Mehdi Mortazavi

Microscale Layering of Liquid and Vapor Phases Within Microstructures for Self-Regulated Flow Delivery to Local Hot Spots

In this study, a new two-phase heat sink architecture is introduced that operates in two different phase change modes. At low wall superheat temperatures, the heat sink operates at the thin film evaporator mode and transitions to boiling when the wall superheat temperature is increased. This unique function is enabled through constraining the liquid and vapor phases into separate domains using capillary-controlled meniscus formed within a hierarchical 3D structure. The structure is designed to form thin layers of vertically oriented liquid films that directly evaporate into their neighboring vapor space. The dominant mode of heat transfer in this design is thin film evaporation, a very effective boiling sub-process. As the surface superheat temperature is increased and boiling starts, the capillary-controlled meniscus breaks down. A heat transfer coefficient of greater than 200 kW/m2K is achieved at less than 1 °C wall superheat temperature.Copyright

Absorption Characteristics of Multilayered Thin Lithium Bromide (LiBr) Solution Film

In this study, an alternative absorber design suitable for the plate-and-frame absorber configuration is introduced. The design utilizes a fin structure installed on a vertical flat plate to produce a uniform solution film and minimize its thickness and to continuously interrupt the boundary layer. Using numerical models supported by experiments employing dye visualization, the suitable fin spacing and size and wettability are determined. The solution flow thickness is measured using the laser confocal displacement measurement technique. The new surface structure is tested in an experimental absorption system. An absorption rate as high as 6×10−3 kg/m2s at a driving pressure potential of 700 Pa is achieved, which is considerably high in comparison with conventional absorption systems. The effect of water vapor pressure, solution flow rate, solution inlet concentration, cooling water inlet temperature and solution inlet temperature on the absorption rate is also investigated. The proposed design provides a potential framework for development of highly compact absorption refrigeration systems.Copyright