Adsorption Cooling System Employing Activated Carbon / R 32 Adsorption Pair

Ahmed A. Askalany, Bidyut B. Saha and Khairul Habib Mechanical Engineering Department, Faculty of Industrial Education, Sohag University, 82524, Egypt Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-Koen, Kasuga-Shi, Fukuoka 816-8580, Japan International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan Malaysia


Introduction
Energy reduction has become one of the most interesting points of research due to the global energy crisis.Renewable and/or waste energies may be considered as one of the solutions for the energy problems.Unfortunately, most of these energies are usually having a low grade temperature below 100ºC which is difficult to use.One of the smart solutions is to use the adsorption cooling system which could be driven by the low grade heat source temperatures.Many researches tried to introduce an adsorption cooling system powered by low grade heat source temperature but they faced the problem of low COP and high specific volume due mainly to batched cycle operation and poor thermal conductivity in the adsorbent bed [1][2][3][4][5][6][7][8][9][10].This paper introduces an adsorption cooling cycle employing activated carbon powder (ACP)/R32 adsorption pair.

System Description
An adsorption cooling cycle has been simulated employing ACP/R32 adsorption pair.A proposed design as shown in Fig. 1 which is mainly consists of an adsorption bed, an evaporator and a condenser.The adsorber is a finned tube type heat exchanger with 500 W capacity. The condenser is cooled using ambient air directly by natural convection.An expansion valve has been attached after the condenser to throttle the refrigerant to evaporator pressure.Both of the adsorber and the evaporator are assumed to be isolated.The adsorber is assumed to contain 200 grams of the adsorbent.A bypass tube has been allocated between the adsorber and evaporator.This bypass tube is assumed to be used during adsorption process.Table 1 shows the designing parameters of the system.

Mathematical model
Dubinin-Astakhov (D-A) (Eq. 1) and linear driving (LDF) model (Eq.2) are used to estimate the adsorption isotherms and kinetics respectively for the various adsorption pairs.

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(2) The isosteric heat of adsorption has been determined in the model by using Eq. 3. ( Using lumped approach for the adsorption bed, the heat exchanger fins and tubes, the energy balance equation, is given by [11]: The energy balance equation of the evaporator can be expressed as, (7) The mass balance of refrigerant in the adsorption chiller is expressed by,

Conclusions
A single bed adsorption cooling system employing ACP/R32 has been simulated and a proposed design has been introduced.The system has been powered a heat source temperature below 90ºC.The effect of changing the operation conditions (regeneration temperature and evaporator temperature) on the SCC and COP has been studied.It has been noted that the cycle time of the system is less than 10 minutes.The system has been found to a achieve SCC and COP values of about 0.25 kW/kg and 0.23 respectively at 355 K regeneration temperature and 383 K evaporator temperature.Raising the regeneration or evaporator temperatures is found to increase the SCC and COP of the system.It can be concluded that ACP/R32 adsorption pair can be employed effectively in an adsorption cooling system.However, the COP of the system is relatively low but the system could be driven by low grade solar heat and/or waste heat sources otherwise it should be purged to the ambient.

Figure 2
Figure2shows the heat transfer fluids (heating, cooling and chilled) and temperature profile of the adsorbent adsorption bed at 350 K regeneration temperature and 277 K evaporator temperature.It is clear from the figures that the cycle time of ACP/R32 is about 550 seconds and about 270 seconds of them are consumed in heating.Figure3shows the effect of regeneration temperature on specific cooling capacity (SCC) respectively.The figure indicates that raising the evaporator temperature up to 283 K raises the SCC.Increasing regeneration temperature also has a positive effect on the SCC.The cycle

Figure 2 .
Figure 2. Heat transfer fluids and temperature profile of the proposed adsorption bed.

Figure 3 .
Figure 3.Effect of regeneration temperature on SCC of ACP/R32 at various evaporator temperatures.

Figure 4 .
Figure 4. Effect of regeneration temperature on COP of ACP/R32 at various evaporator temperatures.

Table 1 .
Design parameters of ACP/R32 adsorption cooling system