  Thermopower and the Lorentz number for an edge-free (Corbino) graphene disk
in the quantum Hall regime is calculated within the Landauer-B\"{u}ttiker
formalism. We find, by varying the electrochemical potential, that amplitude of
the Seebeck coefficient follows a modified Goldsmid-Sharp relation, in which
energy gap is identified with the interval between zero-th and first Landau
level in bulk graphene. Analogous relation for the Lorentz number is also
determined. Therefore, these thermoelectric properties are solely defined by
the magnetic field, temperature, the Fermi velocity in graphene, and
fundamental constants including the electrons charge, the Planck and Boltzmann
constants, being independent on the system geometric dimensions. This suggests
that the Corbino disk in graphene may operate as a thermoelectric thermometer,
allowing to determine small temperature difference between two reservoirs, if
mean temperature and magnetic field are known.
