Optimization Design Method of Adjustable Steam Ejector Nozzle and Steam Ejector Nozzle

Abstract

The present invention relates to an optimized design method for an adjustable steam ejector nozzle and the steam ejector nozzle, which determines the length of the converging section of the steam ejector nozzle, the inlet radius of the nozzle, the profile of the converging section of the nozzle, the profile of the diverging section of the nozzle, and the structure of the adjusting cone according to the throat radius of the nozzle. The profiles of both the converging section and the diverging section of the nozzle are composed of arc lines and straight lines. The radius of the arc line in the converging section is k times (4 ≤ k ≤ 8) of the throat radius of the nozzle, and its straight line is tangent to the arc line; the radius of the arc line in the diverging section is greater than or equal to 8 times the throat radius, and the slope of the straight line is the tangent value of γ , where γ is the maximum expansion angle of the nozzle calculated according to the Mach number at the nozzle outlet β minus 1°; the bottom radius of the adjusting cone is equal to the throat radius of the nozzle, and the half vertex angle α of the adjusting cone satisfies the relational expression α=‑ 2 k + 40. The adjustable steam ejector designed by this method has good adjustment stability, high adjustment accuracy, good flow field quality at the nozzle outlet, and high ejector efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of steam ejectors, and particularly relates to an optimized design method for an adjustable steam ejector nozzle, and a steam ejector nozzle obtained by the optimized design method. Background Art

[0002] A steam ejector is a fluid mechanical device that uses high-pressure steam to suck low-pressure steam, and has the advantages of simple structure, low operating cost, and remarkable energy-saving effect, and is widely used in the fields of water conservancy, petroleum, chemical industry, refrigeration, seawater desalination, etc. An adjustable ejector changes the equivalent throat area of the nozzle by axially moving the adjusting cone in the nozzle to achieve the purpose of adjusting the ejector flow rate.

[0003] Shock waves are likely to occur in the divergent section of the ejector converging-diverging nozzle. Moreover, due to the axial movement of the adjusting cone in the nozzle, the shock wave intensity in the divergent section of the nozzle is increased, resulting in an extremely uneven flow field at the nozzle outlet, large energy loss, and weakening of the ejector suction effect. Therefore, it is necessary to reasonably design the profile of the converging-diverging nozzle and the structure of the adjusting cone to improve the working efficiency of the ejector. At the same time, both the nozzle profile and the structure of the adjusting cone affect the flow field at the nozzle outlet, and they jointly determine the stability, adjustment accuracy, and sensitivity of the flow rate adjustment process. Therefore, coupling and optimizing the design of the nozzle profile and the structure of the adjusting cone is of great significance for improving the efficiency of the ejector and increasing the adjustment stability and adjustment accuracy of the adjustable ejector. At present, there is no research report on the coupling and optimized design of the nozzle profile and the structure of the adjusting cone of the adjustable ejector. Existing research mainly focuses on the overall structure design of the adjustable ejector, such as invention patents CN201610321926.X and CN201110027632.3, and does not involve the relevant content of the coupling and optimized design of the nozzle profile and the adjusting cone. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an optimized design method for an adjustable steam ejector nozzle and a steam ejector nozzle to achieve the purposes of good adjustment stability, high adjustment accuracy, and high adjustment efficiency.

[0005] To solve the above technical problems, according to one aspect of the present invention, an optimized design method for an adjustable steam ejector nozzle is provided, including the following steps:

[0006] Step 1, calculating and determining the throat radius of the nozzle R t ;

[0007] At a known inlet steam temperature T p 、pressure p p 、flow rate G p and isentropic efficiency ηn Under the condition, according to the conservation of mass, momentum and energy, combined with the physical properties of real fluids, calculate the nozzle throat radius R t ;

[0008] Step 2, determine the length of the converging section of the adjustable steam ejector nozzle according to the nozzle throat radius R t and the nozzle inlet radius l c 0; R 0;

[0009] Step 3, determine the profile of the converging section of the nozzle according to the nozzle throat radius R t The profile of the converging section of the nozzle consists of two parts: a tangent straight line and an arc line.

[0010] Step 4, determine the profile of the diverging section of the nozzle according to the nozzle throat radius R t The profile of the diverging section of the nozzle consists of two parts: an arc line and a straight line.

[0011] Step 5, determine the structure of the regulating cone according to the nozzle throat radius R t including the bottom radius R 2 and the half cone angle α .

[0012] Further preferably, in step 1, the steps of determining the nozzle throat radius R t include:

[0013] Step 1, from the inlet steam temperature of the nozzle T p and pressure p p the specific enthalpy h p and specific entropy s p of the working steam can be obtained;

[0014] (1)

[0015] Step 2, assume the throat pressure p t , according to the throat pressure p t and specific entropy s p obtain the ideal specific enthalpy h t,s and the throat sound speed a t,s ;

[0016] (2)

[0017] Step 3, calculate the specific enthalpy corresponding to the actual expansion state of the steam at the nozzle throat according to the following formula h t ;

[0018] (3)

[0019] Step 4, calculate the steam velocity at the nozzle throat according to the following formula v t ;

[0020] (4)

[0021] Step 5, compare v t and a t,s . If the accuracy requirement is met, the calculation ends; otherwise, let p t1 = p t + ∆ p t , and return to step (2) until a result that meets the accuracy requirement is obtained;

[0022] Step 6, calculate the nozzle throat radius v t and the flow rate G p : R t :

[0023] (5) 。

[0024] Further preferably, in step two, the nozzle inlet radius R 0 is 3 times the nozzle throat radius R t , that is R 0 = 3 R t ; the length of the nozzle converging section l c is 6 times the throat radius R t , that is l c = 6 R t .

[0025] Further preferably, in step three, the radius of the arc line of the nozzle converging section Rc is the throat radius R t of k times, that is R c = kR t, , where k takes values of 4 ≤ k ≤ 8.

[0026] Further preferably, in step four, the radius of the arc line of the nozzle divergent section R d ≥ 8 R t ; the slope of the straight line of the nozzle divergent section is the tangent value of γ , where γ is the maximum expansion angle of the nozzle calculated according to the Mach number at the nozzle outlet β minus 1°.

[0027] Further preferably, in step five, the radius of the bottom surface of the regulating cone R 2 is equal to the throat radius of the nozzle R t ; the half vertex angle of the regulating cone α=- 2 k + 40, k takes values of 4 ≤ k ≤ 8.

[0028] According to another aspect of the present invention, there is provided a steam ejector nozzle, the length of the convergent section of the steam ejector nozzle l c , the inlet radius of the nozzle R 0, the profile of the convergent section of the nozzle, the profile of the divergent section of the nozzle and the regulating cone structure are obtained by the above-mentioned optimization design method of the adjustable steam ejector nozzle.

[0029] According to another aspect of the present invention, there is provided a steam ejector, including the above-mentioned steam ejector nozzle.

[0030] Compared with the existing design method of the adjustable steam ejector nozzle, the present invention can weaken the shock wave intensity in the ejector nozzle by coupling and optimizing the design of the nozzle profile and the regulating cone structure, thereby enhancing the steam extraction capacity of the ejector; at the same time, the regulation stability, regulation accuracy and regulation sensitivity of the adjustable ejector are increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Attached Figure 1 is a schematic structural diagram of the ejector of the present invention;

[0032] Attached Figure 2 is a schematic structural diagram of the nozzle of the present invention;

[0033] AttachedFigure 3 is the radial Mach number distribution at the nozzle exit with different nozzle convergent section lengths adopted in the present invention;

[0034] Appendix Figure 4 is the radial Mach number distribution at the nozzle exit with different nozzle inlet radii adopted in the present invention;

[0035] Appendix Figure 5 is the radial Mach number distribution at the nozzle exit with different nozzle divergent section angles adopted in the present invention;

[0036] Appendix Figure 6 is the flow rate characteristic curve with different nozzle profiles adopted in the present invention;

[0037] Appendix Figure 7 is the axial Mach number distribution of the nozzle with different nozzle profiles adopted in the present invention;

[0038] Appendix Figure 8 (a) and (b) are the flow rate characteristic curves of the nozzle with different radii of the arc line in the nozzle convergent section adopted in the present invention;

[0039] Appendix Figure 1 In the figure: 1 nozzle, 2 regulating cone, 3 absorption chamber, 4 constant cross-section mixing section, 5 diffuser section;

[0040] Appendix Figure 2 In the figure: ab is the straight line of the convergent section, bc is the arc line of the convergent section, cd is the arc line of the divergent section, de is the straight line of the divergent section. Specific implementation mode

[0041] An optimization design method for an adjustable steam ejector nozzle provided by a typical implementation mode of the present invention includes the following steps.

[0042] Step 1, calculate and determine the nozzle throat radius R t ;

[0043] Under the conditions of known steam temperature T p , pressure p p , flow rate G p and isentropic efficiency η n at the nozzle inlet, calculate the nozzle throat radius R t according to the conservation of mass, momentum and energy, combined with the physical properties of real fluids.

[0044] The relatively specific steps to determine the nozzle throat radius R t are as follows:

[0045] Step 1, from the steam temperature Tp 、 Pressure p p The specific enthalpy of the working steam can be obtained h p and specific entropy s p ;

[0046] (1)

[0047] Step 2, assume the throat pressure p t , according to the throat pressure p t and specific entropy s p obtain the ideal specific enthalpy at the throat h t,s and the sonic velocity at the throat a t,s ;

[0048] (2)

[0049] Step 3, calculate the specific enthalpy corresponding to the actual expansion state of the steam at the nozzle throat from the following formula h t ;

[0050] (3)

[0051] Step 4, calculate the steam velocity at the nozzle throat from the following formula v t ;

[0052] (4)

[0053] Step 5, compare v t and a t,s , if the accuracy requirement is met, the calculation ends; otherwise, let p t1 = p t + ∆ p t , and return to step (2) until a result that meets the accuracy requirement is obtained;

[0054] Step 6, calculate the nozzle throat radius v t and flow rate G p : R t :

[0055] (5).

[0056] Step 2: Determine the length of the convergent section of the adjustable steam ejector nozzle R t and the radius of the nozzle inlet l c based on the throat radius of the nozzle R 0.

[0057] The length of the convergent section of the nozzle l c is designed to be 6 times the throat radius of the nozzle R t . Attached Figure 3 is the Mach number distribution at the nozzle exit when the length of the convergent section of the nozzle l c takes 3 R t , 4.5 R t , 6 R t respectively. It can be seen from Figure 3 that when the length of the convergent section of the nozzle l c = 6 R t , the Mach number distribution along the radius at the nozzle exit is relatively uniform, that is, the flow field quality at the nozzle exit is relatively high.

[0058] The radius of the nozzle inlet R 0 is designed to be 3 times the throat radius of the nozzle R t . Attached Figure 4 is the Mach number distribution at the nozzle exit when the radius of the nozzle inlet R 0 takes 2 R t , 3 R t , 4 R t respectively. It can be seen that when the radius of the nozzle inlet R 0 = 3 R t , the Mach number distribution along the radius at the nozzle exit is relatively uniform, that is, the flow field quality at the nozzle exit is relatively high.

[0059] Step 3: Determine the profile of the convergent section of the nozzle according to the throat radius of the nozzle R t The profile of the convergent section of the nozzle consists of two parts: a tangent straight line ab and an arc line bc. As Figure 2 shown, the radius of the arc line is R c , and it is designed to be k times the throat radius of the nozzle, that isR c = kR t , the coefficient k takes values of 4 ≤ k ≤ 8. k Within this range, the nozzle flow rate characteristic curve has a parabola characteristic with relatively sensitive regulation, as Figure 8 shown.

[0060] Step four, determine the diverging section profile of the nozzle according to the nozzle throat radius R t ;

[0061] The diverging section profile of the nozzle consists of two parts: an arc line cd and a straight line de (as Figure 2 shown), the radius of the arc line cd is R d , R d ≥ 8 R t , the inclination angle γ of the straight line de in the diverging section satisfies the relational expression γ = β - 1°, where β is the maximum expansion angle of the nozzle calculated according to the nozzle exit Mach number. Due to the existence of the regulating cone, the shock wave in the diverging section of the nozzle is relatively strong, so the angle of the diverging section is 1° smaller than the maximum expansion angle to weaken the shock wave in the diverging section. When there is no regulating cone in the nozzle, the angle γ of the diverging section of the nozzle is the maximum expansion angle β, and the shock wave in the diverging section can be eliminated. As Figure 5 shown, when the calculated maximum expansion angle β is 4°, and the angle γ of the diverging section of the nozzle with a regulating cone is 3°, the flow field at the nozzle exit is relatively uniform.

[0062] The comparison of the flow rate characteristic curves between the arc line - straight line nozzle described in the present invention and the conventional straight line nozzle can be seen in Figure 6 , during the process of the regulating cone of the arc line - straight line nozzle moving from -0.5 mm to 2.6 mm, the flow rate decreases from the maximum value to the minimum value, the flow rate characteristic curve shows a parabola change trend, the flow rate change is smaller when the flow rate is small, and the flow rate change is larger when the flow rate is large; the regulation law of the flow rate characteristic curve of the nozzle with a straight converging section is not obvious, and the regulation stability is poor.

[0063] The variation law of the axial Mach number of the straight line nozzle and the optimized arc line - straight line nozzle is as Figure 7 shown. Compared with the straight line nozzle, after optimization, there is no obvious sudden rise and sudden drop in the axial velocity inside the nozzle, the shock wave inside the nozzle is weaker, the flow field at the nozzle exit is uniform, the flow field quality is higher, and the ejector efficiency is high.

[0064] Step five, according to the nozzle throat radius Rt Determine the structure of the adjusting cone, including the bottom radius R 2 and the half vertex angle of the cone α .

[0065] The bottom radius of the adjusting cone R 2 is equal to the throat radius of the nozzle R t ; The half vertex angle of the cone α satisfies the relationship α=- 2 k +40, and the coefficient k takes values of 4 ≤ k ≤ 8; The position of the nozzle throat is the coordinate origin O. The displacement of the adjusting cone towards the nozzle inlet is negative, and the flow rate increases. The displacement of the adjusting cone towards the nozzle outlet is positive, and the flow rate decreases. The attached instructions of the present invention Figure 8 (a) and (b) show that when k = 6, the change of the flow rate with the displacement of the adjusting cone satisfies the parabolic change trend, and the change rate of the flow rate is approximately a straight line. At this time, the flow rate adjustment is relatively stable, and the adjustment accuracy and sensitivity are high; When k does not satisfy the above relationship ，k = 2 or k = 10, the flow rate characteristic curve does not satisfy the parabolic change trend.

[0066] The coupling optimization design method of the ejector nozzle profile and the adjusting cone structure of the present invention enables the flow rate characteristic curve to satisfy the parabolic flow rate characteristic, with a smaller change in the flow rate when the flow rate is small and a larger change in the flow rate when the flow rate is large, ensuring the stability, accuracy and sensitivity of the adjustment.

[0067] Next, taking a relatively specific embodiment as an example, the technical solution claimed in the present invention will be further clearly and completely described.

[0068] Refer to Figure 1 , An adjustable steam ejector described in this embodiment includes a nozzle 1, an adjusting cone 2, an absorption chamber 3, an equal cross-section mixing section 4 and a diffuser section 5; The absorption chamber 3, the equal cross-section mixing section 4 and the diffuser section 5 are arranged in sequence along the fluid flow direction. The nozzle 2 is arranged inside the absorption chamber 3. The nozzle 2, the equal cross-section mixing section 4 and the diffuser section 5 are all coaxially arranged, and the adjusting cone 2 is arranged on the central axis of the middle part of the nozzle 2. A drainage fluid channel is formed between the outer surface of the pipe wall of the nozzle 2 and the inner cavity wall of the absorption chamber 3, and a working fluid channel is formed between the inner surface of the pipe wall of the nozzle 2 and the adjusting cone 2.

[0069] The pipe wall of the nozzle 2 includes a straight section at the front end and a tapered section and a divergent section at the rear end. As Figure 2 shown, the profile of the tapered section of the nozzle consists of two parts: a tangent straight line ab and an arc line bc; The profile of the divergent section of the nozzle consists of two parts: an arc line cd and a straight line de.

[0070] Ejector working steam inlet temperature T p =500℃, injection fluid inlet temperature t s =300℃, working steam flow G P =0.2t / h, working steam pressure p p and the ejection steam pressure p s The ratio is γ = 4.4.

[0071] Based on the above parameters, according to the conservation of mass, momentum and energy, combined with the real fluid properties, the nozzle throat radius is calculated using formulas (1) to (5): R t =1.20mm.

[0072] According to the nozzle throat radius R t = Determine the nozzle converging section entrance radius R 0 and length l c , radius of the arc line of the nozzle's tapering section R c , radius of the arc line of the nozzle expansion section R d , adjust the radius of the cone bottom R 2 and cone half apex angle α。 Nozzle inlet radius R 0 is the nozzle throat radius R t 3 times of R 0=3 R t ; Length of nozzle tapering section l c is the throat radius R t 6 times of l c =6 R t . Radius of the arc line of the nozzle's tapering section R c is the throat radius R t of k times, that is R c = kR t, ,in k The value is 4≤ k ≤8. Radius of the arc line of the nozzle expansion section R d ≥8 Rt ; The linear slope of the nozzle divergent section is γ the tangent value of, where γ is the maximum expansion angle of the nozzle calculated according to the Mach number at the nozzle exit β minus 1°. The bottom radius of the adjustment cone R 2 is equal to the throat radius of the nozzle R t ; The half vertex angle of the adjustment cone α=- 2 k +40, k takes values of 4 ≤ k ≤ 8.

[0073] According to the above coupling optimization design method, the simulated and calculated nozzle structure parameters and adjustment cone structure parameters are: the throat radius of the nozzle R t = 1.20 mm; the inlet radius of the nozzle R 0 = 3 R t = 3.60 mm, the length of the convergent section l c = 6 R t = 7.20 mm; k = 8, the radius of the arc line of the convergent section R c = 8 R t = 9.60 mm, the radius of the arc line of the divergent section R d = 8 R t = 9.60 mm. From the Mach number Ma = 1.63 at the nozzle exit, the maximum expansion angle β = 4°, the angle between the straight line section of the divergent section and the horizontal direction γ = β- 1° = 3°; the bottom radius of the adjustment cone R 2 = R t = 1.20 mm, the half vertex angle of the cone α=- 2 k +40 = 24°.

[0074] The comparison of the flow rate characteristic curves of the straight nozzle and the optimized arc line - straight nozzle of this embodiment is shown in Figure 5, during the process that the nozzle regulating cone after optimization moves from -0.5 mm to 2.6 mm, the flow rate decreases from the maximum value to the minimum value, and the flow rate characteristic curve shows a parabolic change trend. When the flow rate is small, the change in the flow rate is small, and when the flow rate is large, the change in the flow rate is large; the flow rate characteristic curve of the converging section being a straight line has an unclear regulation law and poor regulation stability. The variation law of the axial Mach number of the straight nozzle and the optimized arc-line - straight nozzle is as Figure 6 shown. Compared with the straight nozzle, there is no obvious sudden increase or decrease in the axial velocity inside the nozzle after optimization. The shock wave inside the nozzle is weak, the flow field at the nozzle outlet is uniform, the flow field quality is high, and the ejector efficiency is high.

Claims

1. An optimized design method for an adjustable steam ejector nozzle, characterized in that, comprising the following steps: Step 1, calculate and determine the nozzle throat radius R t ; At the known inlet steam temperature of the working nozzle T p , pressure p p , flow rate G p and isentropic efficiency η n , calculate the throat radius of the nozzle according to the conservation of mass, momentum and energy, combined with the physical properties of real fluids R t ; Determine the nozzle throat radius R t The steps include: Step 1, from the steam temperature at the nozzle inlet T p , pressure p p , the specific enthalpy of the working steam can be obtained h p and specific entropy s p ; （1） Step 2, assume the throat pressure p t , according to the throat pressure p t and the specific entropy s p , look up the ideal specific enthalpy at the throat h t,s and the speed of sound at the throat a t,s ; （2） Step 3, calculate the specific enthalpy corresponding to the actual expansion state of the steam at the nozzle throat according to the following formula h t ; （3） Step 4, calculate the steam velocity at the nozzle throat using the following formula v t ; （4） Step 5, compare v t and a t,s . If the accuracy requirement is met, the calculation ends; otherwise, let p t1 = p t + Δ p t , and go back to Step 2 until a result that meets the accuracy requirement is obtained; Step 6, from the throat velocity v t and the flow rate G p calculate the nozzle throat radius R t ; （5）； Step 2: Determine the length of the converging section of the nozzle of the adjustable steam ejector R t and the radius of the nozzle inlet l c according to the throat radius of the nozzle R 0; Nozzle inlet radius R 0 is the nozzle throat radius R t 3 times that of, i.e., R 0 = 3 R t ; Nozzle converging section length l c is the throat radius R t 6 times that of, i.e., l c = 6 R t ; Step 3: Determine the nozzle converging section profile according to the nozzle throat radius R t The nozzle converging section profile consists of two parts: a tangent straight line and an arc line Radius of the arc line of the nozzle converging section R c is the throat radius R t of k times, that is R c = kR t, where k takes a value of 4 ≤ k ≤ 8; Step 4: Determine the contour line of the nozzle divergent section according to the nozzle throat radius. R t The contour line of the nozzle divergent section consists of two parts: an arc line and a straight line. Radius of the arc line of the nozzle divergent section R d ≥8 R t ; The slope of the straight line of the nozzle divergent section is γ the tangent value of, where γ is the maximum expansion angle of the nozzle calculated according to the Mach number at the nozzle exit β minus 1°; Step 5, according to the nozzle throat radius R t determine the regulating cone structure, including the bottom radius R 2 and the half-cone angle α ; Radius of the bottom surface of the adjusting cone R 2 is equal to the radius of the nozzle throat R t Equal; half apex angle of the adjusting cone α=- 2 k +40 k The value range is 4 ≤ k ≤ 8 2. A steam ejector nozzle, characterized in that: The length of the converging section of its steam ejector nozzle l c , the inlet radius of the nozzle R 0, the profile of the converging section of the nozzle, the profile of the diverging section of the nozzle, and the structure of the regulating cone are obtained by the optimization design method of the adjustable steam ejector nozzle described in claim 1.

3. A steam ejector, characterized in that: comprising the steam ejector nozzle according to claim 2.

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