Experimental Analysis Of Twisted Shaped Spot Evaporators At High Heat Fluxes

Devices for cooling high heat fluxes within small available spaces are called spot evaporators. Areas of application are for example the cooling of molds, power electronics or electrical mobility. The functionality of the spot evaporator bases on its geometry and is a combination of spray-cooling and pipe flow. Spray-cooling or jet impingement cooling is able to achieve high heat fluxes even at overcritical wall temperatures. To reach the same effects within the pipe-flow part of the spot evaporator, this part has to be twisted shaped. The paper focuses on the experimental analysis of the twisted shaped spot evaporator by varying fundamental parameters corresponding to the Model of Yagov. Two methods of generating the twist have been developed and compared to each other. The experimental results will be discussed. They show that the averaged critical heat flux can be raised up to 30 % compared to spot evaporators without twisted flow. As refrigerant R404A has been used

Forced Bulk Boiling At High Heat Fluxes

The influence of very high heat fluxes (105 to 106 W/m²) on the boiling behavior of R404A are investigated. By using a new evaporator design it is possible to change the evaporating effects even at these high heat fluxes to bulk boiling. This paper focusses on the experimental analysis of the new evaporator by varying the parameters geometry, mass flux, subcooling and fluid velocity. The results are compared with experimental works and mathematical models at lower heat fluxes. The results show, that fluid velocity, mass flux and geometry have high influence on the transferred heat flow, while the subcooling of the liquid phase has only a small effect