I'm building an ultrasound cleaner. The main chamber is filled with water and it is heated. The chamber is completely sealed so the pressure inside increases with the temperature. An ultrasound emitter will be added to the bottom to increase cleaning effectiveness. Do I have to worry about the temperature/pressure increasing considerably inside the chamber because of the added ultrasound energy? Are the cavitation bubble's effects localized do the bubble itself or should I expect a considerable increase in pressure/temperature inside the chamber?
If the vessel can go above 15psi, you will need a pressure relief device. This is the case for any pressure vessel irrespective of the ultrasonic consideration. A standard water heater pop off will probably work fine provided your vessel is rated for that pressure.
Most ultrasonic cleaners run at atmospheric pressure. There is no real reason to run at higher pressure unless you are using a solution other than water and don't want it to evaporate.
Heat addition can be calculated from power input. For example if the unit is 12vdc at 2amps it will add 24watts of heat to the system. Your ultrasonic piezo element will have a maximum design temperature. You will need to keep below this temperature by either cooling the piezo element or the whole vessel.