scholarly journals Структура потока в межлопаточном канале соплового аппарата с поворотной диафрагмой

2021 ◽  
pp. 35-43
Author(s):  
Александр Григорьевич Жирков ◽  
Александр Павлович Усатый ◽  
Елена Петровна Авдеева ◽  
Юрий Иванович Торба
Keyword(s):  
Pressure Drop ◽  
Kinetic Energy ◽  
Energy Loss ◽  
Numerical Study ◽  
Working Fluid ◽  
Relative Pressure ◽  
Pressure Drops ◽  
Vortex Zone ◽  
Flat Flow ◽  
Tube Channel

In the process of developing a numerical study method of a flat flow around a snap line with a rotary diaphragm, calculations were made at various degrees of opening the rotary diaphragm δ and pressure drops on the grille. As a result of calculations, for small degrees, the opening of the rotary diaphragm, complex patterns of the flow were obtained, in the inter-tube channel of the nozzle apparatus. The article presents some results of a numerical study of the supersonic flow in the channel of the nozzle apparatus with the degree of opening the rotary diaphragm δ = (0.15 ÷ 0.3). Modeling and calculating the flow of the working fluid is made using the Fluent software package. The construction of the calculated areas bounded by one inter-tube channel, for varying degrees of opening the diaphragm of the nozzle apparatus. Grids are built for calculated areas. Calculations were carried out for δ = (0.15 ÷ 0.3) and with different degrees of pressure drop on the grille. As a result of the calculations performed, the flow patterns in the inter-tube canal were obtained and behind it, and the distribution of the coefficients of the kinetic energy loss on the lattice front at various degrees of the discovery of the diaphragm at the inlet in the nozzle apparatus. According to the results of the work carried out, the following conclusions can be drawn: the structure of the stream in the inter-tube channel, the nozzle apparatus at small detection of the discovery, is divided into two parts: a supersonic core of the spawth of the blade and a dialing, the vortex zone at the back of the blade; The supersonic thread kernel at certain values of the relative pressure drop on the lattice (or the air flow values through the grid) is separated by shock fronts into several areas; The coefficients of energy loss, for small degrees of discovery, decrease with a decrease in the relative pressure drops (with an increase in the rate of expiration of the flow from the nozzle lattice); The greatest contribution to the magnitude of the loss of kinetic energy is introduced by a vortex zone in the inter-tube channel, and not wave phenomena in the core of the flow; Optimization of the flow part of the nozzle apparatus must be carried out in order to reduce areas with vortex flow. The results obtained in this work will be used to develop a methodology for a numerical study of the spatial flow around the nozzle lattices with rotary diaphragms.

Power and efficiency optimization for combined Brayton and two parallel inverse Brayton cycles. Part 1: Description and modelling

2008 ◽  
Vol 222 (3) ◽  
pp. 393-403 ◽  
Author(s):  
L Chen ◽  
W Zhang ◽  
F Sun
Keyword(s):  
Pressure Drop ◽  
Power Output ◽  
Pressure Ratio ◽  
Current Paper ◽  
Working Fluid ◽  
Relative Pressure ◽  
Pressure Drops ◽  
Compressor Inlet ◽  
Flow Resistances ◽  
Top Cycle

A thermodynamic model for open combined Brayton and two parallel inverse Brayton cycles is established using finite-time thermodynamics in part A of the current paper. The flow processes of the working fluid with the pressure drops of the working fluid and the size constraints of the real power plant are modelled. There are 17 flow resistances encountered by the gas stream for the combined Brayton and two parallel inverse Brayton cycles. Six of these, the friction through the blades and vanes of the compressors and the turbines, are related to the isentropic efficiencies. The remaining flow resistances are always present because of the changes in flow cross-section at the compressor inlet of the top cycle, combustion inlet and outlet, turbine outlet of the top cycle, turbine outlets of the bottom cycle, heat exchanger inlets, and compressor inlets of the bottom cycle. These resistances control the air flowrate and the net power output. The relative pressure drops associated with the flow through various cross-sectional areas are derived as functions of the compressor inlet relative pressure drop of the top cycle. The analytical formulae about the relations between power output, thermal conversion efficiency, and the compressor pressure ratio of the top cycle are derived with the 17 pressure drop losses in the intake, compression, combustion, expansion, and flow process in the piping, the heat transfer loss to ambient, the irreversible compression and expansion losses in the compressors and the turbines, and the irreversible combustion loss in the combustion chamber. The performance of the model cycle is optimized by adjusting the compressor inlet pressure of the bottom cycles, the mass flowrate and the distribution of pressure losses along the flow path in part B of the current paper.

Effect of Cross Aspect Ratio on Flow in Diverging and Converging Microchannels

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
V. S. Duryodhan ◽  
Shiv Govind Singh ◽  
Amit Agrawal
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Hydraulic Diameter ◽  
Working Fluid ◽  
Cross Sectional ◽  
Flow Acceleration ◽  
Three Dimensional Models

Aspect ratio is an important parameter in the study of flow through noncircular microchannel. In this work, three-dimensional numerical study is carried out to understand the effect of cross aspect ratio (height to width) on flow in diverging and converging microchannels. Three-dimensional models of the diverging and converging microchannels with angle: 2–14 deg, aspect ratio: 0.05–0.58, and Reynolds number: 130–280 are employed in the simulations with water as the working fluid. The effects of aspect ratio on pressure drop in equivalent diverging and converging microchannels are studied in detail and correlated to the underlying flow regime. It is observed that for a given Reynolds number and angle, the pressure drop decreases asymptotically with aspect ratio for both the diverging and converging microchannels. At small aspect ratio and small Reynolds number, the pressure drop remains invariant of angle in both the diverging and converging microchannels; the concept of equivalent hydraulic diameter can be applied to these situations. Onset of flow separation in diverging passage and flow acceleration in converging passage is found to be a strong function of aspect ratio, which has not been shown earlier. The existence of a critical angle with relevance to the concept of equivalent hydraulic diameter is identified and its variation with Reynolds number is discussed. Finally, the effect of aspect ratio on fluidic diodicity is discussed which will be helpful in the design of valveless micropump. These results help in extending the conventional formulae made for uniform cross-sectional channel to that for the diverging and converging microchannels.

An Experimental Investigation of Condensation Heat Transfer Coefficients and Pressure Drops of Refrigerants Inside Multiport Mini-channel Tubes

2017 ◽  
Vol 25 (02) ◽  
pp. 1750013 ◽  
Author(s):  
Pham-Quang Vu ◽  
Kwang-Il Choi ◽  
Jong-Taek Oh ◽  
Honggi Cho
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients

The condensation heat transfer coefficients and pressure drops of R410A and R22 flowing inside a horizontal aluminum multiport mini-channel tube having 18 channels are investigated. Experimental data are presented for the range of vapor quality from 0.1 to 0.9, mass flux from 50 to 500[Formula: see text]kg/m2s, heat flux from 3 to 15[Formula: see text]kW/m2 and the saturation temperature at 48[Formula: see text]C. The pressure drop across the test section was directly measured by a differential pressure transducer. At a small scale, the noncircular cross-sections can enhance the effect of the surface tension. The average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux. Under the same test conditions, the heat transfer coefficients of R22 are higher than those for R410A, the pressure drops for R410A are 7–19% lower than those of R22. The lower pressure drop of R410A has an important advantage as an alternative working fluid for R22 in air-conditioning and heat pump systems.

The Inlet Air Pre-Cooling of Natural Draft Dry Cooling Towers-Wetted Medium Issue

2017 ◽  
Author(s):  
Suoying He ◽  
Guanhong Zhang ◽  
Yi Xu ◽  
Fengzhong Sun
Keyword(s):  
Pressure Drop ◽  
Ambient Air ◽  
Western China ◽  
Working Fluid ◽  
Cooling Towers ◽  
Pressure Drops ◽  
Natural Draft ◽  
Western Asia ◽  
Cooling Enhancement ◽  
Dry Cooling

Dry cooling towers are an alternative cooling method when large quantities of water are not available. Examples of the proposed applications are the enhanced geothermal and concentrated solar thermal (CST) power plants in arid or semi-arid areas, like south-western United States, Australia, western Asia, north-western China and the rest of the world. Natural draft dry cooling towers (NDDCTs) have received widespread attention because they do not consume water, have low maintenance requirements and cause small parasitic losses. Unfortunately, the performance of a NDDCT is severely reduced when the ambient air is hot, which is because the NDDCT is driven by buoyancy effect and relies solely on air to cool the working fluid. The present study introduces inlet air pre-cooling using wetted media, which combines dry and wet cooling. The wet cooling system only operates at high ambient temperatures to assist dry cooling. However, wetted-medium cooling introduces extra pressure drop which reduces the air flow passing through the NDDCT and thus impairs the tower heat rejection. To this end, this paper takes into account the trade-off between the wetted-medium cooling and the extra pressure drop. Early studies find that the performance of NDDCTs can be improved by wetted-medium evaporative pre-cooling when the ambient air is hot and dry. However, the pre-cooling enhancement is seasonal-dependent and is significantly affected by wetted media. To further investigate the effect of wetted medium type on pre-cooling performance, the current study simulates a pre-cooled NDDCT using five selected wetted media (i.e., three film and two trickle media) based on a self-developed MATLAB program. The innovations of the current study are: (1) two typical types of wetted media with the potential of evaporative pre-cooling are comparatively studied to give suggestions for future pre-cooling design; (2) the characteristics of wetted media suitable for evaporative pre-cooling of NDDCTs are summarized. The simulation finds that the media with high or low cooling efficiencies and pressure drops are not promising while those media with middle cooling efficiencies and pressure drops intend to produce much performance enhancement of the studied NDDCT. The film medium, Cellulose7060 with pressure drops of 28.6–272.1 Pa/m and cooling efficiency range of 44.7–88.5% is most promising for such pre-cooling enhancement. For the studied NDDCT, the critical temperatures below which the tower performance does not benefit but is hindered by wetted-medium pre-cooling are 28, 16, 30, 26 and 26°C for cellulose7090, cellulose7060, PVC1200, Trickle125 and Trickle100, respectively (ambient humidity of 20% and medium thickness of 200mm). The pre-cooling enhancements can go up to 100% by 200mm-thick cellulose7060 at extreme hot and dry climate (i.e., ambient temperature of 50°C and humidity of 20%). The simulation will give instructions for the design of pre-cooled NDDCTs.

Experimental Investigation of Flow Boiling Pressure Drop of R134A in a Microscale Horizontal Smooth Tube

2011 ◽  
Vol 3 (1) ◽  
Author(s):  
Cristiano Bigonha Tibiriçá ◽  
Jaqueline Diniz da Silva ◽  
Gherhardt Ribatski
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Flow Boiling ◽  
Smooth Tube ◽  
Working Fluid ◽  
Prediction Methods ◽  
Internal Diameter ◽  
Two Phase ◽  
Pressure Drops ◽  
Frictional Pressure Drop

This paper presents new experimental flow boiling pressure drop results in a microscale tube. The experimental data were obtained under diabatic conditions in a horizontal smooth tube with an internal diameter of 2.32 mm. Experiments were performed with R134a as working fluid, mass velocities ranging from 100 kg/m2 s to 600 kg/m2 s, heat flux ranging from 10 kW/m2 to 55 kW/m2, saturation temperatures of 31°C, and exit vapor qualities from 0.20 to 0.99. Flow pattern characterization was also performed from images obtained by high-speed filming. Pressure drop gradients up to 48 kPa/m were measured. These data were carefully analyzed and compared against 13 two-phase frictional pressure drop prediction methods, including both macro- and microscale methods. Comparisons against these methods based on the data segregated according to flow patterns were also performed. Overall, the method by Cioncolini et al. (2009, “Unified Macro-to-Microscale Method to Predict Two-Phase Frictional Pressure Drops of Annular Flows,” Int. J. Multiphase Flow, 35, pp. 1138–1148) provided quite accurate predictions of the present database.

Numerical Study on the Performance Characteristics of Cylindrical Heat Pipes With Differing Wick Type

2018 ◽  
Author(s):  
Mahboobe Mahdavi ◽  
Saeed Tiari ◽  
Ajaysinh Solanki ◽  
Vivek Pawar
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Numerical Study ◽  
Operating Conditions ◽  
Liquid Sodium ◽  
Working Fluid ◽  
Liquid Pressure ◽  
Pressure Drops ◽  
Sintered Powder

In the current study, the performance of a high temperature, cylindrical heat pipe under various operating conditions is investigated numerically. To find the appropriate geometrical and working parameters of the heat pipe, a two-dimensional axisymmetric model is developed to describe the vapor and liquid flows and heat transfers in the vapor core, the wick, and the wall regions. Sodium and stainless steel are selected as the working fluid, the wick material, and the container material. The compressibility of the vapor and viscous dissipation are taken into account. In the wick region, the Darcy–Brinkman–Forchheimer model is applied to simulate the liquid sodium characteristics. The effect of wick type, heat input, and operating temperature are studied on the overall performance of the heat pipe as well as vapor and liquid pressure drops. Screen wick, sintered powder wick and felt wick are selected. The results showed that, for the selected wick types, the sintered powder wick resulted in the largest liquid pressure drop and the felt wick resulted in the lowest thermal resistance. In addition, the influence of operating temperature on thermal resistance diminishes with increasing temperature.

Annular Recuperator Development and Performance Test for 200kW Microturbine

2003 ◽  
Author(s):  
Yungmo Kang ◽  
Robert McKeirnan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Performance Test ◽  
Relative Pressure ◽  
Test Results ◽  
Pressure Drops ◽  
Design Goal ◽  
Cfd Models ◽  
Model Predictions ◽  
And Performance

Capstone Turbine Corporation developed and rig tested a new annular type primary surface recuperator for a 200kW microturbine. Rig testing was conducted for performance verification. The first development recuperator core is scheduled for assembly with a 200kW microturbine engine in 2003. This recuperator is designed using internally developed analytical and 2D & 3D CFD models. The analytical model is used to determine the heat transfer and pressure drop of the recuperator in the microturbine engine. CFD models were used to optimize the flow distributions in the recuperator core and the manifold sections. The prototype recuperator core segments were assembled and tested with the flow condition of the 200kW microturbine engine. The mass flow rate, temperatures, and pressures were measured to obtain effectiveness and pressure drops. Design goal of 90% effectiveness and 2.5% total relative pressure drop was achieved with some margin. The model predictions also agreed well with the rig test results.

scholarly journals Numerical Investigation on the Dielectric Working Fluid Effect on the Flow and Thermal Parameters of an Electrohydrodynamic Flat Heat Pipe

2020 ◽  
Vol 79 (1) ◽  
pp. 128-152
Author(s):  
Imène Saad ◽  
Samah Maalej ◽  
Mohamed Chaker Zaghdoudi
Keyword(s):  
Pressure Drop ◽  
Vapor Pressure ◽  
Electric Field ◽  
Heat Pipe ◽  
Liquid Velocity ◽  
Thermal Parameters ◽  
Working Fluid ◽  
Liquid Pressure ◽  
Pressure Drops ◽  
Capillary Limit

The present work highlights the impact of the working dielectric fluid on the flow and the thermal parameters of an axially grooved flat mini heat pipe (FMHP) submitted to Electrohydrodynamic (EHD) effects. Three dielectric working fluids are considered: pentane, R123, and R141b. A model is developed by considering the Laplace-Young, mass, momentum, and energy balance equations. The numerical results show that the electric field affects the liquid distribution along the heat pipe and helps the condensate to flow back to the evaporator section. Moreover, under the electric field conditions, the vapor pressure drop increases, however, the liquid pressure drop decreases. The effect of the electric field on the liquid velocity depends on the FMHP zone, and the vapor velocity is hardly affected by the EHD effects. Furthermore, lower capillary driving pressures are required to provide the necessary capillary pumping under EHD conditions. Besides, pentane allows for higher vapor pressure drops compared to those obtained with R123 and R141b, while the liquid pressure drops are highest for R123. It is found that with R123, the liquid velocity is higher than that reached with R141b and pentane. It is also demonstrated that the capillary limit increases under EHD conditions, and for R141b, the capillary limit is the highest either in zero-field and EHD conditions. Best heat pipe thermal performances are observed for wide and deep grooves with R141b. Finally, the optimum fill charge allowing the maximum heat transfer capacity is determined for each working fluid and different groove dimensions. It is shown that the optimum fill charge is hardly affected by the electric field whatever the working fluid. R123 requires the highest optimum fill charge, however, the heat transport capacity of the FMHP is the lowest when using this working fluid.

scholarly journals Numerical Calculation of Fracture Seepage in Rough Rock and Analysis of Local Pressure Drop

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Gang Chen ◽  
Ling Ma ◽  
Hongsheng Gong ◽  
Fengqiang Luo
Keyword(s):  
Numerical Calculation ◽  
Pressure Drop ◽  
Kinetic Energy ◽  
Energy Loss ◽  
Fracture Aperture ◽  
Rock Fractures ◽  
Local Pressure ◽  
Numerical Calculation Method ◽  
Kinetic Energy Loss ◽  
Aperture Function

The seepage performance of a rock mass mainly depends on the rock fractures developed in it. Numerical calculation method is a common method to study the permeability properties of fractures. Seepage in rock fractures is affected by various factors such as fracture aperture, roughness, and filling, among which aperture and roughness are the two most widely influenced factors. The Navier-Stokes (NS) equation can be solved directly for the seepage flow in rock fractures with good accuracy, but there are problems of large computational volume and slow solution speed. In this paper, the fracture aperture space data is substituted into the local cubic law as an aperture function to form a numerical calculation method for seepage in rough rock fractures, namely, the aperture function method (AFM). Comparing with the physical seepage experiments of rock fractures, the calculation results of AFM will produce a small amount of error under the low Reynolds number condition, but it can greatly improve the calculation efficiency. The high efficiency of calculation makes it possible to apply AFM to the calculation of large-scale 3D rough fracture network models. The pressure drop of fluid in the fracture has viscous pressure drop (VPD) and local pressure drop (LPD). VPD can be calculated using the AFM. After analyzing the results of solving the NS equation for fracture seepage, it is concluded that the LPD includes the pressure drop caused by area crowding in the recirculation zone (RZ), kinetic energy loss in the RZ, kinetic energy loss in the vortices, and other reasons.

scholarly journals Experimental and Numerical Study on the Resistance Performance of an Axial Flow Cyclone Separator

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Yigang Luan ◽  
Haiou Sun
Keyword(s):  
Pressure Drop ◽  
Numerical Study ◽  
Ambient Pressure ◽  
Axial Flow ◽  
Operating Conditions ◽  
Cyclone Separator ◽  
Pressure Drops ◽  
Axial Flow Cyclone ◽  
Cfd Method ◽  
Resistance Performance

The purpose of this paper is to study the pressure drop of an axial flow cyclone separator as a function of inlet velocities using experimental and computational fluid dynamics (CFD) methods. First, the resistance performance of the separator was acquired under ambient pressure and temperature with little change by wind tunnel experiments. Then, numerical simulations were carried out in CFD code Fluent 6.3 under standard operating conditions. A comparison between the experimental and CFD data demonstrates that the CFD method can predict the pressure drop of the axial cyclone separator excellently. Additionally, the results show that the axial flow cyclone separators have a pressure drop coefficient of approximately 7.5. To study the effect of ambient pressure and temperature on pressure drops, the same CFD method was employed to predict the resistance performance under various operating conditions. Then the numerical results were compared with the data of a normalization process method of pressure drops raised in this paper. Their comparison demonstrated that the normalization method had a high precision in predicting the influence of ambient operating parameters on pressure drops of an axial flow cyclone separator.

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