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Abstract An ionic wind pump is an energy-saving device that can produce a volume flow when electrodes are applied with high voltage. Compared to the traditional methods, ionic wind pumps possess the advantages of low energy consumption, no moving parts, compact structure and flexible design. In this study, a large-size ionic wind pump, consisting of many single regular hexagonal needle-ring ionic wind generators, was developed as the preliminary model. However, its experimental performance was not as good as our expectations. In order to improve this preliminary model, a simulation method was used to investigate the configuration factors of the single ionic wind pump. In the optimized model, mesh gap is 6 mm, eccentricity is 0.26, section area is 238.44 mm2 and needle electrode number is 3. In subsequent experiments, the final optimized large-size ionic wind pump showed a great promotion in velocity, and the maximum average velocity of the optimized pump was higher than the preliminary model by 13.3%. Our numerical simulation and experiment results have practical significance in designing ionic wind pumps. Highlights • A 3D numerical model is established for large size ionic wind pump. • Influences of multi-parameter on the performance of ionic wind pump are investigated by numerical and experimental method. • Optimized large-size ionic wind pump showed a great promotion in velocity. [ABSTRACT FROM AUTHOR]

As a solid waste, a coal−based humic acid residue (HAS) is less researched for its resource utilization. HAS is advantageous to the adsorption of heavy metals in water bodies because of its high adsorption capacity and low cost. In this study, HAS was modified using KMnO 4 solution to improve the adsorption of Hg(Ⅱ)/Pb(Ⅱ), while the modification process was optimised by response surface methodology (RSM) and named K−HAS. The Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X − ray photoelectron spectroscopy (XPS) and X − ray diffraction (XRD) were jointly adopted to characterize the HAS and K−HAS. The batch sorption experiments were used to study the adsorption characteristics of external factors such as initial concentration, pH, and reaction time on the adsorption of Hg(Ⅱ)/Pb(Ⅱ) by K−HAS, and the isothermal adsorption model and kinetic model were used to fit the behavior of Hg(Ⅱ)/Pb(Ⅱ) adsorption by K−HAS. The results show that the pseudo−second−order model and the Langmuir adsorption isotherm model can better describe the adsorption behavior of K−HAS on Hg(Ⅱ)/Pb(Ⅱ), with the maximum adsorption amounts of 128.40 and 342.43 mg·g−1, respectively; there is competitive adsorption between Hg(Ⅱ) and Pb(Ⅱ), and Pb(Ⅱ) has a stronger competitive ability, as the concentration of Hg(II) increased, the adsorption of Pb(II) by K-HAS decreased by 20.29% and the adsorption of Hg by K-HAS decreased by 22.77% as the concentration of Pb(II) increased; the thermodynamic parameters indicate that the adsorption of Hg(Ⅱ)/Pb(Ⅱ) by K−HAS is a spontaneous heat absorption reaction. The adsorption mechanism of K−HAS for Hg(Ⅱ)/Pb(Ⅱ) mainly consisted of precipitation and complexation, which contributed 58.7% and 20.6% to Hg(Ⅱ) and 50.7% and 27.5% to Pb(Ⅱ), respectively. In addition, the site energy distribution (SED) shows that Hg(Ⅱ)/Pb(Ⅱ) preferentially occupy the high−energy adsorption sites and then gradually occupies the low−energy sites and that the K−HAS surface becomes more and more inhomogeneous as the solution temperature increases. The experiments demonstrate that K−HAS is effective in the adsorption of Hg(Ⅱ)/Pb(Ⅱ), and the investigation of the adsorption mechanism can be useful for further studies. • KMnO 4 enhances the adsorption capacity of HAS for Hg(Ⅱ)/Pb(Ⅱ). • The adsorption of Hg(Ⅱ)/Pb(Ⅱ) by K-HAS was 128.4 and 342.43 mg·g−1 respectively. • The main sorption mechanisms were precipitation, complexation and physical action. • Study of adsorption processes using SED. [ABSTRACT FROM AUTHOR]

A water drop impacts a thin heated wafer which is being cooled by a film flow generated from water jet impingement. The drop impact breaks the steady-state cooling and causes the local temperature around the drop landing location to change. This transient heat transfer process is experimentally investigated using an IR camera to record the surface temperature ( T s ) of the wafer’s underneath. The measured temperature shows two stages of the process: a response stage when the temperature quickly decreases as a result of the drop impact, followed by a recovery stage during which the temperature returns to the steady state. It is found the recovery time decreases with increasing the film flow rate. Although during the entire process T s is lower than the steady state, the heat transfer coefficient ( h t ) is revealed to change by three steps. The first step is the increase of h t across the impact area, which indicates enhanced convection. In the second step, h t decreases toward and eventually below the steady state. In the third step the heat transfer coefficient increases toward and returns to the steady state. An enhancement factor based on the change of heat transfer coefficient rather than the temperature change is introduced to evaluate the enhancement of convection. The distribution of local maximum enhancement ( η max ) along the center line of the impact area and the peak value of η max are used to investigate the enhancement effects of film flow rate, drop diameter, and drop impact velocity. It is found η max does not follow a monotonic trend with increasing the impact velocity. The peak enhancement is found to be proportional to the square root of the ratio of the drop flow rate to the film flow rate. [ABSTRACT FROM AUTHOR]

The helically coiled tubes with two-phase flow are widely used as heat transfer equipment in power stations, chemical plants, nuclear reactors, refrigeration systems, and many others. This paper investigates experimentally the subcooled boiling heat transfer characteristics of R134a in vertical helically coiled tubes with heat flux varying from 0.1 to 14.5 kW m −2 , mass flux from 147.5 to 443.7 kg m −2 s −1 , inlet subcooled temperature from 4.7 to 15.0 °C and pressure from 450 to 850 kPa. Experimental results indicate that the generated bubbles always slide along the heated surface in the vertical helically coiled tube while the radial component force is negative, which contributes significantly to the heat transfer enhancement and nonuniformity of the wall temperature in subcooled flow boiling. Moreover, the temperature distribution in the vertical helically coiled tube is totally different from that of the horizontal one which is affected by the secondary flow, velocity profile of main flow and bubble behaviors. However, there is no much difference in the parametric effects on the heat transfer coefficient between vertical and horizontal arrangements. The heat transfer coefficients of vertical and horizontal helically coiled tube increase with system pressure, but decrease with subcooling. Based on the experimental data, the correlation of subcooled boiling heat transfer coefficient in helical coil is developed by using dimensional analysis, correlating 96.6% of the data within ±20%. [ABSTRACT FROM AUTHOR]

The heat transfer of boiling flows in helically-coiled tubes has significant relation with the bubble dynamics in the curved flows. To understand the bubble dynamics in curved flows, we experimentally study air bubbles in water flows in a coiled tube, which is approximately considered as a toroidal tube. The torus is perpendicular to the ground. Air bubbles are generated by injecting constant air flow at varied locations of the torus. Focus is put on the relationship of the bubble departure and traveling path with the water flow and injection location. The force analysis includes the gravitational force, the drag forces by the main and secondary flows, and the centrifugal force. Injection at the outer side of the torus shows higher bubble departure rate than the inner side, which is caused by the higher drag force of main flow at the outer side. The displacement of bubble traveling path between the inner and outer sides is mainly affected by the gravitational force for slow curved flows, and is dominated by the centrifugal force for fast curved flows. [ABSTRACT FROM AUTHOR]

• The phenomenon of ONB is investigated by visualization and temperature measurement. • The heat concentration promoted the bubbles formation at the corner of micro pin fin. • Subcooling, mass flux, and micro rib shape have a great impact on the ONB. • The predictive correlation fits 85.7% of the experimental data within ±15%. The micro pin fin heat sink has great application potential in the heat dissipation of high-power LED chips, phased array radars and semiconductor lasers. The onset of nucleate boiling (ONB) is a critical limit in designing heat dissipation systems. A simultaneous visualization and measurement study is conducted to investigate the ONB phenomenon of deionized water in circular, diamond, and oval micro pin fin heat sinks. Experiments are conducted under inlet subcooling of 29.6–49.5 °C, mass flux of 147.4–355.4 kg m−2 s−1 and heat flux of 4.8–55.8 W cm−2. Visualization result indicates that the ONB is always initiated at the surrounding region of a micro pin fin. The effects of additional nucleation sites caused by a micro pin fin and the temperature distribution of the surrounding region captured by an infrared camera can be used to explain the occurrence of the first bubbles. In this study, the effects of inlet subcooling, mass flux, and the cross-section shape of the micro rib on the ONB characteristics are investigated. Results show that the heat flux and wall superheat needed for the ONB increase as the mass flux and inlet subcooling increase. Moreover, the heat flux required for the ONB in the diamond and oval micro pin fin heat sinks is higher than that in the circular one. On the basis of the experimental data, the correlation of heat flux at the ONB in the micro pin fin heat sink is established, with 85.7% of the data falling within an error band of ±15%. [ABSTRACT FROM AUTHOR]

In this paper, a 3-D model of an electrostatic fluid accelerator was simulated using the finite element method (as implemented in COMSOL Multiphysics). To investigate the heat transfer performance of the accelerator, the impinging flow of the accelerator was used to cool down a heating round plate. The heat transfer coefficient and temperature distribution of the plate were numerically investigated with respect to the heat flux and radius of the round plate, and a comparison was made between the impinging flow of the accelerator and a uniform jet flow. To explore this in greater depth, a non-uniform heat flux was applied on the round plate to study the cooling effect of the accelerator on the surface with a hot spot. The effects of the hot spot heat flux and the hot spot size were then investigated. This study provides a reference for the practical cooling process of commercial chips, with and without hot spots, by adopting electrostatic fluid accelerators. [ABSTRACT FROM AUTHOR]

A combined power generation system is proposed based on SOFC/GT and transcritical carbon dioxide cycle, which employs the transcritical carbon dioxide cycle to recover the waste heat from SOFC/GT. The proposed system performance is evaluated by mathematical models and thermodynamic laws. Results indicate that the SOFC, TRCC and overall system electrical efficiencies are 49.21%, 29.14% and 69.26% under the designed conditions, and the last increases with increase in compressor pressure ratio. The entrance pressures of expansion machine in TRCC also affect the performance of the combined power generation system. [ABSTRACT FROM AUTHOR]