Ping Cheng

Shanghai Jiao Tong University, School of Mechanical egineering, Faculty Member

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Papers by Ping Cheng

Flow past a circular cylinder embedded in a porous medium based on the brinkman model

International Journal of Engineering Science, 1992

... is (r )sm 0. (26) rr The tangential velocity is then given by d 1. i . v=[!+, si 3r r2) 1 + ,... more ... is (r )sm 0. (26) rr The tangential velocity is then given by d 1. i . v=[!+, si 3r r2) 1 + , sin 6 rl (27) It follows that v 2 sin 6 near the ... 4. Variation off&#x27;(r) with r. 262 I. POP and P. CHENG where R = (r 1)1 a. For the outer flow region, we have (r)=r(l+2a)+(a2) (29) Substituting equation (28 ...

Natural convection of a Darcian fluid about a cone

International Communications in Heat and Mass Transfer, 1985

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Transient free convection about a horizontal circular cylinder in a porous medium

Fluid Dynamics Research, 1993

... Pop et ai, Transient free convection composite tangential velocity are therefore given by V/,... more ... Pop et ai, Transient free convection composite tangential velocity are therefore given by V/, = - 2(r*/Ra)1 &#x27;2 ( ?y erfc W - e &quot;2 ) sin 0 - ^f^/Ras&#x27;-n-(- \ V&#x27;Tt ,./ - 2(r*/7tRa/2i&#x27;I&quot; - + (r*/Ra)((i+ 3^2)erfc(^- ^.c &quot;^sin^ -(?*Ra)1 ^(( -^lf^^)erfc(^7 -:--(i+ 8^)e &quot;&#x27;&#x27;)sin^ &#x27; 3 ^ Tt / + =(f*/Ra)3&#x27;-&#x27; M&quot;- + i ...

Frequency-dependent resonance and asymmetric droplet oscillation under ac electrowetting on coplanar electrodes

Journal of Micromechanics and Microengineering, 2012

Sessile droplet oscillations in electrowetting on dielectric with a coplanar-electrode configurat... more Sessile droplet oscillations in electrowetting on dielectric with a coplanar-electrode configuration are studied experimentally under the actuation of ac voltage with different frequencies. It was found that the experimental resonance frequencies and the number of lobes at different resonance modes agree reasonably well with a previous linear analysis. Oscillations of contact width and droplet height are in-phase at resonance modes

Transport Phenomena Analysis in Proton Exchange Membrane Fuel Cells

Journal of Heat Transfer, 2005

The objective of this review is to provide a summary of modeling and experimental research effort... more The objective of this review is to provide a summary of modeling and experimental research efforts on transport phenomena in proton exchange membrane fuel cells (PEMFCs). Several representative PEMFC models and experimental studies in macro and micro PEMFCs are selected for discussion. No attempt is made to examine all the models or experimental studies, but rather the focus is to elucidate the macro-homogeneous modeling methodologies and representative experimental results. Since the transport phenomena are different in different regions of a fuel cell, fundamental phenomena in each region are first reviewed. This is followed by the presentation of various theoretical models on these transport processes in PEMFCs. Finally, experimental investigation on the cell performance of macro and micro PEMFC and DMFC is briefly presented.

An experimental investigation on effects of an electric field on bubble growth on a small heater in pool boiling

International Journal of Heat and Mass Transfer, 2013

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Understanding triggering mechanisms for critical heat flux in pool boiling based on direct numerical simulations

International Journal of Heat and Mass Transfer, 2020

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3D Printed Ultrastretchable, Hyper-Antifreezing Conductive Hydrogel for Sensitive Motion and Electrophysiological Signal Monitoring

Research, 2020

Conductive hydrogels with high stretchability can extend their applications as a flexible electro... more Conductive hydrogels with high stretchability can extend their applications as a flexible electrode in electronics, biomedicine, human-machine interfaces, and sensors. However, their time-consuming fabrication and narrow ranges of working temperature and working voltage severely limit their further potential applications. Herein, a conductive nanocomposite network hydrogel fabricated by projection microstereolithography (P μ SL) based 3D printing is proposed, enabling fast fabrication ability with high precision. The 3D printed hydrogels exhibit ultra-stretchability (2500%), hyper-antifreezing (-125°C), extremely low working voltage (<100 μ V), and super cyclic tensile stability (1 million cycles). The hydrogel-based strain sensor can probe both large-scale and tiny human motions, even with ultralow voltage of 100 μ V at extremely low temperature around −115°C. It is demonstrated that the present hydrogels can be used as a flexible electrode for capturing human electrophysiolog...

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A numerical and experimental study of two-phase flow and heat transfer in a porous formation with localized heating from below

Understanding and predicting two-phase flow and heat transfer in porous media is of fundamental i... more Understanding and predicting two-phase flow and heat transfer in porous media is of fundamental interest for a number of engineering applications. Examples include thermal technologies for remediation of contaminated subsurfaces, the extraction of geothermal energy from vapor-dominated reservoirs, and the assessment of high-level nuclear waste repositories. A numerical and experimental study is reported for two-phase flow and heat transfer in a horizontal porous formation with water through flow and partial heating from below. Based on a newly developed two-phase mixture model, numerical results of the temperature distribution, liquid saturation, liquid and vapor phase velocity fields are presented for three representative cases with varying inlet velocities. It is found that the resulting two-phase structure and flow patterns are strongly dependent upon the water inlet velocity and the bottom heat flux. The former parameter measures the flow along the horizontal direction, while th...

Hawaii Geothermal Project: Modeling of Hawaiian Geothermal Resources

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Two Large-Amplitude/Long-Period Oscillating Boiling Modes in Silicon Microchannels

1st International Conference on Microchannels and Minichannels

A simultaneous visualization and measurement study has been carried out to investigate flow boili... more A simultaneous visualization and measurement study has been carried out to investigate flow boiling of water in the 8 parallel silicon microchannels heated from below. It is found that there are two large-amplitude/long-period oscillating boiling modes exist in microchannels depending on the amounts of heat flux and mass flux. When the outlet water temperature is at saturation temperature and the wall temperatures are superheated, while the inlet water temperature is still subcooled, a Liquid/Two-phase Alternating Flow (LTAF) mode appears in the microchannels. This LTAF mode disappears when the inlet temperatures reaches the saturation temperature. As the heat flux is further increased such that the outlet water is superheated while the inlet water temperature is oscillating between subcooled and saturation temperature, a Liquid/Two-phase/Vapor Alternating Flow (LTVAF) mode begins. During these two unstable boiling modes, there are large-amplitude and long-period oscillations of wat...

Solar Energy Harvesting by Perfect Absorbers Made of Natural Hyperbolic Material

Nanostructured Materials for Next-Generation Energy Storage and Conversion, 2019

A perfect absorber, with pyramidal nanostructures made of a natural hyperbolic material, for sola... more A perfect absorber, with pyramidal nanostructures made of a natural hyperbolic material, for solar energy harvesting is proposed in this chapter. A numerical investigation is first carried out for regularly arranged bismuth telluride (Bi2Te3, an anisotropic and natural hyperbolic material) pyramidal nanostructures placed on top of a Ag substrate, and the metamaterial is submerged in water. The calculated results show that the absorptance of the absorber exceeds 99.9% in the wavelength range of 300–2400 nm. The underlying mechanisms are revealed by the electric field and power dissipation density distribution in the absorber. It is found that the slow light effect in the type-II hyperbolic region (300–1000 nm) and the gradient index effect in the long wavelength range (1000–2400 nm) contribute to the perfect absorption of the solar energy for the proposed absorber. Effects of geometry parameters of nano-pyramids and the substrate on optical properties of the proposed absorber are illustrated. In addition, a rough surface with sharp nanostructures made of Bi2Te3 is also numerically studied. Based on simulation results of rough Bi2Te3 surface, samples with nanostructures made of Bi2Te3 are experimentally manufactured and optical properties of the samples are measured by using an integrating sphere with a grating monochromator. The absorptance of the samples can be as high as 97.5%, and the lowest absorptance of the sample is still higher than 94% in the wavelength range of 380–1800 nm. Moreover, other samples are also fabricated and studied to validate underlying mechanisms of the perfect absorption of solar energy. The results of the present study open a new revenue for effectively harvesting solar energy by using metamaterials with nanostructures made of natural hyperbolic materials submerged in water.

Perfect Absorption in the Broad Solar Spectrum with Bi2Te3 Hyperbolic Metamaterials

Advanced Photonics 2017 (IPR, NOMA, Sensors, Networks, SPPCom, PS), 2017

A numerical study has been carried out on optical properties of an absorber made of a natural ani... more A numerical study has been carried out on optical properties of an absorber made of a natural anisotropic hyperbolic material, subject to normally incident light. The proposed absorber, consisting of an array of pyramidal nanostructures, made from bismuth telluride (Bi2Te3, a hyperbolic medium) on the top of a smooth substrate, is submerged in water. The designed absorber was numerically studied by using finite-difference time-domain (FDTD) method and rigorous coupled-wave analysis (RCWA) method. Numerical results show that such an absorber has a perfect absorptance for solar energy in a broadband wavelength range of 300 - 2400 nm by combining the slow-light effect and gradient index effect together. The unique optical property of such absorber contributes to the potential application in solar energy harvesting.

Mesoscale and Microscale Phase-Change Heat Transfer

Advances in Heat Transfer, 2006

... in conventional channels, meso (mini) heat exchangers are more compact and lighter in weight ... more

Numerical Study on Sample Stacking in Capillary Electrophoresis

Chinese Journal of Chromatography, 2007

Sample stacking in capillary electrophoresis is one of the effective techniques to concentrate sa... more Sample stacking in capillary electrophoresis is one of the effective techniques to concentrate sample species, thus improving the detection sensitivity. A 1 -D mathematical model, including the electrical potential distribution equation, the buffer concentration equation, as well as the sample electromigration and diffusion equation, is developed through proper simplifications and assumptions to study the sample stacking process in capillary electrophoresis. These coupled governing equations are solved using finite element method (FEM). The variations of the buffer concentration and the electrical field strenthe distribution with time as well as the electrical potential distribution in capillary during sample stacking are obtained. The sample stacking and the sample diffusion after stacking as well as the separation process of sample cations and anions are presented. It is found that the best stacking effect occurs near the entrance where the species have not been separated well. With the development of time, the stacking effect deteriorates while the distance between the positively and negatively charged particles becomes larger, and the separation effect becomes better. The effect of buffer concentration ratio on sample stacking is also analyzed. It is found that the relationship between sample stacking effect and the buffer concentration ratio is not linear and the maximum stacking effect is achieved within less time and migration distance when the buffer concentration ratio is higher because of the stronger electrical field strength in sample plug region. It is anticipated that the numerical model developed in this paper is helpful for the design and optimization of sample stacking devices.

Lattice Boltzmann Simulations of Macro/Microscale Effects on Saturated Pool Boiling Curves for Heated Horizontal Surfaces

Journal of Heat Transfer, 2017

Results of lattice Boltzmann (LB) simulations of macroscale effects (heating modes, heater size, ... more Results of lattice Boltzmann (LB) simulations of macroscale effects (heating modes, heater size, and saturation temperature) as well as microscale effects (wettability and roughness) on saturated pool boiling from superheated horizontal surfaces are summarized in this paper. These effects on pool boiling curves from natural convection through nucleate boiling to critical heat flux (CHF) and from transition boiling to film boiling are illustrated. It is found that macroscale effects have negligible influence on nucleate boiling heat transfer, and Rohsenow's correlation equation fits well with the simulated nucleate boiling heat transfer on smooth hydrophilic and hydrophobic horizontal surfaces. Both macroscale and microscale effects have important influence on critical heat flux and transition boiling heat transfer.

Recent Work on Flow Boiling and Condensation in a Single Microchannel

AIP Conference Proceedings, 2007

Recent visualization and measurements results on flow boiling of water and condensation of steam ... more Recent visualization and measurements results on flow boiling of water and condensation of steam in a single microchannel, carried out at Shanghai Jiaotong University, is summarized in this paper. For flow boiling of water, experiments were conducted in a single microchannel with a trapezoidal cross-section having a hydraulic diameter of 186 mum and a length of 30 mm. A boiling