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 INTRODUCTION Concept: Extraction of waste heat from an automotive microCHP engine using a portable thermal storage device (Millar & Huang, 2009) Specific design of the portable thermal energy storage adopting phase change materials (PCMs) REQUIREMENTS OF THE DEVICE •Compact •Light •Modular •Stackable PORTABILITY FLEXIBLE THERMAL CAPACITY •High thermal energy storage •Efficient heat transfer MAXIMISED PERFORMANCE DEVICE DESIGN Modular unit: Mass = 15kg Dimensions = 20cm x 35cm x 18cm Component Material PCM Paraffin wax Piping Copper Fins Aluminium Internal case Steel Insulation Reflective foam External case Plastic 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 Enthalpy of System PCMs – materials which exhibit a phase change (from one state to another) PHASE CHANGE GAS LIQUID SOLID ENTHALPY SELECTION OF DEVICE’S PCM SOLID-LIQUID PHASE TRANSITIONS ORGANICS INORGANICS • Not corrosive SOLID-GAS • Low or no undercooling • Chemically and thermally ostable • Greater phase change oenthalpy GAS-LIQUID SOLID-LIQUID Paraffin Wax SOLID-SOLID Relatively high heat of fusion Stable heating and cooling cycle Economical and abundant PROPERTIES OF THE DEVICE’S PCM Density, ρ (solid) 896 kg/m3 Density, ρ (liquid) kg/m3 820 Melting temperatures, T 328K – 330K Specific heat capacity, cs 3412 J/kgK Specific heat capacity, cl 4466 J/kgK Latent heat of fusion, L 197 kJ/kg Governing equations: Q = mc∆ϴ Sensible heating Q = mL Latent heating 60 Where Q = Pt Temperature (degC) 50 40 30 20 10 0 0 500 1000 1500 2000 Time (s) 2500 3000 3500 4000 SIMULATION Boundary Simulation conditions: software had to be modelled to account for the • Mass phase flow change rate of material. heat transfer medium 0.108kg/s at 333.2K • Fluid outlet subject to normal environmental conditions (293.2K Assumptions: and 101325Pa) • Paraffin wax is homogenous and isotropic Initial • Heat conditions: is transferred only by conduction • Same • Simulation as normal is time environmental dependentconditions Hence the paraffin wax’s thermal properties had to be designed as Results a model scale device): a series of (for sensible heating stages. Cs = 3412J/kgK for T<328K • Thermal heat capacity – 381.7kJ Csl = 98587J/kgK for 328K<T<330K Cl = 4466J/kgK for T>330K TESTING OF 1/5th SCALE PROTOTYPE “CHARGING” of Device: “DISCHARGING” of Device: Heat supplied thermal store = 595.8kJ Heat retrieved from thermal store = 247.0kJ η = 64.1% 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 ansources: automotive Two primary heat vehicle • Exhaust gas • Engine cooling process • 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. Retrieved from duaemanus.blogspot.com OVERVIEW OF A MICRO-CHP INTEGRATED DEVICE Increase mass implies: • a larger CAPEX • greater operating costs • enhanced revenue Scenarios Displacement of gas heating Displacement of electricity heating 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 THANK YOU ANY QUESTIONS?