The effect of Fe
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nanoparticles and carbon nanotubes (CNTs) on the viscosity of a nanofluid is experimentally investigated from 278 to 313 K by changing the nanoparticle volume fraction. These ...nanoparticles were put into distilled water with various surfactants, i.e., Colace (docusate sodium), trisodium citrate dihydrate (TSC), polyvinyl pyrrolidone, cetyl trimethylammonium bromide, tetramethylammonium hydroxide (TMAH), acacia senegal (GA), sodium dodecyl benzene sulfonate, sodium dodecyl sulfate (SDS), and sodium laurylsulfonate (SLS). Based on the present measurements, new empirical formulas are proposed for Fe
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–water, CNT–water and Fe
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–CNT–water nanofluids to provide accurate predictions for the nanofluid viscosity. Based on the viscosity testing, stabilities and thermal conductivities of Fe
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–TMAH, Fe
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–Colace, Fe
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–TSC, CNT–SDS, CNT–GA, Fe
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–CNT–SLS, and Fe
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–CNT–TSC nanofluids with a volume concentration of 0.5% are investigated in the present research. Results indicate that better stability, smaller viscosity, and higher thermal conductivity are obtained, when the surfactants TMAH, SDS, and SLS are added into the Fe
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–water, CNT–water, and the Fe
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–CNT–water nanofluid, respectively. The CNT–water and Fe
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–CNT–water nanofluids exhibit a shear-thinning behavior, whereas a linear rheological behavior can be observed by water-based Colace–Fe
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, TMAH–Fe
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, and TSC–Fe
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nanofluids.
A numerical study was conducted to investigate the mechanism of laminar flow and heat transfer enhancement in an interrupted microchannel heat sink (IMCHS) with different shaped ribs at Reynolds ...number ranging from 100 to 900. The global flow features, heat transfer and friction for IMCHS with no ribs, rectangle ribs, triangle ribs and trapezoid ribs are detailed compared. The results show that the local heat transfer and friction performance of IMCHS with ribs show significant increase at the windward side of the ribs. Additionally, the smaller the chamfer of ribs, the larger average heat transfer and friction performance. For IMCHS with rectangle ribs, the maximum increment of Nu and
f
can reach to 1.81 and 2.59, respectively. Concerning the overall heat transfer performance (PEC), the trapezoid ribs show the best behavior with PEC = 1.65–1.38 at Re = 100–900.
In this paper, convective heat transfer of Fe
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–carbon nanotubes (CNTs) hybrid nanofluid was studied in a horizontal small circular tube under influence of annular magnets. The pipe has an inner ...diameter of 3 mm and a length of 1.2 m. Heat transfer characteristics of the Fe
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–water nanofluid were examined for many parameters, such as nanoparticle volume fraction in the range of 0.4–1.2% and Reynolds number in the range of 476–996. In order to increase the thermal conductivity of the Fe
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–water nanofluid, carbon nanotubes with 0.12–0.48% volume fraction were added into the nanofluid. It was observed that for the Fe
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–CNTs–water nanofluid with 1.44% volume fraction and under a magnetic field, the maximal local Nusselt number at the Reynolds number 996 increased by 61.54% compared with without a magnetic field. Results also show that compared with the deionized water, the maximal enhancements of the average Nusselt number are 67.9 and 20.89% for the Fe
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–CNTs–water nanofluid with and without magnetic field, respectively.
Modulated nanoparticle-coating surfaces were fabricated by an improved electrophoretic deposition technique in this study. Pool boiling experiments were studied for HFE-7200 on the modulated ...nanoparticle-coating surfaces, with a smooth surface and uniform coating surfaces as comparison. It was found that the present modulated coating surfaces can enhance the heat transfer coefficient and the critical heat flux by 60% and 20%–40%, respectively, in comparison to the smooth surface, while the uniform coating surface can improve heat transfer coefficients by maximum 100%, but cannot enhance critical heat fluxes. Heat transfer on the modulated nanoparticle-coating surfaces was theoretically analyzed by a mechanistic model which considered free convection, transient conduction and microlayer evaporation. The heat transfer can be predicted by the model, especially at low-to-moderate heat fluxes. Additionally, referring to the bubble visualization at critical heat fluxes, possible mechanisms to trigger critical heat fluxes were discussed. Afterwards, a critical heat flux model originating from the Zuber hydrodynamic instability model, was employed to predict the experimental results, showing a good prediction ability.
This paper presents three-dimensional numerical simulations with the established realizable
k
−
ε
model to clarify the underlying and interacting mechanisms between the film cooling and the internal ...cooling. On the one hand, the effects of three different internal cooling channels, i.e., smooth channel, continuous ribbed channel, and truncated ribbed channel, on the film cooling effectiveness and the discharge coefficients are investigated. On the other hand, the influences of three different film cooling holes, i.e., cylindrical hole, two elliptical holes and two circular-to-elliptical holes, on the heat transfer performances and pressure loss of the internal cooling channel are revealed. Especially, the suction effects of the film cooling holes are analyzed through setting up baselines with only internal cooling channels. Results show that the placement of ribs in the internal channel has different influences on the film cooling effectiveness with respect to different hole shapes depending on the blowing ratio. The discharge coefficient of the film hole can be improved by introducing ribs to the internal channel. Suction of film hole is helpful for enhancing the heat transfer performance and reducing the pressure loss of the internal channel. Besides, ribs instead of the suction effect of film hole play a major role to enhance the heat transfer performance in the internal cooling channel.
In the present study, experimental studies are carried out to investigate the heat transfer and friction characteristics in a square duct roughened by various-shaped ribs on one wall. The ribs are ...oriented transversely to the main stream in a periodic arrangement. Liquid crystal thermography is employed to measure the local and average heat transfer coefficient on the ribbed surface. The rib height-to-duct hydraulic diameter ratio is fixed at 0.1; the rib pitch-to-height ratio varies from 8 to 15 and the test Reynolds number spans from 8,000 to 20,000. The results show that the trapezoidal-shaped ribs with decreasing height in the flow direction (case C) provide the highest heat transfer enhancement factor and are likely to be used to suppress the local hot spot which usually occurs in the region just behind the ribs.
Due to the increasing cooling power and space limitation in vehicles, a new compact heat exchanger – graphite foam heat exchanger is proposed for vehicle cooling application. The graphite foam has ...high thermal conductivity (the effective thermal conductivity is 40–150 W/m K) and low density (0.2–0.6 g/cm3), but it has high flow resistance which is a problem in heat exchanger applications. In order to find a graphite foam heat exchanger with low flow resistance, four different configurations (baffle, pin-finned, corrugated, and wavy corrugated) of graphite foam fins are analyzed in terms of thermal performance and pressure drop by using a computational fluid dynamics approach. The simulation results show that the wavy corrugated foam presents high thermal performance and low pressure drop. Moreover, a comparative study between the wavy corrugated foam heat exchanger and a conventional aluminum louver fin heat exchanger is carried out to evaluate the performance of graphite foam heat exchangers in terms of coefficient of performance (removed heat/air pumping loss), power density (removed heat/mass of heat exchangers), and compactness factor (removed heat/volume of heat exchangers). Finally, this paper concludes that graphite foam heat exchangers should be further developed in vehicles, and presents several recommendations for how such development can be promoted.
► Graphite foam wavy corrugated fins present good thermal and flow characteristics. ► The graphite foam wavy corrugated fin heat exchanger presents a high power density. ► A high compactness factor is provided by the graphite foam heat exchanger. ► The graphite foam heat exchanger has a low coefficient of performance (duty/pumping loss). ► Graphite foam heat exchangers have great potential in vehicle cooling applications.
Turbulent flow and heat transfer in outward transverse and helically corrugated tubes are performed with large eddy simulation by the ANSYS Fluent software. The prediction accuracy is validated by ...comparison with experimental data and empirical correlations for a wavy surface wall and smooth tube, respectively. The turbulent flow patterns, local heat transfer, and friction factor are discussed. The results show that the secondary and turbulent eddies are inhibited by the spiral flow. Otherwise, the flow impact of the wall is the key factor for heat transfer enhancement, and the spiral flow has of small effect on heat transfer performance, however it can decrease the flow resistance significantly. The overall heat transfer performance for the helical corrugated tube is 1.23, which is superior to the value of 1.18 for the transverse corrugated tube.
Addition of nanoparticles into a fluid can improve the heat transfer performance of the base fluid in heat exchangers. In this work, the preparation method and process of nanofluids are introduced, ...and thermal properties of nanofluids, such as thermal conductivity and viscosity, are discussed deeply. This paper summarizes various theoretical models of thermal conductivity and viscosity of nanofluids. A comprehensive literature survey on applications and limitations of nanofluids has been compiled. This paper also aims to review the natural and forced convective heat transfer characteristics of nanofluids with and without magnetic fields. The discussion for the natural convective heat transfer of nanofluids focuses on the heat transfer performance of non-conventional enclosures and electric heaters. The effects on heat transfer due to variations of heated walls are also investigated. Specific applications of nanofluids in a tube with trapezoidal ribs, double-tube heat exchangers, and plate heat exchangers have been reviewed and presented in a discussion about forced convective heat transfer. The previous results show that the inlet temperature of nanofluids obviously affects the heat transfer characteristics of double-tube heat exchangers, whereas a multi-walled carbon nanotube–water nanofluid shows significant advantages in plate heat exchangers. Finally, this paper studies natural convective heat transfer of magnetic fluids in a square cavity and forced convection heat transfer in a straight tube and a corrugated structure under the action of magnetic fields. It is found that the heat transfer performance of an Fe
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–water nanofluid is enhanced when a magnetic field is applied to the corrugated plate heat exchangers, and the pressure drop can be reduced by around 10%. It is recommended that natural convection of magnetic fluids needs to be investigated experimentally in a real cavity and a corrugated channel under the influence of a magnetic field. In addition, studies of alternating magnetic field are recommended to reveal any improvements of thermal performance of magnetic fluids in heat exchange devices. This review puts forward an effective solution for improvement of the thermal performance of heat transfer equipment and serves as a basic reference for applications of nanofluids in heat transfer fields.
The energy usage of parallel chillers systems accounts for 25–40 % of the total energy cost of a building. In light of global warming concerns and the need for energy conservation, it is essential to ...distribute the load of the parallel chillers systems effectively to achieve energy savings in buildings. Accordingly, this study presents a multi-strategy improved sparrow search algorithm (MSSA) to address optimization of the optimal chillers loading (OCL) problem. The proposed algorithm augments the basic sparrow search algorithm (SSA) by introducing the Sine chaotic map, Levy flight method, and Cauchy variation to enhance diversity, avoid local optima, and increase global and local search capacities. We use 9 benchmark functions to check the performance of the proposed MSSA algorithm, and the results are better than the selected algorithms such as particle swarm algorithm (PSO), harris hawks optimization (HHO), artificial rabbit optimization (ARO) and sparrow search algorithm (SSA). In addition, MSSA is applied to two typical cases to demonstrate its performance to optimal chillers loading and the results indicate that the MSSA outperforms similar algorithms. This study validates that MSSA can provide a promising solution to resolve the OCL problem.
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