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In order to improve the thermal conductivity of pure paraffin (RT4) which is regarded as cool storage of phase change material (PCM), four kinds of paraffin-carbon nanotubes cool storage of composite PCMs are prepared by adding different amount of carbon nanotube (CNT) into paraffin, and their thermo-physical properties are tested by using differential scanning calorimeter (DSC) and laser thermal conductivity meter. The results show that, with the increasing of carbon nanotubes, the phase transition temperature of the cool storage of composite PCMs diminishes, phase change latent heat dwindles while thermal conductivity gradually increases. Compared with the pure paraffin, increase in mass fraction of carbon nanotube 3% can provide an increase in thermal conductivity of the solid and liquid 30.3% and 28.5%, and a reduce in the melting and solidification phase change latent heat of composite PCM 8.9% and 9.3%, respectively. Further investigation applies the composite PCMs into the shelf of vertical open -type refrigerated display cabinet to improve the performance. The results show that the shelf filled with the composite PCMs can decrease the internal temperature of the VORDC and temperature fluctuation during the defrosting period. Compared with the ordinary shelf, the lengthways and depthwise temperature different of composite shelf filled into only RT4 reduce by 80.0% and 7.6%, respectively; the lengthways and depthwise temperature different of composite shelf filled into 3%-CNT composite PCMs reduce by 92.0% and 12.2%, respectively. It indicates that the composite PCMs further increases the thermal conductivity of composite shelf and improve the performance of VORDC.

The two-dimensional steady-state heat conduction in irregular geometry is solved by a MLPG–FVM coupled method. The meshless local Petrove–Galerkin (MLPG) method is applied to the sub-region with skewed wall surface while the finite volume method (FVM) is used in the rest of the domain. The Dirichlet–Dirichlet method is adopted to couple the temperature between MLPG and FVM methods. In MLPG method, the Dirac's Delta function is taken as the test function to avoid the local domain integration which does not need the numerical integration and the solution is independent of the size of the test function. The proposed MLPG–FVM method is validated and proved to be an efficient numerical method for 2-D heat conduction in irregular geometry, which can exert their own advantages of MLPG and FVM.

Hollow silica nanosphere packings (HSNSPs) can significantly suppress heat conduction through solid and gas phases due to the voids, small interparticle contact areas, and nanosized pores, showing promising potentials towards energy-efficient building applications. The HSNSPs display a two-level structure, where the solid silica nanoparticles form the shells of hollow spheres, and the accretion of hollow spheres form the porous powder packing structures. Investigating thermal transport in HSNSPs helps to understand the fundamental thermal transport processes and to guide the design of their geometric structures. Herein, we developed a numerical model based on the two-level structure of HSNSPs to explore their effective thermal conductivities. The developed numerical model considers the geometric parameters such as sphere size, shell thickness, interparticle contact resistance, and the gas pressure inside and outside the hollow spheres. The developed numerical model was validated by the measured thermal conductivities of HSNSPs fabricated via the sacrificial template method. The results show that the effective thermal conductivity of HSNSPs can be reduced by decreasing sphere diameter, contact area and shell thickness. The influence of ratio of contact diameter to sphere diameter on the effective thermal conductivity becomes weaker as the hollow sphere size decreases (e.g.

Hollow fiber-based porous structures (HFPSs) demonstrate promising potentials in thermal insulations. However, the thermal transport in HFPSs was not explored yet. Herein, we developed a unit cell model to explore the effect of both geometric and thermophysical parameters on the effective thermal conductivity of HFPSs. The predictions from the developed model agree with the experimental data in the literature. The modeling results show that decreasing external hollow fiber diameter, shell thickness, the thermal conductivity of solid backbone, and gas pressure can reduce the effective thermal conductivity of the HFPSs. The effective thermal conductivity of the HFPSs trends to that of stationary air (0.026 W/(m⋅K), 300 K, 1.0 atm) as porosity increases. Reducing the pore size to nanometer-scale or decreasing the gas pressure is the most effective way to achieve a thermal conductivity below that of stationary air. This work guides the structural design and optimization of HFPSs as lightweight super-thermal insulating materials.

It is challengeable to obtain the stable and accurate solutions of convection-diffusion problems with large Peclet number (Pe) since the convection term may cause oscillation solutions at large Pe. In this paper, a unit operator (first level) and an orthogonal project operator (second level) are constructed to act as the stability terms for meshless local Petrov-Galerkin (MLPG) method, which is called a two-level variational multiscale MLPG (VMS-MLPG) method. The VMS-MLPG method is applied to eliminate oscillation, overshoots and undershoots of MLPG method at large Pe. The prediction accuracy and the numerical stability of the proposed method for the Smith-Hutton and the Brezzi problems are analyzed and validated by comparing with the MLPG method and the finite volume method (FVM) with various difference schemes. It is showed that the present VMS-MLPG method can guarantee the stable and reasonable solutions of convection-diffusion problems with large Peclet number.

A meshless local Petrov–Galerkin (MLPG) approach based on the streamline upwind (SU) idea and the variational multiscale (VMS) concept, called as VMS-SUMLPG method, is herein proposed to solve the ...

Pseudomonas fluorescens 2P24 produces 2,4-diacetylphloroglucinol (2,4-DAPG) as the major antibiotic compound that protects plants from soil-borne diseases. Expression of the 2,4-DAPG biosynthesis enzymes, which are encoded by the phlACBD locus, is under the control of a delicate regulatory network. In this study, we identified a novel role for the outer membrane protein gene oprF, in negatively regulating the 2,4-DAPG production by using random mini-Tn5 mutagentsis. A sigma factor gene sigX was located immediately upstream of the oprF gene and shown to be a positive regulator for oprF transcription and 2,4-DAPG production. Genetic analysis of an oprF and sigX double-mutant indicated that the 2,4-DAPG regulation by oprF was dependent on SigX. The sigX gene did not affect PhlA and PhlD expression, but positively regulated the level of malonyl-CoA, the substrate of 2,4-DAPG synthesis, by influencing the expression of acetyl-CoA carboxylases. Further investigations revealed that sigX transcription was induced under conditions of salt starvation or glycine addition. All these findings indicate that SigX is a novel regulator of substrate supplements for 2,4-DAPG production.

In order to improve the performance of refrigerated display cabinet, decrease the food temperature, improve the uniformity of food temperature and restrain the temperature fluctuation during the defrosting time, a new kind of composite shelf is designed for the food vertical open refrigerated display cabinet (VORDC), which is based on the heat pipe technology and the cool storage characteristics of phase change materials (PCMs) among the heat pipes. Experimental results show that the novel composite shelf can enhance the heat transfer between food and shelf, reduce the core temperature of food, decrease temperature fluctuation in defrosting process and reduce the temperature difference along height, width and depth direction. Compared with the normal shelf, the temperature differences of food packages on both sides of the composite shelves (RT3, RT4 and RT5) are reduced by 40%, 80% and 40%, respectively. The average temperature of food packages is reduced by 13.7–32% and the temperature fluctuation of food packages is reduced by 53.3–83.3% during defrosting. For these kinds of composite shelves, the temperature of food packages of RT4 composite shelf is lowest, and the average temperature of food packages at each layers and rows are controlled in 5 °C. This novel composite shelve can effectively reduce the temperature rise during defrosting, and improve the performance of VORDC obviously.

Paraffin is widely used in medium- and low-temperature storage because of its excellent properties. To improve thermal conductivity of paraffin, carbon nanomaterials filler with high thermal conductivity was gradually added to. In this paper, composite phase change materials (PCMs) composed of cold storage paraffin with a phase transition temperature of 4°C and two types of high thermal conductivity nanoparticles, graphene nano-platelets (GNPs) and carbon nanotubes (CNTs), were selected and prepared by mechanical separation with a suitable dispersant. The relationship between thermal conductivity and standing time of two composite PCMs revealed that the thermal conductivity of the composite PCMs of GNPs/paraffin and CNTs/paraffin remained stable at room temperature for 20 days and 40 days, respectively. When the mass fraction of GNPs or CNTs is 5%, the thermal conductivities of the composites, which are 0.266 W / ( m·K ) and 0.250 W / ( m·K ) , respectively, increase the most. Compared to those of pure paraffin and the CNTs/paraffin composites, the DSC curves of the GNPs/paraffin composites moved forward due to the higher thermal conductivity of the composite PCMs, which was more accurate for the experimental operation procedure. Due to the different structure and arrangement of particles, the latent heat of CNTs/paraffin was slightly lower than that of GNPs/paraffin with the same mass fraction of paraffin. The composites exhibited stable and excellent phase transition characteristics after 100 melting and solidification cycle tests.

Nanoporous insulating materials are of importance for applications such as energy-efficient buildings, energy storage and savings, and cryogenic engineering. Recent progress on manufacturing technology has enabled the fabrication of ordered nanostructures to be practical, providing a possibility to fabricate high-performance insulation materials. In this work, three kinds of nanoporous insulating materials with regular geometric structures and controllable thermal conductivities, including a simple cubic packing, a face-centered cubic packing, and a cubic array of intersecting spheres packing of uniform-sized hollow nanospheres, were designed. The effective thermal conductivity models of each packing structure were developed according to the assumption of one-dimensional heat transfer, in which the following factors including material types, size of the hollow nanosphere packing structure (e.g., sphere size, spherical shell thickness, contact ratio), gas pressure, the rarefaction effect of gas and the mean free path of phonons were considered. The developed models of the hollow nanosphere packing structures were validated by the experimental results from the literature. It is found that the effective thermal conductivity can be lowered to ~ 0.01 W/(m⋅K) by tuning the packing style and size of hollow nanosphere packing structures in the room environment, showing excellent thermal insulation performance. The work provides a new strategy for the design of super-insulation materials.

The uneven distribution of refrigerants in tube of a microchannel heat exchanger has a serious impact on the performance of the microchannel heat exchanger. The addition of a deflector in the microchannel heat exchanger can play a role in the secondary distribution. The difference in structure significantly affects the distribution uniformity of the refrigerant. In this paper, air and water are used as two-phase working fluids, and the effect of inserting a deflector on the distribution uniformity of the fluid in the header of a parallel flow heat exchanger with horizontal round tubes and 24 parallel flat tubes is studied. The superficial velocity ranges of the gas and liquid were 2.47–3.04 m/s and 0.67–0.86 m/s, respectively. Six kinds of deflector structures were studied in the experiment, in which the total cross-sectional area of the deflector and the total flow area of the flat tubes were tested as both different and the same. The experimental results show that under the experimental conditions, the uniformity of the gas and liquid distributions in the three-symmetrical deflector structure is better, followed by the two-symmetrical deflector structure, and then the uniform aperture deflector structure is the worst. Through a comparative analysis of these six deflector structures, the distribution uniformity of the gas and liquid two-phase fluid in the A1 variable-aperture deflector is the best. The open-area of the deflector is 670.39 mm2, which is the best value and is different from the total flow area of the flat tubes.

To help customers to estimate the result of product configuration during design, a new evaluation model was developed. Combining advantages of AHP and FCEM, the model took CSR as the goal, based on F-AHP. Dividing customer demands into different groups, the model had multiple structural layers. It took customer demands as target layers, evaluation indexes as criterion layers, and satisfactions as scheme layers. Triangular fuzzy membership function helped to define the relationship between the upper and lower level of structural layers. Then the method of weighted distance minimum integrated the weight of all experts for each criterion layer as the fuzzy weight of each layer. Linear weight integrated all expert evaluation. Finally, total utility of each evaluation was calculated from bottom to top, namely total satisfaction. So the maximum total utility was the evaluation result. Through analyzing the configuration result of grader, it verifies the feasibility of evaluation methods, and the rationality of the evaluation model.

Delta winglet works better than other vortex generators in improving the performance of fin-tube heat exchangers. In this paper, Response Surface Approximation is used to study the effects of the fin pitch, the ratio of the longitudinal tube pitch to transverse tube pitch, the ratio of both sides V 1 , V h of delta winglets and the attack angle of delta winglets on the performance of fin-tube heat exchanger. Firstly, Twenty-nine numerical group experiments including five times repeated experiments at the central point are conducted. Then, the analyses of variable (ANOVA) and regression are performed to verify the accuracy of the polynomial coefficients. Finally, the optimization of the fin-tube heat exchanger using the Genetic Algorithm is conducted and the best performance of j/f (1/3) is found to be 0.07945, which is consistent with the numerical result.

This paper focuses on improving the performance of the vertical open refrigerated display cabinets (VORDC) by optimizing the structure of deflector, which is affected by inlet velocity and velocity distribution of air curtains. The results show that the temperature of products located at the front and at the rear reduces as the increases of inlet velocity of air curtains. The increase of the inlet velocity of air curtains can strengthen the disturbance inside the VORDC, and also decrease the temperature of products inside the VORDC; the increase of the outer velocity of air curtain will exacerbate the disturbance outside the VORDC and decrease air curtain’s performance. The present study can provide a theoretical foundation for the design of VORDC.

A multi-scale approach has been formulated in a previous work. The influence of HVAC system in supermarket on the performance of vertical open refrigerated display cabinet (VORDC) is considered. The influence is evaluated by varying the supply air temperature and velocity at the diffusers of HVAC. The computational results show that there is a direct interaction between the HVAC system and VORDC in supermarket. When the supply air temperature of HVAC system decreases from 19 °C to 16 °C, the electricity energy input in VORDC system decreases by 6.36%, and the highest products temperature is reduced by 0.18 °C. When the diffuser supply air velocity of HVAC system increases from 2.0 m/s to 3.5 m/s, the energy input in VORDC system decreases by 23.4%, and the highest product temperature reduces by 0.4 °C.

The heat transfer and fluid flow characteristics of a new type of fin with built-in interrupted delta winglets is studied in this paper by three-dimensional numerical simulation. In order to ensure reliability of numerical model, plate fin with common-flow-up delta winglets is firstly simulated. The comparison of numerical and experimental results shows a maximum deviation of 11.4% within the entire range of Reynolds number. The computational results show that heat transfer capacity and overall performance increase by 35–60% and 19–64%, respectively. The flow field visualization shows that the interrupted delta winglets can produce longitudinal vortices at the rear of delta winglets and reduce the wake zone behind the tube, so the proposed fin can enhance heat transfer accompanied by low pressure loss. The field synergy theory and entransy dissipation extremum principle are employed on analyzing the mechanism of heat transfer enhancement. The results indicate that enhancement heat transfer mechanism of in...

The numerical simulation of the methanol synthesis process by using HT-L pulverized coal gasification is studied in the work. Pulverized coal gasification are simulated by Aspen Plus industrial systems flower software, and the optimum condition can be gained by calculation. The pulverized coal entrained-flow gasifier adopts the minimization method of Gibbs free energy. Under the given conditions of 1500°C and carbon conversion of 99%, when coal flow volume is 3265.87 kg/h and the ratio of air and coal is 4:1, the content of effective gas is maximal, and also the content of effective gas increased with increasing of the pressure.

The composite fin is presented based on the advantage of longitudinal vortex generator and slit fin, respectively. The performance of air-side heat transfer and fluid flow is investigated by numerical simulation for Reynolds number ranging from Re = 304 to 2130. Stepwise approximation method is applied on the mesh generation for the irregular domains of delta winglets and slit fins. The mechanism for augmenting heat transfer is also analyzed based on the local fluid field, field synergy principle and entransy dissipation principle. The computational results show that some eddies are developed behind the X-shaped slit and delta winglet, which produce some disruptions to fluid flow and enhance heat transfer; compared with plain fin and slit fin, it shows the composite fin has better heat transfer performance. By applying on the field synergy principle and entransy dissipation principle to analyze the composite fin, the computational results show that composite fin can improve the synergy of temperature gradient and velocity fields, and its equivalent thermal resistance is smaller and its irreversibility of heat transfer is lower.

In this paper, the effect of the back panel structure on the performance of fluid flow and heat transfer of vertical open refrigerated display cabinets (VORDC) is presented by experiments and numerical simulation. Experimental tests are performed to validate the accuracy of numerical predictions. The characteristics of heat transfer and fluid flow of VORDC are investigated at the different locations of the perforations of back panel at the same porosity and the different flow ratios between back panel and air curtain at different porosities. By comparing numerical results with experimental results, the predictive abilities of the computational model have been revealed. Further computational results have also shown that less than 3% porosities can provide a better performance in the VORDC; the location of perforations has a minor influence on the temperature distribution of products. Furthermore, the suitable porosities in the back panel among the shelves are more likely to improve the uniformity of products temperature in the VORDC. As a result, the overall uniformity of product temperature inside the refrigerated display cabinet and the maximum deviation values of product temperature have been improve to 41% and 49%, respectively. The present study can provide the theoretical guide for the design of the narrow VORDC.

In this paper, the semi-dimpled slit fin is proposed and the characteristics of heat transfer and fluid flow are analyzed based on the orthogonal experiment design method. A serial studies on the effects of fin pitch, arrangement of semi-dimple, dimple radius on heat transfer and flow characteristics of semi-dimpled slit fin are investigated. The computational results show fin pitch (Fp) has significantly effected on the performance of heat transfer and fluid flow, the influence of arrangement of semi-dimple, the dimple radius (R) and the opening direction of semi-dimples dwindle. At the same time, compared to the general semi-dimpled slit fin, the heat transfer coefficient and JF factors of the optimized fin increase by 10.7–25.1 and 2.6–7.7 %, respectively. When Re ≤ 1,521, the overall performance of slit fin is better than that of optimized fin; while Re > 1,521, the overall performance of optimized fin is better than that of slit fin. Finally, the performance evaluation plot of enhanced heat transfer of heat exchanger is applied to analyze the optimized fin, it can be seen that optimization fin have better heat transfer performance under the same power consumption.

A real-time mechanism as a level of electricity price is proposed to dispatch electric vehicle fast charging load. Considering the peak load shifting effect of grid, the benefit of charging station and the desire of customer, the mathematics model is built. And a genetic algorithm is used to solve this problem. Finally, a simulation based on an areas predicted data of year 2020 is made to show that the proposed method can lower the peak-valley difference, promise charging station benefit as well as meet customers desire, and achieve a win-win result.

The calculation of the gas radiation process plays an important role in the study of atmospheric remote sensing and climatic effects of greenhouse gas. The remote sensing of rocket plume has important significance for early warning, interception, detection, identification and tracking of flight vehicle. A model was established to calculate the remote sensing signal of rocket plume by wide band k-distribution, the liquid rocket plume remote sensing signals in atmospheric window region and the detectors’ working spectrum are calculated, and the results were compared with the results calculated by line-by-line approach. The results showed that in some of the detectors’ working spectral regions, the wide band k-distribution model can be used for the calculation of the remote sensing of liquid rocket engine exhaust plume.

The performance of the CO2 trans-critical system is affected significantly not only by optimal system pressure but also by instantaneous ambient temperatures. This paper presents the results of a study carried out to elucidate the influence of the source and sink temperatures on the experimental research of a CO2 trans-critical refrigeration and heat pump system which used a new dual expansion valve and a balance CO2 liquid receiver adjustment device. The unit had been fully tested along a multistate experimental study, at various evaporating temperatures and different gas cooler outlet pressures. The results showed that: the source and sink temperatures rose from 15°C to 25°C, trans-critical CO2 systems COPH average increase of 4.4% each 5°C, but COP decrease of 6.8%. The influence of the source temperature on the chilled water outlet temperature which is less than the sink temperature. The effect of the source or sink temperature on the cooling water outlet temperature to average every 5°C to change the range of from 0.7°C to 1.9°C.

This work present the experimental evaluation of the energy performance of trans-critical CO2refrigeration and heat pump systems. The optimal gas cooler pressure and the optimal COP have been analysed from a thermodynamic point of view. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler outlet pressures (75 to 120bar). It is concluded that: With the the internal heat exchanger (IHX) system compressor power is relatively low, when the high side pressure is over 100bar, and the evaporation temperature is below 0°C. The COP of the system without IHX is slightly higher than the system with the IHX, it is increase about 3% to 5%, when the evaporation temperature is over 5°C.

The numerical solution of the convection–diffusion equation represents a very important issue in many numerical methods that need some artificial methods to obtain stable and accurate solutions. In this article, a meshless method based on the local Petrov–Galerkin method is applied to solve this equation. The essential boundary condition is enforced by the transformation method, and the MLS method is used for the interpolation schemes. The streamline upwind Petrov–Galerkin (SUPG) scheme is developed to employ on the present meshless method to overcome the influence of false diffusion. In order to validate the stability and accuracy of the present method, the model is used to solve two different cases and the results of the present method are compared with the results of the upwind scheme of the MLPG method and the high order upwind scheme (QUICK) of the finite volume method. The computational results show that fairly accurate solutions can be obtained for high Peclet number and the SUPG scheme can very well eliminate the influence of false diffusion.

It is well known that convection-diffusion equations suffer from the most difficult problems to gain a stable and accurate solution. Sometimes, the convection terms may cause oscillatory behavior of solutions. In this article, the streamline upwind Petrov-Galerkin (SUPG) scheme is applied to eliminate overshoots and undershoots produced by the convection term in the meshless local Petrov-Galerkin (MLPG) method. The accuracy and stability of the present method are discussed using two test cases. The results of the present method are compared with results of other upwind schemes and the finite volume method (FVM) using a high-order upwind scheme. Our analysis shows that the present method, with its simple implementation, can give excellent results for convection-dominated problems.

In this paper, three-dimensional numerical simulation is conducted on the flow and heat transfer process for elliptical tube heat exchanger with rectangular vortex generators and triangular vortex generator by Fluent software, respectively, and the performance for elliptical tube heat exchanger with plate fin is compared. The results show that the Nusselt number increases with the increase in Reynolds number for the inlet velocity range from 1 to 5m/s, friction coefficient decreases with the increase in Reynolds number; at the same Reynolds number, Nusselt number for fin with Vortex Generators and friction coefficient are higher than that of elliptical tube with plate fin ; the vortex generator shape and angle of attack have a great impact on the comprehensive performance within a simulated attack angle and the velocity, at the same pump power, the comprehensive performance for heat exchanger with the rectangular vortex generator increase up to 10%.

In this article, the weighted least-squares collocation method (WLSCM) is adopted to deal with two- and three-dimensional heat conduction problems in irregular domains. A radial basis function (RBF) is selected to construct the approximation function. To improve the accuracy and stability, some auxiliary points are increased within the domain of interest. Only inner nodes are used to construct the approximation function, and the equilibrium equations are satisfied not only at collocation points but also at auxiliary points, so the equations should be solved in a least-square sense. A 2-D case that has an analytical solution is simulated by the proposed method and the outcome verifies that the present method can obtain desired accuracy and efficiency. Then the current method is adopted to compute one 2-D and two 3-D cases of engineering heat conduction problems in irregular complex domains. The results show that the present method can deal effectively with the heat conduction problems of both 2-D and 3-D i...

In this paper, the meshless local Petrov-Galerkin (MLPG) method is extended to solve the incompressible fluid flow problems. The streamline upwind Petrov-Galerkin (SUPG) method is applied to overcome oscillations in convection-dominated problems, and the pressure-stabilizing Petrov-Galerkin (PSPG) method is applied to satisfy the so-called Babuska-Brezzi condition. The same stabilization parameter @t(@t"S"U"P"[email protected]"P"S"P"G) is used in the present method. The circle domain of support, linear basis, and fourth-order spline weight function are applied to compute the shape function, and Bubnov-Galerkin method is applied to discretize the PDEs. The lid-driven cavity flow, backward facing step flow and natural convection in the square cavity are applied to validate the accuracy and feasibility of the present method. The results show that the stability of the present method is very good and convergent solutions can be obtained at high Reynolds number. The results of the present method are in good agreement with the classical results. It also seems that the present method (which is a truly meshless) is very promising in dealing with the convection- dominated problems.

In this article, the meshless local Petrov–Galerkin (MLPG) method is applied to compute two steady-state heat conduction problems of irregular complex domain in 2D space. The essential boundary condition is enforced by the transformation method, and the MLS method is used for interpolation schemes. A numerical example that has analytical solution shows the present method can obtain desired accuracy and efficiency. Two cases in engineering with irregular boundary are computed to validate the approach by comparing the present method with the finite volume method (FVM) solutions obtained from a commercial CFD package FLUENT 6.3. The results show that the present method is in good agreement with FVM. It is expected that MLPG method (which is a truly meshless) is very promising in solving engineering heat conduction problems within irregular domains.

High-bay depot plays an important role in the storage industry. Due to large and high space of high-bay depot, it is difficult to make temperature distribution uniform, which will influence the storage time of raw materials. In this paper, the aim is to find the reasonable air supply and energy-saving method; a supply-air method of high-bay depot is investigated as an example. The results show the radius and spacing of the supply-air inlet have great influence on temperature distribution. The temperature nonuniformity coefficient of summer is smaller than that of winter. The investigated results can provide a theoretical reference for the high-bay depot design and economic operation.

The power loss and voltage distribution of distribution network are closely related to the site and size of DG and the load distribution. A new method of DG optimal placement is proposed based on load centroid. The district DG supplied is thought as an irregular shape load block and the load size is thought as quality. The power loss is the least when the DG is installed at the load centroid. The load weight is introduced according to the reliability requirement of load to ensure the continuity and reliability of power supply to the important load. This method avoids the complicated process of traditional optimization algorithms. Finally, through the simulation example, the method is prove to be effective and accurate.

A fast and efficient method based on the proper orthogonal decomposition (POD) technique for predicting fluid flow and heat transfer problems is proposed in this paper. POD is first applied to an ensemble of numerical simulation results at design parameters to obtain the empirical coefficients and eigenfunctions, and then the fluid and temperature fields in the range of design parameters are resolved by a linear combination of empirical coefficients and eigenfunctions. The empirical coefficients at off-design parameters are obtained by a cubic spline interpolation method for steady problems and a Galerkin projection method for transient problems. Finally, the efficiency and accuracy of the algorithm are examined by three examples. The POD based algorithm can predict both the velocity and temperature fields in the range of design parameters accurately at a price of a large number of precomputed cases (snapshots). It also brings significant computational time savings for the new cases within the parameter range presimulated compared with the finite volume method with SIMPLE-like algorithm.

The dimpled fin has excellent heat transfer performance and has attracted a lot of attention to apply on the fin and tube heat exchanger. A study presents to investigate the effects of number of tube rows on the air-side heat transfer characteristics of dimpled fin for velocity ranging from 1 to 3 m/s. The Q/Δ P and Q/((Δ P × V)) are used to evaluate the heat transfer performance of the heat exchanger. The results show that the dimpled arrangement can change the mainstream direction, increase the disturbance, and enhance the heat transfer. With the increase of the number of tube rows, the average Nusselt number decreases and Q/Δ P and Q/((Δ P × V)) increase gradually. Compared with the multipipe tube rows, the performance of two-row tube is better.

This work presents the experimental evaluation of the energy performance of transcritical CO2 refrigeration and heat pump systems. The optimal gas cooler pressures and the optimal COP have been analyzed from a thermodynamic point of view. The systems used a new dual expansion valve and a balance CO2 liquid receiver adjustment device, which can control high and low side pressure effectively. Moreover, we demonstrate the influence of the internal heat exchanger (IHX) on the systems' performances, on the basis of the analysis of the relative COP index RCOPI, the compressor power index RPCI and other parameters which can confirm the truth of. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler pressures (75 to 120 bar). It is concluded that with the IHX system, compressor power is relatively low when the high side pressure is over 100 bar, and the evaporation temperature is below 0°C. The COP of the system without the IHX is slightly higher than the system with the IHX; it is increasing about 3% to 5%, when the evaporation temperature is over 5°C. Relative to the single expansion process, the dual expansion cycle can decrease the influence of pressure fluctuations of CO2 supercritical fluid and liquid mixture on the systems.

In this paper, the Meshless Local Petrov-Galerkin (MLPG) method is applied to compute convection-dominated flow problems. The results of the MLPG method are compared with the results of the finite volume method. The results show that the first-order upwind (FUD) scheme exhibits the false diffusion at a larger-Peclet number; the QUICK scheme and the MLPG method can obtain much closed solutions; but they have small overshoots produced at larger-Peclet number. The results also indicate that the MLPG method is a highly effective and accurate numerical method to deal with convection-dominated flow problems and can eliminate the effect of the false diffusion.