I hope anyone could be able to help. Am trying to simulate heat pipe using fluent, when i used the built in Lee model i ve got non applicable result, so i had to use UDF for evaporation and condensation. However, when i load the UDF no errors occur, when i start to initialize i get the following error: Error: FLUENT received fatal signal (ACCESS_VIOLATION) 1. Note exact events leading to error. 2. Save case/data under new name. 3. Exit program and restart to continue. 4. Report error to your distributor. Error Object: () the udf used is attached. I need to know rather is there an error in the UDF formula or am not identifying it in the most proper way. Am using interpret method and identify the UDF in phase interaction under mass transfer for evaporation and condensation, also in source terms for boundary conditions i defined the energy UDF.