% Units
atm = 101325 ; % [Pa]
kJ  = 1000   ; % [J]

% Functions for saturation & absolute humidity
p_sat = @(t) 610.5 * exp( 17.269*t / (237.3+t) ) ; % [Pa]
t_sat = @(p) 237.3 / ( 17.269/log(p/610.5)-1 ) ;   % [°C]
w     = @(p_vap, p) 0.622 * p_vap / (p-p_vap) ;    % [kg_vap/kg_as]
p_vap = @(w, p) p / ( 0.622 / w + 1 ) ;            % [Pa]

% Same pressure
p_bu = 1*atm ;
p_bs = p_bu ;

% Wet & dry bulb temperatures
t_bu = 15 ; % [°C]
t_bs = 20 ; % [°C]

% Quantities for mix enthalpy
cp_as  = 1.005 * kJ ; % [kJ/(kg K)]
cp_vap = 1.875 * kJ ; % [kJ/(kg K)]
h_lv   =  2501 * kJ ; % [kJ/(kg)]

% Wet bulb mix enthalpy
p_vap_bu = p_sat(t_bu) 
w_bu     = w(p_vap_bu, p_bu) 
J_bu     = cp_as * t_bu + w_bu * (h_lv + cp_vap * t_bu) 

% Dry bulb
w_bs = (J_bu - cp_as * t_bs) / (h_lv + cp_vap * t_bs) 
p_vap_bs = p_vap(w_bs, p_bs) 
phi_bs = p_vap_bs / p_sat(t_bs)