Low Grade Waste Heat RecoveryProfessor HoSung Lee

10/3/2018

Mechanical and Aerospace Engineering

Western Michigan University

1

Chapter 7 of My book

Ideal Equation can be realistic.

2

Models

• Working fluid is ethylene glycol (Otherwise the same as Chapter 7)

• With and without aluminum block

• With or without Heat Sinks (Junction temperature = fluid inlet)

3

Two Flow System for Thermoelectric Generator

Ws

Ls

bs

tszs

4

Inputs for Modeling

• High fluid inlet temperature of 120 C

• Low fluid inlet temperature of 25 C

• Both volume flow rates of 1 gpm

• Thermoelectric module TE-127-1.0-2.5 (Ae = 1mm^2, L = 2.5 mm)

5

Mathcad Results

TEG RL Th.i Vol Ae le 3.701 %

TEG RL Th.i Vol Ae le Pout RL Th.i Vol Ae le Qh RL Th.i Vol Ae le

I RL Th.i Vol Ae le Qh RL Th.i Vol Ae le Qc RL Th.i Vol Ae le Th RL Th.i Vol Ae le

Tc RL Th.i Vol Ae le

Th.o RL Th.i Vol Ae le Tc.o RL Th.i Vol Ae le

Find I Qh Qc Th Tc Th.o Tc.o

6

With Aluminum Block Without Aluminum Block

0 1 2 3

40

60

80

100

120

Load Resistance Ratio

Jun

ctio

n T

emp

erat

ure

(°C

)

Hot Junction

Cold Junction

0 1 2 3

40

60

80

100

120

Load Resistance Ratio

Jun

ctio

n T

emp

erat

ure

(°C

)

Hot Junction

Cold Junction

0 0.5 1 1.5 2 2.5 30

0.2

0.4

0.6

0.8

1

0

1

2

3

4

5

Power outout

Efficiency

Load Resistance Ratio

Ou

tpu

t P

ow

er (

W)

Eff

icie

ncy

(%

)

0 0.5 1 1.5 2 2.5 30

0.2

0.4

0.6

0.8

0

1

2

3

4

5

Power outout

Efficiency

Load Resistance Ratio

Ou

tpu

t P

ow

er (

W)

Eff

icie

ncy

(%

)

7

With Aluminum Block Without Aluminum Block

0 50 100 150 2000

1

2

3

0

1

2

3

Matched Output Power

Max. Possible Output Power

High Temperature Inlet (C)

Mat

ched

Outp

ut

Pow

er (

W)

Max

imum

Poss

ible

Outp

ut

Pow

er (

W)

0 50 100 150 2000

2

4

6

8

0

2

4

6

8

Max. Efficiency

Max. possible Efficiency

HighTemperature Inlet (C)

Max

imu

m E

ffic

ien

cy (

%)

Max

imu

m P

oss

ible

E

ffic

ien

cy (

%)

0 50 100 150 2000

1

2

3

0

1

2

3

Matched Output Power

Max. Possible Output Power

High Temperature Inlet (C)

Mat

ched

Outp

ut

Pow

er (

W)

Max

imum

Poss

ible

Outp

ut

Pow

er (

W)

0 50 100 150 2000

2

4

6

8

0

2

4

6

8

Max. Efficiency

Max. possible Efficiency

HighTemperature Inlet (C)M

axim

um

Eff

icie

ncy

(%

)

Max

imu

m P

oss

ible

E

ffic

ien

cy (

%)

8

With Aluminum Block Without Aluminum Block

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

0

1

2

3

4

5

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

0 1 2 3 4 50

1

2

3

0

1

2

Matched Output Power

Max. Possible Output Power

Leg length (mm)

Mat

ched

Outp

ut

Pow

er (

W)

Max

imum

Poss

ible

Outp

ut

Pow

er (

W)

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

0

1

2

3

4

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

0 1 2 3 4 50

1

2

3

0

1

2

Matched Output Power

Max. Possible Output Power

Leg length (mm)M

atch

ed O

utp

ut

Pow

er (

W)

Max

imum

Poss

ible

Outp

ut

Pow

er (

W)

9

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

0

1

2

3

4

5

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

0

1

2

3

4

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

With Aluminum Block Without Aluminum Block

0 1 2 3 4 50

1

2

3

0

1

2

Matched Output Power

Max. Possible Output Power

Leg length (mm)

Mat

ched

Outp

ut

Pow

er (

W)

Max

imum

Poss

ible

Outp

ut

Pow

er (

W)

0 1 2 3 4 50

1

2

3

0

1

2

Matched Output Power

Max. Possible Output Power

Leg length (mm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m P

oss

ible

Ou

tpu

t P

ow

er (

W)

0 1 2 3 4 50

2

4

6

8

0

2

4

6

8

Max. Efficiency

Max. possible Efficiency

Leg length (mm)

Max

imu

m E

ffic

ien

cy (

%)

Max

imu

m P

oss

ible

E

ffic

ien

cy (

%)

0 1 2 3 4 50

2

4

6

8

0

2

4

6

8

Max. Efficiency

Max. possible Efficiency

Leg length (mm)M

axim

um

Eff

icie

ncy

(%

)

Max

imum

Poss

ible

E

ffic

iency

(%

)

10

With Aluminum Block Without Aluminum Block

0 0.5 1 1.5 20

1

2

3

4

0

1

2

3

4

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

le 0.5mm=

0 0.5 1 1.5 20

1

2

3

4

0

1

2

3

4

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

le 0.5mm=

110 0.5 1 1.5 2

0

0.2

0.4

0.6

0.8

0

1

2

3

4

5

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

0

1

2

3

4

Matched Output Power

Maximum Efficiency

Volume Flow Rate (gpm)

Mat

ched

Ou

tpu

t P

ow

er (

W)

Max

imu

m E

ffic

ien

cy (

%)

OTEC (Ocean Thermal Energy Conversion)

Bi-Te element size: 10 x 1.5 mm.Total number of n-p couples: 10,000 couples/Number of TEG modules: 500 modules.

12

Kusatsu Hot-springs TEG System

13

Waste Heat Recovery

• Geothermal Energy

14

15

Table 1. Summary for three specific waste heat recovery cases.

Performance of TEG Heat Recovery Units

(Performance for maximum power output)

Waste heat sources Hot Water 80 °C

Cold Water 25 °C

Hot Water 80 °C

Cold Water 25 °C

Hot oil and water

mixture 200 °C

Cold water 25 °C

Thermoelectric material

used

Bismuth telluride

nanocomposites

ZT = 1.4 at 80 °C

(Poudel, Hao et al. 2008)

Bismuth telluride

Bulk

ZT = 1.0 at 80 °C

(Poudel, Hao et al.

2008)

Bismuth telluride

nanocomposites

ZT = 1.1 at 200 °C

(Poudel, Hao et al.

2008)

Optimal calculations for one module

Power output (W)

per module base area 25

cm^2

~ 5 W (6.5 W) ~ 3.5 W (4.8 W) ~ 35 W

Total heat delivered (W)

~ 200 W ~ 194 W ~700 W

Conversion efficiency

(%)

~ 2.5 % (1.7 %) ~ 1.8 % (1.3 %) ~ 5 %

Ideal efficiency* /Carnot

efficiency (%)

3.4 % / 15.5 % 2.5 % / 15.5 % 6.6 % / 31 %

Estimate cost $ per

watt**

~ $2/W ~ $3/W < $1/W

Element length (mm)

0.5 mm 0.6 mm 0.3 mm

Calculations for 1000 kW power output

Total # of modules

(= 1000 kW / module

power output)

200,000 286,000 28,000

Volume of total arrays

(= Volume of array × #

of array)

10 m^3 15 m^3 1.5 m^3

Power density

(= 1000 kW / volume of

total arrays)

100 kW/m^3 70 kW/m^3 700 kW/m^3

Total hot water flow rate

(kg/s) based on water

velocity (m/s) in channel

~ 230 kg/s

0.5 m/s

~ 230 kg/s

0.5 m/s

~ 215 kg/s

0.5 m/s

Power generation (kW)

1000 kW 1000 kW 1,000 kW

Total waste heat (kW)

40,000 kW 56,000 kW 20,000 kW

Pump power (kW) for

hot & cold water flows

80 kW 80 kW 80 kW

Power generation

efficiency (%)

(1,000kW-80kW) /

40,000kW = 2.3 %

(1,000kW-80kW) /

56,000 kW = 1.6 %

(1,000kW-80kW) /

20,000 kW = 4.6 %

Payback (years) with

electricity price $0.1/kW

and operating time at

7000 hours/year

~ 3 years

=(1000kW*$2/W) /

[(1000kW-80kW)

×7000hr×$0.1/kWh]

~ 4.5 years

=(1000kW*$3/W) /

[(1000kW-80kW)

×7000hr×$0.1/kWh]

< 1.5 years

=(1000kW*$1/W) /

[(1000kW-80kW)

×7000hr×$0.1/kWh]

The End

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