Experimental and Numerical Study of Mixing in a Horizontal Hot-Water Storage Tank

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
A. Aviv ◽  
S. Morad ◽  
Y. Ratzon ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Numerical Study ◽  
Tap Water ◽  
Three Dimensional ◽  
Hot Water ◽  
Outlet Temperature ◽  
Dimensionless Time ◽  
Water Storage Tank ◽  
Thermal Mixing ◽  
Horizontal Cylindrical Tank ◽  
Port Location

Thermal mixing and stratification are explored experimentally in a horizontal cylindrical tank, which simulates a storage of water heated by a solar collector. The tank is 70 cm long and 24 cm in diameter. The study is conducted in a transient mode, namely, the tank is filled with hot water, which in the course of operation is replaced by the tap water in a stratified way or by mixing. The flow rates of 2 l/min, 3 l/min, 5 l/min, and 7 l/min are explored. Temperature of hot water is usually about 55°C, while the tap water is about 20°C. In the experiments, both flow visualization and temperature measurements are used. The effects of port location and deflector installation are examined. The experimental results are presented in a dimensionless form, as the normalized outlet temperature versus dimensionless time. Three-dimensional transient numerical simulations, done using the FLUENT 6 software, provide an additional insight in the process of mixing inside the tank.

Experimental and Numerical Study of Mixing in a Horizontal Hot-Water Storage Tank

2008 ◽  
Author(s):  
A. Aviv ◽  
S. Morad ◽  
Y. Ratzon ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Numerical Study ◽  
Tap Water ◽  
Three Dimensional ◽  
Hot Water ◽  
Outlet Temperature ◽  
Dimensionless Time ◽  
Water Storage Tank ◽  
Thermal Mixing ◽  
Horizontal Cylindrical Tank ◽  
Port Location

Thermal mixing and stratification are explored experimentally in a horizontal cylindrical tank, which simulates a storage of water heated by a solar collector. The tank is 70 cm long and 24 cm in diameter. The study is conducted in a transient mode, namely, the tank is filled with hot water, which in the course of operation is replaced by the tap water in a stratified way or by mixing. The flow rates of 2, 3, 5 and 7 liters per minute are explored. Temperature of hot water is usually about 55 °C, while the tap water is about 20 °C. In the experiments, both flow visualization and temperature measurements are used. The effects of port location and deflector installation are examined. The experimental results are presented in a dimensionless form, as the normalized outlet temperature vs. dimensionless time. Three-dimensional transient numerical simulations, done using the Fluent 6 software, provide an additional insight in the process of mixing inside the tank.

Experimental and Numerical Study of Mixing in a Hot-Water Storage Tank

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
A. Aviv ◽  
Y. Blyakhman ◽  
O. Beeri ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Numerical Model ◽  
Storage Tank ◽  
Numerical Study ◽  
Tap Water ◽  
Three Dimensional ◽  
Hot Water ◽  
Software Validation ◽  
Water Storage Tank ◽  
Thermal Mixing ◽  
Numerical Investigations

Thermal mixing and stratification are explored numerically and experimentally in a cylindrical tank, which simulates a storage of water heated by a solar collector. The tank is 70cm in height and 24cm in diameter. The inlet and outlet are vertical and located off the centerline of the tank. The study is conducted in a transient mode, namely, the tank is filled with hot water, and as the hot water is being withdrawn, the tap water replaces it in a stratified way or by mixing. The flowrates of 2l∕min, 3l∕min, 5l∕min and 7l∕min, which correspond to superficial velocities of 4.35cm∕min, 6.52cm∕min, 10.87cm∕min, and 15.2cm∕min, are explored. Temperature of hot water ranges within 40–50°C, while the tap water is about 25–27°C. Installation of one and two horizontal baffles above the inlet is examined. Simultaneous experimental and numerical investigations are performed. In the experiment, both flow visualization and temperature measurements are used. Three-dimensional transient numerical simulations are done using the FLUENT 6 software. Validation of the numerical model is achieved by comparison with the experimental results. Then, the numerical model is applied to a study of various possible changes in the system. The results show that at low flowrates, up to a superficial velocity of about 11cm∕min through the tank, the baffles have no effect on tap water mixing with the stored hot water. At higher flowrates, a single horizontal baffle prevents the mixing and preserves the desired stratified temperature distribution in the storage tank.

scholarly journals The impact of inflow velocity on thermal stratification in a water storage tank

2018 ◽  
Vol 44 ◽  
pp. 00079 ◽  
Author(s):  
Kamila Kozłowska ◽  
Piotr Jadwiszczak
Keyword(s):  
Storage Tank ◽  
Thermal Stratification ◽  
Heat Storage ◽  
Three Dimensional ◽  
Hot Water ◽  
Thermal Processes ◽  
Water Storage Tank ◽  
Thermal Mixing ◽  
Computational Fluid Dynamics Cfd ◽  
The Impact

The paper presents the analysis of thermal processes occurring in thermal energy storage tanks used for heating hot water systems. Three-dimensional Computational Fluid Dynamics (CFD) methods were used. The standard buffer charging stage was modelled for three tank inlets’ diameters DN20, DN40 and DN80. With a constant charging water flow and temperature the port diameter affects inlet velocity, heat storage dynamics, thermal stratification and thermocline thickness in storage tank. The smallest diameter causes unfavourable thermal mixing of accumulated water, and the largest diameter supports thermal stratification

scholarly journals A Numerical Study for a Double Twisted Tube Heat Exchanger

2021 ◽  
Vol 39 (5) ◽  
pp. 1583-1589
Author(s):  
Ali K. Abdul Razzaq ◽  
Khudheyer S. Mushatet
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Hot Water ◽  
Flow Mode ◽  
Outer Diameter ◽  
Outlet Temperature ◽  
Ansys Fluent ◽  
Tube Heat Exchanger ◽  
Twisted Tube

The thermal and fluid physiognomies of a double twisted tube heat exchanger was examined numerically. Twisted engineering is a wide-use method to improve heat transfer in heat exchangers. A counter-flow mode utilizing hot water in the inner tube and cold air in the outer tube was considered. This study aims to progress the thermal performance of the double tube heat exchanger by using twisted tubes instead of plane tubes. The heat exchanger was (1m) length, outer diameter (0.05m) and inner diameter (0.025m), both with a thickness (0.004m). It was tested for different values of twist ratios (Tr= 5, 10, and 15 respectively) and Reynolds numbers (Re=5000 to 30000). The Navier - Stockes and energy equations besides the turbulence model in demand for modelling this physical problem. ANSYS Fluent code was used for the numerical simulation. The results showed that the twisted tube heat exchanger showed increasing heat transfer compared with a plain tube heat exchanger. It was found that the cold outlet temperature, pressure drop and effectiveness are increased as the twist ratio increases.

Effects of Baffle Width on Heat Transfer to an Immersed Coil Heat Exchanger: Experimental Optimization

2019 ◽  
Author(s):  
Julia Haltiwanger Nicodemus ◽  
Xiaoqi Huang ◽  
Emily Dentinger ◽  
Kyle Petitt ◽  
Joshua H. Smith
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Convection Heat Transfer ◽  
Hot Water ◽  
Outlet Temperature ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Water Storage Tank ◽  
Coil Heat Exchanger

Abstract In this work, we investigate the effects of the width of an annular baffle region on natural convection heat transfer to an immersed, coiled heat exchanger in an otherwise quiescent sensible hot water storage tank. In experiments, the coiled heat exchanger sits in an annular region created by the tank wall and a straight, cylindrical baffle. The width of this baffle region is 1.5, 2, 3, or 4 times the heat exchanger diameter, These experiments are compared to each other and to corresponding control experiments with no baffle. In general, all baffles create considerable benefits over their respective control experiments, consistent with past studies. The considered metrics of heat transfer rate, fraction of energy discharged from the tank, and heat exchanger outlet temperature show that heat transfer is improved slightly by narrowing the baffle region. For example, relative to their respective controls, the energy extracted from the tank after 30 min of discharge in the 1.5D, 2D, 3D and 4D experiments is 23.2%, 20.8%, 18.1%, and 14.7% higher, respectively. This improvement in natural convection heat transfer as the baffle region narrows is attributed to the increasing thermal stratification observed in experiments with increasingly narrow baffle regions.

Effects of Baffle Width on Heat Transfer to an Immersed Coil Heat Exchanger: Experimental Optimization

2019 ◽  
Vol 142 (5) ◽  
Author(s):  
Julia Haltiwanger Nicodemus ◽  
Xiaoqi Huang ◽  
Emily Dentinger ◽  
Kyle Petitt ◽  
Joshua H. Smith
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Convection Heat Transfer ◽  
Hot Water ◽  
Outlet Temperature ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Water Storage Tank ◽  
Coil Heat Exchanger

Abstract In this work, we investigate the effects of the width of an annular baffle region on natural convection heat transfer to an immersed, coiled heat exchanger in an otherwise quiescent sensible hot water storage tank. In the experiments, the coiled heat exchanger sits in an annular region created by the tank wall and a straight, cylindrical baffle. The width of this baffle region is 1.5, 2, 3, or 4 times the heat exchanger diameter. These experiments are compared to each other and to corresponding control experiments with no baffle. In general, all baffles create considerable benefits over their respective control experiments, consistent with past studies. The considered metrics of heat transfer rate, fraction of energy discharged from the tank, heat exchanger outlet temperature, and heat exchanger effectiveness show that heat transfer is improved slightly by narrowing the baffle region. For example, relative to their respective controls, the energy extracted from the tank after 30 min of discharge in the 1.5D, 2D, 3D, and 4D experiments is 23.3%, 20.8%, 18.1%, and 14.6% higher, respectively. This improvement in natural convection heat transfer as the baffle region narrows is attributed to the increasing thermal stratification observed with increasingly narrow baffle regions.

Temperature Distribution Inside Hot Water Storage Tanks of Solar Collectors

1989 ◽  
Vol 111 (4) ◽  
pp. 311-317 ◽  
Author(s):  
M. Issa ◽  
M. AL-Nimr
Keyword(s):  
Storage Tank ◽  
Radial Direction ◽  
Water Storage ◽  
Convection Heat Transfer ◽  
Axial Direction ◽  
Operating Conditions ◽  
Hot Water ◽  
Outlet Temperature ◽  
Axial Conduction ◽  
Water Storage Tank

An analytical experimental investigation into the temperature field inside the hot water storage tank of a solar collector was carried out. A transient two-dimensional semi-infinite cylindrical length model with time-and-space boundary-conditions dependency was selected. Conduction and convection heat-transfer modes in the axial direction together with conduction in the radial direction were neglected, since these were considered to be small in comparison with the axial conduction and convection diffusion terms, which in turn were considered small relative to the energy stored. Good agreement between theoretical and experimental prediction was verified. The radial direction temperature dependency disappeared for axial lengths greater than one quarter of the tank depth for most practical operating conditions especially for low inflow velocities and low inlet to outlet temperature ratios. The axial conduction term in the governing equation can be dropped out for inflow velocities greater than a certain critical value without distorting the theoretical consequences. Temperature profiles in the axial direction of a cylindrical storage tank can be assumed to be linear especially for high inflow velocities as well as low temperature differences at inlet and outlet of the storage tank.

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