Thermal Hydrodynamic Performance Research Articles

Flow and thermal performance of a multi-jet twisted square microchannel heat sink using CuO-water nanofluid

Due to the rapid development in micro manufacturing and 3D printing technology, the complex shape of microchannel heat sink (MCHS) can be realized, instead of just the traditional rectangular channels. It is recognized that twisted square channels which are similar to a kind of internal thread channel have favorable effects on heat transfer because of its enhancement of turbulence intensity. In this work, a geometry of twisted tube is applied to the microchannel and the thermal and hydrodynamic performance of twisted square microchannels with jet impingement are investigated. The arrangement of the jet channels is the research focus and one-jet and multi-jet microchannel heat sinks are compared by discussing the temperature profile, pressure drop and heat transfer characteristics. By applying the twisted geometry to the microchannel, the Nusselt number can be increased by 16.48% with little increase in pressure drop. However, with the increase in torsion angle of the twisted microchannel (from 90° to 720°), the thermal performance changes little for the limited effect on the temperature uniformity of the cross section. Integration of jet impingement further improves the thermal-hydrodynamic performance of MCHS. Specifically, the thermal resistance of MCHS was reduced by 41% at most. Finally, by comparing the comprehensive performance of the cases with varied jet arrangement, it is concluded that jets distributed at the cross section with the torsion angle of 45°, 135°, and 225° can induce better performance. The present investigation combines the twisted geometry and jet impingement into microchannel, quantitatively characterizes the performance of MCHS and gives the guidance for the jet arrangement design.

Experimental and Computational Study of Enhanced Forced Convection Heat Transfer in Novel Slotted Wavy-Plate-Fin Channels

Abstract Forced convective enhanced heat transfer performance of airflows (50 ≤ Re ≤ 4000, Pr ∼ 0.71) in novel slotted sinusoidal wavy-plate-fins is investigated both experimentally and computationally. The slotted wavy fin core evaluated in the experiments was produced by direct metal laser sintering (DMLS). Compared with the equivalent or nonslotted wavy fin core, also produced by DMLS, while the heat transfer was found to be similar, the pressure drop was reduced by as much as 31%. This very attractively significant enhancement was further explored in a three-dimensional computational analysis. Besides validating experimental results, it is seen that a significant part of pressure loss in plain wavy-fin channels is due to form drag induced by flow recirculation in the trough region. This is shown to be reduced substantially if the fins are slotted at large form drag locations. Their position and size, characterized, respectively, by phase angle (β) and dimensionless slot size (δ), are varied in the simulations to explore their role in the enhanced thermal-hydrodynamic performance. One such modified design exhibits a characteristically unusual performance at low Re, where improvement in heat transfer (+17%) is accompanied by a reduction in pressure loss (–16.8%). Additionally, at high Re, though a slight decline in heat transfer (–7.6%) is evidenced, the pressure drop is nearly cut in half (–46.6%). Moreover, the overall thermal-hydrodynamic performance based on the metric of fixed heat transfer rate and pressure drop constraint shows that ∼15% reduction in the required heat transfer surface area can be achieved with slotted wavy fins.

Numerical study of entropy generation and forced convection heat transfer of a nanofluid in a channel with different fin cross-sections

PurposeThis study aims to numerically investigate the thermal-hydrodynamic performance of silicon oxide/water nanofluid laminar flow in the heat sink miniature channel with different fin cross-sections. The effect of the fin cross-section including semi-circular, rectangular and quadrant in two directions of flat and curved, and channel substrate materials of steel, aluminum, copper and titanium were examined. Finally, the analysis of thermal and frictional entropy generation in different channels is performed.Design/methodology/approachAccording to the numerical results, the highest heat transfer coefficients belong to the rectangular, quadrant 2, quadrant 1 and semi-circular fins compared to the channel without fin is 38.65%, 29.94%, 27.45% and 17.1%, respectively. Also, the highest performance evaluation criteria belong to the rectangular and quadrant 2 fins, which have 1.35 and 1.29, respectively. Based on the thermal conductivity of the substrate material, the best material is copper. According to the results of entropy analysis, the reduction of thermal irreversibility of the channel with rectangular, quadrant 1, quadrant 2 and semi-circular compared to non-finned channel is equal to 72%, 57%, 63% and 48%, respectively.FindingsThe rectangular and quadrant 2 fins are the best fins and the copper substrate material is the best material to reduce the entropy generation.Originality/valueThe silicon oxide/water nanofluid flow in the heat sink miniature channel with various fin shapes and the curvature angle against the fluid flow was simulated to increase the heat transfer performance. The whole test section is simulated in three-dimensional. Different channel materials have been investigated to find the best channel substrate material.

Effect of rib shape and fillet radius on thermal-hydrodynamic performance of microchannel heat sinks: A CFD study

New designs for ribbed microchannels (semi-circular and semi-elliptic) and filleted ribs are numerically studied in the present paper. Four presented configurations include: microchannel with semi-circular ribs (MC-SCR), microchannel with semi-elliptic ribs (MC-SER), microchannel with semi-circular ribs and filleted corner (MC-SCR-FR) and microchannel with semi-elliptic ribs and filleted corner (MC-SER-FR). Thermal and hydraulic performance of these configurations are evaluated by comparing Nusselt number, fanning friction factor, and performance evaluation criteria (PEC). Based on the results, the ribs corner curvature leads to a significant increase in heat transfer coefficient, accompanied by a minor increase in pressure drop. Compared to MC-SCR and MC-SER heat sinks, the two designs of MC-SCR-FR and MC-SER-FR enhance Nusselt number about 18–21% and 0.5–10%, increase the fanning friction factor about 0.1–7% and 1–9%, and improve the performance evaluation criteria (PEC) about 19–22% and 19–21%, respectively. In addition, because of the re-development of thermal boundary layer and higher mixing level, MC-SCR-FR configuration revealed the best performance among all other configurations. Moreover, the effect of relative fillet radius on thermal-hydrodynamic performance of MC-SER-FR configuration is investigated, and R* > 1.2 is selected as the appropriate value for design of microchannel heat sinks.

Improvement of the performance of solar channels by using vortex generators and hydrogen fluid

An attempt is made to enhance the thermal hydrodynamic performance of a solar channel by using vortex generators including attached fins and detached bars. Hydrogen gas is used as a working fluid under turbulent flow conditions. The computational fluid dynamics method is used to achieve the investigations. Governing equations among fluid and solid sections are determined and solved by the computational finite volume method. The hydrodynamic characteristics, dynamic pressure, turbulent kinetic energy, turbulent viscosity, Nusselt number, skin friction, and the thermal enhancement factor (TEF) are investigated for a range of Reynolds number (Re) from 5000 to 20,000. The obtained results revealed that the TEF values are important (TEF > 1) for all Re values under investigation. The TEF values are between 1.2 and 3.5. An increase in the TEF values was observed with increased Reynolds number, where the maximum value of TEF of about 3.5 was achieved at Re = 20,000. At this value of Re, the normalized heat transfer value (Nu/Nu0) is the highest, while the normalized friction values (f/f0) are the lowest. This demonstrates the usefulness of the suggested vortex generators combined with the fluid (H2) for the successful thermal and dynamic performance within the smooth channels.

Parametric investigation of thermal-hydrodynamic performance in the innovative helically coiled heat exchangers in the heat pump system

This work aims to study the thermal-hydrodynamic performance of innovative multi tubes in tube helically coiled (MTTHC) heat exchanger used in the heat pump system. The 3D finite volume method and realizable k-ε turbulence model is considered to investigate the mechanism of flow and heat transfer in this MTTHC heat exchanger with the different coiled diameter and coiled pitch. Predicted values of pressure drop and outlet temperature are compared with our previous experimental results. The comparison shows the numerical method can be well to use for evaluating the performance of this novel MTTHC. The distributions of velocity, temperature and pressure along the flow direction for the certain cross-sections are presented. The effects of structural parameters of MTTHC and flow rates of inner and outer tube on the overall heat transfer coefficient, effectiveness and NTU, pumping power and pressure drop, thermal and hydrodynamic performance index (ξ) and inner and outer tube Nusselt number are investigated. It is found that decreasing the coiled diameter or increasing the coiled pitch can improve thermal performance. In addition, increasing the flow rate leads to an increase in pressure drop and pumping power. However, ξ enhances with increasing mw, and it worsens with increasing mref.

Prediction of flow and heat transfer through a microtube filled with bidisperse porous medium under local thermal nonequilibrium condition

AbstractIn this paper, the thermal and hydrodynamic solutions of a microtube filled with bidisperse porous medium (BDPM) under the local thermal nonequilibrium (LTNE) condition are presented. Considering the LTNE condition, the energy equations have been numerically solved. The rarefaction effects are considered for Knudsen numbers ranging from 0 to 0.1; therefore, first‐order boundary condition is applied on the wall. The temperature distribution of each phase is examined with respect to the involved parameters in the BDPM system. For the first time, the Nusselt number ratio (NRDP) is introduced to study the influence of Darcy number on the Nusselt number more precisely. Also, the effect of different thermophysical parameters on the Nusselt number is studied. The advantage of BDPM system over monodisperse porous medium (MDPM) structure is examined through the heat transfer performance parameter. The findings exhibit a good agreement with the literature. Also, the LTNE condition produces more realistic results in comparison to local thermal equilibrium assumption. On the whole, although implementing the BDPM enhances the heat transfer rate compared with the MDPM, it does not improve the thermal hydrodynamic performance significantly.

Numerical study of hydrodynamics and thermal characteristics of heat exchangers with delta winglets

The comprehensive performance of heat exchangers is represented by the maximum thermal transfer, the minimum pressure loss, and the smallest pumping power. In recent years, the application of longitudinal vortex generators is developed as an effective technique and important research topic, which could increase the heat transfer enhancement of compact heat exchangers. A 3-D CFD numerical simulation is successfully carried out on thermohydraulic characteristics of the fin-and-tube compact heat exchanger with new types of vortex generators. The effects of six different arrangement of delta winglets are studied, which are front-up-rear-down, front-down-rear-up, common-flow-up, and common-flow-down. In addition, there are also different direction of hole position in the same delta winglets arrangement. The investigation of thermal-hydraulic performance is conducted for Reynolds number in the range of 204-2034. The overall and local performance comparisons among the fin with delta winglets and the wavy fin are performed. Then, the comprehensive performance evaluation diagram was adopted to analyze the combined index point of thermal and flow. This study shows that the flow distinction between different fins has a profound influence on the thermal-hydrodynamic performance. The results reveal that the fin with delta winglets can considerably strengthen the thermal efficiency with a moderate pressure loss penalty. The computational results indicate that the average j-factor for the fin with delta wing-lets can be increased up to 41.9% over the baseline case and the corresponding f-factor decreased up to 19.5%. The combination property of front-up-rear-down are better the others at lower Reynolds number, and that of front-down-rear-up are better at higher Reynolds number. Compare with the traditional arrangement (common-flow-up and common-flow-down), The newly designed fin has great effectiveness and uniform performance in the local region.

Effect of helical perforated twisted tape parameters on thermal and hydrodynamic performance in heat exchanger circular tube

Effect of helical perforated twisted tape parameters like diameter ratio (dR/DI), relative pitch ratio (PPT/LT), perforation index (PA/TA) and Reynolds number(Re) on the thermal and hydrodynamic performance of heat exchanger circular tube experimentally analysed. Experimental data pertinent to air flow and heat transfer is generated and thermal hydrodynamic performance is determined for different sets of helical perforated twisted tape insert and flow parameters. The highest value of thermal hydrodynamic is observed at dR/DI of 0.65, PPT/LT of 0.086 and PA/TAof 10%. The maximum value of the thermal hydrodynamic performance was found to be 2.12 for the range of parameters examined.

Thermo-Elastohydrodynamic Study on Textured Journal Bearing with High-Speed and High-Specific-Pressure

The performance of supporting journal bearing of the star gear transmission system in the geared turbo fan engine (GTF) is analyzed. A thermal-elastohydrodynamic analysis model was developed for textured journal bearing used in high-speed and high-specific-pressure conditions. The Navier-Stokes equation, energy equation, and viscosity-temperature equation were calculated by the computational fluid dynamics method. The influence of elastic deformation on bearing thermal hydrodynamic performance was studied in detail. The results indicate that the elastic deformation has an influence on the distribution of oil temperature and oil pressure. Besides, a comparative thermo-elastohydrodynamic analysis was conducted between the textured bearing and the un-textured bearing, and the discrepancies of maximum oil pressure, load carrying capacity and the maximum oil temperature are few. However, the textured bearing has a lower elastic deformation than the un-textured bearing.

Development of new correlations for heat transfer and friction loss of solid ring with combined square wing twisted tape inserts heat exchanger tube

ABSTRACT An experimental analysis has been carried out for heat transfer and turbulent flow in a heat exchanger circular tube with solid ring with combined square wing twisted tape (TT) inserts. Experimentations are performed varying the solid ring with combined square wing TT insert parameters, such as changing the number of TT inserts from 1.0 to 4.0, ring pitch ratio from 0.5 to 2.0, wing pitch ratio from 2.0 to 3.5, wing depth ratio from 0.083 to 0.333, ring diameter ratio from 0.831 to 0.932, and Reynolds number in the range of 3,000–21,000. The experimental results show that the heat transfer is increased around 5.66 times more than the plane circular tube. The thermal hydrodynamic performance is evaluated for the optimum range of solid ring with combined square wing TT insert parameters. Statistical correlations are developed and a deviation of correlation data from the experimental data of Nusselt number and friction factor is about ± 9% and ± 6%, respectively. The correlation is helpful in prediction of the thermal performance for turbulent flow through a circular tube with solid ring with combined square wing twisted tape inserts.

Effect of square wing with combined solid ring twisted tape inserts on heat transfer and fluid flow of a circular tube heat exchanger

ABSTRACTThis work presents the heat transfer and friction characteristics of turbulent circular tube flow through a square wing with combined solid ring twisted tape inserts have been analyzed experimentally. Experiments have been carried out for the range of Reynolds number (Re) from 3000 to 21000, number of twisted tape inserts from 1.0–4.0, ring pitch ratios from 0.5 to 2.0, wing pitch ratios from 2.0 to 3.5, wing depth ratios from 0.083 to 0.333 and ring diameter ratio from 0.831 to 0.932. The experimental results show that the heat transfer is increased around 5.66 times higher than plane circular heat exchanger tube. The optimum value of thermal hydrodynamic performance has been found corresponds to = 3.0, = 1.0,= 3.0, = 0.167 and . The finest value of thermal and hydrodynamic performance has been found to be 2.74 for of 3,000 within the range of the parameters investigated.

Performance evaluation of eddy current flowmeter in Monju

ABSTRACT Measurement of the temperature and flow rate at each fuel subassembly outlet is an effective way for a liquid metal fast breeder reactor to detect a loss of coolant accident or reactivity-initiated accident in the early stage and to understand the reactor’s thermal hydrodynamic performance. Japan Atomic Energy Agency has developed the eddy current flowmeter in practical use and installed 34 of them in the upper core structure of fast breeder reactor, Monju. This report presents data obtained by using the flowmeters in Monju. We observed high linearity between each of the flowmeter’s signal intensity and the primary sodium’s flow rate under 10–100% flow rate condition. High linearity was also observed in a region of low velocity (approx. 0.25 m/s). The fluctuation of flow rate observed by the flowmeters was below 0.2 m/s which is 5% of the time-averaged velocity under a rated condition. These experimental results show that the eddy current flowmeter is an effective tool to detect the changes in relative flow rate.

An experimental study on the hydrodynamic performance of the water-wall system of a 600 MW supercritical CFB boiler

The temperature distribution on the backside of the water-wall tubes in the first 600 MW CFB boiler operating at 60%, 80% and 100% of the boiler Maximum Continuous Rating (MCR) loads was experimentally determined and the thermal-hydrodynamic performance of water-wall system based on the mass and energy equations using the measured temperature was calculated. The results showed that the temperature of the water-wall tubes increased as the furnace height increased, showing a positive response characteristic in the water-wall system. However, the temperature of the water-wall tubes in the upper furnace was obviously declined at the places where the superheaters and cyclone separator inlet-channels were arranged. This suggests that the arrangement of the heat-transfer surfaces in the upper furnace was significantly influenced the temperature distribution of the water-wall tubes. Meanwhile, the calculated total pressure-drop and mass flux in the water-wall system increased as the boiler’s load raised, showing an energy-efficiency for the vertical once-through boiler. In addition, the metal temperature was calculated to check the working condition of the water-wall tubes and the results showed the highest metal temperature of 426.3 °C of the water-wall tubes was found at the tip of the fin at 100% MCR. This temperature was far below the permissible temperature of the metal, implying that a safe working condition of the metal at three loads was guaranteed. Nonetheless, analysis into the heat-transfer characteristics of the water in the water-wall reflects that the water temperature in the water-wall at 80% MCR load was adjacent to the boundary of the large specific-heat region, implying that heat-transfer deterioration was more likely to occur at such condition. Therefore, the metal temperature of the water-wall tubes operating at 80% MCR load requires the most concern and monitor to avoid overheating of the water-wall tubes.

Thermal performance modeling of turbulent flow in multi tube in tube helically coiled heat exchangers

Heat transfer characteristics and performances of a multi tubes in tube helically coiled (MTTHC) heat exchanger are numerically investigated. The effects of operating and geometrical parameters on the thermal and hydrodynamic performances of the coil are studied and presented for turbulent flow regimes. The current simulation model is compared and validated with available experimental results and a good agreement is obtained. The numerical results showed that, the overall heat transfer coefficient (Uo) enhanced by 23% and 28% with increasing Reynolds numbers of hot and cold water (Rehw and Recw) from 9000 to17000 and 14,000 to 22,000, respectively. Coil effectiveness (ε) increased by 28% and 60% with increasing coil diameter (Dc) from 100–150 mm and 100 to 250 mm, respectively and increased with 20% with increasing the number of inner tubes (N) from 1 to 5. Moreover, the maximum values of the thermal-hydrodynamic performance index and coil effectiveness occurs at N = 3. The coil pitch has slight effect on the coil performance. Comparisons between the presented MTTHC with concentric tube in tube helically coiled (CTTHC) and multi tubes in straight tube (MTST) heat exchangers are conducted and showed that MTTHC heat exchangers displayed higher thermal performance. General numerical correlations for thermal and hydraulic coil performance are developed within acceptable errors.

Investigation of thermal and hydrodynamic performance of impingement jets solar air passage with protrusion with combination arc obstacle on the heated plate

ABSTRACTIn this article an experimental analysis has been conducted to study the effect obstacle parameters on thermal and hydrodynamic performance of impingement jets solar air passage having protrusion with combined arc obstacles on the heated surface. The study has involved the values of Reynolds number from 4000 to 18000, relative height ratios () from 0.8 to 1.7, relative pitch ratios () from 9.0 to 12, angle of arc () from 40 to 80, stream wise variation () from 0.39 to 0.56, and span wise variation () from 0.82 to 0.99, and jet diameter ratio of 0.065 respectively. Experimental data pertinent to Nusselt number () and friction factor () were generated for various sets of roughness and flow parameters. The highest improvement is obtained at a range of =1.1,=10, =60°, =0.43, =0.86, and 0.065 respectively. The maximum value of the thermal hydrodynamic performance was found to be 1.50 for the range of parameters investigated.

The effect of shape of winglet vortex generator on the thermal–hydrodynamic performance of a circular tube bank fin heat exchanger

In real application, the shape of the vortex generator has great influence on the heat transfer and flow resistance characteristics of tube bank fin heat exchanger. Therefore, the effect of the shape of the vortex generator on heat transfer performance of such heat exchanger should be considered. In this paper, the effect of three different shaped vortex generators (i.e. delta winglet, rectangular winglet and trapezoid winglet) on heat transfer intensity and secondary flow intensity of a circular tube bank fin heat exchanger was numerically studied. The results show that with increasing Re, overall average Nu and the non-dimensional secondary flow intensity Se m increase however friction factor f decreases. A corresponding relationship can be found between Nu and Se m, which indicates that the secondary flow intensity determines the heat transfer intensity in the fin-side channel of circular tube bank fin heat exchanger with different shaped vortex generators on the fin surfaces. Under the identical pumping power constrain, the optimal shape of the vortex generators is the delta winglet vortex generators for the studied cases.

Turbulent heat transfer and nanofluid flow in a protruded ribbed square passage

In this article, turbulent heat transfer of nanofluid flow in square passage with protruded rib shape is numerically and experimentally studied over Reynolds number ranges of 4000–18000. Different nanoparticles (Al2O3, CuO, and ZnO), with different concentration (φ) range of 1–4% and different nanoparticle diameter (dnp) range of 30–45nm are disperse in water (base fluid). Several parameters such as stream wise distance (Xs/dp) range of 1.4–2.6, span wise distance (Ys/dp) range of 1.4–2.6, ratio of protruded height to print diameter (ep/dp) range of 0.83–1.67 also studied to find the consequence on thermal and hydrodynamic characteristics. Simulations were carried out to obtain heat and fluid flow behaviour of smooth and ribbed square channel using commercial CFD software, ANSYS 15.0 (Fluent). Renormalization k-ε model was employed to assess the influence of protruded ribs on turbulent flow and velocity field. The outcome indicates that Al2O3 nanofluid has the highest value of average Nusselt number as compare to other nanofluids. The average Nusselt number increases as the concentration increases and it decreases as nanoparticle diameter increases. The thermal hydrodynamic performance parameter based on equal pumping power, average Nusselt number and average friction factor were found to be highest for Al2O3, φ=0.04, dnp=30nm, Xs/dp=1.8, Ys/dp=1.8 and ep/dp=1.0. The numerical data are compared with the corresponding experimental data. Comparison between CFD and experimental analysis results showed that good agreement as the data fell within ±7.0% error band.

Thermal–hydraulic performance of fin-and-oval tube compact heat exchangers with innovative design of corrugated fin patterns

The flow field inside the heat exchangers is associated with maximum heat transfer, minimum pressure drop and smallest pumping power. During the recent decades, the developments in the application of longitudinal vortex generators as an effective technique and important research topic have increased the heat transfer enhancement in the design of compact heat exchangers. The main motivation of this research is to study thermal–hydraulic performance characteristics in a tube bank compact heat exchanger with introducing new design of fins and tube by using computational fluid dynamics approach. One-corrugated and three-corrugated fins with oval tubes are innovative design of the FTCHE (fin-and-tube compact heat exchanger) that promises a large leap in the development of minimized FTCHEs with increased thermal efficiency. The major advantage of such design is its ability to produce substantially increased thermal efficiency and performance criteria of FTCHE. The investigation of thermal–hydraulic performance criteria is conducted for Reynolds number in the range of 200–900. This study shows that the flow distinction between plain and corrugated fins has a profound influence on the thermal-hydrodynamic performance. The results reveal that the corrugated fins can considerably advance the thermal efficiency of the FTCHE with a moderate pressure loss penalty. The computational results indicate that the average Nusselt number for the FTCHE with corrugated fin can be increased up to 20.0% over the baseline case and the corresponding pressure difference decreased up to 19.0%. In addition, the results show that the average value of performance in one-corrugated and three-corrugated fins and oval tube compact heat exchangers up to 5% and 15% over the baseline case, respectively. The newly designed fin with oval tube shows potential improvement of heat transfer performance and moderate pressure loss in the FTCHE compared with the baseline case.