吸着式熱交換器および海水淡水化のための吸着現象のマルチスケール解析

概要

九州大学学術情報リポジトリ
Kyushu University Institutional Repository

Multiscale Investigation of Adsorption
Phenomena for Adsorption Heat Transformer and
Desalination
サガル, サレン

https://hdl.handle.net/2324/7157380
出版情報：Kyushu University, 2023, 博士（学術）, 課程博士
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氏

名 ：Sagar Saren

Name

論 文 名 ：Multiscale Investigation of Adsorption Phenomena for Adsorption Heat
Transformer and Desalination (吸着式熱交換器および海水淡水化のための吸着現象のマルチ
スケール解析)
Title

区

分 ：甲

Category

論 文 内 容 の 要 旨
Thesis Summary
Rampant emission of greenhouse gases in the atmosphere is the primary contributor to the global
warming and climate change phenomena. The primary sources of these greenhouse gases include the
fossil-fuel based power generation and its utilization in the conventional mechanical vapor compression
and thermal desalination systems. Furthermore, the waste heat generated due to the thermal
inefficiencies of the energy systems exacerbates the given crises. In order to mitigate these crises, the
incessant switch to renewable energy and waste heat recovery for use in thermal systems are gaining
importance. Adsorption-based thermal systems, including cooling and desalination applications, are
becoming promising alternatives to the conventional energy-based thermal systems. The use of adsorption
phenomena for these given applications is still at a developing stage. The primary research on the
adsorption-based thermal systems encapsulates from material characterization to system-level
performance optimization. Therefore, the adsorption phenomena can be investigated from microscopic to
macroscopic perspectives. The present study concerns with the equilibrium adsorption phenomena, for
which three types of studies are conducted: (i) molecular simulation, (ii) adsorbed phase thermodynamic
property determination, and (iii) adsorption heat transformer cycle simulation.
The adsorption properties, viz., isotherm and isosteric heat of adsorption, are dependent upon the
adsorbent material characteristics such as its pore size distribution and pore surface chemistry. Influence
of these factors is evaluated by performing a Grand Canonical Monte Carlo (GCMC) simulation of the
adsorption process. CO2 adsorption in activated carbon is taken as an example for this simulation study.
The activated carbon is modeled as graphite slit pore structures with or without surface functional groups.
Three oxygen containing functional groups are considered, viz., carbonyl, hydroxyl, and carboxyl groups.
The results indicate favorable impact of smaller pore size and the presence of functional groups on the
low-pressure adsorption uptake and isosteric heat of adsorption. Furthermore, a GCMC simulation is
performed for water adsorption in hydroxyl functional group-based graphite slit pore. This study
elucidates the adsorbed phase formation process and the resultant adsorption isotherm shape. The
molecular level investigation of the adsorption phenomena is followed by the bulk thermodynamic
property determination of the resultant adsorbed phase. Three properties are determined, viz., specific

heat capacity, specific entropy, and specific enthalpy. The rigorous mathematical development of these
properties is carried out considering the key variables of pressure, temperature, uptake, isosteric heat of
adsorption, and gaseous phase properties. The path integrals present in the entropy formulation is
calculated by choosing accurate reference uptake value and consistent reference entropy values between
the gaseous phase and adsorbed phase. These thermodynamic properties are compared against the
corresponding gaseous phase and saturated liquid phase values, to evaluate the relative behavior of the
adsorbed phase with respect to the pure adsorbate property values.
Finally, an equilibrium cycle development of the heat upgrading adsorption heat transformer cycle
(AHT) is performed. The heat upgrading cycles can elevate the low-grade heat source temperature to a
higher value, for increasing its exergetic potential. Recently, these cycles are gaining attraction for its use
in cooling, desalination, and power generation applications as opposed to the conventional
adsorption-based thermal systems. However, given the relative scarcity in the available studies on the
heat upgrading cycles, a detailed equilibrium performance evaluation for the AHT cycle is carried out.
Non-linear optimization based mathematical model is developed for characterizing the non-isosteric
preheating and precooling phases of the AHT cycle. The performance parameters are defined by the useful
heat ratio (UHR) and condensation heat ratio (CHR), denoting the heat upgrading and desalination
potentials, respectively. Detailed parametric evaluation of these performance parameters and the output
adsorption heat amount is carried out with respect to operating temperature range, adsorber bed thermal
mass, and type of adsorbent-adsorbate pair. This study is accompanied by the performance enhancement
of the AHT cycle via an internal heat recovery scheme. Moreover, the theoretical maximum temperature
lift of the AHT cycle is determined from both the reversible and irreversible thermodynamic process-based
approaches. The ability to augment the desalination performance of an existing multi-effect distillation
(MED) system is realized by the hybridization of the AHT cycle with the MED system. The resultant
AHT-MED system elucidates a significant improvement in the performance ratio and water production
rate as compared to the standalone MED system with the same working temperature range.

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