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This study experimentally determined the flapping dynamics of dual self-oscillating inverted flags placed inside turbulent channel flows in side-by-side and staggered configurations and their ability to enhance wall heat removal. Three clearance-distance to channel-width ratios (Gc/W = 0.19, 0.31, and 0.5) and three streamwise-distance to channel-width ratios (Gy/W = 0, 2, and 4) were used to examine distinct flag behaviors. A single flag mounted to the heated wall with various gap clearances was chosen as the benchmark. The flags’ time-varying motions were recorded by a high-speed camera system. Three dynamic regimes were identified on the basis of the flags’ dimensionless stiffness and the channel flow’s Reynolds number: the biased mode, the flapping mode, and the deflected mode. Temperature sensitive paint (TSP) measurements demonstrated that the best cooling enhancement, with a local Nusselt number ratio of over 1.6, was achieved for the single flag system at Gc/W = 0.19. Adding another inverted flag to the side-by-side configuration at Gc/W = 0.19 further enhanced the heat removal performance on both channel walls, and the flapping period increased by nearly 50%. However, placing two side-by-side flags close to each other (Gc/W = 0.31) led to chaotic flapping motions, resulting in diminutive augmentation in heat transfer and an appreciable penalty in pressure drop. In the staggered configuration at Gy/W = 2 and 4, the two inverted flags synchronously flapped with a stable phase difference, and the flapping periods were similar to those of the single flag. The peak Nusselt number ratio was 1.9 for Gy/W = 2, which was attributed to the concerted influence of the staggered inverted flags. The system with staggered flags placed close to the heated wall had a higher thermal enhancement factor than the system with flags mounted in tandem along the channel centerline.

NaBr is considered as one of the typical low temperature salts employed for solid sorption refrigeration. The novel concept of solid sorption heat pipe (SSHP) which integrates heat and mass transfer with solid-gas sorption technology is expected to fulfill the continuous heat transfer and alleviate the drawbacks of both conventional heat pipe and thermosyphon. In this paper, an experimental system for both sorption/desorption unit and heat transfer unit is designed and the experiments of non-equilibrium sorption/desorption performances of NaBr-NH3 and heat transfer performances of SSHP with different molar amounts and inclination angles are carried out, respectively. The test results of sorption/desorption unit demonstrate that the increase of desorption quantity becomes very slow when the heating temperature reaches up to 75 °C and above, and with the increase of condensing pressure, the mass of ammonia desorbed from the ammoniate NaBr becomes less. The investigations of SSHP with 3 mol sorbates show that the heat transfer quantity increases significantly with the heating temperature reaches to 55 °C and above, in which the relatively higher desorption rate can be obtained. The largest value of heat transfer quantity per unit molar ammonia for 3 mol sorbates is close to that of 5 mol under the condition of heating temperature of 90 °C and cooling temperature of 20 °C. When the angle of inclination changes from 90° to 45°, the heat transfer capacity of SSHP declines more significantly compared with that of the angle from 45° to 0°.

The pinned and clamped configurations of a single piezoelectric membrane placed in free stream flow were extensively compared in terms of energy harvesting performance and spatiotemporal variations in the membrane's displacement and curvature. The results convincingly show a considerable gain in the harvested energy of the pinned membrane due to the broad region with large curvature. The self-adaptive nature of the pinned membrane in response to different flow directions was also demonstrated. A comprehensive study at the reduced flow speed regime U* =22.8 to 38 was made of two parallel pinned membranes with different cross-flow separation distances ( D/L =0.6 to 2.2). The shapes of the two flapping membranes were visualized with a high-speed camera while the synchronous variation of the terminal load's voltage on each membrane was recorded. At small separation distance 0.6 ≤ D/L ≤ 0.8 , the membranes flapped with a phase difference of 0.5 π at U* =22.8 to 28.5; the increase in velocity resulted in a switch to the in-phase flapping mode. At D/L = 1.0 to 1.8, the two membranes flapped in the anti-phase mode for the entire velocity region U* = 22.8 to 38.0, along with a considerable gain in the harvested energy over the other coupled modes. The results indicated that a large region ( D/L =1.0–1.8, U* =22.8–38) with the anti-phase coupling in the D / L - U* plane was suitable for energy harvest. As the separation distance increases further to 2.0≤ D/L ≤ 2.2, the membranes flapped at different frequencies. Finally, the influence of the terminal load on the power was determined for the separation distance D/L =1.2; the anti-phase flapping membranes were connected into circuits with reversed electrode arrangements, reaching a peak power P =10.31 mW at the optimal terminal load for U* =36.1.

The flapping dynamics of a piezoelectric membrane placed behind a circular cylinder, which are closely related to its energy harvesting performance, were extensively studied near the critical regime by varying the distance between the cylinder and the membrane. A total of four configurations were used for the comparative study: the baseline configuration in the absence of the upstream circular cylinder, and three configurations with different distances ( S ) between the cylinder and the membrane ( S / D =0, 1, and 2). A polyvinylidene fluoride (PVDF) membrane was configured to flutter at its second mode in these experiments. The Reynolds number based on the membrane’s length was 6.35×10 4 to 1.28×10 5 , resulting in a full view of membrane dynamics in the subcritical, critical, and postcritical regimes. The membrane shape and the terminal voltage were simultaneously measured with a high-speed camera and an oscilloscope, respectively. The influence of the upstream cylinder on the membrane dynamics was discussed in terms of time-mean electricity, instantaneous variations and power spectra of terminal voltage and membrane shape, fluctuating voltage amplitude, and flapping frequency. The experimental results overwhelmingly demonstrated that the terminal voltage faithfully reflected various unsteady events embedded in the membrane’s flapping motion. For all configurations, dependency of the captured electricity on a flow speed beyond the critical status was found to follow the parabolic relationship. In the two configurations in which S / D =0 and 1, the extraneously induced excitation by the Karman vortex street behind the circular cylinder substantially reduced the critical flow speed, giving rise to effective energy capture at a lower flow speed and a relatively high gain in power output. However, in the configuration in which S / D =2, the intensified excitation by the Karman vortex street on the membrane considerably reduced the captured energy. Finally, a transient analysis of the membrane’s flapping dynamics in the configuration in which S / D =0 was performed in terms of phase-dependent variations of the membrane segment’s moving speed, membrane curvature, and terminal voltage; the analysis resulted in a full understanding of the energy harvesting process with consecutive inter transfer of elastic, kinetic, and electric energies.

A series of carboxylic acid functionalized hybrid linear-dendritic block copolymers (LDBCs) derived from methoxy poly(ethylene glycol) (MPEG) and variant generation dendrons from 2,2-bis(hydroxymethyl) propionic acid were synthesized and employed as CaCO3 crystallization growth modifiers. Mainly spherical vaterite particles of gradually reduced sizes were produced with the increase of the polymer additive concentration and/or the dendron segment generation number, while the incorporated polymer organic components in the particles increased for the promoted binding efficiency and ever enhanced adsorption ability. A higher mineralization temperature resulted in significantly larger particle size and partly calcite formation. Under the same molar concentration of carboxylic acid, the same size level particles were obtained which manifested the crucial role of the functional group, meanwhile, the slight decrease of the spherical vaterite diameters with increasing generation number and especially the formation of particular pine-cone shaped calcite crystals also revealed the significant effect of the architectural structure of variant generations and some special characters of the hybrid LDBC structures.