Jingzhi Zhang

• Doctor of Engineering
• Shandong University

Electronic components are increasingly being centralized and miniaturized, leading to a rise in heat flux. As a result, there is a growing interest in high heat flux heat dissipation technology. Manifold microchannel (MMC) heat sinks have proven to be effective in dissipating heat from the chip. The Z-type manifold heat sink is more favored in prac...

Internal micro-finned tubes are widely used in modern air conditioning and refrigeration systems due to their excellent thermal performance during two-phase flow conditions. This study begins with a numerical simulation that examines the boiling heat transfer and two-phase flow characteristics of different refrigerants—R32, R410A, and R1234ze—insid...

Nowadays, there is a growing emphasis on the miniaturization and integration of electronic equipment in the field of advanced engineering. The increasing power of electronic devices and the trend towards miniaturization have resulted in higher levels of heat generation. Manifold Microchannels (MMC) heat sinks have emerged as effective solutions for...

In the published experimental results, it has been observed that when high-speed steam spurt into the subcooled waterflow, the total pressure along the axial direction at trailing edge of the steam plume shows a pressure-lift. To reveal the mechanism behind this phenomenon, this study utilizes a particle model to investigate the pressure profile of...

Micro and sub-micro-spherical copper powder slurries were elaborately prepared to fabricate different types of porous coating surfaces. These surfaces were further treated with low surface energy modification to obtain the superhydrophobic and slippery capacity. The surface wettability and chemical component were measured. The results showed that b...

Experimental studies of air–water two-phase flows in a mini tube with an inner diameter of 3.12 mm have been conducted in terms of the flow pattern, void fraction, and pressure gradients. The fluid velocities range from 0.065 to 21.78 m/s and from 0.109 to 1.835 m/s, respectively. A right-angle prism is applied to capture images simultaneously from...

During the operation of supercritical CO2 (sCO2) turbomachineries, large pressure ratios, supersonic conditions and non-ideal gas fluid dynamic phenomenon may happen, which will decrease the whole cycle efficiencies. Hence non-standard designs for the turbomachineries geometry are needed. Successfully simulations in capturing non-ideal gas fluid dy...

Nanofluids are an emerging class of heat transfer fluids that are engineered by dispersing nanoparticles in conventional fluids. They represent a promising, multidisciplinary field that has evolved over the past two decades to provide enhanced thermal features, as well as manifold applications in thermal management, energy, transportation, MEMs and...

Two-phase flow in non-circular cross-section flow channels such as micro-heat sinks and micro-channel heat exchangers has received extensive attention due to its heat-enhancing properties. In this paper, under the boundary of constant heat flux, an experimental investigation of the heat transfer properties of gas–liquid two-phase flow in horizontal...

A visualization study was performed to investigate the effect of non-condensable gas on stable submerged steam jet condensation in water flow in a narrow pipe. The direct contact condensation (DCC) characteristics including jet plume shapes, dimensionless penetration length and average heat transfer coefficient were analyzed in a wide range of wate...

It is a central challenge for energy self-supplied underwater vehicles converting the huge ocean thermal energy to electrical energy effectively. However, the energy storage efficiency of ocean thermal energy storage (OTES) unit limits the conversion efficiency. Fins are proposed for OTES unit to improve energy storage efficiency in this paper. Fir...

Vapor condensation on bioinspired hierarchical nanostructured surfaces with hybrid wettabilities has been investigated using molecular dynamics simulations. A series of hierarchical surfaces consisting of nanocylinder arrays with hydrophilic top and hydrophobic nanopillar arrays are constructed. The results manifest that the condensed nanodroplets...

Heat transfer and flow resistance characteristics of a novel plate heat exchanger (PHE) with multi-chevron corrugate furrows have been studied experimentally and numerically for Reynolds Numbers (Re) ranging from 1200 to 5000. Numerical results obtained from 5 different turbulent models all show similar trends and good agreement with experimental v...

Dispersed bubbly flow is important to understand when working in a wide variety of hydrodynamic engineering areas; the main objective of this work is to numerically study bubble-induced instability. Surface tension and bubble-induced turbulence effects are considered with the momentum and k-ω transport equations. Steady dispersed bubbly flow is gen...

The experimental method is used to study the droplet breaking characteristics of an immiscible liquid–liquid t8wo-phase fluid in symmetric Y-junction microchannels. Silicone oil is used as the dispersed phase and distilled water containing 0.5% SDS is used as the continuous phase. Three breakup behaviors were observed: breakup with permanent obstru...

Numerous direct-contact condensation (DCC) and boiling issues are numerically investigated with the Lee model under an assumed constant mass transfer coefficient through trial and error. A new mass transfer coefficient correlation is proposed, and the accuracy of the correlation is confirmed via comparison to Kim and Park’ experimental results from...

Thermal management is restricting the further development of electronic devices. The rapid development of communication and chip manufacturing technologies results in an unprecedented increase on heat dissipation of electronics, which also makes the thermal management system consume a substantial amount of energy. Therefore, the manifold microchann...

The dynamic behavior characteristics of droplet impact on superhydrophobic microstructured surfaces vibrating in the vertical direction are evaluated with Computational Fluid Dynamics combined with Volume of Fluid technique. The effects of wall vibration amplitude, vibration frequency, phase angle and droplet velocity on contact time and maximum pe...

The flow and heat transfer characteristics of gas-liquid Taylor flows in a horizontal tube with 3.12 mm inner diameter were studied numerically with the volume of fluid method. The bubbles are patched using the user defined functions based on the experimental volumes and formation frequencies. Numerical results agree well with the experimental resu...

The immiscible liquid-liquid two-phase flows in microchannels with 4 different inlet angles (30°, 60°, 90°, 120°) were analyzed using numerical and experimental methods. Silicone oil was used as the discrete phase, and distilled water containing 0.5wt% SDS was used as the continuous phase. The influences of two-phase flow rates and inlet angles on...

The addition of micro cavities is a promising passive method to enhance mass transfer performance in microchannels. Experimental and numerical methods are adopted to investigate the flow characteristics of velocity field, droplet shape and vorticity for the liquid-liquid two-phase flows in microchannels with micro cavities. The results indicate tha...

In order to investigate the characteristics of gas-liquid two-phase flows in horizontal mini circular tubes with inner diameters of 3.14 and 6.68 mm, a prism is adopted to improve the light path in the visualization experimental setup. The front and top views of air-water two-phase flow patterns in two tubes are captured synchronously based on the...

To look for new refrigerants replacing R134a, environmentally friendly refrigerants R1234yf and R1234ze(E) were chosen as the alternatives in an ejector refrigeration system. The tested system contained a single-phase ejector, and numerical analysis regarding the performance of the ejector was done by CFD. The entrainment ratio, static pressure and...

Engineering the dropwise condensation of water on surfaces is crucial in extensive applications including power generation, thermal management, water harvesting and desalination. Here we propose an efficacious avenue to retard pinning by molecular dynamics simulation, wherein the volume fraction, tilt angle and hybrid wettability ratio are adjusted...

The flow patterns and the plug hydrodynamics of liquid-liquid two-phase flow in a small circular channel were experimentally investigated. Five distinct flow patterns, including droplet flow, slug flow, throat-annular flow, annular flow and stratified flow were observed in the silicone oil-water system. The flow pattern map was present systematical...

In this study, changes in the droplet formation mechanism and the law of droplet length in a two-phase liquid–liquid system in 400 × 400 μm standard T-junction microchannels were experimentally studied using a high-speed camera. The study investigated the effects of various dispersed phase viscosities, various continuous phase viscosities, and two-...

Ocean thermal energy has attracted much attention for its huge potential resources. It's proved that an ocean thermal energy conversion (OTEC) cycle system using ammonia ejectors is beneficial to improve the cycle efficiency. Thus, the performance of an ammonia ejector is studied numerically in this paper. Effects of working conditions which occurr...

The manifold microchannel (MMC) heat sink for high-heat-flux removal in next-generation microelectronic system has received a significant attention recently. A numerical study is performed to analyze thermal performance and pressure loss of subcooled flow boiling in an MMC unit cell model. On the basis of OpenFOAM package, a new solver is developed...

Two-phase Taylor flow in microchannels as a critical way to enhance heat dissipation has attracted extensive attention due to the high integration and miniaturization development of electronic devices. To further elucidate the pressure drop and development process of heat transfer characteristics in Taylor flow, a 2-D planar T-junction microchannel...

In order to study the characteristics of 3D gas-liquid interfaces, flow pattern transitions, and void fraction in mini tubes, virtual multi-vision experiments and numerical simulations are conducted in a 5.16 mm horizontal tube with air as the dispersed phase and water as the continuous phase. Air and water flow velocities range from 0.024 to 12.33...

The manifold microchannel (MMC) heat sink system has been widely used in high-heat-flux chip thermal management due to its high surface-to-volume ratio. Two-phase, three-dimensional numerical methods for subcooled flow boiling have been developed using a self-defined solver based on OpenFOAM. Four different types of manifold arrangements (Z-type, C...

The condensation process of pure propane and propane/methane mixture on the vertical plate were experimentally and numerically researched to clarify the condensation characteristics at the first stage of natural gas liquification. In this work, a visualization experimental system was designed to study the flow pattern and heat transfer characterist...

The manifold microchannel (MMC) heat sink has become the most popular one among emerging technologies for high heat flux thermal management because of its high surface-to-volume ratio. Even though numerous numerical studies have been performed for the single-phase flow in the MMC heat sink, researches on two-phase flow boiling/condensation in this...

The manifold microchannel (MMC) heat sink system has been widely used in high-heat-flux chip thermal management due to its high surface-to-volume ratio. Two-phase, three-dimensional numerical methods for subcooled flow boiling have been developed using a self-programming solver based on OpenFOAM. Four different types of manifold arrangements (Z-typ...

The understanding of the convective heat transfer process for fluid flows through nanochannels becomes imperative due to the wide application of the micro/nanochannel cooling technology. In this work, thermal and flow characteristics in nanochannels with tunable surface wettability are investigated systematically using the molecular dynamics method...

Inferior heat transfer between metal and organic semiconductor is a challenge for the performance improvement of organic semiconductor devices. In this paper, we use non-equilibrium molecular dynamics to study the thermal energy transport between the functionalized gold (Au) and pentacene interfaces. The functionalized modifications of Au surface a...

Heat transfer and pressure drop characteristics of gas-liquid Taylor flows in a mini tube with 1 mm inner tube diameter were investigated numerically using a moving frame of reference method. A CuO/water nanofluid was used as the continuous phase, while nitrogen was adopted as the dispersed phase. The inlet Reynolds number ranged from 250 to 600, a...

Ocean thermal energy conversion (OTEC) has attracted lots of attention for its potential in clean energy production. In order to further improve system efficiencies, a new type of OTEC system using two ammonia ejectors is proposed. Effects of working pressures and geometrical parameters on vapor-vapor ammonia ejectors are studied numerically. The r...

To improve the transportation efficiency and reduce the supply cost, the liquefaction becomes an important technology to store and transport the natural gas. During the liquefaction, the various components (e.g. propane, ethane, methane etc.) undergo fractional condensation phenomenon due to their different boiling points. This means that when one...

The anisotropic wetting behaviours of water droplets on six surfaces with different solid–liquid interaction intensities are systemically investigated by molecular dynamics simulation. The six surfaces include Smooth, Square, Triangle, Sin, Sin-plus and Cylinder surfaces, and the interaction potentials between surface atoms and water molecules are...

Recently, various miniaturized electronic systems and the rapid increase in power density of microelectronic devices have created additional requirements for micro-scale heat dissipation technology. To dissipate heat in a micro-scale region efficiently, several creative cooling methods for high heat flux dissipation have been designed on the order...

A two-phase flow ejector is an important part of a water mist fire suppression system, and these devices have become a popular research topic in recent years. This paper proposes a supersonic ejector that aims to improve the efficiency of water mist fire suppression systems. The effects of ejector geometric parameters on the entrainment ratio (ER)...

The manifold microchannel heat sink receives an increasing number of attention lately due to its high heat flux dissipation. Numerical investigation of boiling phenomena in manifold microchannel (MMC) heat sinks remains a challenge due to the complexity of fluid route and the limitation of numerical accuracy. In this study, a computational fluid dy...

The manifold microchannel heat sink receives an increasing number of attention lately due to its high heat flux dissipation. Numerical investigation of boiling phenomena in manifold microchannel (MMC) heat sinks remains a challenge due to the complexity of fluid route and the limitation of numerical accuracy. In this study, a computational fluid dy...

This study numerically investigated the condensation heat transfer and flow characteristics of refrigerants R134a in rectangular minichannels. Three-dimensional simulations were carried out at different mass flux values, vapor qualities and gravity conditions through using the VOF model, the turbulence model and the phase transition model. The effe...

One of two-dimensional transition metal dichalcogenide materials, tungsten disulfide (WS2), has aroused much research interest, and its mechanical properties play an important role in a practical application. Here the mechanical properties of h-WS2 and t-WS2 monolayers in the armchair and zigzag directions are evaluated by utilizing the molecular d...

This study numerically investigated the condensation heat transfer and flow characteristics of refrigerant R134a in a rectangular minichannel. Three-dimensional simulations were carried out at different mass fluxes, vapor qualities, and gravity conditions using the volume-of-fluid (VOF) model, a turbulence model, and a phase transition model. The e...

Liquefied natural gas (LNG) is one of the key technologies in the development and utilization of natural gas. To clarify the condensation characteristics at the last stage of natural gas liquification, saturated methane mixed with nitrogen was chosen as the study object. A numerical model was proposed to predict the filmwise condensation characteri...

Heat transfer and pressure drop characteristics of R410A condensing flow in horizontal small microfin and smooth tubes with outer diameter of 5.0 mm were studied experimentally at relatively high mass fluxes ranging from 390 to 1583 kg/m² s with different saturation temperatures of 309.15 K, 316.15 K, and 323.15 K. The results indicate that heat tr...

Heat transfer and flow characteristics of Taylor flows in vertical capillaries with tube diameters ranging from 0.5 mm to 2 mm were studied numerically with the volume of fluid (VOF) method. Streamlines, bubble shapes, pressure drops, and heat transfer characteristics of the fully developed gas-liquid Taylor flow were investigated in detail. The nu...

Gas-liquid two-phase flow in curved channels is widely found in various heat exchangers and transport pipes. The fluid flow and heat transfer characteristics are closely related to flow patterns. This work experimentally investigated flow patterns for air-water flows in a U-bend and its contiguous straight tubes at a pressure of 0.1 MPa and a tempe...

To explore the mechanism of flow boiling in microchannels, the processes of a single-vapor bubble evaporating and two lateral bubbles merging in a 2D microchannel are investigated. The temperature recovery model based on volume of fluid method is adopted to perform the flow boiling phenomena. The effects of wall superheat, Reynolds number, contact...

In the study numerical simulations are performed to investigate the saturated fluid flow through a two dimensional microchannel (1000μm×200μm, with a superheated bottom wall) by building a comprehensive physical method and updating the standard solver in the OpenFOAM software package. On basis of previous numerical study, most of the numerical meth...

The heat transfer characteristics of condensation for R410A inside horizontal microfin tubes with 0° and 18° helical angles were investigated numerically. The numerical data fit well with the experimental results and with the empirical correlations. The results indicate that local heat transfer coefficients increase with increasing mass flux, vapor...

Heat transfer characteristics of R410A condensation in horizontal tubes with the inner diameter of 3.78 mm under normal and reduced gravity are investigated numerically. The results indicate that the heat transfer coefficients increase with increasing gravitational accelerations at a lower mass flux, whereas their differences under varying gravity...

Heat transfer characteristics for condensation for R410A inside horizontal round (dh=3.78 mm) and flattened tubes (aspect ratio (AR)=3.07, 4.23, and 5.39) with larger horizontal than vertical dimensions at a saturation temperature of 320 K are investigated numerically. The flattened tube has flat upper and lower walls and circular end walls. The he...

Numerical work of fully developed gas-liquid Taylor flow in vertical upward capillaries with inner diameter of 1 mm under isothermal wall boundary condition was performed with the dynamic mesh model. The effects of inlet Reynolds number and gas void fraction on thermal and flow characteristics of Taylor flow were discussed. Results indicate that th...

The hydrodynamic and heat transfer characteristics of the fully-developed gas-liquid Taylor flow in a 0.5 mm capillary were studied numerically using the moving frame method. The bubble shapes, pressure drops and heat transfer characteristics were analyzed. The numerical results show that the liquid film thickness, the bubble length and the length...

Condensation heat transfer and pressure drop characteristics for R410A and R134a in horizontal round (dh = 3.78 mm) and flattened tubes [aspect ratio (AR) = 3.07, 4.23, and 5.39] at saturation temperature Tsat = 320 K were investigated numerically. Liquid-vapor interfaces and stream traces are also presented to give a better understanding of the co...

Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 3.78 mm) under normal and micro gravity are investigated numerically. The Volume of Fluid method is used to acquire liquid-vapor interface, while the low-Reynolds form of the Shear Stress Transport k∼ω (SST k∼ω) model is adopted to taking turbule...

Heat transfer and pressure drop characteristics of mini smooth and microfin tubes were studied numerically using water as working fluid at Reynolds number ranging from 7500 to 17500. Seven microfin tubes were used with the same inner diameters of 4.6 mm and 18° helix angle and with number of fins ranging from 30 to 50, fin apex angle ranging from 1...

The heat transfer characteristics of supercritical China RP-3 aviation kerosene flowing downward in a vertical circular tube are numerically investigated. A ten-species surrogate model is used to calculate the thermophysical properties of kerosene and the Re-Normalization Group (RNG) k-ε model with the enhanced wall treatment is adopted to simulate...

Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal circular tubes with inner diameters ranging from 0.25–4 mm were investigated numerically. The effects of mass flux, vapour quality, tube diameters, and gravity on heat transfer and pressure drop characteristics were discussed. Liquid-vapour interfaces and st...

Heat transfer and flow characteristics of Taylor flow in vertical capillaries with diameters of 0.5, 1, and 2 mm have been investigated numerically with the volume of fluid method. 30 different cases have been conducted with inlet Reynolds number ranging from 100 to 500 and initial void fraction ranging from 0.2 to 0.4. Simulation results of the no...

Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 0.25, 1, and 4 mm) at saturation temperatures Tsat = 310, 320, and 330 K are investigated numerically. Liquid–vapor interfaces and stream traces are also presented to provide a better understanding of the effect of saturation temperature on the c...

Heat transfer and flow characteristics of Taylor flow in vertical capillaries with tube diameters ranging from 0.5 mm to 2 mm have been investigated numerically with the Volume of Fluid (VOF) method. Streamlines, bubble shapes, pressure drops, and heat transfer characteristics of Taylor flow were investigated in detail. The results indicate that th...

Heat transfer characteristics of aviation kerosene were investigated numerically using a three-dimensional model. The influence of the ratio of longer axis to short axis of elliptical tubes (r), inlet Reynolds number (Re), and pressure (P) of kerosene on local heat transfer characteristics were discussed in detail. The results indicate that the hea...

Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 0.25, 1, and 2 mm) at saturation temperatures Tsat = 310, 320, and 330 K are investigated numerically. The results indicate that local heat transfer coefficients and pressure drop gradients increase with increasing mass flux and vapor quality and...

A numerical simulation of fully developed gas-liquid Taylor flow in mini/micro tubes with tube diameters of 0.5, 1, and 2 mm was conducted with the moving frame method. The bubble shape, bubble rising velocity, liquid film thickness, and pressure drop characteristics of Taylor flow were analyzed. The numerical data fit well with theresults in open...

Heat transfer and flow characteristics of Taylor flow in micro capillary tubes have been investigated numerically with the Volume of Fluid (VOF) method. A constant heat flux (32kwm⁻²) is adopted at the tube wall. All seven computational cases have the same Reynolds number (Re=280), Capillary number (Ca=0.006) and homogenous void fraction (β=0.51),...

With the physical property changing dramatically, the supercritical aviation kerosene obtains unique heat transfer characteristics. In this way, it is difficult to investigate the heat transfer characteristics by normal experiment and therefore we resort to numerical analysis to address the scientific questions in this study. The project is propose...

In order to obtain the frictional characteristics of fully developed Taylor flow in the vertical capillary tube, numerical simulations of the flow in the capillary tube with diameter of 2 mm were conducted by using the moving frame reference method. The shape, rising velocity of Taylor bubble, liquid film thickness and pressure drop were obtained u...

This gif file shows the typical motion inside Taylor flow.

This gif file describes the evolution of Taylor bubble, where the computional geometry moving with Taylor bubble.

A simple example of film boiling.