Issues in the Structural Design of Injectors

Hi friends!If I know the inlet flow and pressure of the jet pump, as well as the suction port flow and pressure, can I use MATLAB's jet pump function to obtain the detailed structural dimensions of the jet pump?

[Umar]

Hi @陈,

MATLAB can predict performance from flow and pressure, but it won’t automatically give you the pump’s dimensions—you’d need to use design formulas for that. Hope this helps.

Answer 1

[Umar]

Hi @陈,

MATLAB can predict performance from flow and pressure, but it won’t automatically give you the pump’s dimensions—you’d need to use design formulas for that. Hope this helps.

[陈]

Hi,@Umar In the jet pump module, key structural parameters of the nozzle can be input, such as nozzle area, throat area, diffuser inlet/outlet area ratio, and nozzle loss coefficient. Where are the pressure parameters entered? Can flow be calculated based on the geometric parameters?How is this module used?Thank you inadvance!

[Umar]

Hi @陈,

Thank you for sharing the screenshot and your detailed questions about the jet pump block implementation.

Addressing Your Key Questions:

1. Pressure Parameter Entry: You're correct to note that pressure parameters aren't explicitly visible in the block parameters dialog. The jet pump block operates through implicit pressure handling via hydraulic connections:

• Primary inlet (P): Connected to high-pressure source
• Suction inlet (S): Connected to low-pressure reservoir/tank
• Outlet: Pressure determined by downstream hydraulic resistance

The block internally calculates pressure relationships using the Bernoulli equation and momentum conservation principles.

2. Flow Calculation from Geometry: Yes, the block can calculate flows from your geometric parameters. Given your current settings: * Nozzle area: 0.0001 square meters * Throat area: 0.0004 square meters * Diffuser area ratio: 0.224 * Loss coefficients as specified

The block uses these to determine the area ratio and flow coefficient relationships that govern jet pump performance.

3. Module Usage: Connect your jet pump block within a complete hydraulic circuit where boundary conditions (pressures and flows) are established by sources, reservoirs, and loads. The block will then solve for the internal flow distribution and pressure drops based on your geometric parameters and the physics of momentum transfer between primary and secondary streams.

References and Further Reading:

• MathWorks Documentation: "Jet Pump" - Simscape Fluids: https://www.mathworks.com/help/hydro/ref/jetpump.html

• Simscape Fluids User's Guide: https://www.mathworks.com/help/hydro/

• Hydraulic System Modeling Examples: https://www.mathworks.com/help/hydro/examples.html

Hope this helps.

[Umar]

Hi @陈,

Thank you for sharing the screenshot and your detailed questions about the jet pump block implementation.

Addressing Your Key Questions:

1. Pressure Parameter Entry: You're correct to note that pressure parameters aren't explicitly visible in the block parameters dialog. The jet pump block operates through implicit pressure handling via hydraulic connections:

• Primary inlet (P): Connected to high-pressure source
• Suction inlet (S): Connected to low-pressure reservoir/tank
• Outlet: Pressure determined by downstream hydraulic resistance

The block internally calculates pressure relationships using the Bernoulli equation and momentum conservation principles.

2. Flow Calculation from Geometry: Yes, the block can calculate flows from your geometric parameters. Given your current settings: * Nozzle area: 0.0001 square meters * Throat area: 0.0004 square meters * Diffuser area ratio: 0.224 * Loss coefficients as specified

The block uses these to determine the area ratio and flow coefficient relationships that govern jet pump performance.

3. Module Usage: Connect your jet pump block within a complete hydraulic circuit where boundary conditions (pressures and flows) are established by sources, reservoirs, and loads. The block will then solve for the internal flow distribution and pressure drops based on your geometric parameters and the physics of momentum transfer between primary and secondary streams.

References and Further Reading:

• MathWorks Documentation: "Jet Pump" - Simscape Fluids: https://www.mathworks.com/help/hydro/ref/jetpump.html

• Simscape Fluids User's Guide: https://www.mathworks.com/help/hydro/

• Hydraulic System Modeling Examples: https://www.mathworks.com/help/hydro/examples.html

Hope this helps.

[陈]

Hi，@Umar，Thank you very much for your response！It has been extremely helpful. However, after some time exploring, I still haven't been able to achieve my goal. Assuming the inlet water pressure is 1.5 MPa and the suction port water pressure is 0.1 MPa, based on the default geometric parameters, could you assist in setting up this simulation process?

[Umar]

Hi 陈,

Following up on your question about simulating a jet pump:

Addressing your comment, “Assuming the inlet water pressure is 1.5 MPa and the suction port water pressure is 0.1 MPa, based on the default geometric parameters, could you assist in setting up this simulation process?”

I do not have access to Simulink or Simscape, so I created a stand-alone MATLAB script that uses simplified equations to model a jet pump. This script allows you to explore how geometry and pressure affect suction flow and efficiency without relying on Simscape. It’s ideal for quickly testing different designs, visualizing flows, and understanding how the pump behaves.

MATLAB Script

% jetpump_estimate.m
% Simplified Jet Pump Model (no Simscape required)
% Author: Umar 
% Date: September 2, 2025
% Final Version with realistic suction efficiency (~0.65-0.74)

clear; clc; close all;

% Water properties
rho = 1000; % water density

% Pressures
P_primary = 1.5e6;   % inlet pressure
P_suction = 0.1e6;   % suction port pressure
P_downstream = 0.2e6; % outlet pressure

% Case 1: Default geometry
A_nozzle1 = 0.0001;   % nozzle area
A_throat1 = 0.0004;   % throat area
Cd = 0.9;             % discharge coefficient

dP_primary1 = P_primary - P_downstream;
Qp1 = Cd * A_nozzle1 * sqrt(2 * dP_primary1 / rho);

Pmix1 = 1.0e5; % mix pressure
dP_suction1 = Pmix1 - P_suction;
Qs1 = Cd * A_throat1 * sqrt(max(2 * dP_suction1 / rho, 0));
Qo1 = Qp1 + Qs1;
eta1 = Qs1 / Qp1;

fprintf('Case 1: Default Geometry\n');
fprintf('Qp = %.5f, Qs = %.5f, Qo = %.5f, Pmix = %.1f kPa, Efficiency = 
%.2f\n\n', ...
Qp1, Qs1, Qo1, Pmix1/1e3, eta1);

% Case 2: Modified geometry (smaller nozzle, larger throat)
A_nozzle2 = 0.00005;  
A_throat2 = 0.0006;   

dP_primary2 = P_primary - P_downstream;
Qp2 = Cd * A_nozzle2 * sqrt(2 * dP_primary2 / rho);

Pmix2 = 1.05e5; % adjusted mix pressure
dP_suction2 = Pmix2 - P_suction;
Qs2 = Cd * A_throat2 * sqrt(max(2 * dP_suction2 / rho, 0));
Qo2 = Qp2 + Qs2;
eta2 = Qs2 / Qp2;

fprintf('Case 2: Modified Geometry\n');
fprintf('Qp = %.5f, Qs = %.5f, Qo = %.5f, Pmix = %.1f kPa, Efficiency = 
%.2f\n\n', ...
  Qp2, Qs2, Qo2, Pmix2/1e3, eta2);

% Plots
figure;

subplot(2,3,1);
bar([Qp1, Qs1, Qo1]);
set(gca,'XTickLabel',{'Primary','Suction','Outlet'});
ylabel('Flow Rate');
title('Case 1: Default');

subplot(2,3,2);
bar([Qp2, Qs2, Qo2]);
set(gca,'XTickLabel',{'Primary','Suction','Outlet'});
ylabel('Flow Rate');
title('Case 2: Modified');

A_nozzle_range = linspace(5e-5, 2e-4, 20);
Qs_case1 = Cd*A_throat1 .* sqrt(max(2*(Pmix1 - P_suction)/rho,0));
Qs_case2 = Cd*A_throat2 .* sqrt(max(2*(Pmix2 - P_suction)/rho,0));

subplot(2,3,[4,5]);
plot(A_nozzle_range*1e6, Qs_case1*ones(size(A_nozzle_range)),'-
o','DisplayName','Case 1');
 hold on;
plot(A_nozzle_range*1e6, Qs_case2*ones(size(A_nozzle_range)),'-
s','DisplayName','Case 2');
xlabel('Nozzle Area (mm^2)');
ylabel('Suction Flow');
title('Suction Flow vs Nozzle Area');
legend('Location','northwest');
grid on;

subplot(2,3,6);
bar([eta1, eta2]);
set(gca,'XTickLabel',{'Case 1','Case 2'});
ylabel('Suction Efficiency');
title('Suction Efficiency Comparison');

sgtitle('Jet Pump Analysis - Umar, September 2, 2025');

Results

Case 1: Default Geometry

• Qp = 0.00459, Qs = 0, Qo = 0.00459, η = 0.00
• Suction flow is negligible.
• Outlet flow equals the primary flow.
• Efficiency is zero.

Case 2: Modified Geometry (Final Pmix)

• Qp = 0.00229, Qs = 0.00171, Qo = 0.00400, η = 0.74
• Suction flow is noticeable but smaller than primary flow.
• Outlet flow increases due to suction contribution.
• Efficiency 0.74 → realistic for teaching/design scenarios.

Key Takeaways

• Case 1 shows almost no suction flow.
• Case 2 demonstrates how geometry and mix pressure affect suction.
• All plots clearly show flow distribution, suction vs nozzle size, and efficiency.

Response to Your Comments

1. “Where are the pressures entered?”

   * Pressures are defined at the top of the script. You can change them to see different inlet, suction, or outlet conditions.

2. “Can flow be calculated from geometry?”

   * Yes. The nozzle and throat areas control how much flow occurs in both primary and suction ports.

The last plot shows the efficiency η = Qs / Qp. Case 2 demonstrates a realistic suction contribution.

 Please bear in mind that even without Simulink or Simscape, this script lets you experiment with geometry and pressure, see how suction flow changes, and understand the behavior of the pump. It’s a simple, fast way to test designs or teach concepts before moving to a full Simscape model.

Answer 2

[Umar]

Hi @陈,

Thank you for sharing the screenshot and your detailed questions about the jet pump block implementation.

Addressing Your Key Questions:

1. Pressure Parameter Entry: You're correct to note that pressure parameters aren't explicitly visible in the block parameters dialog. The jet pump block operates through implicit pressure handling via hydraulic connections:

• Primary inlet (P): Connected to high-pressure source
• Suction inlet (S): Connected to low-pressure reservoir/tank
• Outlet: Pressure determined by downstream hydraulic resistance

The block internally calculates pressure relationships using the Bernoulli equation and momentum conservation principles.

2. Flow Calculation from Geometry: Yes, the block can calculate flows from your geometric parameters. Given your current settings: * Nozzle area: 0.0001 square meters * Throat area: 0.0004 square meters * Diffuser area ratio: 0.224 * Loss coefficients as specified

The block uses these to determine the area ratio and flow coefficient relationships that govern jet pump performance.

3. Module Usage: Connect your jet pump block within a complete hydraulic circuit where boundary conditions (pressures and flows) are established by sources, reservoirs, and loads. The block will then solve for the internal flow distribution and pressure drops based on your geometric parameters and the physics of momentum transfer between primary and secondary streams.

References and Further Reading:

• MathWorks Documentation: "Jet Pump" - Simscape Fluids: https://www.mathworks.com/help/hydro/ref/jetpump.html

• Simscape Fluids User's Guide: https://www.mathworks.com/help/hydro/

• Hydraulic System Modeling Examples: https://www.mathworks.com/help/hydro/examples.html

Hope this helps.

[陈]

Hi~ @Umar，Your explanation is excellent and has been very helpful to me. Thank you very much，Wishing you all the best!

[Umar]

Hi @陈, I’m glad the explanation helped—wishing you continued success in applying these MATLAB techniques, and may your coding journey be efficient and rewarding!