scholarly journals Modeling the Performance of Bi-Textured Micropillar Array as a Wicked Evaporator

2016 ◽  
Author(s):  
Hassan Azarkish ◽  
Amin Behzadmehr ◽  
Luc G. Frechette
Keyword(s):  
Surface Temperature ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pillar Array ◽  
Thin Film Evaporation ◽  
Pillar Arrays ◽  
The Stability ◽  
Micro Pillars ◽  
Evaporation Mechanism

In the present work, the performance of bi-textured micro pillar arrays has been modeled as a wicked evaporator to provide steam flow via the thin film evaporation mechanism. Bi-textured micro pillar evaporator consists of an array with rough hydrophilic pillar bases and smooth hydrophobic tips. Water wicks between the rough hydrophilic sections of the micro pillar array to cover the surface, and vaporizes from the thin films that are formed in the vicinity of the pillar walls. The stability of the phase change mechanism is increased due to the change in direction of the capillary forces at the rough-smooth interface of micro pillars. The experimental results show that the pure evaporation mechanism occurs for a surface temperature above saturation on the bi-textured micro pillar array. The numerical analysis shows that there are optimal micro pillar dimensions for each surface temperature. The evaporation mass flow rate at the optimum dimensions is higher than the pool boiling mass flow rate on a bare surface at the same surface temperature. However, the wicked evaporator performance decreases for larger evaporator sizes.

Control of Self-Excited Oscillations in Centrifugal Blowers

2007 ◽  
Author(s):  
Saad A. Ahmed
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Industrial Applications ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Flow Area ◽  
The Stability

Centrifugal compressors or blowers are widely used in many industrial applications. However, the operation of such systems is limited at low-mass flow rates by self-excited flow instabilities which could result in rotating stall or surge of the compressor. These instabilities will limit the flow range in which the compressor or the blower can operate, and will also lower their performance and efficiency. Experimental techniques were used to investigate a model of radial vaneless diffuser at stall and stall-free operating conditions. The speed of the impeller was kept constant, while the mass flow rate was reduced gradually to study the steady and unsteady operating conditions of the compressor. Additional experiments were made to investigate the effects of reducing the exit flow area on the inception of stall. The results indicate that the instability in the diffuser was successfully delayed to a lower flow coefficient when throttle rings were attached to either one or both of the diffuser walls (i.e., to reduce the diffuser exit flow area). The results also showed that an increase of the blockage ratio improves the stability of the system (i.e., the critical mass flow rate could be reduced to 50% of its value without blockage). The results indicate that the throttle rings could be an effective method to control stall in radial diffusers.

Free Convection Between Series of Vertical Parallel Plates With Embedded Line Heat Sources

1991 ◽  
Vol 113 (1) ◽  
pp. 108-115 ◽  
Author(s):  
S. H. Kim ◽  
N. K. Anand ◽  
L. S. Fletcher
Keyword(s):  
Boundary Condition ◽  
Nusselt Number ◽  
Surface Temperature ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Parallel Plates ◽  
Cold Surface ◽  
Maximum Increase ◽  
Hot Surface

Laminar free convective heat transfer in channels formed between series of vertical parallel plates with an embedded line heat source was studied numerically. These channels resemble cooling passages in electronic equipment. The effect of a repeated boundary condition and wall conduction on mass flow rate (M), maximum surface temperature (θh,max and θc,max), and average surface Nusselt number (Nuh and Nuc) is discussed. Calculations were made for Gr*=10 to 106, K=0.1, 1, 10, and 100, and t/B=0.1 and 0.3. The effect of a repeated boundary condition decreases the maximum hot surface temperature and increases the maximum cold surface temperature. The effect of a repeated boundary condition with wall conduction increases the mass flow rate. The maximum increase in mass flow rate due to wall conduction is found to be 155 percent. The maximum decrease in average hot surface Nusselt number due to wall conduction (t/B and K) occurs at Gr*=106 and is 18 percent. Channels subjected to a repeated boundary condition approach that of a symmetrically heated channel subjected to uniform wall temperature conditions at K≥100.

scholarly journals Modelling Bubble Lifetime of Thin Film Surfactants Solution on Fuel Spillage

2021 ◽  
pp. 20-33
Author(s):  
Shitakha Felistus ◽  
Kimathi George ◽  
Songa Caroline
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rate Change ◽  
Eastern Africa ◽  
Maximum Lifetime ◽  
Catholic University ◽  
Fluid Properties ◽  
Flow Rate Change ◽  
The Stability

Aims / Objectives: To find the lifetime of the bubble by plotting the rate of mass flow rate change against time. Place and Duration of Study: Department of Mathematics and Applied Science, Catholic University of Eastern Africa, Nairobi, Kenya, between February 2020 and March 2021. Methodology: The maximum lifetime of the bubble is assumed to match the time when the mass flow rate change is zero. The study also assumes the velocity of flow rate and other fluid properties at the interface of fuel-surfactant constant other than Re. Re is varied from 0.01 to 100. Results: The graphical plots show that for Re ! 1, and Re " 1, the stability depends on diffusive viscosity and linearized convection, respectively. The simulation suggested that the bubble formed at the fuel-surfactant interface may have Re “ 1 and its lifetime is tb » 0.28. Conclusion: The lifetime of surfactant depends on Re while assuming other interface properties constant. Recommendation: Future studies in the area need to consider the effect of variation in temperature, velocity, and Reynolds number in determining the lifetime of a bubble in the thin foam of the surfactant-fuel interface.

Flow Fields, Emission and Stabilization in Premixed Centrally-Staged Swirl Flames With Different Air Split Ratios

2021 ◽  
Author(s):  
Tong Su ◽  
Yuzhen Lin ◽  
Chi Zhang ◽  
Xiao Han
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Flow Fields ◽  
Design Stage ◽  
Air Mass ◽  
Split Ratio ◽  
Flame Structures ◽  
The Stability

Abstract The flow fields, emission levels, and static stability characteristics were investigated experimentally under various air split ratios (ASR, the ratio of the pilot stage air mass flow rate to the total air mass flow rate) at a fixed equivalence ratio of 0.8 of both main and pilot stages in a premixed centrally-staged swirl flame. The flame structures were captured by a CH* chemiluminescence high-speed camera and the corresponding results were processed by Abel deconvolution. Besides, the flow fields obtained by using planar Particle Image Velocimetry (PIV) technique were combined with flame structures to make a better study on the aerodynamic structures of the centrally-staged swirl flames. The emission levels of NOx and CO were measured by a gas analyzer. The stability boundaries and flame structures at different equivalence ratios under three ASRs were also studied. It is found that the size of the reacting primary recirculation zone (PRZ) becomes larger as more air is distributed to the pilot stage. This can be explained by the fact that the majority of the pilot fluid participates in the formation of the PRZ and also as a result of a stronger penetrability of the pilot jet. Moreover, the NOx emission levels increase while CO levels decrease, which is because of the longer residence time of the radicals within a larger PRZ and less impingement of the main flame on the combustor liner. Finally, the stability boundary is extended, and the total blowout equivalence ratio was decreased as the air split ratio increases, which demonstrates the flame stabilization effect of the pilot flame. In brief, the above findings can be a help to choose the appropriate air split ratio in the early design stage of the centrally-staged aero-engine combustors.

Safety Analyses of the Lead-Bismuth Eutectic Cooled Accelerator Driven System XT-ADS

2010 ◽  
Author(s):  
Xue-Nong Chen ◽  
Danilo D’Andrea ◽  
Claudia Matzerath Boccaccini ◽  
Werner Maschek
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equation Model ◽  
Safety Code ◽  
Driven System ◽  
Damped Oscillation ◽  
Set Up ◽  
The Stability ◽  
Flow Blockage

Safety analyses for the XT-ADS were performed with the reactor safety code SIMMER-III. Besides a brief description of the numerical model, three typical transients are presented in this paper, namely, the unprotected loss of flow (ULOF), unprotected transient over-current (UTOC), and the unprotected coolant flow blockage accident (UBA). Because of the important phenomenon of mass flow rate undershooting in the ULOF case, an integral equation model was set up for a further theoretical study of ULOF. The model confirms the numerical simulation results for various cases and gives a deeper understanding of this phenomenon. The faster the pump shut down, the larger is the undershooting of the mass flow rate. On the other hand a larger coolant cold leg area leads to a weaker undershooting. The stability analysis shows that the natural convection state is in the region of the damped oscillation for the current XT-ADS design.

scholarly journals A Study on Developing an Automatic Controller with an Inverter Collector Pump for Solar-Assisted Heating System

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2128
Author(s):  
Le Minh Nhut ◽  
Youn Cheol Park
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Variable Mass ◽  
Heating System ◽  
Input Module ◽  
Embedded Controller ◽  
Useful Heat Gain ◽  
Variable Mass Flow ◽  
The Stability

In this study, based on the optimal equation m = 0.05 Δ T A c (kg/min) of the variable mass flow rate in the collector loop, an automatic controller with an inverter collector pump for the collector loop of the solar-assisted heating system is designed for these experiments and to then be used for real industry. The pump for the collector loop is an inverter type that is controlled by an embedded controller with Windows, based on C# language, and the change of speed depends on the variation of the mass flow rate through the collector loop. The input of the automatic controller with an inverter collector pump is given by a thermocouple input module that is connected to the embedded controller with the RS-485 communication protocol. In this work, the experiments were carried out on three different days, namely a clear day, an intermittently cloudy day and an overcast day, to evaluate the stability and the precision of the automatic controller, as well as the contribution of the useful heat gain from the collector for the solar-assisted heating system. Simulation and experimental results are also validated and analyzed.

Numerical Research on Performance of AP1000 Passive Containment Cooling System Without Falling Film

2013 ◽  
Author(s):  
Hui Wang ◽  
Qiang Guo ◽  
Qiaoyan Chen
Keyword(s):  
Natural Convection ◽  
Thermal Radiation ◽  
Surface Temperature ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Environmental Temperature ◽  
Cooling System ◽  
Heat Removal ◽  
Falling Film

Passive Containment Cooling System (PCS) is one of the most important passive safety features in AP1000 nuclear power plant. Numerical Simulation of PCS without falling film was conducted using CFD method in this paper to investigate heat transfer performance of PCS. The results indicate that: at the time of 72 hours after break accident, there is no water in passive containment cooling water storage tank (PCCWST), PCS cannot completely remove reactor core decay heat to environment just with the effect of natural convection and thermal radiation; mass flow rate of natural convection and PCS heat removal power increase with the increase of the outside surface temperature of steel containment, but the increasing amplitude of the former is smaller than the latter significantly, and the fraction of thermal radiation in the PCS heat removal power is the smallest when the outside surface temperature of steel containment is 80 °C; mass flow rate of natural convection and PCS heat removal power decrease with the increase of environmental temperature, while the fraction of thermal radiation in the whole heat removal power becomes bigger with the increase of environmental temperature.

The standard unit mass flow rate of gas-liquid mixtures

2020 ◽  
pp. 13-16
Author(s):  
V.N. Petrov ◽  
◽  
V.F. Sopin ◽  
L.A. Akhmetzyanova ◽  
Ya.S. Petrova ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Liquid Mixtures ◽  
Unit Mass ◽  
Standard Unit

Prediction of Leakage Mass Flow Rate Through Gas Springs

1987 ◽  
Author(s):  
Roberto Bruno Bossio ◽  
Vincenzo Naso ◽  
Marian Cichy ◽  
Boleslaw Pleszewski
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate
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