bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a generalized compressor modeling framework for simulating an oil-injected twin-screw compressor
Authors: Salts Nicholas , Ziviani Davide , Groll Eckhard A.
Published: September 2019

Oil-injected twin-screw compressors are widely employed in many commercial and industrial applications because of their high efficiency and reliability. Although extensive literature on modeling techniques applied to twin-screw machines exists, researchers are continuously developing models to capture advanced physical phenomena occurring during the compression process (e.g., mass and heat transfer mechanisms). In order to generalize the concept of mechanistic compressor modeling, a framework for the simulation of positive displacement compressors and expanders (PDSim) has been developed and validated by the authors. The platform has been utilized to model a number of compressor types including scroll, reciprocating, linear, single-screw, rolling-piston, Z, and spool. In this work, the simulation tool has been extended to include twin-screw machines. Beside the detailed geometry model needed to obtain volume curves of the working chambers, sealing lines, and rotor surface areas, three main aspects have been enhanced with respect to the existing literature: (i) a two-fluid (refrigerant and lubricant oil) chamber model with mass and heat transfer interactions; (ii) computation of gas forces, loads on the bearings, and hydrodynamic bearing sub-models; (iii) detailed overall energy balance with a multi-lumped temperature thermal network and a discharge gas pulsations post-processing model. A 4/6 oil-injected twin-screw compressor has been considered to conduct experimental analyses with internal pressure and force sensors, modeling and validation as well as sensitivity analyses.
Validation of FlowVision CFD on ICCS2015 Test Case: Application of Gap ModelTM and SGGRTM for Leakage Flow Prediction in a Dry Screw Compressor
Authors: Ozturk U , Soganci S , Akimov V , Tutkun O , Aksenov A
Published: September 2019

Clearances and leakages through them play a vital role in determining the efficiency of positive displacement machines, especially of screw compressors. It is of interest to accurately predict the overall machine behavior including the leakage flows, even during the early design phases.

CFD (Computational Fluid Dynamics) methodologies can potentially address this problem; however, the computational efficiency is limited by the well-known issue: dimensionality. This issue arises due to the fact that rotors are sized in tens of centimeters whereas the clearances are in the order of (sub) microns.

Here we present a reduced order model called the Gap Model, embedded in FlowVision CFD software package to overcome this problem. Our approach is based on Poiseuille flow assumption and intends to evaluate fluid flows within very thin channels without resolving these regions with traditional fine mesh discretization. In such cases when two wall boundary conditions, such as rotor-to-rotor or rotor-to-chamber in a screw compressor, are close to each other less than mesh resolved dimensions, only one row of computational cells are constructed between the walls and an extra source term is added to the momentum equation, describing the frictional force produced by clearance walls.

The presented model is applied to ICCS2015 Test Case Screw Compressor developed by Centre for Compressor Technology of City, University of London. CFD predictions using this leakage model is in agreement with experimental results within 6.3 percent maximum error. The calculation times are reduced down to less than a day for obtaining stable and converged results.
User defined nodal displacement of numerical mesh for analysis of screw machines in FLUENT
Authors: Basha N , Kovacevic A , Rane S
Published: September 2019

Growing demands to reduce energy consumption are driving researchers towards in-depth analysis of positive displacement machines. Twin screw compressors are amongst the most common types of positive displacement machines. These machines have inherently complex geometry due to intricate rotor profiles used. As the details of the internal flows are difficult to obtain experimentally, Computational Fluid Dynamics (CFD) offers a good alternative for evaluation of internal flow patterns. However, implementation of CFD is challenging due complex deforming geometries.

In this paper, a customised grid generator SCORGTM developed by authors is used to generate numerical meshes for commercially available solver ANSYS FLUENT. FLUENT is an unstructured solver which offers flexibility of using both segregated and coupled solution algorithms. Segregated algorithms are generally faster which results in shorter product development time. Interface with FLUENT is implemented by performing User Defined Nodal Displacements (UDND) of grids generated by SCORG in a parallel framework. For this purpose, SCORG and UDND are coupled and extended to work with FLUENT’s parallel architecture. The developed code is compiled within the solver. The oil free air screw compressor with ‘N’ profile rotors and 3/5 lobe combination is modelled for 8000 RPM and 6000 RPM. Finally, the predicted performance values with FLUENT are compared to previously calculated CFX predictions and experimental results. FLUENT requires shorter solution time to obtain same accuracy of CFX.
Operation and performance of screw machines with high built-in volume ratio
Authors: Stosic N
Published: September 2019

A performance calculation of a screw compressor with increased built-in volume ratio was performed in this paper to establish how increased built-in volume ratio influences its efficiency. It is known that screw compressors have limited built-in ratio which is determined by their standard discharge port size and position. However, if the discharge port is reduced beyond its cusp position, the screw machine built-in volume is increased. In such a case, influence of the oil volume in the air-oil mixture of oil-flooded compressors increases the machine built-in volume further. The performance improvement achieved if the built-in volume ratio is doubled in comparison with the standard port during the machine operation at high pressure ratio of more than 20, is up to 26% for the specific power and adiabatic efficiency. This confirms superiority of the reduced size high pressure port for compressors which operate at high pressure ratio.
Dynamic research of piston/piston assembly in labyrinth reciprocating compressor
Authors: Zhang Wenshan , Zhang Zhao , Qian Lv , Feng Quanke , Wu Weifeng
Published: September 2019

The piston of labyrinth reciprocating compressor is often in the eccentric running state during operation, which leading to serious gas leakage and reduced compressor volume efficiency. To optimize the performance of labyrinth reciprocating compressor, the main reasons of piston eccentric operation are analyzed in detail in this paper. Based on the theory of multi-body dynamic and influence of piston bending and vibration, a rigid-flexible coupling multi-body virtual simulation model of piston/piston rod assembly is established by using numerical analysis software. The factors causing eccentric running of piston in cylinder are investigated and the eccentric running track of piston in cylinder and its dynamic characteristics are obtained.
Simulation and Prediction of Thermodynamic Performance of Reciprocating Compressor utilizing Physical Models Combining with Generalized Regression Neural Network
Authors: Qian Lv , Xiaoling Yu , Kun Wang , Junchao Ye , Shiyi Fan , Wang Xiaolin
Published: September 2019

Thermodynamic performance of a reciprocating compressor is generally evaluated or predicted by its physical models (PM). However in conventional PM, some key parameters are not easy to be determined and most time they can only be set values empirically. This article presented and experimentally verified physical models combining with generalized regression neural network (PMCGRNN) for the simulation and prediction of reciprocating compressor thermodynamic performance including the discharge temperature, and the volume flow rate. In PMCGRNN model of the compressor, firstly, the key parameters of compression polytropic exponent and the volume efficiency were obtained by generalized regression neural network (GRNN) with the input variables of suction temperature, suction pressure, discharge pressure, compressor rotate speed. Then the discharge temperature and the volume flow rate of the compressor were simulated respectively by their physical models (PM). The simulation results of discharge temperature and the volume flow rate by PMCGRNN were validated by a test bench of an air compressor. It was found that PMCGRNN has reliable prediction accuracy, and the relative errors of two PMCGRNN models are between −3.5% and +1.5%. and between −5% and 4%, respectively.
Modelling the Cylinder Cooling in an Oil-free Reciprocating Air Compressor
Authors: Tang Zhou , Wang Ting , Zhao Bin , Wang Mingfeng , Peng Xueyuan
Published: September 2019

Oil-free air compressors are widely applied in new energy vehicles, pharmaceutical, textile, food and the chemical industry for providing clean air. However, high temperature inside the cylinder due to compression heat and oil-less lubrication may lead to premature failure of the self-lubricating sealing rings and the grease-lubricating bearings. This paper presents the simulation of the cylinder cooling in an oil-free reciprocating air compressor for new energy vehicles. Based on the modelling, the cooling channel outside the cylinder was optimized to enable more effective cooling with limited air flow, obtaining lower temperature level of the cylinder, and therefore higher reliability of the sealing rings and bearings. The results show that the heat transfer model of the cylinder with numerical simulation is effective in predicting the cylinder temperature level as well as the cooling capacity of the air flow. The heat exchange efficiency of the compressor can be improved significantly by applying the optimized cooling duct structure. Compared with the model A, the maximum cylinder temperature was decreased by 13.1°C in the model B, and it also was decreased by 6.3°C in the model C.
A theoretical simulation model for optimization of fins on the shell of a hermetic reciprocating compressor
Authors: Dutra T , Moratelli S
Published: September 2019

The cost of a hermetic reciprocating compressor is quite dependent on the electric motor employed to drive it. Usually, the higher the motor efficiency, the higher the costs. Therefore, some compressors are designed to operate with low-efficiency electric motors. The main difficulty in such a case is to ensure that the motor operates at a temperature below the upper threshold. This paper presents a simulation model for optimization of fins on the shell of a hermetic reciprocating compressor which operates with a low-efficiency motor. The objective of the simulation is to obtain a set of fins with minimum volume that allows the compressor to operate under a critical operating condition without overheating the electric motor. The simulation model is implemented by coupling a lumped-parameter thermal simulation model of the reciprocating compressor with an optimization algorithm. The results of the thermal simulation are validated with experimental data. Different fin profiles are considered in the analysis. It is concluded that the optimum heat sink solution is conditioned to the minimum fin thickness or to the minimum fin diameter allowed, which are dependent on other compressor design constraints.
Opening up the lubricant toolbox
Authors: Karnaz J
Published: September 2019

Frequently, we fall back to concepts or ideas that we are comfortable with or have more understanding of. In these cases, we don’t always utilize all the resources available to us in make advancement or just try something new. This is sometimes true when it comes to using or evaluating lubricants for various refrigerants or refrigerant related applications. Too often we try to fit what is currently being used in existing applications into new applications instead of expanding our thinking and overall understanding. Usually these efforts are not put forward because we are not taking advantage of all the resources available to us to make good technical decisions. This paper will focus on the various types of lubricant chemistries available for use in the refrigeration and air conditioning industry and markets. Why some lubricants are used, while others are not used and while some lubricants are impractical. Various tools, techniques and computer assisted programs will be outlined that are useful when evaluating lubricant and refrigerant interaction properties.

A few key examples of refrigerants particular to current lower global warming potential reduction efforts will be investigated and what systematic approach can be used to make sure we don’t exclude potential lubricant candidates as viable options.
Understanding and improving the 9-coefficient pressure viscosity temperature (PVT) model
Authors: Barthel Anthony J , Majurin Julie
Published: September 2019

Data describing the physical properties of a mixed refrigerant-lubricant blend is necessary for compressor and system design and is measured using a pressure, viscosity, temperature (PVT) instrument setup. Measurements are taken at discrete conditions and refrigerant concentrations and a model is regressed which can describe pressure (refrigerant solubility), working viscosity, and density across the range of interest. Understanding the applicability of the model is crucial in choosing a suitable lubricant, since the tested conditions are unlikely to exactly match all operating conditions of interest.

This paper describes how the PVT model is created, and how choices in input data can affect the resulting model. Emphasis is placed on the range over which PVT models are valid and what can be done to increase model accuracy.
Performance optimization of two-stage compressor system using transcritical R744
Authors: Elbel S , Hrnjak P
Published: September 2019

The use of transcritical R744 systems has become increasingly popular in recent years in a variety of different applications. For applications that span a wide temperature range between the heat source and heat sink, the use of two-stage compressor results in numerous advantages in terms of efficiency and compressor discharge temperature. This paper presents experimental data for a transcritical R744 compressor system operating at high heat rejection temperatures. A comprehensive system model was developed and validated with the experimental results. Based on this, the simulation tool was used to further optimize the system design specifically to accommodate the two-stage compression process. The optimum heat transfer area distribution has been determined to simultaneously ensure efficient intercooling at intermediate pressure and gas cooling at the high-pressure level. Simultaneously, the system was also optimized with respect to optimal intermediate pressure and the results show that for this particular system, the optimum intercooler pressure deviated substantially from the standard design approach that uses the geometric mean between suction and discharge pressures.
Analysis of the thermodynamic disequilibrium loss of the two-phase expansion process and its influence on the performance of a reciprocating expander
Authors: Wang Qi , Huang Hao , Xu Liangcong , Yang Xiaotian , He Zhilong , Wu Weifeng
Published: September 2019

The screw expander and the reciprocating expander were considered as the suitable technologies to be employed as two-phase expanders of the Trilateral Flash Cycle (TFC) systems. The two-phase expansion process in the screw expander could be approximately viewed as the thermodynamic equilibrium process due to the strong disturbing and mixing between the two-phase working fluids in the chamber volume. However, for the reciprocating expander, the situation was different. The flashed vapor in the reciprocating expander cylinder was separated from liquid in the flash chamber, which would result in a significant thermodynamic disequilibrium loss. To assess this loss, the thermodynamic equilibrium model (TEM) and the flash vaporization model (FVM) were simultaneously proposed in this paper. Water was used as the two-phase working fluid. The two-phase expansion processes, the isentropic efficiencies and the output expansion works of the two models were obtained. Predicted results were analyzed and compared under different rotation speeds and injection temperatures. The results showed that when rotation speed of the expander was increased from 50 r/min to 1000 r/min, the thermodynamic disequilibrium loss was approximately increased from 5.3% to 6.3%, and when injection temperature was decreased from 523.15 K to 473.15 K, the thermodynamic disequilibrium loss was approximately increased from 4.5% to 6.2%.
Two-Phase Flow Analysis and Design of Geothermal Energy Turbine
Authors: Rane S , He L
Published: September 2019

A two-phase geothermal turbine generates mechanical energy by means of a total flow system. Literature references are available for experimental investigation of such flow machines but there is no validated numerical model for prediction of flow field and flashing for optimal design of the turbine’s flow channels. This paper presents a test reaction-turbine design study with two-phase flow using CFD. An Eulerian-Eulerian multiphase model with the Thermal Phase-Change criteria for two-phase heat, mass and momentum transfer has been used. Phase change validation has been conducted on published experimental data on a converging-diverging nozzle flow at various operating conditions. The stationary nozzle model was then extended to curved nozzle turbine and the results of flow and power has been validated with the data available in literature. Liquid water and vapour distribution due to flash evaporation was predicted by the analysis. Two-phase turbine model so established has been used further to re-design and optimise turbine nozzle by evaluating its cross section, area ratio, throat design, specific torque variation and curvature. Two new channel geometries, square and blended, were compared with the base circular channel and it was found that a blended channel offers on an average 6% higher specific power at 4623rpm. For the same rotor diameters and feed water flow rate, the power output could thus be improved by 4.5%. Isentropic efficiency in the range of 10 to 19% was estimated. Final design will be prototyped and tested in the laboratory for validation of design and deployment in eastern Africa.
Experience of application the computer program based on a simplified mathematical model for industrial centrifugal compressors candidates
Authors: Rekstin A F , Soldatova K V , Galerkin Yu B
Published: September 2019

Various engineering techniques are used to calculate and design centrifugal compressors, one of which is the Universal Modelling Method developed at SPbPU. Variants’ of centrifugal compressors analysis is the first step in gas-dynamic design. Brief information on the simplified mathematical model of efficiency is presented. It is possible to compare the variants of compressors with different number of shafts, shafts RPM, the number and location of intercoolers, the type of impellers and diffusers. Examples of a variants’ calculation of a pipeline compressors, a compressor for underground gas storage and a general-purpose air compressor are presented. It is shown that single-shaft compressors for underground gas storages should be optimized by selecting the maximum possible number of stages, by selecting the ratio of loading factors and the diameters of the impellers. It is shown that the single-shaft scheme of a general-purpose air compressor is inferior in efficiency to a two-shaft scheme with larger number of intercoolers. The presented samples have demonstrated that computer program based on a simplified mathematical model for industrial centrifugal compressors provides reliable and sufficient information for different compressors variants’ analysis.
Experimental study and optimal control strategy of a transcritical CO2 heat pump water heater
Authors: Ye Zuliang , Wang Yikai , Cao Feng
Published: September 2019

In this study, a transcritical CO2 heat pump water heater prototype was experimentally investigated in order to clarify the effects of the opening of electronic expansion valve (EEV), research the optimal discharge pressure and obtain an optimal control strategy for performance optimization. The tests were carried out by regulating the opening of EEV in multiple working conditions. The results showed that the decrease of opening led to reduction in evaporator inlet pressure and gas cooler outlet temperature, augment in discharge temperature, and decrease first then increase in discharge pressure. The optimal opening to reach maximum coefficient of performance (COP) always existed in all working conditions, however, there were two different situations where the corresponding optimal discharge pressure was near or away from the minimal value of the pressure curve. The reason for this phenomenon was the difference in water inlet temperature. Moreover, a correlation for the optimal discharge pressure was established with ambient temperature, water inlet and outlet temperature as independent variables. Furthermore, an optimal control strategy, in which the control of discharge pressure and superheat degree was considered, was proposed based on the correlation. Testing results proved that the optimization of performance could be achieved by using the strategy and the deviations between the COP under the control strategy and the optimal COP measured by experiments were within 5%.
Experimental testing of pneumatically forced actuated compressor-expander valves
Authors: Stoeckel C , Thomas C , Nickl J , Hesse U
Published: September 2019

The possibility of forced actuation of valves enables new operation modes for existing reciprocating compressors, e.g. capacity control or reverse operation as expander. A pneumatically forced actuated valve was tested within a reciprocating compressor and a quite complex behaviour was found, as shown in previous publications. A test rig outside of the compressor was set up for a better understanding of the system. Two measurement techniques were used to observe the sealing element motion over the time at varying operating conditions, like applied pressure levels and actuation time. The dependency of the valve motion to those operation conditions is evaluated and discussed. Improvements to the test bench and measurement techniques are also proposed to achieve more accurate results.
Testing and calculation of impact fatigue strength of Flap-X and SS 716 flapper valve steel grades
Authors: Tofique Muhammad Waqas , Löf Alexander , Millward Chris , Günther Zippl
Published: September 2019

During the operation of reciprocating compressors, the flapper valve opens and closes under fluid pressure and flow. As it closes, it strikes against the valve seat, generating stresses and noise. This cycle of loading produces bending and impact fatigue stresses in the reed. This load pattern is repeated billions of times during the service life of a compressor and it defines the service life and reliability. The goal of this study was to calculate the impact fatigue strength of the Flap-X and the SS 716 grades and, to provide the compressor manufacturers with the information they can use to specify a steel grade to be used in their compressors, for reliable service. Impact fatigue tests were conducted on a custom-built impact fatigue test rig that used air pulses to produce movement of the reed valves manufactured by a major European compressor manufacturer Nidec Global appliance GmbH, at a frequency of 315 Hz and pulse width of 2.2 milliseconds. The testing was conducted according to the staircase test method detailed in the International Standard SS-ISO 12107:2012. The impact fatigue strength of the Flap-X and SS 716 steel valves was calculated in terms of the impact velocity according to the modified staircase test method in the standard. The test results and their statistical analysis showed that the impact fatigue strength of the Flap-X grade was higher compared to the SS 716 grade. The calculation and testing of the impact fatigue strength of the flapper valve steel grades could help the compressor designers to select the optimum material for their compressor designs, to provide reliable service. The higher impact fatigue strength of the Flap-X grade, lower failure rate and longer impact fatigue life will allow the compressor manufacturers to design thinner valves, as Flap-X can sustain higher impact fatigue stresses reliably for longer time and, at the same time help reduce noise, as thinner valves produce less noise for a given pressure and frequency.
Clean, flawless and thinner stainless steel valves by strip casting
Authors: Barani Araz Ardehali , Campbell Paul , Haggeney Manfred
Published: September 2019

Compressor valves are made of hardened and tempered martensitic stainless steels. They were first produced from ingot cast material. Later continuous casting technology largely replaced this process, which led to improved, more uniform, properties and higher yields in the production of hot strip. A further development was made around the turn of the millennium, when strip casting was first used for the production of stainless steel strip, directly from the melt. In this paper the steel grade Zapp 1.4028MO produced via both production routes: a) Continuous casting - hot rolling - cold rolling and b) Strip casting - cold rolling, are compared with respect to their microstructure evolution and static/dynamic mechanical properties. It is shown that strip cast material can not only substitute that of the traditional continuous casting route, but moreover deliver performance advantages with thin stainless steel valves used within air conditioning units and household refrigerators.
Experimental investigation on the extreme cold start-up of an air compressor for electric heavy vehicles
Authors: Valenti Gianluca , Murgia Stefano , Costanzo Ida , Ravidà Antonino , Piscopiello Giovanni Pio
Published: September 2019

Engine-driven reciprocating air compressors are employed on fuel-powered heavy vehicles to actuate a number of auxiliary systems, like brakes and suspensions. Electrically-driven sliding-vane air compressors turn particularly suited for electric heavy vehicles. Unlike in fuel-powered vehicles, the compressor is not heated up in the case of electric mobility, a situation that may lead to potential issues in extreme cold weathers. This paper investigates experimentally the start-up of a sliding-vane air compressor designed specifically for electric heavy vehicles. The compressors, equipped with instruments, is positioned in a climatic chamber. During the tests, the chamber is set to a desired ambient temperature, 0, -10, -20, - 30 °C or 20 °C taken as reference following ISO 1217, and the compressor is started-up when a steady-state initial condition is achieved. The delivery pressure is controlled at 10 bar(g) and all measurements are recorded until a temperature of 80 °C is reached in the air-lube oil separator. No issues are encountered during the tests, such as sudden damage due to improper lubrication. Moreover, the curves of the measured temperature within the air-lube oil separator show similar trends but higher initial plateaus and lower slopes at lower ambient temperatures resulting into lower oil flow rates, higher energy spent for heating up the system as well as higher warm-up times, from 15 minutes at 20 °C up to 69 minutes at -30 °C.
A Theoretical Study on the Novel Structure of Vane Compressor for High Efficiency
Authors: Hu Y S , Wei H J , Xu J , Wan P K , Wu F , Luo F Y , Ren L P
Published: September 2019

Aiming at the problem of excessive mechanical loss of the conventional vane compressor, this paper proposes a novel vane compressor structure. This compressor can significantly reduce the mechanical frictional loss through converting sliding friction between vane tip and cylinder into rolling friction by using a rolling bearing. The structure and operation principle are introduced in this paper, and mechanical friction loss calculation models of these two kinds of compressor are theoretically analyzed. The results show that mechanical loss of the novel vane compressor can be reduced by nearly 38% under the same working conditions. At the same time, the actual tested results indicated that the total power consumption of compressor decreased 160.1W (6.89%), and the COP increased by 11.89%.
Performance evaluation of a rotating sleeve vane compressor
Authors: Sarip A R , Musa M N
Published: September 2019

This paper presents the performance study of a new designed rotating sleeve vane (RSV) compressor. The aim of this study was to develop a more compact semi-hermetic refrigerant compressor for refrigeration and air-conditioning systems, which will improve the conventional design in terms of sizing and operating mechanism. Experimental study was carried out on the prototype of a single and multi-vane (three and five-vane) RSV compressor prototypes with identical size of rotor and sleeve and tested the in a test bench of R134a refrigeration system. Each test was carried out in a steady state of refrigeration thermodynamic cycle at operating speed varied between 1000 rpm to 1500 rpm to obtain the mechanical and volumetric efficiencies. The experimental results on the three of the new prototypes were analyzed and found that that the single vane compressor prototype has a similar volumetric efficiency of about 90% with that of rolling piston compressor of equivalent capacity. A double increment in capacity to about 48 cc was observed in the five vane prototype models with the same overall dimension and configuration of the rotating components to that of the single vane. The volumetric efficiency was also comparable of about 70% to an existing multi vane rotary compressor.
Study on leakage loss via the radial clearance in a double-swing vane compressor for electric vehicle air conditioning systems
Authors: Zhong Hua , Li Xiaoran , Yang Xu
Published: September 2019

The leakage loss in a novel double-swing vane compressor (DSVC) for use in electric vehicle air conditioning systems is theoretically analysed. The leakage flow through the radial clearance between the rotor and cylinder in the DSVC is modelled by considering both the section change of the leakage channel and the viscous friction of the working fluid. Under the same operating conditions and dimensions, the radial leakage loss of DSVC is more than that of the swing vane compressor (SVC) with a single swing vane. However, the theoretical suction volume of the DSVC is larger than that of the SVC. The relative volumetric leakage loss is almost equal to that of the SVC, which indicates that compared to the SVC, the effects of the structural changes of the DSVC on the volumetric efficiency is neglectable. Considering the larger work capacity and higher mechanical performance of the DSVC, it is suggested that the DSVC is a better choice for the electric vehicle air conditioning system.
Research on the Vapor Injection of Two-stage Rotary Compressor
Authors: Hu Y S , Wei H J , Yu B , Yang O X , Wang J , Wu J
Published: September 2019

In order to understand the vapor injection flow characteristics of two-stage rotary compressor in the course of compression, a mathematical model based on mass conservation equation, energy equation and thermodynamic identity was established and proved by P-V diagram testing results. Some useful conclusions about pressure in the intermediate chamber and mass flow of vapor injection in the course of compression were also given out. The results show that, gas backflow between the intermediate chamber and the vapor injection channel is an important defection of two-stage rotary compressor which can be solved by the application of injection valve in vapor injection channel. The injection valve can obviously reduce the gas backflow and the power loss in the course of compression while increasing the pressure fluctuation in the intermediate chamber. Experiments show that the COP of two-stage rotary compressor with the injection valve increased by over 2% in ASHRAE/T working condition.
The Theoretical and Experimental Research of a Novel Rotary Cylinder Compressor
Authors: Hu Y S , Wei H J , Xu J , Du Z C , Yang S , Ren L P
Published: September 2019

Rotary compressor has been widely used in home air conditioning. The sealing forms of roller-vane and roller-cylinder in rotary compressor are linear sealing, resulting in large leakage and low volumetric efficiency. The performance of the compressor tempestuously reduces with the running frequency decreasing. A novel positive displacement compressor was introduced in this paper: rotary cylinder compressor. The cylinder and shaft rotate around their own axes, and the piston reciprocates relative to them, in order to implement suction and exhaust process. Further, the volume efficiency and mechanical efficiency of rotary cylinder compressor and rotary compressor was analyzed and compared theoretically. The results indicated that the sealing forms of all leaking channels in rotary cylinder compressor are face sealing, which results in less leakage and higher volumetric efficiency than linear sealing. The novel compressor has a significant advantage at the medium and low frequency, and the advantage shows more obvious with the decreasing frequency. Finally, the experimental results of the prototype fully verified the performance advantages of rotary cylinder compressor at volumetric efficiency and electrical efficiency, which was consistent with the theoretical analysis.
Numerical investigation of oil injection in a Roots blower operated as expander
Authors: Casari Nicola , Fadiga Ettore , Pinelli Michele , Suman Alessio , Kovacevic Ahmed , Rane Sham , Ziviani Davide
Published: September 2019

The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. At the same time, these devices often serve as compressor in Vapor-Compression Refrigeration Systems. In both cases, the application of Computation Fluid Dynamics (CFD) to optimize such machines has become an integrated tool in the design process. As a consequence, several challenges associated with the numerical simulation have to be taken into account. For example, the modeling of the gap represents a challenge for the stability of the numerical analysis. The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care.

To raise the efficiency of the machine, oil is typically injected. Its numerical modeling imply an extra challenge in the simulation of the actual operation of the machine. The present work is mainly focused on the multi-phase nature of the flow, with a particular analysis of the lubricant oil injected. In this work, a two-lobe Roots blower operated as expander has been simulated with the open-source software OpenFOAM-v1812, using the SCORG-V5.2.2. This analysis highlights the areas that are affected the most by the oil presence in order to highlight the sealing effect it provides
Model predictive control of a free piston compressor/expander with an integrated linear motor/alternator
Authors: Gusev Sergei , Ziviani Davide , Paepe Michel De
Published: September 2019

Linear positive displacement machines are becoming increasingly more attractive for applications that are normally known as unconquerable niches of rotary and scroll machines. Free-piston machines are characterized by the absence of a crank mechanism, since there is a direct transformation of electrical energy into the piston movement. From the point of view of manufacturing, these machines benefit from a higher robustness and reliability because of less mechanical components involved and reduced frictional losses associate with a conventional crank mechanism.

However, the major challenge in replacing the rotary machines by linear ones is a lower efficiency at lower speeds which is unavoidable because of the nature of linear motion: continuous operation means a reciprocating movement within a stroke length with significantly long periods of acceleration and deceleration when the speed is far from its optimal value. However, the advantage of free-piston machines is the fact that the motion profile is freely configurable within physical constraints, which provides a possibility to optimize the speed given the efficiency map of particular linear motor.

While the methods and results of the efficiency assessment for rotary machines are widely available, there is a lack of these analyses for linear machines. The current study provides in-depth analyses of a double-coil iron core linear motor also acting as a generator.
Investigation on the Performance Improvement of the Scroll Compressor by DLC Film
Authors: Ji Lantian , He Zhilong , Han Yaoxiang , Chen Weiqing , Xing Ziwen
Published: September 2019

The material property of orbiting scroll surface, mainly affects the life and performance of scroll compressors. Generally, the anodic oxide film (AOF) is used in the surface treatment of the domestic orbiting scroll, which has numerous drawbacks such as poor adhesion of the film-substrate and easy wear failure. In this paper, a process producing the diamond-like carbon film (DLCF) on the surface of an orbiting scroll by unbalanced magnetron sputtering technology was proposed based on the mechanical characteristics of the scroll compressor and the surface treatment method of the orbiting scroll. The friction coefficient, microhardness, film-substrate adhesion and other performances of the AOF and DLCF were analyzed from the data measured by various test facilities. The refrigeration capacity, power and volumetric efficiency of compressors with different coatings were analyzed and compared by tests under different operating conditions with fixed values of refrigerant charge and oil content. The surface morphology of the coatings was then studied by scanning electron microscope to identify the microstructure after the operation. The results showed that a more even and dense surface was obtained by the DLCF compared with the AOF, which improved the wear resistance of the surface. The surface friction coefficient was only 0.11 as the Cr transition layer markedly enhanced the bonding strength. The DLCF displayed more properties of graphite with the thickness of only 0.73 μ m. The volumetric efficiency of the compressor under the nominal operating condition increased by 5.8%.
Comparison between single and cascaded organic Rankine cycle systems accounting for the effects of expansion volume ratio on expander performance
Authors: White M T , Read M G , Sayma A I
Published: September 2019

Compared to single-stage organic Rankine cycle (ORC) systems, cascaded ORC systems, in which a high-temperature topping cycle and low-temperature bottoming cycle are coupled together, could have advantages in terms of removing the potential for sub-atmospheric condensation conditions and improving expander performance as the expansion process is effectively divided across two stages. Moreover, reducing the expansion volume ratio could facilitate the use of volumetric expanders, such as twin-screw expanders, which, in turn, could facilitate two-phase expansion to be utilised in one, or both, of the cycles. The aim of this paper is to compare single-stage and cascaded ORC systems, accounting for the effect of the expander volume ratio on expander performance. To investigate this, thermodynamic models for single-stage and cascaded ORC systems are developed, which include variable efficiency expander models for both radial turbines and twin-screw expanders that can estimate the effect of the expansion volume ratio on the expander isentropic efficiency. Using this model, three different scenarios are compared for different temperature heat-source temperatures, namely: (i) single-stage ORC systems with vapour-phase expansion obtained using a turboexpander; (ii) single-stage ORC systems operating with a twin-screw expander, with the possibility for two-phase expansion; and (iii) cascaded cycles with either vapour- or two-phase expansion. The results from this comparison are used to identify applications where cascaded ORC systems could offer performance benefits.
Investigation of a Thermo-Fluidic Exchange Pump in Trilateral Flash and Organic Rankine Cycles
Authors: Baggley C R , Read M G
Published: September 2019

It is well known that large amounts of energy loss occurs at low temperature states in a wide range of industrial processes., The recovery and reuse of this energy is at the forefront of increasing the overall efficiencies of industrial systems. The aim of this paper is to investigate the effectiveness of using a Thermo-Fluidic Exchange (TFE) pump at low temperature conditions in both a Saturated-Vapour Organic Rankine Cycle (SORC) and a Trilateral Flash Cycle (TFC).

For some low temperature applications, TFCs have been shown to achieve higher net power output than conventional SORCs, due to their ability to extract more heat from the source fluid. This is the subject of current research as a result of advancements made in the design of positive displacement machines for operation as two-phase expanders. Conventional turbines cannot be used for TFCs as they must operate in the vapour phase.

One drawback of the TFC is the higher working fluid mass flow rate required. Depending on the scale of the system, this can potentially cause difficulties with pump selection. A TFE pump uses heat input to the system to increase the pressure and temperature of the working fluid, rather than the work input in a standard mechanical pump. This paper compares the net power output achievable using both mechanical and TFE pumps with SORC and TFC systems. The results suggest that the TFE pump could be a viable option for TFC systems.
Heterogeneity introduced by EHR system implementation in a de-identified data resource from 100 non-affiliated organizations
Authors: Glynn Earl F , Hoffman Mark A
Published: September 2019

Objectives

Electronic health record (EHR) data aggregated from multiple, non-affiliated, sources provide an important resource for biomedical research, including digital phenotyping. Unlike work with EHR data from a single organization, aggregate EHR data introduces a number of analysis challenges.

Materials and Methods

We used the Cerner Health Facts data, a de-identified aggregate EHR data resource populated by data from 100 independent health systems, to investigate the impact of EHR implementation factors on the aggregate data. These included use of ancillary modules, data continuity, International Classification of Disease (ICD) version and prompts for clinical documentation.

Results and Discussion

Health Facts includes six categories of data from ancillary modules. We found of the 664 facilities in Health Facts, 49 use all six categories while 88 facilities were not using any. We evaluated data contribution over time and found considerable variation at the health system and facility levels. We analyzed the transition from ICD-9 to ICD-10 and found that some organizations completed the shift in 2014 while others remained on ICD-9 in 2017, well after the 2015 deadline. We investigated the utilization of “discharge disposition” to document death and found inconsistent use of this field. We evaluated clinical events used to document travel status implemented in response to Ebola, height and smoking history. Smoking history documentation increased dramatically after Meaningful Use, but dropped in some organizations. These observations highlight the need for any research involving aggregate EHR data to consider implementation factors that contribute to variability in the data before attributing gaps to “missing data.”
Obesity as a Risk Factor Among Hospitalized Patients with Infective Endocarditis
Authors: Harris Ché Matthew , Albaeni Aiham , Wright Scott , Norris Keith C
Published: September 2019

Objective

Obesity contributes to diagnostic and management challenges for many hospitalized patients. The impact of obesity on in-hospital outcomes in patients with infective endocarditis has not been studied and was the focus of this investigation.

Method

We used the 2013 and 2014 Nationwide Inpatient Sample to identify adults ≥18 years of age with a principle diagnosis of endocarditis. We divided the sample into 2 groups based on presence of absence of obesity. Multivariate linear and logistic regression analysis was used to compare in-hospital mortality, valvular replacement, length of stay (LOS), and hospitalization charges.

Results

A total of 24 494 adults 18 years and older were hospitalized with infective endocarditis, of which 2625 were classified as obese. Patients with obesity were older (mean age, 57.8 ± 0.3 vs 54.3 ± 0.6 years; P < .01), more likely to be female (50.1% vs 36.1%; P < .01), and had more comorbidities (Charlson comorbidity score ≥ 3, 50.6% vs 28.8%; P < .01). Multivariate regression analysis found no differences between the 2 groups for mortality or repairs or replacements for any valve. On evaluation of resource utilization, patients with obesity had longer average LOS (13.9 days; confidence interval [CI], 12.7–15.1 vs 12.4 days; CI, 12.0–12.8; P = .016) and higher total hospital charges (US $160 789.90; CI, $140.922.40–$180 657.50 vs US $130 627.20; CI, $123 916.70–$137 337.70; P <.01). After adjustment for LOS for total hospital charges, there was no observed difference $11436.26 (CI, -$6649.07–$29521.6; P = .22).

Conclusions

. Obesity does not significantly impact in-hospital mortality or surgical valvular interventions among patients hospitalized with infective endocarditis, but obesity is associated with increased utilization of hospital resources.
Treatment and surveillance of advanced, metastatic iodine-resistant differentiated thyroid cancer
Authors: Ibrahim Eiman Y. , Busaidy Naifa L.
Published: September 2019

Purpose of review

This review will focus on the management and treatment of metastatic thyroid cancer that is radioactive iodine refractory and review the new drugs and their mechanism of actions as well as their adverse events.

Recent findings

Until recently, there were no efficacious therapeutic modalities for these patients. With advancement in knowledge and research of the molecular aberrations and oncogenic mutations in thyroid cancer as well as further understanding the role of angiogenesis in tumor growth molecular pathogenesis, novel targeted therapies are available for these patients. Some of these drugs have successfully prolonged progression free survival and are now Food and Drug Administration approved. Additional agents are approved for the treatment of other types of cancers and are currently under investigation for differentiated thyroid cancer treatment.

Differentiated thyroid cancer (papillary and follicular) is the most common endocrine malignancy. It is generally known to have an excellent prognosis and patients are usually cured with the conventional primary treatments including surgery, radioactive iodine, and thyroid stimulating hormone suppression. A minor proportion of patients do not fully recover mainly because they develop radioactive iodine-resistant disease. These patients have few treatment options, which we aimed to describe here.