Developing an Optimal Helix Angle As a Function of Pressure for Helical Groove Seals

2017 ◽  
Author(s):  
Cori Watson ◽  
Houston G. Wood
Keyword(s):  
High Pressure ◽  
Mass Flow ◽  
Helix Angle ◽  
Pressure Differential ◽  
Lower Pressure ◽  
Inlet Pressure ◽  
Circumferential Velocity ◽  
Labyrinth Seals ◽  
Screw Pump ◽  
Helical Groove

Helical groove seals are non-contacting annular seals used in pumps between impeller stages and at the balance drum. These seals have helically machined grooves on the surface of the rotor and/or stator. They work to sustain a pressure difference given a mass flow rate of the impeller through two flow phenomena which can be characterized by their flow direction. Fluid flowing axially dissipates kinetic energy through turbulent mixing as fluid is pushed through the jet stream region and mixes in the larger groove region, thus producing a pressure differential. Fluid flowing in the groove direction rotates with the rotor wall and is positively displaced toward the high pressure region, essentially acting as a screw pump. Previous work with optimization of helical groove seals has shown that the ideal helix angle of the seal is steeper for lower pressure applications and shallower for higher pressure applications. This is due to lower pressure applications having higher circumferential velocity in the grooves. In high pressure applications, the groove circumferential velocity has even been shown to be negative, and therefore the fluid leaks out the end of the grooves. The objective of this study is to use computational fluid dynamics simulations to find the optimal helix angle of the seal given the pressure differential. To accomplish this goal, simulations were run in ANSYS CFX for various inlet pressures, given zero gauge outlet pressure, and the helix angle of the grooves are varied. The helical grooves seals in this study have grooves on only the stator surface. The number of grooves is varied with the angle to keep the axial cross section of the seal consistent. By doing this, the study is able to focus in on the pumping mechanism of the helical groove seal without substantially changing the energy dissipation. The mass flow rates from each simulation for a given inlet pressure are plotted and quadratic regression was used to calculate an optimal helix angle as a function of inlet pressure. This study also answers the question of whether is there a limit where circumferentially grooved, i.e. labyrinth, seals outperform helical groove seals for very high pressures. Results comparing the powerloss of helical groove seals versus labyrinth seals and the effect of helix angle on powerloss are also given.

Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements vs. Predictions

2019 ◽  
Author(s):  
Luis San Andrés ◽  
Tingcheng Wu ◽  
Jose Barajas-Rivera ◽  
Jiaxin Zhang ◽  
Rimpei Kawashita
Keyword(s):  
Mass Flow ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Inlet Pressure ◽  
Steam Turbines ◽  
Rotor Speed ◽  
Labyrinth Seals ◽  
Gas Seals

Abstract Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Amongst seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and on the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3 MPa ∼ 1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (ṁ) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m.T/PinD1-PR2 characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.

scholarly journals Leakage Characteristic of Helical Groove Seal Designed in Reactor Coolant Pump

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Meng Zhang ◽  
Xiao-fang Wang ◽  
Sheng-li Xu ◽  
Shuo Yin
Keyword(s):  
Reynolds Number ◽  
High Pressure ◽  
Friction Factor ◽  
Helix Angle ◽  
Operation Condition ◽  
Coolant Pump ◽  
Reactor Coolant ◽  
Friction Factors ◽  
Helical Groove ◽  
Groove Seal

Helical groove seal is designed in reactor coolant pump to control the leakage along the front surface of the impeller face due to its higher resistance than the circumferentially grooved seal. The flow and the friction factors in helical groove seals are predicted by employing a commercial CFD code, FLUENT. The friction factors of the helical groove seals with helix angles varying from 20 deg to 50 deg, at a range of rotational speed and axial Reynolds number, were, respectively, calculated. For the helically grooved stator with the helix angle greater than 20 deg, the leakage shows an upward trend with the helix angle. The circumferentially grooved stator has a lower resistance to leakage than the 20 deg and 30 deg stators. It can be predicated that, for a bigger helix angle, the friction factor increases slightly with an increase in high axial Reynolds number, which arises from the high-pressure operation condition, and the friction factor is generally sensitive to changes in the helix angle in this operation condition. The study lays the theoretical foundation for liquid seal design of reactor coolant pump and future experimental study to account for the high-pressure condition affecting the leakage characteristic.

The Impact of Adding a Labyrinth Surface to an Optimal Helical Seal Design

2018 ◽  
Author(s):  
Wisher Paudel ◽  
Cori Watson ◽  
Houston G. Wood
Keyword(s):  
High Pressure ◽  
Kinetic Energy ◽  
Labyrinth Seal ◽  
Groove Width ◽  
Design Parameters ◽  
Labyrinth Seals ◽  
Pressure Application ◽  
Helical Groove ◽  
Helical Grooves ◽  
Annular Seals

Non-contacting annular seals are used in rotating machinery to reduce the flow of working fluid across a pressure differential. Helical and labyrinth grooved seals are two types of non-contacting annular seals frequently used between the impeller stages in a pump and at the balance drum. Labyrinth seals have circumferential grooves cut into the surface of the rotor, the stator, or both. They function to reduce leakage by dissipating kinetic energy as fluid expands in the grooves and then is forced to contract in the jet stream region. Helical groove seals have continuously cut grooves on either or both the rotor and stator surfaces. Like labyrinth seals, they reduce leakage through dissipation of kinetic energy, but have the added mechanism of functioning as a pump to push the fluid back towards the high-pressure region. Previous work has shown that mixed helical-labyrinth seals with labyrinth grooves on stator and helical grooves on rotor or labyrinth grooves on rotor and helical grooves on stator have an approximately 45% lower leakage than an optimized helical groove seal with grooves just on the stator in a high pressure application. The primary objective of this study is to determine whether the same performance gains can also be achieved in a low pressure application. Simulations were run in ANSYS CFX for seal designs with a helical stator and labyrinth rotor. Several labyrinth design parameters including the number of grooves and the groove width and depth are varied while the helical variables such as the groove width and depth as well as helix angle are kept constant. The data obtained are analyzed using backward regression methods and various response plots to determine the relationship between the design parameters and mass flow and power loss. The optimized helical design was simulated and the axial pressure profiles of the designs were compared to analyze the mechanism of the mixed helical-labyrinth seal. Then, the same labyrinth seal designs were simulated for a labyrinth rotor and a smooth stator to determine whether the optimal number of grooves, groove width and groove depth change due to the helical stator. The findings of this study show the effectiveness of mixed helical labyrinth grooved seals for both low and high pressure cases, and thus their efficiency and reliability for numerous industrial applications.

Optimizing a Helical Groove Seal With Grooves on Both the Rotor and Stator Surfaces

2017 ◽  
Author(s):  
Cori Watson ◽  
Houston G. Wood
Keyword(s):  
Axial Flow ◽  
Helix Angle ◽  
Operating Conditions ◽  
Design Parameters ◽  
Screw Pump ◽  
Performance Function ◽  
Seal Design ◽  
Interaction Terms ◽  
Helical Groove ◽  
Groove Seal

Helical groove seals are non-contacting annular seals commonly used in pumps within the impeller stages to sustain a pressure differential for a given leakage. Helical groove seals have continuously cut grooves, like the threads of a screw, on the surface of the rotor, the surface of the stator, or both. The two main components of the flow within helical groove seals are axial flow and groove flow. The axial flow serves to reduce the leakage by dissipating kinetic energy as the fluid expands in the grooves and then is forced to contract within the jet stream region. The groove flow serves to reduce the leakage by acting as screw pump. The fluid within the grooves is displaced towards the high pressure region as it spins with the rotor. Previous work has shown that seals with grooves on both the surface of the rotor and the surface of the stator can sustain higher pressure differentials for a given leakage than seals with grooves on only one surface. The goal of this study is to optimize the leakage performance of a double surface helical groove seal for a given set of operating conditions. To accomplish this goal, simulations are run in ANSYS CFX. A sufficient mesh with appropriate boundary layers is determined from the mesh independence study. The turbulence model is k-ε turbulence for water at 25°C. This is the first paper to present numerical results for the performance of helical groove seals with grooves on both the rotor and the stator. The design parameters used in the optimization are inner (rotor) groove size, inner helix angle, outer (stator) groove size, and outer helix angle. A Kennard-Stone algorithm, which optimally spaces the simulations within the design space, is used to select the designs to be simulated. A multifactor quadratic regression is derived. Backward regression is used to reduce the performance function to only statistically significant terms. Finally, the optimal seal design is derived from the performance function and is simulated to demonstrate the predictive power of the performance function. Interaction terms for the rotor and stator design parameters will be used to explore the mechanism whereby helical groove seals with grooves on both the rotor and the stator surfaces are able to have lower leakage than helical groove seals with grooves on just one surface. The end result of this study is a seal design which minimizes leakage and therefore improve machine efficiency.

Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements Versus Predictions

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Luis San Andrés ◽  
Tingcheng Wu ◽  
Jose Barajas-Rivera ◽  
Jiaxin Zhang ◽  
Rimpei Kawashita
Keyword(s):  
Mass Flow ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Inlet Pressure ◽  
Steam Turbines ◽  
Rotor Speed ◽  
Labyrinth Seals ◽  
Gas Seals

Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Among seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor (TOR) or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3–1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (m˙) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate that the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m˙T/(PinD1−PR2) characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.

A Novel X-Ray Based High Pressure Mass Flow Rate Sensor for MPD Operations

2018 ◽  
Author(s):  
Vivek Singhal ◽  
Pradeep Ashok ◽  
Eric van Oort ◽  
Paul Park
Keyword(s):  
High Pressure ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
X Ray ◽  
Rate Sensor

scholarly journals Harvesting the Potential of CO2 before it is Injected into Geological Reservoirs

2021 ◽  
Vol 3 (4) ◽  
pp. 1-1
Author(s):  
Tran X Phuoc ◽  
◽  
Mehrdad Massoudi ◽  
Keyword(s):  
High Pressure ◽  
Mechanical Work ◽  
Lower Pressure ◽  
Co2 Injection ◽  
Gas Temperature ◽  
Expansion Valve ◽  
Useful Power ◽  
Turbine Disks ◽  
Pressure Transport ◽  
The Cost

To store CO2 in geological reservoirs, expansion valves have been used to intentionally release supercritical CO2 from high-pressure containers at a source point to lower-pressure pipelines and transport to a selected injection site. Using expansion valves, however, has some shortcomings: (i) the fluid potential, in the form of kinetic energy and pressure which can produce mechanical work or electricity, is wasted, and (ii) due to the Joule-Thomson cooling effect, the reduction in the temperature of the released CO2 stream might be so dramatic that it can induce thermal contraction of the injection well causing fracture instability in the storage formation. To avoid these problems, it has been suggested that before injection, CO2, should be heated to a temperature slightly higher than that of the reservoir. However, heating could increase the cost of CO2 injection. This work explores the use of a Tesla Turbine, instead of an expansion valve, to harvest the potential of CO2, in the form of its pressure and kinetics, to generate mechanical work when it is released from a high-pressure container to a lower-pressure transport pipeline. The goal is to avoid throttling losses and to produce useful power because of the expansion process. In addition, due to the friction between the gas and the turbine disks, the expanded gas temperature reduction is not as dramatic as in the case when an expansion valve is used. Thus, as far as CO2 injection is concerned, the need for preheating can be minimized.

Measurement and Analysis of Flame Transfer Function in a Sector Combustor Under High Pressure Conditions

2003 ◽  
Author(s):  
W. S. Cheung ◽  
G. J. M. Sims ◽  
R. W. Copplestone ◽  
J. R. Tilston ◽  
C. W. Wilson ◽  
...  
Keyword(s):  
High Pressure ◽  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Mass Flow ◽  
Atmospheric Pressure ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Transfer Functions ◽  
Unsteady Pressure

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. A flame transfer function describes the change in the rate of heat release in response to perturbations in the inlet flow as a function of frequency. It is a quantitative assessment of the susceptibility of combustion to disturbances. The resulting fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. Flame transfer functions for LPP combustion are poorly understood at present but are crucial for predicting combustion oscillations. This paper describes an experiment designed to measure the flame transfer function of a simple combustor incorporating realistic components. Tests were conducted initially on this combustor at atmospheric pressure (1.2 bar and 550 K) to make an early demonstration of the combustion system. The test rig consisted of a plenum chamber with an inline siren, followed by a single LPP premixer/duct and a combustion chamber with a silencer to prevent natural instabilities. The siren was used to induce variable frequency pressure/acoustic signals into the air approaching the combustor. Both unsteady pressure and heat release measurements were undertaken. There was good coherence between the pressure and heat release signals. At each test frequency, two unsteady pressure measurements in the plenum were used to calculate the acoustic waves in this chamber and hence estimate the mass-flow perturbation at the fuel injection point inside the LPP duct. The flame transfer function relating the heat release perturbation to this mass flow was found as a function of frequency. The same combustor hardware and associated instrumentation were then used for the high pressure (15 bar and 800 K) tests. Flame transfer function measurements were taken at three combustion conditions that simulated the staging point conditions (Idle, Approach and Take-off) of a large turbofan gas turbine. There was good coherence between pressure and heat release signals at Idle, indicating a close relationship between acoustic and heat release processes. Problems were encountered at high frequencies for the Approach and Take-off conditions, but the flame transfer function for the Idle case had very good qualitative agreement with the atmospheric-pressure tests. The flame transfer functions calculated here could be used directly for predicting combustion oscillations in gas turbine using the same LPP duct at the same operating conditions. More importantly they can guide work to produce a general analytical model.

scholarly journals Assessment of Severe Accident Management for Small IPWR under an ESBO Scenario

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Hao Yu ◽  
Minjun Peng
Keyword(s):  
High Pressure ◽  
Low Pressure ◽  
Lower Pressure ◽  
Severe Accident ◽  
Maximum Temperature ◽  
Pressurized Water ◽  
The Core ◽  
Severe Accidents ◽  
Accident Management ◽  
Degradation Studies

Interest in evaluation of severe accidents induced by extended station blackout (ESBO) has significantly increased after Fukushima. In this paper, the severe accident process under the high and low pressure induced by an ESBO for a small integrated pressurized water reactor (IPWR)-IP200 is simulated with the SCDAP/RELAP5 code. For both types of selected scenarios, the IP200 thermal hydraulic behavior and core meltdown are analyzed without operator actions. Core degradation studies firstly focus on the changes in the core water level and temperature. Then, the inhibition of natural circulation in the reactor pressure vessel (RPV) on core temperature rise is studied. In addition, the phenomena of core oxidation and hydrogen generation and the reaction mechanism of zirconium with the water and steam during core degradation are analyzed. The temperature distribution and time point of the core melting process are obtained. And the IP200 severe accident management guideline (SAMG) entry condition is determined. Finally, it is compared with other core degradation studies of large distributed reactors to discuss the influence of the inherent design characteristics of IP200. Furthermore, through the comparison of four sets of scenarios, the effects of the passive safety system (PSS) on the mitigation of severe accidents are evaluated. Detailed results show that, for the quantitative conclusions, the low coolant storage of IP200 makes the core degradation very fast. The duration from core oxidation to corium relocation in the lower-pressure scenario is 53% faster than that of in the high-pressure scenario. The maximum temperature of liquid corium in the lower-pressure scenario is 134 K higher than that of the high-pressure scenario. Besides, the core forms a molten pool 2.8 h earlier in the lower-pressure scenario. The hydrogen generated in the high-pressure scenario is higher when compared to the low-pressure scenario due to the slower degradation of the core. After the reactor reaches the SAMG entry conditions, the PSS input can effectively alleviate the accident and prevent the core from being damaged and melted. There is more time to alleviate the accident. This study is aimed at providing a reference to improve the existing IPWR SAMGs.

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