Refprop 91 Patched Free -

A single-user license for the latest version of REFPROP is sold directly through the NIST store. For a typical user, the cost is several hundred dollars. For example, an upgrade to the latest version (e.g., from version 9.x to version 10.x) is priced around $125.00. For institutions, the costs scale significantly. A license for 25 users, for instance, costs approximately $7,300, and large site licenses can exceed $19,000. These fees reflect the immense investment in research, development, and data validation that goes into maintaining such a high-accuracy database.

No. NIST REFPROP has never been freeware. A single-user license for REFPROP 9.1 was ~$325 (later versions are $375+). However:

Searching for "REFPROP 9.1 free download" may point to third-party "software informer" sites or trial versions. Use caution with these sources: Security Risk refprop 91 free

If you’ve ever worked in chemical engineering or HVAC design, you’ve likely encountered (Reference Fluid Properties). Developed by the National Institute of Standards and Technology (NIST), it is the gold standard for calculating the thermophysical properties of fluids.

The search for —NIST’s industry-standard Reference Fluid Thermodynamic and Transport Properties database—is common among engineering students, researchers, and HVAC professionals. However, because this is a proprietary software developed by the National Institute of Standards and Technology (NIST), finding a "free" version comes with significant caveats. A single-user license for the latest version of

A commercial license for the full version of REFPROP costs $325.00 for a single-user license. Upgrades from version 9.x to version 10.x cost $125.00. Additionally, the single-user license is intended for the individual purchaser and can be installed on all their personal computers, as NIST prioritizes proper use over policing multiple installations. For organizations, site licenses and distributor agreements are available for integration into other software products.

Released by NIST to accurately calculate fluid behavior across liquid, gas, and supercritical phases, REFPROP 9.1 relies on highly precise, mathematically intensive Helmholtz energy equations of state. mini-REFPROP - Version 10.0 For institutions, the costs scale significantly

You can then calculate properties, such as the enthalpy of R134a at a specific temperature and pressure, with a simple script:

However, I can offer a about REFPROP 9.1, its capabilities, and how to access it legally — including free/low-cost options if they exist.

For many engineers, REFPROP 9.1 was the reliable workhorse of the early 2010s. It provided critical data for refrigerants, hydrocarbons, and cryogens. Its accuracy made it the gold standard against which other commercial simulators, such as Aspen HYSYS or COOLPROP, were often validated. The specific demand for version 9.1, even years after its successor was released, stems from its stability and the familiarity long-time users have with its specific input/output structures. However, it is crucial to acknowledge its limitations; version 9.1 lacks the expanded fluid lists and modern interface features of the current version (version 10 and beyond), and it may not include the most recent refrigerant blends required for modern environmental compliance.