#!/usr/bin/python
# -*- coding: utf-8 -*-
"""Viscosity computation for various media"""
from __future__ import division, print_function, unicode_literals
import numpy as np
[docs]def get_viscosity(medium="CellCarrier", channel_width=20.0, flow_rate=0.16,
temperature=23.0):
"""Returns the viscosity for RT-DC-specific media
Parameters
----------
medium: str
The medium to compute the viscosity for.
One of ["CellCarrier", "CellCarrier B", "water"].
channel_width: float
The channel width in µm
flow_rate: float
Flow rate in µl/s
temperature: float or ndarray
Temperature in °C
Returns
-------
viscosity: float or ndarray
Viscosity in mPa*s
Notes
-----
- CellCarrier and CellCarrier B media are optimized for
RT-DC measurements.
- Values for the viscosity of water are computed using
equation (15) from :cite:`Kestin_1978`.
"""
if medium.lower() not in ["cellcarrier", "cellcarrier b", "water"]:
raise ValueError("Invalid medium: {}".format(medium))
# convert flow_rate from µl/s to m³/s
# convert channel_width from µm to m
term1 = 1.1856 * 6 * flow_rate * 1e-9 / (channel_width * 1e-6)**3 * 2 / 3
if medium == "CellCarrier":
temp_corr = (temperature / 23.2)**-0.866
term2 = 0.6771 / 0.5928 + 0.2121 / (0.5928 * 0.677)
eta = 0.179 * (term1 * term2)**(0.677 - 1) * temp_corr * 1e3
elif medium == "CellCarrier B":
temp_corr = (temperature / 23.6)**-0.866
term2 = 0.6771 / 0.5928 + 0.2121 / (0.5928 * 0.634)
eta = 0.360 * (term1 * term2)**(0.634 - 1) * temp_corr * 1e3
elif medium == "water":
# see equation (15) in Kestin et al, J. Phys. Chem. 7(3) 1978
if np.min(temperature) < 0 or np.max(temperature) > 40:
msg = "For water, the temperature must be in [0, 40] degC! " \
"Got min/max values of '{}'.".format(np.min(temperature),
np.max(temperature))
raise ValueError(msg)
eta0 = 1.002 # [mPa]
right = (20-temperature) / (temperature + 96) \
* (+ 1.2364
- 1.37e-3 * (20 - temperature)
+ 5.7e-6 * (20 - temperature)**2
)
eta = eta0 * 10**right
return eta