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Flow and heat transfer in curve channel have been studied extensively due to the presence of the secondary flow induced by the centrifugal force. However, for the curved channel with small curvature, weakened centrifugal force reduces the intensity of secondary flow and heat transfer enhancement is attenuated accordingly. For sake of maintaining high heat transfer efficiency in curve channel with a wide range of curvature, periodical wave structure was introduced into the smooth-curve channel by this study. A three-dimensional model of the curve-wave structure was established and numerical simulation was carried out to explore the flow characteristics and heat transfer performance in the proposed channel. In addition, the effects of the wave amplitude on the channel performance were analyzed. The results showed that the heat transfer of smooth-curve channel can be enhanced remarkably by applying wave structure on the channel wall, and the overall performance factor indicates that the heat transfer argumentation outweighs the pressure loss penalty. It was also found that the heat transfer in the curve-wave channel can be further enhanced by increasing wave amplitude. The most effective heat transfer enhancement can be achieved based on the evaluation of the overall performance factor.

Solidification of distilled water saturated in open-cell metallic foams with graded morphologies was investigated experimentally. Open-cell foams having different morphological properties including porosity, pore density (PPI) and materials for the porous matrix were cut into pieces and stacked up, forming a whole porous layer with gradient morphological features. Systematic measurements of temporal solidification front and full solidification time for distilled water saturated in the morphology gradient foams were carried out. Meanwhile, numerical simulations of solidification in fluid-saturated metallic foams with uniform morphological properties were performed. It was found that the presence of gradient in foam properties affect significantly the solidification rate and full solidification time. The results showed that compared to the single-layered foam with fixed morphology, the stacked foams with properly designed morphology gradient would reduce more effectively the full solidification time, due to the enhanced heat transfer.

The thermal characteristics of lithium-ion battery affect significantly charging/discharging performance, cycle life and safety of electric vehicles (EVs) battery packs. In this study, a stagger-arranged battery pack consisting of three battery modules was developed to explore its transient thermal characteristics in charging/discharging process under the two cooling strategies, i.e., natural cooling and forced air cooling. The investigation of heat generation behavior of the battery with Li(NixCoyAlz)O2 cathode showed that the heat generation rate of the battery remains almost unchanged along the main discharging process, while a rapid increase in heat production is detected at the end of discharging. It was found that the maximum temperature and temperature difference in the battery pack subject to a moderate charging/discharging rate, e.g., 0.5 C, can be maintained within the desirable ranges by natural cooling. The forced air cooling strategy employing longitudinal airflow remarkably improves the battery’s transient thermal characteristics with achieving the depth of discharge (DOD) up to 84.2%, which is capable to prolong the battery pack’s cycle life to a large extent. Lastly, the appropriate air supply velocity of 0.8 m⋅s−1 is recommended for the proposed battery pack subject to a higher discharging rate, e.g., 1 C, from the viewpoint of cooling effectiveness.

In this study, we explain the causes and effects of the geometrical impossible result encountered in the widely adopted tetrakaidecahedron model (Boomsma and Poulikakos, 2001; Dai et al., 2010) for the effective thermal conductivities (ETCs) of metal foam. The geometrical impossible result is successfully eliminated by accounting for the size variation of the node with porosity. The improved model provides predictions of ETCs that are more precise than available models. For aluminum foams (ks=218Wm-1K-1) using water and air as fluid media, the relative root-mean-square (RMS) deviation of the present predictions from the experimental data is about 5.3%; for the reticulated vitreous carbon (RVC) foams (ks=8.5Wm-1K-1), the relative RMS deviation is about 7.4%.

This paper reports both experimental and numerical studies of our proposed electrokinetic focusing technique. The technique utilizes a combined AC and DC field for enhancing Joule heating induced temperature gradient focusing (TGF) of sample solutes in a microfluidic device. Our experimental results show that introducing an AC field component can provide sufficient Joule heating to generate temperature gradient required for achieving TGF of sample solutes, while the electroosmotic flow is suppressed under the relatively high frequency of the AC electric field. Consequently, concentration enhancement of sample solutes is considerably increased by using the combined AC and DC electric field technique. A numerical model including a set of multi-physical governing equations is presented to describe the complex TGF of sample solutes under a combined AC and DC field, and a scaling analysis of the time scales of several transport processes is conducted to simplify the numerical model. The numerical predictions are found in reasonable agreement with the measured Joule heating induced temperature profiles and electrokinetic flow field but show less dispersive than the observed focusing band of sample solutes and slightly over-estimate the experimental concentration enhancement. Several factors such as mass dispersion and photobleaching effect can contribute to the discrepancies between the model predictions and the experimental results.

A novel cylindrical oblique fin minichannel heat sink was proposed and studied for cooling heat source with cylindrical surfaces. To optimize and analyze the heat transfer performance of the heat sink, a similarity analysis and parametric study on the geometric dimensions of the heat sink were performed. Three dimensional conjugated heat transfer simulation using CFD (Computational Fluid Dynamics) approach was used to analyze the laminar convective heat transfer and apparent friction characteristics for 43 different cylindrical heat sinks with varied geometric dimensions. The studies were performed by varying the oblique angle from 20° to 45°, secondary channel gap from 1 mm to 5 mm and Reynolds number from 200 to 900. In this paper, the flow distribution was also investigated and reported, as the secondary channel gap, oblique angle and Reynolds number were varied. Based on the 259 numerical data points, multiple correlations for the average Nusselt number and the apparent friction constant were formulated, verified and presented. The average deviation for the approximation of average Nusselt number is from −5.8% to 7.0% while it is from −5.1% to 7.1% for the apparent friction constant. These correlations can be used for further studies such as performance prediction or geometrical optimization.

A novel cylindrical oblique fin minichannel heat sink was proposed to fit over cylindrical heat sources in the form of an enveloping jacket. The periodic cylindrical oblique fin causes the hydrodynamic boundary layer development to be reinitialized at the leading edge of the next downstream fin. This decreases the average thermal boundary layer thickness, enhances the heat transfer performance and yields negligible pressure drop penalty due to combined effect of thermal boundary layer re-development and flow mixing. Its cooling effectiveness is compared with conventional straight fin minichannel heat sinks through experimental and numerical approach for the Reynolds number ranged from 50 to 500. The results showed that the averaged Nusselt number, Nu ave for the cylindrical oblique-cut fin minichannel heat sink increases up to 75.6% and the total thermal resistance decreases up to 59.1% when compared with the conventional straight fin minichannel heat sink. It is also found firstly that a flow recirculation zone will form at larger Reynolds number in the secondary channel however this recirculation is insignificant in the present low Reynolds number study. Heat transfer enhancement ( E Nu ) and pressure drop penalty ( E f ) show that a significant improvement of the cylindrical oblique fin minichannel over conventional straight fin minichannel overall.

Two phase microgap heat sink has a large potential to minimize the drawbacks associated with two phase microchannel heat sink, especially flow instabilities, flow reversal and lateral variation of flow and wall temperature between channels. This new concept of the two-phase microgap heat sink is very promising due to its high heat transfer rate and ease of fabrication. However, comparison of the performance of microgap heat sink (heat transfer, pressure drop and instability characteristics) with some conventional heat sink has not been investigated extensively. In this study, experiments have been conducted to investigate the heat transfer and pressure drop characteristics of deionized water (DI) in microgap heat sink and compare these experimental results with similar data obtained for microchannel heat sink. These studies are carried out with the inlet DI water temperatures 86 °C at different mass fluxes ranging from 400 to 1000 kg/m2 s, for effective heat flux 0–85 W/cm2. High speed flow visualizations are conducted simultaneously along with experiments to illustrate the bubble characteristics in the microchannel and microgap heat sink. Experimental result shows that microgap heat sink performs better at high heat flux and low mass flux due to confined slug and annular boiling dominance and consequent delay of dryout phase. So, this microgap technology is promising and an effective method to dissipate very high heat fluxes in compact space with a smaller rate of coolant flow. Moreover, pressure drop is higher in microchannel than microgap heat sink at all the heat fluxes. In addition, encouraging results have been obtained using microgap as it can potentially mitigate local hotspot, reduce flow instabilities, flow reversal and maintain uniform wall temperatures over the heated surface.

The rapid increase of heat flux in high performance electronic devices has necessitated the development of high capacity thermal management techniques that can support extremely high heat transfer rates. Flow boiling in microgap is very promising for this purpose due to its high heat transfer rate and ease of fabrication. However, the effects of microgap dimension on heat transfer and pressure drop characteristics along with flow visualization have not been investigated extensively. This paper focuses on flow boiling experiments of deionized water in silicon microgap heat sink for ten different microgap dimensions from a range of 80 μm–1000 μm to determine the most effective and efficient range of microgap dimensions based on heat transfer and pressure drop performance. High speed flow visualization is conducted simultaneously along with experiments to illustrate the bubble characteristics in the boiling flow in microgap. The results of this study show that confinement in flow boiling occurs for microgap sizes 500 μm and below and confined slug/annular flow is the main dominant regime whereas physical confinement does not occur for microgap sizes 700 μm and above and bubbly flow is the dominant flow regime. The microgap is ineffective below 100 μm as partial dryout strikes very early and the wall temperature is much higher for a fixed heat flux as microgap size increases above 500 μm. In addition, results show that pressure drop and pressure fluctuation decrease with the increases of gap size whereas wall temperature and wall temperature fluctuation increase with the increases of gap size. A strong dependence of heat transfer coefficient on microgap sizes is observed for microgap sizes 500 μm and below. However, the heat transfer coefficient is independent of microgap size for microgap sizes 700 μm and above.

An experimental study has been conducted on the heat transfer of oscillating flow through a channel filled with aluminum foam subjected to a constant wall heat flux. The surface temperature distribution on the wall, velocity of flow through porous channel and pressure drop across the test section were measured. The characteristics of pressure drop, the effects of the dimensionless amplitude of displacement and dimensionless frequency of oscillating flow on heat transfer in porous channel were analyzed. The results revealed that the heat transfer in oscillating flow is significantly enhanced by employing porous media in a plate channel. The cycle-averaged local Nusselt number increases with both the kinetic Reynolds number Re ω and the dimensionless amplitude of flow displacement A 0 . The length-averaged Nusselt number is effectively increased by increasing the kinetic Reynolds number from 178 to 874 for A 0 = 3.1–4.1. Based on the experimental data, a correlation equation of the length-averaged Nusselt number with the dimensionless parameters of Re ω and A 0 is obtained for a porous channel with L / D h = 3.