The thermal patterns on a heated wall, as related to the flow regime, were studied by using the heated foil infrared technique. The thermal pattern on the heated wall for the single-phase water flow has a streaky structure. For the bubble flow, the streaky structure is destroyed. This phenomenon is accompanied by a significant increase in the heat transfer coefficient. For the slug flow regime, the thermal pattern on the wall depends on whether water containing small gas bubbles (slug) or water surrounding a Taylor bubble passes the heated wall. Simultaneously, the temperature and pressure fluctuations at the wall were measured. The level of these fluctuations was discussed together with the data about the average heat transfer. The excess form of heat transfer coefficient was introduced. A correlation for the dimensionless heat transfer coefficient at slug flow was suggested. (C) 2000 Elsevier Science Ltd. All rights reserved.