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Energy Storage Thermal Energy Storage Anis Allagui University of Sharjah Sustainable and Renewable Energy Engineering [email protected] Last Updated: April 12, 2017
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Introduction Modes of Heat Transfer Thermal Energy Storage Technologies of TES Outline 1 Introduction 2 Modes of Heat Transfer 3 Thermal Energy Storage Definition Fundamentals of TES Efficiency 4 Technologies of TES Anis Allagui Energy Storage | Thermal Energy Storage 2/36
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Introduction Modes of Heat Transfer Thermal Energy Storage Technologies of TES General Aspects of Heat Transfer Thermal processes involve the transfer of heat from one point to another: heating and cooling of gases, liquids, and solids, evaporation of water, and removal of heat liberated by chemical reaction Driving force is the temperature difference between the location where heat is taken and where heat originates ( temperature gradient ) Anis Allagui Energy Storage | Thermal Energy Storage 3/36
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Introduction Modes of Heat Transfer Thermal Energy Storage Technologies of TES Conduction, Convection & Radiation I Heat Conduction: Fourier’s law of heat conduction, Q = - kA T , for rate of heat flow through a homogeneous solid object. Heat Convection: heat transfer mode within a fluid by mixing * one portion of the fluid with another; forced vs. natural (free, buoyancy forces) convection. heat transfer from solid to fluid: conduction/convection (flow , convection , conduction ; Bi = hL / k s ; Nu = hL / k l ) Q = hA ( T s - T f ) h : convection coefficient convection heat transfer within a fluid that is transferred is the sensible or internal thermal heat of the fluid convection heat transfer with phase change liquid–vapor is called latent heat. Anis Allagui Energy Storage | Thermal Energy Storage 4/36
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Introduction Modes of Heat Transfer Thermal Energy Storage Technologies of TES Conduction, Convection & Radiation II L T A T B T s 1 T s 2 D B D A Figure 2.1: A wall subject to convection heat transfer on both sides; fluid A and fluid B Newton’s law of cooling: q = h A ( T A - T s 1 ) (1) q = h B ( T s 2 - T B ) (2) Heat transfer in thin films is by con- duction only: q = k A Δ A ( T A - T s 1 ) (3) q = k B Δ B ( T s 2 - T B ) (4) h A = k A / Δ A and h B = k B / Δ B Anis Allagui Energy Storage | Thermal Energy Storage 5/36
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Introduction Modes of Heat Transfer Thermal Energy Storage Technologies of TES Conduction, Convection & Radiation III Heat transfer in the wall is: q = k L ( T s 1 - T s 2 ) If steady-state heat transfer: q = h A ( T A - T s 1 ) = h B ( T s 2 - T B ) = k L ( T s 1 - T s 2 ) (5) which yields to: q = T A - T B 1 / h A + L / k + 1 / h B (6) The term 1 1 / h A + L / k + 1 / h B is the overall heat transfer coefficient including different heat transfer coefficients. Anis Allagui Energy Storage | Thermal Energy Storage 6/36
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Introduction Modes of Heat Transfer Thermal Energy Storage Technologies of TES Conduction, Convection & Radiation IV Heat Radiation: object emits radiant energy in all directions if T > 0 . If there is a receiver ( solid to solid ), a part may be: absorbed ( α ), transmitted ( τ ), reflected ( ρ ). By definition we have α + τ + ρ = 1 .
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