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Novel Design of a Portable Heat Energy Storage Device Adopting a Phase Change Material for CHP and Solar Energy Applications. K. TRAPANI. BSc. Renewable Energy Final Year Dissertation. Project Supervisor: Dr. Dean Millar. Concept:
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Novel Design of a Portable Heat Energy Storage Device Adopting a Phase Change Material for CHP and Solar Energy Applications K. TRAPANI BSc. Renewable Energy Final Year Dissertation Project Supervisor: Dr. Dean Millar
Concept: • Extraction of waste heat from an automotive micro-CHP engine using a portable thermal storage device (Millar & Huang, 2009) • Specific design of the portable thermal energy storage adopting phase change materials (PCMs) INTRODUCTION
REQUIREMENTS OF THE DEVICE PORTABILITY Compact Light Modular Stackable High thermal energy storage Efficient heat transfer FLEXIBLE THERMAL CAPACITY MAXIMISED PERFORMANCE
Modular unit: Mass = 15kg Dimensions = 20cm x 35cm x 18cm DEVICE DESIGN Model unit (1/5th scale): Mass = 3kg Dimensions = 12cm x 35cm x 6cm SOLIDWORKS DESIGN OF A 1/5th SCALE MODEL
PHASE CHANGE MATERIALS (PCMs) TEMPERATURE PHASE CHANGE PCMs – materials which exhibit a phase change (from one state to another) GAS Enthalpy of System LIQUID SOLID ENTHALPY
SELECTION OF DEVICE’S PCM GAS-LIQUID • Not corrosive • Low or no undercooling • Chemically and thermally ostable SOLID-GAS • Greater phase change oenthalpy PHASE TRANSITIONS SOLID-LIQUID Relatively high heat of fusion Paraffin Wax SOLID-SOLID Stable heating and cooling cycle Economical and abundant
Governing equations: Q = mc∆ϴ Q = mL PROPERTIES OF THE DEVICE’S PCM Sensible heating Latent heating Where Q = Pt
Boundary conditions: • Mass flow rate of heat transfer medium 0.108kg/s at 333.2K • Fluid outlet subject to normal environmental conditions (293.2K and 101325Pa) • Initial conditions: • Same as normal environmental conditions • Simulation software had to be modelled to account for the phase change material. • Assumptions: • Paraffin wax is homogenous and isotropic • Heat is transferred only by conduction • Simulation is time dependent SIMULATION Hence the paraffin wax’s thermal properties had to be designed as a series of sensible heating stages. Cs = 3412J/kgKfor T<328K Csl = 98587J/kgKfor 328K<T<330K Cl = 4466J/kgKfor T>330K • Results (for a model scale device): • Thermal heat capacity – 381.7kJ
“CHARGING” of Device: “DISCHARGING” of Device: TESTING OF 1/5th SCALE PROTOTYPE Heat supplied thermal store = 595.8kJ η = 64.1% Heat retrieved from thermal store = 247.0kJ η = 64.7% Overall efficiency = 41.5%
DEVICE INTEGRATION The device is primarily designed to be integrated with a central domestic heating system.
APPLICATIONS FOR THE DEVICE The main heat sources for the device are: Micro – CHP (automotive vehicle engines) Surplus solar thermal heat Micro-CHP Solar • Requires a portable heat transfer medium • Integration with an automotive vehicle • Stationary application • Integration with the domestic central heating system Yu, C., & Chau, K.T. (2009) Review on thermal energy storage with phase change. Renewable and Sustainable Energy Reviews, 13, 318 – 345. • Two primary heat sources: • Exhaust gas • Engine cooling process Retrieved from duaemanus.blogspot.com
Increase mass implies: • a larger CAPEX • greater operating costs • enhanced revenue OVERVIEW OF A MICRO-CHP INTEGRATED DEVICE
CONCLUSION Main application for device is in micro-CHP Economically device is currently not very feasible for displacing the heating load from a gas boiler Optimisation of the design (improving PCM to total device mass ratio) Simulation testing for practical maximum efficiency Consequent optimisation of the practical model Further development of device fittings is crucial to the installation of the device
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