Are these two words interchangeable in the examples above?
In short, yes they are, though the third example sounds rather jarring (as Marina Yegorova says, most english speakers would use "Traveling by air" instead of "Air travelling"). At least for those three sentences.
Is there any difference in meaning?
Yes, there is. The reason that the common idiom is travel broadens the mind as opposed to traveling broadens the mind is the fact that the word travel embodies a fundamental concept, while traveling is simply engaging in the act. Allow me to explain.
In order to travel, it's common to make plans. Making plans forces you to make decisions about where you wish to go, when, and why. So before you've ever put one foot in front of the other, the process of deciding where to go (part of what is implied by the concept of travel) forces you to learn about your destination. It also means you'll learn about the methods of getting there so you can decide which one you want to use.
Once you actually start your trip by putting yourself in motion you've begun engaging in the act of traveling and the definitions meet.