Fan

Experimental work was carried out to investigate the convection heat transfer enhancement of channel flow using a piezoelectric fan oriented along the streamwise direction. The piezoelectric fan was operated at its first natural frequency of 90.3 Hz with various excitation voltages. The average velocity of channel flow was ranged up to 3 m/s, which has the corresponding channel Reynolds number of 3,616. The experimental methodology was numerically and analytically validated. The effects of fan location on the heat transfer performance were evaluated by changing the relative position of the fan tip to the heated surface. The convection heat transfer coefficient and channel pressure drop were measured at different operational conditions of the fan and channel flow. The maximum heat transfer enhancement of 102% was achieved at a flow rate of 15 LPM when the piezoelectric fan was excited with 170 V at the front-end of the heated surface. For a fixed channel flow condition, the piezoelectric fan improved the heat transfer performance only when it was operated with amplitudes larger than the critical value. The overall heat transfer performance of the heated surface in the channel was found to be dependent on the channel flow rate and the amplitude and frequency of the piezoelectric fan.

Analysis of enhanced turbulent heat transfer in a sharp turn channel having novel designed endwall with longitudinal vortex generator

This work provides a new method to enhance endwall heat transfer of a sharp turn channel. Several longitudinal vortex generators (LVGs) at various spacing and aspect ratio are placed in parallel on the inner side of endwall in a sharp turn channel. Liquid crystal thermography, pressure difference measurements, and a statistical method are applied to analyze the thermal behavior, friction factor, and temperature uniformity on the endwall mounted with an array of LVGs. The Reynolds number are in the range of 10,000 to 20,000. A comparison between the novel designed endwall and conventional turbulators in the same U bend channel is also conducted. Results indicate that the local Nusselt number is greatly augmented with the application of LVGs on the endwall, especially at the downstream part of the endwall. The LVGs with an aspect ratio of 2 and a spacing of 20 mm (dense case) provides the optimal thermal characteristics. The optimal design provides augmentation of heat transfer rate and thermal performance factor by up to 35.1% and 25.5%, respectively. The endwall fitted with delta-winglet vortex generators is a promising enhanced heat transfer method compared with the conventional design available for the same U-duct model.

Modelling of boiling in square channels partially filled with porous medium

Investigation of boiling in a square channel, which is filled partly with porous medium, is reported. Influence of major parameters such as porosity and extent of filling of the porous medium on heat transfer rate, vapour volume fraction, vapour generation rate and pressure drop are analyzed. A new solver utilizing the framework of open-source CFD code OpenFOAM is developed to investigate the problem. It is found that addition of porous medium increases fluid temperature, vapour volume fraction, heat transfer and vapour generation rate. It is also established that heat transfer increases on lowering the porosity of porous matrix, when the ratio of thickness of porous medium to channel height (Hp⁎) is greater than 0.4. In addition, heat transfer rate increases if the porosity increases for Hp⁎ < 0.4, but not significantly, as compared to the cases with Hp⁎ > 0.4. Moreover, there is an increase in pressure drop for an increase in thickness and a decrease in the porosity. It is also found that for two-phase heat transfer, the maximum Nusselt number is approximately 4.8 times higher than that for the single-phase heat transfer in the same channel.

Turbulent Heat Transfer in Channels with Additively Manufactured Roughness

Turbulent Heat Transfer in Channels with Additively Manufactured Roughness

Simulation of Non-Isothermal Turbulent Flows Through Circular Rings of Steel

This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries. Such an organization is used to generate the heat exchangers with tube and shell because of the production of more turbulence due to zigzag path which is in favor of rapid heat transformation. Because of little maintenance, the heat exchanger of such type is extensively used. Here, we generate simulation of flow and heat transfer using non-isothermal flow interface in the Comsol multiphysics 5.4 which executes the Reynolds averaged Navier stokes equation (RANS) model of the turbulent flow together with heat equation. Simulation is tested with Prandtl number (Pr = 0.7) with inlet velocity magnitude in the range from 1 to 2 m/sec which generates the Reynolds number in the range of 2.2 × 105 to 4.4 × 105 with turbulence kinetic energy and the dissipation rate in ranges (3.75 × 10−3 to 1.5 × 10−2) and (3.73 × 10−3−3 × 10−2) respectively. Two correlations available in the literature are used in order to check validity. The results are displayed through streamlines, surface plots, contour plots, isothermal lines, and graphs. It is concluded that by retaining such an arrangement a quick distribution of the temperature over the domain can be seen and also the velocity magnitude is increasing from 333.15% to a maximum of 514%. The temperature at the middle shows the consistency in value but declines immediately at the end. This process becomes faster with the decrease in inlet velocity magnitude.

Flow Behavior and Heat Transfer in a Rectangular Channel with Miniature Riblets

Flow Behavior and Heat Transfer in a Rectangular Channel with Miniature Riblets

Analysis of heat transfer of turbulent channel using different geometries using ANSYS

2-D numerical simulations were conducted for surveying heat transfer and friction factor attributes for a turbulent channel of peculiar designs while applying iso-flux thermal boundary condition to the bottom plate, and insulation to the upper plate. ANSYS Workbench v14.5 software was used for simulating the fluid domain. The Realizable k-ɛ model along with the upwind scheme and SIMPL equation was used for solving turbulence, and handling the pressure–velocity coupling for the fluid domain. Groove, rib, and rib-groove geometries with different B/H ratios are used for bottom plate and for obtaining such ratios channel height (H) is kept constant and alterations in groove length/rib length (B) has been done. The main objective of the work performed was to compare the result of above-mentioned geometries and find the best heat transfer enhancement geometry under similar working conditions for above geometries and the optimum B/H ratios for such turbulent channels. For all the Reynolds number and B/H range examined the maximum heat transfer was achieved by ribbed geometry which is 149% more than smooth channel followed by rib-grooved geometry which is 131% and least increment is shown by grooved geometry which is only 69%. The ratio B/H best suited for heat transfer enhancement is identified the same as the earlier research which is B/H = 0.75 for all three geometries.

Intensification of heat and mass transfer of the gas channel of the multi-temperature condensation filter

The principle of operation and features of hydrodynamics and heat-mass transfer in the working channel of a multi-temperature condensation filter for gas purification are described. Promising methods of gas flow purification using porous surfaces are described. The modeling and comparison of the laminar air flow in channels of various shapes: in a flat channel, in a channel with webs and in a spiral channel are performed. An analysis of their effectiveness is carried out.

Heat Transfer and fluid flow analysis of porous channel with radiative heating

Heat Transfer and fluid flow analysis of porous channel with radiative heating

Influence of Entrance Geometry and Thermal Boundary Conditions on Heat Transfer in a Rectangular Channel with 45 Deg Angled Ribs on One or Two Principal Walls

Influence of Entrance Geometry and Thermal Boundary Conditions on Heat Transfer in a Rectangular Channel with 45 Deg Angled Ribs on One or Two Principal Walls

Enhancement of Heat Transfer and Hydrogen Fuel Flow Characteristics in a Wavy Cooling Channel with Secondary Branch Design

Enhancement of Heat Transfer and Hydrogen Fuel Flow Characteristics in a Wavy Cooling Channel with Secondary Branch Design

Highly-efficient radiative thermal rectifiers based on near-field gap variations.

Near-field radiative thermal rectifiers (NFRTRs) enabling directional heat transport hold great promise for various applications, including thermal logic computing, thermal management, and energy conversion. Current NFRTR designs rely on dissimilar terminal materials with high contrasts in their temperature-dependent dielectric properties, which in turn hinders the spectral match for radiative heat transfer and thus limits the device's efficiency. Herein, this dilemma is solved by designing heterostructures where a pair of polaritonic layers are separately stacked on a thermally-expanding layer and a rigid substrate, spaced by a vacuum gap. In this scheme, the symmetric polaritonic layers can provide stable near-field radiative channels for heat transfer, while the thermally-expanding layer can modulate the gap size with flipped temperature bias to allow high contrasts in heat flux. In exemplified implementations, the hBN-based design has achieved a record-high thermal rectification factor (TRF, ∼104) even under small thermal gradients (∼20 K), which can be further boosted by polaritonic hybridizations in the graphene/hBN-based design. This study paves the way to design novel NFRTRs with 2D materials, thus providing enriched polaritons to realize higher TRFs.

The effect of using staggered and partially tilted perforated baffles on heat transfer and flow characteristics in a rectangular channel

Experimental and numerical studies have been carried out to study the effect of using baffles on the flow and heat transfer characteristics in a rectangular channel with an aspect ratio of 3:1. The baffles were mounted on the top and the bottom surfaces in a staggered arrangement with a constant pitch (P=100 mm). Uniform heat flux was applied on the upper and lower surfaces while the side walls were insulated. Over a range of Reynolds numbers from 12,000 to 42,000, the effect of tilting angles (θ=0°,30°,45°and60° ) and perforation ratios from 10% to 40% on the heat transfer enhancement and flow resistance features have been reported in the form of flow structure contours, temperature contours, local Nusselt numbers, average Nusselt numbers, Nusselt number ratios, friction factors, friction factor ratios and thermal enhancement factor (TEF). Additionally, based on the study outcomes, correlations for the Nusselt number and the friction factor have been developed. Among all the studied cases, baffles with tilting angle (θ=0°) and perforation ratio (β=10%) showed the highest heat transfer enhancement and the greatest flow resistance while the case of the lowest heat transfer augmentation and the minimum friction factor is the baffle configuration with tilting angle (θ=60°) and perforation ratio (β=40%). Moreover, it is noticed from the predicted flow field that the baffles with lower tilting angles and lower perforation ratios provide stronger reattachment and recirculating flow on the heating surfaces. In addition, the insertion of the proposed baffles leads to higher heat transfer augmentation compared to the smooth channel such that the Nusselt number ratio (Nurs/Nuss) reaches 2.6. The TEF showed that the optimum condition has been achieved at the baffle configuration with tilting angle (θ=60°) and perforation ratio (β=10%) at Re=12,000 where it reached the peak (about 0.7).