relaxtion time ? in MCMP model

[sup]hi,everyoone.I am a new LBMer. My present work is dealing with multicompoent multiphsae flows. In my model,there are two disrtibution fuction .so there are two relaxtion time ?1,?2 which are related to viscosity . the probelm is how to determine the value of ?1,?2. If i use
?=cs2*(?-0.5)?t, I cannot use practical ?1,?2 due to limit of the range of ?. Who can help me solve this problem?Thank you!