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The twin-screw expander is widely used in many low-grade energy recovery systems. Its built-in volume ratio has a crucial impact on the system performance. Large built-in volume ratio can expand both the application and scope of the twin-screw expander, and can improve the efficiency of the power generation cycle as well. In this study, a novel pair of intermeshing cross-axis conical twin-screw rotors (CCSRs) with large built-in volume ratio and large expansion ratio for the twin-screw expander was proposed. The conjugate meshing of CCSRs can be achieved by using spherical-sectional profiles. Geometric performance of the proposed CCSRs was studied. Moreover, a thermodynamic model and numerical simulations of the working process of the proposed cross-axis conical twin-screw expander (CCSE) were established, and the working performance and thermodynamic characteristics during the expansion process were analyzed. Study results indicate that the proposed CCSRs exhibit a larger built-in volume ratio, and the corresponding twin-screw expander has a larger expansion ratio than that of the traditional one. The contents will be beneficial to the improvement and development of the twin-screw expander and energy recovery systems.

Compared to traditional air freezing, immersion chilling and freezing shows an improvement in the freezing effect on meat quality, but it is not known whether this advantage persists over longer storage periods. Therefore, the objective of the current study was to compare the effects of immersion chilling and freezing (ICF) and traditional air freezing (TAF) on the physical and chemical indexes in beef longissimus muscle during a storage period of 150 days. In the current study, the longissimus muscle from Luxi cattle (aged 20–24 months) was analyzed, with samples independently frozen by ICF and TAF. After the core temperature was frozen to below −18 degrees by the two chilling methods, samples were transferred to a −18 degrees cold room for further storage. During the storage period, physical and chemical indexes, mainly including color and texture qualities, total volatile base nitrogen (TVB‐N) and peroxide value (POV) were measured and comparatively analyzed at several fixed time points. A higher freezing rate was observed in ICF (5.124 cm/h) than in TAF (0.194 cm/h), and better microstructure was observed in ICF treatment. Besides, peak force values and total energy values were significantly lower in the TAF group than in the ICF group during the first 45 days of freezing storage time (p, Freezing is one of the most effective ways to preserve the quality of beef and is used to minimize the product loss. Many studies have demonstrated that the immersion chilling and freezing shows good improvement on the freezing effect of meat quality; however, it is not known whether this advantage will still exist in a longer storage period. The aim of current study was to explore the effects of different freezing methods, including the immersion chilling and freezing (ICF) and traditional air freezing (TAF), on the physical and chemical indexes in beef longissimus muscle during a period of 150‐day storage.

This article examines whether different levels of entry controls impact burglary rates in gated communities. It differs from the previous studies that only distinguish gated communities from non-gated communities but ignore important variation in different levels of entry controls. A sample of 698 gated communities in a large Chinese city are selected for this study. A negative binomial regression model estimates the relationships between entry control levels and burglary rates in gated communities. The test of these relationships accounts for the control of other important explanatory variables, including management fee, building height, building age, housing price, house for sale, rental house and floating population. Results indicate that higher entry control levels are associated with significantly lower burglary rates in gated communities. This is the first study that reveals a quantitative relationship between burglary and entry control level in gated communities at the city-wide scale.

As a new type of fluid machinery, the disc-seal single screw pump (DSSP) is vital for energy conversion in oil sludge energy recovery systems and natural gas liquefaction system due to the advantages of wide flow range, strong self-absorption and well adaptability to organic solid impurities. However, no research work has focused on the working mechanism and performance of this pump at present, which makes its application limited. In view of this, the in-depth theoretical study on the meshing characteristics and operating performance of the DSSP must be carried out. In this paper, the profile equations of the meshing pair and the working process mathematical model were established for the first time based on three-dimensional space meshing theory, coordinate transformation principle. By using this model, the working performance of this pump was investigated, and the influence mechanism of the profile parameters on the theoretic volume was analyzed. The results of the analysis show that DSSP has the best leakage characteristics when the seal disc rotation center fell on the screw rotor touchline. All these analyses can provide the theory basis for improving the performance of the pump and optimized design of the meshing pair.

The disc-seal single screw pump (DSSP) is the key devices for liquid refrigerant conveying. However, there is little research on the suction capacity of this pump at present, which makes its application limited. In view of this, a mathematical model of the suction volume was established firstly based on the three-dimensional meshing theory. By using this model, the suction capacity calculation model was put forward, and the suction capacity and the impact mechanism of working parameters on it were investigated. The theoretical calculation results are in good agreement with the actual engineering data with the deviation not more than 6.5%. The results obtained by this validated model show that DSSP has abundant suction capacity with a suction capacity far more than 1 and the suction capacity varies in inverse proportion to density and rotation speed. All of these studies can provide theoretical basis for improving the performance of the DSSP.

Accurate crime prediction can help allocate police resources for crime reduction and prevention. There are two popular approaches to predict criminal activities: one is based on historical crime, a...

In single screw compressor (SSC), the inner surface of the working chamber has always been a key issue that affects oil application and heat transfer. However, the geometric characteristics for the inner surface of the working chamber in SSC with Multicolumn Envelope Meshing Pair (MEMP) have not been carried out yet. Therefore, in this paper, a geometric model of working chamber inner surface for the SSC with MEMP is established to predict the geometric characteristics of the working process. The presented model is verified as a powerful tool for geometric characteristics analysis by the simulation results. With the validated model, the geometric characteristics of the working process and the effect of MEMP structural parameters on the geometric characteristics and the working performance for the SSC with MEMP have been analyzed. Through the comparison of the inner surface area with different structural parameters, optimization analysis of the structural parameters can be obtained. All of this work can provide the basis for the later heat transfer analysis and optimization structural design of the SSC.

Purpose Shear stresses have a considerable influence on the characteristics of lubricants and become significant at high rotating speeds. This study aims to investigate the influences of shear cavitation (SC) on loading capacity of journal bearings. Design/methodology/approach A principal normal stress cavitation criterion based on the stress applied to flowing lubricant in journal bearings is developed and used to investigate SC in journal bearings. A computational fluid dynamic (CFD) model for calculating the loading capacity is established using this criterion. After validation with experimental results, the loading capacity is calculated under different conditions. Findings The calculation results indicate that SC intensifies when viscosity, speed and eccentricity increase. Angle of loading capacity with SC is larger than that without SC. The magnitude of loading capacity with SC is smaller than that without SC due to the decrease in the ultimate pressure. In addition, the magnitude difference between the loading capacity with and without SC increases when viscosity, speed and eccentricity increases. Originality/value Present research can provide some guidance for calculating the loading capacity when a journal bearing is operating at high speed or with a high viscosity lubricant.

In single screw refrigeration compressor (SSRC), the wear of meshing pair has always been a key issue that restricts its development. In order to solve this problem, a Multicolumn Envelope Meshing Pair (MEMP) was proposed. However, the theoretical research on wear resistance of MEMP has not been carried out yet. Therefore, in this paper, a theoretical calculation model describing the influence of the MEMP profile parameters on wear characteristics of the SSRC with MEMP is established to predict the wear resistance. The presented model is verified as a powerful tool for wear characteristics analysis by the experimental results. With the validated model, the effect of MEMP profile parameters on the wear characteristics of SSRC has been analyzed. Optimization analysis shows that in the design stage more envelope columns with a larger center distance and larger envelope column diameter should be chosen for the MEMP to get a better wear resistance.

The claw rotor profile is one of the key factors for improving the performance of claw vacuum pumps. In order to develop novel types of claw rotor profiles, the conjugate curves of claw rotor profiles were calculated, and therefore two types of straight claw rotors, a cusp claw rotor and a smooth claw rotor, were proposed in this study. Geometric models of the proposed claw rotors were established, and profile equations were also derived. Moreover, effects of the independent geometric parameters on shapes of the claw rotors and the performance of pumps were analyzed. The stress and deformation of two proposed claw rotors loaded by gas pressures at the end moment of the discharge process were analyzed and compared. The study results indicate that the cusp claw rotor is a special case of the smooth claw rotors, when the value of tip circular arcs equals to zero. The smooth claw rotor is superior to the cusp claw rotor in terms of the working performance and mechanical property.

Purpose Surface texturing has been proven as an effective means of contact performance enhancement. However, limited work has been done to investigate the regular relationship to solve the multi-parameters problem of textures, and inertia effect and elastic deformation were seldom considered together in previous optimization work. This paper aims to quantitatively obtain the relationship between the textured depth and liquid film thickness and find the effect of deformation on the optimal textured height ratio in elastic parallel sliders. Design/methodology/approach Numerical models of hydrodynamic lubrication are established based on the computational fluid dynamic method. Elastic deformation is considered through fluid–structure interaction (FSI) method. Using response surface optimization method, textured parallel sliders are optimized with maximum loading capacity as the objective. Findings The results show that the optimal height ratios are all within the range of 0.60-0.65 when textured parallel sliders are considered as rigid. After considering the effect of elastic deformation, loading capacity drops and is reduced more obviously with a decrease in the elastic moduli. The optimal height ratios are within the range of 0.60-0.63, which shows that FSI has a considerable influence on loading capacity but has no significant influence on the optimal height ratio. Originality/value The present research provides a theoretical reference for engineering application of elastic textured parallel sliders.

A geometric model of a 1-pair of circular arcs modified wrap (1-CMW), the existing circular arc modified wrap (CMW), was developed. In order to improve the performance and overcome its shortcoming of the CMW, a novel n-pair of circular arcs modified wrap (n-CMW) for scroll compressors was proposed based on the midline design method. A 2-CMW was analyzed, and then a general geometric model of n-CMW with arbitrary pair number n was established. In addition, the generation procedure, general mutual dependence of geometric parameters as well as equations of wrap profiles were obtained, and the influence of geometric parameters on shapes of the n-CMW was analyzed. Flow simulations of the 1-CMW, 2-CMW, 3-CMW and 4-CMW during the working process with the same conditions were conducted. Study results indicate that the proposed n-CMW increases the built-in volume ratio and design flexibility, and is superior to the existing CMW.

The screw rotor and its cross-section profile primarily determine the performance and efficiency of the twin-screw vacuum pump (TSVP). However, the traditional cross-section profile (CSP) contains cusps or unsmooth points, so that screw rotor surfaces generated by this CSP contain unsmooth edges, which will lead to wear, deformation, and difficulty of coatings for corrosion protection in the unsmooth region. With the aim of solving this problem caused by cusps or unsmooth points of the CSP, we put forward a meshing model of a circular arc and an equidistant curve of an epicycloid (ECE), and then proposed a design methodology for generating a completely smooth CSP. Screw rotors generated by the proposed CSP were completely smooth, and the proposed screw rotors could correctly mesh. Moreover, a geometric model of the proposed CSP was established, and the influence of the geometric parameters on its shapes and characteristics were studied. In addition, the proposed screw rotor was compared with the traditional screw rotor in terms of stress and deformation. Results indicated that the proposed screw rotor had continuous meshing and contact lines, and small values of maximum stress and deformation. The proposed smooth screw rotor is superior to the traditional one.

The Multicolumn Envelope Meshing Pair (MEMP) is a significant influence factor of single screw compressor (SSC) performance. It is necessary to carry out an optimization study on MEMP to improve the SSC performance. In this paper, a theoretical calculation model containing three leakage influencing factors is presented to research the influence of the MEMP profile parameters on the leakage characteristics of the SSC. Experiment investigations on the performance of a SSC with MEMP are carried out to verify the theoretical calculation model. With the validated model, the effect of MEMP profile parameters on the leakage characteristics of SSC has been analyzed. Optimization analysis shows that in the design stage more envelope columns with smaller center distance and larger radius should be chosen for the front side of the MEMP, but less envelope columns with smaller center distance and smaller radius should be chosen for the back side of the MEMP.

The rotor profile is one of the key factors for improving the performance of the Roots vacuum pump. A novel elliptical rotor profile consisting of the elliptical arc and its conjugate curve is proposed in this paper. The mathematical model of the elliptical rotor profile is established, and profile equations without incurring undercutting and carryover are derived. The elliptical rotor profile is tested using six Roots rotors, including five new elliptical rotors and one conventional circular arc rotor. Additionally, to assess the performance of the elliptical rotor profile, three-dimensional numerical simulations of the above six Roots rotors are conducted, and then the working process of the Roots vacuum pump is analyzed. The results indicate that all the new designs produce higher flow rate than the traditional circular rotor under the same conditions. As the elliptical axial ratio decreases, the area efficiency of the elliptical rotor increases.

A novel design methodology has been proposed based on the equidistant curve approach for constructing the complete meshing profiles (CMPs) of scroll compressors. The CMPs, including the peripheral profiles and central profiles for both the orbiting and fixed scrolls, can be generated simultaneously by offsetting the midline in the convex and concave direction. Three examples of the CMPs, named the circular arc modified wrap, circular arc add line modified wrap and asymmetric circular arc modified wrap, have been designed and illustrated by using the proposed design method. Geometric models of these three CMPs are established. Effects of geometric parameters of the modified wrap on performance of the scroll compressor are analyzed. The discharge pressure under the same suction volume of the scroll compressors with these three modified wraps are compared using numerical simulation. Results show that the discharge pressure of the circular arc modified wrap is bigger than that of the circular arc add line modified wrap with the same conditions, and the symmetric wrap is better than the asymmetric wrap in terms of the compression efficiency. The proposed design method is convenient to design new types of the advanced CMPs with better thermal and mechanical properties for scroll compressors.

In single screw refrigeration compressor (SSRC), the liquid refrigerant injected into the working chamber is used to reduce the exhaust gas temperature and improve the compressor performance. In this paper, a new calculation model of the injection process considering internal compression, leakage and heat transfer is presented based on the meshing principle of the meshing pair and the working mechanism of the SSRC with injection. By this model, the actual capacity and injection quality can be obtained using the calculated effective injection area. The influence of the structural parameters such as the initial position and the injection-hole diameter to the characteristics of the injection process and the thermodynamic properties of the SSRC are analyzed. Through the comparison of the injection process with different structural parameters, optimization analysis of the structural parameters can be obtained. All of this work can provide the basis for the later optimization design of the injection process.

Molecular dynamics simulations of droplets in gas forced vortexes by applying a virtual rotational potential were presented. The result showed that the flow field scale of the simulation performed can reflect the macroscopic characteristics. The trajectories of water droplets are longer than that of oil droplets within a certain radius of flow field. A droplet trajectory model was proposed to predict droplet behavior. The study continued to investigate droplet collisions. It was observed that the large oil droplet and the downwind small water droplets produced near head-on, highly off-centre and scraping-adhering collisions, forming stable two-phase interfaces. The slight changes of the interfaces between water and oil droplets under the action of rotating flow field can be reflected by van der Waals interaction. The intermolecular hydrogen bonds form when two water droplets collide. Our study provides a new idea for further understanding of droplet collision in gas flow field.

In view of the problems that the existing rotor profiles of claw vacuum pumps contain non-smooth connection points, a novel smooth rotor profile was proposed in this paper. The proposed profile, which can achieve correct meshing, is composed of 6 circular arcs and 3 equidistant curves of epicycloid, and its design procedures as well as equations were given. The effects of geometric parameters on the shape and performances of the claw rotor were analyzed. Besides, 3D numerical simulations of the entire working process of the claw vacuum pump with the proposed rotor profile were performed, and its performances were analyzed. The study results indicate that the proposed rotor profile of claw vacuum pumps, compared with the existing rotor profiles, has remarkable advantages of better meshing performance, smaller carryover and better mechanical properties. Thus, the new rotor profile designed and the data obtained can be applied to the design and optimization of claw vacuum pumps.

In the single screw refrigeration compressor (SSRC), the capacity control mechanism is normally employed to meet the actual required cooling capacity under different load conditions. In this paper, theoretical calculation models describing the working process of the SSRC with the single slide valve capacity control mechanism (SVCCM) and SSRC with the frequency conversion regulating mechanism (FCRM) are established to research the thermal dynamic characteristics for variable load SSRC under part-load conditions. Experimental investigation on a SSRC under part-load conditions is also carried out to verify the theoretical calculation models. By using these validated models, the thermodynamic performances and dynamic characteristics of the SSRC with different capacity control mechanism under part-load conditions have been analyzed and compared. Through the comparison, the economical efficiency and reliability of the SSRC with different capacity control mechanism were obtained. All of these works can provide the basis for the later optimization design for the variable load single screw refrigeration compressor.

In single screw refrigeration compressor (SSRC), the Multicolumn Envelope Meshing Pair (MEMP) was proposed to reduce the wear of the meshing pair. However, the application of this new type meshing pair will change the thermodynamic performance of SSRC. It is necessary to research the thermodynamic performance of the SSRC with MEMP to evaluate the value of the proposed MEMP. In this paper, a theoretical calculation model describing the working process of the SSRC with MEMP is established to predict the thermodynamic performance of the SSRC. Experimental investigations on the performance of a SSRC with MEMP under different conditions are also carried out to verify the theoretical calculation model. Obtained results show that the theoretical calculation results are in good agreement with the experimental ones, which means that the presented theoretical calculation model is a powerful tool for performance analysis of the SSRC with MEMP. With the validated model, thermodynamic performances of the SSRC with MEMP have been analyzed. The SSRC with MEMP is proved to have high volume displacement and volumetric efficiency but needs slightly more shaft power. The maximum increment of shaft power and volumetric efficiency of SSRC with MEMP is 5.06% and 3.7% respectively in all working conditions.

The Multicolumn Envelope Meshing Pair (MEMP) was proposed and has been applied for the single screw refrigeration compressor (SSRC) to reduce the wear of the meshing pair. However, the geometric model shows its changed shape of the leakage paths compared with the existing straight line envelope meshing pair (LEMP). It is necessary to research the leakage characteristics of the SSRC with MEMP and LEMP, to evaluate the value of the proposed MEMP. In this paper, the geometric model of the leakage paths between star-wheel and screw rotor is established. A two-phase leakage mathematical model for gas-oil flow is presented to predict the gas leakage rate of the SSRC with MEMP. The experiments of the performance of a SSRC with MEMP were conducted to verify the leakage mathematical model. Obtained results show the leakage of the SSRC with MEMP is a little bit smaller than that of the SSRC with LEMP.

In single screw refrigeration compressor (SSRC), the heat transfer has always been a key issue that affects its performance. However, the theoretical research on heat transfer characteristics of SSRC with Multicolumn Envelope Meshing Pair (MEMP) has not been carried out yet. Therefore, in this paper, a geometric model of heat transfer area and a theoretical calculation model describing the heat transfer process of the SSRC with MEMP are established to predict the heat transfer characteristics. The presented model is verified as a powerful tool for heat transfer characteristics analysis by the experimental results. With the validated models, heat transfer characteristics of the SSRC with MEMP under different operating parameters were researched and the effect of operating parameters on the heat transfer characteristics has been analyzed. All of these works can provide the basis for the later optimization design of heat transfer performance for the SSRC.

In the single screw refrigeration compressor (SSRC), the single slide valve capacity control mechanism (SVCCM) is the functional component used to achieve capacity control under different load conditions with cooperation of screw rotor and housing. In this paper, a new calculation model considering internal compression and leakage is presented to research the capacity control process and built-in volume ratio control process. By this model, the actual capacity and built-in volume ratio at different slide valve work locations can be determined using the calculated by-pass area and discharge area. The influences of structural parameters of the slide valve to the control characteristics of the capacity control process and the thermodynamic properties of the compressor are analyzed. Through the comparison of the capacity control process and the built-in volume ratio control process, the axial displacements of the slide valve required in the capacity control and in the built-in volume ratio control were obtained. All of this work can provide the basis for the later optimization design for the slide valve.

As a measurement of the residential population, the Census population ignores the mobility of the people. This weakness may be alleviated by the use of ambient population, derived from social media data such as tweets. This research aims to examine the degree in which geotagged tweets, in contrast to the Census population, can explain crime. In addition, the mobility of Twitter users suggests that tweets as the ambient population may have a spillover effect on the neighboring areas. Based on a yearlong geotagged tweets dataset, negative binomial regression models are used to test the impact of tweets derived ambient population, as well as its possible spillover effect on theft crimes. Results show: (1) Tweets count is a viable replacement of the Census population for spatial theft pattern analysis, (2) tweets count as a measure of the ambient population shows a significant spillover effect on thefts, while such spillover effect does not exist for the Census population, (3) the combination of tweets and its spatial lag outperforms the Census population in theft crime analyses. Therefore, the spillover effect of the tweets derived ambient population should be considered in future crime analyses. This finding may be applicable to other social media data as well.

In the rotary compressor, the rolling piston and the contacted rotor-journal bearing system are main moving components. They suffer very large periodically varying loads introduced by the inertia force, the contact force and the gas force. These loads change rapidly with speed variation of the compressor. They always lead to serious vibration of the system, and then result in abrasion and performance reduction. In this paper, the dynamic behavior of the rotor-journal bearing system were calculated by solving three-dimensional numerical model using finite element method, and the vibration characteristics of the system were investigated according to the calculation results. The natural frequencies and vibration modes were obtained. The stress, displacement and axis orbit of the rotor center were calculated considering the speed variation of the motor. Via the established numerical model, vibration characteristics of a newly designed compressor can be predicted, and optimization can be done to reduce the vibration.