How to do an iteration with while loop

May somebody help me out with this. I want to do the iteration until Tf-T_average = 0. I want to put T_f as new Tf, however i do not know how. Attached is the iteration that I want to do and below is my Matlab code. I had try while and end code

%Iteration-----------------------------------------------------------------%

Tf         = 140 ;  %Assumed temperature (°F)
Viscousity = V_1*exp(V_2/(Tf + 95)); % Viscousity (reyn)
S               = (C_ratio)^2*((Viscousity*(N/60))/P); %Sommerfeld Number
delta_T    = (TRV_2 + (TRV_3*S)+(TRV_4*(S^2)))*(P)/9.7; % Temperature Rise (°F)
T_average  = Temp_in + (delta_T/2); % Average temperature
T_f = (Tf + T_average)/2; % Average assumed temperature (°F)

delta_T2 = Tf -T_average
while delta_T2 > 0
    delta_T2 = Tf -T_average
end