Rapid Fire Arrows are used to fire the arrows rapidly on the mobs. You can add a lava element to fire flaming arrows. Go through this guide and follow step-by-step instructions to make Rapid Fire Arrows.
In order to make Rapid Fire Arrows, the first thing you have to do is to place four gray concrete blocks in the same way as shown in the image below.
After this, add two redstone torches on the lower blocks and use redstone dust at the top.
Now you have to add a redstone repeater on the right side of concrete blocks and a dispenser just next to this repeater.
Fill the dispenser with arrows and it will start firing arrows rapidly.
You can also use lava for the flaming arrows. Add gray concrete blocks on either side of the dispenser and add a bucket of lava in it. Fill the dispenser with arrows and watch out for the result.