Question

imagine the lungs and size of elephant. is there any relation between body size and lung size?

Answer 1

The size of the lungs of elephant and size of elephant are directly proportional i.e. since the size of elephant is huge so their lungs will also be large as they will require more oxygen for their body metabolism. Due to it's massive size the lungs of elephant have few adaptations. The lungs of elephants  are divided into smaller units by a network of septa.They causes their lungs to expand and contract by moving the muscles in their chest. 

Answer 2

Elephants are one of the largest land living animals. Since these mammals are so massive, they would definitely require more supply of oxygen to the tissues around the body. Elephants have very large lungs, as compared to other land animals. Despite being large, the elephant lungs also have other adaptations. These adaptations include, lack of plural cavity, instead, their lungs are directly attached to the rib cage and the diaphragm through collagen connective tissues. This anomaly helps the elephant's lung to have more sucking power than usual and also prevents rupturing of the capillaries when subjected to high pressures. This is useful to the elephant when it sucks water by its trunk and also when its snorkeling( that is submerged under water with its trunk exposed to the atmosphere drawing in air.

Studies have shown that  there could either be either allometric or isometric translation when it comes to the relationship between body size and lung size of animals. That means, the larger the animal, the larger the lungs.