The present study proposed a triangular-pitch shell-and-tube spray evaporator featuring an interior spray technique. In the proposed approach, the nozzle tubes are positioned within the tube bundle in such a way that the surface of each heater tube is sprayed simultaneously by two cooling sprays. As a result, the dry-out phenomenon is prevented, and thus the heat transfer performance is improved. An analytical expression is derived for the optimal spray cone angle for the proposed evaporator. It is shown that the optimal spray cone angle increases with an increasing diameter of the heater tubes, but decreases with an increasing distance between the heater tubes and nozzle tubes. The analytical expression for the optimal spray cone angle was validated by experimental spray tests using spray cone angles of 0, 30, 40, 45 and 60, respectively. It is shown that a good agreement exists between the experimental results for the optimal spray cone angle and the theoretical results. Furthermore, the experimental results confirm that the shell-side heat transfer coefficient obtained using the interior spray technique is significantly higher than that achieved in a conventional flooded-type evaporator over a wide range of surface heat fluxes. (C) 2015 Elsevier Ltd. All rights reserved.