add Bolin number formulae

PySDM/physics/isotope_relaxation_timescale/bolin_1958.py

@@ -1,5 +1,4 @@
-"""Timescale derived for tritium with assumption of zero ambient concentration - see text above
-Table 1 [Bolin 1958](https://digitallibrary.un.org/record/3892725)"""
+"""Bolin number"""
 
 import numpy as np
 
@@ -11,5 +10,5 @@ def __init__(self, const):
         assert np.isfinite(const.BOLIN_ISOTOPE_TIMESCALE_COEFF_C1)
 
     @staticmethod
-    def tau(const, dm_dt_over_m):
-        return 1 / (const.BOLIN_ISOTOPE_TIMESCALE_COEFF_C1 * dm_dt_over_m)
+    def bolin_number(const):
+        return const.BOLIN_ISOTOPE_TIMESCALE_COEFF_C1

PySDM/physics/isotope_relaxation_timescale/zaba_et_al.py

@@ -19,3 +19,29 @@ def tau(
             * D_iso
             * (S * (alpha * R_vap / R_liq - 1) + (S - 1) / (1 + D * Fk))
         )
+
+    @staticmethod
+    def bolin_number(
+        const,
+        diffusivity_ratio_heavy_to_light,
+        alpha,
+        rho_s,
+        Fd,
+        Fk,
+        saturation,
+        R_vap,
+        R_liq,
+    ):  # pylint: disable=too-many-arguments
+        """
+        Bolin number (Bo) - c1 in Bolin 1958
+        """
+        return (
+            alpha
+            / diffusivity_ratio_heavy_to_light
+            / (
+                (1 + const.rho_w / rho_s * Fk / Fd)
+                * saturation
+                * (alpha * R_vap / R_liq - 1)
+                + (saturation - 1)
+            )
+        )

PySDM/physics/trivia.py

@@ -161,3 +161,10 @@ def poissonian_avoidance_function(r, dt):
         process with a constant rate `r`
         """
         return np.exp(-r * dt)
+
+    @staticmethod
+    def tau(Bo, dm_dt_over_m):
+        """
+        Timescale derived for tritium with assumption of zero ambient concentration - see text above
+        Table 1 [Bolin 1958](https://digitallibrary.un.org/record/3892725)"""
+        return 1 / Bo / dm_dt_over_m