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As the crucial material of photovoltaic field, the development of polysilicon has attracted intense attention on reducing its cost and improving the polysilicon chemical vapor deposition (CVD) performance. Two-dimensional numerical models have been developed to investigate the local heat and mass transfer performance of polysilicon CVD system by introducing wave-like and trapezoid-like obstacles in the gas flow channels. Effects of different channel configurations on the local velocity, temperature, concentrations of six components, Nusselt number (Nu), Sherwood number (Sh) and seven coordinate angles along the flow direction are presented and detailed analyzed. The disturbing obstacles increase both the local and total Nu, as well as Sh. The seven coordinate angles caused by velocity vector, temperature gradient, and concentration gradient increase near the disturbing structures and decrease out of the disturbing obstacles. However, the disturbing obstacles decrease the total intersection angles leading better heat and mass transfer performance. In brief, compared to conventional straight channel, the proposed channels increase the gas flow velocity and, hence, improved the silicon CVD characteristics.

The present study proposes a model to predict the heat transfer coefficient in R134a liquid&ndash, vapor two-phase pulsating flow boiling in an evaporator using the experimental data and response surface methodology (RSM). The model is based on the current existing empirical correlation for R134a liquid&ndash, vapor two-phase continuous flow with an imposed modification factor. The model for the imposed modification factor is the function of the pulsating period and inlet/outlet vapor quality, which is obtained using the limited experimental data. An analysis of variance (ANOVA) is carried out to test the significance of the model and normal probability of residuals is analyzed as well. Results show that the regression model produces a mean error of &minus, 4.3% and a standard deviation of 15.4%, compared to experimental results. Of the data 95.1% is contained inside a &plusmn, 50% error window, which indicates that the proposed model could predict the heat transfer coefficient of R134a liquid&ndash, vapor two-phase pulsating flow boiling well.

In this study, response surface methodology (RSM) and the desirability approach are applied to study and optimize the performance of a free piston Stirling engine (FPSE). A regression model is presented to investigate the influences of operating and structural parameters of the FPSE on its performance. The analysis of variance (ANOVA) is conducted to describe the rationality of the regression model and examine the statistical significance of factors. Also, the relationship between output power, thermal and exergy efficiency and these parameters of Stirling engine is presented via 2D contour and 3D surface plots. Moreover, the operating and structural parameters of FPSE are optimized to achieve maximal output power, thermal and exergy efficiencies simultaneously. The multi-objective optimal results are confirmed by Sage software simulation results. It is found that the errors between the Sage modeling and RSM values for output power, thermal and exergy efficiency are 0.37%, 1.51% and 1.40%, respectively. Therefore, the model based on the RSM method is an efficient and fast way for the design and optimization of the FPSEs.

This paper addresses the complex component evolution and silicon dynamic deposition characteristics in the traditional Siemens reactor. A two-dimensional heat and mass transfer model coupled with a detailed chemical reaction mechanism was developed. The distributions of temperature, velocity, and concentration are presented in detail. The influencing factors (such as feeding mole ratio, inlet velocity, base temperature and reactor pressure) on the molar concentration evolutions of ten major components and silicon growth rate were obtained and analyzed. Results show that base temperature is main influence of HCl mole fraction. In order to get more growth rate of silicon and better silicon quality, the complex operating parameters need to be reasonably designed on collaborative optimization.

In order to evaluate the irreversibility and exergy losses of the regenerators in a solar beta-type free piston Stirling engine due to flow friction, 1-D thermodynamic model to quantify exergy loss in the regenerators are built. The effects of important parameters, such as oscillating flow pressure drop, the exergy loss to flow friction, the exergy losses to conduction heat transfer at the hot and cold side of the regenerator and the percentage of Carnot efficiency of Stirling engine are presented and studied in detail. Results show that exergy loss decreases with the increase of the porosity and matrix diameter. As for the regenerator length, there is an optimum value that is equal to 0.035 m where the exergy loss is minimal and the percentage of Carnot efficiency is maximal. Therefore, some parameters should be selected reasonably to meet the overall design requirements of a solar Stirling engine.

A jet pump used in the thermoacoustic engine can improve the performance by suppressing the Gedeon streaming. In this paper, response surface methodology (RSM) and desirability approach are used to investigate and optimize the jet pump in a thermoacoustic Stirling heat engine (TASHE). The position, length, diameter and tapered angle of jet pump are selected as the designing parameters, and pressure amplitude and time-averaged power dissipation across the jet pump are adopted as responses. The analysis of variance (ANOVA) is conducted to identify the significant influences of jet pump's parameters on responses. The regression models are obtained, and prediction deviations for pressure amplitude and power dissipation are within ±2% and ±5% respectively. In addition, the influences of jet pump’s parameters on responses are plotted by 3D surface. Eventually, the designing parameters of jet pump are optimized to achieve both maximal pressure amplitude and minimal power dissipation. The optimal results are validated by comparing with DeltaEC simulation. Results show that the deviations between DeltaEC and RSM for pressure amplitude and power dissipation are 1.86% and 2.88%, which indicates that RSM as an assessment methodology in optimizing jet pump is feasible.

The SPRIGT team in TIPC has achieved the most stable long-term pressure in the world in the range from 30 to 90 kPa. The pressure instability is less than 0.1 ppm (0.0032 Pa at 30 kPa, 0.009 Pa at 90 kPa), which can build the foundation for the success of SPRIGT.

Stability of objects in fluid flow is an interesting and significant subject in many fields. From thermodynamics point of view, the constructal law by Bejan et al. proposed that in some scenario, objects tend to be stable when the drag reaches maximum. To investigate the relation between drag and stable positions, we analyzed two simple cases by the finite element method: an elliptical cylinder and a rectangular cylinder immersed in 2D uniform laminar flow. The ellipse is stable when its major axis is perpendicular to the mainstream and the drag reaches maximum; yet the rectangle is stable when the length is perpendicular to the mainstream, with drag ranging from minimum to maximum depending on its aspect ratio. Our results show that there is no universal relation between drag and stability. Keywords: Stability, Constructal law, Laminar flow, Computational fluid dynamics

A thermoelectric generator was applied to the liquid air energy storage system to utilize the excess heat, whereas their coupled thermodynamic characteristics were rarely reported. This article conducted the thermodynamic and parametric analyses on system performance in detail. The effects of the hot water mass flow and outlet temperature of thermoelectric generator, the discharging pressure, and stages of expansion on the performance were investigated. The results showed that the hot water outlet temperature had significant impact on the thermoelectric and energetic characteristics. The optimal hot water outlet temperature of 60–80 °C and discharging pressure of around 16 MPa improved the efficiency by 1.7%. In addition, two different configurations of the thermoelectric generator were presented based on the effective cold energy utilization of the air turbine exhaust. The economic analysis indicated that compared with the organic Rankine cycle and Kalina cycle, the use of thermoelectric generator had economic advantage with a payback period of 2.99 years at an investment cost of $10703.

The novel concept of “low pressure drop instead of the low temperature difference to obtain high heat flux” is proposed to improve the performance of recuperator for Hampson cryocoolers. The equivalent temperature Teqva is introduced to repaint the T-Q diagram for intuitively observing the variation of the total exergy destruction in different structures in this study. By substituting the total exergy destruction for the heat transfer exergy destruction, the flow resistance is also considered in the recuperator optimization. It is discovered that the recuperator with first-dense-then-sparse type structure reduces the average equivalent temperature greatly, leading to lower exergy destruction. Otherwise, the non-isometric structure offers the possibility to gain both larger heat flux and decreased flow resistance at the same time. With the pressure-enthalpy diagram analysis, the favourable temperature behaviour is explained. The supercritical fluids in the recuperator of Hampson cryocoolers can obtain lower enthalpy when higher temperatures and pressure are obtained at the same time. Therefore, the optimization of the recuperator should not only concentrate on improving the temperature difference but also on reducing the pressure difference. And the average equivalent temperature will be an effective parameter to evaluate the performance of the recuperator in the future study.

Free piston Stirling engine is a popular area of research in high-efficiency thermal power conversion technology. However, owing to its strong coupling, nonlinearity, and parameter interactions, building an effective model to predict the performance is of great importance. This study was to investigate and derive the prediction models of a nonlinear free-piston Stirling engine using response surface methodology and artificial neural network. The interactive influences of thermodynamic and dynamic parameters which have significant effects on the amplitudes of the displacer and piston, operating frequency, and output power were illustrated in detail. Also, error analyses were then performed between the simulated and predicted values for both methods by comparing the mean absolute percentage errors, mean-squared errors, and correlation coefficients. The results indicated the correlation coefficients for the four output parameters from the response surface methodology as 0.9998, 0.9998, 0.9999, and 0.9994, and approximately 95% of the output parameter data were predicted with

Jet pumps are widely used in thermoacoustic Stirling heat engines and pulse tube cryocoolers to restrain acoustic streaming and improve the system performance. In this paper, a regression model is presented to predict the acoustic streaming in a thermoacoustic Stirling heat engine (TASHE) with different structure parameters of the jet pump. These parameters include position, length, inner diameter and tapered angle. Response surface methodology (RSM) is used to study the relationship between structure parameters of jet pump and acoustic streaming. A regression model is developed to predict the acoustic streaming. The analysis of variance (ANOVA) is conducted to describe the rationality of regression model and examine the statistical significance of factors. In addition, the relationship between acoustic streaming and structure parameters of jet pump is presented using 2D contour and 3D surface plot. It reveals that small position, length, tapered angle and large inner diameter can help suppress acoustic streaming. Eventually, four random confirmation tests are performed to verify that the regression model can predict acoustic streaming reasonably. This work provides theoretical guidance for controlling acoustic streaming using jet pump.

In this paper, a three-dimensional numerical model of H-type finned tube heat exchangers has been built. In order to optimize its structure and improve its performance, Taguchi method is applied to investigate the influence of seven geometric parameters including slit width, row number, fin height, spanwise tube pitch, longitudinal tube pitch, fin thickness and fin pitch. Numerical simulations are performed on eighteen cases with different combinations of seven geometric parameters and the overall thermal–hydraulic performance and its characteristics of heat transfer and flow friction are discussed in detail. The results show that fin pitch and fin height play a significant role on the heat transfer characteristics while the flow friction characteristics are mainly affected by fin height, spanwise tube pitch and fin pitch. The intuitive analysis and analysis of variance show that fin pitch, fin height and fin thickness have much stronger influence on its overall thermal–hydraulic performance than the rest four parameters. Finally, the optimal parametric combination of the H-type finned tube is obtained with an improvement of overall thermal–hydraulic performance by 11.4–16% for Re in range from 9000 to 24,000.

In this study, to reveal the phase characteristics of a beta-type free piston Stirling engine (β-FPSE), a thermodynamic-dynamic coupled model is proposed and verified experimentally. With the phasor notation method, the influences of the heating temperature, cooling temperature, spring stiffness and damping coefficients on the phases of displacer and power piston, and the output performance are investigated. The results indicate that the phase angles of the displacer and power piston increase with the heating temperature, and decrease with the cooling temperature. In the variation of power piston phase with its spring stiffness, a point of temperature independence (PTI) is identified. In the variation in the power piston phase with the displacer damping coefficient, a point of damping balance (PDB) is identified. A hysteresis of the PDB will occur if the heating temperature increases. In addition, the output power and power angle are obtained at the same damping coefficient of the displacer, which is equal to the displacer damping coefficient at the PDB if the spring stiffness ratio is less than 3.31. Moreover, based on the PV diagrams of different spring stiffness and damping coefficients, the compression ratio and pressure ratio for the optimum output power and efficiency are determined, respectively.

Insufficient dynamic information on helium piping systems limits our ability to understand and identify thermoacoustic oscillation (TAO) phenomena in these systems. In this study, we investigate the associated oscillation behaviours and the effects of the temperature distribution steepness, S, and the inflection point position, x0, on the TAO characteristics through numerical simulations. The results indicate that x0 has a greater impact on the oscillation behaviour and is a decisive factor for oscillation-free operation. It is found that oscillation-free operation can be achieved when x0 = 0.9 m. To identify the nonlinear dynamic characteristics related to TAO, the original pressure time series are unfolded in phase portraits and Poincare maps. In contrast to the period-1 and period-2 limit circle oscillations at other positions, the trajectory at x0 = 0.9 m displays a transition from limit circles to a fixed point (zero amplitude), corresponding to a series of points including the point (0,0) in the Poincare map. Therefore, an approach of adjusting the inflection point position can be used to control the state of the TAO, and the transition in the nonlinear dynamic characteristics can be identified, which can also provide guidelines for designers to mitigate unfavourable TAO.

A reliable thermodynamic-dynamic coupled model for a gamma-type FPSE possessing nonlinear load damping coefficient has been proposed in this study. Simultaneously, the experimental results are compared with the model and a satisfactory agreement is obtained. The output power is predicted with less than 5% error under different hot-end temperatures. Then the amplitude of displacer and piston with time at different pistons’ positions are obtained, and the effects of load damping and nonlinear coefficients on the amplitude values of two pistons and output power are presented. Finally, a simulation study is carried out to investigate the sensitivity of thermodynamic-dynamic parameters to the amplitude of two pistons, operating frequency and output power, and the fitting formulas for evaluating the performance of FPSE are presented. It is found that the initial positions of two pistons have little effect on pistons’ amplitude in the FPSE nonlinear system. High charge pressure, hot-end temperature, and spring stiffness of the displacer can increase the output power and amplitude of the pistons while other parameters have a negative effect on them. The fitting equations have high accuracy. This work provides a reliable model and theoretical guidance for improving the FPSE’s performance.

A three-stage looped traveling-wave thermoacoustic system with high efficiency thermoacoustic conversion and acoustic power transmission potential is studied through computational fluid dynamics simulation. ωτ, an important dimensionless parameter representing the heat exchange efficiency of the system, is related to the efficiency of sound production and depends on the frequency, hydraulic radius and temperature of the regenerator. The influence of resonance tube radius on the system performance is analyzed, while the acoustic impedance and exergy loss of main components are given. The proposed unequal-radius resonance tubes help with the realization of acoustic power amplification and impedance matching. After parameter evaluation, the proportion of traveling wave in the whole system increases, and the impedance amplitude of some resonance tubes also becomes higher. The mechanism and effect of ωτ on the system performance are expounded. The simulation results show that when the ωτ is 5.7, acoustic power of 8.9 kW and relative Carnot efficiency of 53.1% are obtained, which are higher than the performance of the baseline model.

To achieve an uncertainty of 0.25 mK in single-pressure refractive-index gas thermometry (SPRIGT), the relative pressure variation of He-4 gas in the range 30 kPa to 120 kPa, should not exceed 4 ppm (k = 1). To this end, a novel pressure control system has been developed. It consists of two main parts: a piston gauge to control the pressure, and a home-made gas compensation system to supplement the micro-leak of the piston gauge. In addition, to maintain the piston at constant height, a servo loop is used that automatically determines in real time the amount of extra gas required. At room temperature, the standard deviations of the stabilized pressure are 3.0 mPa at 30 kPa, 4.5 mPa at 60 kPa and 2 mPa at 90 kPa. For the temperature region 5 K–25 K used for SPRIGT in the present work, the relative pressure stability is better than 0.16 ppm i.e. 25 times better than required. Moreover, the same pressure stabilization system is readily transposable to other primary gas thermometers.

A multiphase flow numerical model based on Eulerian is built to simulate the characteristics of subcooled boiling. The thermodynamic performance in a single rod channel with/without spacer grid are obtained by numerical simulation, and the influence of spacer grid on flow and heat transfer characteristics of subcooled boiling is studied. The model is verified by comparing with the experimental results. After passing through the spacer grid, the high-temperature zone departures from the surface of fuel rod moves towards the cold wall. This impact extends to a certain downstream distance, and then it gradually declines. The influence of different components in spacer grid on the pressure drop is detailed. The pressure drop with spacer grid is 5% higher than that without spacer grid, within the allowable design limitation. The maximum value of section average secondary flow can reach 13.5% of the inlet velocity, indicating that the mixing vanes have stronger ability to produce transverse flow. The influence length of spacer grid on heat flux partitioning is about 27Dh. The effect of spacer grid on the wall heat flux partitioning mainly lies in the decrease of the evaporation heat flux, benefited to reduce the risk of nuclear reactor approaching DNB.

In this study, the model basing on Monte Carlo ray tracing method is built to analyze the radiative energy loss in the polysilicon CVD reactor. It can be conveniently applied to arbitrary distribution with any number of silicon rods and solve the complex problem of radiative blockage between the rods effectively. The effects of the rod's number, thermal shield and surface emissivity on the radiative energy loss of CVD reactor were investigated in detail. Results show that the average saving energy rate is 39% when the rod number changes from 36 to 72, and it can reach 58% after using thermal shield in 72 rods reactor. Otherwise, results show that the computing time using the Monte Carlo ray tracing method only increased by 66.70% when the number of rod increased from 36 to 72, while the computing counts of cross-string method increased by 711.43%. Therefore, the model based on Monte Carlo ray tracing method is an efficient and fast way to design and optimize any complex CVD reactor in Siemens process and achieve the goal of energy conservation.

In this study, an artificial neural network model is built to predict the dynamic performance of a beta-type free piston Stirling engine. The influences of six input dynamic parameters on operating frequency, amplitude ratio and phase angle are analyzed. The operating frequency is significantly affected by the spring stiffness and the mass of the pistons. However, the relationships of the dynamic parameters are comprehensive, which are determined by multiple parameters. Then, a number of dynamic output parameters are used as training and testing data. The best results are obtained by 6-6-1, 6-6-1 and 6-10-6-1 network architectures for the operating frequency, amplitude ratio and phase angle respectively. For these network architectures, the back propagation algorithm, namely Levenberg-Marguardt is applied. Stirling engine’s dynamic performance predicted with the network model is compared with the actual values. After training, correlation coefficients (R2) values for training and testing data are close to 1. The mean relative errors of the operating frequency, amplitude ratio and phase angle are 0.85%, 2.78% and 3.19% for the training process. These results show that the artificial neural network model is an acceptable and powerful approach for predicting the dynamic performance of the beta-type free piston Stirling engine.

A novel non-isometric helically coiled heat exchanger, with first-dense-then-sparse type structure, was proposed to improve the performance of Joule-Thomson (J-T) cryocoolers. The physical model and analysis model of exergy destruction of this new non-isometric helically coiled heat exchanger were developed. The influence of three key geometrical parameters (the separation position i, the fin pitch of the dense part fp1, the fin pitch of the sparse part fp2) on the performance of heat exchanger were investigated, and the structure of recuperator was further optimized using response surface methodology (RSM). The results show that the total exergy destruction of the optimum recuperator decreased by 8% and the material consumption reduced by 4%. Furthermore, the refrigeration capacity increased by 9%, which proves the potential of this novel non-isometric helically coiled heat exchanger in heat transfer performance and material consumption. This study provides helpful guidance for geometrical optimization of the recuperator for J-T cryocoolers.

In a thermoacoustic engine, the ratio of the plate spacing to the thermal penetration depth crucial to the performance and efficiency of thermoacoustic conversion. However, the temperature gradient in the regenerator or stack causes the non-uniform distribution of the thermal penetration depth. In this paper, the thermoacoustic stack comprised of converging channels has been put forward and applied in a standing wave thermoacoustic engine. The influence of the ratio of the plate spacing to the thermal penetration depth at the cold end of the stack, yc/δkc, on the performance parameters of different models is investigated in detail. Results show that suitable value of yc/δkc in parallel and converging stack models can improve the acoustic power and efficiency. It is also found that the converging stack can basically replace the parallel stack with the same yc/δkc and reduce the cost of consumptive materials. A dimensionless parameter β is defined to evaluate the comprehensive performance of thermoacoustic engine and used to guide the design of the stack.

The Internet applications, such as network searching, electronic commerce, and modern medical applications, produce and process massive data. Considerable data parallelism exists in computation processes of data-intensive applications. A traversal algorithm, breadth-first search (BFS), is fundamental in many graph processing applications and metrics when a graph grows in scale. A variety of scientific programming methods have been proposed for accelerating and parallelizing BFS because of the poor temporal and spatial locality caused by inherent irregular memory access patterns. However, new parallel hardware could provide better improvement for scientific methods. To address small-world graph problems, we propose a scalable and novel field-programmable gate array-based heterogeneous multicore system for scientific programming. The core is multithread for streaming processing. And the communication network InfiniBand is adopted for scalability. We design a binary search algorithm to address mapping to unify all processor addresses. Within the limits permitted by the Graph500 test bench after 1D parallel hybrid BFS algorithm testing, our 8-core and 8-thread-per-core system achieved superior performance and efficiency compared with the prior work under the same degree of parallelism. Our system is efficient not as a special acceleration unit but as a processor platform that deals with graph searching applications.

In this paper, a two-dimensional axisymmetric model of a thermoacoustic Stirling engine with a short tube where the cross section narrows has been developed. The transient streamlines and vortex formation through short tubes with different diameters in oscillatory flow have been investigated visually by computational fluid dynamics. Three dimensionless parameters, Reynolds number (Re), Keulegan-Carpenter number (KC), and Womersley number (Wo), are used to describe the flow regime and vortex characteristic throughout the short tube. High Re and Wo numbers indicate that the oscillatory flow develops into the turbulent flow through the short tube. The KC number has a direct effect on the transition of streamlines and the development of the vortex. For a small cross section where KC ≈ 1, streamlines rotate and the vortex forms at both sides of the short tube. The vortex stays in the main flow region, and intensity varies as streamlines are convected downstream. The velocity along the radius presents a Poiseuille profile within the influence of the vortex. For a large cross section where KC