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To provide a feasible heat dissipation solution for a high heat flux, in this study, the internal flow and heat transfer characteristics of an externally heated concentric double tube were numerically studied via the implicit finite difference method. The outer ring and inner tube were filled with a phase change nanofluid and water, respectively. The parameter ranges were as follows: the mass fractions of the phase change material (PCM) emulsions were 2.04 %, 2.91 %, and 7.11 %, the relative flow ratio was 0.33–4.0, the heat power inputs were 70 W and 150 W, and the total tube flow rates were 304.83 cm3/min and 465.98 cm3/min. The results showed that incorporating PCM emulsions can effectively improve heat transfer performance; however, the PCM concentrations, heating conditions, and outer-annulus/inner-tube flow rates (relative flow ratios) must be properly matched so that the phase change of the working fluid occurs in the expected section. Within these parameter ranges, in the heated section, the latent heat utilization of the PCM emulsion is lower than that of the sensible heat, and only when the flow ratio is greater than 1 is the latent heat utilization of the 7.11 % PCM emulsion similar to that of the sensible heat.

To effectively improve internal convection, in this study, the heat transfer enhancement using concurrent forced flows of phase change nanofluids/water through the outer ring/inner tube of a double tube was investigated experimentally and compared to that of an identical tube filled with water, for which limited information is available. The parameters are described as follows: heating powers of 70, 110, and 150 W; mass fractions of the phase change nanofluid of 2.04 %, 2.91 %, and 7.11 %; flow ratios of 0.33–4.0; and a total flow rate of 304 cm3/min. The results indicated that the PCM concentration, flow ratio, and heating power must be correctly matched so that the phase change in the working fluid falls in the expected position and the effect of the latent heat can be fully realized. For a 2.04 % PCM emulsion, when the heating wattage is 70 W and the flow ratio is approximately intermediate (0.51), the local heat transfer effectiveness of the heated section is >1, indicating that using a PCM emulsion as the working fluid instead of water can effectively increase the heat transfer rate.

This paper describes the design and proof of concept for an active eddy current damper which is integrated into a single-axis linear motor. Although developments on active eddy current damper are well documented, none has been implemented in a linear motor. The advantage of such a system is two-fold. Firstly, the relative motion between the magnets and the conducting sheet produces eddy currents resulting in an electromagnetic force opposing the direction of motion; which can be utilized to suppress vibrations. Secondly, it is possible to enhance the damping effect of the system; Due to environmental noise, it is normally not possible to increase the D coefficient in a PID controller as much as desirable. The damper is thus able to supplement this damping effect to improve settling time. Here, we will present the damper design as well as the preliminary experiment results for both vibration suppression and motion damping.

AbstractAn innovative indoor LED lighting prototype that uses pressed-flat grooved heat pipes as heat transfer channels to conduct LED-released heat to heat-sink-fins is proposed. Natural convection inside the flow channels within the heat-sink fins serves as the main heat dissipation mechanism. In order to accommodate different illumination directions, the thermal performance of the LED lighting prototype at different inclination and rotation angles (different heat pipe performances) were experimentally investigated. The results show that the temperature distribution of the prototypes is dependent on inclination angles, however, independent of rotation angles. FFT analysis reveals that dominant fluctuation frequencies of the temperature around the central area of the prototype with different inclination angles are about 4.7 minutes.

In the present study, the processing-properties relationships of the ZrO2/(Ni+Al2O3) composites are examined. Dense composites were prepared either by pulse electrical current sintering (PECS) at 1350C for 5 minutes or by pressureless sintering (PLS) at 1600C for 1 h. The size of Ni particles is as small as 30 nm to 50 nm. Though the size of ZrO2 grains in the matrix increases as alumina and nickel particles are added, the strength of the ZrO2/(Ni+Al2O3) composites is significantly higher than that of monolithic ZrO2.

This work aims to focus on the performance of water-based microencapsulated phase change material (MEPCM) suspension flow, as the coolant, in the mini-channel heat sinks. This system can be used for battery thermal management. The pressure drop, wall temperature distribution, and thermal resistance are presented at different flow rates and heat fluxes. In addition, to assess the effectiveness of this coolant, the coefficient of performance (COP) and the figure of merit (FOM) are presented. The measured data showed that as the MEPCM particle concentration is increased to 10%, a significant increase in the pressure drop, up to 120%, occurs. The addition of MEPCM reduces the wall temperature, leading to the decrease in the thermal resistance and the increase in the heat transport. The highest heat transport effectiveness of 1.223 was observed under the heating power of 32 kW/m2, Re number of 689, and actual latent heat sensible heat ratio of 0.623. The maximum value of FOMwas observed under the conditions of low heating power, Re number of 1368, and MEPCM particle concentration of 5%.

The spontaneous formation of surface electron accumulation (SEA) was observed in synthesized molybdenum diselenide (MoSe2) layered crystals with two-hexagonal (2H) structure. An anomalously high electron concentration at the surface up to 1019cm-3is several orders of magnitude higher than that (3.6 × 1012cm-3) of the inner bulk. The SEA is found to be generated easily by mechanical exfoliation and room temperature deselenization. Se-vacancies have been confirmed to be the major source resulting in SEA and n-type conductivity, and also the active sites for electrochemical catalysis in MoSe2. Noted that the SEA conjugated with the Se-vacancy-related surface defects enhances the electrochemical hydrogen evolution reaction (HER) activity substantially. The optimized HER efficiency with an overpotential at 0.17 V and Tafel slope at 60 mV/dec of the basal plane of 2H-MoSe2was achieved by the nitrogen plasma treatment, which has outperformed several nanostructures, thin films, and hybrid counterparts. This study reveals the intriguing surface-dominant electronic property and its effect on the HER enhancement of the basal plane, which is crucial for development of a stable, low-cost and highly efficient catalyst using 2H-MoSe2.

•Natural convection in an enclosure with PCM suspension was numerically investigated.•Enclosure bottom and top are isothermal heating and cooling respectively.•Transient and steady-state natural convection are considered.•All the parameters (RaT, Ste, Sb, and cm,i) affect the flow pattern.•Heat flow oscillations occur at Sb= 0.5-1.