Abstract

The rotary regenerator (also called the heat wheel) is an important component of energy intensive sectors, which is used in many heat recovery systems. In this paper, a model-based analysis of a rotary regenerator is carried out with a major emphasis given to the development and implementation of mathematical models for the thermal analysis of the fluid and wheel matrix. The effect of heat conduction in the direction of the fluid flow is taken into account and the influence of variations in rotating speed of the wheel as well as other characteristics (ambient temperature, airflow and geometric size) on dynamic responses are analysed. The numerical results are compared with experimental measurements and with theoretical predications of energy efficiencies.

Keywords: Heat recovery systems; Heat transfer in rotary regenerators; Numerical methods; Modeling

Nomenclature

A

heat flow cross-area (m²)

A_w

cross-area of matrix (m²)

B_w

width of the surface through which heat transfer (m)

c_p

specific heat at constant pressure (J/(kg °C))

C

flow stream thermal capacity rate of one side (J/(s °C))

C_r

ratio of heat capacity of the matrix to the minimum air heat capacity rate in a rotary air-to-air heat exchanger, thermal capacitance

d

diameter of flute (m)

D

inside diameter of the circular tube on one side estimated by all the free-flow flute (m)

h

convective heat transfer coefficient of fluid flow (W/(m² °C))

k

thermal conductivity (W/(m °C))

L

length of heat wheel (m)

mass flow rate (kg/s)

M

mass (kg)

Nu

Nusselt number

NTU

number of transfer unit

Pr

Prandtl number

q″

heat flux, heat transfer rate per unit of surface area (J/(s m²))

heat transfer rate on whole cross-area (J/s)

R

heat transfer resistance (m² °C/W)

Ratio

ratio of minimum to maximum air heat capacity rates in an air-to-air heat exchanger

Re

Reynold number

T

temperature (K)

U

total heat transfer coefficient (W/(m² °C))

v

velocity of airflow (m/s)

volumetric airflow rate (m³/s)

Greek letters

_cf

effectiveness of counter flow heat exchanger

rotational frequency (revolution per second) (Hz (s⁻¹))

μ

absolute viscosity coefficient (kg/(m s))

ν

kinematic viscosity coefficient (m²/s)

ρ

density (kg/m³)

Subscripts

c

cold fluid side of heat exchanger

h

hot fluid side of heat exchanger

w

wheel matrix

f

fluid

in

inlet

out

outlet

max

maximum value

min

minimum value

hy

hydraulic

Article Outline

Nomenclature

1. Introduction

2. Mathematical modeling of heat wheel

2.1. Physical principles and simplifying assumptions

2.2. Development of mathematical models

2.3. Evaluation of overall heat transfer coefficient

2.4. Influence of the rotational speed of the wheel matrix

3. Numerical methodology and results of simulation

3.1. Numerical methodology

3.2. Results of simulations

4. Theoretical verification and experimental comparisons

4.1. Analysis of the factors of major influence

4.2. Theoretical verification

4.3. Discussion of experimental results

5. Conclusions

Appendix A. Appendix

References