Thermal Energy Storage - gob.mx · 2017-11-17 · Testing Thermal Energy Storage System Three configurations of thermal energy storage system Results Analysis 1. Temperature trace

Thermal Energy Storage

Sudhakar Neti

Senior Research Scientist

Energy Research Center, Lehigh University

Bethlehem, PA 18015 USA

Project Researchers

• Profs. S. Neti and A. Oztekin, Carlos Romero

Students – James Blaney#, Weihuan Zhao, Bandar Alzahrani*,Abdul Al Kurdi*, Ali El Mozhughi, Laura Solomon, Xing Chao,Josh Charles, He Yun, C J Pan

Department of Mechanical Engineering and Mechanics and ERC

# now with Air Products and Chemicals Inc., in Saudi Arabia

• Profs. J. C. Chen and K. Tuzla

Students – Ying Zheng, John Barton, Arunachalam,

Department of Chemical Engineering

• Prof. W. Z. Misiolek

Students – J. C. Sabol, Mike Kracum

Department of Materials Science and Engineering

2

TES Research Needs

Research needs based on applications HVAC Dr. Carlos RomeroProcess heat use – Temporal, Spatial shiftsPower generation applicationsEnergy capture, regenerative appsAutomotive applications, etc.

Research areas includeMATERIALS, methods, processes, thermodynamics, economic optimization

TES Implementation

TES entails energy capture/reuse TES can be implemented using

the manipulation of .H2O (as in salts, low temp)

Storage of sensible heat (salts, concrete, sand)

Storage using latest heat of phase change Thermo-chemical changes in media

Current CSP systems use two (hot/cold) tank systems using sensible heat storage in KNO3-NaO3 salts between 200oC and 550oC.

• ASME Standards Committee for TES

Thermal Energy Storage Schematic

Thermal Energy can be stored directly in hundreds of MWh quantities

Large scale TES

TES needs for CSP are large scale, ~1,800 MWhth

Smaller and larger prototype studies are needed

Economic studies are needed determining the real impact on LCOE

DOE goal is ~ $15/kWhth . . . . . . . .. …………(and going down)

• Sensible Heat Storage• Solid or liquid •𝐐 = 𝐦𝐜𝐩∆𝐓

• Latent Heat Storage• Solid-Liquid, Liquid-Gas, Solid-Solid•𝐐 = 𝐦𝐋

• Thermochemical Energy Storage• Reversible chemical reactions•𝐐 = 𝐦𝐇𝐫

Thermal Energy Storage - Methods Temperature Ranges of Interest –HIGH 500 to 750C, MEDIUM 300C, LOW 29C

Analysis of Thermal Energy Storage

• Structural Analysis and Corrosion issues of EPCM

• Choice of PCM – Zn, Al, NaNO3, KNO3, MgCl2 -NaCl, MgCl2, NaCl, Metal Oxides

• Calorimetry -- Energy Storage & Retrieval

• Heat Transfer Analysis of PCM

• Thermocline Experiments

• Numerical Predictions – HT & Exergy

• Cost Analysis of Energy Storage Systems

8



9

Stress Analysis of Cylindrical Shell

0

50

100

150

200

250

300

350

400

450

70% 72% 74% 76% 78% 80% 82% 84% 86% 88%

Str

ess

[Mp

a]

Initial PCM Content

Corner

Tangential

Point force

Yield Stress

UTS

10

Materials and Structural Analysis of Encapsulation

The EPCM capsule void is filled with an inert gas such as Argon.

Photo of sectioned EPCM capsule with NaCl-

MgCl2 eutectic after significant thermal

cycling for temperatures ~500 °C.

Photo of sectioned MgCl2 EPCM capsule

after significant thermal cycling for

temperatures ~750 °C.

Multiple shapes and materials analyzed including plastic deformation

Inter-metallic Studies Ni/Zn /SS316

Region 1Region 2

Region 3

Region 4

Region 5

Region 6

Region 7Region 8

Region 9Region 10

Ni

Zn

Photomicrograph of the Ni/Zn specimen

Region 5

Region 4

Region 3

Region 2

Region 1

Photomicrograph of the SS316L/Zn specimen




13

MgCl2-NaCl Eutectic Preparation

The melting temperatures

of NaCl or MgCl2 are 804oC

and 714oC respectively.

The eutectic composition of

55 wt% MgCl2 – 45 wt%

NaCl has a melting point

(444oC).

The Eutectic PCM enclosed

in 304 stainless steel and 1018

carbon steel. 14

TES Systems Considered • Zn• Al• NaCl• MgCl2

• NaCl / MgCl2

• KNO3

• NaNO3

• KNO3/ NaNO3

• NaNO2

• NaNO3/NaNO2

• KNO3/NaNO3/NaNO2

• Sensible heat only

• Convection and Void I EPCM

• Charging and DichargingTemps (~551 K, ~660 K)

• 12 hr charging & discharging cycles

• 0.26 kg/m2-s mass flux

Energy and Exergy Analysis

Metal Oxides as PCM -- Comparison

MaterialTm

(°C)

Latent Heat

(kJ/kg)

Solid Cp

(J/kg K)

Liquid Cp

(J/kg K)Material

Tm

(°C)

Latent Heat

(kJ/kg)

NaNO3 308 162.5 1588 1650 K2B4O7 816 446.4

MgCl2 714 454 798 974 KBO2 947 383.4

NaCl 800 481 987 1200 Na4P2O7 970 220.4

Al 660 397.3 903 1177 KPO3 810 74.5

Na2B4O7 742 403.5 1174.3 2213.3 K2SiO3 976 325.4

NaBO2 967 509.1 1349.8 2218.8

Na4B2O5 641 617.3 1166.4 2048.8

Oxides have higher energy densities at comparable melting temperatures

Metal OXIDES

Phase Diagram of Li Na-KNO3 System

Phase Diagram of Li NaNO3 System

Viscocity of Li NaNO3 System

Latent Heat of AB-NaNO3 System

Specific Heat of NaKNO3 System

Specific and Latent Heats of PCMs

Nacl-MgCl2 NaNO3

23

Storage Capacity of EPCM

0 250 3500

200

400

600

800

Temperature (oC)

Sto

rage C

ap

acit

y (

kJ/k

g)

0 Tm0

200

400

600

800

1000

Temperature (oC)

Sto

rage C

ap

acit

y (

kJ/k

g)

Present Work for NaNO3 Bauer,T. et al.2012Jriri,T. et al. 1995 Takahashi,Y. et al. 1988

MgCl2-NaCl (m.p.: 450 °C)

328 kJ/kg

Latent Heat: 54% 370 kJ/kg

Latent Heat: 67%

NaNO3 (m.p.: 308 °C)

NaNO3 and MgCl2-NaCl are promising as storage medium.





24

EPCM Sample:

TS

TCalo.

Ta

Stirrer

Silicon Oil

EPCM

DAS &

Computer

25

Characterization of EPCM by Calorimetry Calorimeter Design, Operation and Principle

~ 5 minTime

Tem

per

atu

re

EPCM

Calorimeter

Ambient

TCalo.,t

TS,t

t0 te

TS,0

Ta, t

400 °C

40 °C

Q = Q + QEPCM Calo. Loss

Calorimetry and Numerical Simulations

Air

Oil

PCM

Air

Shell

Experimental Setup Computational Domain

Calorimeter Simulations – Chloride Salts

MgCl2

Accurately capture solid-liquid interface and void expansion

SteFo=0.08

30 s 60 s 120 s 200 s

SteFo=0.16 SteFo=0.31 SteFo=0.52






28

• ANSYS-FLUENT is applied to analyze the heat transfer process in EPCM capsules using theenthalpy method

• Equations are solved by iteration method.

• 2,560 nodes in finite volume discretization with time step of 2 seconds are sufficient to achievespatial convergence as well as temporal convergence.

Number of

nodes

Melting times

(Seconds)

170 2748

802 2766

2922 2772

Number of

nodes

Dimensionle

ss time step,

Δτ

Melting

times

(Seconds)

2922

0.0006 2772

0.00024 2772

0.00012 2772

Spatial convergence Temporal convergence

29

29LTES-ELMInterface - Charging Process with Air Isotherms after 3 hrs – HTS is Air Interface - Charging Process with VP-1

(Fig. for 76.2 mm diameter NaCl-MgCl2 eutectic capsule)

ANSYS-FLUENT Results

Assumptions and considerations:

NaNO3 is used as pure PCM material

76.2 mm diameter of 2-D capsule

Air is HTF for Re = 1230.

Various convective heat transfer coefficients as boundary at Re = 1230

The density of solid is constant, but the density of molten salt varies with temperature

Gravity effect is considered.

Boussinesq approximation is applied for buoyancy flow.

No volume changing between solid and molten salt

The effect of buoyancy-driven convection in the molten PCM enhances melting

30

Interface movement and temperature profiles in NaNO3 using air as HTF

Long cylinder 89 minutes during charging process

Effects of • Property

changes• Void• Buoyancy• Solid PCM

sinking

Void Constant Wall Temperature Sphere Melting

22mm Stainless steel sphere capsule with Sodium Nitrate. Liquid Fraction @240s

Spherical EPCM Capsule

SteFo=0.011 (t=5s)12.9% Void

SteFo=0.034 (t=15s)7.9% Void

SteFo=0.057 (t=25s)6.1% Void

SteFo=0.004 (t=5s)6.7% Void

SteFo=0.047 (t=60s)9.9% Void

SteFo=0.19 (t=240s)11.4% Void

Melting is convection-dominated Solidification is conduction-dominated

Solid

Void

Liquid

Effects of:• Shape• Gravity• Properties• Void• Conve-

ction• Solid

sinking• Power of

(J/s) Storage


• Structural Analysis and Corosion issues of EPCM





34

Thermocline Experimental Systems to TEST EPCM

Thermocline Test Section Copper capsules placed without insulation into the Test Section

EPCM

CapsulesStore Energy

36

Heater

HTF

Thermal Energy Storage System A pilot-scale TES system is designed, built and tested.

EPCM

EPCM

EPCM

EPCM

Insulation

wall

Q =Q (Q +Q +Q )Capsules HTF wall insulation loss

37

Measurements of Thermal Energy – Methodology

0 0.2 0.4 0.6 0.8 1 1.20

2

4

6

8

10

12

14

16

18

20

Time (hr)

En

erg

y S

tore

d i

n C

op

per

Cap

sule

s (M

J)

Meas. of Capsule Temperature

Meas. and Calc. by Energy Balance

38

Verification of Experimental Methodology

(1)

(2)

Q =Q -(Q +Q +Q )Capsules HTF wall insulation loss

Q = m Cp (T -T )Capsules s s s s,0

The instrumentation is qualified (>95%), for measurements of

energy storage and retrieval in thermal cycles

ProcessTemp. Range (°C)

of copper capsule

Difference

(Q2-Q1)/Q1

Heating #1 27-425 1.0%

Cooling #2 425-65 0.8%

Heating #3 65-421 1.8%

Cooling #4 421-148 2.2%

Heating #5 148-421 4.9%

Cooling #6 421-53 1.4%

Heating #7 281-431 -1.6%

Cooling #8 431-47 0.2%

Heating #9 47-426 -0.3%

39

Testing Thermal Energy Storage System Three configurations of thermal energy storage system

Results Analysis1. Temperature trace of outlet HTF in the storage system.

2. Temperature history of PCM in a charging and a discharging process.

3. Energy storage and retrieval of EPCM capsules in a thermal cycle.

4. Rates of energy storage or retrieved in a thermal cycle.

10 NaNO3 -- 308 °C10 MgCl2-NaCl

-- 444 °C

5 MgCl2-NaCl (444°C)

+ 5 NaNO3 (308°C)

1

2

3

4

5

6

7

8

9

10

1

2

3

4

5

6

7

8

9

10

1

2

3

4

5

6

7

8

9

10

40

NaNO3 Tests – Energy Storage and Retrieval

0 0.5 1 1.5 2 2.5 3 3.50

5

10

15

20

Time (hr)

En

erg

y S

tore

d i

n N

aN

O 3 C

ap

sule

s (M

J)

QNaNO

3

0 0.5 1 1.5 2 2.5 3 3.50

100

200

300

400

Time (hr)

NaN

O3 T

em

pera

ture

(oC

)

NaNO3 Temperature

~ 100°C

∆Q ~100°C

Phase change

contributes

37% of ∆ Q ~100°C

41

NaNO3 Tests – Rate of Energy Storage and Retrieval

0 0.5 1 1.5 2 2.5 3 3.5-10

-8

-6

-4

-2

0

2

4

6

8

10

Time (hr)

Rate

of

En

erg

y S

tora

ge o

r R

em

ov

al

(kW

)

HTF - Air

NaNO3 Capsules

Energy stored / retrieved is ~ 6 kW, at its maximum.

dtdQ

Q

TTCpmQ

EPCMEPCM

outfinfffAir

)( ,,

Overall temperature difference is at

its maximum, between HTF and

EPCM capsules








42

Numerical Prediction of Thermocline Flow and Heat Transfer

Stream lines for Re = 38,000, 0.038 kg/s, Inlet temp of 400 C

Flow is symmetric around the

rear stagnation point in laminar ,

the counter – rotating vortices

become larger and the wake

region extends downstream

several times.

Temperature counter, during

charging process, the melting

interface much faster in

turbulent and also with 𝜻 = 𝟎.9

Laminar at 5400 s Turbulent at 1800 s Laminar at 5400 s Turbulent at 900 s

= 0.7 = 0.9

44LTES-ELM

Instantaneous streamlines and isotherms of HTF for EPCM in channel:

Computational Results and discussion

Fig. streamlines and isotherms of HTF for EPCM in channel

LES – RSM: Numerical Analysis

Fig. vorticity contour – stream function

The Strouhal number (St = 0.36) for = D/Dw = 0.7

The comparison of the heat transfer coefficient predicted between RANS and LES for Re = 38,334 and = 0.7. The heat transfer coefficient predicted by the LES displays small amplitude fluctuation as the heat transfer from HTF to the EPCM is influenced by the vortex shedding. The time averaged value of the heat transfer coefficient predicted by both LES and RANS agree well.

This will ensure that the phase change phenomenon and the heat transfer inside the EPCM will hardly be influenced by the vortex shedding or other smaller scale flow structure.

45LTES-ELMFig. Comparison between the LES and the RANS for the heat transfer coefficient

46

Temperature of Heat Transfer Fluid

Temperature of HTF at outlet are well predicted by the model.

0 0.5 1 1.5 2 2.5 3 3.50

50

100

150

200

250

300

350

400

450

Time (hr)

Air

Tem

pera

ture

(oC

)

Model - Air - Inlet

Model - Air - Outlet

Experiment - Air - Inlet

Experiment - Air - Outlet

47

Energy into PCM from HTF Air – Expt vs. Numerical

Temperature distribution for one charging and discharging cycle of the last capsue in the thermocline 6 mm away from the capsule








• Cost Analysis of Energy Storage Systems

48

Cost Analysis of Thermal Energy Storage

System

Cost of storage units ($/kWh) as a function of the D, diameter of

the cylindrical EPCM capsule.

49


System

Cost of storage unit ($/kWh) as a function of length of the

capsule

50


System

Cost of pumps and balance of plant for storage system based on 2010 NREL

Report ~ $ 6,963,600

51

Cost Analysis of Thermal Energy Storage System

Cost of the storage unit ($/kWh) for different combinations of PCM and

encapsulation materials for D = 75 mm and Length of Capsule 15 D.

52

The best EPCM geometry based on heat transfer considerations, stress analysis, large-scale fabrication (millions of EPCM capsules) and cost analysis is a large aspect ratio cylinder (L/D of cylinder > 5) and diameter > 75 mm containing a salt.

Storage System cost $/kWh for D = 75 mm and H/D = 15

53

Cost of Thermal Energy Storage System

Thermal Storage Technologies for Solar Power KEY CONTRIBUTIONS

• Demonstrated Storage Technology – Sensible + Latent• Choice of PCM & EPCM – Materials for Temperature (29C to 750C)• Testing of EPCM – Calorimetry, Thermocline Flow Experiments• Numerical prediction of Transient Temperature Distributions• Numerical predictions of TES Exergy Analysis• New Metal Oxide PCMs and Corrosion considerations• Cost analysis for high temperature EPCM with continued decrease

of costs (~$15/kWhth).

Summary• Fossil fuels will be in use for decades

• Energy challenges driven by CO2 and global warming

• Nuclear has its own uncertainties

• Abundance of solar energy – PV, CST

• Costs of implementation of solar energy needs to be brought down

• Challenges – Capital, Bankability!

• Thermal Energy Storage has great potential – has broad implications.

55

Thank you.QUESTIONS ?

Gracias.¿Preguntas?

Gràcies. Preguntes?

All our life and energy

come from our Sun

S. Neti 6/28/12

Documents

Thermal Energy Storage - gob.mx · 2017-11-17 · Testing Thermal Energy Storage System Three configurations of thermal energy storage system Results Analysis 1. Temperature trace