NUMERICAL STUDY ON THE PERFORMANCE IMPROVEMENT OF A ROTARY VANE EXPANDER FOR A CO2 HEAT PUMP CYCLE

2011 ◽  
Vol 19 (04) ◽  
pp. 311-319 ◽  
Author(s):  
HYUN JIN KIM ◽  
WOO YOUNG KIM ◽  
JONG MIN AHN ◽  
SUNG OUG CHO
Keyword(s):  
Numerical Simulation ◽  
Performance Improvement ◽  
Heat Pump ◽  
Numerical Study ◽  
Friction Loss ◽  
Inlet Temperature ◽  
Cylinder Wall ◽  
Operating Pressure ◽  
Expansion Process ◽  
Crank Angle

In order to recover friction loss in the expansion process and increase refrigeration effect in a CO2 heat pump cycle, a rotary vane expander has been designed. Numerical simulation has been carried out to estimate the performance of designed expander, and it has been found that vane jumping or vane recession from the cylinder wall occurs in a certain range of the crank angle. To improve the vane motion, a way of pressurizing the vane back chamber has been employed, and elimination of the vane jumping phenomenon has been confirmed by the numerical simulation. With the operating pressure conditions of 9 MPa/4.5 MPa and inlet temperature of 35°C, the expander efficiency has been calculated to be 42.72%, and improvement of COP of a CO2 heat pump cycle with this expander has been estimated to be about 12.82%.

scholarly journals Numerical Study of Pollutant Emissions in a Jet Stirred Reactor under Elevated Pressure Lean Premixed Conditions

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Karim Mazaheri ◽  
Alireza Shakeri
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Computational Cost ◽  
Elevated Pressure ◽  
Pollutant Emissions ◽  
Inlet Temperature ◽  
Operating Pressure ◽  
Experimental Distribution ◽  
Stirred Reactor ◽  
Lean Premixed

Numerical study of pollutant emissions (NO and CO) in a Jet Stirred Reactor (JSR) combustor for methane oxidation under Elevated Pressure Lean Premixed (EPLP) conditions is presented. A Detailed Flow-field Simplified Chemistry (DFSC) method, a low computational cost method, is employed for predicting NO and CO concentrations. Reynolds Averaged Navier Stokes (RANS) equations with species transport equations are solved. Improved-coefficient five-step global mechanisms derived from a new evolutionary-based approach were taken as combustion kinetics. For modeling turbulent flow field, Reynolds Stress Model (RSM), and for turbulence chemistry interactions, finite rate-Eddy dissipation model are employed. Effects of pressure (3, 6.5 bars) and inlet temperature (408–573 K) over a range of residence time (1.49–3.97 ms) are numerically examined. A good agreement between the numerical and experimental distribution of NO and CO was found. The effect of decreasing the operating pressure on NO generation is much more than the effect of increase in the inlet temperature.

Numerical simulation of the effects of coating on thermal elastohydrodynamic lubrication in cam/tappet contact

2016 ◽  
Vol 231 (2) ◽  
pp. 221-239 ◽  
Author(s):  
Changya Yu ◽  
Xianghui Meng ◽  
Youbai Xie
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Reynolds Equation ◽  
Thermal Inertia ◽  
Elastohydrodynamic Lubrication ◽  
Friction Loss ◽  
Inlet Temperature ◽  
The Finite Element Method ◽  
Lubrication Performance ◽  
Energy Equations

Investigating the effects of coating on cam/tappet thermal elastohydrodynamic lubrication through numerical simulation has great significance in the design of coated cam/tappet conjunctions. This paper presents a numerical model for the prediction of the thermal elastohydrodynamic lubrication of a coated cam/tappet and the results of a study of the effects of coating parameters on cam/tappet lubrication performance. In the model, the Reynolds equation is solved by the damped Newton method to obtain the pressure distribution, and energy equations are used to obtain the temperature distribution. The total elastic deformation is calculated by the finite element method. The effects of the coating’s mechanical properties on pressure and temperature were found to be significant, as were the effects of the coating’s thermal properties on temperature. These effects were found to increase with increasing coating thickness. A soft coating with low thermal inertia has the greatest ability to reduce friction loss, and the higher the inlet temperature is, the lower the friction loss is. The influence of coating of both the cam and tappet on friction loss is greater than the effect of coating of the tappet only, which is greater than the effect of coating of the cam only.

The Effects of Pressure on Gas Turbine Combustor Performance: An Investigation via Numerical Simulation

2006 ◽  
Author(s):  
Yufeng Cui ◽  
Gang Xu ◽  
Bin Yu ◽  
Chaoqun Nie ◽  
Weiguang Huang
Keyword(s):  
Numerical Simulation ◽  
Gas Turbine ◽  
Radiation Heat Transfer ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Operating Pressure ◽  
Gas Turbine Combustor ◽  
Flamelet Model ◽  
Air Inlet ◽  
Operation Pressure

Performance tests of a gas turbine combustor are usually conducted at atmospheric or medium pressure which is quite different from its real operating condition. The effects of pressure on the performance of a gas turbine combustor for burning medium-heating-value syngas are researched by numerical simulation in this paper. The geometry of the combustor is modeled by coupling all its components including nozzle, combustor liner and sealant tube. In the simulation a laminar flamelet model and P-1 radiation model are adopted. The numerical results show that at the same fuel and air inlet temperature and the same equivalence ratio, the operation pressure has less effect on the flow fields, but its effect on the temperature distribution is obvious. Both the highest temperature in the combustor and the outlet temperature increase with increasing operating pressure because of the weakening of the dissociation of the H2O, CO2 and so on. Moreover, as pressure increases, the concentration of H2O and CO2 in the combustor increase, and so to does the absorption coefficient and the emissivity of gas inside the liner. As a result, the radiation heat transfer between the gas and the combustion liner wall is enhanced, and the wall temperature of the liner increases. The NOx emissions of the combustor are also distinctly higher at high pressure than at low pressure.

scholarly journals Experimental and numerical simulation investigation on tubular expansion process

2021 ◽  
Vol 651 (3) ◽  
pp. 032050
Author(s):  
Xiucheng Li ◽  
Shuai Ren ◽  
Dejun Li ◽  
Jingliang Wang ◽  
Xiao Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Expansion Process

scholarly journals Development of Depth-Limited Wave Boundary Layers over a Smooth Bottom

2020 ◽  
Vol 9 (1) ◽  
pp. 27
Author(s):  
Hitoshi Tanaka ◽  
Nguyen Xuan Tinh ◽  
Xiping Yu ◽  
Guangwei Liu
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Boundary Layers ◽  
Wave Motion ◽  
Numerical Study ◽  
Experiment Data ◽  
Tidal Motion ◽  
Long Period ◽  
Simulation Results ◽  
Wave Boundary

A theoretical and numerical study is carried out to investigate the transformation of the wave boundary layer from non-depth-limited (wave-like boundary layer) to depth-limited one (current-like boundary layer) over a smooth bottom. A long period of wave motion is not sufficient to induce depth-limited properties, although it has simply been assumed in various situations under long waves, such as tsunami and tidal currents. Four criteria are obtained theoretically for recognizing the inception of the depth-limited condition under waves. To validate the theoretical criteria, numerical simulation results using a turbulence model as well as laboratory experiment data are employed. In addition, typical field situations induced by tidal motion and tsunami are discussed to show the usefulness of the proposed criteria.

Numerical Simulation of Premixed Propane/Air Flame Propagation Using a Dynamically Thickened Flame Approach

2013 ◽  
Vol 444-445 ◽  
pp. 1574-1578 ◽  
Author(s):  
Hua Hua Xiao ◽  
Zhan Li Mao ◽  
Wei Guang An ◽  
Qing Song Wang ◽  
Jin Hua Sun
Keyword(s):  
Numerical Simulation ◽  
Flame Propagation ◽  
Numerical Study ◽  
Vortex Motion ◽  
Combustion Process ◽  
Single Step ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Flame Surface ◽  
Arrhenius Kinetics

A numerical study of premixed propane/air flame propagation in a closed duct is presented. A dynamically thickened flame (TF) method is applied to model the premixed combustion. The reaction of propane in air is taken into account using a single-step global Arrhenius kinetics. It is shown that the premixed flame undergoes four stages of dynamics in the propagation. The formation of tulip flame phenomenon is observed. The pressure during the combustion process grows exponentially at the finger-shape flame stage and then slows down until the formation of tulip shape. After tulip formation the pressure increases quickly again with the increase of the flame surface area. The vortex motion behind the flame front advects the flame into tulip shape. The study indicates that the TF model is quite reliable for the investigation of premixed propane/air flame propagation.

scholarly journals Performance improvement of double-tube gas cooler in CO2 refrigeration system using nanofluids

2015 ◽  
Vol 19 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jahar Sarkar
Keyword(s):  
Performance Improvement ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Cooling Capacity ◽  
Inlet Temperature ◽  
Refrigeration Cycle ◽  
Particle Volume ◽  
Transcritical Carbon Dioxide ◽  
The Given ◽  
Theoretical Analyses

The theoretical analyses of the double-tube gas cooler in transcritical carbon dioxide refrigeration cycle have been performed to study the performance improvement of gas cooler as well as CO2 cycle using Al2O3, TiO2, CuO and Cu nanofluids as coolants. Effects of various operating parameters (nanofluid inlet temperature and mass flow rate, CO2 pressure and particle volume fraction) are studied as well. Use of nanofluid as coolant in double-tube gas cooler of CO2 cycle improves the gas cooler effectiveness, cooling capacity and COP without penalty of pumping power. The CO2 cycle yields best performance using Al2O3-H2O as a coolant in double-tube gas cooler followed by TiO2-H2O, CuO-H2O and Cu-H2O. The maximum cooling COP improvement of transcritical CO2 cycle for Al2O3-H2O is 25.4%, whereas that for TiO2-H2O is 23.8%, for CuO-H2O is 20.2% and for Cu-H2O is 16.2% for the given ranges of study. Study shows that the nanofluid may effectively use as coolant in double-tube gas cooler to improve the performance of transcritical CO2 refrigeration cycle.

Numerical Simulation of Gas Flow and Heat Transfer in Cross-Wavy Primary Surface Channel for Microtubine Recuperators

2005 ◽  
Author(s):  
H. X. Liang ◽  
Q. W. Wang ◽  
L. Q. Luo ◽  
Z. P. Feng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Numerical Study ◽  
High Reliability ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
The Cross

Three-dimensional numerical simulation was conducted to investigate the flow field and heat transfer performance of the Cross-Wavy Primary Surface (CWPS) recuperators for microturbines. Using high-effective compact recuperators to achieve high thermal efficiency is one of the key techniques in the development of microturbine in recent years. Recuperators need to have minimum volume and weight, high reliability and durability. Most important of all, they need to have high thermal-effectiveness and low pressure-losses so that the gas turbine system can achieve high thermal performances. These requirements have attracted some research efforts in designing and implementing low-cost and compact recuperators for gas turbine engines recently. One of the promising techniques to achieve this goal is the so-called primary surface channels with small hydraulic dimensions. In this paper, we conducted a three-dimensional numerical study of flow and heat transfer for the Cross-Wavy Primary Surface (CWPS) channels with two different geometries. In the CWPS configurations the secondary flow is created by means of curved and interrupted surfaces, which may disturb the thermal boundary layers and thus improve the thermal performances of the channels. To facilitate comparison, we chose the identical hydraulic diameters for the above four CWPS channels. Since our experiments on real recuperators showed that the Reynolds number ranges from 150 to 500 under the operating conditions, we implemented all the simulations under laminar flow situations. By analyzing the correlations of Nusselt numbers and friction factors vs. Reynolds numbers of the four CWPS channels, we found that the CWPS channels have superior and comprehensive thermal performance with high compactness, i.e., high heat transfer area to volume ratio, indicating excellent commercialized application in the compact recuperators.

Investigation of a Rotor Blade With Tip Cooling Subject to a Nonuniform Temperature Profile

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Harika S. Kahveci
Keyword(s):  
Temperature Profile ◽  
Turbine Blade ◽  
Numerical Study ◽  
Turbine Rotor ◽  
Inlet Temperature ◽  
Pressure Side ◽  
Engine Operation ◽  
Pressure Losses ◽  
Blade Tip ◽  
Temperature Levels

Abstract One of the challenges in the design of a high-pressure turbine blade is that a considerable amount of cooling is required so that the blade can survive high temperature levels during engine operation. Another challenge is that the addition of cooling should not adversely affect blade aerodynamic performance. The typical flat tips used in designs have evolved into squealer form that implements rims on the tip, which has been reported in several studies to achieve better heat transfer characteristics as well as to decrease pressure losses at the tip. This paper demonstrates a numerical study focusing on a squealer turbine blade tip that is operating in a turbine environment matching the typical design ratios of pressure, temperature, and coolant blowing. The blades rotate at a realistic rpm and are subjected to a turbine rotor inlet temperature profile that has a nonuniform shape. For comparison, a uniform profile is also considered as it is typically used in computational studies for simplicity. The effect of tip cooling is investigated by implementing seven holes on the tip near the blade pressure side. Results confirm that the temperature profile nonuniformity and the addition of cooling are the drivers for loss generation, and they further increase losses when combined. Temperature profile migration is not pronounced with a uniform profile but shows distinct features with a nonuniform profile for which hot gas migration toward the blade pressure side is observed. The blade tip also receives higher coolant coverage when subject to the nonuniform profile.

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