Thermal Energy Storage Heat

Exchanger with Embedded

finned Heat Pipe and PCM

10th of Feb 2015

Amir Amini CEng , FIMechE Group Senior Research Specialist

The 32nd HEXAG Meeting Newcastle University

19th May 2015

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Summary

• Introduction

• PCM

• TES Prototype Heat Exchanger

• Experimental Rig

• Results and discussions

• Recommendation

• Barrier to develop large scale PCM

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Thermal

properties

• Phase change

temperature in

suitable

operating

range

• High latent

heat

per unit mass

• High specific

heat

Physical

properties

• High density

• Low density

variation during

phase change

• Little or no

super-

cooling

Chemical

stability

•No chemical decomposition

•Compatibility with container

materials

•Non-poisonous, non-

flammable

and non-explosive

• Available in large quantities

• Inexpensive

Economic factors

*PCM selection

* Regin, A.F., Solanki, S.C. and Saini, J.S., Heat transfer characteristics of thermal

energy storage system using PCM capsules: A review. Renewable and Sustainable

Energy Reviews, 12 (2008), p. 2438–2458 Feasibility studies is based on the currently

available PCMs.

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0

50

100

150

200

250

300

350

400

-75 -50 -25 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350

Late

nt

Hea

t (k

J/kg

)

Phase Change Temperature (⁰C)

Physical Properties of Various Manufacturers' Phase Change MaterialsACME PCP Australia PureTemp RGEES Rubitherm Salca Sasol Finoric Microtek Labs Climator Sweden AB PlusICE

>200 O C

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Sub-

cooling

Temperature below melting point

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SH Storage system vs. LH Storage system

Q = 𝑚 𝐶𝑝 DT= V cp ∆T ρ Q=m ( cp · ΔT + Δhmelt )PCM

= V ρ ( cp · ΔT + Δ

hmelt )PCM

Utilised heat capacity and change in Temp during charging and

discharging

The smaller the working temperature difference, ΔT , the bigger the

advantage of a latent heat storage unit versus a hot water storage

unit.

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• Automotive Direct / Indirect Passive Cooling

• Temperature Controlled Packaging & Shipping

• Military Backpack Battery Cooling

• Formula-1 Driver Comfort

• Datasafe Protection against Fire

• Integrated Domestic Solar Cooling & Heating

• Drink Can Passive Cooling

• Car Exhaust Heat Recovery Device for

Domestic Hot water Application

Typical small scale

applications

8Thermal Energy Storage with PCMBased on literature search, only a relatively small number of

results have been reported on successful system studies with

high capacity and high power rated storage units, especially for

solar heating systems

Changzhou Sunhome Solar Water

Heater Manufacture Co. 100ton

high temperature molten salt

storage tank.

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PCM Selected Product name: PLUSICE S89

Hydrated Salt base PCM, Mg

(NO3)2.6H2O 252

Melting point Tm = 89ºC

Latent heat Capacity = 151 kJ/kg

Volumetric Heat Capacity=234 MJ/m3

Liquid density = 1550 kg/m3

Specific Heat Capacity = 2.48 KJ/kg・KThermal conductivity = 0.67 W/m・KMaximum Operation Temperature=120 ºC

TES Prototype

Heat Exchanger

Thermocouples

Stainless Steel

Working Fluid Coil

Stainless Steel Heat Pipe

PCM Tank

Heat Transfer

Fluid, in &out

PCM_mpeg4.mp4

Schematic Diagram of the Experimental Rig

Thermal Energy Storage Heat Exchanger

test rig

Working Fluid (Water)

inlet and outlet

Thermocouples

Steam supply

line

Condensate

line

PCM

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Real Time PCM Charging and Discharging Data

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Experimental Results

Charging, PCM melting

(A) (B) (C)

(D) (E) (F) (G)

(H) (I)

A:t = 90 min

B:t = 140 min

C to H

I:fully melted PCM at time=500 min

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Discharging

A:Solidification began DB EC

GF JI K: 50 minutes

16Energy stored in PCM and Energy released from

PCM during Charging and Discharging.

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Two phase

Liquid/SolidPhase

ChangeLiquid

Melting

point

Charging Discharging

Variation of PCM temperature during heating

and cooling process using steam as HTF

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Recommendations

• Identify advanced heat transfer mechanisms for charging and discharging.

• Increasing the efficiency of long term heat storage systems with better insulation

• Higher efficiency could be achieved by optimising the performance of the Heat exchanger and selecting PCM with higher thermal conductivity.

• Further investigations require determining how heat pipe might be adjusted and optimized in TES heat exchanger to improve phase change rate in charging and discharging the PCM

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Barrier to the development of large scale TES system:

• Size of the system

• Low thermal conductivity of most PCMs

•Use of Heat Pipe to increase heat transfer rates, but they all occupy volume within the PCM heat exchanger, reducing stored Energy

• Enhance the process of heat transfer.

• Finding suitable applications

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Continue

Barrier to the development of large scale TES system:

• Too high investment costs of the total storage system

• Materials for use as PCM are still too expensive

• Low energy density of thermal storage systems

• Reliability of thermal energy storage systems

• Too large loss of heat over time

• Insufficient knowledge about system integration

• Insufficient knowledge about environmental impacts

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Thank You