Abstract: The Niyama number of a flow path for phase change ink is the ratio of cooling rate of the ink to the thermal gradient of the ink along the ink flow path. Print head assemblies can be designed and configured to achieve ink flow paths having Niyama numbers that are greater than a critical Niyama value. These designs reduce entrapment of air in the ink as the ink is changing phase and provide optimal bubble and void mitigation for phase change ink. The thermal gradient of the ink flow path can be achieved using passive and/or active thermal elements disposed along the ink flow path.

Abstract: A particle removal device for an ink jet printer is discussed. The particle removal device includes a first separator comprising an arrangement of obstacles including at least two rows of obstacles that extend laterally with respect to a flow path of ink in the first separator. The rows of obstacles are offset from one another by a row offset fraction. The arrangement of obstacles is configured to preferentially route larger particles having diameters greater than a critical diameter through the arrangement and along a first trajectory vector that is angled with respect to the direction of the flow path of the ink. The angle of the first trajectory vector with respect to the ink flow path is a function of the row offset fraction. Smaller particles having diameters less than the critical diameter travel through the arrangement along a second trajectory vector that is not substantially angled with respect to the flow path of the ink.

Abstract: Approaches to remove bubbles from ink in an ink jet printer are described. Bubble removal may be implemented using one or more separator elements configured to separate bubbles of a vapor from ink. Each separator element includes wicking features having dimensions sufficient to allow capillary movement of the ink in the wicking features and to substantially exclude the bubbles from the wicking features. One or more inlets allow passage of the ink that includes the bubbles into the separator element. At least one vapor outlet allows vapor that has been separated from the ink to exit from the separator element. The ink exits from the separator element thought one or more ink outlets.