Chana Dal is considered pretty dense and hence traditional pappadums are not normally made with it. The most popular ones are moong because it's a more tender bean.
Andy, traditionally pappadums are eaten as an accompainement to dahl and rice or anything that goes with soft rice (we have our own version of risotto made with rice and moong or tur beans with some pure ghee).
In India you normally crunch it all up and add it to your dahl and rice or rice and another gravy (we call it kadhi and it's made with lots of yogurt and spices, almost like a soup). It adds a nice crunchy element to the soft food.
A traditional Indian comfort meal is a bowl of dahl, soft rice cooked with a touch of pure ghee or clarified butter, some roasted pappadums on the side and a pickle (sweet or spicy, ours are laced with a ton of spices, oil and sugar).
Indian restaurants in the West use them as a starter course with numerous sweet and savory dipping sauces but that's a very west thing.