Originally Posted by
buddychang
D352 and D356 are overnight long-haul trains to Chengdu and Chongqing in the southwest, with most cars equipped with sleepers, so they are not suitable for travelers between Shanghai and Hefei. Instead, you'd better choose trains like D5xxx or D30xx, which are all seats.
On tielu.org, sleeper prices aren't listed for 352 (which doesn't mean they don't exist). But, if they are offered, I would absolutely grab one for a 2.5 hour trip.