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Simple inlet devices and their influence on thermal stratification in a hot water storage tank
HighlightsStratification and hydrodynamics of a hot water tank during charging are studied.A 3D-CFD model was used to supplement previous experimental analyses.A high degree of correlation with experiments and versatility was achieved.New inlet configurations and two inflow rates were simulated and compared.The role of some inlet characteristics on stratification is clarified.
AbstractThermal energy storage is a technology used mostly in buildings and industries in order to preserve thermal energy so that the stored energy can be used at a later time. Thermal stratification during the charge process in a cylindrical water tank was investigated using tools of Computational Fluid Dynamics (CFD). Simulations were validated by means of experimental measurements of time-dependent temperature profiles. The results showed that the model was able to adequately capture the experimental temperature evolution in the tank for all the validation cases. Once validated the model, simple modifications of the usual inlet devices and inflow rate by CFD techniques were accomplished with the intention of improving the tank performance. It was found that the modifications of the simulated inlet devices affected the stratification level. This could lead to improve designs and optimize system efficiency. The analyses confirmed numerically the results obtained experimentally, and it was evidenced that a sintered bronze conical diffuser can improve stratification compared to a conventional bronze elbow inlet. Therefore, CFD techniques proved to be quite a valuable complement of experimental studies. The use of low inflow, smooth out inlet velocity and operate inflow upwards near the top of the tank enhanced stratification.
Simple inlet devices and their influence on thermal stratification in a hot water storage tank
HighlightsStratification and hydrodynamics of a hot water tank during charging are studied.A 3D-CFD model was used to supplement previous experimental analyses.A high degree of correlation with experiments and versatility was achieved.New inlet configurations and two inflow rates were simulated and compared.The role of some inlet characteristics on stratification is clarified.
AbstractThermal energy storage is a technology used mostly in buildings and industries in order to preserve thermal energy so that the stored energy can be used at a later time. Thermal stratification during the charge process in a cylindrical water tank was investigated using tools of Computational Fluid Dynamics (CFD). Simulations were validated by means of experimental measurements of time-dependent temperature profiles. The results showed that the model was able to adequately capture the experimental temperature evolution in the tank for all the validation cases. Once validated the model, simple modifications of the usual inlet devices and inflow rate by CFD techniques were accomplished with the intention of improving the tank performance. It was found that the modifications of the simulated inlet devices affected the stratification level. This could lead to improve designs and optimize system efficiency. The analyses confirmed numerically the results obtained experimentally, and it was evidenced that a sintered bronze conical diffuser can improve stratification compared to a conventional bronze elbow inlet. Therefore, CFD techniques proved to be quite a valuable complement of experimental studies. The use of low inflow, smooth out inlet velocity and operate inflow upwards near the top of the tank enhanced stratification.
Simple inlet devices and their influence on thermal stratification in a hot water storage tank
Moncho-Esteve, Ignacio José (author) / Gasque, María (author) / González-Altozano, Pablo (author) / Palau-Salvador, Guillermo (author)
Energy and Buildings ; 150 ; 625-638
2017-06-10
14 pages
Article (Journal)
Electronic Resource
English
a , face area vector , <italic>A</italic> (m<sup>2</sup>) , cell area , <italic>c</italic>(J K<sup>−1</sup> kg<sup>−1</sup>) , specific heat capacity , c<inf>fg</inf>(J K<sup>−</sup> 1 kg<sup>−1</sup>) , specific heat capacity for fibreglass , c<inf>st</inf> (J K<sup>−1</sup>kg<sup>−1</sup>) , specific heat capacity for steel , CFD , computational fluid dynamics , D , sintered bronze conical diffuser , <italic>E</italic> (J) , total energy , E , elbow , <italic>f</italic><inf>g</inf> (N) , body force vector , <italic>GCI</italic> , grid convergence index , <italic>H</italic> (J) , total enthalpy , H , high case , <italic>I</italic> , identity matrix , L , low case , LES , Large Eddy Simulation , M (m<sup>4</sup> s<sup>−2</sup>) , jet momentum flux , <italic>MSE</italic> (K<sup>2</sup>) , mean squared error , <italic>n</italic> , n°of experimental observations in a specific point along time , <italic>p</italic> (Pa) , = pressure , <italic>q</italic> , heat flux vector , Q<inf>in</inf> (L min<sup>−1</sup>) , inflow , <italic>RE</italic> (−) , relative error , <italic>RMSE</italic> (K) , root mean squared error , <italic>t</italic> (min) , time , <italic>t</italic><sup>*</sup> (−) , dimensionless time , <italic>t</italic><inf>r</inf> (min) , residence time , <italic>t</italic><inf>ct</inf> (min) , charge time , <italic>T</italic> (K) , temperature , <italic>T</italic><inf>avg</inf> (K) , average temperature in the water domain , <italic>T</italic><inf>amb</inf> (K) , ambient temperature , <italic>T<inf>i</inf></italic>(K) , computed value of <italic>T</italic> at each ith experimental time step , experimental value of <italic>T</italic> at each ith experimental time step , <italic>T</italic><inf>in</inf> (K) , inlet temperature , <italic>T</italic><inf>o</inf> (K) , initial water tank temperature , TC , thermocouple in the central zone , TES , thermal energy storage , TL , thermocouple in the lateral zone , <italic>U</italic> (m s<sup>−1</sup>) , velocity vector module , <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mover><mi>U</mi><mo>¯</mo></mover></mrow></math>(m s<sup>−1</sup>) , volume-weighted average velocity magnitude , <italic>U</italic><inf>jet</inf>(m s<sup>−1</sup>) , area-weighted average velocity on the nozzle section , <italic>U<inf>n</inf></italic>(m s<sup>−1</sup>) , normal velocity in the nozzle tip of the elbow , <italic>U<inf>t</inf></italic> (m s<sup>−1</sup>) , tangential velocity in the nozzle tip of the elbow , URANS , unsteady Reynolds-average Navier-Stokes , <italic>v</italic> (m s<sup>−1</sup>) , velocity component , <italic>V</italic> (m<sup>3</sup>) , volume cell of each grid point , <italic>V</italic><inf>t</inf> (L) , tank volume , <italic>y</italic><sup>+</sup> (−) , non-dimensional wall distance , <italic>η</italic>(−) , thermal charging efficiency , <italic>θ</italic>(−) , dimensionless temperature , <italic>λ</italic>(W m<sup>−1</sup>K<sup>−1</sup>) , thermal conductivity , <italic>λ<inf>fg</inf></italic>(W m<sup>−1</sup>K<sup>−1</sup>) , thermal conductivity for fibreglass , <italic>λ<inf>st</inf></italic>(W m<sup>−1</sup>K<sup>−1</sup>) , thermal conductivity for steel , <italic>μ</italic>(Pa s) , dynamic viscosity , <italic>ρ</italic>(kg m<sup>−3</sup>) , density , <italic>ρ<inf>fg</inf></italic>(kg m<sup>−3</sup>) , density for fibreglass , <italic>ρ<inf>st</inf></italic>(kg m<sup>−3</sup>) , density for steel , [T] , viscous stress tensor , Hot water storage tank , Water stratification , Inlet parameters , Thermal charging efficiency , Unsteady reynolds-Average navier-Stokes (URANS)
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