Is 1/2" PVC conduit sized properly for three #10 THHN wires ?
Yeah, that's legal.
If it's a particularly complex pull, larger pipe size can help. It can also help with the fact that you can easily put 4 circuits in a conduit (if it meets the fill rules).
Now, since you mentioned this is a dryer and you are running hot/neutral/ground... If it's a gas dryer you are on the right track.
If it's an electric dryer, we must deep-dive into the arcana of dangerous and obsolete dryer connections. Old 3-prong dryers used no ground, and worse, they attached the chassis of the dryer to neutral. This has the potential of being dangerous in several ways. As such they have been outlawed for 30 years. And even when they were legal, it was NEVER legal to use /2+gnd (black white bare) to connect them - though it was done shamefully often.
Since you are doing a new cable run, you MUST bring it up to current Code. This isn't far out of your way; you just need to use 4 wires in the conduit instead of 3. The 2 hot wires can be the same color - but neutral must be white, and ground must be green or bare.
I for one recommend using stranded wire, because it's a lot easier to pull.
By the way, if you use EMT metal conduit, the conduit is the ground - one less wire.
And yes, you will need to convert the dryer socket and cord to NEMA 14-30.