首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
A Stirling-type pulse tube cryocooler （PTC） with precooling was designed and manufactured to investigate its performance at 4 K. Numerical simulation was carried out based on the well-known regenerator model REGEN with an emphasis on the performance of a 4 K stage regenerator of the Stifling-type PTC as influenced by the warm end temperature, pressure ratio, frequency and average pressure with helium-4 and helium-3 as the working fluid respectively. This study demonstrates that the use of a cold inertance tube can significantly improve the efficiency of a 4 K Stirling-type PTC. A preliminary experimental investigation was carried out with helium-4 as the working fluid and a refrigeration temperature of 4.23 K was achieved. The experimental results show that the operating frequency has a significant influence on the performance of the Stirling-type PTC and a relatively low average pressure is favorable for decreasing the loss associated with the real gas effects of a 4 K Stirling-type PTC.  相似文献   

2.
The hydrodynamic characteristic of a new rotating stream tray(NRST) was investigated. The tests were carried out using an air–water/oxygen experimental system in a column with a diameter of 500 mm. The hydrodynamic parameters studied were dry plate pressure drop, wet plate pressure drop, weeping, entrainment, and Murphree liquid efficiency. The results showed that the NRST has excellent performance in terms of high operational flexibility. The pressure drop, weeping rate, and entrainment rate remained low even under a high-capacity operation. Correlations of pressure drop, weeping, and entrainment for the NRST were obtained by regression analysis. The results can provide some important theoretical guidance for the development of this type of trays.  相似文献   

3.
Performance of a pulse tube cooler significantly depends on the efficient operation of its regenerator. Influence of input acoustic power on regenerator's performance is simulated and analyzed with simple harmonic analysis method. Given regenera-tor's dimensions and pressure ratio,there is an optimal input acoustic power for achieving a highest coefficient of performance,due to a compromise between relative time-averaged total energy flux in regenerator and relative acoustic power at regenerator's cold end. Additionally,optimal dimensions of regenerator are also estimated and presented for different input acoustic powers. The computed optimal diameter obviously increases with increase of input acoustic power,while the optimal length decreases slightly,and as a result,a larger input acoustic power requires a smaller aspect ratio (length over diameter).  相似文献   

4.
In 1987, the Montreal Protocol prohibited the worldwide use and production of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and hydro fluorocarbons (HFCs) were proposed as alternative refrigerants. Unfortunately, HFCs have non negligible global warning potential and therefore new refrigerants must be proposed or old refrigerants must be used associated with HFC. Accurate experimental thermodynamic data and predictive techniques are required for better under-standing of the performance of the newly proposed refrigerants. In this communication, experimental techniques based on either analytic or synthetic methods are first described. Data are reported. Then two newly developed predictive models based on thermodynamic approach with the isofugacity criterion and artificial neural network method are presented. The results can provide better evaluation of refrigerants, especially with the aim of studying global warning effects.  相似文献   

5.
New numerical solution for self-acting gas journal bearings   总被引：1，自引：0，他引：1  
Taking a small pressure change in the gas film of self-acting gas-lubricated journal bearings into account, the corresponding nonlinear Reynolds equation is linearized through appropriate approximation and a modified Reynolds equation is derived and solved by means of the finite difference method （FDM）. The gas film pressure distribution of a self-acting gas-lubricated journal bearing is attained and the load capacity is calculated. The numerical solution has a better agreement with experimental data than a direct numerical solution for different values of the bearing number. It is of interest to note that the eccentricity ratio, at which the new numerical solution is in better agreement with experimental data, is different when the bearing number is changing. The new numerical solution is slightly larger when the eccentricity ratio is smaller, and becomes slightly smaller when the eccentricity ratio is larger.  相似文献   

6.
Auto-ignition and heat release correlations for controlled auto-ignition(CAI)combustion were derived from extensive in-cylinder pressure data of a four-stroke gasoline engine operating in CAI combustion mode.Abundant experiments were carried out under a wide range of air/fuel ratio,speed and residual gas fraction to ensure that the combustion correlations can be used in the entire CAI engine operation range.Furthermore,a more accurate method to compute the residual gas fraction was proposed by calculating the working fluid temperature at the exhaust valve close timing in the experiments.The heat release correlation was described in two parts,one is for the first slower heat release process at low temperature,and the other is for the second faster heat release process at high temperature.Finally the heat release correlation was evaluated on the single cylinder gasoline engine running with CAI combustion by comparing the experimental data with the 1-D engine simulation results obtained with the aid of the GT-Power simulation program.The results show that the predicted loads and ignition timings match closely with the measurements.  相似文献   

7.
This paper describes a Least Squares （LS） channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error （MSE） of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio （SNR）. To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.  相似文献   

8.
Influence of input acoustic power on regenerator＇s performance   总被引：2，自引：0，他引：2  
Performance of a pulse tube cooler significantly depends on the efficient operation ofits regenerator. Influence of input acoustic power on regenerator＇s performance is simulated and analyzed with simple harmonic analysis method. Given regenerator＇s dimensions and pressure ratio, there is an optimal input acoustic power for achieving a highest coefficient of performance, due to a compromise between relative time-averaged total energy flux in regenerator and relative acoustic power at regenerator＇s cold end. Additionally, optimal dimensions of regenerator are also estimated and presented for different input acoustic powers. The computed optimal diameter obviously increases with increase of input acoustic power, while the optimal length decreases slightly, and as a result, a larger input acoustic power requires a smaller aspect ratio （length over diameter）.  相似文献   

9.
In this study, a porous inserted regenerative thermal oxidizer （PRTO） system was developed for a 125 kW industrial copper-melting furnace, due to its advantages of low NOr emissions and high radiant efficiency. Zirconium dioxide （ZrOz） ce- ramic foams were placed into the combustion zone of a regenerative thermal oxidizer （RTO）. Different performance characteris- tics of the RTO and PRTO systems, including pressure drop, temperature distribution, emissions, and energy efficiency, were evaluated to study the effects of the porous inserts on non-premixed CH4 combustion. It was found that the PRTO system achieved a significant reduction in the NOx emission level and a fuel saving of approximately 30% compared to the RTO system. It is most suitable for a lean combustion process at an equivalence ratio 〈0.4 with NOx and CO emission levels within 0.002%~）.003% and 0.001%q3.002%, respectively.  相似文献   

10.
Theoretical research on aggregative dynamic pressure damper   总被引：1，自引：0，他引：1  
To broaden the frequency width and increase the damping coefficient of a dynamic pressure damper, we designed an aggregative dynamic pressure damper （ADPD）. Combined with the advantages of traditional dynamic pressure dampers （TDPD）, ADPD can not only increase the damping coefficient in wide frequency range for valve control system, but also absorb partial pressure pulsations and impacts in the low and high frequency fields. Based on the theoretical research and the analysis compared with TDPD, we concluded that the ADPD was superior to the TDPD in the middle high frequency field, and the main parameters influencing the performance of the damper were the damping stiffness, orifice flow coefficient, pre-charge pressure, and the volume of the damper accumulator.  相似文献   

11.
Sewage source heat pump unit operates under partial load most of the time, and study on the law of coefficient of performance (COP) of the unit varying with load ratio can provide basis for the heat pump units running in high efficiency. A mathematical model determining COP, evaporation temperature and condensation temperature of a single unit was proposed. Under the condition of uniform load distribution, the model was established according to different ways of bearing partial load with the same type multiple units but different parallel operation models, and the operation characteristics of units were analyzed as well. Results show that the single screw water-source heat pump can maintain high COP only at 60%—100% load ratio, COP decreases sharply with the decrease of load ratio, and the units with parallel operation are controlled by the load ratio of a single unit according to the reduction of total load which can keep the average COP at high level within a wide load range.  相似文献   

12.
Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The material is a new generation of fine grain and high purity SS400 steel that has the same ingredients as the traditional low carbon steel. The specimens are in two different states:welded and ultrasonic peening conditions. The corresponding fatigue testing data were analyzed according to the regulation of the statistical method for fatigue life of the welded joints established by International Institute of Welding(IIW). Welding residual stress was considered in two different ways: the constant stress ratio R = 0.5 and the Ohta method. The nominalstress-number (σ-N) curves were corrected because of the different plate thickness compared to the standard and because there was no mismatch or angular deformation. The results indicated that: 1 ) Compared with the welded specimens, when the stress range was 200 MPa, the fatigue life of the SS400 steel specimens treated by ultrasonic peening is prolonged by over 58 times, and the fatigue strength FAT corresponding to 106 cycles is increased by about 66％; 2) As for the SS400 butt joint ( single side welding double sides molding) , after being treated by UPT, the nominal S-N curve (m = 10) of FAT 100 MPa(R =0.5) should be used for fatigue design. The standard S-N curves of FAT 100 MPa (R = 0.5, m = 10) could be used for fatigue design of the SS400 steel butt joints treated by ultrasonic peening.  相似文献   

13.
Currently there are two approaches for a multi-class support vector classifier （SVC）. One is to construct and combine several binary classifiers while the other is to directly consider all classes of data in one optimization formulation. For a K-class problem （K〉2）, the first approach has to construct at least K classifiers, and the second approach has to solve a much larger optimization problem proportional to K by the algorithms developed so far. In this paper, following the second approach, we present a novel multi-class large margin classifier （MLMC）. This new machine can solve K-class problems in one optimization formulation without increasing the size of the quadratic programming （QP） problem proportional to K. This property allows us to construct just one classifier with as few variables in the QP problem as possible to classify multi-class data, and we can gain the advantage of speed from it especially when K is large. Our experiments indicate that MLMC almost works as well as （sometimes better than） many other multi-class SVCs for some benchmark data classification problems, and obtains a reasonable performance in face recognition application on the AR face database.  相似文献   

14.
An inter-phasing pulse tube cooler （IPPTC） consists of two pulse tube units, which are connected to each other at hot ends of the pulse tubes through a needle valve. This paper presents the computational fluid dynamic （CFD） results of an IPPTC using a 2D axis-symmetrical model. General results such as the phase difference between pressure and velocity at cold end and hot end, the temperature profiles along the wall, the available lowest temperature as well as its oscillations and the coefficient of performance （COP） for IPPTC are presented. The formation of DC flow and its effects on the performance of the cooler are investigated and analyzed in detail. Turbulence, which is partially responsible for the poor overall performance of a single orifice pulse tube cooler （OPTC）, is found to be much reduced in IPPTC and its performance is improved significantly compared with the single OPTC.  相似文献   

15.
By an iteration method, the influence of oil film inertia on piston skirt lubrication in a high speed engine is investigated. By alternately solving the Navier-Stocks equations and the Reynolds equation, the new iteration method can trace the variations of velocity field and pressure field with time. Based on this, the mixed-lubrication model suitable for the piston skirt of high engines is proposed. By introducing the inertia coefficient, the new lubrication model includes the inertia term in oil film. The model can be also used to solve for the lubrication performances of a piston skirt in low or medium speed engines and for lubrication problem in general excluding  相似文献   

16.
Lithium-ion batteries(LIBs) have been developed for over 30 years; however, existing electrode materials cannot satisfy the increasing requirements of high-energy density, stable cycling, and low cost. Here, we present a perovskite-type LaNiO_3 oxide(LNO) as a new negative electrode material. LNO was successfully synthesized by a sol–gel method. The microstructure and electrochemical performance of LNO calcined at various temperatures have been systematically investigated. The LNO electrode shows a high rate capability and long cycling stability. In a C-rate test, a specific capacity of 77 mAh/g was exhibited at 6 C. LNO can also deliver a specific capacity of 92 mAh/g after 200 cycles at 1 C. This paper presents a type of binary metal oxide as a new anode material for high-performance LIBs.  相似文献   

17.
An acoustic pressure amplifier （APA） is capable of improving the match between a thermoacoustic engine and a load by elevating pressure ratio and acoustic power output. A standing-wave thermoacoustic engine driving a resistance- and-compliance （RC） load through an APA was simulated with linear thermoacoustics to study the impact of load impedance on the performance of the thermoacoustic system. Based on the simulation results, analysis focuses on the distribution of pressure amplitude and velocity amplitude in APA with an RC load of diverse acoustic resistances and compliance impedances. Variation of operating parameters, including pressure ratio, acoustic power, hot end temperature of stack, etc., versus impedance of the RC load is presented and analyzed according to the abovementioned distribution. A verifying experiment has been performed, which indicates that the simulation can roughly predict the system operation in the fundamental-frequency mode.  相似文献   

18.
Local mate competition (LMC) was firstly used to explain extra-ordinary female-biased sex ratios. However, some observations have found that the sex ratios of some species are more female-biased than the predictions of LMC and its extensions; there is not yet a theory that accounts for the mechanisms of more female-biased sex ratio. Here, we assume that LMC occurs at a destructed habitat that reduces the resource for production, and present a new extension for the LMC model. Consequently, our model shows that the evolutionarily stable strategy (ESS) for sex ratio depends on two parameters: the number of foundresses and the degree of habitat destruction. Moreover, the sex ratio decreases as the degree of habitat destruction increases, i.e., the proportion of female increases. These results generally agree with experimental data, and may provide a new basis for the evolution of female-biased sex ratios in local mate competition and a new theory support for conservation of some species  相似文献   

19.
An adjustable ejector expansion device for a CO2 heat pump water heater （HPWP） is proposed to improve the system performance. It has been designed to investigate experimentally the effects of the motive nozzle throat area of the ejector, entrained flow pressure, back pressure and primary flow pressure on the entrainment ratio. Experiments based on different motive nozzle throat areas were conducted and the results of the prototype ejector using CO2 as working fluid are presented. The results show that an adjustable ejector can achieve high performance and work well in a wide range of working conditions.  相似文献   

20.
This paper proposes a design optimization method for the multi-objective orbit design of earth observation satellites, for which the optimality of orbit performance indices with different units, such as: total coverage time, the frequency of coverage, average time per coverage and maximum coverage gap, etc. is required simultaneously. By introducing index normalization method to convert performance indices into dimensionless variables within the range of [0, 1], a design optimization method based on the principal component analysis and cluster analysis is proposed, which consists of index normalization method, principal component analysis, multiple-level cluster analysis and weighted evaluation method. The results of orbit optimization for earth observation satellites show that the optimal orbit can be obtained by using the proposed method. The principal component analysis can reduce the total number of indices with a non-independent relationship to save computing time. Similarly, the multiple-level cluster analysis with parallel computing could save computing time.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号