Working Medium Flow Research Articles

Characterization of a new total heat recovery system using CaCl2 as working fluid: Thermal modeling and physical analysis

• A new type of heat pump system is proposed. • The variation trend of three working medium in absorber is analyzed. • The rise of flue gas temperature can reduce the harmful substances by more than 50%. • The advantages of the system compared with LiBr absorption heat pump are analyzed. This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl 2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step. As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl 2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the "white smoke" from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.

Impact of pressure drop in combustion chamber on gas turbine performance

Paper discusses the problem of pressure drop in the process of working medium flow through combustion chamber of gas turbine. The pressure loss is an internal disadvantage of combustion chamber depends on many parameters, especially the chamber design and working gas flowrate. There is a problem to calculate the parameters of working medium in characteristic points of gas turbine thermodynamic cycle because the total pressure before and after combustion chamber is not known. There is a lack of information from manufacturer about it and in publications as well (mainly no experimental data, only theoretical considerations). It will be important information because the pressure drop has an meaningful influence on gas turbine performance. The paper presents an estimation of decreasing the performance of gas turbine from discussed reason. Author of that manuscript recognized the necessity of showing the importance of that parameter and turning the attention to not fully recognized problem.

Modelling, performance improvement and emission reduction of large two-stroke diesel engine using multi-zone combustion model

The main energy source in marine industry is fossil fuel. Diesel engines are main power supply in sea transport at present times and will also be in the future. Energy conservation and environmental protection are the main problems that engine manufacturers are facing. Researchers have been making a lot of effort over the last decades to analyse energy conversion in large two-stroke engines. A 1-dimensional large two-stroke low-speed diesel engine model is developed, along with a multi-zone combustion model (MZCM), in which the losses of exchanging working medium and gas composition are calculated in the whole engine, unlike the preceding 0-dimensional and quasi-dimensional engine models that are only calculated in engine cylinder chamber. The model of a low-speed two-stroke marine diesel engine is calibrated and validated with experimental data and is used for simulation and analysis of the engine performance, combustion behaviour and emission of harmful exhaust gases. Large two-stroke marine diesel engines are problematic for modelling due to very few researches on this issue, due to the unsuitability of applying model on a low-speed two-stroke big diesel engines, large number of parameters that affect combustion behaviour, shape of ports and exhaust valves, working medium flow as well as because of shape of combustion chambers in these engines. For the reasons above, this research paper and its experiments contribute to better understanding large two-stroke low-speed marine diesel engine process. Analysis of engine characteristic was done by varying the most important parameters. Optimization of fuel injection characteristic and exhaust timing is achieved. The parameter of changing injection profile from classic to pre-injection was performed, and the effects on engine performance, NOx, CO and soot emissions were showed. With a pre-injection profile it is possible to reduce NOx emission by 9%, but a decrease in engine power is significant.

Modification of the solar heating system diagnostic method under operating conditions

One of the problems with the operation of solar heating systems is the variable capacity of the system dependent on the prevailing operating conditions. One of the methods for increasing the capacity of a solar system is to control the volume flow of the working medium. Volume flow of working medium in solar heating installation should be follow operating conditions. Designing a continuous control system based eg. on the PID controller requires knowledge of the dynamic properties of a solar system under operating conditions: gain coefficient, equivalent time constant and delay time of the solar collector response to a change in solar radiation intensity and the inlet temperature of a working medium. To date, the delay time has been omitted in the analyses. It is necessary to know the value of the delay time for proper design of the solar system controls, because the object response cannot be simultaneous with the moment of the input function. The paper presents the method for determining the dynamic properties of a solar system under operating conditions. The method is based on the comparison of two models: an analog model based on the energy balance of a collector and a digital model developed with the use of parametric identification based on a short-term measurement of solar radiation intensity and working medium temperatures. In the collector analog model, on the basis of the design and operating parameters of the collector, the transport delay time has been defined, which is an innovative aspect of this study. The modified analog collector model was verified on the basis of the step response determined experimentally in accordance with the applicable ISO 9806: 2017 standard. A very good convergence of the model with actual data was achieved for the time constant – 87%, effective thermal capacity – 85.9%, and the delay time – 96%. Practical application of the modified diagnostic method is presented on the example of a solar heating system composed of five flat-plate collectors with a total absorber area of 10 m2.

Factors and Mechanisms Causing Wear of Turbine Heating Steam Condensate Pipeline Components at a Nuclear Power Plant

The article considers the specific features related to operation of the power valve and orifice lines within turbine plant piping systems whose inlets receive water medium with saturation parameters (separated moisture or condensate). It is shown that transportation of working medium in these piping systems is accompanied by pressure drop, boiling, and formation of various two-phase flow patterns from bubble in the initial segment to dispersed-annual in the end segment. Under certain conditions, a slug flow pattern can occur, which behaves as a source of piping vibration. Practical experience has shown that the use of homogenizing inserts for suppressing vibration load in the heating steam condensate (HSC) discharge lines downstream of the moisture separator reheaters (MSRs) of nuclear power plant (NPP) turbines often leads to intensified local flow-accelerated corrosion and pipeline failures. The article considers examples illustrating failures of piping segments downstream of homogenizing inserts and presents statistical data on damageability of heating steam and separated moisture piping of NPP turbines. The steam–water flow patterns in the MSR HSC transportation line of an NPP turbine are determined. The results from hydrodynamic modeling of working medium flow under the conditions of an abrupt expansion at the outlet from the homogenizing insert channel are presented. It is shown that the location of zones characterized by the maximum wear of piping downstream of homogenizing inserts in the MSR HSC discharge lines is determined by the flow pattern and specific features of the working medium flow hydrodynamics. It has been established that droplet impingement erosion is the dominating mechanism causing destruction of stainless-steel piping segments downstream of the homogenizing inserts in the MSR HSC lines of NPP turbines. It is important to note that, if the pipeline is made of carbon or low alloy steel, its metal experiences a combined effect of droplet impingement erosion and flow-accelerated corrosion. The obtained study results can be used in elaborating measures aimed to prevent wear of piping components in the heating steam condensate and separated moisture discharge lines of NPP turbines.

Performance assessment of a CCHP and multi-effect desalination system based on GT/ORC with inlet air precooling

This paper proposes a combined cooling, heating and power (CCHP), and multi-effect desalination system to supply cooling, heating, power and freshwater. The proposed system mainly includes a gas turbine (GT), a multi-effect desalination unit with a thermal vapor compressor (MED-TVC), an organic Rankine cycle (ORC) integrated with a steam ejector refrigerator (SER), and heat exchangers. The mathematical model is developed to thermodynamically conduct energy-exergy analysis, and a parametric study is performed to explore the effects of key design parameters such as air compressor pressure ratio, inlet air temperature of air compressor, pinch point temperature difference of waste heat boiler, motive steam pressure of MED-TVC unit, TVC compression ratio and working medium flow rate of ORC on the system performance. The proposed system can provide power, heating, cooling and freshwater at loads of 31.25 MW, 1.108 MW, 4.203 MW and 85.89 kg/s under the design conditions. The electrical, the exergy, and the overall energy efficiencies of the present system are 36.44%, 41.26% and 46.70%, respectively. The results indicate that the power output of GT can be increased by precooling the inlet air of air compressor, and the integration of GT with MED-TVC unit, ORC and heat exchangers can efficiently recover the waste heat from exhaust gas based on the principle of “energy cascade utilization”. In addition, the largest exergy destruction occurs in the combustion chamber followed by regenerator 1 and the MED-TVC unit.

Исследование течения рабочей среды в проточной полости элементов пневмогидравлических систем

Исследование течения рабочей среды в проточной полости элементов пневмогидравлических систем

Experimental studies of correction propulsion system elements for small space vehicles manufactured due to additive method

Producing ammonia correction propulsion system (CPS) elements for maneuvering satellite platforms (MSP) of small space vehicles (SSV) is a relevant problem. The investigation is devoted to the solution of the named problem with the use of direct metal laser sintering (DMLS) method. The research objective is to confirm the feasibility of manufacturing ETMT and CPS evaporator with autonomous heating elements (AHE) by DMLS method, based on the prototypes experimental testing. During the research the following tasks were solved: creating 3D models for ETMT and double-threaded evaporator and producing experimental prototypes by DMSL method. 3D models of ETMT and evaporator casings were developed following the prototypes produced by the conventional methods of turning and milling. 3D models of ETMT and evaporator casings represent complex integral parts with multiple passages for working medium flow. Experimental studies of ETMT and the evaporator were performed with nitrogen as a working medium. ETMT and evaporator temperature characteristics were determined during the experiments. The investigation was made of ETMT with nominal thrust of 30 mN and power consumption in the range of 5-60 W with and without heat insulation. AHE with embedded thermocouples, having the diameter of 6 mm and power consumption of 60 W, was used. AHE temperature was limited by 973 K. A double-threaded evaporator was investigated for power consumption of 5-30 W, the evaporator casing temperature limited by 393 K. The maximal increase in the gas temperature equaled no more than 8.6 % at the nozzle exit in the power consumption range of 10-60 W for ETMT with heat insulation. At ETMT power consumption of 5–50 W, the build-up time for ETMT was 400–600 s. While at power consumption of 50–60 W, it was 200–400 s. At power consumption of 10–30 W, the evaporator casing temperature reached 393 K in 100–340 s, AHE temperature being 400–460 K and the gas temperature at the evaporator throttle exit being no more than 290 K. At power consumption of 5 W, the maximum evaporator casing temperature of 375 K was reached in 1200 s, AHE temperature being 370 K and the gas temperature at the evaporator throttle exit being no more than 302 K.

Влияние внешних электромагнитных полей на значение градиента скорости сдвига слоев магнитореологической рабочей среды

The importance of improving machine drives requires constant development of alternative drive technologies which include magnetorheological, magnetodynamic and magneto-liquid technologies. In the recent years, magnetorheological, magnetodynamic, and magneto-liquid devices have proved to be effective; therefore their further development is considered relevant. Combined magnetorheological drives are promising innovation in drive systems. Such drive systems control the flow of magnetorheological working medium by changing its viscosity and generating rheological effects. It is obvious that in combined magnetorheological systems there is additional external shear force in working fluids. This requires revision of the main theoretical approaches to estimating the viscosity of the working medium in combined magnetorheological systems. When calculating and modeling combined or regular magnetorheological systems, it is important to estimate the viscosity characteristics of the working medium and forecast its possible rheological anomalies. The article describes a method for modeling the viscosity properties of magnetorheological working medium. A distinctive feature of the proposed method is that it allows us to take into account the effect of external electromagnetic fields on the shear rate gradient of magnetorheological liquid layers. The paper presents the results of numerical modeling obtained with the Matlab application package. The results of the computer experiment show that the proposed method can assess the effect of external electromagnetic fields on the shear rate gradient of layers under shear stresses and the electromagnetic component. This makes it possible to determine the probability of development of viscoplastic, pseudoplastic, and dilatant properties in the magnetorheological working medium and of appearance of rheological effects which are characteristic of magnetorheological working media.

Heat pump coefficient of conversion and power on off-nominal modes

The article considers the variation of heat pump (HP) compression parameters which define its effectiveness: power and coefficient of conversion (μ) on off-nominal modes of operation. Taking into account that the parameters of low-potential sources of heat for HP change, the demand for thermal energy also changes; study of HP operating on off-nominal modes is relevant. To analyze the operating process on partial power modes of HP, a reciprocating compressor is used. The following options are examined by authors as conditions of HP transitioning to the off-nominal mode: change in temperature of water at the condenser inlet; change in flow rate of water passing through the condenser, change in flow rate of the working medium. Based on the analysis of relationships for determining the coefficient of conversion and power consumed by HP, it is shown that these parameters change if HP transitions to off-nominal mode. The increase of temperature entering the condenser leads to decrease in μ, and with temperature decrease μ increases. Decrease in flow rate of water cooling the condenser moves the beginning point of compression of the working medium to higher moisture region and reduces the efficiency of the compressor. Working medium flow rate decrease virtually does not affect the Carnot cycle efficiency and μ decreases because of rising moisture of gas.

Specific features of the flow structure in a reactive type turbine stage

The results of experimental studies of the gas dynamics for a reactive type turbine stage are presented. The objective of the studies is the measurement of the 3D flow fields in reference cross sections, experimental determination of the stage characteristics, and analysis of the flow structure for detecting the sources of kinetic energy losses. The integral characteristics of the studied stage are obtained by averaging the results of traversing the 3D flow over the area of the reference cross sections before and behind the stage. The averaging is performed using the conservation equations for mass, total energy flux, angular momentum with respect to the axis z of the turbine, entropy flow, and the radial projection of the momentum flux equation. The flow parameter distributions along the channel height behind the stage are obtained in the same way. More thorough analysis of the flow structure is performed after interpolation of the experimentally measured point parameter values and 3D flow velocities behind the stage. The obtained continuous velocity distributions in the absolute and relative coordinate systems are presented in the form of vector fields. The coordinates of the centers and the vectors of secondary vortices are determined using the results of point measurements of velocity vectors in the cross section behind the turbine stage and their subsequent interpolation. The approach to analysis of experimental data on aerodynamics of the turbine stage applied in this study allows one to find the detailed space structure of the working medium flow, including secondary coherent vortices at the root and peripheral regions of the air-gas part of the stage. The measured 3D flow parameter fields and their interpolation, on the one hand, point to possible sources of increased power losses, and, on the other hand, may serve as the basis for detailed testing of CFD models of the flow using both integral and local characteristics. The comparison of the numerical and experimental results, as regards local characteristics, using statistical methods yields the quantitative estimate of their agreement.

Design and Research of Vehicle Organic Rankine Cycle Waste Heat Power Generation System Based on Preheater

A small vehicle-mounted, organic Rankine cycle (ORC) waste heat power generation system is built and optimized based on recovering expansion preheater after exhausting high temperature steam. Using the first and second law of thermodynamics, thermodynamic analysis, energy analysis and energy calculation of the small vehicle-mounted ORC waste heat power generation system were established. Taking R123 as working medium, heat source temperature 300℃, the thermal efficiency and total thermal efficiency of the system were calculated with given working medium flow and pressure. The total thermal efficiency of the system with/without preheater are 23.1% and 10.8% respectively. The heat transfer of the evaporator is 7.35kJ and 4.67kJ respectively. The results show that compared with the traditional ORC system without a preheater, the heat efficiency of the ORC system and the heat transfer coefficient of the evaporator are greatly improved.

Hybrid solar receiver as a source of high-temperature medium for an absorption chiller supply

This article discusses the problems related with the cold production, i.e. energy efficiency of the process. The idea of solar cooling systems has been presented as the solution of the problem of big electricity demand. The paper discusses the principle of the operation of absorption chillers. Disadvantages and advantages of the solar cooling systems were discussed. The installation for manufacturing high-temperature heat based on solar collectors and concentrator of solar radiation constructed in AGH in Cracow has been presented. This installation is a first stage of projected, complete solar cooling system. The special attention is paid to the dedicated solar high-temperature heat receiver as a most important element of the system. The achieved values of temperature, power and efficiency depending on the working medium flow has been presented and discussed. The intensity of solar radiation during the measurements has been taken into account. Two versions of heat receiver were investigated: non-insulated and insulated with mineral wool. The obtained efficiency of the heat receiver (less than 30%) is not satisfactory but possibility of improvements exist.

Mathematical Modeling of the Fluid Flow Irregularity within Vacuum DNA Separation Installation Cells

The article describes the most common methods of DNA extraction. A mathematical model of two-phase unsteady working medium flow under the influence of the pressure difference through the cells with porous bodies in the vacuum DNA separation equipment was developed. A numerical study of the mathematical model was conducted and working characteristics of cells were obtained. The analysis of the calculated data was conducted. It was concluded that the model possibly applied to describe the working medium inequality flow through the multiple cells with different coefficients of porous bodies permeability.

Working Processes in Systems for DNA Sample Preparation

The working process for flow of a solution containing various organic structures through a cell with adsorbent powder used for the isolation of DNA molecules in sample preparation units was studied. Special attention was given to experimental, computational, and theoretical study of the uneven flow of working medium through the porous body in the cells. A mathematical model of the process was developed – a model of working medium flow through the cell with porous body due to pressure difference.

Heat transfer and pressure drop in rectangular channels with crossing fins (a Review)

Channels with crossing finning find wide use in the cooling paths of high-temperature gas turbine blade systems. At different times, different institutions carried out experimental investigations of heat transfer and pressure drop in channels with coplanar finning of opposite walls for obtaining semiempirical dependences of Nusselt criteria (dimensionless heat-transfer coefficients) and pressure drop coefficients on the operating Reynolds number and relative geometrical parameters (or their complexes). The shape of experimental channels, the conditions of experiments, and the used variables were selected so that they would be most suited for solving particular practical tasks. Therefore, the results obtained in processing the experimental data have large scatter and limited use. This article considers the results from experimental investigations of different authors. In comparing the results, additional calculations were carried out for bringing the mathematical correlations to the form of dependences from the same variables. Generalization of the results is carried out. In the final analysis, universal correlations are obtained for determining the pressure drop coefficients and Nusselt number values for the flow of working medium in channels with coplanar finning.

A Numerical and Experimental Investigation of the Characteristics of an On-Off Valve with Permanent Magnet

Results of numerical and experimental studies of the characteristics of a direct-acting on-off valve with spherical cut-off element and permanent magnet are presented. A mathematical model of the flow of a compressible working medium (air) in the flow-through segment of the valve is presented and numerical modeling with the use of the STAR-CCM+ CFD package is implemented. Results of the simulation are confirmed by experimental data. A technique of designing pneumatic systems that utilize valves with permanent magnet as the limiter of the maximal flow of the working medium is proposed.

The outlet flow structure of vortex chamber with dead end jet actions

The analysis of the flow structure uniformity in the running (active) part of the vortex chamber in conditions of organizing various control jets, which affect coherent energy-carrying vortex formations in the dead end region of the vortex chamber is conducted. Thermoanemometry data on multiscale outlet flow structure of chamber in the form of distributions of axial and transverse components of the averaged velocity and the corresponding relative intensity of velocity pulsations depending on the control jet parameters is given. The effect of the ratio of working medium flow rate through the control nozzle and at the vortex chamber outlet on the velocity profiles and their pulsations is studied. For the analysis of the flow structure in the active part of the vortex chamber, a new integral parameter - the intensity irregularity degree of velocity pulsations in the exit section is proposed. It is found that the highest values of the integral intensity irregularity degree of axial pulsations are provided by the flow structure control scheme using a coaxial dead end jet, and transversal pulsations - by control scheme using concurrently directed jet with respect to the spiraling energy-carrying vortex formation in the dead-end part of the chamber. The research results are of interest to vortex chamber developers since the obtained profiles of hydrodynamic characteristics of the outlet flows with the investigated jet control schemes indicate the zones of maximum shear effects, so they allow approximately take into account the anisotropy of mass and energy transfer in evaluating the operating modes of chambers with relatively elongated dead end part. These data may be also useful in selecting rational design solutions at the design stage of vortex devices in energy, metallurgical, chemical, aerospace and other industries depending on the purpose of chambers (mixing, separation of media with different densities, the second component supply to the swirling flow and etc.).

Mathematical Simulation of Kinematics of Vibrating Boiling Granular Medium at Treatment in the Oscillating Reservoir

The results of mathematic simulation of directed motion of the circulating flow of granulated working medium in the oscillating reservoir of finishing-grinding vibration machine are given. The model is based on the physical phenomenon, at which the granulated medium changes into vibro-boiling state clue to the action of vibrations. The solutions of Navier-Stokes implicated equations give the expressions of Bessel functions and their integral transformations. The model solutions ground the complex cycloid-trochoid nature of working medium kinematics on the vibration treatment operations and allow to determine the velocities of displacements of medium flows in any point of the reservoir. It is necessary for determination of the technological parameters and required equipment as well as their complex influence on the vibration treatment effectiveness. The zones of reservoir with increased impulse loading at combining the schemes of energetic action into the working medium and processed products are observed.

Unit for automatic calibration of gas flow rate controllers

A unit is described for automatic calibration of gas flow controllers, within which there is a reference flowmeter device ERU-0.5, making it possible to measure gas working medium flow rates of 0.01–0.5 cm3/sec with a total error of ± (0.3–0.7)%. The operating principle of the construction, a procedure for determining gas mass flow rate, the main parameters of the flow rate device, and measurement errors are considered.