Pool nucleate boiling heat transfer experiments were performed for water using heat transfer surfaces having unified cavities. Cylindrical holes of 10 μm in diameter and 40 μm in depth were formed on a mirror-finished silicon wafer of 0.2 mm in thickness using Micro-Electro Mechanical Systems (MEMS) technology. This silicon plate was used as the heat transfer surface. The test heat transfer surface was heated by a semiconductor laser beam. Experiments were conducted in the range of up to 1.35 × 105 W/m2. When the cavity spacing was narrow such as S = 1 or 2 mm, the convection created by the departure of coalesced bubbles played a main role in heat transfer when the heat flux was low. As the heat flux was increased, the coalesced bubbles absorbed enough heat to become large while the frequent bubble departure was maintained. As a result of it, the latent heat term in heat transfer became large to approximately 40%. When the cavity spacing was wide such as S = 4 mm, a bubble absorbed heat enough to become large before departure and the coalescence of bubbles were not prominent. Thus, the latent heat term took approximately 50% in heat transfer. With an increase in the heat flux, the vertical coalescence became to happen quite frequently. This coalescence made convection vigorous to increase the heat transfer. As a result of it, the convection term increased to 60% and the latent term decreased to 40%.

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