Surya means the sun and, according to Yoga the Surya Nadi is the right nostril. In this type of pranayama you use your right nostril for inhalation and the left one for exhalation. The same procedure is repeated in each round.
This is also called a Viloma type of pranayama.
Yoga propounds that in our body the Sun is located near the navel and the moon in the skull. While the moon has a cooling effect, the sun a heating effect.
This concept has been probably derived from the fact that the food we eat is digested in the part of the body near the navel. Digestion is supposedly carried out by heat, of which the Sun is the source of. The air breathed through the right nostril is supposedly makes an impact on other forms of vital energies in our body. Because of this impact these energies amass near the root of the navel, which is supposed to have a great significance in awakening the Kundalini.
Suryabhedana Pranayama creates heat in the body and activates that part of the brain, which holds the vital life-force. It is said to fortify the liver and immune system, purifies the blood and cures gas problems, intestinal ailments, leucoderma and other skin diseases. Suryabhedana stops vata problems in the stomach and prevents throat trouble.