As temperature is high at 97 C, the sample in PCR is going to?
I know of three solutions: Heated lid. The lid temperature is usually set to 105C or greater, preventing evaporation (it can be adjusted on newer thermocyclers). Mineral oil or paraffin. This was common before everyone had heated lids. But I've never used it. There are some special PCR reactions where mineral oil is needed, but someone else will need to contribute (on a quick google, I passed by digital PCR and droplet PCR). High capacity PCR uses water baths. You have complete immersion of the array tape so evaporation isn't an issue (as far as I know). A note on the heated lid. Make sure your seals are tight! I've had a few inaccurate PCRs because I didn't properly seal the reuseable mat, seal the PCR film, or close the lids. Manufacturers will provide a tool to ensure a good seal. A heat conducting pad can also be added to some thermocyclers. Attention to detail is important for a lot of lab work (and don't work when you're tired). That is especially true if you are running quantitative assays. Qualitative assays can get away with less precision. This sounds like a homework question, but it's worth a discussion for anyone who is learning bench work.