  We numerically study the thermoelectric transports of Dirac fermions in
graphene in the presence of a strong magnetic field and disorder. We find that
the thermoelectric transport coefficients demonstrate universal behavior
depending on the ratio between the temperature and the width of the
disorder-broadened Landau levels(LLs). The transverse thermoelectric
conductivity $\alpha_{xy}$ reaches a universal quantum value at the center of
each LL in the high temperature regime, and it has a linear temperature
dependence at low temperatures. The calculated Nernst signal has a peak at the
central LL with heights of the order of $k_B/e$, and changes sign near other
LLs, while the thermopower has an opposite behavior, in good agreement with
experimental data. The validity of the generalized Mott relation between the
thermoelectric and electrical transport coefficients is verified in a wide
range of temperatures.
