Wei-Mon Yan

A comprehensive review of last experimental studies on thermal conductivity of nanofluids

In this paper, the last experimental results of the thermal conductivity of nanofluids have been investigated; therefore, because of the enormous numbers or some repetitions of such studies, it just tried to focus on those which had more acceptable results; however, it is not intended to present a systematic summary of the available references from the literature. All kinds of nanoparticles such as Al2O3, Fe3O4, TiO2, and CuO and their base fluids such as water, engine oil, glycol, and ethylene glycol have been investigated. The results showed that the effect of particle size of nanoparticle has a reversed impact on the value of thermal conductivity. To clarify, the thermal conductivity could increase by reduction in size of nanoparticles. On the other hand, the lower the suspension volume fraction is, the higher the thermal conductivity will be in nonlinear relation. Also the thermal conductivity and the temperature of the suspension have the direct influence on each other. In addition to the fact that a review paper has been prepared, the belief is to start this research with the scientific classification in order of all terms and expressions which have been used by previous scholars.

Molecular Dynamics Simulations on Coalescence and Non-coalescence of Conducting Droplets.

When an electric field with various strengths is applied to two adjacent conducting droplets, the droplets may completely coalesce, partially coalesce, or bounce off one another. To reveal an atom-scale mechanism of coalescence or non-coalescence, dynamic behaviors of two conducting nanodroplets at a homogeneous electric field are studied via molecular dynamics simulations in this work. The results show that there is a critical field strength and a critical cone angle above which the two droplets partially coalesce or bounce off. Charge transfer between the two droplets is observed when the droplets are brought into contact. The partial coalescence and the bounce-off of the two droplets at strong field strengths are found to be due to the high charge transfer rate, which leads to the breakup of the coalescing droplet at different locations.

A Comprehensive Review on Measurement and Correlation Development of Capillary Pressure for Two-Phase Modeling of Proton Exchange Membrane Fuel Cells

Water transport and the corresponding water management strategy in proton exchange membrane (PEM) fuel cells are quite critical for the improvement of the cell performance. Accuracy modeling of water transport in porous electrodes strongly depends on the appropriate constitutive relationship for capillary pressure which is referred to as - correlation, where is the capillary pressure and is the fraction of saturation in the pores. In the present PEM fuel cell two-phase models, the Leverett-Udell - correlation is widely utilized which is proposed based on fitting the experimental data for packed sands. However, the size and structure of pores for the commercial porous electrodes used in PEM fuel cells differ from those for the packed sands significantly. As a result, the Leverett-Udell correlation should be improper to characterize the two-phase transport in the porous electrodes. In the recent decade, many efforts were devoted to measuring the capillary pressure data and developing new - correlations. The objective of this review is to review the most significant developments in recent years concerning the capillary pressure measurements and the developed - correlations. It is expected that this review will be beneficial to develop the improved PEM fuel cell two-phase model.

Optimization of Design Parameters for a Sandwich-Distribution Porous-Microchannel Heat Sink

This study optimizes the thermal performance of a microchannel heat sink with a sandwich-distribution porous medium using the geometric variables as search parameters. The optimal approach integrates the simplified conjugate-gradient method and a three-dimensional porous heat sink model as an optimiser. The proposed optimal design parameters, i.e., the channel number, channel width, and porous medium thickness, enhance the thermal performance by 50% and reduce the pressure drop by 52.2% over those of a porous-heat sink without geometric optimisation. The proposed combined approach is robust because the same optimal set of parameters is obtained with different initial guesses. Simulations indicate that the optimal thermal resistance decreases and the corresponding optimal values of both the channel number and the porous medium thickness increase, whereas the channel width decreases with increasing pumping power. However, the effectiveness reduces significantly at high pumping power. Additionally, the effects of porosity of the porous medium on the optimal thermal resistance are insignificant.

Novel bufferless photosynthetic microbial fuel cell (PMFCs) for enhanced electrochemical performance

Photosynthetic microbial fuel cells (PMFCs) are novel bioelectrochemical transducers that employ microalgae to generate oxygen, organic metabolites and electrons. Conventional PMFCs employ non-eco-friendly membranes, catalysts and phosphate buffer solution. Eliminating the membrane, buffer and catalyst can make the MFC a practical possibility. Therefore, single chambered (SPMFC) were constructed and operated at different recirculation flow rates (0, 40 and 240 ml/min) under bufferless conditions. Furthermore, maximum power density of 4.06 mW/m2, current density of 46.34 mA/m2 and open circuit potential of 0.43 V and low internal resistance of 611.8 Ω were obtained at 40 ml/min. Based on the results it was decided that SPMFC was better for operation at 40 ml/min. Therefore, these findings provided progressive insights for future pilot and industrial scale studies of PMFCs.

MIXED CONVECTION OF FUNCTIONALIZED DWCNT/WATER NANOFLUID IN BAFFLED LID-DRIVEN CAVITIES

The present study aims to evaluate the mixed convection flow and heat transfer of functionalized DWCNT/water nanofluids with variable properties in a cavity having hot baffles. The investigation is performed at different nanoparticles volume fraction including 0, 0.0002, 0.001, 0.002, and 0.004, Richardson numbers ranging from 0.01 to 100, inclination angles ranging from 0 to 60° and at constant Grashof number of 104. The results presented as streamlines and isotherms plot and Nusselt number diagrams. According to the finding with increasing nanoparticles volume fraction and distance between the left hot baffles of nanoparticles average Nusselt number enhances for all considered Richardson numbers and cavity inclination angles. Also with increasing Richardson number, the rate of changes of average Nusselt number increase with increasing distance between the left hot baffles. For example, at Richardson number of 0.01, by increasing L1 from 0.4 to 0.6, the average Nusselt number increases 7%; while for similar situation at Richardson number of 0.1, 1.0, and 10, the average Nusselt number increases, respectively, 17%, 24%, and 26%. At all Richardson numbers, the maximum value of average Nusselt number is achieved for a minimum length of left baffles. This article has been corrected. Link to the correction 10.2298/TSCI190203032E

Application of interface material and effects of oxygen gradient on the performance of single-chamber sediment microbial fuel cells (SSMFCs)

Single-chamber sediment microbial fuel cells (SSMFCs) have received considerable attention nowadays because of their unique dual-functionality of power generation and enhancement of wastewater treatment performance. Thus, scaling up or upgrading SSMFCs for enhanced and efficient performance is a highly crucial task. Therefore, in order to achieve this goal, an innovative physical technique of using interface layers with four different pore sizes embedded in the middle of SSMFCs was utilized in this study. Experimental results showed that the performance of SSMFCs employing an interface layer was improved regardless of the pore size of the interface material, compared to those without such layers. The use of an interface layer resulted in a positive and significant effect on the performance of SSMFCs because of the effective prevention of oxygen diffusion from the cathode to the anode. Nevertheless, when a smaller pore size interface was utilized, better power performance and COD degradation were observed. A maximum power density of 0.032mW/m2 and COD degradation of 47.3% were obtained in the case of an interface pore size of 0.28μm. The findings in this study are of significance to promote the future practical application of SSMFCs in wastewater treatment plants.

Implementation of surface modified carbon cloth electrodes with biochar particles in microbial fuel cells

ABSTRACT Microbial fuel cells (MFC) are bioelectrochemical reactors that convert chemical energy in organic substrates to electrical energy through catalytic reactions of microorganisms. The relationship between microorganisms and electrodes plays a vital role for effective functioning of an MFC. The physical and chemical properties of the electrodes are more crucial for a feasible MFC performance. Plain Carbon cloth (CC) and surface modified CC with four different sizes of Biochar (BC) particles such as 2 mm BC< 2, BC2-4, BC4-6, and BC6-10 were employed as anode electrodes in dual-chambered MFCs and their performance was compared. Results showed that the electrode with BC< 2 enhanced the MFC performance to with power density of 312 mWm−2 and BC6-10 facilitated the maximum COD degradation performance of 77% in the MFC both due to electrode properties like high porosity and large surface area. This study in general is a proof that BC has high feasibility for usage in MFC electrode modification studies.