Novel Design of a Portable Heat Energy Storage Device

Report
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?

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