CFD-Based Study of Nozzle Section Geometry Effects on the Performance of an Annular Multi-Nozzle Jet Pump

Study on the key parameters of ice particle air jet ejector structure

Existing ice particle jet surface treatment technology is prone to ice particle adhesion during application, significantly affecting surface treatment efficiency. Based on the basic structure of the jet pump, the ice particle air jet surface treatment technology is proposed for the instant preparation and utilization of ice particles, solving the problem of ice particle adhesion and clogging. To achieve efficient utilization of ice particles and high-speed jetting, an integrated jet structure for ice particle ejection and acceleration was developed. The influence of the working nozzle position (Ld), expansion ratio (n), and acceleration nozzle diameter ratio (Dn) length-to-diameter ratio (Ln) on the ice particle ejection and acceleration was systematically studied. The structural parameters of the ejector were determined using the impact kinetic energy of ice particles as the comprehensive evaluation index, and the surface treatment test was conducted to verify the results. The study shows that under 2 MPa air pressure, the ejector nozzle parameters of n = 1.5, Dn = 4.0, Ld = 4, and Ln = 0 mm can effectively eject and accelerate the ice particles. The aluminum alloy plate depainting test obtained a larger paint removal radius and resulted in a smoother aluminum alloy plate surface, reducing the surface roughness from 3.194 ± 0.489 μm to 1.156 ± 0.136 μm. The immediate preparation and utilization of ice particles solved the problems of adhesion and storage in the engineering application of ice particle air jet technology, providing a feasible technical method in the field of material surface treatment.

Improvement of sand-washing performance and internal flow field analysis of a novel downhole sand removal device

With the progression of many shale gas wells in the Sichuan-Chongqing region of China into the middle and late stages of exploitation, the problem of sand production in these wells is a primary factor influencing production. Failure to implement measures to remove sand from the gas wells will lead to a sharp decline in production after a certain period of exploitation. Moreover, As the amount of sand produced in the well increases, the production layer will be potentially buried by sand. To boost the production of shale gas wells in the Sichuan-Chongqing region and improve production efficiency, a novel downhole jet sand-washing device has been developed. Upon analyzing the device's overall structure, it is revealed that the device adopts a structural design integrating a jet pump with an efficient sand- washing nozzle, providing dual capabilities for jet sand- washing and sand conveying via negative pressure. To enhance the sand- washing and unblocking performance of the device, various sand- washing fluids and the structures of different sand- washing nozzles are compared for selection, aiming to elevate the device's sand- washing and unblocking performance from a macro perspective. Subsequently, drawing on simulation and internal flow field analysis of the device's sand- washing and unblocking process through CFD and the control variable method, it is ultimately found that the length diameter ratio of the cylindrical segment of the nozzle outlet, the outlet diameter, and the contraction angle of the nozzle greatly influence the device's sand- washing and unblocking performance. And the optimum ranges for the length-diameter ratio of the cylindrical segment of the nozzle outlet, the outlet diameter, the contraction angle of the nozzle, and the inlet diameter are 2 to 4, 6 mm to 10 mm, 12° to 16°, and 18 mm and 22 mm, respectively. The findings of the research not only provide new insights into existing sand removal processes but also offer a novel structure for current downhole sand removal devices and a specific range for the optimal size of the nozzle.

Effect of the Nozzle Geometry on Flow Field and Heat Transfer in Annular Jet Impingement

The effects of nozzle shape modifications on the flow phenomena and heat transfer characteristics in annular jet impingement are investigated numerically. The numerical simulations are conducted applying the shear stress transport (SST) k−ω model in the ANSYS CFX. Two modified nozzles: the converging nozzle and the diverging nozzle, are investigated in this study, and the straight nozzle serves as the base case. The geometric parameters and settings are based on an annular jet ejected from an axial fan used for electronic cooling: the Reynolds number Re= 20,000 and the blockage ratio Br=0.35 in the computation, and the target plate is placed at three representative separation distances: H=0.5,2, and 4. Compared with the base nozzle, the converging nozzle can accelerate the cooling flow and promote turbulence to enhance local and overall heat transfer (about 20%) over the target surface. In addition, the converging nozzle reduces the sizes of the recirculation zones, and this promotes the convective heat transfer transport near the axis. The diverging nozzle experiences a similar flow pattern and thermal field as the base nozzle, while the diverging nozzle achieves a slightly lower heat transfer with a pronounced pressure drop reduction. In addition, given that the value of the Nusselt number over the target plate is dependent on the Reynolds number, the simulations are also performed at Re=5000 and 40,000 to establish the correlations between the Nusselt number and the Reynolds number as Nu∝Rem. The value of m varies depending on the nozzle shapes and the separation distances.

Estimation of Reverse Flow Rate in J-Groove Channel of AJP and SCP Models Using CFD Analysis

An annular jet pump (AJP) and a screw centrifugal pump (SCP) are special-purpose pumps used for transportation. The flow fields in the AJP and SCP are like those in a diffuser without and with an impeller, respectively. The flow from diffuser inlet to outlet takes place via the conversion of kinetic energy to static pressure. J-Groove is installed in the diffuser wall of an AJP and SCP to induce reverse flow from the diffuser outlet to the inlet, which suppresses the cavitation. CFD analysis was carried out to verify the conceptual design and understand the internal flow field of an AJP and SCP with J-Groove. The CFD analysis showed that the J-Groove installation in the AJP and SCP improved suction performance. The reverse flow in the J-Groove is due to the pressure difference between the diffuser outlet and the inlet. The numerical analysis results showed that the reverse flow mechanism is dependent on the flow conditions, cavitation number, and presence of the impeller. In a higher flow rate, the reverse flow rate is higher in the AJP model and lower in the SCP model and vice versa. Finally, CFD analysis concluded that the reverse flow rate in J-Groove improves the suction performance of the AJP and SCP models.

Numerical Simulation for the Combustion Chamber of a Reference Calorimeter

This paper focuses on the numerical modeling of the effect of the height of a combustion chamber on the development of a reference calorimeter whose objective is to measure the calorific value of natural gas. The impacts of temperature, velocity, and mass fraction on the exhaust gases were evaluated by varying the height of the combustion chamber. The eddy dissipation concept (EDC) approach was used to model combustion with two different chemical kinetic mechanisms: one with three steps, called the three-step mechanism defined by default in the software used, and second skeletal model, which consists of 41 steps, through the ChemKin-import file with 16 species. The main result of this study is the selection of a combustion chamber height for the reference calorimeter that produces the best performance in the combustion process, which is 70 mm, as well as the main differences in using a three-step mechanism and a skeletal model to simulate an oxy-fuel combustion reaction.