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TitleDynamics of Adsorptive Systems for Heat Transformation: Optimization of Adsorber, Adsorbent
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Table of Contents
1 Adsorptive Heat Transformation and Storage: Thermodynamic and Kinetic Aspects
	1.1 Thermodynamic Cycles for AHT
		1.1.1 Temperature-Driven Cycles
		1.1.2 Pressure-Driven Cycles
		1.1.3 Other Presentations of the AHT Cycles
	1.2 The AHT Efficiency
		1.2.1 The First Law Efficiency
		1.2.2 The Second Law Efficiency
	1.3 Dynamics of AHT Cycles
	1.4 Adsorbents Optimal for AHT
		1.4.1 The First Law Efficiency
		1.4.2 The Second Law Efficiency
		1.4.3 Adsorbent Optimal from the Dynamic Point of View
2 Measurement of Adsorption Dynamics: An Overview
	2.1 Differential Step (IDS) Method
	2.2 Large Pressure Jump (LPJ) Method
	2.3 Large Temperature Jump (LTJ) Method
		2.3.1 Volumetric Large Temperature Jump Method (V-LTJ)
		2.3.2 Gravimetric Large Temperature Jump Method (G-LTJ)
3 Experimental Findings: Main Factors Affecting the Adsorptive Temperature-Driven Cycle Dynamics
	3.1 Adsorbate and Adsorbent Nature
		3.1.1 Water Sorption Dynamics
		3.1.2 Methanol Sorption Dynamics
	3.2 Adsorbent Grain Size
		3.2.1 Water Sorption Dynamics
		3.2.2 Methanol Sorption Dynamics
		3.2.3 Ethanol Sorption Dynamics
	3.3 Geometry of the Adsorber
		3.3.1 Water Sorption Dynamics
		3.3.2 Methanol Sorption Dynamics
		3.3.3 Ethanol Sorption Dynamics
	3.4 Cycle Boundary Conditions
		3.4.1 Methanol Sorption Dynamics
		3.4.2 Ethanol Sorption Dynamics
	3.5 Residual Gases
		3.5.1 Water Sorption Dynamics
	3.6 Flux of Cooling/Heating Heat Carrier Fluid
4 Optimization of an “Adsorbent/Heat Exchanger” Unit
	4.1 Optimization of the “Adsorbent—Heat Exchanger” Unit
		4.1.1 Adsorbent Grain Size
		4.1.2 The Ratio “Heat Transfer Surface”/“Adsorbent Mass”
		4.1.3 The Effect of the Flow Rate of External Heat Carrier
		4.1.4 Comparison of the Model Configurations with Full-Scale AHT Units
	4.2 Compact Layer Versus Loose Grains
	4.3 The Effect of Residual Gases
	4.4 Reallocation of Adsorption and Desorption Times in the AHT Cycle
Document Text Contents
Page 1


Alessio Sapienza
Andrea Frazzica
Angelo Freni
Yuri Aristov

Dynamics of
Systems for Heat
Optimization of
Adsorber, Adsorbent
and Cycle

Page 2

SpringerBriefs in Applied Sciences
and Technology

Series editor

Janusz Kacprzyk, Polish Academy of Sciences, Systems Research Institute,
Warsaw, Poland

Page 47

This confirms the “grain size insensitive” or “lumped” regime already observed
for a FAB configuration. Despite the highest (S/m) ratio (3.2 m2 kg−1), the Ad-HEx
charged with the AQSOA Z02 grains of 1.00–1.18 mm size shows a desorption rate
that is slower by a factor of 1.8. Indeed, increasing the particles size slows down the
mass transport inside the grains and the process becomes “grain size sensitive”. The
intra-granular mass transfer resistance is likely a reason of the adsorption rate
reduction for the AQSOA Z02 grains of 1.00–1.18 mm size (Fig. 3.9).

For adsorption, the “lumped” regime is found for the narrower range of the grain
size, c.a. 0.30–0.71 mm. For smaller grains, a dramatic rate slowdown (by a factor
of 1.55) is detected. That may be due to the reduced bed permeability and the
consequent inter-grain mass transfer resistance along the narrow triangular channels

Fig. 3.7 View of tested representative piece of real adsorbers [13]

Fig. 3.8 Grain size (in mm) effect on the adsorption/desorption dynamics for a representative
piece of a real adsorber Ad-HEx 1 [13]

40 3 Experimental Findings: Main Factors Affecting …

Page 48

between the secondary fins. This resistance is absent in the FAB configuration. In
sum, when the sorption rate is controlled by the heat transfer between the adsorbent
and the metal support no effect of the grain size is observed. The “grain size
insensitive” mode, similar to that first revealed for a flat-plate configuration, takes
place also for more complicated configurations. Under this mode, it is not necessary
to precisely select the adsorbent grain size: the grains should just be sufficiently
small to assure the “lumped” mode. On the other hand, using too small grains is not
recommended, as the inter-grain diffusional resistance may become a rate-limiting
process [13].

3.2.2 Methanol Sorption Dynamics

The effect of grain size on the dynamics of methanol sorption on the LiCl/silica
composite was deeply investigated in [5]. Experimental tests were conducted on
monolayers of the adsorbent grains with three grain sizes, namely 0.4–0.5 mm,
0.8–0.9 mm and 1.6–1.8 mm, and two different salt contents. As reported in
Fig. 3.10, only the smallest grains show an exponential ad/desorption evolution of
the kinetics. Differently, a clear deviation from the exponential evolution was
highlighted for larger grains. In particular, a dramatic increase of time to reach 90%
of total conversion (3920 s) was achieved by the largest grains (1.6–1.8 mm).
Furthermore, as can be highlighted in Table 3.3, the total uptake variation for the

Fig. 3.9 Grain size effect for
Ad-HEx 1 on the adsorption/
desorption dynamics with the
main resistances depicted
(namely inter-particle
diffusion, heat transfer metal/
adsorbent, intra-particle
diffusion). Blue—adsorption,
red—desorption [13]

Table 3.3 Effect of the grain
size on dynamics of methanol
ad/desorption on/from the
monolayer of LiCl(21 wt%)/
SiO2 composite [5]

Dgr, mm Δw, g/g Adsorption Desorption

s, s s0.9, s s, s s0.9, s

0.4–0.5 0.50 107 251 – 650

0.8–0.9 0.36 196 520 – 920

1.6–1.8 0.30 – 3920 – 4550

3.2 Adsorbent Grain Size 41

Page 93

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