Search

The basal texture of traditional magnesium alloy AZ31 is easy to form and exhibits poor plasticity at room temperature. To address these problems, a multi-micro-alloyed high-plasticity Mg–1.8Zn–0.8Gd–0.1Ca–0.2Mn (wt%) alloy was developed using the unique role of rare earth and Ca solute atoms. In addition, the influence of the annealing process on the grain size, second phase, texture, and mechanical properties of the warm-rolled sheet at room temperature was analyzed with the goal of developing high-plasticity magnesium alloy sheets and obtaining optimal thermal-mechanical treatment parameters. The results show that the annealing temperature has a significant effect on the microstructure and properties due to the low alloying content: there are small amounts of larger-sized block and long string phases along the rolling direction (RD), as well as several spherical and rodlike particle phases inside the grains. With increasing annealing temperature, the grain size decreases and then increases, and the morphology, number, and size of the second phase also change correspondingly. The particle phase within the grains vanishes at 450°C, and the grain size increases sharply. In the full recrystallization stage at 300–350°C, the optimum strength-plasticity comprehensive mechanical properties are presented, with yield strengths of 182.1 and 176.9 MPa, tensile strengths of 271.1 and 275.8 MPa in the RD and transverse direction (TD), and elongation values of 27.4% and 32.3%, respectively. Moreover, there are still some larger-sized phases in the alloy that influence its mechanical properties, which offers room for improvement. [ABSTRACT FROM AUTHOR]

In terms of developing supercritical CO2 (sCO2) coal-fired power plants, enhancing cooling wall performance is one of significant factors to improve system performance. In this paper, a new cooling wall tube structure is proposed to match the non-uniform heat flux (NUH) with the thermal resistance by changing the cooling wall tube eccentricity. A three-dimensional multi-physical coupling model of cooling wall is constructed to compare the novel structure to the conventional structures. The properties of fluid dynamics, thermal stress, coupled heat transfer and cooling wall deformation are analyzed. In contrast to the traditional structure, the maximum temperature and circumferential temperature difference (CTD) of the proposed structure can be reduced by 2% and 27.4%, respectively. The essential working parameters related to the performances of the cooling wall tube are discussed. The maximum temperature of the new structure is reduced by 8–13 K and the maximum thermal stress is reduced by about 10%–15% under all the simulated working conditions when the eccentricity changes from 0 to 0.2. The proposed structure can effectively reduce the maximum temperature and circumferential temperature gradient under NUH. Consequently, a novel insight is put out for the design and optimization of the cooling wall tube in coal-fired power plants. [ABSTRACT FROM AUTHOR]

Carbon emission changes significantly when the vehicle is driving at a variable speed. Given that the rule of vehicle carbon emissions under different driving behaviors is underexplored, this study filled this research gap by establishing a theoretical carbon emission model when vehicles are driving at fluctuating speed. The model was established based on the law of conservation of mechanical energy, the first law of thermodynamics, the theory of vehicle dynamics. Two passenger cars and three trucks were selected as typical vehicles. A field test was carried out under different driving behaviors with uniform acceleration. The proposed model can forecast the carbon emissions of vehicles that fluctuate in speed during travel and showed strong accuracy in model validation. As the speed fluctuation increased, the influence of acceleration on carbon emissions became more apparent. Gradient has a more significant influence on vehicle carbon emissions, followed by acceleration. By controlling the driving behavior of the vehicle on the round trip, the same carbon emissions as driving on a flat route at a constant speed can be achieved. The findings of this study will provide a theoretical basis for low-carbon transportation. [ABSTRACT FROM AUTHOR]

Using supercritical CO2 (S-CO2) instead of water steam as heat transfer fluid for coal-fired power plants is another way to further improve the power generation efficiency. In this paper, a multi-field coupling model that integrates fluid flow, heat transfer and thermal stress is proposed to solve the complex problem. The effects of the key operating parameters on the performances of the cooling wall are numerically investigated. More details of the characteristics of fluid dynamics, thermal stress, pressure drop, coupled heat transfer and the whole flow and temperature fields in the S-CO2 cooling wall are revealed and discussed. A comparison study is made between the cooling wall tube and waterwall tube. Both temperature and thermal deformations of cooling wall tube are much higher than that of water. Numerical simulation results indicate that inclination angle has little effects on the temperature distribution, while increase of pressure drop is obvious as the inclination angle increases. Increasing tube diameter can effectively reduce both the pressure drop and the temperature of the cooling wall tube. As a result, a new insight is introduced for the design of S-CO2 power cycle. [ABSTRACT FROM AUTHOR]

In order to explore the directional support method of jointed rock mass and ensure the stable operation of roadway, the support effect of jointed rock mass was analyzed by numerical simulation and on-site monitoring. The results showed that directional support could effectively reduce the deformation and ensured the stability of surrounding rock. In the process of directional reinforcement support construction, the plane formed by multiple bolts was guaranteed to be perpendicular to the structural plane, and the bolt hole extended along the normal plane of roadway, the control effect of this support mode was the best. The stress change law of surrounding rock of roadway was monitored by using borehole force meter. The results showed that the stress released occurs in surrounding rock of roadway after excavation, and the cumulative stress change value did not increase 5 to 7 days after excavation. The jointed rock mass remained in a stable state under the action of directional reinforcement support. The directional reinforcement of roadway surrounding rock had a good control effect on roadway stability. [ABSTRACT FROM AUTHOR]

Supercritical water (scW) is important for various engineering applications. The structure and distribution of scW is key to dominate the related processes and phenomena. Here, scW is investigated using molecular dynamics (MD) simulation with controlled pressure and temperature. Density oscillation is observed to occur in a 1 nm thickness bin, indicating mass exchange of particles across the bin interface. We show that the low density scW behaves strong heterogeneity. Quantitative analysis of system density fluctuations is performed by square root error and maximum structure factor, demonstrating the agreement between the two methods. The scW molecules are tightly gathered to form "liquid island" locally, but are very sparse in other regions, which are similar to the gas-liquid mixture in subcritical pressure. A target molecule is tracked to plot 3D displacements and rotating angles, with the former indicating large amplitude ballistic (diffusing) motion and small amplitude oscillation, and the latter displaying two scales of angle jumping. Both translation and rotating motion are related to hydrogen bond break up and reorganization. The low density scW behaves isolated molecules with few combinations of hydrogen bonds between molecules, while the high density scW behaves more combinations of molecules via hydrogen bonds. The two scales motion is expected to influence thermal/chemical process in supercritical state, deepening the fundamental understanding of scW structure. [ABSTRACT FROM AUTHOR]

The objective of this paper is to understand the benefits that one can achieve for large-scale supercritical CO2 (S-CO2) coal-fired power plants. The aspects of energy environment and economy of 1000 MW S-CO2 coal-fired power generation system and 1000 MW ultra-supercritical (USC) water-steam Rankine cycle coal-fired power generation system are analyzed and compared at the similar main vapor parameters, by adopting the neural network genetic algorithm and life cycle assessment (LCA) methodology. Multi-objective optimization of the 1000 MW S-CO2 coal-fired power generation system is further carried out. The power generation efficiency, environmental impact load, and investment recovery period are adopted as the objective functions. The main vapor parameters of temperature and pressure are set as the decision variables. The results are concluded as follows. First, the total energy consumption of the S-CO2 coal-fired power generation system is 10.48 MJ/kWh and the energy payback ratio is 34.37%. The performance is superior to the USC coal-fired power generation system. Second, the resource depletion index of the S-CO2 coal-fired power generation system is 4.38 µPRchina,90, which is lower than that of the USC coal-fired power generation system, and the resource consumption is less. Third, the environmental impact load of the S-CO2 coal-fired power generation system is 0.742 mPEchina,90, which is less than that of the USC coal-fired power generation system, 0.783 mPEchina,90. Among all environmental impact types, human toxicity potential HTP and global warming potential GWP account for the most environmental impact. Finally, the investment cost of the S-CO2 coal-fired power generation system is generally less than that of the USC coal-fired power generation system because the cost of the S-CO2 turbine is only half of the cost of the steam turbine. The optimal turbine inlet temperature T5 becomes smaller, and the optimal turbine inlet pressure is unchanged at 622.082°C/30 MPa. [ABSTRACT FROM AUTHOR]

Accurate prediction of supercritical CO2 (scCO2) heat transfer is important for heat exchanger design and safe operation of scCO2 power cycles. The main prediction method is empirical correlation. This paper demonstrates an alternative way by artificial neural networks (ANN) model with two hidden layers. To assess widely cited correlations and newly developed ANN model, scCO2 heat transfer experiment in vertical tube with pressure up to 20.8 MPa was performed to extend experiment database, which includes 2674 runs. Compared with empirical correlations, the ANN model is promising for following advantages: (1) ANN model has much better prediction accuracy. The mean relative error, mean absolute relative error and the root-mean-square relative error between predicted and measured wall temperatures are eA=0.38%, eR=4.88% and eS=7.29%, respectively. (2) ANN model performs faster computation speed. (3) ANN model can accurately and speedily predict scCO2 heat transfer performance for both normal heat transfer and heat transfer deterioration modes. The trained ANN program is provided with this paper, which is a useful tool and can be directly applied in engineering of scCO2 heat transfer. [ABSTRACT FROM AUTHOR]

Required by the supercritical carbon dioxide (sCO2) coal-fired power cycle, sCO2 entering a boiler has a high temperature and can cause overheating of tubes. To eliminate the pressure drop penalty effect, the sCO2 boiler consists of several modules, each having different heat flux received from the furnace side (q) and different CO2 temperature in the cooling wall tube (Tf). We aim to search for the best matching strategy coupling furnace side and tube side to obtain the lowest temperature of tubes. By theoretically analyzing the wall temperature influenced by q, Tf and a comprehensive thermal resistance C, two matching methods are introduced: the heat flux-temperature matching (HTM) which matches higher q with lower Tf, and the heat flux-heat flux matching (HHM) that matches higher q with higher allowable-heat-flux at the temperature limit of tubes. HTM is a conventional method but HHM is newly proposed here. We show that, if C is identical for different modules, the two methods coincide; otherwise, HHM is recommended. For a sCO2 boiler driving 1000 MWe power plant, smaller cooling wall temperatures are obtained by HHM than HTM. Based on HHM, the mid-partition wall, heat transfer enhancement, and downward flow are comprehensively used, decreasing the wall temperature significantly. [ABSTRACT FROM AUTHOR]

The experimental measurement of supercritical pressure carbon dioxide (sCO2) heat transfer in vertical downward flow was performed in a circular tube with inner diameter of 10 mm. Then, a three-dimensional numerical investigation of sCO2 heat transfer in upward and downward flows was performed in a vertical heated circular tube. The influence of heat flux, mass flux, and operating pressure on heat transfer under different flow directions were discussed. According to the "pseudo-phase transition" viewpoint to supercritical fluids, the analogy to the subcritical inverted-annular film boiling model, the physical model to sCO2 heat transfer was established, where fluid region at the cross-section of circular tube was divided into gas-like region covering heated wall and core liquid-like phase region. Then, the thermal resistance mechanism which comprehensively reflected the effect of multiple factors including the thickness of the gas-like film or liquid-like region, fluid properties and turbulence on heat diffusion was proposed. Surprisingly, thermal resistance variation in upward flow is well identical with that of wall temperature and heat transfer deterioration is predicted successfully. In addition, compared with thermal resistance in the core liquid-like region, gas-like film formation is determined to be the primary factor affecting heat transfer behavior. Results also show that total thermal resistance in upward flow is always larger than that in downward flow. The investigation can provide valuable guide to design and optimize sCO2 heaters. [ABSTRACT FROM AUTHOR]

Since service level agreement (SLA) is essentially used to maintain reliable quality of service between cloud providers and clients in cloud environment, there has been a growing effort in reducing power consumption while complying with the SLA by maximizing physical machine (PM)-level utilization and load balancing techniques in infrastructure as a service. However, with the recent introduction of container as a service by cloud providers, containers are increasingly popular and will become the major deployment model in the cloud environment and specifically in platform as a service. Therefore, reducing power consumption while complying with the SLA at virtual machine (VM)-level becomes essential. In this context, we exploit a container consolidation scheme with usage prediction to achieve the above objectives. To obtain a reliable characterization of overutilized and underutilized PMs, our scheme jointly exploits the current and predicted CPU utilization based on local history of the considered PMs in the process of the container consolidation. We demonstrate our solution through simulations on real workloads. The experimental results show that the container consolidation scheme with usage prediction reduces the power consumption, number of container migrations, and average number of active VMs while complying with the SLA. [ABSTRACT FROM AUTHOR]

The objective of this paper is to provide the optimal choice of single-reheating or double-reheating when considering residual flue gas heat in S-CO2 coal fired power system. The cascade utilization of flue gas energy includes three temperature levels, with high and low temperature ranges of flue gas heat extracted by S-CO2 cycle and air preheater, respectively. Two methods are proposed to absorb residual flue gas heat Qre in middle temperature range. Both methods shall decrease CO2 temperature entering the boiler T4 and increase secondary air temperature Tsec air, whose maximum value is deduced based on energy conservation in air preheater. The system is analyzed incorporating thermodynamics, boiler pressure drop and energy distribution. It is shown that at a given main vapor temperature T5, the main vapor pressure P5 can be adjusted to a value so that Qre is completely eliminated, which is called the main vapor pressure adjustment method. For this method, single-reheating is only available for higher main vapor temperatures. The power generation efficiency for single-reheating is obviously higher than double-reheating. If residual flue gas heat does exist, a flue gas heater FGC is integrated with S-CO2 cycle, which is called the FGC method. Both single-reheating and double-reheating share similar power generation efficiency, but single-reheating creates less residual flue gas heat. We conclude that single-reheating is preferable, and the pressure adjustment method achieves obviously higher power generation efficiency than the FGC method. [ABSTRACT FROM AUTHOR]

Chinese fir (Cunninghamia lanceolata) is an excellent fast-growing timber species occurring in southern China and has significant value in the forestry industry. In order to enhance the phosphorus utilization efficiency in Chinese fir, four clones named X6, S3, S39 and FK were used, and low phosphorus (LP) stress experiments were performed to analyze the response of different clones to phosphorus deficiency. According to the results on seedling height, maximum root length, leaf blade aspect ratio, root ratio, malondialdehyde content, acid phosphates activity, proline content, soluble protein level, and chlorophyll a and b levels of the tested clones, compared to the control groups (CK), the phosphorus high efficiency clone X6 was screen out for transcriptome sequencing experiments. De novo RNA-seq was then used to sequence the root transcriptomes of X6 under LP stress and CK, and we then compared the gene expression differences under the two conditions. A total of 3416 SDEGs were obtained by comparing the LP and CK groups, among which 1742 were up-regulated and 1682 were down-regulated. All SDEGs obtained from the LP and CK treated samples were subjected to KEGG annotation and classification. Through classification statistical analysis using WEGO software, 607 SDEGs obtained KEGG pathway annotations, which were related to 206 metabolic pathways. In Chinese fir subjected to LP stress, 53 SDEGs related with phosphorus metabolism, and phosphate uptake and transport were obtained from our transcriptome data. Based on the phosphorus metabolism pathway obtained by KEGG classification, combined with previously report on gene annotation related with phosphorus metabolism, the enzymes encoded by SDEG related with phosphorus metabolism and their expression pattern were mapped onto phosphorus metabolism pathway. [ABSTRACT FROM AUTHOR]

In this paper, an approach to optimize set points is proposed for controlled Organic Rankine Cycle (ORC) systems. Owing to both disturbances and variations of operating point existing in ORC systems, it is necessary to optimize the set points for controlled ORC systems so as to improve the energy conversion efficiency. At first, the optimal set points of controlled ORC systems are investigated by revisiting performance analysis and optimization of ORC systems. The expected set points of the evaporating pressure and the temperature at evaporator outlet are then determined by combining genetic algorithm with least squares support vector machine (GA-LSSVM). Simulation results show that the predicted results by GA-LSSVM can be regarded as the optimal set points of controlled ORC systems with varying operating conditions. [ABSTRACT FROM AUTHOR]

The design, construction and test of an Organic Rankine Cycle (ORC) with R123 as the working fluid were performed. A scroll expander was integrated in the system. The conductive oil with its temperature of 150 °C was used to simulate the low-grade heat source. An AC dynamometer unit measured the expander shaft torque, rotating speed and shaft power. The experiments were conducted in two operating modes: the constant mass flow rate and the constant shaft torque. Under the constant mass flow rate operating mode, the stepped increase of the shaft torque increased the expansion ratios of the expander and decreased the vapor superheats at the expander inlet. Thus, the shaft power and thermal efficiency were increased. Alternatively, the constant shaft torque operating mode involved two different regions, interfaced at the pumping frequency of 9 Hz. By the increase of the mass flow rates, the vapor superheats at the expander inlet was decreased and the shaft power was increased, but the ORC thermal efficiencies were slightly decreased. Both operating modes yielded the saturation shaft powers that were the maximum values one could use. It was found that the measured shaft powers and ORC thermal efficiencies were lower than the enthalpy determined values based on the fluid pressures and temperatures at the expander inlet and outlet. The maximum measured shaft power and thermal efficiency were 2.63 kW and 5.31 %, compared with the enthalpy determined values of 3.87 kW and 9.46 %, respectively. [ABSTRACT FROM AUTHOR]

Renewable energy or low grade energy utilizations need high performance of phase change heat exchangers. Suspending micromembrane cylinder in tube (called modulated heat transfer tube) increases the void fractions or vapor qualities near the tube wall to significantly enhance heat transfer. The R123 condensation heat transfer with horizontal position was investigated. The results for the bare tube and modulated heat transfer tube were tested case by case. It is found that the modulated heat transfer tube significantly enhance the condensation heat transfer, with the heat transfer enhancement factors (EF) covering the range of 1.118-2.124. The comprehensive performance evaluation criteria (PEC) had the range of 0.71-1.66, with most of runs behaving PEC larger than 1.0. For the two-phase outlet conditions, the EF values are increased with increases in the vapor mass fluxes, Gx, where G is the mass flux and x is the inlet vapor mass quality. The EF values are inversely related to Gx for the subcooled liquid outlet cases. The enhanced heat transfer mechanisms are analyzed with the observed images together with the discussion of pressure and velocity distributions. [ABSTRACT FROM AUTHOR]

Recently, our research group proposed the phase separation condenser tube, in which a mesh cylinder was inserted to form the flow structure of 'gas near the tube wall and liquid in the tube core', significantly enhance the condensation heat transfer. But the bubble leakage towards the core region may worsen the heat transfer enhancement. In order to prevent the bubble leakage, the critical criterion was proposed based on the Young-Laplace equation, considering the inertia force, viscous force and pulsating flow. It was found that the critical criterion depends on the dimensionless parameter G, the We number and a coefficient C. The numerical model was developed in terms of the volume of fluid method to predict the two-phase laminar flow in the phase separation condenser tube. The results show that the bubble leakage takes place at the bubble tip, which is agreed with the experimental observations. The critical curve distinguishing the non-bubble-breaking and bubble-breaking was obtained by comparing the bubble dynamics at different G* and We. The coefficient C was determined. The critical criterion for the bubble leakage is given as $$ G^{*} \times We = \left( {0.22We^{0.99349} - \frac{{G^{*} }}{{4.7 \times 10^{3} \times We^{0.00651} }} + \frac{196.39}{{We^{0.00651} }}} \right) \times \frac{{4{ \cos }\alpha }}{\Delta \varTheta W} $$ , providing the design and operation guidance for the phase separation condenser tube. [ABSTRACT FROM AUTHOR]

In this study, GaN-based light-emitting diodes (LEDs) with and without AlGaInN electron blocking layer (EBL) under self-heating effect are numerically studied. The energy band diagram, carrier transport and distribution characteristics, internal Joule heat and non-radiative recombination heat characteristics, and internal quantum efficiency are investigated. The effect of Auger recombination coefficient on efficiency droop under self-heating effect is also studied. The simulation results show that efficiency droop is markedly improved when an AlGaInN EBL is placed between p-type GaN layer and active region. However, the chip temperature of LED is significantly increased simultaneously. The results also indicate that Auger recombination can be neglected because it is not the major contributor for the internal heat source. The efficiency droop is unrelated to the internal heat source. However, both electron leakage and Auger recombination play important roles in efficiency droop mechanism under self-heating effect. [ABSTRACT FROM AUTHOR]

High boiling incipience temperature and flow instabilities in silicon-based microchannels with smooth surface are challenging issues. This work numerically investigates the seed bubble-triggered evaporation heat transfer in a microtube, with a length of 5.0 mm and diameter of 106 μm. Acetone was the working fluid. Seed bubbles were assumed to be generated periodically at the microtube upstream. The fixed grid allocation technique was proposed to successfully perform the parallel computation via a set of computer core solvers. It is found that the seed bubble-guided heat transfer consists of a start-up stage and a steady operation stage. The start-up time equals to the residence time of the first seed bubble growing and traveling in the microtube. The seed bubble frequency is a key parameter to influence the performance. Low-frequency seed bubbles cause alternative flow patterns of liquid flow and elongated bubble flow, corresponding to the apparent spatial-time oscillations of wall and bulk fluid superheats. High-frequency seed bubbles result in quasi-stable elongated bubble flow, corresponding to quasi-uniform and stable wall and fluid superheats. There is a saturation seed bubble frequency beyond which no further performance improvement can be made. There are residual fluid superheats specifying the required minimum superheats to sustain the evaporation heat transfer between the two phases. Elongated bubbles with thin liquid films are responsible for the heat transfer enhancement. Contrary to wall temperatures, the transient local Nusselt numbers are slightly changed due to the fact that heat transfer is more closely related to the dynamic elongated bubble flow evolution within millisecond timescale in the microchannel. The heat transfer coefficients can be 2.0 to 3.5 times of that for the superheated liquid flow before seed bubble injections. [ABSTRACT FROM AUTHOR]

The passive phase separation concept was proposed to modulate flow patterns for heat transfer enhancement. By the flow pattern modulation, the gas tends to be near the wall and the liquid tends to be in the tube core. Experiment has been performed to verify the fresh idea and the flow pattern modulation mechanism was analyzed qualitatively. This paper focuses on the numerical simulation of the bubble dynamics for a single bubble in the vertical phase separation condenser tube to quantitatively explore the flow pattern mechanism, based on a multiscale grid system and the volume-of-fluid (VOF) method. It is found that: (1) the modulated liquid film thickness can be decreased by 70% compared to that in the bare tube region; (2) the modulated bubble traveling velocity can be doubled, causing the increased liquid velocity and velocity gradient in the annular region to weaken the fluid boundary layer; (3) the significantly increased bubble traveling velocity in the annular region promotes the mass and momentum exchange between the annular region and the core region, and yields the self-sustained pulsating flow in the core region. The above three factors are benefit for the performance improvement of the heat transfer facilities. [ABSTRACT FROM AUTHOR]

A multi-quantum barrier structure is employed as the electron blocking layer of light-emitting diodes to enhance their performance. Using the non-isothermal multi-physics-field coupling model, the internal quantum efficiency, internal heat source characteristics, spectrum characteristics, and photoelectric conversion efficiency of light-emitting diodes are analyzed systematically. The simulation results show that: introducing multi-quantum barrier electron blocking layer structure significantly increases the internal quantum efficiency and photoelectric conversion efficiency of light-emitting diodes and the intensity of spectrum, and strongly ensures the thermal and light output stability of light-emitting diodes. These results are attributed to the modified energy band diagrams of the electron blocking layer which are responsible for the decreased electron leakage and enhanced carrier concentration in the active region. [ABSTRACT FROM AUTHOR]

Pool boiling of saturated water on a plain Ti surface and surfaces covered with vertically-oriented TiO nanotube arrays (NTAs) has been studied. The technique of potentiostatic anodization using non-aqueous electrolytes was adopted to fabricate three types of TiO NTAs distinguished by their anodization time. Compared to the bare Ti surface, the incipient boiling wall superheat on the TiO NTAs was decreased by 11 K. Both the critical heat flux and heat transfer coefficient of pool boiling on the TiO NTAs were higher than those from boiling on a bare Ti surface. The measured maximum critical heat flux and heat transfer coefficient values were 186.7 W/cm and 6.22 W/cmK, respectively. Different performances for the enhancement of heat transfer by the three types of TiO NTAs were attributed to the different degrees of deformation in the nanostructure during boiling. Long-term performance of the nanomaterial-coated surfaces for enhanced pool boiling showed degradation of the TiO NTAs prepared with an anodization time of 3 hours. [ABSTRACT FROM AUTHOR]

Experiments were performed to study pressure drops in copper foams embedded in a rectangular copper channel. De-ionized water was used as the working fluid with mass fluxes of 30-200 kg/m s, and inlet temperature of 40-80°C. The copper foam has the porosity of 0.88 and the pore densities of 30, 60 and 90 ppi (pores per inch). Both single-phase liquid flow and boiling two-phase flow are studied. Effects of mass fluxes, vapor mass qualities, and average pore diameters of metallic foams are investigated. It is found that friction factors for the single-phase liquid flow are mainly dependent on the Reynolds number and the average pore diameter of metallic foams. The friction factors are decreased with increases in the Reynolds numbers, and will approach 0.22 at high Reynolds numbers. For the boiling two-phase flow, two-phase pressure drops are increased with increases in the outlet vapor mass qualities, mass fluxes, and ppi values. The two-phase multiplier is increased with increases in the outlet vapor mass qualities and mass fluxes, and it is decreased with increases in the Martinelli parameter and will attain a constant value depending on the mass fluxes. The larger the mass fluxes, the larger the constant value is. An experimental correlation considering the effects of vapor mass qualities, mass fluxes, and average pore diameters of metallic foams is recommended, showing good accuracy to predict the two-phase pressure drops in metallic foams. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation is a powerful tool to investigate the nanoscale fluid flow. In this article, we review the methods and the applications of MD simulation in liquid flows in nanochannels. For pressure-driven flows, we focus on the fundamental research and the rationality of the model hypotheses. For electrokinetic-driven flows and the thermal-driven flows, we concentrate on the principle of generating liquid motion. The slip boundary condition is one of the marked differences between the macro- and micro-scale flows and the nanoscale flows. In this article, we review the parameters controlling the degree of boundary slip and the new findings. MD simulation is based on the Newton's second law to simulate the particles' interactions and consists of several important processing methods, such as the thermal wall model, the cut-off radius, and the initial condition. Therefore, we also reviewed the recent improvement in these key methods to make the MD simulation more rational and efficient. Finally, we summarized the important discoveries in this research field and proposed some worthwhile future research directions. [ABSTRACT FROM AUTHOR]

Effect of inclination angles on the pool boiling heat transfer on ultra-light copper foam covers was studied using acetone as the working fluid. The inclination angle was from 0° to 90°. It is found that copper foam covers decrease the surface superheat at the onset of nucleate boiling and extend the operation ranges of surface superheats and heat fluxes, significantly. Boiling curves are crossed between low and high inclination angles. Heat transfer coefficients are increased, attain maximum values, and then are decreased with continuous increases in heat fluxes. The thermal performance is very insensitive to inclination angles at low pool liquid temperatures. The thermal performance is better for the saturation pool boiling heat transfer at small surface superheats, but it is better for the subcooled pool boiling heat transfer at high surface superheats. The Nusselt number is well correlated using the 812 data points, with the maximum error of 20%. [ABSTRACT FROM AUTHOR]

The smooth channel surface of microsystems delays boiling incipience in heated microchannels. In this paper, we use seed bubbles to trigger boiling heat transfer and control thermal non-equilibrium of liquid and vapor phases in parallel microchannels. The test section consisted of a top glass cover and a silicon substrate. Microheater array was integrated at the top glass cover surface and driven by a pulse voltage signal to generate seed bubbles in time sequence. Each microheater corresponds to a specific microchannel and is located in the microchannel upstream. Five triangular microchannels with a hydraulic diameter of 100 μm and a length of 12.0 mm were etched in the silicon substrate. A thin platinum film was deposited at the back surface of silicon chip with an effective heating area of 4,500 × 1,366 μm, acting as the main heater for the heat transfer system. Acetone liquid was used. With the data range reported here, boiling incipience was not initiated if wall superheats are smaller than 15°C without seed bubbles assisted. Injection seed bubbles triggers boiling incipience and controls thermal non-equilibrium between liquid and vapor phases successfully. Four modes of flow and heat transfer are identified. Modes 1, 2, and 4 are the stable ones without apparent oscillations of pressure drops and heating surface temperatures, and mode 3 displays flow instabilities with apparent amplitudes and long periods of these parameters. The four modes are divided based on the four types of flow patterns observed in microchannels. Seed bubble frequency is a key factor to influence the heat transfer. The higher the seed bubble frequency, the more decreased non-equilibrium between two phases and heating surface temperatures are. The seed bubble frequency can reach a saturation value, at which heat transfer enhancement attains the maximum degree, inferring that a complete thermal equilibrium of two phases is approached. The saturation frequency is about a couple of thousand Hertz in this study. [ABSTRACT FROM AUTHOR]

The typical MEMS fabrication of micro evaporators ensures the perfect smooth wall surface that is lack of nucleation sites, significantly decreasing the heat transfer coefficients compared with miniature evaporators fabricated using copper or stainless steel. In the present paper, we performed the boiling heat transfer experiment in silicon triangular microchannel heat sink over a wide parameter range for 102 runs. Acetone was used as the working fluid. The measured boiling heat transfer coefficients versus the local vapor mass qualities are compared with the classical Chen’s correlation and other correlations for macro and miniature capillary tubes. It is found that most of these correlations significantly over-predict the measured heat transfer coefficients. New correlations are given. There are many reasons for such deviations. The major reason is coming from the perfect smooth silicon surface that lowers the heat transfer performances. New theory is recommended for the silicon microchannel heat sink that should be different from metallic capillary tubes. [ABSTRACT FROM AUTHOR]

To understand the progress in surgical treatment of 12 970 patients with carcinoma of esophagus and gastric cardiac during 1965–1998. The patients were divided into A, B and C groups: 3 155 patients (group A) were treated surgically in the first 14 years, 5 952 patients (group B) in the next 10 years, and 3 863 patients (group C) in the last 10 years. The early stage lesions (Tis, T1) were assigned as a separate group. The results of these groups were compared. The resectability for esophageal and gastric cardiac carcinoma was 94.0% and 84.4% respectively, and the overall resectability was 91.3%. The resectability for groups A, B, C and the early stage group was 82.1%, 85.1%, 90.2% and 100%, respectively. The overall operative mortality was 1.8%, it was 4.4% for group A, 1.6% for group B, and 0.5% for group C. The overall 5-year survival was 31.6%. The 5-year survival for groups A, B, C and the early stage group was 27.0%, 29.1%, 32.0% and 92.6%, respectively. Among the 3 temporal groups, differences were observed in terms of lesion stage, location and size, surgery with or without combined therapy and postoperative complications. Best results were achieved in the early cases, with a resectability of 100% and a 5-year survival of 92.6%. The indications for surgical treatment were extended with increased resectability and decreased mortality. Subtotal esophagectomy combined with cervical esophagogastrostomy was advocated as the procedure of first choice for esophageal carcinoma in attempt to diminish the chance of recurrence, and to achieve better outcomes by using combined therapy for patients with≥stage III lesion. [ABSTRACT FROM AUTHOR]

Flow rate distribution is important in a multi channel system when the flow is heated non-uniformly. This paper describes a steady state approach for obtaining the flow distribution among various tubes of complex multi channel system. Based on the present approach, a program has been developed, which is directly applied in thermal hydraulic design and investigation of 600MW supercritical variable-pressure once through boiler. [ABSTRACT FROM AUTHOR]

The transient critical flow experiment with sharp-edged tubes as the break geometries is conducted in high pressure convective circulation test loop of Xi'an Jiaotong University. The initial steady operation pressure is up to 22.0MPa. An empirical correlation was made to obtain the critical mass flow rates, the critical pressure ratio and the thermal nonequilibrium number were correlated as the functions of the tube length to tube diameter ratio L/D. The predicted critical mass flow rate gets a higher accuracy for short tubes with L/D<12, the prediction accuracy is higher than that of Henry model prediction for long tubes with L/D>12. [ABSTRACT FROM AUTHOR]

The transient two-fluid model has been used to develop a general relation for acoustic waves. The analysis is valid in principle over the whole void fraction region. Flow pattern transitions from one flow regime to the other are assumed to occur at certain void fractions. Different correlations are used to calculate the interfacial area and interfacial drag force per unit mixture volume for bubbly flow, slug flow and annular flow respectively. The vapour-liquid interphase heat flux is derived from the one dimensional Fourier heat conduction equation to evaluate the interphase evaporation or condensation rate. Based on the present theory, a program has been carried out. Calculations are performed for pressure from 0.07 MPa to 16.0 MPa, void fractions from 0.0 to 1.0. The predicted sound speeds are compared with some experimental data for low pressures, good agreement has been achieved between sound speed predictions and experimental data. [ABSTRACT FROM AUTHOR]

We developed a novel micro-droplet array system, which is based on the distinct three dimensional mesh screen structure and sintering and oxidation induced thermal-fluid performance. Mesh screen was sintered on a copper substrate by bonding the two components. Non-uniform residue stress is generated along weft wires, with larger stress on weft wire top location than elsewhere. Oxidation of the sintered package forms micro pits with few nanograsses on weft wire top location, due to the stress corrosion mechanism. Nanograsses grow elsewhere to show hydrophobic behavior. Thus, surface-energy-gradient weft wires are formed. Cooling the structure in a wet air environment nucleates water droplets on weft wire top location, which is more 'hydrophilic' than elsewhere. Droplet size is well controlled by substrate temperature, air humidity and cooling time. Because warp wires do not contact copper substrate and there is a larger conductive thermal resistance between warp wire and weft wire, warp wires contribute less to condensation but function as supporting structure. The surface energy analysis of drops along weft wires explains why droplet array can be generated on the mesh screen piece. Because the commercial material is used, the droplet system is cost effective and can be used for large scale utilization. [ABSTRACT FROM AUTHOR]