Flow and heat transfer characteristics of offset unsubmerged jets impinging on rotating disks

•Decreasing jet offset improves heat transfer performance.•Increasing rotational speeds enhance Nusselt number up to a limit.•High rotational speeds result in lower amount of oil on disk surface.•Optimal Nusselt numbers occur at mid rotational speeds and small jet offsets.•Nusselt number correlation proposed based on rotational speed and jet offset. A study of an unsubmerged jet impinging on a heated rotating disk is conducted to investigate the multi-phase flow dynamics and heat transfer characteristics. The effects of varying the disk rotational speeds, ranging from 240 to 16,000 revolutions per minute, and the jet location, ranging from a symmetrical condition to offset conditions up to 80 % of the disk radius, are analysed. The jet nozzle diameter and the ratio of the jet impingement distance to nozzle diameter are held constant at 4 mm and 10, respectively. The Volume of Fluid method is employed to model the two-phase flow, with a conjugate heat transfer boundary condition applied at the fluid–solid interface. A moving mesh rotation model is employed for the computations. The results show that changes in jet offset positions at different rotational speeds lead to distinct flow and temperature patterns, significantly impacting the heat transfer on the top surface of the rotating disk. With decreasing jet offset distances, better overall heat transfer performance and lower surface average temperatures are obtained. While increasing rotational speed up to 1930 revolutions per minute at a high jet offset (0.6) enhanced the average Nusselt number by 50 %, at very high speeds (16,000 revolutions per minute), low film thickness or poor oil contact with the hot surface reduced heat transfer performance to 3 %. Consequently, maximum average Nusselt numbers are achieved at mid rotational speeds (1930 revolutions per minute) and small jet offsets (less than 0.4). Poor heat transfer performance was observed at higher speeds (above 1930 revolutions per minute) and larger offsets (above 0.4). A new correlation is proposed for the average heat transfer based on the rotational Reynolds number and jet offset location.