fluids

1.3.0 verified Fri May 01 auth: no python

Fluid dynamics component of the Chemical Engineering Design Library (ChEDL). Provides correlations for fluid properties, friction factors, pipe flow, pumps, valves, fittings, separators, two-phase flow, and more. Current version 1.3.0. Release cadence is irregular, with major updates every 1-2 years.

pip install fluids

Common errors

error ModuleNotFoundError: No module named 'fluids.core' ↓

cause Importing `fluids.core` directly is incorrect; core functions are exposed via `fluids` or submodules.

fix

Use import fluids then fluids.dP_from_f(...) or from fluids import dP_from_f.

error AttributeError: module 'fluids' has no attribute 'FrictionFactor' ↓

cause FrictionFactor is not in the top-level namespace; it's in fluids.friction.

fix

Change import to from fluids.friction import FrictionFactor.

error ImportError: cannot import name 'HasNumericData' from 'fluids' ↓

cause In version 1.0.0, HasNumericData was renamed or moved. Old import pattern is broken.

fix

Use from fluids.constants import HasNumericData or remove dependency; check documentation.

error TypeError: FrictionFactor() got an unexpected keyword argument 'Method' ↓

cause In older versions, the argument was `method` (lowercase). Changed to `Method` in newer versions.

fix

Use lowercase method if using version <1.0.26; or upgrade and use Method.

error ValueError: Unknown method '' for function FrictionFactor ↓

cause Empty or invalid method string; must be one of the known methods (e.g., 'Colebrook', 'Blasius').

fix

Specify a valid method or omit to use default.

Warnings

breaking In version 1.0.26, compatibility with numpy 2.0 and scipy 1.14 was added. Code that relied on older numpy/scipy APIs may break if upgrade to 1.0.26+ without updating. ↓

fix Use numpy>=2.0 compatible code; update scipy usage to 1.14 patterns.

breaking Version 1.1.0 removed deprecated methods and renamed several functions. Code using old names like `K_from_f` (now `K_from_f` still works? check) may break. ↓

fix Check the changelog for renamed functions and update calls accordingly.

deprecated The `fluids.geometry` module is mostly deprecated in favor of more specific modules. Functions moved to `fluids.piping` or `fluids.tanks`. ↓

fix Use imports from `fluids.piping`, `fluids.tanks`, etc.

gotcha Unit conventions: Many functions expect SI units (m, kg, Pa, etc.). Mixing units (e.g., bar instead of Pa) leads to incorrect results without error. ↓

fix Always convert to SI units before calling fluids functions.

gotcha Friction factor functions (e.g., `FrictionFactor`) return Darcy-Weisbach friction factor, not Fanning. If using Fanning, divide by 4. ↓

fix Check that you are using the correct friction factor type for your calculation.

Imports

from fluids import *
wrong
```
from fluids import *
```
correct
```
import fluids
```
Star import pulls many names into namespace; use explicit imports instead.
FrictionFactor
wrong
```
from fluids import FrictionFactor
```
correct
```
from fluids.friction import FrictionFactor
```
FrictionFactor is in the friction submodule, not top-level.

Quickstart

Basic usage: compute friction factor and pressure drop.

import fluids
from fluids.friction import FrictionFactor
# Compute friction factor for turbulent flow (Colebrook)
Re = 100000.0  # Reynolds number
roughness = 0.0015  # relative roughness e/D
ff = FrictionFactor(Re=Re, roughness=roughness, Method='Colebrook')
print(f'Friction factor: {ff}')
# Compute pressure drop in a pipe
dP = fluids.core.dP_from_f(fd=ff, L=100.0, D=0.1, rho=1000.0, V=2.0)
print(f'Pressure drop: {dP} Pa')