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Experimental study of operation performance of a low power thermoelectric cooling dehumidifier

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The present work was performed to apply thermoelectric technology to a low power dehumidifying device as an alternative to the conventional vapor-compression refrigeration systems. The experimental prototype of a small-scale thermoelectric dehumidifier (TED) with rectangular cooling fins was built and its operation performance was studied experimentally. The results showed that the TED experienced two typical thermodynamic processes including the cooling dehumidification and the isothermal dehumidification, where the latter was dominated. It was found that there existed a peak during the variation of the average coefficient of performance (COP) as a function of the input power of the thermoelectric module. Under the present experimental conditions, the COP of the TED reached the maximum of 0.32 and the corresponding dehumidifying rate was 0.0097 g/min, when the input power was kept at 6.0 W. The rapid elimination of condensed liquid-drops on the cooling fins amounted on the thermoelectric module is a major approach to improving the operation performance of the TED.
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INTERNATIONAL JOURNAL OF
ENERGY AND ENVIRONMENT
Volume 1, Issue 3, 2010 pp.459-466
Journal homepage: www.IJEE.IEEFoundation.org
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
Experimental study of operation performance of a low
power thermoelectric cooling dehumidifier
Wang Huajun, Qi Chengying
School of Energy and Environment Engineering, Hebei University of Technology, Tianjin, China.
Abstract
The present work was performed to apply thermoelectric technology to a low power dehumidifying
device as an alternative to the conventional vapor-compression refrigeration systems. The experimental
prototype of a small-scale thermoelectric dehumidifier (TED) with rectangular cooling fins was built and
its operation performance was studied experimentally. The results showed that the TED experienced two
typical thermodynamic processes including the cooling dehumidification and the isothermal
dehumidification, where the latter was dominated. It was found that there existed a peak during the
variation of the average coefficient of performance (COP) as a function of the input power of the
thermoelectric module. Under the present experimental conditions, the COP of the TED reached the
maximum of 0.32 and the corresponding dehumidifying rate was 0.0097 g/min, when the input power
was kept at 6.0 W. The rapid elimination of condensed liquid-drops on the cooling fins amounted on the
thermoelectric module is a major approach to improving the operation performance of the TED.
Copyright © 2010 International Energy and Environment Foundation - All rights reserved.
Keywords: Cooling dehumidification, Thermoelectric module, COP, Dehumidification rate.
1. Introduction
For the indoor thermal comfort of buildings, the relative humidity is a key control parameter. At present,
there exist a number of dehumidifying devices based on the traditional vapor-compression technology.
Though these devices are widely applied, they still have many problems to be solved, such as high noise
level, strong compressor vibration, and excessive weight and so on [1-2]. In fact, what’s more important
is the extensive use of CFCs or HCFCs, which has a great negative impact on the present crisis of energy
and environment [3].Under this background, it is required to seek for other clean dehumidifying
approaches. Thermoelectric cooling technology is just the case in point, which is based on the Peltier
effect of semiconductor materials [4]. At present, the thermoelectric cooling technology has been
developed rapidly, as an alternative to the conventional systems based on the vapor-compression
refrigeration cycles.
For the thermoelectric dehumidification, however, only a few studies were performed. In fact,
thermoelectric dehumidifiers have a promising potential in the situations where both a lower power and a
smaller space are required. Such applications can be seen in the space crafts, submarines, robots,
tunnels,
and industrial control cabinets and so on [5-6]. In previous studies, Chen [7] presented a TED with an
improved fin heat exchanger, reaching a COP ranging from 0.12 to 0.29. Sumrit [8] tested the
performance of a TED in a residential apartment, and obtained a COP of 0.27. In fact, except the
difference in the thermoelectric module materials, the better performance of the TED depends mainly on
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
460
an optimal layout of heat transfer surfaces. However, too much complex controls on heat transfer usually
mean a higher construction cost of TEDs, which may reduce the feasibility in practical applications. The
purpose of this work was to test the operation performance of the TED, and to obtain the relationship
between the COP and the input power, which is helpful for the optimal design of similar TEDs.
2. Experimental system and procedure
2.1 Experimental setup
Figure 1 shows the experimental setup of a small-scale TED. It mainly consisted of a closed cabinet, a
thermoelectric module, a DC power meter, a humidifier, a humidiometer, temperature sensors, and a data
acquisition system. The cabinet made of organic glass plates was used to simulate a small room. The
cabinet was cube-shaped, with 400 mm in length, 400 mm in width, and 400 mm in height. A TEC-
12705 type thermoelectric module made of BiTe was used to provide a cold source for dehumidification.
The module was 40 mm in length, 40mm in width, and 4mm in thickness, and its maximum working
voltage and current were 15 V and 4 A. In order to enhance heat transfer, two rectangular fin heat
exchangers were amounted on the heat and cold side of the thermoelectric module, with an extended area
of about 91 cm
2
and 128 cm
2
, respectively. A 2.4W axial fan for forced convection was amounted on the
fin heat exchanger of the heat side of the TED. In order to eliminate the effect of contact resistances as
possible, a thin layer of silicone grease with silver was covered on the heat-transfer surfaces of the TED.
An adjustable WYJ-20 type DC power meter was used to electrically driven the thermoelectric module.
Its maximum voltage and current output were 20 V and 10 A, respectively.
The relative humidity inside the cabinet was measured by a HT-3005A type humidiometer with ± 1%
accuracy installed at the middle of the cabinet. The temperatures of the cabinet and heat/cold fin heat
exchangers were measured by copper- constantan thermocouples with ± 0.1
o
C accuracy. The temperature
data were recorded by a HP 34970A type recorder. All measuring sensors were calibrated carefully
during the experimental preparation. The ambient atmospheric pressure was measured by a mercury
manometer. According to the Chinese Code for Design of Heating Ventilation and Air Conditioning (GB
50019-2003), the allowable indoor relative humidity should range from 40 % to 65 % in summer and
from 40 % to 60 % in winter. Therefore, in this experiment, the lower limit of the relative humidity was
set as 40 ±1 %, and the upper limit was set as 98 ±1 % to simulate the situation with a high humidity
environment of buildings. Before the experiment, the cabinet was humidified to a high relative humidity
by a humidifier. After 10 min, the DC power supply of the thermoelectric module was connected. During
the dehumidifying process, the variations of the temperature and relative humidity were recorded at an
interval of 5 min.
humidifier
Data recorder
Computer
Ambient monitoring meters
Camera
Cabinet
Humidity sensor
Cold-side fins
Thermoelectric module
Cooling fan
DC
p
ower mete
r
Heat-side fins
Thermocouple wires
Figure 1. Schematic diagram of the experimental setup of a TED
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
461
2.2 Experimental data reduction
In order to evaluate the performance of the TED, the COP is defined as
c
TE F
Q
COP
PP
=
+
(1)
where P
TE
is the power of the thermoelectric module (W), and P
F
is the power of the cooling fan(W).
The total heat-transfer rate (Q
c
) of the fin heat exchanger on the cold side of the TED is calculated as
()
cccoc wc
QhAtt mH=−+ (2)
where h
c
is the coefficient of convective heat transfer (W/m
2
K), A
c
is the heat transfer area (m
2
), t
o
is the
temperature at the middle of the cabinet (
o
C), t
c
is the average temperature of cold fins (
o
C), and H
c
is the
latent heat of condensation (J/kgK).
The dehumidifying rate (m
w
, kg/s) is calculated as
()
12a
w
m
m
T
φ
φ
= (3)
where m
a
is the mass of the wet air inside the cabinet (kg), T is the dehumidifying period (s), Φ
1
and Φ
2
are the relative humidity before and after dehumidification (%).
According to the previous study by Bejan [9], the coefficient of convective heat transfer (h
c
, W/m
2
K)
between adjacent fins and the ambient can be determined by
0.25
0.517
c
hRa
H
λ
= (4)
where λ is the thermal conductivity of air (W/mK), H is the height of fins (m), and Ra is the
dimensionless Rayleigh number, and its definition and calculations can be seen in the previous studies by
Bejan and Cengel [9-10].
3. Results and discussion
3.1 The analysis of the dehumidifying process of the TED
Figure 2 shows a typical dehumidifying process of the TED, when the input power of the thermoelectric
module is 5.5 W. It can be seen that, except the first 10 min, the average temperature of heat-side fins as
well as the cabinet kept relatively steady during the dehumidifying process. The average temperature of
cold-side fins appeared a slowly decreasing tendency, and finally reached a steady state. It was also
found that the relative humidity experienced two accelerating stages (i.e.98-90% and 70-50%) and two
decelerating stages (i.e.90-70% and 50-40%). This phenomenon is related with the condensing behavior
of cold-side fins, which is discussed in the later section.
The variation of the relative humidity shown in Figure 2 can also been plotted in the enthalpy-humidity
diagram. As shown in Figure 3, the TED experienced two typical thermodynamic processes, including
the cooling dehumidification and the isothermal dehumidification. During the cooling dehumidifying
process from A to B, the variation of the relative humidity was weak, proceeding from 98 % to 90 %. In
contrast, the isothermal dehumidifying process from B to C experienced a major change of the relative
humidity varying from 90 % to 40 %. From the point of view of the dehumidifying period, the cooling
dehumidification and isothermal dehumidification experienced 44 min and 145 min, respectively.
Therefore, the isothermal dehumidifying process is dominated during the operation of the TED.
The above experimental characteristics of the dehumidifying process depended on condensing heat
transfer on cold-side fin heat exchangers of the TED. Figure 4 shows the photos of cold-side fins before
and after dehumidification. It can be found that there existed many condensed liquid drops on the
extended surfaces. At the bottom of local fins, there appeared the liquid-bridge phenomenon. Such an
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
462
adherence of condensed liquid drops on the fin surfaces has an important role in the dehumidifying
process of the TED, which can be further explained as follows.
-5
0
5
10
15
20
25
30
35
40
0 20 40 60 80 100 120 140 160 180 200
Time
(
min
)
Temperaure (
o
C )
30
40
50
60
70
80
90
100
Relative humidity (%
)
Cabinet temperature
Cold fin temperature
Heat fin temperature
Relative humidity
Figure 2. A typical dehumidifying process of the TED
Figure 3. The dehumidifying process in the enthalpy-humidity diagram
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
463
(a) before dehumidification (b) after dehumidification
Figure 4. Photos of cold-side fins before and after dehumidification
At the initial dehumidifying process, the temperature of cold-side fins dropped rapidly, which promoted
the vapor condensation inside the cabinet. This indicated that a number of liquid drops was created and
adhered on the fin surfaces. Soon these liquid drops became a thin layer of liquid film, driven by the
surface tension. Such a liquid film was a great thermal resistance and then led to a weak heat and mass
transfer between the fin surfaces and the ambient inside the cabinet. As a result, the dehumidifying rate
began to decrease, and this was the so-called first decelerating stage ranging from 90% to 70%. When the
film became thicker and thicker, the runoff flow along the gravity direction was dominated. The fin
surfaces became relatively clean again. At the same time, the temperature of cold-side fins still remained
a steady low temperature close to 0
o
C. Thus, the dehumidifying process began to accelerate for the
second time. Repeatedly, when the liquid film on the fin surfaces became thick enough, the
dehumidifying process experienced the second decelerating stage till the dehumidification was ended.
From the analysis above, it can be seen that a rapid elimination of condensed liquid-drops on the cooling
fins amounted on the thermoelectric module is a major approach to improving the performance of the
TED. Such efforts can be realized by using superhydrophilic (SH) or super-water repellent (SWR)
surfaces [11-12]. Related experimental work is expected to be reported in our later studies.
3.2 The analysis of the dehumidifying performance of the TED
Figure 5 compares the dehumidifying processes under different input powers of the thermoelectric
module. It can be seen the dehumidifying period depends strongly on the input power of the
thermoelectric module. In this experiment, when the input power was 6.0 W, the dehumidifying period
reached the minimum of 120 min. In contrast, for the input powers lower or higher than 6.0 W, the
dehumidifying period showed an increasing tendency. For instance, the dehumidifying period was 180
min at 5.0W and 150 min at 7.0W, respectively. This result can be explained by the characteristics of
thermoelectric module materials.
For a thermoelectric module, the heat absorption from the ambient consists of two sources. One is from
the Peltier effect, which is proportional to the current through the module. Another is from the Joule
effect, which is proportional to the square of the current through the module [4]. When the input power is
too low, the Peltier effect is weak, resulting in a low dehumidifying rate. On the contrary, when the input
power is too high, the Joule effect is dominated, resulting in a high heat load imposed on the heat-cold
heat exchangers. Once the heat generated can not be released into the ambient, the extra heat will be
transferred by heat conduction towards the cold side, and finally weaken the condensing heat transfer on
the fin heat exchanger. Therefore, for the minimum dehumidifying period, there is an optimal input
power of the thermoelectric module.
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
464
0 20 40 60 80 100 120 140 160 180
30
40
50
60
70
80
90
100
110
Relative humidity (%)
Time (min)
4.0W
5.0W
5.5W
6.0W
7.0W
8.0W
Figure 5. Dehumidifying processes under different input powers of the thermoelectric module
Figure 6 compares the variations of COP under different input powers of the thermoelectric module. It
can be seen that the COP of the TED increases rapidly during the initial stage, then keeps a slowly
growing tendency till reaching the maximum level, and finally drops quickly. For instance, when the
input power was 6.0 W, the COP began to accelerate at 80 min, which was the start of the second
accelerating stage shown in Figure 5, and reached the maximum of 0.32 at about 100 min, which was just
the end of the second accelerating stage shown in Figure 5. For the most dehumidifying period, however,
the COP remained an average level of about 0.17, about half of the maximum level. When the input
power increased to 7.0 W and 8.0 W, the corresponding COP reduced to 0.26 and 0.20, respectively.
This experimental phenomenon can fully reflect the working mechanism of the TED where the complex
heat and mass transfer related with condensation on the cold-side fin heat exchanger is a critical
influencing factor. Compared with the previous results obtained by Chen [7] and Sumrit [8], the present
experimental COP was higher.
0 20 40 60 80 100 120 140 160 180
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
COP
Time (min)
4.0W
5.0W
6.0W
7.0W
8.0W
Figure 6. Variations of COP under different input powers of the thermoelectric module
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
465
45678
0.12
0.14
0.16
0.18
0.20
2
3
4
5
6
Average COP
Average dehumidifying rate
Average dehumidifying rate
(10
-3
g/min)
Average COP
Input power (W)
Figure 7. Variations of the average COP and the average dehumidifying rate under different input powers
of the thermoelectric module
Figure 7 further shows the variations of the average COP and the average dehumidifying rate under
different input powers of the thermoelectric module. In the present experiment conditions, the average
dehumidifying rate was about 0.005 g/min at the input power of 6.0W, though the maximum reached
0.0097g/min. It should be noted that the performance of practical TEDs varies greatly in the present
studies. A generally acceptable COP of TEDs ranges from 0.1 to 0.6[13]. In addition, Vian [14]
established a numerical model of a TED. Through optimizing the heat transfer, a COP of 0.8 was
obtained in the computation conditions. As far as the author’s knowledge, this value is the highest in the
available literatures. Therefore, compared with Vian’s theoretical prediction, there is still a great space
for the performance improvement of the present TED. In contrast, the COP of conventional
dehumidifiers usually ranges from 0.7 to 1.3 [15]. On the other hand, at present the figure of merit (ZT)
of most commercial thermoelectric materials is lower than 1.0. For instance, the ZT of BiTe used in this
experiment was about 0.6. However, the value of ZT has been improved to 2.4 for some novel
thermoelectric materials [16]. It can be expected that, with a continuing advance in the thermoelectric
technology, the performance of the TED will be improved drastically. In summary, despite that the COP
obtained by the present experimental setup is at a relatively low level, a lower power TED is of certain
commercial interest. From the present experimental results, it can be seen that, during the use of
thermoelectric cooling technology, the relative humidity can be controlled more accurately through an
adjustable input power, which provides an important approach to improving the indoor thermal comfort
of buildings.
4. Conclusion
TEDs have a promising potential in the situations where both a lower power and a smaller space are
required. The present work was performed to develop a low power TED as an alternative to the
conventional vapor-compression refrigeration systems. From the experimental results discussed above,
the following conclusions can be obtained:
(i)
The TED experienced two typical processes including the cooling dehumidification and the
isothermal dehumidification, but the latter was dominated. The relative humidity experienced two
accelerating stages and two decelerating stages. This phenomenon is related with the condensing
behavior on the extended surfaces of the cold-side fin heat exchanger.
(ii)
There exists a peak during the variation of the COP as a function of the input power of the
thermoelectric module. Under the present experimental conditions, the COP of the TED reached
the maximum of 0.32 and the corresponding dehumidifying rate was 0.0097 g/min, when the input
power was kept at 6.0 W.
(iii)
There is still a great space for the performance improvement of the present TED. The effective
elimination of condensed liquid-drops on the cold-side fins is a major work in the future.
International Journal of Energy and Environment (IJEE), Volume 1, Issue 3, 2010, pp.459-466
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
466
Acknowledgements
This work was supported by Program for Young Talents in Hebei University of Technology, and Natural
Science Foundation of Tianjin (No. 07ZCKFSF00400).
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H. Wang is Ph.D in Thermal Engineering from Tianjin University in 2008. He completed M.Sc and B.Sc
in Engineering Thermophysics from Tianjin University in 2003 and 1998, respectively. At present, he is an
associate professor of School of Energy and Environment, Hebei University of Technology. His wor
k
focus mainly on heat and mass transfer related with renewable energies, HV&AC, and energy saving o
f
buildings. He has published over 20 research papers including 8 in the international journals. He takes as a
reviewer of several international journals in the energy field.
E-mail address: huajunwangl@126.com
C. Qi is Ph.D in Thermal Engineering from Tianjin University in 1997. He completed M.Sc and B.Sc in
Engineering Thermophysics from Tianjin University in 1988 and 1985, respectively. He is a professor o
f
School of Energy and Environment, Hebei University of Technology. Since from 2005, he has taken as the
dean of School of Energy and Environment of HBUT. His work focus mainly on heat and mass transfe
related with renewable energies, HV&AC, and energy saving of buildings. He has published several
research papers in the international journals.
E-mail address: qicy@mail.hebut.edu.cn
... The total heat transfer rate (Q c ) of the fin heat exchanger on the cold side of the thermoelectric module (TEM) is given by [13]: ...
... The dehumidifying rate (m w , kg/s) is calculated as [13]: ...
... In order to improve the performance of fins for dehumidification, rapid elimination of condensed water is necessary. This is achieved by specially treated heat transfer surfaces (fins) with superhydrophilic or super water repellant surfaces [13]. ...
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The review describes the development and advancement of thermoelectric based dehumidifier systems. Thermoelectric cooling in thermoelectric dehumidifiers has various advantages over conventional techniques, such as lightweight, compact size, noise-free (no moving part), and eco-friendly operation. The review initially describes the basic principle and different techniques used for dehumidification. Then, thermoelectric dehumidifiers are introduced and their governing parameters are discussed. Further, thermoelectric dehumidifier-based prototypes are reviewed and discussed over their design and performance. The patents and commercialized products developed on thermoelectric dehumidifiers were also briefly discussed and compared. Lastly, this review states the challenges for the more efficient and large-scale operation of thermoelectric-based dehumidifiers and simplifies ways for further improvement. Thus, the study illustrates the current status of thermoelectric dehumidifiers and provides futuristic scopes for their development.
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The extensive effort has made to fabricate and analyze the evaporative cooler with liquid-desiccant regeneration process. A temperature drop of around 4 degrees and a humidity reduction of around 14-16 percent as compared to direct contact evaporative cooler achieved. The enhanced average cooling efficiency of the evaporative cooler is41.828 % achieved with Average dehumidification capacity obtained at different concentrations of desiccantare: At 20% concentration of desiccant = 4.3695 lph, At 30% concentration of desiccant = 5.4845 lph, At 40% concentration of desiccant = 6.391 lph
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A thermoelectric dehumidifier may be built smaller than a compressor type dehumidifier of the same capacity; however, its efficiency is lower. This study proposes a new heat dissipation structure to improve the performance of a thermoelectric module (TEM) for the dehumidifier. The new structure ensures that cooled and dehumidified air flows through one or more holes inside the heatsink base. The design parameters selected for the orthogonal array experiments are existence of the holes, drive voltage of the TEM, air inflow rate, and the cooling fan position. Experimental results reveal that the air flow through the holes has the greatest effect on dehumidification efficiency. Through subsequent experiments, the number of holes and drive voltage of TEM required to maximize dehumidification capacity and coefficient of performance are obtained.
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Thermoelectric devices are solid state devices. They are reliable energy converters and have no noise or vibration as there are no mechanical moving parts. They have small size and are light in weight. As refrigerators, they are friendly to the environment as CFC gas or any other refrigerant gas is not used. Due to these advantages, the thermoelectric devices have found a large range of applications. In this paper, basic knowledge of the thermoelectric devices and an overview of these applications are given. The prospects of the applications of the thermoelectric devices are also discussed.
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This paper presents a theoretical analysis based on the second law of thermodynamics to estimate the minimum work required for air cooling and dehumidification. Isothermal dehumidification and sensible cooling processes can be combined to give an equivalent path capable of representing the conventional air conditioning process in hot and humid climates. Dehumidification is analysed as a separation process of an ideal mixture of air and water vapour. In this paper, contours of minimum work required for air cooling and dehumidification are plotted on a psychrometric chart and presented as a handy design tool. The effect of small variations in the final conditions on the minimum required work shows that tolerating a warmer or more humid final condition can be an easy solution to reduce energy consumption during critical load periods.
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This paper investigates the performance characteristics of three domestic refrigerators, namely the vapour compression (VC), the thermoelectric (TE) and the absorption refrigeration (AR). AR and TE refrigerators are the result of research and development in refrigeration system in the quest to find a cooling system which does not use any refrigerant that damages the ozone layer. Three refrigerators of similar capacity (about 50 l) were compared for their usage in the hotel industry in view of their energy efficiency, noise produced and cost (owning as well as running). It was found that the VC refrigerator consumed the least energy, was least costly but was the noisiest. The absorption refrigerator was the quietest of the three but was the least energy efficient and most expensive. The thermoelectric refrigerator was the costliest, nearly as noisy as the VC but was a little less energy efficient than the absorption refrigerator. Copyright © 2000 John Wiley & Sons, Ltd.
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This paper, on the basis of the main literature indications, deals with moisture control in buildings during the summer season; so, the dehumidification of the air is analysed. Dehumidification is considered as a key feature of HVAC systems for thermal comfort. Initially, the principles of mechanical and chemical dehumidification are shown. The first one utilises mechanical means—compression refrigeration systems—to cool the air and so to dehumidify it; the latter removes the water vapour from the air by transferring it towards a desiccant material (adsorption or absorption). In the mechanical dehumidification field, a proper control of ambient temperature and humidity can be obtained by means of an air handling unit (AHU) which treats outside air alone, while recirculating air is treated by a simple cooling coil. Various possible AHU configurations are examined. Afterwards, HVAC systems for a theatre and for a supermarket are analysed. The use of hybrid systems with desiccant wheel for these applications has provided the following main results: remarkable savings in operating costs and higher plant costs (a simple payback time of 2–3 years for supermarket); a notable reduction of the power electric demand; a better control of ambient humidity.
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A system design method of thermoelectric cooler is developed in the present study. The design calculation utilizes the performance curve of the thermoelectric module that is determined experimentally. An automatic test apparatus was designed and built to illustrate the testing. The performance test results of the module are used to determine the physical properties and derive an empirical relation for the performance of thermoelectric module. These results are then used in the system analysis of a thermoelectric cooler using a thermal network model. The thermal resistance of heat sink is chosen as one of the key parameters in the design of a thermoelectric cooler. The system simulation shows that there exists a cheapest heat sink for the design of a thermoelectric cooler. It is also shown that the system simulation coincides with experimental data of a thermoelectric cooler using an air-cooled heat sink with thermal resistance 0.2515 °C/W. An optimal design of thermoelectric cooler at the conditions of optimal COP is also studied. The optimal design can be made either on the basis of the maximum value of the optimal cooling capacity, or on the basis of the best heat sink technology available.
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If a current pulse with a magnitude several times higher than the steady state optimum current is applied to a thermoelectric cooler, an instantaneously lower temperature than that reachable at the steady state can be obtained. Most previous studies of this transient cooling effect focus on the minimum temperature achievable for free standing thermoelectric (TE) elements. In this work, we systematically study the transient response of thermoelectric coolers with and without mass loads through examination of both the minimum temperature reached and the time constants involved in the cooling and the recovering stages. For integrated thermoelectric cooler-passive mass load systems, two distinguishable cooling regimes, uniform cooling and interfacial cooling, are identified, and the criterion for utilization of the transient cooling effect is established based on the time constants. Although the results of this work are generally applicable, the discussions are geared towards cooling of microdevices that are of current interests.
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This paper compares the performance of three types of domestic air-conditioners, namely the vapour compression air-conditioner (VCAC), the absorption air-conditioner (AAC) and the thermoelectric air-conditioner (TEAC). The basic cycles of the three types of air-conditioning systems are described and methods to calculate their coefficients of performance are presented. General specification data for each type of air-conditioner are given, and performance characteristics are presented. The comparison shows that although VCACs have the advantages of high COP and low purchase price, use of these systems will be phased out due to their contribution to the greenhouse effect and depletion of the ozone layer. AACs are generally bulky, complex and expensive but operate on thermal energy, so their operational consumption is low. TEACs are environmental friendly, simple and reliable but still very expensive at present. Their low COP is an additional factor limiting their application for domestic cooling. TEACs however, have a large potential market as air-conditioners for small enclosures, such as cars and submarine cabins, where the power consumption would be low, or safety and reliability would be important.
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A prototype dehumidifier was designed and built based on thermoelectric cooling technology. A computational calculation model based on electric analogy was used in the device's design and optimisation (AERO), meaning that effects occurring inside the equipment, such as heat transfer, thermoelectric effects and the phase change which occurs during condensation and evaporation could be solved simultaneously. The thermoelectric dehumidifier prototype was built after performing several simulations using this calculation model. Numerous tests were carried out in order to optimise the Peltier pellet and fan supply voltages in experimental conditions. The prototype was also compared to conventional vapour-compression systems, thermoelectricity showing significant potential in the field.
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Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.