Effect of prolonged ultrasonication on the thermal conductivity of ZnO-ethylene glycol nanofluids

► ZnO-EG nanofluids display thermal conductivity enhancement of ∼40% at 30 °C. ► Highest enhancement for ZnO-EG nanofluids reported so far. ► Earlier existing theoretical models under-predict our results. ► A new expression is proposed which explains the observed results very well.