6MD32型二氧化碳压缩机节能方案的选择及应用

对往复式压缩机低负荷工况下调节方式进行研究,结合6MD32型二氧化碳压缩机自身的特点,探讨降转速调节、气缸余隙调节、全行程气量无级调节和入口节流降压调节等方式,从技术、投资、可靠性等方面进行综合对比,最终选择进气减压调节方式,取得明显的节能效果。     

Effect of rotor cage's outer and inner radii on the inner flow field of the turbo air classifier

The effects of rotor cage's outer and inner radii on flow field of the turbo air classifier are comparatively analyzed by numerical simulation using ANSYS-FLUENT. The results of quantitative analysis show when the rotor cage's outer and inner radii are increased, the tangential velocity, radial velocity and upward axial velocity decrease in the annular region and near the entrance of the rotor cage. However, when the rotor cage's outer and inner radii are too large or too small, the tangential velocity and radial velocity will be fluctuated greatly. Moreover, the rotor cage's outer and inner radii directly influence the radial velocity distribution in the rotor cage channel. The rotor cage's outer and inner radii should not be too large or too small. Therefore, in the seven contrast rotor cage models, model 100–70 and 90–60 are selected to carry out the calcium carbonate classification experiments due to their small tangential velocity and radial velocity fluctuations and well-distribution in the rotor cage channel. The experimental results reflect the characteristics of the numerically simulated flow field in the classifier.     

Efficiency of urban water supply in Sub-Saharan Africa: Do organization and regulation matter?

Using the model developed by Battese and Coelli (1995), we compare the technical efficiency of urban water utilities in Sub-Saharan Africa countries. We examine how private-sector participation, economic regulation, and their combination affects technical efficiency. We find that regulating water utility operations via performance contracts leads to higher technical efficiency compared to control by an independent regulatory agency. Private-sector participation in management has a positive effect on technical efficiency. However, there is no evidence of a statistically significant difference between the technical efficiency of publicly and privately owned utilities, respectively, when they are regulated by either an independent agency or a performance contract.     

Numerical investigation of a two-phase CO2 ejector

Using an ejector as an additional component in a vapor compression refrigeration system is a promising way to increase the system efficiency. The efficiency increase of the refrigeration system depends strongly on the ejector. Using CFD simulations, it is possible to obtain a better understanding of two-phase CO₂ ejectors in order to design more efficient ejectors. In this work, a numerical model based on a homogeneous equilibrium approach, which is implemented in OpenFOAM, is used to simulate the CO₂ ejector. The numerical investigation of an ejector operated with and without a suction mass flow is presented and the numerical results are compared to experimental data published in previous works to validate the simulations. If the ejector is operated without a suction flow, no mixing losses occur and the friction losses are one of the main losses affecting the flow. Thus, this operating condition is suitable to validate if the friction losses are determined correctly by the numerical model. Afterwards, an ejector which is operated with a suction flow is simulated in order to validate the accurate prediction of the mixing losses by the numerical model. In the presented data range, the numerical model predicts the driving mass flux within an error margin of 10%. The pressure recovery of the ejector operated without a suction flow is determined with an error of 10%. This error increases to 20% when the ejector is operated with a suction flow.     

Entropy and entropy of mixing

Entropy as a function of temperature at constant volume, S(T), can be determined by integrating the molar specific entropy capacity C_V/T (C_V: molar specific heat capacity at constant volume). As a second approach, S(T) at constant volume can be determined by differentiating the free energy with respect to the temperature, T. Recently, it has been shown for a system obeying Boltzmann statistics that these mathematical approaches are equivalent to applying the formula of the mixing entropy, if the ground and excited states of the same sub‐systems or elementary systems are considered as mixing objects or quantum components. This result considerably extends the applicability of the formula of the mixing entropy, which is derived in textbooks just for mixing real indifferent components. In the present paper, it is shown that the formula of the mixing entropy can also be applied to calculate the entropy of Bose and Fermi systems. Thus, all entropy can be calculated and interpreted as mixing entropy of real components or quantum components. In reverse, the transitions between the ground and the excited states of any system can be explained as mixing processes. This interpretation is applied to the melting transition of chemically bonded solids and in particular to the glass transition whereby upon cooling the mixing entropy of the melt is (at least partly) frozen in the configuration. These results suggest a new interpretation of the glass transition and a new definition of structural glass.     

Qualitative data modeling: application of a mechanism for interpreting graphical data

This paper describes a qualitative technique for interpreting graphical data. Given a set of numerical observations regarding the behaviour of a system, its attributes can be determined by plotting the data and qualitatively comparing the shape of the resulting graph with graphs of system behaviour models. Qualitative data modeling incorporates techniques from pattern recognition and qualitative reasoning to characterize observed data, generate hypothetical interpretations, and select models that best fit the shape of the data. Domain-specific knowledge may be used to substantiate or refute the likelihood of hypothesized interpretations. The basic data modeling technique is domain independent and is applicable to a wide range of problems. It is illustrated here in the context of a knowledge-based system for well test interpretation.     

In-storage softening of kiwi fruit: effects of delayed cooling

Rapid softening of kiwi fruit while in storage at 0°C limits the marketing period for this crop and contributes to economic loss. The time required to bring fruit to optimum storage temperature is affected by delays between harvest and placing fruit in the cooling facility and by the completeness of cooling. Incomplete cooling of fruit in commercial forced-air coolers results in overall above-optimal average fruit temperatures for undesirable lengths of time and also results in a wide range of temperature among individual fruits. The half cooling time for palletized kiwi fruit packed in wooden trays with liners was 7 h in the coolers tested; thus seven-eighths cooling required 21 h. Delays of 24 h or more before the start of cooling accelerated the softening of fruit, enhanced soluble solids content, and increased the incidence of rotting and shrivelling during storage.     

Plastic bending of an edge-cracked specimen

The plastic zones and the rotation of the cracked planes of an edge-cracked bend specimen are investigated by a numerical three-dimensional analysis. For an alloy-steel, for bending moments up to the first yielding moment of the uncracked specimen, it is shown that the crack tip is in small scale yielding.     

Data mining for government construction procurement

A new data-mining model for government construction procurement was developed to consider data preparation, domain knowledge and a conceptual model to reflect the needs of the knowledge economy. Prototype experiments and analysis were performed to test the data mining using information from a typical Taiwanese local construction procurement unit. The application of the data-mining algorithm to this construction procurement management model improves government procurement effectiveness and efficiency. By complying with this governmental procurement information system and revealing the information required by the World Trade Organization and the Government Procurement Agreement, the model has the potential to improve government procurement and industry effectiveness and efficiency. It also provides a platform for government access to the international community.     

Distributed dynamic modelling of a refrigerated room

The prediction of velocity and temperature distributions in a refrigerated room generally requires the simultaneous solution of the equations governing the flow pattern (Navier-Stokes equations) and the energy equation. Basically these are interacting non-linear differential equations requiring simultaneous integration by an iteration process. The specific application of advanced computer packages for this purpose in refrigeration is still in the early stages; even for one steady-state simulation the computation times are high because of the very complicated shape of the air space in a refrigerated room loaded with produce. The method of simultaneous integration becomes unattractive, especially for non-steady-state thermal conditions, if many runs are to be made with different values of the input parameters. In instances where the air cooler fans dominate the flow pattern, the equations can be decoupled. Moreover, the energy equation can be linearized with reasonable model assumptions, and will then not require an iteration process for integration. The simulation described here includes a compression refrigerating machine with capacity control, and was validated by measurements taken from a laboratory-scale cold store.