1) To simulate the mass flow rate of the analyte and ensure uniform pressure distribution on the working electrode surface, you can set up the simulation in fluent by defining the flow cell as the domain and the electrode surface as the boundary. You can use the "inlet" and "outlet" boundary conditions to specify the flow rate and pressure at the inlet and outlet of the flow cell. 

2) You have to define the properties of the analyte such as density, viscosity, and mass flow rate. These properties will be used to simulate the flow of the analyte through the tube.

3)  Make sure to refine the mesh near the electrode surface to ensure accurate results.

4) To obtain the uniform pressure distribution, please run the simulation and monitor the pressure distribution on the electrode surface. Analyze the results of the simulation to ensure that there is uniform pressure distribution on the working electrode surface. If there are any areas of non-uniform pressure, you may need to adjust the design of the flow cell or electrode to improve the performance of the measurement system.

Hope you find it useful.

Thank you.