•Novel fin structures are proposed for heat transfer enhancement of PCM.•Visualization of the melting process of PCM within the BTMS is presented.•Thermal management performance of PCM-Fin based BTMS ...is evaluated.
Phase change materials (PCM) based battery thermal management system (BTMS) usually suffers from the low thermal conductivity of PCM. In this paper, novel fin structures which consist of longitudinal fins and cylindrical rings are proposed for heat transfer enhancement. Experiments are firstly designed to compare the thermal performance of different BTMSs. Results demonstrate that the PCM-Fin system shows superior performance over the pure battery system and the PCM system. Numerical simulations are also conducted based on the model validation with the experimental data to reveal the underlying mechanisms. It is found that fin structures not only increase the heat transfer area but also introduce a thermal conductive network within the PCM, which contributes positively to the improvement of thermal performance of the battery. Moreover, the effects of the position of rings, the number of rings and fins, and the heat generation rate on the thermal management performance are evaluated. Results show that the optimal numbers for rings and fins are 1 and 8, respectively, and the recommended dimensionless distance between ring and battery is 0.2. It is also found that the PCM-Fin system can control the temperature rise of the battery even under the heat generation rate of 20 W.
•Heat transfer enhancement based on multi-longitudinal vortices is reviewed.•Heat transfer optimization gives the optimal flow fields for heat transfer.•Generating multi-longitudinal vortices results ...in heat transfer enhancement.•Research gaps and future research directions are provided.
In this work, a review on single-phase convective heat transfer enhancement based on multi-longitudinal vortices is carried out. Theoretical investigations on convective heat transfer optimization from different principles such as entropy generation minimization principle, field synergy principle, entransy dissipation extremum principle, power consumption minimization principle, and exergy destruction minimization principle for the better trade-off between heat transfer augmentation and flow resistance reduction are firstly evaluated. It is found that the optimal flow fields are mainly characterized by multi-longitudinal vortices, implying that heat transfer enhancement techniques which can generate the flow patterns similar to the optimal flow fields may also enjoy the satisfactory balance between heat transfer enhancement and flow resistance reduction. Then, various techniques such as artificial roughness, special-shaped tubes, multiple swirl devices, and longitudinal vortex generators that can construct the flow pattern of multi-longitudinal vortices are summarized. Results indicate that most of the techniques show excellent thermal-hydraulic performance, but some techniques still suffer from high flow resistance. Based on the discussion, some new perspectives on the existing research gaps, challenging, and future research directions have been provided for the development of enhanced heat transfer techniques by generating multi-longitudinal vortices in heat exchanger tubes.
It is desired to apply deep learning models (DLMs) to assist physicians in distinguishing abnormal/normal lung sounds as quickly as possible. The performance of DLMs depends on feature-related and ...model-related parameters heavily. In this paper, the relationship between performance and feature-related parameters of a DLM, i.e., convolutional neural network (CNN) is analyzed through experiments. ICBHI 2017 is selected as the lung sounds dataset. The sensitivity analysis of classification performance of the DLM on three parameters, i.e., the length of lung sounds frame, overlap percentage (OP) of successive frames and feature type, is performed. An augmented and balanced dataset is acquired by the way of white noise addition, time stretching and pitch shifting. The spectrogram and mel frequency cepstrum coefficients of lung sounds are used as features to the CNN, respectively. The results of training and test show that there exists significant difference on performance among various parameter combinations. The parameter OP is performance sensitive. The higher OP, the better performance. It is concluded that for fixed sampling frequency 8 kHz, frame size 128, OP 75% and spectrogram feature is optimum under which the performance is relatively better and no extra computation or storage resources are required.
Summary
A fin‐enhanced phase change material (PCM) system was introduced for cylindrical lithium‐ion batteries. Experiments were performed to explore the performance of the systems during ...discharging. The working time of the PCM‐Fin system is improved by 75%, 68%, and 61% compared to that of the system without fins under the heat production rate of 10, 12.5, and 15 W, accordingly. Simulations were performed by ANSYS Fluent to explore the influence of the geometric parameters (thickness, length, and number) and materials (nylon, titanium, steel, Al alloy, and copper) of the fins on the thermal performance. A function considering both the improvement in thermal performance and the increase in system weight was defined to assess the overall performance. Results indicate that fins made of Al alloy with the number of 8, a length of 7.5 mm, and a thickness of 0.5 mm give the best performance. Besides, the working time of the PCM‐Fin system is 2150, 2490, 2940, and 3570 seconds for the coefficient of heat transfer of 5, 10, 15, and 20 W m−2 K−1, respectively, which is increased by 14%, 32%, 56%, and 90%, compared to that of the adiabatic condition, demonstrating the effectiveness of the PCM‐Fin system.
A fin‐enhanced phase change material (PCM) system is proposed for the battery thermal management. The safe working time of the fin‐enhanced system is found to be approximately 1.61–1.75 times as that of the PCM system. Numerical results demonstrate that the added fins form a network for thermal conduction within the PCM, which enhances the heat dissipation rate considerably.
Using a light-emitting diode (LED) as the light source, the effects of eight different light treatments white light (control, W), purple light (P), blue light (B), red light (R), green light (G), ...yellow light (Y), red–blue light in a 9:1 ratio (9R/1B), and red–blue light in a 4:1 ratio (4R/1B) on the growth, quality and nitrogen metabolism of lettuce were studied. The results showed that compared with the white light, the purple light, blue light, red light, and the red-blue light combination could all increase the biomass of the aboveground part of lettuce to various degrees, while green light and yellow light inhibited lettuce growth. Under blue light, the contents of soluble protein and flavonoid in lettuce were the highest; under red light, the soluble sugar content was the highest, while the contents of soluble protein, free amino acids, and vitamin C (VC) were relatively higher under the 4R/1B light condition. Compared with white light, the sources of purple, blue, and red lights as well as the red–blue light combination all significantly reduced nitrate accumulation in lettuce, and the activities of the nitrogen (N) metabolism-related enzymes such as nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were increased to varying degrees. In contrast, the contents of nitrate and ammonium N were significantly accumulated in lettuce under green light, and the activities of relative enzymes were significantly reduced. Therefore, the purple light, blue light, and red–blue combination light sources could promote N assimilation and improve the aboveground biomass accumulation in lettuce by improving the activity of the N metabolism-related enzymes in lettuce. Particularly under the 4R/1B light source, the biomass, soluble protein, VC, and total amino acid content were rather high in lettuce, which indicated that the 4R/1B light source could better effectively improve the nutritional quality and promote the growth of lettuce, while yellow light and green light are not suitable to serve as direct sources in a plant factory. These results provide a certain theoretical basis for the regulation of the light environment in cultivation facilities.
Ammonia is an indispensable raw material in the chemical industry. A hybrid biomass conversion to ammonia system (HBCAS) is developed by means of the chemical looping process with the assistance of ...solar energy and wind power. The system consists of six modules: i) biomass gasification, ii) oxy-syngas combustion, iii) chemical looping air separation (CLAS), iv) chemical looping ammonia production (CLAP), v) power generation, and vi) water electrolysis. A simulation was conducted for feasibility analysis and parameter optimization using ASPEN Plus, focusing on the development of a coordinated distribution network of energy and materials. Multi-generation of NH3, N2, and H2 was achieved using biomass cascading. The thermally neutral requirements of HBCAS and the effects of the operating conditions of each module on the selectivities (MnO2, AlN, and NH3), product concentrations, production rates, and reactant conversions were comprehensively considered. The results indicate that ammonia selectivity of 79.36%, production rate of 34.1 kmol/h, and concentration of 65.65 vol% can be obtained under typical conditions with 1 kg/s biomass input, confirming the feasibility of the HBCAS and providing guidance for its use.
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•A novel hybrid system, HBCAS, is developed with multi-generation of NH3, N2, and O2.•Ammonia is produced from carbothermal reduction via a chemical looping scheme.•Feasibility of HBCAS was verified with operating parameters optimization.•Auto-thermal operation can be achieved with the assistance of solar and wind.•NH3 selectivity of 79.26% and single-day system efficiency of 45.46% are obtained.
•Effects of ultrasonication on the stability of FLG nanofluids at given energy consumption were revealed.•The stability of nanofluids was more sensitive to ultrasonication time than power.•FLG ...nanofluids prepared at 20% amplitude-135 min presented the highest stability.
Few-layer graphene (FLG) nanofluids have received widespread interest in recent years due to their excellent thermal and optical properties. However, the low dispersion stability is one of the main bottlenecks for their commercialization. Ultrasonication is an effective method and almost an essential step to improve the stability of nanofluids. This work aimed to determine the optimal ultrasonication process for preparing stable FLG nanofluids, particularly under the constant ultrasonic energy consumption condition. For this purpose, FLG nanofluids were prepared under various amplitudes (20%–80%) and times (33.75–135 min) and evaluated by both sedimentation and optical spectrum analysis techniques. It was found that ultrasonication treatment at 30% amplitude for 90 min was sufficient for proper dispersion of FLG, and a further increase in the ultrasonication power would not benefit the stability enhancement much. However, for FLG nanofluids prepared at amplitudes higher than 30% under the constant ultrasonic energy consumption condition, their stability deteriorated seriously due to the reduced ultrasonication time, while for FLG nanofluids prepared at 20% amplitude for 135 min, they showed the higher stability, which indicates that the stability of FLG nanofluids is more sensitive to ultrasonication time than power. Therefore, a relatively longer ultrasonication time rather than a higher amplitude is recommended to prepare stable FLG nanofluids for practical applications at given ultrasonic energy consumption.
This article reviews recent developments in self-assembly of polymer colloids into colloidal crystals, a good candidate material for photonic crystals. Self-assembly strategy has developed as a ...facile and efficient method to fabricate colloidal crystals. Much research work has been focused on controlling the morphology and improving the quality, as well as finding applications of the colloidal crystals.
Diabetic nephropathy (DN) is characterized by inflammatory responses and extracellular matrix (ECM) accumulation. Astilbin is an active natural compound and possesses anti-inflammatory activity. The ...aim of this study was to evaluate the anti-inflammatory effect of astilbin on high glucose (HG)-induced glomerular mesangial cells and the potential mechanisms. The results showed that HG induced cell proliferation of HBZY-1 cells in a time-dependent manner, and astilbin inhibited HG-induced cell proliferation. The expression and secretion of inflammatory cytokines, including interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α), and ECM components, including collagen IV (Col IV) and fibronectin (FN), were induced by HG. Moreover, TGF-β1 and CTGF were also induced by HG. The induction by HG on inflammatory response and ECM accumulation was inhibited after astilbin treatment. Astilbin treatment also attenuated HG-induced decrease in expression of matrix metalloproteinase (MMP)-2 and MMP-9. The TLR4/MyD88/NF-κB pathway was activated by HG, and the inhibitor of TLR4 exhibited the same effect to astilbin on reversing the induction of HG. TLR4 overexpression attenuated the effect of astilbin on HG-induced inflammatory cytokine production and ECM accumulation. The results suggested that astilbin attenuated inflammation and ECM accumulation in HG-induced rat glomerular mesangial cells via inhibiting the TLR4/MyD88/NF-κB pathway. This work provided evidence that astilbin can be considered as a potential candidate for DN therapy.
In this study, zwitterionic polymer brushes with controlled architecture were grafted on the surface of gravity-driven membrane (GDM) via surface-initiated reaction to impart antifouling property. A ...variety of membrane characterization techniques were conducted to demonstrate the successful functionalization of zwitterionic polymers on PVDF hollow fiber membrane. The membrane underwent 90 min of reaction time possessing strong hydrophilicity and high permeability was determined as the optimal modified membrane. Long-term GDM dynamic fouling experiments operated for 30 days using sewage wastewater as feed solution indicated zwitterionic polymer modified membrane exhibit excellent membrane fouling resistance thus enhanced stable flux. Confocal laser scanning microscopy (CLSM) imaging implied that zwitterionic polymer modification significantly inhibit the adsorption of extracellular polymeric substances (EPS) which dominates fouling propensity, resulting in the formation of a thin biofilm with high porosity under synthetic functions of foulants deposition and microbial activities. Interfacial free energy prediction affirmed the presence of zwitterionic functional layer on membrane surface could substantially decrease the interactions (e.g., electrostatic attractions and hydrophobic effects) between membrane and foulants, thereby reduced flux decline and high stable flux. Our study suggests surface hydrophilic functionalization shows promising potential for improving the performance of ultra-low pressure filtration.
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•Zwitterionic polymers were grafted on PVDF HFM surface via ATRP with controlled architecture.•Functionalized membrane exhibited improved stable flux under GDM dynamic fouling tests.•Presence of zwitterion layer led to the formation of compressed biofilm with high porosity.•Zwitterion grafting reduced membrane-foulant electrostatic and hydrophobic interactions.
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