Question

if door of fridge is opened then what happened

Answer 1

The room would get warmer! Think of a refrigerator as a device that transfers heat from inside a box to its surroundings. The room around a refrigerator is warmed as it receives the heat removed from inside the box.

If you leave the door open, heat is merely recycled from the room into the refrigerator, then back into the room. A net room temperature increase would result from the heat of the motor that would be constantly running to move energy around in a circle. It would be like hooking up a water pump to remove water from your basement and routing the discharge tube back to the basement.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

Answer 2

If the door of fridge or refrigerator is left open, then the temperature will rise and the microbes will start growing causing the spoilage of food.