Outlet Parameters Research Articles

Measurement of Thoracic Inlet Alignment on MRI: Reliability and the Influence of Body Position.

A retrospective radiographic study. To investigate the reliability of using magnetic resonance imaging (MRI) to measure thoracic outlet parameters and whether supine MRI could supersede upright x-ray in measuring these parameters. On x-ray, overlapped soft and bony tissues make sternum contour invisible. Thus, measuring thoracic inlet (TI) alignment on x-ray may be inaccurate. MRI could clearly show anatomy around TI. A total of 124 adolescents with idiopathic thoracolumbar/lumbar scoliosis were recruited. The visibility of T1 upper endplate and the upper end of sternum on the lateral standing x-ray films was rated. For patients with moderate or good clarity forT1 upper endplate and the upper end of sternum on x-ray films, thoracic inlet angle (TIA), T1 slope (T1S), and neck tilt (NT) were measured by 3 observers on standing x-ray films and supine MR images, respectively. Intraclass correlation coefficients (ICC) were used to determine the intraobserver, interobserver, and method reliability. The paired t test was performed to compare the measurements between the 2 methods. The correlation coefficients between the 2 methods were analyzed by regression analysis. The visibility of TI region on x-ray films was unsatisfactory, whereas all the landmarks were clear on MR images. Only 81 patients' x-ray films were graded as moderate or good visibility in the TI region. Both the intraobserver ICC and interobserver ICC were better in the MRI set than in the x-ray set among all the observers for 3 TI parameters. The paired t test demonstrated that no significant difference was noted in terms of TIA, T1S, and NT (P=0.572, 0.203, and 0.637, respectively). Regression analysis demonstrated high correlation coefficients for TIA, T1S, and NT (R=0.612, 0.629, and 0.722, respectively). MRI serves as a good substitute for x-ray scans with regard to the measurement of TI alignment, with superior reliability.

STATISTICAL OPTIMIZATION OF FREQUENCY REGULATED INDUCTION ELECTRIC DRIVES WITH SCALAR CONTROL

Purpose. Working out of technique of synthesizing statistically optimal controllers of induction electric drives with frequency scalar control operating under stochastic loads. Methodology. It is shown, that one of the ways of increasing the energy efficiency of induction electric drives at random changes of loads is to create closed systems of electric drives with statistically optimal regulators that would take into account the stochastic nature of the disturbances and acted as filters of occasional high frequency fluctuations. The structure of such controls depends on the statistical characteristics of stochastic loads – correlation function and spectral density. In this mode, the minimum loss in dynamic mode with random intensive changed loads is provided by criterion of minimum mean square error of optimal parameter control. In the case of frequency controlled electric drive such a parameter is the optimum rotor flux. Results. The optimal structures of regulators of electric drives under stochastic loads according to type of random disturbances are identified. Originality. The technique of statistically optimal synthesis with feature of the expansion of a random process load on average, served as a useful signal, and high-frequency fluctuations around the average value, served as barrier, is developed. Practical value. On an example of simulation of work of the electric drive of a crusher of grain it is shown efficiency of a filtration by statically optimal regulator of the high-frequency components of random torques of load, reduction of dispersions of its outlet parameters, increase of cyclic indicators of energy efficiency of the electric drive, such as cyclic efficiency and power factor.

Exergy optimization of cooling tower for HGSHP and HVAC applications

In the present work, a constrained inverse optimization method for building cooling applications is proposed to control the mechanical draft wet cooling tower by minimizing the exergy destruction and satisfying an imposed heat load under varying environmental conditions. The optimization problem is formulated considering the cooling dominated heating, ventilation and air conditioning (HVAC) and hybrid ground source heat pump (HGSHP). As per the requirement, new second degree correlations for the tower outlet parameters (water temperature, air dry and wet-bulb temperatures) with five inlet parameters (dry-bulb temperature, relative humidity, water inlet temperature, water and air mass flow rates) are developed. The Box–Behnken design response surface method is implemented for developing the correlations. Subsequently, the constrained optimization problem is solved using augmented Lagrangian genetic algorithm. This work further developed optimum inlet parameters operating curves for the HGSHP and the HVAC systems under varying environmental conditions aimed at minimizing the exergy destruction along with the fulfillment of the required heat load.

Maximizing performance of fuel cell using artificial neural network approach for smart grid applications

This paper presents an artificial neural network (ANN) approach of a smart grid integrated proton exchange membrane (PEM) fuel cell and proposes a neural network model of a 6 kW PEM fuel cell. The data required to train the neural network model are generated by a model of 6 kW PEM fuel cell. After the model is trained and validated, it is used to analyze the dynamic behavior of the PEM fuel cell. The study results demonstrate that the model based on neural network approach is appropriate for predicting the outlet parameters. Various types of training methods, sample numbers and sample distribution methods are utilized to compare the results. The fuel cell stack efficiency considerably varies between 20% and 60%, according to input variables and models. The rapid changes in the input variables can be recovered within a short time period, such as 10 s. The obtained response graphs point out the load tracking features of ANN model and the projected changes in the input variables are controlled quickly in the study.

Efficiency analysis of a novel electricity and heat co-generation system in the basis of aluminum–water reaction

With high calorific value and the environmental friendly features, hydrogen has been attached much importance. Aluminum–water reactions at medium–high temperature perform well in hydrogen generation as well as heat utilization. Active researches of the aluminum–water reactions in recent years can be attributed to the increasing interest of hydrogen generation and energy conversion.In the basis of aluminum–water reactions, the concept of a novel electricity and heat co-generation system was proposed here and it was primarily composed of a reactor, one or two turbines and generators, heat exchanger for heat user, a fuel cell and a pump. Two layouts were designed and analyzed: the one turbine layout (OTL) and the two turbine layout (TTL).The effects of key parameters, such as the steam temperature and pressure at turbine inlet, the heat user temperature and fuel cell conversion efficiency were investigated. The co-generation system could generate heat and electricity of about 22.2 MJ/kg (Al) in the OTL design. The system utilization efficiency, the ratio of the output was approximate 70% and the electricity generation efficiency could reach up to 41.52% (OTL) and 49.25% (TTL) in the two cases respectively. The OTL presented a higher heat user utilization efficiency than TTL, because of the higher turbine outlet parameters. The TTL layout with the integration of fuel cell and heat user enhanced electricity output by 45.06% in comparison with the OTL layout. The steam temperature at turbine inlet showed considerable impacts on the system utilization efficiency at the TTL case. Enhancing fuel cell conversion efficiency benefited the system and fuel cell utilization efficiencies, especially at the TTL case.

Effects of rotational speed on the leakage behavior, temperature increase, and swirl development of labyrinth seal in a compressor stator well

The stator well in a compressor is the space between the rotor and stator inside the mainstream annulus flow. Labyrinth seals are normally used to control the internal flow in the stator well. The upstream and downstream rotating cavities of the labyrinth seal can lead to substantial temperature rise and swirl development in this region. Additionally, due to the centrifugal expansion and thermal expansion, the tip clearance of labyrinth seal changes dramatically at different rotational speeds and temperatures in the stator well. A test rig capable to establish different rotational speeds and pressure ratios was designed according to the simplified model of the labyrinth seal in a compressor stator well (one stage). The leakage flow rate and change in total temperature across the stator well were measured. This paper also contains the experimental results of swirl ratios in the outlet rotating cavity to reveal the swirl development. Special emphasis in this work lies on acquiring the working tip clearance precisely. The set up tip clearance was measured with plug gauges, while the radial displacements of labyrinth ring and stator casing were measured separately with two high precision laser distance sensors. Two-dimensional, axisymmetric swirl flow numerical simulations were performed to get a further understanding about the basic flow characteristics and to evaluate their ability to predict the experimental results. The computational results of discharge coefficient, windage heating, and swirl ratio were compared to those obtained from test rig measurements. Particularly, when calculating, the tip clearance, the inlet parameters, and the outlet parameters of numerical model at a specific rotating speed were set to be the same with the experimental conditions.

Study on an internally-cooled liquid desiccant dehumidifier with CFD model

The liquid desiccant air conditioning system is considered as a possible substitute of the traditional air conditioner mainly due to its characteristics of energy saving. The dehumidifier is a key component of the system therefore was chosen as the research object. It was found the present models conducted the simulation with lots of assumptions, especially ignoring the effect of flow behavior. Besides, most studies focused on the inlet and outlet parameter changes rather than the interior condition of the dehumidifier. To fill the research gap, a model for an adiabatic dehumidifier was established with CFD technology in authors’ previous study. On the basis of it, a model was further developed in present work for internally-cooled liquid desiccant dehumidifier. The interior heat and mass transfer processes were then simulated with the model, followed by the detailed performance investigation. Analysis was conducted to investigate the influence of some factors, including inlet desiccant temperature, desiccant flow rate and two types of internally cooling, and variable physical properties. The advantage of present study lied in its more in-depth analysis of interior condition of the dehumidifier. Besides, the study also demonstrated the necessity of considering the variable properties of desiccant solution during the simulation.

A new predictive model for the filtered volume and outlet parameters in micro-irrigation sand filters fed with effluents using the hybrid PSO–SVM-based approach

Filtration is a key operation in micro-irrigation for removing the particles carried by water that could clog drip emitters. Currently, there are not sufficiently accurate models available to predict the filtered volume and outlet parameters for the sand filters used in micro-irrigation systems. The aim of this study was to obtain a predictive model able to perform an early detection of the filtered volume and sand filter outlet values of dissolved oxygen (DO) and turbidity, both related to emitter clogging risks. This study presents a novel hybrid algorithm, based on support vector machines (SVMs) in combination with the particle swarm optimization (PSO) technique, for predicting the main filtration operation parameters from data corresponding to 769 experimental filtration cycles in a sand filter operating with effluent. This optimization technique involves kernel parameter setting in the SVM training procedure, which significantly influences the regression accuracy. To this end, the most important physical–chemical parameters of this process are monitored and analyzed: effective sand media size, head loss across the filter and filter inlet values of dissolved oxygen (DO), turbidity, electrical conductivity (Ec), pH and water temperature. The results of the present study are two-fold. In the first place, the significance of each physical–chemical variables on the filtration is presented through the model. Secondly, a model for forecasting the filtered volume and sand filter outlet parameters is obtained with success. Indeed, regression with optimal hyperparameters was performed and coefficients of determination equal to 0.74 for outlet turbidity, 0.82 for filtered volume and 0.97 for outlet dissolved oxygen were obtained when this hybrid PSO–SVM-based model was applied to the experimental dataset, respectively. The agreement between experimental data and the model confirmed the good performance of the latter.

Modelling of mass transfer kinetic in osmotic dehydration of kiwifruit

Abstract Osmotic dehydration characteristics of kiwifruit were predicted by different activation functions of an artificial neural network. Osmotic solution concentration (y1), osmotic solution temperature (y2), and immersion time (y3) were considered as the input parameters and solid gain value (x1) and water loss value (x2) were selected as the outlet parameters of the network. The result showed that logarithm sigmoid activation function has greater performance than tangent hyperbolic activation function for the prediction of osmotic dehydration parameters of kiwifruit. The minimum mean relative error for the solid gain and water loss parameters with one hidden layer and 19 nods were 0.00574 and 0.0062% for logarithm sigmoid activation function, respectively, which introduced logarithm sigmoid function as a more appropriate tool in the prediction of the osmotic dehydration of kiwifruit slices. As a result, it is concluded that this network is capable in the prediction of solid gain and water loss parameters (responses) with the correlation coefficient values of 0.986 and 0.989, respectively.

Experimental investigation on repeatability of CHF in rod bundle with non-uniform axial heat flux distribution

Critical heat flux (CHF) is important to thermal-hydraulics design and safety analysis. In the purpose to validate the CHF data acquired from LS-THTF of NPIC, experimental investigation on repeatability of the CHF data is carried out with full length non-uniform axial heat flux distribution rod bundle. The repeatability of the CHF data from LS-THTF itself is examined by comparing the data from the same run but different time and data from different runs. The rod bundle powers of CHF data acquired under well controlled parameters are directly compared with reference measured data from HTRF of Columbia University. The rod bundle power ratio of CHF data is employed to describe the repeatability of CHF data from LS-THTF to HTRF, and the variations of power ratio with inlet and outlet parameters show a reasonable trend. The point to point differences of CHF power between the two facilities of every single point are found to be within 5%. The result demonstrates good repeatability between data from LS-THTF and data from HTRF. LS-THTF is capable of acquiring reliable and repeatable CHF data to verifying thermal-hydraulics performance of PWR fuel assemblies.

Desiccant cooling systems: a review

Desiccant cooling systems have been considered as an efficient method of controlling moisture content in supply air. They do not use any ozone-depleting coolants and consume less energy as compared with the vapour compression systems. This communication provides an extensive review of liquid desiccant systems (LDSs). All the components of an LDS such as dehumidifier, regenerator, packing material and liquid desiccant properties along with its energy storage capabilities have been discussed in detail. In addition, hybrid of LDSs with sensible cooling technologies has been studied. Various types of mathematical models to predict the outlet parameters of the desiccant system and current issues in liquid desiccants have been reviewed in detail. Moreover, solid and other advanced desiccants have also been discussed briefly. Finally, a summary of some successful case studies and economic evaluation of desiccant systems have been given.

Rule-based Mamdani-type fuzzy modelling of thermal performance of fintube evaporator under frost conditions

Frost formation brings about insulating effects over the surface of a heat exchanger and thereby deteriorating total heat transfer of the heat exchanger. In this study, a fin-tube evaporator is modeled by making use of Rule-based Mamdani-Type Fuzzy (RBMTF) logic where total heat transfer, air inlet temperature of 2 °C to 7 °C and four different fluid speed groups (ua1=1; 1.44; 1.88 m s-1, ua2=2.32; 2.76 m s-1, ua3=3.2; 3.64 m s-1, ua4=4.08; 4.52; 4.96 m s-1) for the evaporator were taken into consideration. In the developed RBMTF system, outlet parameter UA was determined using inlet parameters Ta and ua. The RBMTF was trained and tested by using MATLAB® fuzzy logic toolbox. R2 (%) for the training data and test data were found to be 99.91%. With this study, it has been shown that RBMTF model can be reliably used in determination of a total heat transfer of a fin-tube evaporator.

Experimental study on performance of celdek packed liquid desiccant dehumidifier

Dehumidifier is the main component of liquid desiccant dehumidification system. Effect of the inlet parameters on various outlet parameters of the dehumidifier is studied in the present paper with structured pads as packing material and calcium chloride as liquid desiccant to process the air. The outlet parameters are change in specific humidity, mass transfer coefficient, moisture removal rate, air temperature, solution temperature, effectiveness and the corresponding inlet process parameters; mass flow rate of air, temperature of air, temperature and flow rate of desiccant solution. It is observed that mass transfer coefficient and moisture removal rate increase with increasing mass flow rate of the air and desiccant while these parameters decrease with increasing temperature of air and desiccant solution. Dehumidifier effectiveness gets increased with increasing solution flow rate. The present investigations are compared with the results of the researchers in the past.

Performance characteristics of cross-flow membrane contactors for liquid desiccant systems

Membrane based indirect contact liquid desiccant dehumidification technology subsides the serious concern of liquid desiccant droplet carryover observed in conventional direct contact liquid desiccant systems. In the membrane contactor the air and liquid desiccant streams flow in alternate channels in cross-flow arrangement, separated by micro-porous semi-permeable hydrophobic membranes. Only water vapor can pass through the membranes but liquid desiccant cannot permeate. A two-dimensional steady-state mathematical model for semipermeable membrane based indirect contactors as dehumidifiers for liquid desiccant dehumidification applications has been developed. The model can predict the air and desiccant parameters inside the dehumidifier and the outlet parameters for a given input parameters. Five different membrane contactors have been fabricated and series of experiments have been conducted to validate the mathematical model. Aqueous solution of lithium chloride has been used as desiccant. The maximum deviations between experimental and predicted values are within ±10% for outlet specific humidity and outlet enthalpy of air, ±15% deviation in dehumidification effectiveness and ±20% deviation in enthalpy effectiveness. The distributions of major parameters viz. temperature, humidity, concentration, etc., within the contactor have been presented. Parametric analysis has been carried out to study the effects of membrane characteristics, contactor design, fluid flow rates, ambient conditions and desiccant concentration on the performance of the contactors.

Numerical Analysis of Heat and Mass Transfer Performance of the Packed-Type Parallel Flow Dehumidifier

TA mathematical model describing heat and mass transfer performance of packed-type parallel flow dehumidifier was set up. The numerical solution of differential equations was derived. Taking the heat and mass transfer coefficients obtained by experiments as the input parameters of the model, the impact of solution inlet parameters on outlet parameter of air was described. The simulation results indicated that the mathematical model could be used to predict the performance of liquid dehumidification. The results showed that the mathematical model can be of great value in the design and improvement of dehumidifier.

Experimental Study on Performance of a Cross-Flow Dehumidifier

Experiment was carried out to test heat and mass transfer performance of cross-flow dehumidifier using metal packing. The effects of air flow rate, solution flow rate and inlet parameters of air and solution on the outlet parameters were also investigated. And a great deal of data obtained from experiment was processed using multiple linear regression method. Empirical formulas were given such as the rates and efficiency of dehumidification evaluating performance of dehumidifier, which provided good reference and necessary information for further theoretical investigation.

Use of a Reactor Network Model in the Design and Operation of a New Type of Membrane Wall Entrained Flow Gasifier

China is developing a new type of slurry-feed membrane wall entrained flow gasifier with two-stage oxygen supply in order to improve facility availability and efficiency. Detailed modeling can contribute to obtaining an in-depth understanding of the gasifier and achieving optimal design and operation. In this work, a computationally efficient reactor network model was developed. Available industrial data from a single-stage version of this type of gasifier was used to validate the model. Good agreement was observed in carbon conversion, syngas composition, and steam production in the membrane wall, suggesting that the model was able to provide accurate prediction, including gasifier outlet parameters and internal heat transfer rate. The impact of the five most important parameters on the gasifer performance—the location of second-stage oxygen injectors, the fraction of the second-stage oxygen in total oxygen fed to the gasifier, the thickness of the refractory lining on the membrane wall inner surface, the water tube diameter, and the width of the fins which links the tubes—was investigated. Optimized design and operation guidelines for improving operational economy and availability were provided.

Numerical Simulation on Effect of Obstructing Airflow by Different Outlet Parameters of Mine Air Curtain

According to characteristics of air curtain obstructing airflow in mine tunnel, utilized turbulent flow dynamic viscosity method, and three-dimensional steady-state incompressible Navier-Stokes equations of computational fluid mechanics, the simulation of flow field in mine tunnel was made by changing outlet parameters of air curtain. The results show that the obstructing airflow capability increase with the increase of the outlet airflow velocity, the obstructing airflow capability decrease with the increase of the outlet width when the amount of wind is a certain value, the obstructing airflow capability increase at first, then decrease with the increase of the outlet angle. When the parameters are the same, the obstructing airflow capability of acyclic air curtain is better than that of circular air curtain.The result of simulation analysis of mine air curtain can be used as the basis for optimized design.

Relaminarization in supersonic microjets at low Reynolds numbers

Results of measuring the length of the supersonic portion of the air jets that flow out of axisymmetric sonic nozzles 10.4 μm-1 mm in diameter are presented. The measurements are carried out in a range of degree of jet noncalculation of 1–30 and in a wide Reynolds number range, including the laminar and turbulent flow modes. It is shown that the Reynolds number calculated from the nozzle diameter and the outlet parameters of gas is the parameter that governs jet flow. It is found that, for a laminar jet mixing layer, the length of the supersonic portion sharply increases. When the jet mixing layer becomes turbulent, the length of the supersonic portion decreases. The effect of increasing the length of the supersonic portion after its decrease due to the turbulization of flow in a jet and a growth in the Reynolds number is first discovered.

Modeling of fluid flow and heat transfer in a trough solar collector

This paper analyzed the flow and heat transfer processes in a trough solar collector of the direct steam generation (DSG) system. A flow and heat transfer model of the working fluid in the absorber was established and solved using the finite difference method. Experimental results of liquid water and dry air heating processes validated the model. The experimental results, got under the condition that the vacuum in the tube was destroyed, were used to test the developed model. The calculation results of the model agreed with the experimental data. The dynamic characteristics of the collector outlet parameters under variations of solar radiation intensity were analyzed in this paper. The impulse response of the DSG system was complex as a short-time fluctuation of the solar radiation notably affected the water region length, the two-phase region length and the steam region length, which led to large fluctuations in the outlet temperature. Therefore, the outlet temperature of the once-through DSG system was difficult to control. Extra heat was required to maintain the normal operation of the system.