Experimental Research on Heat Transfer Characteristics of CuO Nanofluid in Adiabatic Condition

The laminar convective heat transfer behavior of CuO nanoparticle dispersions in glycol with the average particle sizes (about 70 nm) was investigated experimentally in a flow loop with constant heat flux. To enhance heat exchange under high temperature condition and get the more accurate data, we try to improve the traditional experimental apparatus which is used to test nanofluid heat transfer characteristics. In the experiment five different nanoparticle concentrations (0.25%, 0.50%, 0.80%, 1.20%, and 1.50%) were investigated in a flow loop with constant heat flux. The experimental results show that the heat transfer coefficient of nanofluid becomes higher than that of pure fluid at the same Reynolds number and increased with the increasing of the mass fraction of CuO nanoparticles. Results also indicate that at very low volume concentrations nanofluid has no major impact on heat transfer parameters and the pressure of nanofluids increased by the mass fraction increase

DYNAMIC ANALYSIS OF HDRB ISOLATED BRIDGES BASED ON SIMPLIFIED MECHANICAL MODEL

High damping rubber bearing（ HDRB） as a kind of isolation bearing has the functions like bearing capacity,restoring force and damping（ energy absorption）. In this paper,a regular continuous girder bridge isolated with high damping rubber bearings was taken as a research object. A simplified Two Degrees of Freedom mechanical model was established in Opensees software,and compared with the FEM model established in SAP2000 to study the feasibility and accuracy of the simplified mechanical model. The results show that the response amplitude of the isolation bridge can be accurately calculated by the simplified mechanical model. Under the same seismic waves,the analysis results obtained from the simplified mechanical model meet the engineering accuracy and agree with the FEM model

Research and practice of the impulse sand fracturing technology

With the deep development of tight sand gas reservoirs, problems such as short stable production period and quick production decline of gas wells after fracturing have become increasingly prominent. Consequently, there is an increasing demand for the effective penetration and conductivity of artificial fractures. Impulse sand fracturing technology introduces a concept of discrete multilayer sanding inside fractures; joint application of pulse blender which can be switched at high frequency, intensive multi-cluster perforation and special fibrous material made it possible to ensure the flow stability of proppant slug, and placement of nonuniformly-laid sand pinnacles and grooves, which markedly upgraded the capacity of the fracture conductivity to several orders of magnitude more than the conventional method. Laboratory engineering simulation evaluation and field test show that pre-fracturing reservoir evaluation, pulse time design and the optimization of degradable fiber and support equipment are the keys to the success of impulse sand fracturing. Compared with the conventional fracturing, this technique can effectively increase well production, decrease the volume of fracturing proppant, and lower sand plugging risks. An independent sand fracturing pilot test has been conducted in 6 layers of 3 wells for the first time in Block Tao 7 of the Sulige Gasfield, Ordos Basin, as a result, the average volume of fracturing proppant dropped by 28.3%, the average sand intensity dropped by 21.88%, and the post-fracturing average daily gas output increased by 26.8%. This technology provides an efficient and environmentally friendly reservoir stimulation option for tight sand gas reservoirs in China

Fault Diagnosis Algorithm Based on Adjustable Nonlinear PI State Observer and Its Application in UAV Fault Diagnosis

Aiming at the problem of fault diagnosis in continuous time systems, a kind of fault diagnosis algorithm based on adaptive nonlinear proportional integral (PI) observer, which can realize the effective fault identification, is studied in this paper. Firstly, the stability and stability conditions of fault diagnosis method based on the PI observer are analyzed, and the upper bound of the fault estimation error is given. Secondly, the fault diagnosis algorithm based on adjustable nonlinear PI observer is designed and constructed, it is analyzed and we proved that the upper bound of fault estimation under this algorithm is better than that of the traditional method. Finally, the L-1011 unmanned aerial vehicle (UAV) is taken as the experimental object for numerical simulation, and the fault diagnosis method based on adaptive observer factor achieves faster response speed and more accurate fault identification results

Following Consistency of Energy-Saving Operation for Urban Rail Trains Based on Event Triggering Mechanism

To reduce the traction energy consumption of urban rail trains by regenerating energy, a train traction and braking model was designed based on algebraic graph theory and train dynamics theory and the following consistency model of energy-saving operation of urban rail trains was constructed based on the conditions of the coordination coefficient and the operating condition conversion of trains. Not only to constantly update the consistency controller and save communication resources but also to optimize the energy-saving effect, the consistency algorithm of event triggering was used to search for the optimal operating conditions of trains and the energy-saving operation scheme for multiple trains was established. Taking the train diagram of a subway line in Jinan as an example, the energy-saving control scheme of four trains was solved by MATLAB simulation. The simulation results show that the model can not only ensure parking accuracy and punctuality but also energy savings effectively; that is, the proportion of the total regenerative energy used by the follower train in the actual energy consumption is increased from 3.32% to 10.76%, and the actual total energy consumption of the train is reduced by 9.23%

Numerical Analysis of Fluid Flow and Heat Transfer in Micro-Channel Heat Sinks with Double-Layered Complex Structure

Micro-channel heat sink (MCHS) has been extensively used in various electronic cooling fields. Double-layered MCHS, or DL-MCHS, is regarded as one effective technique for high-heat-flux transfer and is expected to meet the ever-increasing heat load requirement of future electronic device generations. In order to improve the cooling capacity, two new types of the MCHS, with a double-layered matrix structure (DL-M) and double-layered interlinked matrix structure (DL-IM) are proposed and investigated numerically. The two designs are compared with the traditional double-layered rectangular structure (DL-R) and the double-layered triangular structure (DL-T). Different properties of the heat sink are investigated to assess the overall heat transfer performance, for which coolant flow and heat transfer are both evaluated. The numerical results reveal that the periodical slot subchannel in the matrix has a significant effect on fluid flow for heat transfer. In comparison to the DL-R and the DL-T, the DL-M and DL-IM realize a much lower pressure drop and temperature rise at the base surface and also have higher Nusselt number and secondary flow intensity, therefore, manifesting better overall thermal performance. In the DL-M and DL-IM, the coolant flows along the periodical subchannel in one layer and is redirected into the second layer with vortices being induced. The vortices promote the coolant mixing and enhance the mass and heat transfer. These geometric design strategies can provide references for wide heat sink applications

Application of zipper-fracturing of horizontal cluster wells in the Changning shale gas pilot zone, Sichuan Basin

After several years of exploration practices in the Changning-Weiyuan national shale gas pilot zone, the industrial production has been achieved in a number of vertical and horizontal wells completed by SRV fracturing, and a series of independent shale gas reservoir stimulation technologies have come into being. Next, it is necessary to consider how to enhance the efficiency of fracturing by a factory-mode operation. This paper presents the deployment of Changning Well Pad A, the first cluster horizontal shale gas well group, and proposes the optimal design for the factory operation mode of this Pad according to the requirements of wellpad fracturing stimulation technologies and the mountainous landform in the Sichuan Basin. Accordingly, a zipper-fracturing mode was firstly adopted in the factory fracturing on wellpad. With the application of standardized field process, zipper operation, assembly line work, staggered placement of downhole fractures, and microseismic monitoring in real time, the speed of fracturing reached 3.16 stages a day on average, and the stimulated reservoir volume was maximized, which has fully revealed how the factory operation mode contributes to the large-scale SRV fracturing of horizontal shale gas cluster wells on wellpads in the aspect of speed and efficiency. Moreover, the fracturing process, operation mode, surface facilities and post-fracturing preliminary evaluation of the zipper-fracturing in the well group were examined comprehensively. It is concluded from the practice that the zipper-fracturing in the two wells enhanced the efficiency by 78% and stimulated reservoir volume by 50% compared with the single-well fracturing at the preliminary stage in this area

Stereotactic body radiotherapy versus radiofrequency ablation for hepatocellular carcinoma: a systematic review and meta-analysis

Purpose To compare the efficacy and safety of stereotactic body radiotherapy (SBRT) with radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC). Materials and methods PubMed, MedLine, EMBASE, the Cochrane Library and Web of Science were searched to identify potentially eligible studies comparing the efficacy and safety of SBRT with RFA for HCC from January 1990 to May 2020. Hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (CIs) were used to determine the effect size for overall survival (OS), local control (LC) and complications. Results Seven studies including 7928 patients were enrolled in this meta-analysis. The results showed that SBRT was not inferior to RFA based on the pooled HR for OS (HR = 1.09, 95%CI = 0.78–1.52, p = .62); however, the pooled HR for the LC rate showed the superiority of SBRT (HR = 0.54, 95%CI = 0.35–0.84, p = .006). Subgroup analysis showed that the pooled HR for the LC rate favored SBRT in patients with tumors sized >2 cm (HR = 0.41, 95%CI = 0.23–0.74, p = .003), but no significant difference was observed in patients with tumors sized ≤2 cm (HR = 0.56, 95%CI = 0.25–1.28, p = .17). In addition, no significant differences in the incidence of late severe complications were observed between the SBRT and RFA groups (OR = 1.01, 95%CI = 0.59–1.73, p = .97). Conclusions Based on the current data, we concluded that SBRT was well tolerated with an OS equivalent to that with RFA; SBRT was superior to RFA in terms of LC of HCC, especially in those with tumors sized >2 cm