A high-efficiency propane axial-flow expander design method considering condensation risk constraints

Abstract

This invention discloses a design method for a high-efficiency propane axial flow expander that considers condensation risk constraints, solving the problems of complex calculation processes and high computational costs in existing technologies. The invention includes: obtaining the thermophysical parameters of propane in the axial flow expander according to design parameter requirements; establishing a flow path model of the propane axial flow expander based on the thermophysical parameters; selecting at least three design sections along the blade height direction for each stage of stationary blades and each stage of moving blades in the flow path model to generate corresponding candidate airfoils; performing two-dimensional or quasi-three-dimensional blade cascade analysis on the candidate airfoils to obtain the cross-sectional airfoils that meet the design requirements; establishing a CFD model of the propane axial flow expander to obtain aerodynamic calculation results for each stage of the flow path; constructing a condensation risk criterion to determine whether each stage of the flow path is in the condensation risk zone; setting low humidity thresholds for each stage of the flow path and determining whether the current humidity level of each stage of the flow path is within the low humidity threshold range; and designing the inlet section, diffuser section, and exhaust section to obtain a high-efficiency propane axial flow expander.

Description

Technical Field

[0001] This invention relates to a design method for a propane axial flow expander, specifically to a design method for a high-efficiency propane axial flow expander that takes into account condensation risk constraints. Background Technology

[0002] Axial flow expanders (also known as axial flow turbine expanders) are a type of turbine velocity expander that combines refrigeration and energy recovery as their core functions. During operation, high-pressure gas flows sequentially along an axial direction parallel to the main shaft, passing through stationary and moving blades. This process converts the pressure energy and internal energy of the gas into rotational mechanical work. Simultaneously, the gas undergoes adiabatic expansion, cooling and generating shaft power. Therefore, the design of an axial flow expander requires comprehensive consideration of various factors to ensure its performance meets the required specifications.

[0003] Propane axial flow expanders are a type of axial flow expander that uses high-pressure gaseous propane as the working fluid. Mechanical work is output through the expansion and enthalpy drop of the working fluid within an axial flow channel. Currently, they are mainly used in petrochemical and cryogenic energy systems such as Organic Rankine Cycle (ORC) waste heat power generation, LNG cold energy utilization, and natural gas hydrocarbon recovery. Existing design methods for propane axial flow expanders are mainly divided into two categories: one based on non-equilibrium condensation theory, and the other based on pure-phase equilibrium CFD (Computational Fluid Dynamics). The design principle of the non-equilibrium condensation theory-based method is that, under low-humidity conditions, non-equilibrium condensation is not simply "droplet formation upon reaching the saturation line," but involves supercooling, homogeneous nucleation, droplet growth, and the thermodynamic and kinetic relaxation processes after droplet loading. Building upon this, Kreitmeier's review work (from Franz Kreitmeier's 2005 IMechE, a classic work systematically summarizing the mechanisms of two-phase relaxation and humidity loss) points out that the thermodynamic and kinetic relaxation processes after droplet loading lead to significant dissipation and erosion risks. Starzmann et al. further used two-phase CFD to directly calculate thermodynamic humidity loss and kinetic relaxation loss caused by droplet drag. Petr and Kolovratnik also conducted calculations and analyses of the Baumann rule (Baumann humidity loss rule) and its applicability. Therefore, existing design methods based on nonequilibrium condensation theory fully demonstrate the importance of nonequilibrium condensation, droplet drag, and humidity loss in low-humidity turbine machinery. Nonequilibrium models are more suitable for studying details such as droplet nucleation, droplet growth, and condensation impact. However, existing design methods are computationally complex, especially in three-dimensional multi-level unsteady models where the computational cost is high. Currently, design methods based on pure-phase equilibrium CFD lack explicit humidity criteria and correction steps, and therefore lack information such as the equilibrium properties of real gases, low humidity criteria, humidity correction methods, multi-condition installation angle substitution rules, and intake and exhaust pressure recovery constraints. As a result, the design results cannot fully match the actual operating conditions. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of existing design methods, such as complex calculation processes, high calculation costs, or deviations in design results due to the lack of humidity criteria and correction steps. The invention provides a high-efficiency propane axial flow expander design method that considers condensation risk constraints.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A design method for a high-efficiency propane axial flow expander considering condensation risk constraints, characterized by the following steps:

[0007] Step 1: Based on the initial design parameter requirements of the propane axial flow expander, obtain the thermal properties of propane in the single-phase region and gas-liquid equilibrium region of the axial flow expander from the real gas equilibrium property database;

[0008] Step 2: Based on the thermophysical parameters obtained in Step 1, establish the flow path model of the propane axial flow expander;

[0009] Step 3: Select at least three design sections along the blade height direction for each stage of stationary blade and each stage of moving blade in the flow path model, define the section parameters of each design section, and generate the corresponding candidate airfoil.

[0010] Step 4: Perform two-dimensional or quasi-three-dimensional blade cascade analysis on the candidate air profiles generated in Step 3, and iterate the candidate air profiles with the Mach number distribution on the blade cascade surface, blade cascade load and loss level as the objectives to obtain the cross-sectional air profile that meets the design requirements.

[0011] Step 5: Establish a CFD model of the propane axial flow expander, and solve the whole machine based on the cross-sectional airfoil obtained in Step 4 to obtain the aerodynamic calculation results of each stage of the flow model; the aerodynamic calculation results include the efficiency, mass flow rate, power, outlet swirl angle, inlet humidity, outlet humidity and average humidity of each stage of the flow model.

[0012] Step 6: Construct condensation risk criteria and determine whether each level of the flow path model is in the condensation risk zone based on the aerodynamic calculation results. If yes, proceed to step 7; otherwise, obtain the complete flow path structure of the propane axial flow expander and proceed to step 8.

[0013] Step 7: Set the low humidity threshold for each channel according to the design requirements, and determine whether the current humidity level of each channel is within the low humidity threshold range. If so, perform efficiency correction for the corresponding channel based on the equilibrium properties to obtain the complete flow structure of the propane axial flow expander, and execute Step 8; if not, adjust the first stage blade load and inlet temperature, and return to Step 1.

[0014] Step 8: Based on the complete flow structure of the propane axial flow expander, its inlet section, diffuser section and exhaust section are designed in an integrated manner to obtain a high-efficiency propane axial flow expander that meets the preset requirements.

[0015] Further, in step 1, the initial design parameters include the rotational speed, mass flow rate, target expansion ratio, target power, number of stages, and thermodynamic boundary parameters of the propane axial flow expander under corresponding operating conditions; the thermodynamic boundary parameters include inlet volumetric flow rate, inlet mass flow rate, inlet pressure, inlet temperature, and outlet pressure; the thermophysical parameters include the density, enthalpy, entropy, specific heat, velocity of sound, phase state, saturation parameters, and gas-liquid equilibrium parameters of propane.

[0016] Furthermore, in step 3, there are three design sections, namely the sections at the locations of 10%, 50%, and 90% of the blade height; or the sections at the blade root, the blade median diameter, and the blade tip.

[0017] The cross-sectional parameters include pitch-to-chord ratio, axial chord length, trailing edge thickness ratio, throat opening ratio, throat width, cross-sectional area, inlet angle, and outlet angle.

[0018] Furthermore, in step 4, the peak value of the Mach number on the blade surface in the Mach number distribution is 0.9~1.2;

[0019] The load factor of the cascade load is 0.6~0.9.

[0020] Further, in step 6, the expression for the condensation risk criterion is:

[0021] ;

[0022] In the formula, For the first Local temperature margin of the channel relative to the saturation temperature; Indicates the first The current temperature of the channel, 1≤i≤N, where N is the total number of channels, and 2≤N≤5; This indicates the condensation temperature of propane under static pressure.

[0023] when When the current channel has a heat margin, it indicates that the channel is not in the condensation risk zone.

[0024] when When this occurs, it indicates that the current channel is in a condensation risk zone.

[0025] Further, in step 7, the low humidity threshold for each level of channel includes the average humidity mass fraction threshold for each level of channel and the humidity mass fraction threshold for the outlet cross-section of each level of channel;

[0026] The average humidity mass fraction threshold for each channel level is: , The average humidity mass fraction of the i-th channel;

[0027] The humidity mass fraction threshold at the outlet cross-section of each channel is: , Let be the humidity mass fraction at the outlet section of the i-th channel.

[0028] Furthermore, in step 7, the correction formula for the efficiency correction is:

[0029] ;

[0030] In the formula, The efficiency after correction for the i-th level channel; The efficiency before correction of the i-th channel; This is a correction factor that varies with humidity.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention revolves around the real gas equilibrium properties, low humidity condensation risk constraints, efficiency correction, and multi-condition blade profile substitution. It retains the engineering essence of the two-phase / humidity influence, while avoiding the risks of the designed propane axial flow expander's output power not matching reality due to the core model not being actually completed or insufficiently verified, as well as the risk of excessive humidity damaging the blades. This improves the accuracy and precision of the design results.

[0033] 2. This invention can achieve stable and high-efficiency design results under low humidity and near-saturation conditions, taking into account the overall front and rear channels, and has an engineering evaluation of overall aerodynamic efficiency ≥86%.

[0034] 3. This invention moves the influence of humidity from the interpretation of results to the design constraint. As long as the low humidity range is maintained and a variable correction factor α is used for correction, a reliable design of a high-efficiency propane axial flow expander can be completed without resorting to a complete non-equilibrium nucleation model.

[0035] 4. The overall calculation process of this invention is simple, which greatly shortens the design time, thereby reducing the labor and time costs of the design process.

[0036] 5. The propane axial flow expander designed in this invention has the advantages of high aerodynamic efficiency, matching with actual working conditions, and high safety. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the meridional channel of the flow model designed in step 2 of the embodiment of the present invention.

[0038] Figure 2 This is the blade Mach number distribution diagram corresponding to step 4 of the embodiment of the present invention.

[0039] Figure 3 This is the three-dimensional CFD model diagram obtained in step 5 of the embodiment of the present invention.

[0040] Figure 4 This is the humidity distribution diagram corresponding to the 50% cross-section of the design condition in step 6 of the embodiment of the present invention.

[0041] Figure 5 This is a full-channel flow field distribution diagram of the propane axial flow expander obtained in step 6 of the embodiment of the present invention.

[0042] Figure 6 This is a single-channel flow field distribution diagram of the propane axial flow expander obtained in step 6 of the embodiment of the present invention.

[0043] Figure 7 This is the total pressure loss diagram of the intake section obtained by flow simulation calculation in step 8 of the embodiment of the present invention.

[0044] Figure 8 This is a schematic diagram of the diffuser structure in step 8 of the embodiment of the present invention.

[0045] Figure 9 This is a schematic diagram of the simulated structure of the expansion to the flared flange in step 8 of the embodiment of the present invention. Detailed Implementation

[0046] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0047] The design concept of this invention is as follows: When the working fluid of a propane axial flow expander is close to saturation but the overall humidity is low, making it unsuitable to use a complete non-equilibrium droplet model, based on the premise of real gas equilibrium properties and phase equilibrium model, the condensation risk in the low humidity region is explicitly incorporated into the blade design. A calculable, verifiable, and engineering-deliverable efficient aerodynamic design method is constructed, enabling the three-stage axial flow expander to simultaneously meet the requirements of efficiency, humidity risk, and inlet and outlet pressure recovery under design requirements and typical variable operating conditions.

[0048] This embodiment provides a design method for a high-efficiency propane axial flow expander that considers condensation risk constraints, including the following steps:

[0049] Step 1: Based on the initial design parameter requirements of the propane axial flow expander, obtain the thermal properties of propane in the single-phase region and gas-liquid equilibrium region of the axial flow expander from the real gas equilibrium property database; the thermal properties include the density, enthalpy, entropy, specific heat, sound velocity, phase state, saturation parameters and gas-liquid equilibrium parameters of propane.

[0050] The initial design parameters described in this embodiment include the rotational speed, mass flow rate, target expansion ratio, target power, number of stages, and thermodynamic boundary parameters of the propane axial flow expander under corresponding operating conditions. The thermodynamic boundary parameters include inlet volumetric flow rate, inlet mass flow rate, inlet pressure, inlet temperature, and outlet pressure.

[0051] In this embodiment, four typical operating conditions A, B, C, and D are set, wherein:

[0052] The inlet volumetric flow rate for condition A is 27844.5 m³. 3 / h, inlet mass flow rate is 234326 kg / h, inlet pressure is 0.385 MPa(A), inlet temperature is -7.026℃, and outlet pressure is 0.12MPa(A);

[0053] Condition B is the design condition, with an inlet volumetric flow rate of 16838.7 m³. 3 / h, inlet mass flow rate is 269634 kg / h, inlet pressure is 0.745 MPa(A), inlet temperature is 15.14 ℃, outlet pressure is 0.12 MPa(A);

[0054] The inlet volumetric flow rate for condition C is 21725.6 m³. 3 The inlet mass flow rate is 182833 kg / h, the inlet pressure is 0.385 MPa(A), the inlet temperature is -7.026 ℃, and the outlet pressure is 0.12 MPa(A).

[0055] The inlet volumetric flow rate for condition D is 13895.2 m³. 3 The inlet mass flow rate is 222,500 kg / h, the inlet pressure is 0.745 MPa(A), the inlet temperature is 15.14 ℃, and the outlet pressure is 0.12 MPa(A).

[0056] Based on the above parameter requirements, the density, enthalpy, entropy, specific heat, sound velocity, phase state, saturation parameters, and gas-liquid equilibrium related physical properties of propane under corresponding operating conditions in the single-phase region and gas-liquid equilibrium region of the axial flow expander are obtained from the real gas equilibrium physical property database. This provides a unified thermodynamic basis for subsequent flow path design, blade design, three-dimensional CFD calculation, and humidity correction.

[0057] Step 2: Based on the thermophysical parameters obtained in Step 1, establish the flow model of the propane axial flow expander. The flow model in this embodiment includes the initial design of the meridional channel of the flow model, as well as information such as the distribution of enthalpy drop and velocity triangle of propane at each stage.

[0058] This embodiment uses a three-stage stationary blade and a three-stage moving blade structure as an example to establish a flow path model for a three-stage propane axial flow expander. The structure of the meridional channel of the initial flow path model is as follows: Figure 1 As shown, it is a three-stage axial flow structure with a rotational speed of 5000 rpm. This step will output the outlet flow angle of each stage of the stationary blades, the relative flow angle at the inlet of the moving blades, the target range of relative Mach number, and the geometric constraint boundaries.

[0059] Step 3: Select at least three design sections along the blade height direction for each stage of stationary blade and each stage of moving blade in the flow path model, define the section parameters of each design section, and generate the corresponding candidate airfoil.

[0060] This embodiment describes three design sections: sections at 10%, 50%, and 90% of the blade height; or sections at the blade root, blade median diameter, and blade tip. The corresponding section parameters include the pitch-chord ratio S / C, axial chord length Cx, trailing edge thickness ratio TE / S, throat opening ratio O / S, throat width, cross-sectional area, inlet angle, and outlet angle. Specific section parameters are shown in Table 1.

[0061] Table 1 Cross-sectional parameters

[0062]

[0063] In addition, the pitch chord length ratio S / C is approximately 0.4453 to 0.7730; the axial chord length Cx is approximately 0.0350 to 0.0500 m; the trailing edge thickness ratio TE / S is approximately 0.0100 to 0.0210; and the throat opening ratio O / S is approximately 0.3300 to 0.4300.

[0064] Step 4: Perform two-dimensional or quasi-three-dimensional blade cascade analysis on the candidate air profiles generated in Step 3, and iterate the candidate air profiles with the Mach number distribution on the blade cascade surface, blade cascade load and loss level as the objectives to obtain the cross-sectional air profile that meets the design requirements.

[0065] The goal of this step is to achieve a low-loss state for the peak Mach number location of the suction surface, the diffusion intensity of the pressure surface, and the mixing loss at the exit trailing edge, while meeting the cascade load requirements. The design criterion is "to obtain the desired surface Mach number distribution to meet the load (Zweifel number) and low-loss requirements"; the first-stage stator uses a thicker leading edge to improve the incident tolerance, and iteration continues under multiple operating conditions.

[0066] In this embodiment, the peak Mach number on the blade cascade surface is 0.9~1.2. The blade Mach number distribution at the 50% section of the design condition (i.e., the section at 50% of the blade height) is shown in the figure below. Figure 2 As shown in the figure, the blade Mach number does not show obvious vortex loss, the airflow field is uniform, and the flow conditions are relatively ideal.

[0067] In addition, this embodiment limits the load factor of the blade cascade load to 0.6~0.9. The airflow field corresponding to this load factor is uniform and the aerodynamic efficiency is high.

[0068] Step 5: Establish the CFD model of the propane axial flow expander, and solve the whole machine based on the cross-sectional airfoil obtained in Step 4 to obtain the aerodynamic calculation results of each stage of the flow model; the aerodynamic calculation results include the efficiency, mass flow rate, power, outlet swirl angle, inlet humidity, outlet humidity and average humidity of each stage of the flow model.

[0069] This embodiment establishes a multi-level three-dimensional CFD model ( Figure 3 As shown in the figure, a mixing plane is used between adjacent blade rows (stationary / moving blades); the preferred turbulence model is SST; the tip clearance applied to the rotor blade tips is 1.0 mm; the working fluid (i.e., propane) properties are obtained from the RGP equilibrium property table generated by REFPROP. Aerodynamic calculations are used to obtain the total pressure loss, power, total-total and total-static isentropic efficiency, Mach number and swirl angle at each stage, and inlet humidity, outlet humidity, and average humidity are extracted.

[0070] Step 6: Construct condensation risk criteria and determine whether each stage of the flow path model is in the condensation risk zone based on the aerodynamic calculation results. If so, proceed to step 7; otherwise, obtain the complete flow path structure of the propane axial flow expander. Figure 5 and Figure 6 (as shown), and then proceed to step 8.

[0071] This embodiment employs an engineering method combining low humidity condensation risk constraints and humidity correction to construct a condensation risk criterion. The expression for the condensation risk criterion is as follows:

[0072] ;

[0073] In the formula, For the first Local temperature margin of the channel relative to the saturation temperature; Indicates the first The current temperature of the stage channel; in this embodiment, a three-stage propane axial flow expander is used as an example, i.e., i=1,2,3; This indicates the condensation temperature of propane under static pressure.

[0074] when This indicates that there is an overheat margin and the current channel is not in the condensation risk zone;

[0075] when When this occurs, it indicates that the current channel is in a condensation risk zone.

[0076] Step 7: Set the low humidity threshold for each channel according to the design requirements, and determine whether the current humidity level of each channel is within the low humidity threshold range. If so, perform efficiency correction for the corresponding channel based on the balance properties to obtain the complete flow structure of the propane axial flow expander, and proceed to step 8. If not, it is not recommended to continue relying solely on fixed value correction, but instead adjust the first-stage blade load and inlet temperature to optimize the initial design parameters, and return to step 1.

[0077] The low humidity thresholds for each channel in this embodiment include the average humidity mass fraction threshold for each channel and the humidity mass fraction threshold for the outlet section of each channel; the average humidity mass fraction threshold for each channel is... , denoted as the average humidity quality fraction of the i-th channel.

[0078] The humidity mass fraction threshold at the outlet section of each channel is , Let be the humidity mass fraction at the outlet section of the i-th channel.

[0079] The above thresholds are engineering recommendations, based on low humidity levels from operating conditions and the understanding of increased losses in high humidity areas from humidity loss literature.

[0080] In this embodiment, the humidity distribution diagram corresponding to the 50% cross-section of the design condition (i.e., the cross-section where the blade is located at 50% of its height) is as follows: Figure 4 As shown in the figure, the relative humidity of the airflow at each high-pressure level is at a low level and has not yet reached saturation.

[0081] The correction formula used when performing efficiency correction is:

[0082] ;

[0083] In the formula, The efficiency after correction for the i-th level channel; The efficiency before correction of the i-th channel; The correction factor for humidity variation was obtained using the correlation obtained from the work of Starzmann, Miller and Petr. The Baumann rule can be further generalized to express the wet steam loss correction factor α.

[0084] This invention addresses multiple typical operating conditions by implementing installation angle or re-alignment angle scanning for the first-stage stator blades to balance the flow capacity and outlet swirl at the design point and in key variable operating conditions. In operating conditions A, B, C, and D, the first-stage stator blades employ re-alignment angles of -25°, +5.6°, 0°, and +8°, ​​respectively. A positive sign indicates a narrower throat, while a negative sign indicates a wider throat. This explicitly incorporates available stator blade adjustments under multiple operating conditions into the design, rather than simply providing a single static airfoil result, thereby improving design accuracy.

[0085] Step 8: Based on the complete flow structure of the propane axial flow expander, its inlet section, diffuser section, and exhaust section are designed as a single unit to minimize the total inlet pressure loss and maximize the outlet kinetic energy recovery. This results in a high-efficiency propane axial flow expander that meets the preset requirements.

[0086] This invention is based on the thermodynamic properties of real propane gas equilibrium, uses the flow distribution of at least three stages of axial flow as the framework, takes the high-parameter airfoil design of each blade cascade as the core, uses three-dimensional CFD and humidity correction as closed-loop verification, and uses the pressure recovery design of the inlet section, diffuser section and exhaust collection section as a supplement, and finally outputs a complete machine solution that meets the requirements of efficiency, humidity, strength and frequency margin.

[0087] Flow simulation calculations show that, under operating condition B, the total pressure loss factor in the intake section is... Approximately 0.71% Figure 7 (As shown), diffuser The static pressure recovery coefficient is approximately 0.712. Figure 8 As shown), the hydrostatic recovery coefficient at the collector flange can still reach approximately 0.62 (as shown). Figure 9 As shown in the figure, this method takes into account both the front and rear channels of the whole machine.

[0088] This invention provides a set of coupled design rules: a coupled design employing real gas equilibrium properties + low humidity criterion + variable α (i.e., correction factor) correction + first-stage stationary blade re-substitution + integrated intake and exhaust design. Firstly, it addresses the acquisition and use of propane real gas equilibrium properties; secondly, it establishes multi-segment axial flow distribution and parametric airfoil design across three cross-sections; thirdly, it establishes airfoil iteration rules based on surface Mach number distribution and cascade load requirements; fourthly, it establishes low humidity risk criteria and efficiency correction logic based on average humidity and outlet humidity; and fifthly, it integrates the re-alignment angle of the first-stage stationary blade with the recovery of intake and exhaust pressures.

[0089] The feasibility proof of this embodiment mainly comes from systematic engineering simulation. This design process covers flow design, 2D / Q3D (two-dimensional / quasi-three-dimensional) blade design, three-dimensional multi-level CFD, humidity correction, and flange-to-flange model verification.

[0090] First, the thermal and aerodynamic simulation chain is closed. In this embodiment, the propane equilibrium properties are provided by the RGP file generated by REFPROP property software. The three-dimensional CFD uses a multi-stage mixing plane and an SST turbulence model (shear stress transport turbulence model), and the tip clearance is designed to be 1.0 mm.

[0091] Secondly, the influence of humidity has been quantitatively incorporated. The difference between the non-equilibrium and equilibrium analyses in this embodiment is small, which provides direct evidence for the invention's positioning of "primarily based on equilibrium properties and secondarily based on humidity correction." Meanwhile, the average humidity before the rotor tail edge under the four operating conditions is approximately 0.0111%, 0.0170%, 0.0132%, and 0.0143%, respectively, and the humidity at the flange outlet under condition B is approximately 0.0253%. These values ​​generally fall within the range of "low humidity but not negligible."

[0092] Finally, the overall performance results were corrected to obtain the flange-to-flange total static isoentropic efficiency, where the efficiency under condition B is ≥86%.

[0093] In summary, this invention shifts the impact of humidity from the interpretation of results to a design constraint. Long-standing literature on wet steam demonstrates that humidity causes thermodynamic and kinetic relaxation losses. Traditional Baumann rules estimate efficiency degradation based on average humidity, while recent research has further made the loss coefficient (i.e., correction factor) α explicit and functional. This invention rewrites this path into an engineering criterion adapted to the low-humidity scenario of propane: as long as the low humidity range is maintained and a variable α correction is used, reliable design can be achieved without resorting to a complete nonequilibrium nucleation model.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A design method for a high-efficiency propane axial flow expander considering condensation risk constraints, characterized in that, Includes the following steps: Step 1: Based on the initial design parameter requirements of the propane axial flow expander, obtain the thermal properties of propane in the single-phase region and gas-liquid equilibrium region of the axial flow expander from the real gas equilibrium property database; Step 2: Based on the thermophysical parameters obtained in Step 1, establish the flow path model of the propane axial flow expander; Step 3: Select at least three design sections along the blade height direction for each stage of stationary blade and each stage of moving blade in the flow path model, define the section parameters of each design section, and generate the corresponding candidate airfoil. Step 4: Perform two-dimensional or quasi-three-dimensional blade cascade analysis on the candidate air profiles generated in Step 3, and iterate the candidate air profiles with the Mach number distribution on the blade cascade surface, blade cascade load and loss level as the objectives to obtain the cross-sectional air profile that meets the design requirements. Step 5: Establish a CFD model of the propane axial flow expander, and solve the whole machine based on the cross-sectional air profile obtained in Step 4 to obtain the aerodynamic calculation results of each stage of the flow model; the aerodynamic calculation results include the efficiency, mass flow rate, power, outlet swirl angle, inlet humidity, outlet humidity and average humidity of each stage of the flow model. Step 6: Construct condensation risk criteria and determine whether each level of the flow path model is in the condensation risk zone based on the aerodynamic calculation results. If yes, proceed to step 7; otherwise, obtain the complete flow path structure of the propane axial flow expander and proceed to step 8. Step 7: Set the low humidity threshold for each channel according to the design requirements, and determine whether the current humidity level of each channel is within the low humidity threshold range. If so, perform efficiency correction for the corresponding channel based on the equilibrium properties to obtain the complete flow structure of the propane axial flow expander, and execute Step 8; if not, adjust the first stage blade load and inlet temperature, and return to Step 1. Step 8: Based on the complete flow structure of the propane axial flow expander, its inlet section, diffuser section and exhaust section are designed in an integrated manner to obtain a high-efficiency propane axial flow expander that meets the preset requirements.

2. The design method for a high-efficiency propane axial flow expander considering condensation risk constraints according to claim 1, characterized in that: In step 1, the initial design parameters include the rotational speed, mass flow rate, target expansion ratio, target power, number of stages, and thermodynamic boundary parameters of the propane axial flow expander under the corresponding operating conditions; the thermodynamic boundary parameters include inlet volumetric flow rate, inlet mass flow rate, inlet pressure, inlet temperature, and outlet pressure. The thermophysical parameters include the density, enthalpy, entropy, specific heat, speed of sound, phase state, saturation parameters, and gas-liquid equilibrium parameters of propane.

3. The design method for a high-efficiency propane axial flow expander considering condensation risk constraints according to claim 1, characterized in that: In step 3, there are three design sections, namely the sections at the locations of 10%, 50%, and 90% of the blade height; or the sections at the blade root, blade median diameter, and blade tip. The cross-sectional parameters include pitch-to-chord ratio, axial chord length, trailing edge thickness ratio, throat opening ratio, throat width, cross-sectional area, inlet angle, and outlet angle.

4. The design method for a high-efficiency propane axial flow expander considering condensation risk constraints according to claim 1, characterized in that: In step 4, the peak value of the Mach number on the blade surface in the Mach number distribution is 0.9~1.2; The load factor of the cascade load is 0.6~0.

9.

5. The design method for a high-efficiency propane axial flow expander considering condensation risk constraints according to claim 1, characterized in that: In step 6, the expression for the condensation risk criterion is: ； In the formula, For the first Local temperature margin of the channel relative to the saturation temperature; Indicates the first The current temperature of the channel, 1≤i≤N, where N is the total number of channels, and 2≤N≤5; This indicates the condensation temperature of propane under static pressure. when When the current channel has a heat margin, it indicates that the channel is not in the condensation risk zone. when When this occurs, it indicates that the current channel is in a condensation risk zone.

6. The design method for a high-efficiency propane axial flow expander considering condensation risk constraints according to claim 5, characterized in that: In step 7, the low humidity threshold for each channel includes the average humidity mass fraction threshold for each channel and the humidity mass fraction threshold for the outlet section of each channel; The average humidity mass fraction threshold for each channel level is: , The average humidity mass fraction of the i-th channel; The humidity mass fraction threshold at the outlet cross-section of each channel level is: , Let be the humidity mass fraction at the outlet section of the i-th channel.

7. The design method for a high-efficiency propane axial flow expander considering condensation risk constraints according to claim 6, characterized in that: In step 7, the efficiency correction formula is as follows: ； In the formula, The efficiency after correction for the i-th level channel; The efficiency before correction of the i-th channel; This is a correction factor that varies with humidity.

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