A pebble bed is used to store thermal energy in a solar energy utilization system. The bed is $2m$ long, $1m$ in diameter, and the pebbles can be approximated as $2cm$ diameter spheres packed with a void fraction of $0\mathrm{.}44.$ During the storage phase of the cycle, $0\mathrm{.}8k\frac{g}{s}$ of air at $360K$ and $1$ atm comes from the solar collector. If the outlet temperature of air is $300K,$ determine the surface temperature of pebbles and heat transfer rate from air to pebbles.