# Dimensionless Numbers

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- **Type:** Skill
- **Install:** `agentstack add skill-jskherman-engg-skills-dimensionless-numbers`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [jskherman](https://agentstack.voostack.com/s/jskherman)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** Apache-2.0
- **Upstream author:** [jskherman](https://github.com/jskherman)
- **Source:** https://github.com/jskherman/engg-skills/tree/main/skills/dimensionless-numbers

## Install

```sh
agentstack add skill-jskherman-engg-skills-dimensionless-numbers
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Dimensionless Numbers

## Overview

Calculates the standard engineering dimensionless numbers from SI inputs:

- Flow: Re, Fr, We, Eu.
- Heat transfer: Pr, Nu (Dittus-Boelter screening), Gr, Ra, Bi, Fo, Pe.
- Mass transfer: Sc, Sh (via analogy if requested).

Validity-range warnings (e.g. Dittus-Boelter for Re >= 10000) are appended
when the inputs fall outside common citations.

## Prerequisites

1. `uv` available.

## When to Use

- A correlation needs a Reynolds, Prandtl, or Grashof number.
- A regime check (laminar vs turbulent, natural vs forced convection) is
  needed before picking a correlation.
- Scale-up analysis where matching a dimensionless group is the design
  criterion.

## Don't use for

- Picking the convective heat transfer coefficient (use
  `convective-heat-transfer-correlations`).
- Multi-phase regime classification (use `two-phase-flow`).
- The Reynolds analogy for combined heat / momentum transfer — that is a
  specific correlation, not a single number.

## Utility Scripts

- `uv run scripts/calculate_dimensionless.py reynolds --density 1000 --velocity 1.5 --length 0.05 --viscosity 0.001 --output /tmp/re.json`
- `uv run scripts/calculate_dimensionless.py prandtl --cp 4180 --viscosity 0.001 --thermal-conductivity 0.6 --output /tmp/pr.json`
- `uv run scripts/calculate_dimensionless.py nusselt-dittus-boelter --reynolds 50000 --prandtl 4 --output /tmp/nu.json`

## Procedure

1. Get fluid properties at the relevant film / bulk temperature.
2. Identify the geometric length scale (pipe diameter, plate length,
   particle diameter) — the right one depends on the correlation.
3. Run the script. Note any validity-range warnings.
4. Pass the dimensionless number into the matching skill (correlation,
   pressure drop, etc.).

## Pitfalls

- Using the wrong length scale (pipe diameter vs hydraulic diameter for
  non-circular ducts; characteristic length for natural convection).
- Computing Pr at room temperature and using it for a hot fluid stream.
- Computing Re with mass velocity (G = rho v) where the correlation
  expects bulk velocity, or vice versa.
- Treating Dittus-Boelter Nu as the actual convective coefficient when
  the validity is borderline (Re ~ 5000 or Pr > 100).
- Using the kinematic viscosity in a Re formula that expects dynamic
  viscosity (or vice versa).
- Using Bi to decide a lumped-capacitance analysis without checking
  whether the surface heat transfer coefficient is itself in a turbulent
  regime.
- Computing Sc from a guessed diffusivity; quote the source of D_AB.

## Fallback Strategies

- If a needed property (k, mu, cp) is unknown, surface the missing input
  with a clear error rather than guessing.
- For very high or very low Pr (e.g. liquid metals), use a different
  correlation than Dittus-Boelter; this skill reports the number but the
  correlation choice is downstream.

## Verification

- Run the listed script with representative inputs and an `--output` file when a deterministic calculation is available.
- Confirm the JSON result contains `ok: true`, expected units, and no unhandled warnings.
- Check result magnitudes against the stated assumptions, references, and a hand calculation or known operating range before reporting them.

## References

- `references/equations.md` — formula list and standard length-scale
  conventions.

## Anti-Patterns

- Reporting Re without stating the length scale used.
- Treating Nu = 0.023 Re^0.8 Pr^0.4 as a universal answer.
- Mixing units silently inside the script call.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [jskherman](https://github.com/jskherman)
- **Source:** [jskherman/engg-skills](https://github.com/jskherman/engg-skills)
- **License:** Apache-2.0

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-jskherman-engg-skills-dimensionless-numbers
- Seller: https://agentstack.voostack.com/s/jskherman
- Browse the marketplace: https://agentstack.voostack.com/browse

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