A heat pump dryer is a device that heats air through a heat pump cycle and expels moisture. It can be used to dry a variety of foods, including apples. The drying temperature of apples should be between 60-70 degrees Celsius. The drying time depends on the size and moisture content of the apples, and generally takes about 6-12 hours.

1. Wash the apples, peel and core them, then cut into thin slices or flakes.
2. Place the apple slices evenly on the drying tray of the heat pump dryer, try not to overlap.
3. According to the instruction manual of the dryer, set the drying temperature to 60-70 degrees Celsius and set the drying time.
4. Turn on the dryer and start drying the apples.
5. During the drying process, the apple slices can be properly turned to ensure uniform drying.
6. After drying, take out the apple slices, place them in a ventilated and dry place, and wait for them to cool down.

It should be noted that the drying temperature and time of the heat pump dryer need to be determined according to different foods to ensure their quality and taste. At the same time, the filter screen and heat exchanger of the dryer need to be cleaned regularly to ensure its normal operation.