Primary breakup during atomization is governed by complex mechanisms and is not well understood. Detailed numerical simulations using the volume-of-fluid method augmented with adaptive mesh refinement techniques were performed to study the formation and disintegration of liquid sheets produced from a dual-orifice pressure-swirl atomizer. The calculated atomization characteristics agree with the experimental results given a maximum relative error for the spray cone angle of 4.9% and maximum relative error for the Sauter mean diameter of 7.4%. For the five considered cases, changes in the pressure drop over a certain range do not affect the final spray angle size, but larger pressure drops will cause the liquid sheet to open faster while delaying the merger of the liquid sheets. The perturbation wave that causes the primary breakup of the dual-layer liquid sheets consists of two parts: the initial perturbation wave and the perturbation wave originating from the merger of the dual-layer liquid sheets, which dominates their primary breakup but whose generation is delayed by an increased pressure drop. The axial position when the disturbance wave first grows to its maximum amplitude matches well with the liquid sheet breakup length with a maximum error of 11.9%. Research on the merger of liquid sheets helps to further study the mechanisms of dual-layer liquid sheet primary breakup and guide the understanding of atomization in dual-orifice pressure-swirl atomizers.

As a key component-connecting compressor and the entrance of combustion chamber, the diffuser is able to increase the pressure and slow down the airflow in order to promote efficient combustion as well as avoid a large amount of pressure loss. In this paper, experimental investigation and numerical studies have been carried out to understand the effects of air bleeding from dump region and dump gap ratio on the total pressure loss and static pressure recovery of the dump diffusers. The ultimate objective is optimizing the dump diffuser design to get the maximum static pressure recovery and minimum total pressure loss. A simplified test model is used to study the effect of the air bleeding from the outer dump region and the dump gap ratio on the total pressure loss and static pressure recovery in the dump diffuser. The impact of the dump gap ratio in the performance of the dump diffusers has also been discussed. Nearly all the pressure raise occurs in the prediffuser, and most of the total pressure loss occurs in the dump region. For the recirculating area in the dump region, the controllable vortex can be introduced. Bleeding air from the outer dump region can improve the velocity distribution near the flame tube. The results show that when 0.4% of the air is bled from outer dump region, the performance of the dump diffuser is optimal. Hence, the controllable vortex method is effective for improving the performance of the dump diffuser.

Thermal properties of water-based nanofluid with different mass fraction of the graphene oxide nanosheets, and convective heat transfer capability in the microchannel heat exchangers at different temperature conditions are studied experimentally. Experimental results show that the nanofluid can be stable under 60°C, but it would precipitate after four hours heating at 99°C. The kinematic viscosity decreases with extent of 50%~60% as the temperature of nanofluid increases from 10°C to 45°C and the thermal conductivity arises by 17.54%. The heat transfer experiments show that convective heat transfer capacity of water-based graphene oxide nanofluid is better than water when the wall temperature is below 100°C. When the wall temperature of microchannel heat exchangers is above 100°C, the graphene oxide nanosheets would precipitate which leads to the deterioration of convective heat transfer capacity.