Thermal Stratification in Spherical Tanks

2014 ◽  
Author(s):  
Fahad Khan ◽  
Brian J. Savilonis
Keyword(s):  
Reynolds Number ◽  
Froude Number ◽  
Parametric Study ◽  
Richardson Number ◽  
Storage System ◽  
Discharge Process ◽  
Flow Parameters ◽  
Spherical Tank ◽  
Proportional Decrease ◽  
Tank Diameter

Spherical tanks have the potential for cost reduction in sensible thermal energy storage (TES) systems, by using less tank building material and insulation. The current CFD study compares the Thermal Efficiency (TE) of a thermocline storage system in a spherical tank to a cylindrical tank of the same volume. A parametric study is then performed on a spherical tank during the discharge process to determine the flow parameters that govern the thermocline formation and entrainment. The following parameters are used: tank diameter to inlet diameter ratio D/d = 10, inlet velocity (0.02–0.1 m/s), and ΔT (10–70° C), leading to an inlet Froude number (0.4–3), inlet Reynolds number (500–7500), and tank Richardson number (2–100). The results show a significant correlation between the inlet Reynolds and inlet Froude numbers, and the tank TE, in addition to a weak correlation between the tank Richardson number, based on the tank diameter, and the tank TE. The parametric study also shows a maximum tank TE at a Froude number equal to 0.5, and a proportional decrease of TE as the Reynolds number increases.

Plate Diffuser Performance in Spherical Tank Thermocline Storage System

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Fahad Khan ◽  
Brian J. Savilonis
Keyword(s):  
Flow Rate ◽  
Thermal Efficiency ◽  
Volume Flow Rate ◽  
Storage System ◽  
Water Desalination ◽  
Hot Water ◽  
Discharge Process ◽  
Water Tank ◽  
Dimensionless Numbers ◽  
Spherical Tank

Thermal energy storage (TES) systems that store sensible heat in liquid media require the use of storage tanks. Spherical tanks require less building material and insulation, which might reduce the overall cost of a TES system while providing structural rigidity. The current study investigates an optimized plate diffuser in a thermocline spherical tank storage system to possibly increase the discharge flow rate without disrupting the thermocline region and without reducing the tank thermal efficiency. For low temperature (10–90 °C heat storage applications), such as heating, ventilation, and air conditioning (HVAC) and thermal water desalination, storing hot water in a thermocline system can increase the system thermal efficiency by up to 40% when compared to a fully mixed water tank and reduce the installation cost by 30% compared to a two-tank system. This study examines using a spherical tank in a thermocline system for such applications. A computational fluid dynamic (CFD) study simulated the discharge process from a spherical storage tank thermocline water system. Thermocline thickness and temperature profile in the tank were numerically determined for Reynolds number, Re = 600 and Froude number, Fr = 1.2; results were then experimentally validated. A CFD parametric study with (500 < Re < 7500) and (0.5 < Fr < 3.3): (i) determined the influence of tank flow dimensionless numbers (Reynolds, Froude, Richardson, and Archimedes) on thermal efficiency and thermocline thickness, (ii) produced an equation to predict the tank thermal efficiency using flow dimensionless numbers, and (iii) estimated the thermocline region volume occupation as a percentage of the total volume. The study of an optimized plate diffuser produced an equation for thermal efficiency based on Re and Fr numbers and estimated a thermocline volume equal to 15% of total tank volume. Flow rate ramp up by a factor of 3 was possible after the thermocline region was formed without losing tank thermal efficiency.

A Perspective on Combustion-Driven Flows With Circulation

2001 ◽  
Author(s):  
Francine Battaglia ◽  
Ronald G. Rehm ◽  
Howard R. Baum ◽  
Mohamed I. Hassan ◽  
Kozo Saito
Keyword(s):  
Reynolds Number ◽  
Froude Number ◽  
Theoretical Studies ◽  
Swirl Number ◽  
Dimensionless Parameters ◽  
Parametric Investigation ◽  
Fire Whirl ◽  
Slender Column ◽  
Combustion Processes

Abstract Perhaps the most dramatic example of surprising behavior when circulation is imposed on a combustion-driven flow is the fire whirl, where the burning gases form a tall slender column. Relatively few studies have addressed the influence of circulation on the development of combustion-driven flows. Three dimensionless parameters characterize this interplay: the Froude number, the swirl number and the Reynolds number. It is surprising that for most studies, even with plausible assumptions concerning the experiments, not enough information is given to determine the values of these parameters. We will experimentally reconstruct these studies in an effort to characterize parametrically these interactions. Both buoyancy-driven and momentum-driven combustion processes will be investigated to determine the influence of circulation. Theoretical studies will occur in conjunction to provide the most complete parametric investigation.

scholarly journals Analysis of transient mixed convection in a horizontal channel partially heated from below

2021 ◽  
Vol 4 (8(112)) ◽  
pp. 16-22
Author(s):  
Mahmoud A. Mashkour
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Source ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Stokes Equations ◽  
Heat Convection ◽  
Horizontal Channel ◽  
Outlet Temperature

The heat convection phenomenon has been investigated numerically (mathematically) for a channel located horizontally and partially heated at a uniform heat flux with forced and free heat convection. The investigated horizontal channel with a fluid inlet and the enclosure was exposed to the heat source from the bottom while the channel upper side was kept with a constant temperature equal to fluid outlet temperature. Transient, laminar, incompressible and mixed convective flow is assumed within the channel. Therefore, the flow field is estimated using Navier Stokes equations, which involves the Boussinesq approximation. While the temperature field is calculated using the standard energy model, where, Re, Pr, Ri are Reynolds number, Prandtl number, and Richardson number, respectively. Reynolds number (Re) was changed during the test from 1 to 50 (1, 10, 25, and 50) for each case study, Richardson (Ri) number was changed during the test from 1 to 25 (1, 5, 10, 15, 20, and, 25). The average Nusselt number (Nuav) increases exponentially with the Reynold number for each Richardson number and the local Nusselt number (NuI) rises in the heating point. Then gradually stabilized until reaching the endpoint of the channel while the local Nusselt number increases with a decrease in the Reynolds number over there. In addition, the streamlines and isotherms patterns in case of the very low value of the Reynolds number indicate very low convective heat transfer with all values of Richardson number. Furthermore, near the heat source, the fluid flow rate rise increases the convection heat transfer that clarified the Nusselt number behavior with Reynolds number indicating that maximum Nu No. are 6, 12, 27 and 31 for Re No. 1, 10, 25 and 50, respectively

scholarly journals Numerical Analysis of Mixed Convective Heat Transfer from a Square Cylinder Utilizing Nanofluids with Multi-Phase Modelling Approach

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5485
Author(s):  
Rajendra S. Rajpoot ◽  
Shanmugam. Dhinakaran ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Richardson Number ◽  
Base Fluid ◽  
Square Cylinder ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Multi Phase ◽  
Modelling Approach

The present study deals with the numerical simulation of mixed convective heat transfer from an unconfined heated square cylinder using nanofluids (Al2O3-water) for Reynolds number (Re) 10–150, Richardson number (Ri) 0–1, and nanoparticles volume fractions (φ) 0–5%. Two-phase modelling approach (i.e., Eulerian-mixture model) is adopted to analyze the flow and heat transfer characteristics of nanofluids. A square cylinder with a constant temperature higher than that of the ambient is exposed to a uniform flow. The governing equations are discretized and solved by using a finite volume method employing the SIMPLE algorithm for pressure–velocity coupling. The thermo-physical properties of nanofluids are calculated from the theoretical models using a single-phase approach. The flow and heat transfer characteristics of nanofluids are studied for considered parameters and compared with those of the base fluid. The temperature field and flow structure around the square cylinder are visualized and compared for single and multi-phase approaches. The thermal performance under thermal buoyancy conditions for both steady and unsteady flow regimes is presented. Minor variations in flow and thermal characteristics are observed between the two approaches for the range of nanoparticle volume fractions considered. Variation in φ affects CD when Reynolds number is varied from 10 to 50. Beyond Reynolds number 50, no significant change in CD is observed with change in φ. The local and mean Nusselt numbers increase with Reynolds number, Richardson number, and nanoparticle volume fraction. For instance, the mean Nusselt number of nanofluids at Re = 100, φ = 5%, and Ri = 1 is approximately 12.4% higher than that of the base fluid. Overall, the thermal enhancement ratio increases with φ and decreases with Re regardless of Ri variation.

scholarly journals Parametric Study of the Pressure Profile in a Nozzle as a Function of Compressible Flow Parameters

2018 ◽  
Vol 11 (25) ◽  
pp. 1-4
Author(s):  
Jorge Duarte Forero ◽  
Guillermo E. Valencia ◽  
Luis G. Obreg�n ◽  
◽  
◽  
...  
Keyword(s):  
Compressible Flow ◽  
Parametric Study ◽  
Pressure Profile ◽  
Flow Parameters

Charge-Discharge Characteristics of an Adsorbed Natural Gas Storage System under Ambient Conditions

2014 ◽  
Vol 592-594 ◽  
pp. 1448-1455 ◽  
Author(s):  
Satyabrato Sahoo ◽  
Maddali Ramgopal
Keyword(s):  
Heat Transfer ◽  
Natural Gas ◽  
Storage System ◽  
Ambient Air ◽  
Discharge Process ◽  
Ambient Conditions ◽  
Conduction Model ◽  
Adsorbed Natural Gas ◽  
Bed Temperature ◽  
Adsorbed Phase

The performance of an adsorbed natural gas (ANG) storage system with natural convection heat transfer between the ANG bed and the ambient air is studied. Results are obtained for the bed without and with external fins on ambient air side. A one dimensional transient conduction model with suitable kinetic equation is formulated to simulate the performance of the bed filled with a homogeneous mixture of activated carbon and graphite. The model duly considers non-ideal behaviour of natural gas, variable specific heat of the adsorbed phase and heat of adsorption. Results are obtained for the case of constant pressure charging and constant flow discharging. The performance of the ANG bed is evaluated in terms of delivery capacity and discharge time. Results are obtained at an ambient temperature of 308 K and 35 bar for a charging time of 3.34 min. It is found that under this condition, the bed temperature increases by 70 and 45K and the storage capacity reduces by 75 and 60% without and with external fins, respectively. During discharge also, due to insufficient heat supply the bed temperature drops to very a low value thereby increasing the amount of adsorbate retained at the end of discharge process. This study clearly shows the need for improving the heat transfer rate from or to the ANG bed for higher delivery capacity.

Study on Hybrid Energy Storage System of Super-Capacitors and Batteries

2013 ◽  
Vol 765-767 ◽  
pp. 2435-2438
Author(s):  
Jian Ye Liu ◽  
Shan Shan Jiang ◽  
Chang Ge Tian ◽  
Meng Zhang
Keyword(s):  
Energy Storage ◽  
Storage System ◽  
Energy Storage System ◽  
Discharge Process ◽  
Super Capacitor ◽  
Hybrid Energy ◽  
Battery Charge ◽  
Technical Performance ◽  
Hybrid Energy Storage ◽  
Hybrid Energy Storage System

Designed based on bi-directional DC / DC converter of the super-capacitor and battery hybrid energy storage system, using both on the technical performance have strong complementary features that can improve the battery charge and discharge process, so that the battery charge and discharge cycles decrease, prolong the service life of battery. In matlab/simulink environment, established a system simulation model, the result showed that the hybrid energy storage system can effectively restrain the DC bus voltage fluctuations, make the output voltage relatively stable.

Regeneration of turbulent fluctuations in low-Froude-number flow over a sphere at a Reynolds number of 3700

2016 ◽  
Vol 804 ◽  
Author(s):  
Anikesh Pal ◽  
Sutanu Sarkar ◽  
Antonio Posa ◽  
Elias Balaras
Keyword(s):  
Reynolds Number ◽  
Froude Number ◽  
Qualitative Change ◽  
Turbulence Energy ◽  
Horizontal Shear ◽  
Near Wake ◽  
Turbulent Fluctuations ◽  
Flow Past ◽  
Low Froude Number ◽  
Flow Past A Sphere

Direct numerical simulations (DNS) are performed to study the behaviour of flow past a sphere in the regime of high stratification (low Froude number $Fr$). In contrast to previous results at lower Reynolds numbers, which suggest monotone suppression of turbulence with increasing stratification in flow past a sphere, it is found that, below a critical $Fr$, increasing the stratification induces unsteady vortical motion and turbulent fluctuations in the near wake. The near wake is quantified by computing the energy spectra, the turbulence energy equation, the partition of energy into horizontal and vertical components, and the buoyancy Reynolds number. These diagnostics show that the stabilizing effect of buoyancy changes flow over the sphere to flow around the sphere. This qualitative change in the flow leads to a new regime of unsteady vortex shedding in the horizontal planes and intensified horizontal shear which result in turbulence regeneration.

Heliplat®: high altitude very-long endurance solar powered UAV for telecommunication and Earth observation applications

2004 ◽  
Vol 108 (1084) ◽  
pp. 277-293 ◽  
Author(s):  
G. Romeo ◽  
G. Frulla
Keyword(s):  
Fuel Cells ◽  
High Altitude ◽  
Parametric Study ◽  
Storage System ◽  
Fem Analysis ◽  
Energy Storage System ◽  
Aerodynamic Performances ◽  
Solar Powered ◽  
One Year ◽  
Long Endurance

Abstract Research is at present being carried out at the Turin Polytechnic University with the aim of designing an HAVE/UAV (high altitude very-long endurance/unmanned air vehicle). The vehicle should climb to 17-20km by mainly taking advantage of direct Sun radiation and thereafter maintain a level flight; during the night, a fuel cells energy storage system would be used. A computer program has been developed to carry out a parametric study for the platform design. The solar radiation change over one year, the altitude, masses and efficiencies of the solar and fuel cells, and the aerodynamic performances have all been taken into account. The parametric studies have shown how fuel cells and solar cells efficiency and mass have the most influence on the platform dimensions. A wide use of high modulus CFRP has been made in designing the structure in order to minimise the airframe weight. A first configuration of HELIPLAT® (HELIos PLATform) was worked out, following a preliminary parametric study. The platform is a monoplane with eight brushless electric motors, a twin-boom tail type with an oversized horizontal stabiliser and two rudders. The co-ordinates at the root and along the wing span as well as the wing planform were optimised to achieve the best efficiency. Several profiles and wing plans have been analysed using the CFD software Xfoil and Vsaero. Several wind-tunnel tests were carried out to compare the analytically predicted performances. A preliminary design of a scale-sized technological demonstrator was completed with the aim of manufacturing a proof-of-concept structure. A FEM analysis was carried by using the Msc/Patran/Nastran code to predict the static and dynamic behaviour of the UAV structure.

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