scholarly journals Geometric optimization of cross-flow heat exchanger based on dynamic controllability

2008 ◽  
Vol 12 (3) ◽  
pp. 75-84
Author(s):  
Sorour Alotaibi ◽  
Asad Alebrahim
Keyword(s):  
Aspect Ratio ◽  
Mass Flow ◽  
Numerical Solutions ◽  
Cross Flow ◽  
Internal Flow ◽  
Geometric Optimization ◽  
Transient Model ◽  
The Face ◽  
Mass Flow Rates ◽  
Water Mass Flow Rate

The operation of heat exchangers and other thermal equipments in the face of variable loads is usually controlled by manipulating inlet fluid temperatures or mass flow rates, where the controlled variable is usually one of the output temperatures. The aim of this work is to optimize the geometry of a tube with internal flow of water and an external cross-flow of air, based on its controllability characteristics. Controllability is a useful concept both from theoretical and practical perspective since it tells us if a particular output can be controlled by a particular input. This concept can also provide us with information about the easiest operating condition to control a particular output. A transient model of a tube in cross-flow is developed, where an implicit formulation is used for transient numerical solutions. The aspect ratio of the tube is optimized, subject to volume constraints, based on the optimum operation in terms of controllability. The reported optimized aspect ratio, water mass flow rate and controllability are studied for deferent external properties of the tube.

Numerical Investigation of Local Cooling Enhancement Using Pin-Finned Channel With Incremental Impingement

2017 ◽  
Author(s):  
Susheel Singh ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Aspect Ratio ◽  
Mass Flow ◽  
Cross Flow ◽  
Surface Cooling ◽  
Local Cooling ◽  
Stagnation Region ◽  
Flow Rates ◽  
Pin Fins ◽  
Mass Flow Rates ◽  
The Impact

Flow and heat transfer in a low aspect ratio pin-finned channel, representative of an internally cooled turbine airfoil, is investigated using Large Eddy Simulations (LES). To achieve greater control of surface cooling distribution, a novel approach has been recently proposed in which coolant is injected incrementally through a series of holes located immediately behind a specially designed cutout region downstream of the pin-fins. Sheltering the coolant injection behind the pin-fins avoids the impact of the cross-flow buildup that deflects the impingement jet and isolates the surface from cooling. The longitudinal and transverse spacing of the pin-fins, arranged in a staggered fashion, is X/D = 1.046 and S/D = 1.625, respectively. The aspect ratio (H/D) of pin-fin channel is 0.5. Due to the presence of the sequential jets in the configuration, the local cooling rates can be controlled by controlling the jet-hole diameter which impacts the jet mass flow rate. Hence, four different hole diameters, denoted as Large (L), Medium (M) , Small (S), Petite (P) are tested for impingement holes, and their effects are studied. Several patterns of the hole-size distributions are studied. It is shown that the peak Nusselt number in the stagnation region below the jet correlates directly with the jet-velocity, while downstream the Nusselt numbers correlate with the total mass flow rates or the average channel velocity. The local cooling parameter defined as (Nu/Nu0)(1-ε) correlates with the jet/channel mass flow rates.

Mixing of Dry Air With Water-Liquid Flowing Through an Inverted U-Tube for Power Plant Condenser Applications

2019 ◽  
Author(s):  
Khaled Yousef ◽  
Ahmed Hegazy ◽  
Abraham Engeda
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Water Mass ◽  
Air Entrainment ◽  
Air Mass ◽  
Operational Conditions ◽  
Dry Air ◽  
Mass Flow Rates ◽  
Water Mass Flow Rate

Abstract This paper presents a Computational Fluid Dynamic (CFD) simulation for dry air/water-liquid and two-phase flow mixing in a vertical inverted U-tube using the mixture multiphase and turbulence models. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in dry air/water-liquid flow in the inverted U-tube. Water flows through the inverted U-tube while the dry air is entrained using the side-tube installed after the water flow downward. The inverted U-tube is tested at water mass flow rates of 2,4,6 and 8 kg/s, air mass flow rates, 0.000614–0.02292 kg/s, with dry air volume fractions 0.2–0.9. The obtained results are compared with the experimental data for model validation and the present CFD model is able to give an acceptable agreement. Also, the results show that, at water mass flow rate of 2 kg/s, there are vortices and turbulent intensity disturbances are noticed at the inverted U-tube higher part, which refers to an air entrainment occurrence from the side-tube. Theses disturbances starts to be stabilized at air mass flow rate around 0.00736 kg/s and air volume fraction, αa = 0.75. This means, if the air mass flow rate increases above this limit, the air entrainment may be blocked. On the other side, at water mass flow rate of 4 kg/s, there are little noticed disturbances until air mass flow rate of 0.00368 kg/s and αa = 0.43 and thereafter stabilized. After this point for water mass flow rate of 4 kg/s, increasing air mass flow rate may block the water flow and the whole inverted U-tube system possible stop flowing. Therefore, this study is able to estimate the required operational conditions and mass ratios for stable air entrainment process. Beyond these operational conditions, air entrainment may be blocked and the whole system discontinues its normal induced gravitational flow. In addition, this study proves that the inverted U-tube is able to generate a vacuum pressure up to 53.382 kPa based on the present geometrical configuration. This generated low-pressure by the inverted U-tube can be used for engineering applications which are working under vacuum and need continuous evacuating form the dry air and non-condensable gases. Furthermore, these findings motivate the utilizing of inverted U-tube for the air evacuation purposes for less power consuming in power plants.

Internal Flow and Noise Investigations About the Cross-Flow Fan With Different Blade Angles

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Hua Ouyang ◽  
Jie Tian ◽  
You Li ◽  
Zhiming Zheng ◽  
Zhaohui Du
Keyword(s):  
Relative Velocity ◽  
Numerical Solutions ◽  
Cross Flow ◽  
Internal Flow ◽  
Flow Patterns ◽  
Far Field ◽  
Noise Characteristics ◽  
Aerodynamic Performances ◽  
Field Noise ◽  
Cross Flow Fan

The experimental and numerical studies have been carried out to investigate the flow and the noise characteristics of the three impellers with different blade angles in a cross-flow fan (CFF). First, the aerodynamic performances of the fan with these impellers are obtained experimentally, and the averaged flow patterns inside the impellers are measured by the three-hole probe. Second, the far-field noise generated by CFF with different impellers has been measured in a semianechoic chamber under different throttling conditions. Third, the two-dimensional unsteady CFD simulations have been performed by commercial software. The internal flow patterns influenced by the different blade angles have been summarized through the computational results. The accuracy of the calculations is validated by the corresponding experimental ones. The detail analysis has been carried out on the unsteady vortex flow properties of the three impellers, which is considered to be the main factor that influences the aerodynamic and aeroacoustic performance of the CFF. Finally, the relative far field noise generated by different impellers are evaluated by an empirical formula based on the assumption that the total sound pressure levels are proportional to the sixth power law of the relative velocity on the outer and inner circumferences of the impeller. The circumferential distributions of relative velocity are provided from the numerical solutions. The varying trends of predicted results agree well with the actual relative noise of the CFF with three different impellers.

Experimental Studies of Rotation Efficiency of Packing on Characteristics of Counter Flow Wet Cooling Tower

2014 ◽  
Author(s):  
Khashayar Teimoori ◽  
Ali M. Sadegh
Keyword(s):  
Mass Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
Water Mass ◽  
Water Flow Rate ◽  
Experimental Studies ◽  
Counter Flow ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Water Mass Flow Rate

Packing in cooling towers is commonly used in nuclear power plants and air conditioning systems. However their efficiency with respect to the inlet air flow rate and the temperature of the water has not been fully investigated. In this research, the efficiency of packing rotational speed with respect to the wet counter flow of a cooling tower is experimentally investigated. In our experimental studies, six elliptical wooden plates that are equally spaced are used as a packing tower. The packing area of 0.85 m2 is considered with the following rotor speed ranges: 0.5, 3.5, 10, 15 and 17 rpm. It is assumed that the water mass flow rate is proportional to the inlet air to the tower. Six mass flow rates starting from 0.2 to 2.8 kg/h and the inlet air and water temperatures of 27°C and 45°C, respectively, are considered. The results illustrate that for the range of 0 to 5 rpm of the packing rotational speed the cooling rate of water is increased 3% for the water flow rate of 2.8 kg/h, and 24% for the water flow rate of 0.4 kg/h. Additionally, as a result of the increased rotational speed from 5 to over 17 rpm the cooling rate at both maximum and minimum water mass flow rates are increased from 13.9 to 34.4 percent, respectively. Furthermore, the water outlet temperature is reduced from 8.6°C to 3.3°C in the least and the most mass flow rates leading to the increased speed from 5 to 17 rpm, respectively. The experimental relationship between the inlet air temperature and the rotational speed of the packing has been determined. Also, the inlet water temperature at the maximum flow rate has been decreased to 3.4 and at the least water mass flow rate it has been decreased to 29 percent for the range of rotational speed from 5 to over 17 rpm of the packing rotation. All the results are depicted in several curves to show the actual variations of the variables.

Internal Flow and Noise Investigations About the Cross-Flow Fan With Different Blade Angles

2010 ◽  
Author(s):  
You Li ◽  
Hua Ouyang ◽  
Jie Tian ◽  
Zhiming Zheng ◽  
Zhaohui Du
Keyword(s):  
Relative Velocity ◽  
Numerical Solutions ◽  
Cross Flow ◽  
Internal Flow ◽  
Flow Patterns ◽  
Far Field ◽  
Numerical Studies ◽  
Aerodynamic Performances ◽  
Field Noise ◽  
Cross Flow Fan

The experimental and numerical studies have been carried out to investigate the flow and the noise characters of the three impellers with different blade angles in a cross-flow fan (CFF). Firstly, the aerodynamic performances of the fan with these impellers are obtained experimentally and the averaged flow patterns inside the impellers are measured by the three-hole probe. Secondly, the far-field noise generated by CFF with different impellers has been measured in a semi-anechoic chamber under different throttling conditions. Thirdly, the two-dimensional unsteady CFD simulations have been performed by commercial software. The internal flow patterns influenced by the different blade angles have been summarized through the computational results. The accuracy of the calculations is validated by the corresponding experimental ones. The detail analysis has been carried out on the unsteady vortex flow properties of the three impellers, which is considered to be the main factor that influences the aerodynamic and aeroacoustic performance of the CFF. Finally, the relative far field noise generated by different impellers are evaluated by an empirical formula based on the assumption that the total sound pressure levels are proportional to the sixth power law of the relative velocity on the outer and inner circumferences of the impeller. The circumferential distributions of relative velocity are provided from the numerical solutions. The varying trends of predicted results agree well with the actual relative noise of the CFF with three different impellers.

Parametric Study of the Frequency of Bubble Formation at a Single Orifice With Liquid Cross-Flow

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Miguel A. Balzan ◽  
Franz Hernandez ◽  
Carlos F. Lange ◽  
Brian A. Fleck
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Liquid Velocity ◽  
Bubble Formation ◽  
Cross Flow ◽  
Average Frequency ◽  
Jet Breakup ◽  
Mass Flow Rates ◽  
Experimental Values ◽  
Processing Techniques

The bubble formation frequency from a single-orifice nozzle subjected to the effects of a crossflowing liquid was investigated using high-speed shadowgraphy, combined with image analysis and signal processing techniques. The effects of the nozzle dimensions, orientation within the conduit, liquid cross-flow velocity, and gas mass flow rate were evaluated. Water and air were the working fluids. Existing expressions in the literature were compared to the experimental values obtained. The expressions showed modest agreement with the experimental mean average frequency magnitude. It was found that increasing the gas injection diameter could decrease the bubbling frequency approximately 12% until reaching a certain value (0.52 mm). Further increasing the nozzle dimensions increase the frequency by around 20%. Bubbling frequency is more sensitive to the liquid velocity where changes up to 63% occurred when the velocity was raised from 3.1 to 4.3 m/s. Increasing gas mass flow rates decreased the gas jet breakup frequency in all cases. This phenomenon was primarily attributed to changes in the bubbling mode from discrete bubbling to pulsating and jetting modes. The nozzle orientation plays a role in modifying the bubbling frequency, having a higher magnitude when oriented against gravity.

scholarly journals Numerical Investigation of Transient Flow Characteristics in a Centrifugal Compressor Stage with Variable Inlet Guide Vanes at Low Mass Flow Rates

Energies ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7906
Author(s):  
Shuai Li ◽  
Yan Liu ◽  
Mohammad Omidi ◽  
Chuang Zhang ◽  
Hongkun Li
Keyword(s):  
Mass Flow ◽  
Low Frequency ◽  
Internal Flow ◽  
Aerodynamic Performance ◽  
Compressor Stage ◽  
Unstable Flow ◽  
Flow Rates ◽  
Inlet Guide Vanes ◽  
Mass Flow Rates ◽  
Low Mass

This study numerically investigates the beneficial effects of positive pre-swirl on the aerodynamic performance and internal flow field in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) at low mass flow rates. Four positions of VIGV are considered, including 0°, 30°, 45°, and 60° angle. The latter three positions of VIGV induce positive pre-swirl. Numerical results show that as positive pre-swirl increases, the aerodynamic performance curve of the stage moves in the low mass flow rate direction. In the three cases of positive pre-swirl, there was an improvement of approximately 9.95% of stall/surge margin greater than in conditions with no pre-swirl. The regulation of IGV can effectively improve the unstable flow of the compressor stage at low mass flow rates. A low frequency that has a great influence on the internal flow of the compressor stage is found, and the unstable flow caused by low frequency is analyzed by the combination of streamline distribution, spectrum analysis, vector, entropy increase, and modal decomposition method. Meanwhile, the modal decomposition method and flow field reconstruction techniques are used to investigate the coherent flow structures caused by low frequency under different guide vane openings.

Applications of Performance Tables on Steady State Analysis of Multipass Parallel Cross Flow Heat Exchanger

2017 ◽  
Vol 28 ◽  
pp. 53-72
Author(s):  
Karthik Silaipillayarputhur ◽  
Ali Al-Saif ◽  
Musab Al-Otaibi
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Exchanger ◽  
Mass Flow ◽  
Thermal Performance ◽  
Rate Ratio ◽  
Cross Flow ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Operational Phase

In this paper, steady state sensible performance analysis on multi pass parallel cross flow exchanger was considered. The inputs to the heat exchanger were described through meaningful physically significant parameters such as number of transfer units, capacity rate ratio and dimensionless input temperature. The inputs to the heat exchager were varied systematically and a parametric study was conducted to determine the thermal performance at each individual pass of the heat exchanger. Heat exchanger’s thermal performance was described through the discharge temperatures that were expressed in a dimensionless form. The results from the study were presented in the form of performance tables. The performance tables employed meaningful and industry recognized dimensionless input parameters and the heat exchanger‘s performance was described through dimensionless discharge temperatures at every pass of the heat exchanger. The developed performance tables shall serve two critical aspects. First, it will help the heat exchanger designers to readily choose an optimum heat exchanger. An undersized heat exchanger shall not deliver the requirements and likewise an oversized heat exchanger shall add unnecessary weight and cost. This aspect was clearly observed in this study as indefinetly increasing the number of transfer units (or surface area) beyond a threshold value didn’t enhance the heat transfer. By employing the performance tables as a guide, the heat exchanger designers can quickly ascertain the performance of the heat exchanger without having to perform simulations and/or lengthy calculations. Second, during operational phase of the heat exchanger, the performance tables can be used to understand the performance variation of the heat exchanger with respect to mass flow rates and/or can help the engineers to choose appropriate mass flow rates for the required heat transfer. The highest heat exchanger performance was observed at the lowest capacity rate ratio and likewise the lowest heat exchanger performance was observed at the highest capacity rate ratio. In-addition, during the operational phase, the performance tables can help to detect an underperforming heat exchanger and can help the engineers to schedule maintenance activity on the heat exchanger equipment.

Study of Fully Developed Incompressible Flow in Curved Ducts, Using a Multi-Grid Technique

1987 ◽  
Vol 109 (3) ◽  
pp. 226-236 ◽  
Author(s):  
K. N. Ghia ◽  
U. Ghia ◽  
C. T. Shin
Keyword(s):  
Cross Sections ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Cross Flow ◽  
Internal Flow ◽  
Navier Stokes ◽  
Dean Number ◽  
Similarity Parameter ◽  
Fine Grid ◽  
Curved Ducts

Fully developed flows inside curved ducts of rectangular as well as polar cross sections have been analyzed using the Navier-Stokes equations in terms of the axial velocity and vorticity and the cross-flow stream function. Numerical solutions of the three second-order coupled elliptic partial differential equations governing this flow have been obtained using efficient numerical schemes. For curved-duct flows, the similarity parameter of significance is the Dean number K, rather than the Reynolds number Re. Results have been obtained for curved ducts with square cross sections for K up to 900 which, in the present study, corresponds to Re = 9,000 for this internal flow configuration. The fine-grid calculations show that, for square cross-section ducts, Dean’s instability occurs at K ≈ 125 and, further, that this phenomenon does not disappear even for K = 900. In ducts of polar cross sections, which are geometrically more representative of turbomachinery cascade passages, the phenomenon of Dean’s instability is not seen to occur for K up to 600.

Experimental Study of the Diversion Crossflow Caused by Subchannel Blockages. Part I: Experimental Procedures and Mass Flow Rates in the Channels

1984 ◽  
Vol 106 (4) ◽  
pp. 435-440 ◽  
Author(s):  
S. Genc¸ay ◽  
A. Tapucu ◽  
N. Troche ◽  
M. Merilo
Keyword(s):  
Experimental Study ◽  
Mass Flow ◽  
Short Distance ◽  
Cross Flow ◽  
Geometric Parameters ◽  
Slow Process ◽  
Hydrodynamic Behavior ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Different Shapes

In this research, the hydrodynamic behavior of two laterally interconnected channels with blockages in one of them has been studied experimentally. For blockages of different shapes and severities, the mass flow rates as well as the pressures in the channels upstream and downstream of the blockage were determined. The experiments were conducted on a test sections which consists of two-square channels separated by an intermediate plate with slots of different geometric parameters. Two types of blockages have been considered: plate and smooth. The shape of the smooth blockage was a cosine. In the region upstream of the blockage, the diversion cross-flow takes place over a relatively short distance. Downstream of the blockage, the recovery of the diverted flow by the blocked channel is a slow process and the rate of this recovery worsens with increasing blockage severity. For a given blockage rate, the diversion crossflow caused by a smooth blockage is smaller than that of a plate blockage.

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