Efficient Therm

oelectric Power Conversion from W

aste

Heat for Deployed Forces

Project SI-1651

Chris Caylor and Rama Venkatasubramanian, Center for Solid-State Energetics,

RTI International, Research Triangle Park, NC 27709;

Paul Dev, D-STAR Engineering Corporation, Shelton, CT 06484;

Selma Matthews, U.S. Arm

y CERDEC, Arm

y Power Division, Fort Belvoir, VA 22060

This work was enabled by the DARPA DTEC Program funded through the Office of Naval Research

Perform

ers

Dr. Chris Caylor

RTI International

Specialist in thin film

and bulk m

aterials for therm

oelectric applications.

Dr. Rama Venkatasubramanian

RTI International

Director of Center for Solid-State Energetics, original work on high

perform

ance thin-film

superlattice therm

oelectric m

aterials and devices

Dr. Paul Dev

D-STAR Engineering Corporation

Project manager and president of D-Star Engineering, providing expertise

in heat exchangers for therm

oelectric devices with diesel engines.

Ms. Selm

a Matthews

US Arm

y CERDEC, Arm

y Power Division

Senior Research Engineer in the CERDEC Arm

y Power Divisions Power

Technology Branch and responsible for the identification, research and development

of emerging and advanced power technologies that will support future DoD

platform

s.

Problem Statement

•The DoD and the m

obile forces of its branches m

ust deal with thelarge carbon

footprintof its operations by increasing fuel efficiencyand lowering fuel use.

•Fuel efficiency in m

obile electric power generationis one area where improvements

can be m

ade.

•Furtherm

ore, fuel use, as well as personnel risk, could be lowered by m

ore efficient

power generationby requiring fewer fuel deliveries, which m

ust be accomplished via

manned convoys.

Technical Objective: Develop waste heat recovery systems with power levels up to 500 Watts integrated with mobile diesel generators.

Therm

oelectric Power Generation

�Therm

oelectric (TE) materials joined in

couples (p-type and n-type) can be used

for cooling or power generation

�Power generation uses a temperature

difference (∆T) to drive electric current.

�TE conversion efficiency is based on

materials properties and achievable ∆T in

the application (heat exchangers).

�ZT is TE figure-of-merit, higher ZT m

eans

more efficient power generation

TE Technology for Different Temperature Ranges

Bi-Polar Couple Assembled Module

(BCAM) Device Technology

Traditional

BCAM

Low stress; Scalable; Withstands 16 G’s

RMS acceleration at device level

RTI TE devices can be used independently or can be

combined in cascades

3-4

3-4

9-10

Mid-Temp

Stage

350

500

4-5

4-5

16-18

High/Mid/Low

Cascade

775

800

2-3

3-4

13-14

Mid/High

Cascade

650

800

4-5

4-5

13-14

Mid/Low

Cascade

475

500

Incinerator /

Engine Exhaust

8-11

4-5

5-6

Low-Temp

Stage

150-175

200

Engine Jacket

1-2

0.5-1

2-3

Low-Temp

Stage

50-75

90-100

Hot Water

Specific

Power

(W/gram)

Power

Density

(W/cm

2)

Eff.

(%)

TE Device

Structure

∆ ∆∆∆T (K)

Avail.

Thot

(oC)

Field Application

Scaling of Low-Temperature TE Arrays

4x4 m

odule

P ~ 1 W

6x6 m

odule

P ~ 2.1 W

16x16module

8x8 m

odule

P ~ 3.4 W

Multi-Module-Arrays

1 p-n

couple

P ~ 0.16 W

512-couple

P ~ 15 W

2048-couple

P ~ 19 W

Mid-Temperature Bulk

Device Scale Up Progress

1 Bulk Couple

0.2 W

atts

8 Bulk Couples

1.5 W

atts

15 Bulk Couples

3 W

atts

31 Bulk Couples

6 W

atts

60 Bulk Couples

12 W

atts

124 Bulk Couples

25 W

atts

504 Bulk Couples

40 W

atts

63 Bulk Couples

Technical Approach

Estimated Perform

ance of 2-Stages vs1-Stage Based On

Measured Individual Stage Efficiencies

η~5%

Low-Tem

perature

Single Stage

150°C 450°C 750°C

η~10-13%

Mid-Tem

perature

Single Stage and

2-Stage Devices

η~15-18%

High-Tem

perature

3-Stage Devices

65.8

81.0

92.4

101.9

117.6

129.7

Power/cpl

(mW)

THot~ 500 °C 8.5

9.1

9.8

10.2

11.0

11.6

Eff

(%)

7.6

56.3

6.4

39.6

125

BCA-337

6.9

47.1

5.8

33.1

150

BCA-338

8.3

66.7

6.9

46.7

100

BCA-335

8.6

73.6

7.1

51.0

75

BCA-336

9.5

88.7

8.3

67.5

50

BCA-330

10.0

97.8

8.7

73.9

25

BCA-332

Eff

(%)

Power/cpl

(mW)

Eff

(%)

Power/cpl

(mW)

THot~ 450 °C

THot~ 400 °C

TCold

(°C)

Device

Entrance Cap of Muffler Back of Muffler Muffler Front of Muffler

DRS 3kw gen-set

Generator Engine Engine Cooling Fan Hsg.

DRS Fermont 3 kW Gen-set

Muffler

Possible location of Header Pipe

Thermoelectric Device

Possible Location of Thermoelectric Device

Thermoelectric Device 5cm x 5cm

Rough Guide to Potential Thermoelectric

System

Perform

ance

Phase 2 and Phase 3 will need to see increased therm

al

and converter efficiencies to reach 10% fuel

efficiency increase go

Perform

ance for phase 1 will be based on full loadoperation and using single-stage

thermoelectric devices

CERDEC data on 3kW TQG shows that it is ~24% fuel efficient at full load (12.5kW

heat input and 9.5kW waste heat, of which ½, roughly, makes it into the exhaust)

Thermal efficiency = converting available waste heat to that of heat into

thermoelectric device

Converter efficiency = converting heat into TE device to electricity

52%

36%

14%

Required Therm

al Efficiency

300W

150W

50W

TE Output Power Target

10%

5.0%

1.7%

Fuel Efficiency Increase

12%

9.0%

7.5%

TE Converter EfficiencyTarget

Phase 3

Phase 2

Phase 1

New

Q-m

eter System

at RTI for Larger Power

Device Efficiency M

easurements

5-10 W

atts heat flow (much larger than

earlier Q-m

eter m

easurements)

Used to m

easure single-stage and

multi-stage devices for efficiency

comparison

Comparison of Q-m

eter and Calculated Heat Flows

456789

10

11

12

13

250

350

450

550

Hot-Side Temperature (C)

Thermoelectric

Conversion Efficiency (%)

Calculated Heat Flow

Q-Stick Measured Heat Flow

11.1

2.9

8.5

25

150

500

2-stage PbTe/TAGS//SL

11.3

3.1

8.5

25

150

500

2-stage PbTe/TAGS//SL

11.6

2.9

9.0

25

130

500

2-stage PbTe/TAGS//SL

11.6

11.6

25

500

Single stage PbTe/TAGS

Total η

(%)

Low-Temp

Stage

η(%

)

PbTe/TAGS

Stage η

(%)

TCold

(°C)

TMid

(°C)

THot

(°C)

Device

Single-Stage PbTe/TAGS Efficiency M

atrix

*SL = RTI’s Superlattice Thin Film

Device

�12-13% 2-stage conversion efficiency is the target for phase 2/phase 3 demonstration

for SERDP

�Steady development of superlattice devices has shown improved perform

ance and is

poised to pass the perform

ance of the single-stage device

Entrance End Cap M

uffler Characterization

0

50

100

150

200

250

300

350

400

450

500

00.5

11.5

22.5

3

Generator Load (kW)

Temperature (°C)

Cooling Air

Muffler Metal

Exhaust Gas