•Latest developments on sonication characteristics on nanofluid properties reviewed.•In general, thermal conductivity increases with sonication time.•Viscosity can be reduced with the increase of ...sonication.•Finding optimal sonication time and power is still challenging.
The most crucial step towards conducting experimental studies on thermophysical properties and heat transfer of nanofluids is, undoubtedly, the preparation step. It is known that good dispersion of nanoparticles into the base fluids leads to having long-time stable nanofluids, which result in having higher thermal conductivity enhancement and lower viscosity increase. Ultrasonic treatment is one of the most effective techniques to break down the large clusters of nanoparticles into the smaller clusters or even individual nanoparticles.
The present review aims to summarize the recently published literature on the effects of various ultrasonication parameters on stability and thermal properties of various nanofluids. The most common methods to characterize the dispersion quality and stability of the nanofluids have been presented and discussed. It is found that increasing the ultrasonication time and power results in having more dispersed and stable nanofluids. Moreover, increasing the ultrasonication time and power leads to having higher thermal conductivity and heat transfer enhancement, lower viscosity increase, and lower pressure drop. However, there are some exceptional cases in which increasing the ultrasonication time and power deteriorated the stability and thermophysical properties of some nanofluids. It is also found that employing the ultrasonic horn/probe devices are much more effective than ultrasonic bath devices; lower ultrasonication time and power leads to better results.
•Sinusoidal wavy plate fins with phase shift of 0°, 90° and 180° are investigated.•Thermal performance of SW-PFHS and CCSW-PFHS are compared.•The phase shift has significant effect on the thermal ...performance.•The proper working conditions of sinusoidal wavy fins heat sinks are reported.
This article presents new experimental data on the influence of phase shift, air velocity, heat sink base surface temperature on heat transfer coefficient, and pressure drop of airflow through sinusoidal wavy plate fin heat sinks (SW-PFHS) and crosscut sinusoidal wavy plate fin heat sinks (CCSW-PFHS). Sinusoidal wavy plate fins with a wave length of 18.68 mm, amplitude of 2.0 mm, and phase shift of 0°, 90°, and 180° are used. For CCSW-PFHS, the sinusoidal wavy plate fin is cut transversely at crests and troughs with a 2 mm length. The test runs are performed at an air velocity ranging between 1 and 5 m/s and a heat sink base surface temperature of 70 °C, 90 °C, and 110 °C. The results show that the higher phase shift and air velocity lead to the enhancement of the heat transfer coefficient and pressure drop. Conversely, the heat sink base surface temperature has a slight effect on the heat transfer coefficient and pressure drop. The heat transfer coefficient of SW-PFHS is enhanced when increasing the phase shift compared with a phase shift of 0°. Under the same phase shift, the Nusselt number of CCSW-PFHS is higher than that of SW-PFHS by about 5.9–19.1%. The CCSW-PFHS with a phase shift of 180° yields the highest TPF.
•Plate-fin heat sinks with lateral perforation is numerically studied.•The study on thermal performance of perforated plate-fin heat sinks is proposed.•Diameters and numbers of circular perforations ...on a plate fin are varied.•Flow behavior of air inside laterally perforated plate-fin heat sink is presented.•Optimum design parameters of perforated plate-fin heat sink are reported.
This study presents the thermal performance of laterally perforated plate-fin heat sinks (LAP-PFHSs) with different numbers (Np) and diameters (Dp) of circular perforations. Based on the same plate fin dimension, the available diameter of circular perforations is limited by their number. The largest diameters of perforation for Np = 14, 27 and 75 are 10 mm, 7 mm and 4 mm, respectively. The computational results of solid fin heat sinks (SFHSs) and LAP-PFHSs are validated with the measured data and experimental data from the available literature. The comparison results of LAP-PFHSs give the mean absolute error of about 3.6% and 5.3% for the pressure drop and thermal resistance, respectively. According to the numerical results, the LAP-PFHS with Dp = 3 mm and Np = 75 exhibits the highest heat transfer rate, about 11.6% higher than that of the SFHS. Finally, the thermal performance factor, which is a consideration of the Nusselt number and friction factor, is proposed to find the suitable design parameters. Under the same conditions, the optimized LAP-PFHS demonstrates 10.6% greater thermal performance and 28% lower volume of heat sink material than SFHS.
The effect of characteristic of heating surface on nucleate boiling heat transfer is well reported via many previous results. However, until recently, the study of surface influences on nucleate ...boiling was complicated by coupled surface factors; wettability and surface roughness. This study focuses on nucleate pool boiling under different wetting conditions, in the absence of microscale roughness, which is coupled with wetting phenomena. Heterogeneous boiling occurs on hydrophilic (54°) and hydrophobic (123°) surfaces, even without microstructures that can trap water vapor. In the very low heat flux regime, hydrophobic surfaces offer better nucleate boiling heat transfer than hydrophilic surfaces. Moreover, a heterogeneous wettability surface composed of hydrophobic dots on a hydrophilic surface provides better nucleate boiling heat transfer than a homogeneous wettability surface (hydrophilic or hydrophobic). Analysis of bubble generation and departure was carried out via a high-speed visualization technique in order to understand these experimental results. Based on the bubble analysis, it was inferred that changes in wettability could lead to totally different boiling performance when microstructures are absent. Also, the number of hydrophobic dots and the pitch distance between dots were key parameters for explaining boiling performance under heterogeneous wetting conditions.
Renal fibrosis is the histological manifestation of a progressive, usually irreversible process causing chronic and end-stage kidney disease. We performed genome-wide transcriptome studies of a large ...cohort (n = 95) of normal and fibrotic human kidney tubule samples followed by systems and network analyses and identified inflammation and metabolism as the top dysregulated pathways in the diseased kidneys. In particular, we found that humans and mouse models with tubulointerstitial fibrosis had lower expression of key enzymes and regulators of fatty acid oxidation (FAO) and higher intracellular lipid deposition compared to controls. In vitro experiments indicated that inhibition of FAO in tubule epithelial cells caused ATP depletion, cell death, dedifferentiation and intracellular lipid deposition, phenotypes observed in fibrosis. In contrast, restoring fatty acid metabolism by genetic or pharmacological methods protected mice from tubulointerstitial fibrosis. Our results raise the possibility that correcting the metabolic defect in FAO may be useful for preventing and treating chronic kidney disease.
•The first report that graphene-based adsorbent was evaluated for VOC gas adsorption.•Sufficient amount of graphene-based adsorbent was evaluated (in gram) for toluene and acetaldehyde gas ...(30ppmv).•Their comparable effectiveness was demonstrated with a commercial activated carbon.•The preparation method (microwave irradiation and KOH activation) are appropriate for mass production.
Volatile organic compound (VOC) gases can cause harm to the human body with exposure over the long term even at very low concentrations (ppmv levels); thus, effective absorbents for VOC gas removal are an important issue. In this study, accordingly, graphene-based adsorbents with microsized pores were used as adsorbents to remove toluene and acetaldehyde gases at low concentrations (30ppm). Sufficient amounts of the adsorbents were prepared for use on filters and were loaded uniformly at 0.1–0.5g on a 50×50mm2 area, to evaluate their adsorption features with low gas concentrations. The morphology and chemical composition of the adsorbents were characterized using scanning electron microscopy, N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and Raman spectroscopy. Microwave irradiation and heat treatment near 800°C under KOH activation resulted in enlargement of the pristine graphene surface and its specific surface area; maximum volume capacities of 3510m3/g and 630m3/g were observed for toluene and acetaldehyde gas. The high removal efficiency for toluene (98%) versus acetaldehyde (30%) gas was attributed to π-π interactions between the pristine graphene surface and toluene molecules.
•A state of art of boiling heat transfer on micro/nano structured surface was introduced.•The technique of micro/nano structures fabrication was introduced.•The enhanced boiling heat transfer was ...reviewed by the physical mechanism.•The enhanced critical heat flux was reviewed by the physical mechanism and model.•The further research and new insight was proposed.
In the recent decades, the rapid growth of surface modification and fabrication technologies has facilitated the achievement of boiling heat transfer enhancement on micro/nanostructured surfaces. In this paper, several researches on the micro/nanostructured surfaces that have been designed to enhance boiling heat transfer are introduced and closely reviewed. Firstly, theoretical and experimental researches on nucleate boiling heat transfer (NBHT) and critical heat flux (CHF) are introduced in the outline. The fabrication techniques for achieving these engineered surfaces, which are technically classified into machining, coating, chemical process, and micro/nanoelectromechanical systems, are described in detail in the paper. Explanations and analysis of the results of boiling heat transfer enhancement tests are presented in view of NBHT and CHF. Finally, the special features of the existing surfaces capable of enhancing boiling heat transfer are summarized, and the need for future research is also presented.
•The Venturi nozzle design with entry and exit angles, which leads the self-sucked air flow.•Microbubbles generation regarding to entry and exit angles.•High speed visualization study to track the ...self-sucked air flow stream broken into microbubbles.
We studied the effect of varying the entry and exit angles of Venturi nozzles on the formation of microbubbles in Venturi nozzle-type microbubble generators. We 3D-printed nozzles with five entry angles (15, 22, 30, 38 and 45°) and five exit angles (15, 22, 30, 38 and 45°). For the visualization experiment, we inserted the nozzles into a cover case made of aluminum and transparent acrylic. We measured the pressure drop and the air flow rate with respect to the entry and exit angles, determined the diameters of the bubbles using a digital camera, and analyzed bubble breakage by observing the behavior of the bubbles using a high-speed camera. We confirmed that the exit angle (not the entry angle) is dependent on the pressure drop and found that the air flow rate did not vary linearly with the fluid flow rate, as expected according to Bernoulli's theorem. Instead, it tended to remain constant or decrease as the fluid flow rate increased due to the abnormal flow. The sizes of the bubbles decreased as the exit angle increased, except in cases where the outlet angle was greater than 30° at high flow rates (260–300 LPM). We observed a change in bubble size with respect to exit angle. According to our visualization, the bubbles were broken by the flow separation at the beginning of the divergence at the exit.
•The stainless steel modified surface was fabricated for chevron plate heat exchanger.•The anti-fouling performance would be estimated on bare, modified, PMMA and BN coated.•The dynamic wetting ...characteristics could be possible to explain the anti-fouling performance.
In this study, we aimed to develop a method for modifying SUS304 with micro/nanoscale holes using an electrical etching technique, and evaluated its impact on the anti-fouling performance of chevron plate heat exchangers. The modified SUS304 specimen exhibited hydrophobic wetting characteristics; however, water droplets stuck to the wall under inclined orientations at angles of 30° and 60°. We coated the modified SUS304 specimen with polymer (polymethyl methacrylate; PMMA) and hexagonal boron nitride (BN) particles to realize the hydrophobic and superhydrophobic wetting characteristics. To evaluate the anti-fouling performance of the heat exchanger, we carried out fouling acceleration experiments in a 2000 ppm CaCO3 solution for 2 h. The anti-fouling performance was determined by measuring the overall heat transfer coefficients during fouling acceleration experiments. As the operation time increased, the CaCO3 particles were deposited on the surface of the heat exchanger, the overall heat transfer coefficient decreased, and the fouling factor ultimately increased. Out of bare, modified, PMMA- and BN-coated heat exchangers, the PMMA-coated heat exchanger exhibited the strongest anti-fouling performance, with the lowest increment in the fouling factor. Based on analysis of the contact angle hysteresis (CAH) in each case, we suggest that CaCO3 particles in solution would be deposited better in the case of the highest CAH. This is possible in cases without the triple contact line, and is caused by filling the polymer into micro/nano holes on the modified surface.
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