Thermal performance in a tubular heat exchanger with deltawinglets Pattarapan Tongyote, Pongjet Promvonge, Nattawoot Depaiwa and Withada Jedsadaratanachai MATEC Web Conf., 192 (2018) 02062 Published online: 14 August 2018 DOI: 10.1051/matecconf/201819202062