Boiling phenomena with surfactants and polymeric additives: A state-of-the-art review

Unsteady heat transfer caused by a confined impinging jet is studied using direct numerical simulation (DNS). The time-dependent compressible Navier-Stokes equations are solved using high-order numerical schemes together with high-fidelity numerical boundary conditions. A sixth-order compact finite difference scheme is employed for spatial discretization while a third-order explicit Runge-Kutta method is adopted for temporal integration. Extensive spatial and temporal resolution tests have been performed to ensure accurate numerical solutions. The simulations cover several Reynolds numbers and two nozzle-to-plate distances. The instantaneous flow fields and heat transfer distributions are found to be highly unsteady and oscillatory in nature, even at relatively low Reynolds numbers. The fluctuation of the stagnation or impingement Nusselt number, for example, can be as high as 20 percent of the time-mean value. The correlation between the vortex structures and the unsteady heat transfer is carefully examined. It is shown that the fluctuations in the stagnation heat transfer are mainly caused by impingement of the primary vortices originating from the jet nozzle exit. The quasi-periodic nature of the generation of the primary vortices due to the Kelvin-Helmholtz instability is behind the nearly periodic fluctuation in impingement heat transfer, although more chaotic and non-linear fluctuations are observed with increasing Reynolds numbers. The Nusselt number distribution away from the impingement point, on the other hand, is influenced by the secondary vortices which arise due to the interaction between the primary vortices and the wall jets. The unsteady vortex separation from the wall in the higher Reynolds number cases leads to a local minimum and a secondary maximum in the Nusselt number distribution. These are due to the changes in the thermal layer thickness accompanying the unsteady flow structures.

Unsteady heat transfer analysis of an impinging jet

Cooling of electronic devices: Nanofluids contribution

Nucleate boiling heat transfer and critical heat flux in narrow space between rectangular surfaces

An experimental study of a confined and submerged impinging jet heat transfer using Al2O3-water nanofluid

Heat transfer behaviors of a confined slot jet impingement

Impingement Cooling of an Isothermally Heated Surface With a Confined Slot Jet

An analytical study of local thermal equilibrium in porous heat sinks using fin theory

Experimental results of the pool boiling in horizontal narrow annuli are reported. The effects of fluid properties, pool subcooling, crevice length, and gap size on the boiling behavior and the critical heat flux (CHF) are also studied. The CHF decreases with decreasing gap size or increasing length of the annuli. The lower CHF of narrow crevices may be explained by the thin film evaporation. A semi-empirical correlation is established for the CHF of pool boiling in horizontal confined spaces. This correlation is compared with the CHF data of the present experiment. Satisfactory agreement is obtained.

Pool Boiling Heat Transfer in Narrow Horizontal Annular Crevices

Local steady-state natural convection heat transfer in vertical parallel plates with a two-dimensional rectangular rib

Ying-Huei Hung

Papers

Heat transfer behaviors of a confined slot jet impingement

Impingement Cooling of an Isothermally Heated Surface With a Confined Slot Jet

An analytical study of local thermal equilibrium in porous heat sinks using fin theory

Pool Boiling Heat Transfer in Narrow Horizontal Annular Crevices

Local steady-state natural convection heat transfer in vertical parallel plates with a two-dimensional rectangular rib