Study of Pressurised Adsorption Refrigeration Cycles Driven by

Solar/Waste Heat

EXTENDED PROPOSAL

by

Satish S/O Ganesan

14532

May 2014

Universiti Teknologi PETRONAS

Bandar Seri Iskandar

31750 Tronoh

Perak Darul Ridzuan

i

TABLE OF CONTENTS

Chapters Pages

CHAPTER 1: INTRODUCTION..........................................................

1.1 Background............................................................................ 1

1.2 Problem Statement................................................................. 2

1.4 Objectives and Scope of Study.............................................. 2

CHAPTER 2: LITERATURE REVIEW..............................................

2.1 Conventional Refrigeration Cycle......................................... 3

2.2 Adsorption Refrigeration Cycle............................................. 3-5

2.3 Type of Adsorption Systems and Working Pairs................... 5-6

2.4 Isotherms................................................................................ 6

CHAPTER 3: METHODOLOGY.........................................................

3.1 Key Milestone........................................................................ 7

3.2 Gantt Chart............................................................................. 8

REFERENCES........................................................................................ 9-10

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CHAPTER 1

INTRODUCTION

1.1 Background

A lot of research has gone through in the field of adsorption in recent years to

replace the conventional refrigeration system. This is due to the threats posed by

the current system to the environment in the form of high Global Warming

Potential (GWP) and Ozone Depleting Potential (ODP). According to Jribi et al.

(2010), the GWP of R134a, a common refrigerant in the conventional

refrigeration system, reaches almost a staggering 1300 while Hassan et al. (2011)

stated that the chlorofluorocarbon (CFC) emission also causes serious

consideration for an environmental friendly replacement. So, according to

Hassan et al., adsorption chillers could be the solution for the problem and they

are more appealing as a subject for research and development in the future.

Thermally powered sorption cooling systems have attracted a lot of attention as

they appear to be promising from the view point of greenhouse gas emissions

and ozone layer depletion problems. Loh et al. (2010) stated that the system has

no moving parts, requires relatively lesser maintenance and can be driven by

substandard heat source and hence, holds the advantage in relation to other

options available. This study also includes the effectiveness of each adsorbent-

adsorbate pair for a thermally driven sorption cooling system. Furthermore, it

incorporates the performance analysis of single stage two bed adsorption cooling

cycle at pressurized conditions employing activated carbon of type Maxsorb III

as adsorbent paired with four various refrigerants or adsorbates. The changes in

the adsorption isotherms of each pair will be studied extensively in order to

obtain the best adsorbent-adsorbate pair at different working conditions.

2

1.2 Problem Statement

As specified above, the conventional vapour compression refrigeration cycle has

a lot of downsides, the prominent ones being its vast Global Warming Potential

(GWP) and Ozone Depleting Potential (ODP). Hence, questions were asked

about its eco-friendliness. One of the most economically and environmentally

preferred technology is the sorption cooling system (Hassan et al., 2008).

According to Habib et al. (2011), the thermally driven system is non-toxic, eco-

friendly and employs natural refrigerants such as water, ammonia, methanol,

ethanol etc. Moreover, he added that the system has not need of polyester type

of synthetic lubricants. The main drawback of vacuum based adsorption cooling

cycles, however, is that the leakages will drastically reduce its performance.

1.3 Objectives and Scope of Study

The objectives of this project are:

i. To study performance analysis of single stage two bed adsorption cooling

cycle at pressurized conditions employing activated carbon of type

Maxsorb III as adsorbent and four various refrigerants.

ii. To obtain the best adsorbent-refrigerant pair at different working

conditions.

This analytical project incorporates the research and analyses of adsorption

isotherms of different adsorbent-adsorbate pairs under specified conditions.

3

CHAPTER 2

LITERATURE REVIEW

2.1 Conventional Refrigeration Cycle

Generally, a conventional refrigeration cycle, or commonly known as vapour

compression cycle is made up four main components, namely, the compressor,

evaporator, condenser and an expansion valve. However, regardless of how

efficient the system prove to be performance wise, it is still criticised for its

contribution to global warming and ozone depletion. As stated by Hassan,

Mohamad, and Bennacer (2011), the chlorofluorocarbons (CFC) emission from

the refrigerator is one of the main causes for global warming. Jribi et al. (2010)

added that the Global Warming Potential (GWP) of refrigerant type R134a, a

common refrigerant in a conventional refrigeration system, approaches 1300. On

the other hand, the adsorption refrigeration systems are gaining wide recognition

mainly due to their environmentally benign attribute.

2.2 Adsorption Refrigeration Cycle

Adsorption, a part of sorption process, is defined as the adhesion of atoms, ions,

or molecules from a gas or liquid onto a surface. It is a surface-based

phenomenon where an adsorbent surface is capable of attracting adsorbates.

Adsorption technique has been widely commercialised for industrial uses such

as gas separation, purification, energy storage systems etc. consistent with Saha

et al. (2008). He also stated that each one of the applications stated above needs

a specific adsorption data for the evaluation of adsorption equilibrium and energy

balance calculation. Likewise, the technique has been commercialised for

refrigeration cycles where the conventional compressor is replaced by a

thermally driven reactor, consisting of two adsorbent beds, each for adsorption

and desorption respectively (Chua et al., 1999). The schematic description of a

two-bed adsorption chiller is presented in Figure 1.

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FIGURE 1: A schematic of two-bed adsorption chiller

Figure 1 is the representation of the simplest form of a two-bed adsorption

chiller. The adsorption refrigeration system utilises thermal energy in the waste

heat from cogeneration systems or solar heat in some cases. In general, unlike

the compressor in a conventional system, the refrigerant (adsorbate) will be

adsorbed onto the surface of its adsorbent and deposited onto the cold bed (Chua

et al., 1999). Habib et al. asserted that cooling process of the cold bed, with the

help of coolant, ensures continuity of the adsorption process until the cold bed is

saturated. This phase of the system is called evaporation, or specifically known

as adsorption prompted evaporation. Then, hot bed which regenerated early on

takes over the process while the cold bed get desorbed. Desorption is

contradictory to adsorption where the cold bed needs to be heated at a constant

rate in order to ensure its continuity. Habib, Saha, Chakraborty, Koyama, and

Srinivasan (2011) found that the adsorption process is exothermic while the

desorption process is endothermic, consistent with Chua et al. The refrigerant

vapour desorbed from the hot bed will be condensed at the condenser. This phase

of the system will increase not only the temperature, but also the pressure of the

refrigerant until it reaches the condenser pressure. The warm fluid will then be

passed through the expansion valve where it undergoes abrupt pressure

reduction. Respective roles of two beds are reversed accordingly by swapping

the bed coolant and heat source. It is this behaviour of the system that prompted

it to be declared as an intermittent operation by Hassan et al. When the beds swap

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roles, the instantaneous refrigeration power of the system will undergo a

substantial drop and hence, it is important to maintain minimum switching time

(Chua et al., 1999). In addition, he argued that the diminutive switching period,

however, would result in inadequate cooling of the hot bed. The valves

connecting the condenser and evaporator with the beds will be closed during the

switching period. In the meanwhile, the hot bed will be cooled with a coolant

while the cold bed is heated. Then, the valves will be opened for adsorption and

desorption once the cooling and heating processes are complete. Chua et al.

stated that frequent regeneration contributes to efficient evaporation but the

process consumes high thermal power at the same time. Hassan et al. also

criticised the system in terms of its low specific cooling power (SCP) and

coefficient of performance (COP) in consistent with Habib et al. Hence, Habib

et al. suggested that the performance of two separate sorption cooling system,

when combined together, where one’s waste heat is utilised for another, could

significantly improve the overall efficiency of the system. Apart from that,

Hassan et al. expressed that the thermal powered sorption systems can be of

pressurised or non-pressurised types, depending on the adsorbent-adsorbate

pairs. Loh, Saha, Chakraborty, Ng, and Chun (2010) agreed to the statement by

giving away examples of high pressure and low pressure adsorbent-adsorbate

pairs. The types of adsorption refrigeration systems and the adsorbent-adsorbate

pairs associated with them are discussed further in the next section.

2.3 Type of Adsorption Systems and Working Pairs

The adsorption based refrigeration system is typically split into two types, the

vacuum based adsorption and the pressurised adsorption systems. The vacuum

based system, as the name suggests, is built upon vacuum condition in order to

accelerate the evaporation phase. This is due to the fact that evaporation

temperature is vastly reduced with decreasing pressure. On the other hand, the

pressurised system is the type of system which operates at a pressure more than

the atmospheric pressure. As mentioned in the earlier section, the type of

adsorption system is defined by the working pairs used (Loh, Saha, Chakraborty,

Ng, & Chun, 2010). Adsorbents are generally defined as materials which are

capable of adsorbing substances onto their rigid surface. For instance, water-

silica gel and methanol-activated carbon pairs are of low pressure type.

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Meanwhile, example of high pressure pairs are ammonia-activated carbon and

R134a-activated carbon. Most of the systems that utilise activated carbon as the

adsorbent are of the high pressure type. Saha, El-Sharkawy, Chakraborty and

Koyama (2007) found that most of the commercial adsorption cooling systems

utilise working pairs of water-silica gel, water-zeolite, ammonia-activated

carbon and ammonia-activated carbon fiber, as supported by Hassan et al.

Activated carbon is the most widely used adsorbent for refrigeration systems.

Askalany et al. (2013) found that the activated carbon powder (ACP) is a better

adsorbent compared to activated carbon fiber (ACF). Saha et al. agreed that, not

only they are better performance wise, they also prove to be a better option

financially. He also added that ACP’s superior performance is due to its high

surface area, high apparent density and good heat conductivity. Then, Saha et al.

also proved experimentally that the adsorption capacity of Maxsorb III, the

highly porous activated carbon, is 1.7 times higher than that of ACF. So, it is

essential to choose the right pair of adsorbent-adsorbate pair for an efficient

cooling system. Saha et al. found that the adsorbent manufacturers only provide

the information of pores volume and surface area. Hence, Saha, Jribi, Koyama

and El-Sharkawy (2011) affirmed that it is important to evaluate the right

isotherm and isosteric heat of adsorption for an adsorbent-adsorbate pair in order

to design a good adsorption chiller. As in the case of isotherms, they are

explained further in the following section.

2.4 Isotherms

The sorption process is generally represented by empirical models known as

isotherms. It is represents the isothermal material sorption equilibrium on a

surface. In this case, sorption of a refrigerant (adsorbate) to an adsorbent. It

describes the amount of refrigerant material bound at the adsorbent surface as a

function of the material present in the refrigerant. The isotherm data is not

provided by the adsorbent manufacturers (Saha, Habib, El-Sharkawy, &

Koyama, 2009). Hence, they are attained by means of experimental work and the

subsequent data collected. The most common isotherms used are the Dubinin–

Radushkevich (D-A) adsorption isotherm, the Langmuir isotherm, and the Toth

adsorption isotherm.

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CHAPTER 3

METHODOLOGY

3.1 Key Milestone

Literature Review

• Preliminary study on the pressurised adsoprtion cooling system available at present

• Further understanding about the refrigeration cycle and the utilisation of adsorption in cooling

Research

• Further study for the best adsorbent-adsorbate pair under specified working conditions from existing research

• Collecting information about variables in adsorption cooling system and their effect to the performance

Data Gathering

• Work on the isotherms of each adsorbent-adsorbate pair collected from existing researches

• Study the changes in system performance for varying refrigerants using Maxsorb III as adsorbent

• Data analysis

• Results and discussions

Conclusion

• Conclude the analytical study

• Prepare documentation for interim report

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3.2 Gantt Chart

Table 1: Gantt chart upon project completion

Tasks Week

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Title Selection and Allocation

Submission of Title Selection Form

Preliminary Research Work

Preparing Extended Proposal

Submission of Extended Proposal ֎

Proposal Defence •

Data Analysis for the Best Adsorbent-

Adsorbate Pairs

Preparing Interim Report

Submission of Interim Draft Report •

Submission of Final Interim Report •

“•” represents key milestones

“֎” represents current period

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REFERENCES

Askalany, A. A., Saha, B. B., Uddin, K., Miyzaki, T., Koyama, S., Srinivasan, K., &

Ismail, I. M. (2013). Adsorption Isotherms and Heat of Adsorption of

Difluoromethane on Activated Carbons. Journal of Chemical & Engineering

Data, 58(10), 2828-2834. doi: 10.1021/je4005678

Chua, H., Ng, K., Malek, A., Kashiwagi, T., Akisawa, A., & Saha, B. (1999). Modeling

the performance of two-bed, silica gel-water adsorption chillers. International

Journal of Refrigeration, 22(3), 194-204.

Habib, K., Saha, B. B., Chakraborty, A., Koyama, S., & Srinivasan, K. (2011).

Performance evaluation of combined adsorption refrigeration cycles.

International Journal of Refrigeration, 34(1), 129-137.

Hassan, H., Mohamad, A., & Bennacer, R. (2011). Simulation of an adsorption solar

cooling system. Energy, 36(1), 530-537.

Jribi, S., Koyama, S., Saha, B. B. (2010). Performance Investigation of a Novel CO2

Compression-Adsorption Based Hybrid Cooling Cycle. Engineering Sciences

Reports, Kyushu University, 32(3), 12-18.

Loh, W. S., Saha, B. B., Chakraborty, A., Ng, K. C., & Chun, W. G. (2010).

Performance analysis of waste heat driven pressurized adsorption chiller.

Journal of Thermal Science and Technology, 5(2), 252-265.

Saha, B., El-Sharkawy, I., Chakraborty, A., & Koyama, S. (2007). Study on an

activated carbon fiber-ethanol adsorption chiller: part 1 - system description and

modeling. International Journal of Refrigeration, 30, 86-95.

Saha, B. B., Chakraborty, A., Koyama, S., Yoon, S.-H., Mochida, I., Kumja, M., Yap,

C., Ng, K. C. (2008). Isotherms and thermodynamics for the adsorption of n-

butane on pitch based activated carbon. International Journal of Heat and Mass

Transfer, 51(7), 1582-1589.

Saha, B. B., El-Sharkawy, I. I., Habib, K., Koyama, S., & Srinivasan, K. (2008).

Adsorption of equal mass fraction near an azeotropic mixture of

pentafluoroethane and 1, 1, 1-trifluoroethane on activated carbon. Journal of

Chemical & Engineering Data, 53(8), 1872-1876.

Saha, B. B., Habib, K., El-Sharkawy, I. I., & Koyama, S. (2009). Adsorption

characteristics and heat of adsorption measurements of R-134a on activated

carbon. International Journal of Refrigeration, 32(7), 1563-1569.

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Saha, B. B., Jribi, S., Koyama, S., & El-Sharkawy, I. I. (2011). Carbon dioxide

adsorption isotherms on activated carbons. Journal of Chemical & Engineering

Data, 56(5), 1974-1981.