Electric Current of Cone-jet Increases with Temperature: A Combined Effect of Self-heating and Ion Evaporation

A cone-jet emits charged droplets and ions with an electric current. When the liquid is heated, we observe a sharp increase in current (over 200% current increase with a 20 {degree sign}C temperature rise) for conductive cone-jets, indicating that ion evaporation, a temperature-sensitive process, can contribute significantly to the emission, especially under strong self-heating. We developed an analytical model that incorporates both self-heating and ion evaporation to predict the current as a function of temperature, liquid properties, and flow rate. The model agrees well with measurement. Calculations suggest that ion evaporation takes >70% of total current at high temperatures.