Mass recovery four-bed adsorption refrigeration cycle.pdf
Transcript of Mass recovery four-bed adsorption refrigeration cycle.pdf
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 1/15
Mass recovery four-bed adsorption refrigeration cycle
with energy cascading
Akira Akahira *, K.C. Amanul Alam, Yoshinori Hamamoto,Atsushi Akisawa, Takao Kashiwagi
Department of Mechanical Systems Engineering, Tokyo University of A&T, 2-24-16 Naka-cho, Koganei-shi,
Tokyo 184-8588, Japan
Received 10 March 2004; accepted 12 October 2004
Available online 16 December 2004
Abstract
The study investigates the performance of a four-bed, silica gel–water mass recovery adsorption refrig-
eration cycle with energy cascading. In an adsorption refrigeration cycle, the pressures in adsorber and
desorber are different. The mass recovery cycle utilizes the pressure difference to enhance the refrigerant
mass circulation. Proposed cycle has three main characteristics; (1) The cycle consists of two single-stage
cycles. (2) Hot and cooling water is used in each single-stage cycle with cascading. (3) Adsorber/desorber
heat exchanger of one cycle is connected with another adsorber/desorber heat exchanger of other cycle.
Specific cooling power (SCP) and coefficient of performance (COP) were calculated by cycle simulation
computer program to analyze the influences of operating conditions. The proposed cycle was compared
with the single-stage cycle in terms of SCP and COP. The results show that SCP and COP of proposed cycle
with cascading chilled water are superior to that of conventional, single-stage cycle and the proposed cycle
has high advantage at low heat source temperature.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Adsorption system; Silica gel; Mass recovery; Cascading; Performance; Calculation
1359-4311/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.applthermaleng.2004.10.006
* Corresponding author. Tel./fax: +81 042 388 7282.
E-mail address: [email protected] (A. Akahira).
www.elsevier.com/locate/apthermeng
Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 2/15
Nomenclature
A area (m2
)C specific heat (kJ kgÀ1 KÀ1)Dso surface specific heat (m2 sÀ1)E a activation energy (J kgÀ1)F mass flow (kg sÀ1)K heat transfer coefficient (W mÀ2 KÀ1)L latent heat of vaporization (J kgÀ1)P s saturated vapor pressure (Pa)q fraction of refrigerant which can be adsorbed by the adsorbent (kg kgÀ1)q* fraction of refrigerant which can be adsorbed by the adsorbent under saturation
condition (kg kgÀ1)QIN driving heat (kJ)Qchill cooling output (kJ)Qst isosteric heat of adsorption (J kgÀ1)Rgas gas constant (J kgÀ1 KÀ1)Rp average radius of a particle (m)t time (s)tcycle cycle time (s)W weight (kg)
Subscripts
ads adsorptional aluminumc condenser
chill chilled watercu copper
cw cooling waterdes desorption
e evaporatorfHex fin (aluminum)hex adsorber/desorber heat exchanger
hw hot waterin inletkHex heat transfer tube (cupper)
out outlets silica gelw water
wv vapor
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1765
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 3/15
1. Introduction
Adsorption chiller has lower environmental impact and large energy saving potential, because
the system does not use the fossil fuel and electricity as driving source. Especially, the cycle withsilica gel–water pair utilizes the heat at temperatures below 85 °C as driving source. Waste heat of
near environmental temperature is used to drive the adsorption refrigeration cycle.In the adsorption chiller, it is important to have a good adsorbent–adsorbate pair. Water,
methanol or ammonia has been used as adsorbate, and zeolite or activated carbon has been
combined with the adsorbate as adsorbent. For example, the zeolite–water pair was studied byRothmeyer et al. [1] and Douss and Meunier [2] for heating. The zeolite–ammonia pair was inves-tigated by Critoph and Turner [3]. The activated carbon–methanol pair was studied by Pons and
Guilleminot [4], and the activated carbon–ammonia pair was investigated by Jones and Christo-philos [5]. The systems were either gas-fired or solar-heat-driven. The silica gel–water pair, how-
ever, can utilize the heat sources with temperatures of less than 100°
C [6,7]. It is advantage foradsorption chiller to be operated with low heat source temperature. To use lower temperatureheat source, Saha et al. [8,9] proposed three-stage and two-stage adsorption cycles and investi-
gated the performance of the cycles. Results show that two and three-stage adsorption chillerscould be operated by low temperature heat source between 40 and 60 °C, but the COPs are obsti-
nately low.Pons and Poyelle [10] studied the influence of mass recovery processes in conventional two
beds adsorption cycle to improve the cooling power. In the study, zeolite–water pair was
used, the heat source temperature was 240 °C; their heat source temperature is higher thanthe temperature of low level waste heat and the adsorbent–adsorbate pair is not suitable forusing low temperature waste heat. Recently, Wang [11] investigated the performances of vapor
recovery cycle with activated carbon–methanol as adsorbent–adsorbate pair and demonstratedthat the mass recovery cycle is effective for the low regenerating temperature. The cycle with acti-vated carbon–methanol can be operated with low heat source temperature and the cycle has the
advantage for freezing lower than 0 °C, for example, ice maker. In the present analysis, it isassumed to use the waste heat of temperature below 100 °C for heat source to provide effectivecooling. Therefore, silica gel–water pair is selected due of its ability to be operated with lower
temperatures.In our previous study [12], the performance of two-bed mass recovery cycle with silica gel–water
pair was investigated and improvement of performance was confirmed. Mass recovery processutilizes the pressure difference between adsorber and desorber. Therefore, the bigger the differ-
ence of pressure, the more the refrigerant that could be move from desorber to adsorber. Inthe present study, four-bed mass recovery cycle is proposed to increase the pressure difference.In such a cycle, hot and cooling water is used with cascading flow from one desorber or adsorber
to other desorber or adsorber, where the movement of refrigerant from desorber to adsorber isaccelerated.
The present treatment is concerned with silica gel–water adsorption chiller using pressuredifference of the adsorber/desorber heat exchangers to accelerate adsorption/desorption process.
In the study, the performances of the novel system are compared with those of the conventionalsingle-stage cycle. The effects of operating temperature and cascading chilled water on the perfor-
mance are also presented.
1766 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 4/15
2. Working principle
2.1. Four-bed mass recovery cycle without heating and cooling
The schematic of proposed cycle is shown in Fig. 1. The cycle consists of two single-
stage adsorption cycles, that is, four pairs of heat exchangers, namely an evaporator (EVA1)-adsorber (HEX1) and a condenser (COND1)-desorber (HEX2), EVA2-HEX3, COND2-HEX4.HEX2 connects HEX3 through the valve V9 and HEX1 connects HEX4 through valve V10.
Upper part of mode A on Fig. 1 (HEX1, HEX2, COND1 and EVA1) is denoted as upper cycleas well as lower part (HEX3, HEX4, COND2 and EVA2) is denoted as lower cycle. Hot waterused in upper cycle flows into lower cycle, and cooling water used in lower cycle flows into upper
cycle.Upper part of four-bed mass recovery cycle (HEX1, HEX2, COND1 and EVA1) is similar to
single-stage cycle. The cycle added the valve to connect HEX1 and HEX2 is two-bed mass recov-ery cycle. These mass recovery cycles have six operational modes; Fig. 1 shows half cycle of four-bed mass recovery cycle that has only three modes. The second and fourth modes are mass
recovery process. In this process on two-bed mass recovery cycle, HEX1 is connected withHEX2. If HEX1 is adsorber and HEX2 is desorber in mode A, the pressures of adsorber/desorber
heat exchangers at the beginning of mode B are equal to those in mode A. For example, adsorberconnects with evaporator. Therefore, the pressure of adsorber is equal to that of evaporator.Should the evaporator vapor temperature be 10 °C, the pressure of evaporator is about
1.2 kPa. The pressure of desorber, which is equal to the condenser pressure, is about 4.1 kPa,when the condenser vapor temperature is 30 °C. Because of the pressure difference of the beds,adsorption/desorption process will occur automatically without any heating and cooling applica-
tion. Thus, the desorbed refrigerant from desorber will move to adsorber; the high refrigerantmass circulation provides better performances.
Four-bed mass recovery cycle utilizes same principle. Moreover, the refrigerant mass circula-
tion will be higher than the conventional two-bed mass recovery cycle due to the higher pressuredifference in the present cycle with cooling water cascading on condenser. Fig. 1(a) presents themode A of four-bed mass recovery cycle; in mode A, valves V1, V4, V5, V8, V9 and V10 are
closed in such a manner that EVA1-HEX1 and EVA2-HEX3 are in adsorption process andCOND1-HEX2 and COND2-HEX4 are in desorption process. Refrigerant (water) in evaporator
is evaporated at the temperature (T eva) and thus removing Qeva from the chilled water. The evap-orated vapor is adsorbed by adsorbent (silica gel bed), and cooling water circulated to the beds
removes the adsorption heat, Qads. The desorption–condensaion process takes place at pressure(P cond). The desorbers (HEX2 and HEX4) are heated up to the temperature (T des) by Qdes, pro-vided by the driving heat source. The resulting refrigerant vapor is cooled down to temperature(T cond) in the condenser by the cooling water, which removes the heat, Qcond. When the refrigerant
concentrations in the adsorber as well as in the desorber are at near their equilibrium levels, thecycle is continued by changing into mode B.
In mode B, adsorber (HEX1) and desorber (HEX2) of upper cycle are connected with desorber
(HEX3) and adsorber (HEX4) through the valves V9 and V10, respectively. In this mode, no bedinteracts with the evaporator or condenser. The pressures of adsorber and desorber at the begin-
ning of mode B are equal to those in mode A. Each bed in mode A operates at different pressure
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1767
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 5/15
levels (Fig. 2). The process is same as mass recovery process of conventional two-bed mass
recovery cycle.
V3V1
V2V4
V6
V7
V8
V10
V9
V5
HEX1
HEX2
HEX3HEX4
COND1
COND2
EVA1
EVA2
Refrigerantvapor
Cooling
waterIn/Out
Coolingwater
In/Out
HotwaterIn/Out
HotwaterIn/Out
Chilledwater In Chilledwater Out
Coolin Water
HotwaterIn/Out
HotwaterIn/Out
V3V1
V2V4
V6
V7
V8
V10
V9
V5
HEX1HEX2
HEX3HEX4
COND1
COND2
EVA1
EVA2
Coolingwater
In/Out
Coolingwater
In/Out
Chilledwater In Chilledwater Out
Coolin Water
(a) ModeA
(b) ModeB
(c) ModeC
Refrigerantvapo
V3 V1
V2V4
V6
V7
V8
V10
V9
V5
HEX1HEX2
HEX3HEX4
COND1
COND2
EVA1
EVA2
Chilledwater In Chilledwater Out
Coolin Water
Fig. 1. Schematic of four-bed adsorption refrigeration cycle with mass recovery process.
1768 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 6/15
Mode C is a warm-up process. In this mode, all valves are closed. HEX1 and HEX3 are
heated up by hot water, and HEX2 and HEX4 are cooled by cooling water. When the pres-sures of desorber and adsorber are nearly equal to the pressures of condenser and evapora-tor respectively, then valves between adsorbers and evaporators as well as valves between
desorbers and condensers are opened to flow the refrigerant. The latter mode is denoted asmode D.
It is noted that the right side of the system is in desorption process and left side is in adsorptionprocess. In next mode, the mode E is similar as mode B. Mode F is warm up process as mode C.
The mode is the last process and after the mode, it returns to mode A.
2.2. Mass recovery cycle with heating and cooling
The cycle aims at providing better cooling capacity by applying hot and cooling water in massrecovery process. Therefore, mode A, C, D, and F are same with the cycle without heating and
cooling. In mode B and E, all valves except V9 and V10 are closed. For example, HEX1 andHEX3 are adsorber and HEX2 and HEX4 are desorber, therefore, HEX1 and HEX3 are cooleddown by cooling water and HEX2 and HEX4 are heated by hot water. The input of hot and cool-
ing water increases a quantity of adsorbate moving from desorber to adsorber, which will lead the
system to provide better cooling capacity.
3. Mathematical modeling
The working principle of conventional chiller is available in Ref. [13,14]. In the present study, it
is assumed that the temperature and pressure are uniform throughout the whole adsorber, and thesystem has no heat losses to the environment, i.e. well insulated. According to these assumptions,the dynamic behavior of heat and mass transfer inside the different components of the adsorption
chiller can be written as:
Upper Cycle
Bottom Cycle
Bed Temperature
W a t e r V a p o r P r e s s u r e
Concentration100%
Fig. 2. Conceptual Duhring diagram for four-bed mass recovery cycle.
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1769
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 7/15
3.1. Energy balance in adsorber/desorber
The energy balance in adsorber can be written as
d
dt ½fW s Á ðC s þ C wv Á qÞ þ ðC cu Á W kHex þ C al Á W fHexÞg Á T ads
¼ Qst Á W s Ádq
dt þ F water Á C water Á ðT water in À T water outÞ ð1Þ
The outlet temperature of cooling water can be expressed as
T water out ¼ T ads þ ðT water in À T adsÞ Á expÀ K ads Á AHex
F water Á C water
ð2Þ
The energy balance in desorber can be described by identical equations, where the term for heat
transfer fluid (water) temperature (T water) and the subscript ads, respectively, denote the coolingwater and adsorber upon adsorption, and the hot water and desorber upon desorption.
3.2. Energy balance in condenser
The condenser energy balance equation can be written as
C cu Á W c ÁdT c
dt ¼ À L Á W s Á
dqdes
dt þ C w Á W s Á
dqdes
dt Á T c À C wv Á W s Á
dqdes
dt Á T c þ F c Á C w
Á ðT cool in À T cool outÞ ð3Þ
The outlet temperature of cooling water is given as
T cool out ¼ T c þ ðT cool in À T cÞ Á expÀ K c Á Ac
F c Á C c
ð4Þ
3.3. Energy balance in evaporator
The energy balance in evaporator is expressed as
d
dt fT e Á ðC w Á W ew þ C cu Á W eÞg ¼ À L Á W s Á
dqads
dt À C w Á W s Á
dqdes
dt Á T c À C wv Á W s Á
dqads
dt Á T e
þ F e Á C w Á ðT chill in À T chill outÞ ð5Þ
The outlet temperature of chilled water can be written as
T chilled out ¼ T e þ ðT chilled in À T eÞ Á expÀ K e Á Ae
F e Á C e
ð6Þ
3.4. Adsorption equilibrium
The adsorption equilibrium for silica gel type A/water vapor can be expressed by the followingcorrelation:
1770 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 8/15
qà ¼ AðT sÞ ÂPsðTwÞ
PsðTsÞ
BðT sÞ
ð7Þ
where AðT sÞ ¼ A0 þ A1 Â T s þ A2 Â T 2s þ A3 Â T 3s ð8Þ
BðT sÞ ¼ B0 þ B1 Â T s þ B2 Â T 2s þ B3 Â T 3s ð9Þ
The numerical values of A0–A3 and B0–B3 are determined by the least square method appliedto experimental data; the numerical values have been discussed by Saha et al. [13]. The typical
values of physical property parameters used in the calculations are shown in Table 1.
3.5. System performance equations
The cooling capacity is expressed byCooling capacity ¼
Qchill
t cycle
ð10Þ
where
Qchill ¼
Z t 0
C w Á F e Á ðT chill in À T chill outÞdt ð11Þ
Table 1
Physical property values
Symbol Value Unit
Ac 3.73 m2
Ae 1.91 m2
AHex 2.46 m2
W c 27.28 kg
W e 12.45 kg
W kHex 64.04 kg
W fHex 51.20 kg
W sHex 47.00 kg
K c 4115.23 W m2 KÀ1
K e 2557.54 W m2 KÀ1
K ads 1602.56 W m2 KÀ1
K des 1724.14 W m2 KÀ1
Rgas 4.62 · 102
J kgÀ1
KÀ1
E a 2.33 · 106 J kgÀ1
Dso 2.54 · 10À4 m2 sÀ1
Rp 0.3 · 10À3 m
Qst 2.80 · 106 J kgÀ1
C s 924 J kgÀ1 KÀ1
C w 4180 J kgÀ1 KÀ1
C wv 4190 J kgÀ1 KÀ1
C cu 386 J kgÀ1 KÀ1
C al 905 J kgÀ1 KÀ1
L 2.50 · 106 J kgÀ1
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1771
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 9/15
The COP value is defined by the following equation:
COP ¼Qchill
QIN
ð12Þ
where
QIN ¼
Z t 0
C w Á F hw Á ðT hot in À T hot outÞdt ð13Þ
It is well known that cooling capacity increases as silica gel weight increases if other conditionremains same. If the performance of four-bed cycle is compared with one of two-bed cycle, it isnecessary to calculate cooling capacity per silica gel weight; which is defined as SCP. SCP can
be expressed by the following equation:
SCP ¼Cooling capacity
W sHex
ð14Þ
4. Results and discussion
In the preceding sector, a novel strategy in mass recovery process is proposed and cycle simu-lation runs are performed to evaluate the performance of the proposed mass recovery cycle. Silica
gel–water adsorption refrigeration cycle is designed for utilizing low grade waste heat. Therefore,it is important to utilize the low temperature waste heat as driving source. From this point of view,investigation was conducted for hot water of temperature between 50 and 80 °C. Standard oper-
ating conditions are cited in Table 2 [15]. In all figures, legend ÔwithoutÕ and ÔwithÕ are used whereÔwithout
Õmeans the cycle in which hot and cooling water are not supplied during mass recovery
process while ÔwithÕ means hot and cooling water are supplied during mass recovery process.
4.1. Performance comparison
Fig. 3 shows the effect of heat source temperature on COP and cooling capacity of the proposedsystem. In the calculation, mass flow rate of chilled water is constant at 0.7 kg sÀ1. From the
Table 2
Standard operating conditions
Parameter Value Unit
Hot water in Temperature 70 °C
Flow 1.7 kg sÀ1
Cooling water in Temperature 30 °C
Flow (Ads + Cond) 3.0 (1.7 + 1.3) kg sÀ1
Chilled water in Temperature 14 °C
Chilled water out Temperature 7 °C
Cycle time 1200 s
Adsorption/desorption 490 s
Mass recovery 80 s
Pre-heating/pre-cooling 30 s
1772 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 10/15
figure, it can be seen that the COP values of the cycle without heating/cooling have the best value
and the values are always higher than those of the cycle with heating/cooling. Cooling capacity of each cycle increases as the heat source temperature increases.
Fig. 4 shows the predicted and experimental specific cooling power (SCP) of proposed mass
recovery. The input data of temperature is same with that of standard operating condition.Adsorption/desorption process time is 420 s, mass recovery process time is 60 s and pre-heat-
ing/pre-cooling process time is 30 s. As the prototype experimental machine has the maximumflow rate capacity, therefore, for the figure we considered mass flow rate of hot water is 1.5 kg s À1,
one of cooling water is 2.3 kg sÀ1 and one of chilled water is 0.6 kg sÀ1. It is seen that SCP is
superimposed with the measured SCP at any heat source temperature and it could be claimedthat our calculation agrees well with experimental data. Some values of experimental resultsare higher than those values of simulation results. The chiller operates by continuously switching
0
0.2
0.4
0.6
0.8
1
40 50 60 70 80 90
Heatsource temperature (°C)
C O P [ - ]
0
5
10
15
20
25
30COP (without)
COP (with)
Cooling capacity (without)
Cooling capacity (with)
chilled waterinlet temp.=14°C
cooling water inlet temp.=30°C
C o o l i n g c a p a c i t y ( k W
)
Fig. 3. Effect of heat source temperature.
0
20
40
60
80
100
120
140
160
180
50 60 70 80
Heat source temperature (°C)
S C P ( W
k g - 1 )
Simulation (masswithout)
Simulation (masswith)
Simulaiton (single-stage)
Experiment (mass without)
Experiment (mass with)
Experiment (single-stage)
chilled water inlet temp.=14°Ccooling water inlet temp.=30°C
Fig. 4. Comparison with experimental result on SCP.
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1773
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 11/15
its adsorber/desorber heat exchangers between the adsorption and desorption mode. Therefore,
there are some differences between experimental condition and standard condition. That is whysome experimental results are higher than those values of simulation results.
If the performance of one cycle is compared with that of other cycle, it is important to considerthe outlet temperature of chilled water because performances is strongly dependent on the evap-
orating temperature. Saha et al. [8] showed that the more the mass flow rate of chilled water, thehigher the COP value and cooling capacity. Nonetheless, if the cycle is operated with high flowrate of chilled water for getting high performance, it causes to increase the outlet temperature
of chilled water. Therefore, it is impractical to utilize high flow rates of chilled water; the outlettemperature of chilled water is important and should be used same value for comparison amongthe cycles. Therefore, cyclic average chilled water outlet temperature is fixed at 7 °C for the
following results.Fig. 5 shows the improvement ratio of COPs and cooling capacity on the cycle with heating/
cooling to the cycle without heating/cooling. From the figure, it is seen that improvement ratioof cooling capacity is 23.5% if heat source temperature is 60 °C. The lower the heat source tem-perature, the higher the effect of mass recovery process with hot and cooling water. Nevertheless,
the COP value decreases as the heat source temperature decreases. Therefore, if there is enoughinput heat, that is, waste heat, the mass recovery cycle with heating and cooling has advantage
to conventional mass recovery cycle.
4.2. Effect of cascading chilled water
Mass recovery process utilizes the pressure difference between the adsorber and desorber. Thepressure of adsorber depends on the pressure of evaporator and chilled water inlet temperature
decides the pressure of evaporator. If chilled water flows to evaporator from upper cycle to lowercycle, inlet temperature of lower cycle will be lower than that of upper cycle. Therefore, the pres-sure difference between desorber on upper cycle and adsorber on lower cycle will be higher than
that with chilled water parallel flow; it seems that the amount of refrigerant that moves from de-sorber to adsorber increases. Fig. 6 shows the results of the COP value and cooling capacity withparallel or cascading flow of chilled water. In the calculation, mass flow rate of chilled water is
-30
-20
-10
0
10
20
30
50 60 70 80 90
Heat source temperature (°C)
I m p r o v e m e n t r a t i o ( % )
COP
Cooling capacity
chilled water inlet temp.=14°C
cooling water inlet temp.=30 °C
Fig. 5. Effect of supplying hot and cooling water (average chilled water outlet temperature is 7 °C).
1774 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 12/15
controlled to obtain average outlet temperature of chilled water at 7 °C. In the cascading cycle,chilled water is cooled twice; outlet temperature of chilled water with cascading flow is lower than
that with parallel flow. Mass flow rate of chilled water with cascading flow is more than that withparallel flow. Cooling output increases as mass flow rate increases. Therefore, the cycle with cas-cade flow has the advantage over the cycle with parallel flow. Especially, chilled water outlet tem-perature increases as heat source temperature decreases; cascading chilled water is effective for
operating the chiller at low heat source temperature.
4.3. Comparison with conventional, single-stage cycle
Fig. 7 shows the effect of heat source temperature on COP and SCP of mass recovery cycle with
cascading or parallel flow on chilled water and single-stage cycle. From the figure, COP values of
(b) Cooling capacity
0
100
200
300
50 60 70 80 90
Heat source temperature (°C)
Parallel (without)
Parallel (with)Cascading (without)
Cascading (with)
(a) COP
0
0.1
0.2
0.3
0.4
0.5
0.6
50 60 70 80 90
Heatsource temperature (°C)
C O P [ - ]
Parallel (without)
Parallel (with)
Cascading (without)
Cascading (with)
chilled water inlet temp.=14°C
cooling water inlet temp.=30°C
chilled water inlet temp.=14°C
cooling water inlet temp.=30°C
S C P ( W k g
- 1 )
Fig. 6. Effect of cascading chilled water (average chilled water outlet temperature is 7 °C).
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1775
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 13/15
the mass recovery cycle without heating/cooling and with cascading chilled water are alwayshigher than those of single-stage cycle. For example, if heat source temperature is 70 °C, improve-ment ratio of COP value on mass recovery cycle without heating/cooling and with cascadingchilled water is 30.3%. In the cycle with heating/cooling and with cascading chilled water, the val-
ues are higher than those of single-stage cycle at the heat source temperature lower than 70 °C.SCP values of two mass recovery cycles in which chilled water is used with cascading flow arealways higher than those of single-stage cycle at any heat source temperature. If heat source tem-perature is 70 °C, the improvement ratio of the cycle with heating/cooling and cascading chilled
water is 15.8%. Moreover, the lower the heat source temperature, the higher the improvementratio. Therefore, the cycle with cascading chilled water has the advantage over single-stage cycle
(a) COP
0
0.1
0.2
0.3
0.4
0.5
0.6
50 60 70 80 90
Heat source temperature (°C)
C O P [ - ]
single-stage
mass parallel (without)
mass parallel (with)
mass cascade (without)
mass cascade(with)
(b) SCP
0
20
40
60
80
100
120
50 60 70 80 90
Heat source temperature (°C)
S C P ( W k g - 1 )
single-stage
mass parallel (without)mass parallel (with)
mass cascade (without)mass cascade (with)
chilled water inlet temp.=14°C
cooling water inlet temp.=30°C
chilled water inlet temp.=14°C
cooling water inlet temp.=30°C
Fig. 7. Comparison with single-stage cycle (average chilled water outlet temperature is 7 °C).
1776 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 14/15
at low heat source temperature and it is found that the mass recovery process has the effect on the
performance at low heat source temperature. For the mass recovery cycle with heating/cooling,the improvement ratio of SCP with chilled water parallel flow is 1.8% at heat source temperature
70 °C; the value for the cycle without heating/cooling is À5.9%. In the proposed mass recoverycycle, hot and cooling water flows to adsorber/desorber heat exchanger with cascading: hot water
flows to lower cycle from upper cycle and cooling water flows to upper cycle from lower cycle.Therefore, hot water inlet temperature on lower cycle is lower than that of upper cycle; coolingwater inlet temperature on upper cycle is higher than that of lower cycle because of adsorption
heat on lower cycle. The performance of upper cycle is lower than that of the single-stage cyclewith cooling water inlet temperature 30 °C and the performance of lower cycle is lower than thatof single-stage with hot water inlet temperature 70 °C. Therefore, it is natural the performance of
proposed cycle is lower than single-stage cycle if chilled water is used with parallel flow. The pro-posed cycle has the advantage for conventional single-stage cycle with chilled water cascading and
considering the fixed average chilled water outlet temperature.
5. Conclusion
The mass recovery cycles with silica gel–water pair were presented and the effects of operatingconditions were investigated. For the same operating conditions, mass recovery cycles haveadvantage to conventional single-stage cycle at low heat source temperature with considering fixed
average chilled water outlet temperature. The performance of the cycle with cascaded chilledwater flow is better than that of the cycle with parallel chilled water as the chilled water is coldtwice and outlet temperature is lower than that of the cycle with chilled water parallel flow. That
is why the proposed mass recovery cycle is superior than the conventional single-stage cycle withconsidering the fixed average chilled water outlet temperature and cascading chilled water. Cool-ing capacity of mass recovery cycle with heating and cooling is higher than that of conventional
single-stage cycle. This advantage is higher at low heat source temperature. COP values of pro-posed cycle are also higher than those of single-stage cycle if heat source temperature is lower than70 °C. Therefore, the mass recovery cycle with silica gel–water pair will be effective for using low
temperature waste heat in the future.
Acknowledgement
The authors wish to acknowledge the financial support provided by the New Energy and Indus-trial Technology Development Organization (NEDO), Japan, to conduct the present research.
References
[1] M. Rothmeyer, P. Maier-Laxhuber, G. Alefeld, Design and Performance of Zeolite-Water Heat Pumps, in:
Proceedings of IIR-XVIth International Congress of Refrigeration, Paris, France, 1983, p. 701.
[2] N. Douss, F. Meunier, Experimental study of cascading adsorption cycles, Chem. Eng. Sci. 44 (2) (1989) 225–235.
A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778 1777
7/27/2019 Mass recovery four-bed adsorption refrigeration cycle.pdf
http://slidepdf.com/reader/full/mass-recovery-four-bed-adsorption-refrigeration-cyclepdf 15/15
[3] R.E. Critoph, H.L. Turner, Performance of ammonia-activated carbon and ammonia-zeolite heat pump
adsorption cycle, in: Proceedings of the International Conference on Pompes a Chaleur Chimiques de Hautes
Performances, Perpignan, France, 1988, pp. 202–211.
[4] M. Pons, J.J. Guilleminot, Design of an experimental solar-powered solid adsorption ice maker, Trans. ASME J.Sol. Energy Eng. 108 (1986) 332–337.
[5] J.A. Jones, V. Christophilos, High-efficiency regenerative adsorption heat pump, ASHRAE Trans. 99 (1) (1993)
54–60.
[6] H.T. Chua, K.C. Ng, A. Malek, T. Kashiwagi, A. Akisawa, B.B. Saha, Modeling the performance of two-bed,
silica gel–water adsorption chillers, Int. J. Refrig. 22 (1999) 194–204.
[7] K.C.A. Alam, B.B. Saha, Y.T. Kang, A. Akisawa, T. Kashiwagi, Heat exchanger design effect on the system
performance of silica gel–water adsorption system, Int. J. Heat Mass Transfer 43 (24) (2000) 4419–4431.
[8] B.B. Saha, E.C. Boelman, T. Kashiwagi, Computer simulation of a silica gel–water adsorption refrigeration
cycle—the influence of operating conditions on cooling output and COP, ASHRAE Trans. Res. 101 (2) (1995) 348–
355.
[9] B.B. Saha, E.C. Boelman, T. Kashiwagi, Computational analysis of an advanced adsorption refrigeration cycle,
Energy 20 (10) (1995) 983–994.
[10] M. Pons, F. Poyelle, Adsorptive machines with advantaged cycles for heat pumping or cooling applications, Int. J.Refrig. 22 (1999) 27–37.
[11] R.Z. Wang, Performance improvement of adsorption cooling by heat and mass recovery operation, Int. J. Refrig.
24 (2001) 602–611.
[12] A. Akahira, K.C.A. Alam, Y. Hamamoto, A. Akisawa, T. Kashiwagi, Mass recovery adsorption refrigeration
cycle—improving cooling capacity, Int. J. Refrig. 27 (3) (2004) 225–234.
[13] B.B. Saha, K.C.A. Alam, A. Akisawa, T. Kashiwagi, K.C. Ng, H.T. Chua, Two-stage non-regenerative silica gel–
water adsorption refrigeration cycle, in: Proceedings of ASME Advanced Energy System Division, Orlando, 2000,
pp. 65–69.
[14] K.C.A. Alam, A. Akahira, Y. Hamamoto, A. Akisawa, T. Kashiwagi, B.B. Saha, S. Koyama, K.C. Ng, H.T.
Chua, Multi-bed multi-stage adsorption refrigeration cycle-reducing driving heat source temperature, Trans.
JSRAE 20 (3) (2003) 413–420.
[15] A. Akahira, K.C.A. Alam, Y. Hamamoto, A. Akisawa, T. Kashiwagi, Computational analysis of silica gel–wateradsorption refrigeration cycle with mass recovery, Trans. JSRAE 19 (4) (2002) 367–374.
1778 A. Akahira et al. / Applied Thermal Engineering 25 (2005) 1764–1778