Cover Page

Ultrasonic Technology for Desiccant Regeneration

Ye Yao

Shanghai Jiao Tong University, Shanghai, China

Shiqing Liu

Zhejiang Normal University, Jinhua, China

Title Page

This edition first published 2014

© 2014 Shanghai Jiao Tong University Press. All rights reserved.

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Library of Congress Cataloging-in-Publication Data

Yao, Ye.

Ultrasonic technology for desiccant regeneration / Ye Yao, Shiqing Liu.

pages cm

Includes bibliographical references and index.

ISBN 978-1-118-92160-9 (cloth)

1. Drying agents—Drying. 2. Ultrasonic waves—Industrial applications. 3. Air conditioning—Equipment and supplies. 4. Ultrasonic cleaning. I. Liu, Shiqing (Physicist) II. Title.

TP159.D7Y36 2014

660′.28426—dc23

2014016564

ISBN: 9781118921609

1 2014

About the Authors

Dr Ye Yao is an Associate Professor at the School of Mechanical Engineering, Shanghai Jiao Tong University, China. He received his PhD from Shanghai Jiao Tong University (SJTU), China. He was promoted as Associate Professor of SJTU in December 2008. From September 1, 2009 to September 1, 2010, he performed his research work in the Ray W. Herrick Laboratory at Purdue University (PU), USA. He was awarded as Excellent Reserve Youth Talent (First Class) and SMC Excellent Young Faculty by SJTU, respectively, in the year 2009 and 2010, and got the Shanghai Pujiang Scholars Talent Program in the year 2012. His current interests of research mainly include: (1) heat and mass transfer enhancement assisted by ultrasound; and (2) HVAC modeling and optimal control for energy conservation. He has successfully published about 100 academic publications and 30 patents and one academic monograph (sole author). He is now the peer reviewer of many international academic journals, such as the International Journal of Heat and Mass Transfer, International Journal of Thermal Sciences, International Journal of Refrigeration, Energy, Building and Environment, Energy and Buildings, and Applied Energy.

Dr Shiqing Liu is a Professor at the School of Mathematical and Information Engineering, Zhejiang Normal University, China. He received his PhD from Shanxi Normal University, China. His current interests of research are mainly applied acoustic and ultrasound transducers. He has published about 40 academic publications and over 10 patents in his research domains.

Preface

With global warming and the rapid improvement of people's living standards, energy consumption by air conditioning (AC) systems in buildings is on the rise. It has been noted that the dehumidification process accounts for a large proportion of energy consumption by an AC system. In southern areas of China where the climate is very hot and humid, the percentage of energy to be consumed by the dehumidification process in an AC system will be more than 40%. By using adsorption/absorption dehumidifying technology, the heat and moisture load of air can be processed separately, and a higher energy efficiency will be achieved compared with the conventional cooling dehumidification method. In addition, no condensation of water happens during the air dehumidification process with the adsorption/absorption method, which effectively prevents virus and mold from breeding, and hence improves indoor air quality (IAQ). Therefore, people are paying more attention to the adsorption/absorption dehumidifying method as the key technology for developing high-performance of AC systems.

Regeneration of desiccant is a crucial process during the air dehumidification cycle with the adsorption/absorption method. It will produce great influence on the energy efficiency of desiccant AC systems. The conventional regeneration method by heating is found to be energy-wasting due to the relatively higher regeneration temperature of some desiccant materials. So, we have put forward the ultrasound-assisted regeneration method in this book. The fundamental theory of the novel regeneration method is summarized as follows: 1geninfo The mechanical effect of ultrasound causes a series of rapid and successive compressions. This can reduce the thickness of boundary layer near the surface of solid desiccants and bring about the enhancement of mass transfer during regeneration. Meanwhile, the ultrasonic heating effect causes a temperature rise in solid desiccants and enhances internal moisture diffusivity known as “rectified diffusion.” 1geninfo For liquid desiccants, the cavitation effect induced by power ultrasound sprays the solution into numerous tiny droplets with a size range of 40–80 µm, which improves the regeneration rate of liquid desiccants through enlarging the contact area between the air and the desiccant solute instead of increasing the solution temperature.

The study in this book demonstrates that ultrasound-assisted regeneration can significantly increase energy efficiency of regeneration, shorten regeneration time and hence improve performance of the desiccant AC system. In addition, the temperature for regeneration can be reduced by introducing power ultrasound, which provides favorable conditions for the utilization of low-grade thermal energy (e.g., solar energy and waste heat) in the desiccant regeneration.

This book is edited based on recent studies on ultrasound-assisted regeneration. It consists of six chapters as below:

  1. Chapter 1 introduces the background of the topic to be illustrated in this book; it includes a literature review on up-to-date technologies related to desiccant materials, desiccant dryer systems and regeneration methods, and gives basic knowledge about ultrasound and methods for producing ultrasound.
  2. Chapter 2 deals with models for ultrasound-assisted regeneration for silica gel, presenting experimental and theoretical results and including a parametric study of the new regeneration method.
  3. Chapter 3 investigates the effect of ultrasound on the regeneration of a new honeycomb-type desiccant and includes a parametric study on ultrasound-assisted regeneration.
  4. Chapter 4 introduces the mechanism of the ultrasound-assisted regeneration for the liquid desiccants, and studies the effects of the ultrasonic atomization on the liquid desiccant regeneration.
  5. Chapter 5 deals with the working principle and design calculation method for longitudinal and radial vibration ultrasonic transducers that have potential applications in ultrasound-assisted regeneration.
  6. Chapter 6 presents several desiccant air-conditioning systems in which ultrasound-assisted regeneration is employed.

The book is written by Dr Ye Yao (Associate Professor at the Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, China) and Dr Shiqing Liu (Professor at the Institute of Mathematics and Physics, Zhejiang Normal University, China). Chapters 1, 2, 3, 4 and 6 as well as the appendix have been written by Dr Ye Yao, and Chapter 5 has been written by Dr Shiqing Liu and Dr Ye Yao.

Acknowledgements

The study work related to the book has been financially supported by Shanghai Pujiang Program (2012) and several National Nature Science Foundations (No.50708057; No.11274279; No.11074222) as well as Shanghai Jiaotong University Academic Publishing Fund (2013). Meanwhile, this book has been successfully chosen as China Classics International Academic Publishing Project (2014). The publication of the book will be an important reference for related research fields.

I would like to express my appreciation to those who have educated, aided and supported me: my mentors Prof. Ruzhu Wang (Shanghai Jiao Tong University), Prof. Guoliang Ding (Shanghai Jiao Tong University), Prof. Xiaosong Zhang (Southeast University, China); my collaborators Mr Beixing He (senior engineer at the Institute of Acoustics, Chinese Academy of Sciences) and Prof. Houqing Zhu (Institute of Acoustics, Chinese Academy of Sciences); and my students, including my PhD Candidate Yang Kun (who designed most of the computer programs), Dr Weijiang Zhang (who carried a large number of experimental studies related to this book), my Master Candidate Godwin Okotch (who revised the language errors), Weiwei Wang and Zhengyuan Zhu (who participated in some experimental tests and measurements).

Finally, I offer my heartfelt gratitude to the editorial director Dr Fangzhen Qian and Mrs Yingchun Yang at Shanghai Jiao Tong University Press for their help, cooperation, advice and guidance in preparing this edition of the book.

Ye Yao
Shanghai Jiao Tong University
December 30, 2013

Nomenclature

f04-math-0001 Ultrasonic absorptivity by medium f04-math-0002 Mechanical quality factor of transducer
Ao Pre-exponential factor of Arrhenius equation, m2/s Cw Moisture concentration in the mainstream air, kg/m3
f04-math-0003 Activity of water Cw* Concentration on the surface of liquid droplet, kg/m3
f04-math-0004 Debye-Huckel constant for the osmotic coefficient COP coefficient of performance
AEE Average energy efficiency, % CR Contribution ratio of ultrasonic effect to the total enhancement of regeneration
AMR Additional moisture removal brought about by ultrasound, kg CRT Conditioned regeneration time, s
AMRC Additional moisture removal capacity brought about by ultrasound, kg/s f04-math-0005 Diameter, m
ASEC Adiabatic specific energy consumption, J/(kg moisture desorption) D Diffusion coefficient, m2/s
f04-math-0006 Standard atmosphere pressure, Pa DCOP Dehumidification coefficient of performance
f04-math-0007 Specific heat, J/(kg.°C) E Energy consumption, J;
or NRTL binary interaction energy parameter;
or Young's modulus of the material, Pa;
or electric field
f04-math-0008 Specific heat ratio Ea Activation energy, kJ/mol
cos Cosine function EP Enhancement percentage of regeneration, %
cosh Hyperbolic cosine function ER Enhanced ratio of regeneration brought by ultrasound
cot Cotangent ERE Experimental relative error
f04-math-0009 Adiabatic sound velocity in the air, m/s ERARR Enhancement ratio of average regeneration rate
f04-math-0010 Equivalent vibration velocity, m/s ERERR Experimental relative error of regeneration rate, %
C Heat capacity rate, W/°C ESR Energy-saving ratio
Co One-dimensional cutoff capacitance of the piezoelectric ceramic, F ESEC Excess specific energy consumption, J/(kg moisture desorption)
f04-math-0011 Drag coefficient f Acoustic frequency, Hz
fc Activity coefficient MAMR Maximum additional moisture removal, kg
F Force, N MEEU maximum energy efficiency of ultrasound, %
g Gibbs energy of molecules;
or acceleration of gravity, m/s2		 MMD Mass mean diameter, m
g' Derivative of equilibrium isotherm MR Dimensionless moisture ratio
f04-math-0012 Voltage constant of piezoelectric ceramic MRC Moisture removal capacity, kg/s
G Mass flow rate, kg/(m2.s) MRS Mean regeneration speed, kg/s
h Enthalpy, J/kg; or height, m MRE Mean Relative Error, %
f04-math-0013 Adsorption (desorption) heat of desiccant, kJ/(kg water) n Electromechanical conversion factor of piezoelectric ceramic
f04-math-0014 Coefficient of heat transfer, f04-math-0015 N Molar flux, mol/(m2.s); or number of droplets or piezoelectric ceramic wafers
f04-math-0016 Unit of the imaginary number Nu Nusselt number
f04-math-0017 Sound intensity, f04-math-0018;
or electric current, A		 NRTL Nonrandom two-liquid theory
f04-math-0019 Ionic strength in mole fraction scale f04-math-0020 Pressure or tensile stress, Pa
f04-math-0021 The zero-order Bessel function of the first kind f04-math-0022 Power, W
f04-math-0023 The first-order Bessel function of the first kind PE Prediction error, %
k Wave number, 1/m f04-math-0024 Moisture ratio in medium, kg water/(kg dry medium)
f04-math-0025 Modified complex wave number Q Heat trtansfer rate, W
f04-math-0026 Coefficient of mass transfer or mass transfer flux, f04-math-0027 r Radius, m
l Length, m f04-math-0028 Latent heat of vaporization of water at 0°C, J/kg
f04-math-0029 Height of the packed bed or thickness of particle surface layer or mean free path, m f04-math-0030 Dynamic flow resistance, kg/(m2.s);
or gas constant, kJ/(mol.K)
f04-math-0031 Mass, kg RD Regeneration degree
M M-type honeycomb desiccant;
or molecular weight, kg/kmol		 Rm Mass transfer resistance, f04-math-0032
RV Vibration speed ratio of the front surface to the rear surface of the transducer SPL Sound pressure level
RR Regeneration rate, kg/s f04-math-0033 Temperature
Re Reynolds number tan Tangent function
RE Regeneration enhancement, kg/s;
or regeneration effectiveness		 tanh Hyperbolic tangent function
s Strain, m/m T[t] Temperature, K [°C]
sc Strain constant TSEC Total specific energy consumption, J/(kg moisture desorption)
ssr Elastic flexibility coefficient, m2/N u Velocity or sound wave propagation speed, m/s
sin Sine function f04-math-0034 Induced velocity of air due to ultrasonic oscillation, m/s
f04-math-0035 Elastic flexibility coefficient under constant axial electric displacement, m2/N U Overall heat transfer coefficient of heat exchanger, W/(m2.°C)
f04-math-0036 Elastic flexibility coefficient under constant axial electric field, m2/N UF Ultrasonic frequency, Hz
UP Ultrasonic power, W
sinh Hyperbolic sine function f04-math-0037 Volume, m3; or voltage, V
S Area, m2 f04-math-0038 Humidity of air on the surface of solid or liquid, kg/(kg dryair)
SEC Specific energy consumption, J/(kg moisture desorption) f04-math-0039 Humidity of air in the main stream, kg/(kg dryair)
SMD Sauter mean diameter x Distance or spatial space, m;
or mole fraction in the mixture;
or concentration by mass
Sh Sherwood number f04-math-0040 The zero-order Bessel function of the second kind
Sc Schmidt number f04-math-0041 The first-order Bessel function of the second kind
SV Volumetric surface area of solid desiccant, m2/ m3 f04-math-0042 (or Z) Acoustic impedance in medium, Pa.s/m3
SS ss-type honeycomb desiccant
Greek Letters
f04-math-0043 Thickness, m f04-math-0044 Relative humidity, %
f04-math-0045 Coefficient of thermal conductivity, W/m·°C; or wave length, m f04-math-0046 Density, kg/m3
f04-math-0047 Kinematic viscosity, m2/s;
or Poisson's ratio		 f04-math-0048 Working efficiency
f04-math-0049 Sound attenuation coefficient in medium; or NRTL non-randomness factor f04-math-0050 Electric displacement
f04-math-0051 Voltage constant of the piezoelectric ceramic f04-math-0052 Time, s
f04-math-0053 Void fraction of desiccant bed;
or porosity of particle;
or effectiveness of a heat exchanger		 f04-math-0054 Shear modulus of material
f04-math-0055 Dielectric constant f04-math-0056 Structure factor of the packed bed
f04-math-0057 Transverse electro-mechanical coupling coefficient f04-math-0058 Slope of the straight line
f04-math-0059 Effective electro-mechanical coupling
coefficient		 f04-math-0060 Dynamic viscosity, Pa.s
f04-math-0061 Acoustic angular frequency or resonance angular frequency of transducer, rad/s f04-math-0062 Mass flow rate ratio of liquid desiccant to air;
or the ratio of the outer radius to the inner radius of the metal cylindrical shell
f04-math-0063 Surface tension, N/m;
or stress, Pa		 f04-math-0064 Tortuosity factor
f04-math-0065 Closest approach parameter of
the Pitzer-Debye-Huckel equation		 f04-math-0066 Extension factor of the conical rod
f04-math-0067 Vibration displacement, m f04-math-0068 Increment or absolute error
f04-math-0069 Vibration velocity, m/s
Subscripts
a Air e Equivalent size of pore in the packed bed; or equilibrium state; or effective
ads Adsorption env Environmental or ambient
ave Average f Falling
c Cool fluid fc Front cover of the transducer
dry Dry sample g gas
des Desorption h Hot fluid
deh Air dehumidifier hx Heat exchanger
in Inlet f04-math-0070 Saturated sate
i Inner surface SRC Short-range contribution to the activity of molecules
ini Initial state reg Regenerator or regeneration
K Knudsen rc Rear cover of the transducer
LRC Long-range contribution to the activity of molecules f04-math-0071 Solid desiccant or liquid droplet
m Mechanical; or mean value syn Synergistic effect
mcs Metal thin-walled cylindrical shell ta At the regeneration air temperature
mole Molar tar Target (or terminal) value
min Minimum teff Ultrasonic heating effect
max Maximum
mcs Metal cylindrical shell ts At the solution temperature
NU Without ultrasonic radiation T Ultrasonic transducer
o On the radiation surface of ultrasonic transducer; or outer surface U In the presence of an ultrasonic field
ord Ordinary v At constant volume
out Outlet veff Ultrasonic mechanical effect
p At constant pressure vap Vapor or vaporization
pc Piezoelectric ceramic w Moisture or water