Ф5mm管径换热器在热泵空调上的应用研究

基于一台热泵风管机重新设计了Ф5mm管径蒸发器和冷凝器,对原换热器和Ф5mm管径换热器的性能、成本、分路设计进行分析研究。结果表明,采用Ф5mm管径换热器能够提高空调的性能,降低开发成本。设计Ф5mm管径换热器时,应在流程长度和分路数目之间进行平衡优化,单分路流程长度可控制在4～6m。     

R290微通道冷凝器性能优化及其充注量分析

采用仿真方法,以R290家用空调器用微通道冷凝器为研究对象,比较不同流路布置方案对冷凝器性能的影响,并对外形尺寸相同的微通道冷凝器与翅片管冷凝器充注比进行对比。结果表明：流程布置及各流程扁管分配对微通道冷凝器性能有较大影响,存在较优的流程数及流程扁管数;R290微通道冷凝器充注比与Ф5mm单排冷凝器充注比水平相当,经进一步结构优化后,微通道冷凝器将比小管径换热器在降低冷凝器充注比和材料成本方面具有更大的潜力和优势。     

Influence of the contacting scheme in simulations of radial silicon nanorod solar cells

Silicon nanorod solar cells were simulated using the Silvaco Technical Computer Aided Design (TCAD) software suite. For reasons of speed optimization the simulations were performed in cylinder coordinates taking advantage of the model's symmetry. Symmetric doping was assumed with a dopant density of 10¹⁸ cm⁻³ in the p-type core and in the n-type shell, and the location of the pn-junction was chosen such that the space charge region was located adjacent to the shell surface. Two contact configurations were explored. In configuration A the cathode contact was wrapped around the semiconductor nanorod, while in configuration B the cathode was assumed just on top of the nanorod. In both cases the anode was located at the bottom of the rod. Cell efficiency was optimized with regard to rod radius and rod length. Optimization was performed in a three-step procedure consisting in radius optimization, length optimization and again radius optimization. A maximum in efficiency with respect to rod length L was visible in configuration A, leading to an optimum value of L = 48 μm. This maximum is explained by the combination of an increase of short-circuit current density J_sc and a decrease of open-circuit voltage U_oc with L. In configuration B, J_sc also increases with L, but U_oc stays rather constant and the maximum in efficiency only appears at very large values of L ≈ 12 mm. We restricted the rod length to L ≤ 100 μm for further optimization, in order to stay in an experimentally feasible range. During the optimization of rod radius R in configuration A the open circuit voltage increased continuously, while short circuit current density stayed rather constant. This leads to an increase in efficiency with R, which only stops at very large radii, where R starts to be comparable with L. In configuration B efficiency is almost independent of R, provided that the radius is large enough to comprise a well-formed space charge region, here only a shallow maximum can be estimated. With the demand of rod lengths being smaller than 100 μm, optimum parameters L = 48 μm, R = 32 μm and L = 96 μm, R = 2 μm were extracted for configuration A and B, respectively.     

A very light and thin liquid hydrogen/deuterium heat pipe target for COSY experiments

A liquid hydrogen/deuterium heat pipe (HP) target is used at the COSY external experiments TOF, GEM and MOMO. The target liquid is produced at a cooled condenser and guided through a central tube assisted by gravitation into the target cell. An aluminum condenser is used instead of copper, which requires less material, improves conductivities and provides shorter cooling down time. Residual condenser temperature fluctuations in the order of ≈0.4 K are reduced by using thermal resistances between the cooling machine and the condenser of the heat pipe combined with a controlled heating power. A new design with only a 7-mm-diameter HP has been developed. The diameter of the condenser part remains at 16 mm to provide enough condensation area. The small amount of material ensures short cooling down times. A cold gas deuterium HP target has been designed and developed which allows protons with energy ?1 MeV to be measured. A 7-mm-diameter HP is used to fill a cooling jacket around the D₂ gas cell with LH₂. The D₂ gas is stabilized at 200 mbar to allow for thin windows. Its density is increased by factor 15 compared to room temperature.     

Advances in a 300 Hz thermoacoustic cooler system working within liquid nitrogen temperature range

With the combined advantages of high reliability, compact size and low electromagnetic interference, a high frequency operating thermoacoustic cooler system, i.e. a pulse tube cooler driven by a thermoacoustic heat engine, is quite promising for space applications. This article introduced a high frequency standing-wave thermoacoustic heat engine-driven pulse tube cooler system working around 300 Hz with axial length being 1.2 m. To improve the thermal efficiency of such system, an optimization has been carried out, both analytically and experimentally, by observing the influence of the dimensions of the stack, the hot buffer length and the acoustic pressure amplifier tube length. So far, a no-load temperature of 68.3 K has been obtained with 4.0 MPa helium and 750 W heating power. With 500 W heating power, a no-load temperature of 76.9 K and 0.2 W cooling power at 80 K have been achieved. Compared with former reports, the performance has been improved.     

Synthesis and characterization of SiO2-CaO-P2O5 hollow nanospheres for biomedical applications

A ternary system of SiO₂-CaO-P₂O₅ hollow nanospheres has been successfully prepared by sol-gel method using polystyrene (PS) nanospheres as template. The inorganic shell was produced using tetraorthosilicate (TEOS) as the silica source and tri-calciumphospate as calcium and phosphorus sources, respectively. The positive surface charge of the template and the [template]/[TEOS] ratio were the key parameters for the creation of a stable primary inorganic network and the further growth of the shell. The removal of the polymeric core through a thermal treatment procedure created an inner void space with mean diameter 250 nm while the outer mean diameter was 330 nm.     

Recycled carbon fibre-reinforced polypropylene thermoplastic composites

Comingled carbon fibre (CF)/polypropylene (PP) yarns were produced from chopped recycled carbon fibres (reCF) (20 mm in length, 7-8 μm diameter) blended with matrix polypropylene staple fibres (60 mm in length, 28 μm diameter) using a modified carding and wrap spinning process. Microscopic analysis showed that more than 90% of the reCF were aligned along the yarn axis. Thermoplastic composite test specimens fabricated from the wrap-spun yarns had 15-27.7% reCF volume content. Similar to the yarn, greater than 90% of the reCF comprising each composite sample made, showed a parallel alignment with the axis of the test specimens. The average values obtained for tensile, and flexural strengths were 160 MPa and 154 MPa, respectively for composite specimens containing 27.7% reCF by volume. It was concluded that with such mechanical properties, thermoplastic composites made from recycled CF could be used as low cost materials for many non-structural applications.     

Performance measurements of a 7 mm-diameter hydrogen heat pipe

A gravity assisted heat pipe with 7-mm diameter has been developed and tested to cool a liquid hydrogen target for extracted beam experiments at COSY. The liquid flowing down from the condenser surface is separated from the vapor flowing up by a thin wall 3 mm diameter plastic tube located concentrically inside the heat pipe. The heat pipe was tested at different inclination angles with respect to the horizontal plane. The heat pipe showed good operating characteristics because of the low radiation heat load from the surroundings, low heat capacity due to the small mass, higher sensitivity to heat loads (to overcome the heat load before the complete vaporization of the liquid in the target cell) due to the higher vapor speed inside the heat pipe which transfers the heat load to the condenser.     

Experimental investigation of vortex tube refrigerator with a divergent hot tube

Energy separation performance of vortex tube can be improved by using a divergent hot tube. Experiments are carried out to investigate the influence of the geometrical parameters on vortex tube refrigeration capacity by using nitrogen as the working fluid. In this work, the parameters are focused on the divergence angle of hot tube, length of divergent hot tube and number of nozzle intakes. Experimental results present that there is an optimum angle for obtaining the highest refrigeration performance, and 4° is the optimal candidate under our experimental conditions. Divergent tube length which exceeds a critical length has slight effect on the refrigeration capacity. The critical length to diameter ratio is L/D = 12 in our experiment. Increasing number of nozzle intakes increases the sensitivity of temperature reduction and can obtain the highest possible temperature reduction. Moreover, similarity relations for the prediction of the cold exit stream are presented and confirmed by the experimental data.     

房间空调器缩小换热器管径的表面反应设计方法

在缩小管径后换热器的优化设计中,为了解决传统设计方法不能满足对换热器性能和成本的同时寻优求解问题,采用表面反应法对换热器进行设计.该方法将连续区间内管长和翅片间距与换热性能和成本的关系拟合成可直接求解的二次连续函数,实现了多变量连续区间内的寻优.将该方法用于7mm管换热器缩小管径的优化,其设计结果与实验数据偏差为0.3％,验证了该方法的准确性.采用验证后的设计方法,对9.52mm管换热器进行了优化设计表明,在保证热性能不变前提下,换热器管径从9.52mm缩小为5mm,换热器成本降低28.0％,制冷剂充注量减少39.8％.     

Y2O3:Eu microstructures: Hydrothermal synthesis and photoluminescence properties

Hexagonal microprisms of yttrium hydroxide (Y(OH)₃) with tuned diameter and height have been successfully prepared for the first time via a facile hydrothermal process using sodium citrate as the shape modifying agent. Y(OH)₃ microspheres with diameter of ca. 2.5 μm and microtubes with an average length about 13 μm, outer diameter about 3 μm and tube thickness about 800 nm were also obtained in current reaction systems. The possible formation mechanism for the Y(OH)₃ microstructures was briefly proposed. Y₂O₃:Eu³⁺ (5%) microstructures with similar morphologies was obtained after thermal treatment of the as-prepared Y(OH)₃:Eu³⁺ microstructures at 700 °C for 4 h. Results show that the relative emission intensity of the Y₂O₃:Eu³⁺ microprisms is about 8 times as those of the Y₂O₃:Eu³⁺ microtubes and microspheres under excitation of 259 nm ultraviolet light. The products were characterized by XRD, SEM, and EDS.     

Preparation of VO2 nanowires and their electric characterization

Large-scale VO₂ nanowires have been synthesized by two-step method. First, we have been obtained (NH₄)_0.5V₂O₅ nanowire precursors by hydrothermal treatment of ammonium metavanadate solution at 170 °C. Secondly, the precursors have been sealed in quartz tube in vacuum and annealed to form VO₂ nanowires at 570 °C. Scanning electron microscope and transmission electron microscope analysis show that the nanowires have self-assembling nanostructure with the diameter of about 80-200 nm, length up to125 μm. Electrical transport measurements show that it is semiconductor with conduction activate energy of 0.128 eV. A metal-semiconductor transition can be observed around 341 K.     

The stress transfer efficiency of a single-walled carbon nanotube in epoxy matrix

This paper investigates the effects of tube length and diameter on the distributions of tensile stress and interfacial shear stress of a single-walled carbon nanotube in epoxy matrix. It was shown that a smaller tube diameter has a more effective reinforcement and there exists an optimal tube length at which reinforcement is maximized. It was also found that a carbon nanotube has a greater stress transfer efficiency than a solid fibre, providing flexibility for toughness and tensile strength optimization.     

Thermodynamic optimization of combined power and refrigeration cycle using binary organic working fluid

A combined cycle has been proposed for the production of power and refrigeration simultaneously. The cycle can be driven by low grade heat sources such as solar, geothermal and waste heat sources. In the first part of this paper, a model has been developed to perform a parametric analysis to evaluate the effects of important parameters on the performance of the cycle, which is a combination of Rankine and absorption refrigeration cycle. Propane–decane has been used as an organic dual working fluid. In the second part, multi objective genetic algorithm is applied for Pareto approach optimization of the cycle. There are three important conflicting objectives namely, turbine work (W_t), cooling capacity (Q_c) and thermal efficiency (η_th) which have been selected to find the best possible combination of these performance parameters. Optimization has been carried out by varying turbine inlet pressure, superheated temperature and condenser temperature as design variables. Among optimum design parameters, a trade-off point is selected. Turbine inlet pressure, superheated temperature and condenser temperature are assumed to be 29.5 bar, 410 K and 386.6 K respectively as the values assigned to this point. Furthermore, it has been shown that some interesting and important relationships can be discovered among optimal objective functions and decision variables involved, consequently.     

A heat transfer correlation for natural draft wire-and-tube condensers

A dimensionless correlation to estimate the heat transfer coefficient between the external surfaces of natural draft wire-and-tube condensers and the surrounding air is proposed in this study. The experiments were carried out using a purpose-built testing apparatus that reproduces the actual operating conditions of such heat exchangers. A test section to vary the condenser position in relation to the adjacent surfaces was also developed and mounted within a controlled environmental chamber. The correlation was developed based on a total of 72 experimental data points obtained with 24 different condenser samples with tube outer diameter  ranging from 4.8 to 6.2 mm, number of tube rows from 13 to 25, and number of wire pairs from 10 to 90. The tests were performed with an average temperature difference between the condenser surface and the ambient air ranging from 3.6 to 36.1 °C. The proposed correlation predicts 90% of heat transfer data within an error band of ±10%. Comparisons with other correlations available in the open literature are also reported.     

An evolution strategy in structural optimization problems for plates and shells

For multilayered plated and shell structures the formulation of the optimization problem is strongly dependant on the definition of the design variables. Therefore, the first part of the work is devoted to the definition of design variables and the forms of objective functions. Those design variables define stacking sequences of structures have discrete fiber orientations 0°, ±45°, 90° and a finite number of key points that are required in the evaluation of the curve Γ characterizing an external boundary of the structure or a structural shape understood in the sense of a structural geometry representing a shell/plate mid-surface or thickness distribution of structures. For the curve definition we have adopted one dimensional B-splines. Each curve is formed by an assembly of subsegments passing through certain key points. The positions of key points are randomly generated so that in the generation process it is possible to fulfill the required set of equality or inequality constraints. It is necessary to emphasize that the proposed method is very general and can be applicable to a very broad class of optimization problems. The generality of the approach is confirmed by the proof of the direct equivalence and mapping between discrete fiber orientations and continuous angle ply orientations. The evolution strategy is proposed herein as the optimization algorithm. Similarly as classical ones (e.g. ACO, SS, PS or ISM) it combines all features and advantages of evolution algorithms. It is worth to note that in the evolution strategy the number of children produced in one generation is not limited and it is not necessary to conduct mutation operations as in genetic algorithms. It simplifies significantly the effectiveness of numerical procedures. Then, two numerical examples have been solved to demonstrate the effectiveness of the proposed formulations and the optimization algorithm. They deal with thickness and stacking sequence optimization problems for circular cylindrical shells subjected to various dynamic and static constraints, respectively.     

Fabrication of silica monolithic columns with ordered meso/macropore structure

Recently, much effort has been focused on the materials with ordered meso/macropores, because of their potential applications in catalysis, separations, coatings, microelectronics and electro-optics. In this paper, silica monoliths with well-defined columnar shape more than 1 cm in length are successfully fabricated by using the micelles of triblock copolymer F127 and colloidal crystals composed of polystyrene (PS) latex microspheres as mesopore and macropore template, respectively. The column templated by PS microspheres 870 nm in diameter and 0.5 g F127 (MCL-0.5-870) shows uniform ordered macropores, contact pores connecting macropores together, and assembled and inter-particle pores increasing the BET specific surface area and adsorption capability of the monolithic column. The backpressure curve and hydraulic permeability experiment exhibit its good penetrability and mechanical stability. These excellent characteristics, together with high BET specific surface area (387.4 m² g⁻¹) and porosity (80%), may endow its potential application for chromatography separation. In addition, the size of macropores and mesopores can be easily regulated by changing the diameter of PS spheres and F127 weight, respectively. This indicates that this method is a facile and universal protocol to fabricate the applied monolithic column with ordered meso/macropores.     

Generation of gold-PEDOT nanostructures at an interface between two immiscible solvents

Gold-poly(3,4-)ethylenedioxythiophene (Au-PEDOT) composite with variant morphology was synthesized through interfacial polymerization at room temperature in the absence of a template, phase transfer catalyst or surfactant. A systematic variation of the relative concentration of the reactants yields morphologies typical of nanorods of diameter approximately 20-30 nm and length of few 0.5-1 μm. Transmission electron microscopy reveals the structure of the nanowire to be the one in which the core is Au and the outer shell is made of PEDOT. Oligomer formation, speculated during the interfacial reaction was confirmed by the analysis of the organic phase using ultraviolet-visible (UV-vis) and nuclear magnetic resonance (NMR) spectroscopy techniques.     

结构特征对螺旋管换热器性能的影响

目的研究结构特征对螺旋管换热器换热性能的影响,为换热器设计和结构优化提供理论依据。方法在CFD软件Ansys的FLUENT模块中模拟螺旋管换热器内流体的流动换热过程。在相同边界条件下,不改变总换热面积,通过改变换热器的换热管直径和壳体长度,研究几何参数对换热性能的影响。通过对比单管单螺旋、单管双螺旋、双管双螺旋和内外双螺旋等4种不同缠绕方式换热器中流体的温度分布云图,研究螺旋管的结构对换热器换热性能的影响。结果保持总换热面积不变,减少换热器的管径,增大壳体的长度,都能有效提高换热效率。与单管单螺旋结构的换热器相比,单管双螺旋结构换热器的流体出口温度下降了9.74%,平行双螺旋结构换热器的出口温度下降了5.05%,内外双螺旋结构换热器的出口温度上升了10.11%。结论在螺旋管换热器的设计和优化过程中,可以通过减小换热管径,增大壳体长度,采用内外双螺旋结构,以实现提高传热效率的目的。     

Improving the performance of the cryogenic heat pipe-target system for the COSY-TOF experiment

Very lightweight, thin liquid hydrogen/deuterium heat pipe-target systems are used in the Time Of Flight (TOF) spectrometer at the COSY accelerator facility. The proton beam impinges upon LH₂/LD₂ targets thereby heating the target. The stability of the liquid targets depends on the thermal capacity of the whole system, the energy losses from the proton beam and heat losses from the surrounding of the heat pipe-target system. The radiation heat load has been reduced by a factor of 4.5 by reducing the length of the gas tube from 180 cm (long tube) to 40 cm (short tube). Furthermore, the 40 cm long gas tube was coated with a thin polished gold layer, thereby reducing the heat load by an additional factor 22. The thermal capacity is improved by reducing the mass of the gas tube from 23 g to 5 g. The cool down time of the 7 mm diameter gold coated heat pipe with the gold coated 40 cm gas tube is reduced by 12 min.