BSE Public CPD Lecture – Seminar on Liquid Desiccant A Seminar on Liquid Desiccant delivered by Professor Zhang Xiaosong and Mr. Chang Liang was held on 3 August 2010 (Tuesday). Over 120 participants attended this public CPD lecture co-organized by PolyU Department of Building Services Engineering and The American Society of Heating, Refrigerating and Air-Conditioning Engineers-Hong Kong Chapter (ASHRAE-HKC). Powerpoint file of the CPD lecture Professor Zhang is the Associate Dean of the School of Energy and Environment at Southeast University. He has engaged with the research on liquid desiccant for over 10 years. His research areas include novel dehumidifier, the heat and mass transfer in the liquid desiccant system, solar energy based regenerator, liquid desiccant based novel air conditioning system and the liquid desiccant based ice making. Mr. Chang is a PhD candidate in Building Energy Research Centre at Tsinghua University. He has been doing consulting work in US, Hong Kong and mainland China for 5 years. His research works are related to new technologies applications including liquid desiccant applications with goals of saving energy and low carbon footprint. Professor Zhang Mr. Chang
Transcript
BSE Public CPD Lecture – Seminar on Liquid Desiccant A Seminar on Liquid Desiccant delivered by Professor Zhang Xiaosong and Mr. Chang Liang was held on 3 August 2010 (Tuesday). Over 120 participants attended this public CPD lecture co-organized by PolyU Department of Building Services Engineering and The American Society of Heating, Refrigerating and Air-Conditioning Engineers-Hong Kong Chapter (ASHRAE-HKC).
Powerpoint file of the CPD lecture Professor Zhang is the Associate Dean of the School of Energy and Environment at Southeast University. He has engaged with the research on liquid desiccant for over 10 years. His research areas include novel dehumidifier, the heat and mass transfer in the liquid desiccant system, solar energy based regenerator, liquid desiccant based novel air conditioning system and the liquid desiccant based ice making. Mr. Chang is a PhD candidate in Building Energy Research Centre at Tsinghua University. He has been doing consulting work in US, Hong Kong and mainland China for 5 years. His research works are related to new technologies applications including liquid desiccant applications with goals of saving energy and low carbon footprint.
Professor Zhang
Mr. Chang
The liquid desiccant system, as an energy-efficient, environmentally friendly and healthy means of air dehumidification, can be used to achieve the decoupling of the air latent load and sensible load removal. The driving force of moisture removal by the liquid desiccant is the water vapour pressure difference between the desiccant solution and the air. The moisture in air is absorbed by the strong desiccant solution rather than condensed by low temperature coolants. In addition, the sensible load can be removed by relatively high temperature coolants. Therefore, COP of chilling equipment can be improved and considerable energy can be saved. In the lecture, the two speakers introduced the state-of-the-art research and applications of liquid desiccant. Various kinds of commonly used liquid desiccants were discussed.
Introducing the new liquid dehumidification air-conditioning
systems
Presentation by Dr. Xiao
In addition, Dr. F. Xiao of BSE introduced her research project on application of liquid desiccant based air conditioning system in Hong Kong which is supported by Hong Kong Environment and Conservation Fund (ECF). In the Q&A session, participants interacted with our speakers on their research works and presentations.
Interaction
BSE News 2010 CPD 100803
Fundamental research progresses Fundamental research progresses about the liquid dehumidification about the liquid dehumidification
airair--conditioning systemconditioning system
School of Energy & EnvironmentSoutheast UniversityAug 3th, 2010，Hong Kong
Prof. Xiaosong Zhang
1933:
2000:
2006:
1902成立
1988
1952南京工学院
1928国立中央大学
九龙湖新校区
AUTHOR’S INTRODUCTION
Vice dean of the School of Energy and Environment, Southeast University.Director of the Education Ministry affiliated engineering center “low-carbon
construction environment equipments and energy-conservation systems”；Board members of (IIR)E2, Director of the Chinese Society of Engineering
Thermophysics， of Chinese Association of Refrigeration, Vice Chairman of Jiangsu Province Institute of Refrigeration；
Special expert of the national twelfth five year plan addressing climate change challenge, Leading young talent of Jiangsu Province"333 high-level personnel training project” and the first winners of several awards tem-level scientific and technological achievements，Including the second prize of the Jiangsu Science and Technology Progress Award three times, second prize of the Ministry of Education Science and Technology Invention one time. Obtained 39 national invention patents, authored more than 100 articles.
Prof. Xiao-Song Zhang,
OUR TEAM
Dr. Yong-Gao Yin: PhD., Lecturer, School of Energy and Environment, Southeast UniversityProf. Shu-Hong Li: PhD., Research Fellow, School of Energy and Environment, Southeast UniversityDr. Cai-Hua Liang: PhD., associate professor, School of Energy and Environment, Southeast UniversityDr. Xiu-Wei Li: PhD., Lecturer, College of Power Engineering, Nanjing University of Science and TechnologyDr. Dong-Gen Peng: PhD., Lecturer, School of Civil Engineering and Architecture, Nanchang UniversityMiss. Guo-Ying Xu: PhD Student，…….
Research projects conductedTime series chart of fundamental research projects
in the recent decade
01-03 04-06 07-09 10-13 07-09 08-10
Liquid dehumidifi
cation+
Evaporation cooling
air-conditionin
g system
Liquid-desiccant
-based potential energy storage technolo
gy
Deep-liquid-
dehumidification
assisted ice slurry
production method
Liquid-desiccant based air-
conditioning system with independent
heat and humidity control
Energy storage
mechanism of high density
potential energy storage
technology
Building energy
conservation and
equipments in the
“summer –hot-winter-cold area”
Key project funded by Ministry of Education
Support project of the 11th five year plan
07-09
Heat source
assisted solar
power utilizatio
n
863
95 1500 05 10
Not form a complete decoupling
environmental heat and moisture control system and its thermodynamic
analysis
European and American scholars
suggested independent control of heat and
humidity
Humidity treatment and control: we conceived a new liquid dehumidification air-conditioning system
Academician Jiang, TsinghuaUniversity, used liquid
dehumidification to treat fresh air and promotes the independent
humidity control method
We propose a new air-conditioning system
integrated liquid dehumidification with
radiant cooling
With experiments, Professor of American Goswami proved the energy conservation effect of independent
liquid dehumidification
Research Track: liquid dehumidification air-conditioning system
Outline
Traits and merits of liquid dehumidificationMass transfer mechanism and theoretical models of liquid dehumidificationUtilization of low grade heat in liquid desiccant regenerationNovel liquid-dehumidification based air-conditioning systems and equipmentsApplication of liquid dehumidification in new scientific areas
,0.601 0.25 0.00072 0.0107y s w a inM a Tε = + − − 77 200wa< <0.174
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( )
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2 Complex model (in consideration of the heat and mass transfer resistance of the liquid layer)
Full developed laminar flow/falling film flow
Des
icca
nt Air
H
x
ys
x
ya
δaδs
ua
us
δ
2
2 0ss
s
ugy
ν ∂+ =
∂
2
2
1 aa
a a
upx y
νρ
∂∂=
∂ ∂2
2a a
a aT Tux y
α∂ ∂=
∂ ∂
2
2s s
s sT Tux y
α∂ ∂=
∂ ∂2
2Da ad dux y
∂ ∂=
∂ ∂2
2Ds sux yξ ξ∂ ∂=
∂ ∂
a a s s
a sa a a fg s
a a sy y
T TdD hy y y
δ δ
λ ρ λ= =
⎛ ⎞∂ ∂∂− − =⎜ ⎟∂ ∂ ∂⎝ ⎠
a a s s
a a s sa sy y
dD Dy y
δ δ
ξρ ρ= =
∂ ∂− =
∂ ∂
momentum
energy
mass
boundary conditions of
the layer
Rahamah,1998; Ali et al., 2003,2004; Dai et al., 2004; Yin et al., 2006;
Volume average finite difference model3
Factor and Grossman, 1980; Stevens et al., 1989; Khan, 1994, 1998; Goswami et al., 2002, 2003; Liu et al., 2006; Yin et al., 2008;
dx
dy
Ts Xs Gs
Ts+dTs Xs+dXs Gs+dGs
Ga
Ta
ω
Ga+dGa
Ta+dTa
ω+dω
x
y=L
空气进口 溶液进口 ininsins Xtm ,, ,,inainaa tm ,, ,, ω
Xtm ss ,,
outoutsouts Xtm ,, ,,outaoutaa tm ,, ,, ω
aaa tm ω,,
空气出口 溶液出口
x+dx
H
0
4 Linear-based quasi-analytical model
Chen et al., 2006; Ren, 2007, 2008; Davoud and Meysam, 2009.
Based on Model III- Volume average finite difference modelThe relationship between the desiccant temperature and the air humidity is assumed linearMinor factors are neglected according to the characteristics of the heat and mass transfer process
Precision depends on the assumptions
Popularity is poor
Not good at analyzing the ongoing state of the heat and mass transfer process
Question is？
1, What will be the conclusion in the
case of coupled heat and mass transfer？
2, Will the evaluation method of logarithmic mean temperature difference still OK for the coupled heat and mass transfer process
Treatable area partition determined by the initial air state
10
15
20
25
30
35
40
0 5 10 15 20
含湿量 /(g/kg)
温度
/o C
湿空气饱和线
A2
A5
A11
A1
s
A3
A6
A9
A10 A12
A8
56
10 1112
除湿区域
除湿或再生
再生区域A7
8
A4
2
43
9
Application of the treatable partition
10
15
20
25
30
35
40
0 5 10 15 20
含湿量 /(g/kg)
温度
/o C
s in
湿空气饱和线
A区
B区
C区
D区
RulesRules
PartitionPartition A and A and Partition CPartition Ccountercurrent flow has the best countercurrent flow has the best
mass transfer effect while the mass transfer effect while the concurrent flow has the worstconcurrent flow has the worst
boundary: boundary: ωω = = ωωe,ine,in
Partition A：Dehumidification partition; same direction of heat and mass transfer
Partition B：regeneration partition; opposite direction of heat and mass transfer
Partition C：regeneration partition; same direction of heat and mass transfer
Partition D：Dehumidification partition; opposite direction of heat and mass transfer
PartitionPartition B and B and PartitionPartition DDconcurrentconcurrent flow flow has the best has the best
mass transfer effect while the mass transfer effect while the countercurrentcountercurrent flow flow has the worsthas the worst
boundary: boundary: ωω = = ωω**
Research progress about the heat and mass transfer features of liquid dehumidification (II)Development of evaluation method and theoretical model for
coupled heat and mass transfer performanceC
D a
hLeh Cp
= D t w
a
h V aNTUM
=
cc
m
QhS T
=⋅Δ
vD
m
MhS ω
=⋅Δ
take the method used to solve the conventional heat transfer problems
max min
max minln /mT TT
T TΔ −Δ
Δ =Δ Δ
max min
max minln /mω ωωω ω
Δ −ΔΔ =
Δ ΔRight？
Rem nSh a Sc= ⋅ ⋅
Pr Rep qNu b= ⋅ ⋅
Coupled heat and mass transfer is different from the pure heat transfer
Countercurrent flow dehumidification－Fumo (2002)
Cross flow regeneration (2006)
29
30
31
32
33
34
0 2 4 6 8 10实验数据点
温度
/o C
24
26
28
30
32
34
0 2 4 6 8 10实验数据点
温度
/o C
Inlet desiccant
Inlet air
Outlet Outlet desiccantdesiccant
Outlet airOutlet air
Inlet air
Inlet desiccant
Outlet air
Outlet desiccant
Temperature of the outlet desiccant is higher than that of any inlet desiccant
Temperature of the outlet desiccant is lower than that of any inlet liquid
Ratio=ΔTlogm/ΔTm Ratio=Δωlogm/Δωm
除湿工况D1；D2；D3 0
1
2
0.1 1 5R
Counter Flow Parallel Flow Cross Flow
除湿工况D4；D5；D6
再生工况R1；R2；R3
Will the evaluation method of logarithmic mean temperature difference still OK for the coupled heat and mass transfer process？How can we evaluate the coupled heat and mass transfer coefficient based on the heat and mass transfer model ？
Conclusion：The conventional evaluation method of logarithmic mean temperature difference is not OK for the coupled heat and mass transfer process.
Question 2：Evaluation of the coupled heat and mass transfer coefficient
In consideration of the transfer coefficient distributed along with the transfer potential difference
0 L
ωa
Solution
Air
x
ωa(x)
x
( )v
D L
o
mhx dxω
Δ=
Δ∫
( )C L
o
QhT x dx
Δ=
Δ∫
DM hω=Δ ⋅
( )1a s dS
Sω ω ωΔ = −∫∫
CQ h t= ⋅Δ
( )1a st t t dS
SΔ = −∫∫
hD-Le separation measurement method
, 1 , , , ,( , , , , , , , )deh out deh deh air deh air deh deh sol deh deh sol Df L G T G X T hω ω=
Assume Le
, 1 ( , , , , , , , , )deh out deh a a a s s s Df L G T G X T h L eω ω=
, 2 ( , , , , , , , , )a out deh a a a s s s DT f L G T G X T h L eω=
, 3 ( , , , , , , , , )s ou t deh a a a s a s DT f L G T G X T h L eω=
Calculate hD
, 2 ( , , , , , , , , )a out deh a a a s s s DT f L G T G X T h Leω= Real Le
(Southeast Univ.，Yin Y.G.)
Liquid dehumidification experiment with packing stuff type dehumidifier
cross flow孔板送风
焓差室内环境
试验台本体
电加热器
电加湿器
蒸发器
压缩机
风机
来自节流机构去冷凝器
溶液除湿模块
Influence of air flow rate on the coupled heat and mass transfer process
h C/
W/(
m2·°C
)
Le
h D/
g/(m
2 s)
Influence of air humidity on the coupled heat and mass transfer process
Fresh idea for developing the model of coupled heat and mass transfer process
Ta
显热交换Qs
ωa ωs
传质湿差Δω
耦合传质系数hD
潜热交换 质交换Mw
Ma Ms
Xs
传热温差ΔT
耦合传热系数hC
Ts
The key!
(Southeast Univ.，Yin Y.G.)
3. Utilization of low grade heat in liquid desiccant regeneration
Solar regeneration
mode
Separated type
Direct heating
Indirect heating
Combined type
Solar powered regeneration method
Natural convection C/R
Collier (Unglazed) (1978) Nelson (Glazed) (1990)Gandhidasan (Partly glazed)(1994-1998)
Forced convection C/R
Gandhidasan (Arabia)(1982)Ru Yang (Taiwan)(1994-2001)Saman (Australia)(2002)
Solar powered regeneration process
Experiment platform
Validation of the glass plate temperatureValidation of the glass plate temperature Validation of the outlet regeneration parametersValidation of the outlet regeneration parameters
Multi-stage regeneration systemRegeneration of desiccant solution of different concentration and with
different collector/regeneratorFirst stage: regeneration of the desiccant solution from the pre-
dehumidifier, outdoor air is directly used for regenerationSecond stage: regeneration of the desiccant solution from the dehumidifier,
pre-treated air is used for regeneration
Performance of multi-stage regeneration with different climate parameters
Humidity distribution with different inlet desiccant temperature
Ts=28 ºC Ts=32 ºC Ts=35 ºC
Requirement of the minimum inlet desiccant temperature under the efficient regeneration working condition
( ),min,a s sf X Tω =
Humidity difference distribution between the desiccant surface and the air
Influence of the air flow rate on the regeneration performance
Regeneration thermal efficient is minus: air is dehumidified rather than regeneratedFor a certain desiccant flow rate, air flow rate should be large enough and there exists a best working range
0 5 10 15 20 25
0
1
2
3
4
5
6
7
R
Ms=0.04 kg/sMs=0.08 kg/sMs=0.12 kg/sMs=0.16 kg/s
4. Novel liquid-dehumidification based air-conditioning systems and equipments
Internal cooled/heated dehumidification/regeneration apparatusExperiment system development
Influence of the internal cooled water temperature on the dehumidification process
2.55
2.6
2.65
2.7
2.75
2.8
19 20 21 22 23 24Tw /°C
20
21
22
23
24
25
26
19 20 21 22 23 24
Ts,out Tw,out
Tw /°CInfluence of the air flow rate on the dehumidification
process
1.5
2
2.5
3
0.048 0.06 0.072 0.084 0.096
Ma /kg/s
内冷 绝热
Influence of the desiccant inlet temperature on the dehumidification process
1.5
2
2.5
3
3.5
20 22 24 26 28 30 32
Δω
/ g/
kg绝热除湿‐a
内冷除湿‐a
绝热除湿‐b
内冷除湿‐b
Ts /°C
Performance comparison between the internal heated regeneration method and the adiabatic
regeneration method
36
38
40
42
0.036 0.048 0.06 0.072 0.084 0.096
T a,out
/°C
Ma /kg/s
内热再生绝热再生
The outlet air temperatures are almost equal, which implies a higher regeneration efficient
Influence of the inlet desiccant temperature on the regeneration process
Δω
/ g/
kg
Desiccant solution
Moist AirMoisture
Original dehumidifier
silica gel
Saturated
New surface
Combined dehumidifier
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
时间 (s)
溶液除湿器3: 纯 CaCl
2溶液
混合溶液
ti=27 oC di=15.5 g/(kg air)
除湿量(g/(kg air.s))
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
时间 (s)
除湿量(g/(kg air.s))
溶液除湿器2 溶液除湿器3 ti=27oC di=14.5 g/(kg air)
Dehumidification effect enhancement
5. Application and future of liquid dehumidification in new scientific areas
Development of new liquid dehumidification air-conditioning systemslow operation cost solar-powered refrigeration /dehumidification/air conditioning systemsdeep-liquid-dehumidification assisted evaporative-supercooling method for ice slurry production High efficient air-conditioning system with independent heat and humidity controlLiquid-desiccant-based potential energy storage technology
Development of new liquid dehumidification air-conditioning systems
N
O
D
S100%
T
d
`
冷却水
太阳能集热器
空调房间
回风新风
排风
绝热
加湿器除湿器再生器
冷却水
`
外界环境空气
排放
Liquid dehumidification cooling system driven by solar energy
蒸发
冷却器回热器 除湿器 QdQe 12
3
4
给水
6
5
78
9
10 储液器
再生器
换热器
1712 13 14
15
Qh
储液器16
11
18
其他热源
Integrated system of liquid dehumidification and air conditioning
Humidity Control and Regulation
Steel-making wet blast off---humidity control
Humidity pretreatment of the fresh air
Industrial humidity control and regulation
Evaporative super-cooling method for ice slurry production
Ice storage：the methods for ice slurry productionPrinciple of evaporative super-cooling method for ice slurry production
Evaporation
When the air humidity is very low and the wet bulb
temperature is below 0℃, the water droplets can be super-cooled and form ice particles
Liquid dehumidification canLiquid dehumidification candecrease the air humidity decrease the air humidity
and consequently and consequently decrease the water vapor pressuredecrease the water vapor pressure
Water above 0℃,spray in the chamber
Cooling effect
Renewable energy input
Reutilization of the rejected heat from the condenser
Renewable energy input
Experiment platform
Produced ice particles
High efficient air-conditioning system with independent heat and humidity controlNo dew-point controlRaise the temperature of cold source, No requirement of reheat, Significant energy conservation effectRegeneration process can be driven by varieties of low grade heat sources (like solar energy), as well as the rejected heat from the condenser
高温冷源
除湿器
再生器
太阳能集热器
100%
L
O
N
SC Wh
焓
含湿量d
Liquid-desiccant-based potential energy storage technology
Large storage density, 3 times more than ice storage Long-distance transport, storage at room temperatureLow grade thermal energy storage (65-85oC)
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