Friends, can someone explain to me the working principle between electric water heater and heat exchanger? Take the best.

Electric water heaters and heat exchangers are completely different things.

The function of electric water heater is to consume electric energy through the operation of point heater and convert electric energy into heat energy of water, which can be stored water or directly heated.

Heat exchanger refers to heat exchange equipment, such as finned tube heat exchanger in indoor unit of air conditioner and evaporator in refrigerator. According to the definition of JB/T7249, heat exchanger refers to "the equipment that transfers heat between separated fluids".