A rigorous computational analysis is performed to predict the thermofluidic characteristics from a heated converging–diverging tube suspended in a uniform upstream flow of air with negligible wall thickness within the laminar regime. Several influencing factors, like, Reynolds number \((Re)\) , Rayleigh number \((Ra)\) , and diameter ratio \((D/{D}_{t})\) , are used to fully describe this ongoing research. A detailed interpretation of thermofluidic behaviour is elucidated considering with/without presence of upstream flow. Temperature gradient nearby the walls shoots up in the presence of upstream flow of air, this results in improvement in heat dissipation rate. A non-zero value of \(Re\) is more effective in terms of heat dissipation rate for inner surface compared to outer wall due to the concaveness of the tube. Heat dissipation rate reduces continually as \(D/{D}_{t}\) grows for both inner and outer walls. Again, heat dissipation rate is seen to be higher at a higher \(Ra\) than a lower \(Ra\) . Velocity streams are employed to obtain a thorough understanding of flow pattern.