For　the　flooded　evaporator　in　refrigeration　or　air　conditioning　systems,　refrigerant　is　boiling　on　the　shell　side　and　water　is　flowing　in　the　tube　side.　The　pool　boiling　heat　transfer　coefficient　of　R134a　outside　one　smooth　tube　and　one　reentrant　cavity　enhanced　tube　No.1　is　investigated　with　an　experimental　approach.　At　the　saturate　temperature　of　6,　10　and　16℃,　the　heat　flux　of　10-250　kW·m-2,　the　heat　transfer　coefficient　versus　heat　flux　of　smooth　tube　is　investigated　and　compared　with　Cooper　correlation.　The　external　diameter　of　smooth　tube　and　enhanced　tube　are　15.93　mm　and　25.36　mm,　respectively.　At　the　heat　flux　of　10-250　kW·m-2,　it　is　found　that　the　deviation　of　experimental　result　and　Cooper　correlation　is　within　±15%.　the　average　value　of　m　in　h∝qm,　is　0.67.　For　the　enhanced　tube,　the　enhanced　ratio　is　the　largest　at　the　heat　flux　less　than　40　kW·m-2.　The　enhanced　ratio　is　decreasing　as　the　increment　of　heat　flux.　At　the　heat　flux　larger　than　250　kW·m-2,　the　heat　transfer　coefficient　of　enhanced　tube　is　approaching　the　smooth　tube,　and　even　smaller　than　smooth　tube.　©　All　Right　Reserved.