am calculating htc on a surface due to jet cooling, how much mesh size do u reccomend at the 1st cell(at the heat transfer surface), or is it that it has no effect on accuracy, it only depends on the y+ value there. I am getting erroneous results when i use 4e-4 mesh at the boundry, how much do u suggest. N wat else do u suggest t luk into for accurate HTC's thanks in advance

First cell size will have effect on HTC if you are not choosing standard wall functions. Have your mesh fulfilling the requirements of turbulence model being used. For the requirements for difference turbulence models pls refer to Fluent user guide.