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Numerical study of a waste heat recovery thermogenerator system

  • P. Donoso-GarcíaEmail author
  • L. Henríquez-Vargas
Technical Paper
  • 39 Downloads

Abstract

This paper presents a numerical study on waste heat recovery from a fluid stream using thermoelectric elements for energy harvesting. Two fluids were tested, air and steam, and the voltage and overall efficiency were computed for different sets of operational conditions. The mathematical description considered turbulent regime and coupled transport phenomena for the description of the main thermoelectric effects. Numerical solution was achieved using ANSYS/FLUENT commercial software with complementary implementations of user-defined scalars and user-defined functions to account for the mathematical model specific needs. The system global efficiency was computed for a pair of heat extraction conditions and different operational variables giving values within [0.11–9.22] (%). It was found that the global efficiency increases with the fluid temperature and the decrease in the external thermal resistance. For all cases studied, the global efficiency was greater when air was used as a heat carrier fluid due to its specific heat values which were about half the steam ones.

Keywords

Waste heat Thermoelectricity Heat recovery Seebeck effect 

List of symbols

\(c_p\)

Specific heat capacity

\(c_{1\varepsilon }\)

Turbulent model parameter

\(c_{2\varepsilon }\)

Turbulent model parameter

\(c_\mu\)

Turbulent model parameter

\({\mathbf {D}}\)

Mass transport tensor

\({\text {D}}\)

Square duct side

D

Mass diffusivity

\({\mathbf {E}}\)

Electric field intensity vector

e

Height

\(\mathbf {g}\)

External field acceleration

\(G_k\)

Rate of k generation

H

Specific enthalpy

h

Heat transfer coefficient

\(\mathbf {I}\)

Unitary tensor

I

Current

\(\mathbf {J}\)

Electric current density vector

\({\mathbf {K}}\)

Effective conductivity tensor

k

Turbulent kinetic energy

L

Length

\(\dot{m}\)

Mass flow

M

Molar weight

m

Mass fraction

\(N_n\)

Number of thermoelectric elements

\(p_0\)

Pressure

P

Power

Pr

Prandtl number

\(\varvec{q}\)

Total heat flux vector

\(\dot{q}\)

Heat generation per unit volume

\(Q_C\)

Heat outflow from cold reservoir

\(Q_H\)

Heat inflow from hot reservoir

\(\bar{R}\)

Universal gas constant

\(R_C\)

Heat resistance at cold junction

\(R_e\)

Electrical resistance

\(R_H\)

Heat resistance at hot junction

S

Generic source term

Sc

Schmidt number

T

Temperature

t

Time

\({\mathbf {u}}_{\mathrm{D}}\)

Gas velocity

W

Width

Subscripts

0

Inlet

B

Bottom

C

Center

Ce

Relative to ceramic phase

Cu

Relative to the copper phase

E

Relative to electricity conducting phases

eff

Effective

f

Relative to fluid phase

i

Internal

I

Interspacing between thermoelectric legs

L

Outlet

L

Left

max

Maximum

min

Minimum

n

Relative to n-type semiconductor phase

norm

Normalized variable

o

External

p

Relative to p-type semiconductor phase

R

Right

s

Relative to solid phase

T

Top

t

Turbulent

Greek

\({\varvec{\alpha }}\)

Absolute Seebeck coefficient tensor

\(\varvec{\varGamma }\)

Generic transport property tensor

\(\varepsilon\)

Rate of dissipation of k

\(\eta\)

Global efficiency

\(\lambda\)

Thermal conductivity

\(\mu\)

Dynamic viscosity

\(\varvec{\xi }\)

Permittivity tensor

\(\rho\)

Density

\(\varvec{\sigma }\)

Electric conductivity tensor

\(\sigma _{\varepsilon }\)

Turbulent model parameter

\(\sigma _{k}\)

Turbulent model parameter

\(\overline{\overline{\varvec{\tau }}}\)

Turbulent and molecular stress tensor

\(\varphi\)

Generic transported quantity

\(\psi\)

Voltage

Notes

Acknowledgements

The authors wish to acknowledge DICYT project 091611DG.

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Copyright information

© The Brazilian Society of Mechanical Sciences and Engineering 2019

Authors and Affiliations

  1. 1.Chemical Engineering DepartmentUniversidad de SantiagoSantiagoChile

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