when i render a smoke simulation,the rendered photo in 3D viewport is different from the rendered image when i press F12,in 3D viewport it's more dense and has orange colour but in the final render it's black and white and less dense
Although the quick smoke feature creates the texture nodes for the smoke, it doesn't for the flames. So when you render it, only the smoke is visible.
This has been covered before on Blender StackExchange:
This is also covered in Blender Guru's fire tutorial: