Overview of the ESPET Tools

The Electrospray Engineering Toolkit (ESPET) is a database and collection of tools to support the design of electrospray arrays from propellant reservoir to plume properties. The database contains propellant, substrate and interfacial properties, and is accessed by several web-based utilities. The primary utility is the QuickSolver, which performs performance calculations on simple three-component systems consisting of a reservoir, a propellant feed system, and an emitter (single or array). Tolerances can be affixed to most design properties, thus allowing non-uniformity of arrays to be simulated through a Monte Carlo approach. The Quicksolver is entirely modular, making it quick and easy to introduce new models, plotting key properties as functions of extraction voltage, temperature or reservoir pressure.

Other utilities include the Domain Modeler, Propellant Visualization Utility and Component Export tools. An illustration of how these utilities might fit into a design workflow is shown below. Click on the circles to access the content.

State Diagram

ESPET is especially powerful when coupled with SPICE-based electrical circuit design software, which can solve complex microfluidic circuits through the analogy between Ohm's law and the Hagen-Poiseuille law. ESPET generates components that can be imported into the freely-available electrical circuit simulator, but it is also useful for users who prefer to work solely within the web interface to evaluate single components, such as the output current and onset voltage of a single emitter. ESPET is verbose and provides physics background and references. The ESPET architecture is designed in a way that database growth and new physics models are very straightforward to implement. Do not hesitate to contact us if you have new models or propellant properties that you would like us to incorporate into ESPET and share with the electrospray propulsion development community. Our goal is to grow the ESPET capabilities through user input. SSI is also available for the development and support of custom or proprietary versions.

GETTING ACCESS TO ESPET: For access to the ESPET utilities, contact us through the link: http://www.spectral.com/contact-us-about-espet/. Fill out the email form, and state that you request a username and password for access. Your message also must include reasons for your need to use ESPET, and your affiliation.

0. QuickSolver

The QuickSolver is a tool for simple 3-component networks consisting of a reservoir, a single feed conduit, and an emitter. Configure your emitter and feed system, then plot key results as a function of reservoir pressure, extractor voltage or temperature. The user chooses the independent variable to scan over a specified range. New emitter and feed models can readily be added – it is as simple as dropping a file into a directory. The QuickSolver code is essentially a framework tool, making it easy to test new designs with the database queries, user interface, and matrix operations all happening in the background. SSI recommends first using the QuickSolver framework to learn the workings of ESPET and for testing initial designs. Contact us if you have new emitter models or propellant/substrate data so that we can integrate them for you.

1. Domain Modeler

Choose your microfluidic domain, propellant and substrate. Change the geometry and material properties to suit your design. Or, leave the default values as read from the database. View temperature-dependent properties and compute emitter performance parameters including thrust, Isp and onset voltage. When the desired result is achieved, press the Save button to store your configuration for later download as part of a library of SPICE components.

2. Propellant Visualization Utility

Search the database for propellants that meet your specific search criteria. Search by mobility, solvation energy, molar mass and more. Graph temperature-dependent properties, including surface tension, conductivity and electrical permittivity. View descriptions, annotations and literature citations for the properties in the metadata display window. Export the chart data to a comma-separated-value spreadsheet.

3. Component Selector/Downloader

Review and manage your stored configurations and select the ones to be downloaded. Press the Export button to download a directory of SPICE component files, which can be read by SPICE software such as the freely available LTSPICE. SPICE is an electric circuit simulator that we use by exploiting the Hagen-Poiseuille – Ohm’s Law analogy.

4. Network Solution (SPICE Download or Online Quick Solver)

Import your microfluidic components into your circuit simulator (e.g. LTSPICE). Electrical current in your simulated circuit will be analogous to volumetric fluid flow. Electrical potential will be analogous to a pressure differential. Use simulation features such as graphing and tolerance analysis to characterize your microfluidic electrospray network. View more advanced diagnostic information including thrust, Isp and mass flow by using the labeled nodes available on your ESPET Taylor Cone components. For beginners, we suggest the walkthrough tutorial. Alternatively, complete the analysis online (no downloads required) using the QuickSolver.