To solve the prominent problem of convective heat transfer enhancement in solar collector tubes, experimental investigation on enhancing heat transfer between tube well and medium by copper inserts with double multiple spiral coils and three multiple spiral coils was conducted,by using field synergy theory.The results show that,the convective field synergy number Fc increases sharply with the synergy angle cosine cosβin the multiple spiral coils tubes.Moreover,the velocity field and temperature field also show a good cooperativity.The working fluid with three spiral coils has the best comprehensive heat trans-fer performance,under the condition with constant heat flow (240展开▼