Desalination 439 (2018) 155–161

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Desalination

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Energy recovery from a vapour compression system using T humidification dehumidification desalination ⁎ K. Srithara, , T. Rajaseenivasana, M. Arulmania, R. Gnanavela, M. Vivarb, Manuel Fuentesc a Department of , Thiagarajar College of Engineering, Madurai 625 015, India b Department of Electrical Engineering, Universidad de Cádiz, Cádiz 11519, Spain c Grupo IMDEA, Universidad de Jaén, Jaén 23071, Spain

ARTICLE INFO ABSTRACT

Keywords: Energy consumption of a process can be reduced by properly utilizing the large amount of waste heat liberated Desalination into atmosphere. The aim of this research is to improve the coefficient of performance (COP) of a vapour Vapour compression refrigeration compression refrigeration system, by recovering waste heat from the and the using hu- Waste heat recovery midification dehumidification desalination process. To recover the heat, air from the blower is passed through a Humidification dehumidification desalination humidifier chamber in which water is sprayed over the gunny bag placed in the air passage. The humid air Refrigeration circulated around the condenser coil which sub-cools the and it also absorbs the heat from the condenser, producing hot humid air. The hot humid air is then passed over another (dehumi- difier coil) which heats the refrigerant coming out from the evaporator so the quality of the vapour improves. At the same time, occurs in the hot humid air along the surface of evaporator coil and the distilled water is collected. system is tested with insert like twisted tape and cone type turbulators in the dehumidifier passage to augment the performance. These modifications improved the COP of the refrigeration system up to 7.6 with a distillate water output of 0.4 l/m2 h.

1. Introduction and showed that the COP of the system increased by 6% and reduced the thermal pollution. Since there is a huge demand for electrical energy production and Earlier some researchers analyzed the effect of integrating the air distribution, the available energy must be utilized efficiently. In India, conditioning with desalination system. Hawlader et al. [6] experi- nearly 42% of the electric energy in every house is utilized for operating mentally analyzed the solar assisted desalination and con- refrigeration systems and Heating Ventilation and cluded that the system can be efficiently introduced for the small scale (HVAC) systems [1]. These HVAC system liberate an enormous amount desalination with hot water supply. Gao et al. [7] examined a HDH of heat to the atmosphere as waste. Recovery of this waste heat could desalination system integrated with a vapour compression heat pump. improve significantly the efficiency of the HVAC systems along with a The desalination unit utilizes the waste heat from the condenser and the reduction of their environmental impact. Lokapure and Joshi [2] de- evaporator of the heat pump for the desalination process and achieved signed and fabricated a heat exchanger, which recovers the waste heat the distillate output of 60 kg/day. An experimental research in an in- liberated in the air conditioning system, increasing the coefficient of tegrative air conditioning unit and desalination is (Yuan et al. [8]) re- performance (COP) of the system by 13%. Sapali et al. [3] tested a shell ported that the integration of unit augments the overall system per- and coil type heat exchanger to recover the waste heat from the con- formance. Halima et al. [9] studied a solar still which integrated with a denser of a bulk milk and this heat was used to warm the water. compression heat pump and found 75% higher water output than the The result showed that about 35% of was recovered and the conventional solar still. Transient and economical analysis has been COP of the system increased from 3 to 4.8. Salma [4] coupled the water conducted on an integrated air conditioner HDH desalination system heater with the condenser of a domestic refrigerator and found that powered by Fouda et al. [10] and recommended that the proposed heat liberated from the condenser could heat the water up to 60 °C, with system is more efficient in hot and humid climatic conditions. Diaby a COP increase from 3 to 7. Ramyashree et al. [5] recovered the heat et al. [11] coupled an air gap membrane distillation with an air con- from the condenser unit of a windows air conditioner for water heating ditioner and stated that this system can reduce the energy consumption

⁎ Corresponding author. E-mail address: [email protected] (K. Srithar). https://doi.org/10.1016/j.desal.2018.04.008 Received 22 November 2017; Received in revised form 4 March 2018; Accepted 9 April 2018 0011-9164/ © 2018 Published by Elsevier B.V. K. Srithar et al. Desalination 439 (2018) 155–161

integrating with a single pass air heater. Al-Enezi et al. [17] examined Nomenclature the consequence of varying the parameters such as flow rate of air, feed water and cooling water as well as temperature of air, feed water and Q Refrigeration effect, kJ/kg cooling water in a HDH desalination process. Peak distillate is obtained W Work input, kJ/kg for high feed water temperature and air flow rate and low cooling water H , kJ/kg temperature of the dehumidifier. An energy and exergy analysis was performed by Muthusamy and Srithar [18] on a humidification dehu- Subscript midification desalination system integrated with multiple inserts. The presence of inserts in the humidifier and dehumidifier augmented the 1 inlet energy and exergy efficiency of the HDH desalination. Muthusamy and 2 Compressor outlet Srithar [19] reported that turbulators usage in the humidifier and de- 3 Condenser outlet humidifier saved 40% input power compared to the conventional HDH 4 Evaporator inlet desalination unit. Rajaseenivasan and Srithar [20] experimented a biomass powered bubble column humidification-dehumidification de- in addition to fresh water output. A novel hybrid humidification–de- salination system with the direct and preheated air supply and found that decreasing hole diameter boosted up the specific of air, humidification and air conditioning system reported by Nada et al. [12] ffi shows an increase in specific humidity and air mass flow rate and this, reaching the peak e ciency of 96% at 1 mm hole diameter. The peak distillate output of 6.1 kg/h and 3.5 kg/h was collected with the pre- enhancing the fresh water production rate and refrigeration capacity of the integrated system. Kabeel et al. [13] evaluated a hybrid desiccant heated and direct air supply respectively. Rajaseenivasan et al. [21] made an experiment to improve the efficiency of the humidification- air conditioner with HDH desalinator powered by solar energy and fi observed an increasing distillate water productivity ranging from dehumidi cation desalination system by using a bubble column hu- midification dehumidification desalination system and achieved a dis- 3.175 kg/h to 5.011 kg/h. Elattar et al. [14] performed a parametric 2 and economic study on the potential of a solar hybrid air conditioning tillate of 16.3, 20.6 and 23.9 kg/m day using conventional solar air heater, solar air heater containing turbulators and dual purpose solar and HDH desalination. The study reveals that the total operating cost increases with the increase in outdoor air temperature and outdoor collector containing turbulators respectively. In summary, vapour compression refrigeration systems are widely humidity. Kabeel and Abdelgaied [15] experimentally evaluated a two stage indirect solar dryer coupled with HDH desalination. The experi- used for domestic and commercial applications in day to day life. So, performance improvement of the refrigeration system should be con- mental result showed that the distilled water production improved from fi 29.6 kg/day to 42.3 kg/day and also raises the gained output ratio of centrated in reducing the electricity consumption. Scienti c literature shows that most of the studies are carried out to improve the perfor- the proposed system. Yamili and Solmus [16] analyzed a solar HDH ff desalination system with a single and double pass solar air heater. By mance of the air conditioner by e ectively utilizing the waste heat from air conditioner for the desalination process, but they leave a gap to varying the air mass flow rate and temperature of air, feed water and cooling water it has been observed that the integration of double pass apply the concept of waste heat recovery from vapour compression solar air heater increases the productivity by 8% compared to the refrigeration for desalination process. HDH desalination is a kind of simple water treatment process which is suitable for low temperature

Energy meter T4 P4

T9 T3 P3

Air flow Refrigerant Flow T1 T7 T2 P2 P1 T5 P5

T1

T6 T7 T8

Water pump (to )

P1, T1 – Refrigerant at condenser inlet T6 – Air at humidifier inlet P – Pressure P2, T2 – Refrigerant at condenser outlet T7 – Air at condenser inlet T - Temperature P3, T3 – Refrigerant at evaporator inlet T8 – Air at inlet P4, T4 – Refrigerant at evaporator inlet T9 – Air at dehumidifier outlet P5, T5 – Refrigerant at dehumidifier inlet

Fig. 1. Schematic diagram on experimental VCR integrated desalination system.

156 K. Srithar et al. Desalination 439 (2018) 155–161 desalination applications. In that, open air closed water HDH desali- humid air absorbs the heat liberated from condenser which removes nation system is selected for this study in order to maintain the lower more heat than the atmospheric air due to the usage of low temperature air temperature in the cycle. Because the rise in air temperature will humid air. This process sub-cools the refrigerant and increases the air reduce the refrigeration system performance. However, the water is temperature. Heated humid air is then passed to the dehumidifier replaced in often in order to maintain the lower temperature. Raw (Fig. 3(b)). In dehumidifier, a 0.006 m coil is wounded into water is used for the desalination and the humidifier packing material 0.045 m diameter and the one end is connected to the refrigerator and other systems are periodically cleaned in order to avoid deposition. evaporator outlet and other end is connected to the compressor inlet. In order to fill the research gap, a humidification-dehumidification Heated humid air is circulated over the copper coil and the low tem- (HDH) desalination system is integrated with the vapour compression perature refrigerant from evaporator flows inside of the copper coil. refrigeration system which in turn increases the performance of the The temperature difference to the condensation of water from the refrigerator as well as additionally produces the distilled water. Twisted humid air which is collected in the bottom of the humidifier. It also tape and cone type turbulators are used in the dehumidifier to augment increases the temperature of the refrigerant which enters the com- the distillate output. pressor at superheated state and the air moves to the atmosphere. Pressure-Enthalpy diagram of sub cooling and super heating are re- 2. Experimental setup presented in Fig. 4. Two different types of turbulators (twisted tape and cone) are fab- The experimental setup consists of two segments including a re- ricated using wire mesh with a hole size of 1 mm. The tur- frigeration unit and a desalination unit. The overall system setup is bulators are used to increase the between the refrigerant shown in Figs. 1 and 2. The refrigeration unit consists of a compressor, a and the humidified air in the dehumidifier. Twisted tape turbulator are condenser, a capillary and an evaporator. The refrigerator condenser is fabricated with different pitch of 0.012 m, 0.008 m and 0.004 m of made using copper tube of 0.008 m diameter and 0.027 m length with length 0.060 m and width of 0.040 m (Fig. 5a), similarly cone is fabri- 10 tubes in two rows with aluminium fins of 0.005 m equally spaced. cated at the twist angle of 65o,55o and 45o of length 0.010 m and width The condenser unit is then covered with a of size of 0.040 m (Fig. 5b). The cone is tested for different pitch of 0.045 m, 0.15 m × 0.38 m × 0.30 m, to recover the heat liberated from the 0.035 m, 0.025 m and 0.015 m (Fig. 5c). The flow rates of water and air condenser. The evaporator contains copper tubes of 8 mm diameter and are selected based on the pipe size and size of flow control valve. 0.38 m length with 7 tubes in 4 rows. It is placed inside a refrigerating Four set of experiments are performed. In the first experiment, the cabin of 400 l capacity. potential of a conventional refrigerator is tested without the desalina- Air needed for the HDH desalination process is supplied by a tion unit. In the second set, the VCR is connected to the desalination 0.18 hp. blower and it is connected to a humidifier as shown in Figs. 1 unit and tested with different mass flow rate of air and water supply in and 2. The humidifier chamber is the duct fabricated using GI (Galva- humidifier, and the best water flow rate is selected for the next set of nized Iron) sheet in the size of 0.15 m × 0.38 m × 0.30 m. The air en- experiments. In the third set, turbulators are introduced in the dehu- ters the humidifier allowing to pass through the packing material gunny midifier and tested by varying the pitch of the twisted tape and pitch bag of thickness of 0.005 m × 0.38 m × 0.30 m as shown in Fig. 3(a). and angle of the cone turbulators. In fourth set, the humidifier is re- Raw water from storage tank is supplied over the gunny bag with a moved and the gunny bag is covered over the copper coil of the con- submersible water pump (18 W) from a storage tank. The water flowing denser and the water is sprayed over the gunny bag. So, it directly re- out of the gunny bag is collected at the bottom and sent to the storage moves the heat from condenser. It leads to the reduction in refrigeration tank. Humidifier duct is extended and the refrigerator condenser is temperature and increase in evaporation rate of water. placed next to the humidifier. The air supplied from the blower gets humidified after passing through the humidifier and then it passes 3. Data reduction around the condenser. Humidification process leads to the reduction in air temperature and improves the air humidity. The low temperature The efficiency of refrigeration systems and heat pumps is denoted

Energy meter

Fig. 2. Photographic view of experimental VCR setup.

157 K. Srithar et al. Desalination 439 (2018) 155–161

Fig. 3. Photographic view of (a) Humidifier, (b) Dehumidifier.

needed to drive the compressor is released to the refrigerant as heat. Therefore more heat is available at the condenser than is extracted at the evaporator of the heat pump. Refrigeration effect Q hh− Due to heat COP ===14 recovery from Work input W hh21− (1) 2 condenser 3’ 3 2’ 4. Error analysis h =c – fi Pressure, MPa U tube manometer is connected to the ori ce meter for measuring the air mass flow rate and the flow rate is controlled by the flow control 4’ 1’ 4 1 valve. Pressure gauges (0–500 psi) are fixed at the condenser inlet and Due to heat − recovery from outlet to measure the subsequent pressure and compound gauges ( 30 evaporator to 250 psi) are also connected in the evaporator inlet, evaporator outlet, and dehumidifier outlet. Alcohol (-10 °C to 110 °C) are Enthalpy, kJ/kg placed at condenser inlet, condenser outlet, evaporator inlet, eva- porator outlet, dehumidifier outlet, humidifier outlet, condenser air Fig. 4. T-s diagrams for the ideal vapour compression refrigeration cycle. outlet and dehumidifier air outlet. An energy meter is used to measure the power consumed for refrigeration and desalination process. Uncertainty in a measured value can be defined as chance of error by its Coefficient of Performance (COP). The COP is determined by the occurred in the measured value of the instrument and it can be found ratio between the amount of useful cooling at the evaporator (for a using the following formula [22,23]. (Table 1.) refrigeration installation) or useful heat extracted from the condenser accuracy (for a heat pump) and the compressor work. Most of the electric energy uncertainty = 3 (2)

65º

0.045 m 55º 45º 0.035 m 0.025 m

Fig. 5. (a) Twisted tape turbulators, (b) Cone turbulator with angle variation (65°, 55° and 45°), (c) Cone turbulators with pitch variation (0.045 m, 0.035 m and 0.025 m).

158 K. Srithar et al. Desalination 439 (2018) 155–161

Table 1 increase in turbulence of air and the increased residence time of air in Uncertainty of measuring instruments. the dehumidifier. fl Si. No. Instruments Range Accuracy Uncertainty Fig. 10 shows the power consumption cost for optimum mass ow rate of water, twisted tape of pitch 0.004 m and cone of angle 45° and 1 −10–110 °C ± 1 °C 0.58 °C pitch 0.015 m. The power consumption rate is shown for eight hour – 2 Compound pressure gauge 0 500 psi ± 5 psi 2.89 psi operation. The conventional refrigerator consumes 0.0428 US$. The 3 Pressure gauge −30–250 psi ± 1 psi 0.58 psi 4 Manometer 0–300 mm 1 mm 0.58 mm addition of blower, pump and the presence of turbulator increased the 5 Ammeter 0–20 A ± 1 A 0.58 A pumping power and the cost is raised to 0.060 US$. However when 6 Voltmeter 0–300 V ± 10 V 5.77 V compared to the enhancement in the COP and additional distilled water 7 Energy meter 0–10,000 kWh ± 0.1 kWh 0.06 kWh production, the increase in power consumption is minimum. – 8 Measuring jar 0 1000 ml ± 10 ml 5.8 ml Impact of covering the condenser copper coil with gunny bag and 9 Stop watch 0–99 h 0.01 s 0.005 s spraying the water over is discussed in the Fig. 11(a). This direct re- moval from the refrigerant helps to reduce the refrigerant temperature further and there by enhancement in COP. Also this higher heat re- moval increases the evaporation rate and there by more distilled water 5. Results and discussion output. The increase in air flow rate reduces the air temperature and thereby lower productivity with rise in air flow rate. The result shows A first set of experiments is conducted to analyze the impact of air that the COP and distillate has increased more compared to the other and water flow rate on refrigerator performance. It is observed that the systems. Maximum COP of 7.6 is achieved whereas it is about 6.5 for increase in mass flow rate of air and water leads to the increase in the the system with turbulators which is about 17% higher. Similarly, the refrigerant temperature drop in condenser. Fig. 6 shows the influence of higher distillate of 410 ml/m2 h is obtained with this configuration mass flow rate of air and water on the condenser temperature drop. It which is 24% higher than the previous configurations. Gained output can be inferred that the highest temperature drop occurs at highest ratio shows the effective utilization of thermal energy in the HDH de- mass flow rate of air (ma = 30 kg/h) and water (mw = 544 kg/h). The salination system. It also shows that the gained output ratio reaches the rise in air and water flow rate increases the air humidity which results maximum of 1.2 with the minimum mass flow rate and also it follows in higher heat removal from condenser and it leads to sub cool the the same trend of distillate output. Effectiveness of dehumidifier is refrigerant and contributes to increase in the COP of refrigerator. In shown in the Fig. 11(b). It shows that the increase in air flow rate re- Fig. 6(c), the increment in mass flow rate of water from 270 kg/h to duces the effectiveness due to the reduction in air temperature differ- 544 kg/h has very little significant improvement in temperature drop. ence. Maximum effectiveness of 0.87 is achieved in the minimum air So the water flow rate restricted with 544 kg/h. Similarly, the rise in air flow rate. mass flow rate from 21 kg/h to 29 kg/h increases the temperature drop only by 1 °C. So, the mass flow rates are restricted with these limits and further experiments are conducted. 6. Conclusion Fig. 7 shows the impact of air and water flow rate on COP of re- frigeration system and distillate collection of desalination unit. The A complete set of experiments has been performed to improve the COP of the refrigerator enhances when increasing the air and water COP of a refrigerator unit by reducing the refrigerant temperature (sub mass flow rates. The augment in COP is due to the superheating of cooling) in the condenser and by increasing the refrigeration tem- fi fi refrigerant in condenser and sub cooling of refrigerant in dehumidifier. perature (super heating) at dehumidi er. A humidi cation dehumidi- fi Increase in air flow rate reduces the distillate output due to reduction in cation desalination unit integrated with the refrigerator, including an retention time (contact of air and water in the humidifier) which leads energy recovery stage where the waste heat from condenser and eva- to the reduction of specific humidity of air and thereby distillate output. porator is used for the desalination process. Experiments were con- ff fl ff The refrigeration system reaches the highest COP of 4.61 at the air mass ducted to study the e ect of air and water ow rates and the e ect of fl flow rate of 30 kg/h and water flow rate of 544 kg/h. Therefore, the several types of turbulators by varying the mass ow rate of air and highest distillate of 225 ml/m2 is achieved an air mass flow rate of water; and using of twisted tape turbulators and cone type turbulators 30 kg/h whereas the COP of the desalination system without desali- nation process is 2.6. It is also observed that the distillate collection is Mass flow rate of water, kg/h improved by increasing the supply of water to the humidifier. 50 The impact of twisted tape turbulators with pitch variation on the 72 COP and distillate collection of the integrated system is shown in Fig. 8. 205 The distillate collection and the COP seems to increase with turbulators 270 in comparison with the dehumidifier without turbulators. The twisted tape creates more turbulence in the flow path of air in dehumidifier and 544 increases the contact area of air with dehumidifier coil. A low pitch (0.004 m) increases the heat transfer rate as well as the distillate the turbulence level reduces with an increase in pitch. The impact of cone turbulators angle and pitch variation on the COP and distillate of system is shown in Fig. 9. It can be inferred from the Fig. 9(a) that more distillate is collected and higher COP is attained when using cone type turbulators than twisted type turbulator. From the graph it is observed that the cone with minimum angle 45o has

highest COP and distillate collection. So the experiment was repeated ºC in condenser, drop Temperature for different pitches of cones with angle 45o and the results are shown in the Fig. 9(b). Again the minimum pitch contributes to an increase in 19.8 21.6 23.4 25.2 27 28.8 30.6 COP and distillate. The maximum COP of 6.5 and distillate collection of Mass flow rate of air, kg/h 330 ml/m2 is achieved with the cone type turbulators with the angle of fl 45° and pitch of 0.015 m. The reason for the augmentation is due the Fig. 6. Impact of air and water ow rate variation on refrigerator performance.

159 K. Srithar et al. Desalination 439 (2018) 155–161

Mass flow rate of water, kg/h Mass flow rate of water, kg/h 50 72 50 72 205 270 205 270 544 544

19.8 21.6 23.4 25.2 27 28.8 30.6 19.8 21.6 23.4 25.2 27 28.8 30.6 Mass flow rate of air, kg/h Mass flow rate of air, kg/h

Fig. 7. Significance of mass flow rate on COP and distillate collection.

544 kg/h

19.8 21.6 23.4 25.2 27 28.8 30.6 Mass flow rate of air, kg/h

Fig. 8. Effect of twisted tape turbulator on COP and distillate. by changing the pitch and cone angles. The COP of conventional re- Fig. 10. Power consumption cost for different turbulators. frigerator was recorded as 2.6 and it was escalated up to 4.61 by in- tegrating the HDH system at the flow rate of water of 544 kg/h and air of 30 kg/h. A maximum distillate of 330 ml/m2 and a maximum COP of source of condenser and evaporator. Additionally the heat delivered by 6.13 were achieved for the cone turbulators with angle of 45° and pitch condenser to the atmosphere is reduced in comparison with the con- of 0.015 m. The additional power required to run the modified unit was ventional refrigerator and therefore it reduces the thermal pollution to 0.37 times higher than the conventional setup. However the COP of the the atmosphere, reducing the environmental impact of the system. modified refrigerator setup reaches up to 7.6 with the presence of turbulator in dehumidifier and covering the condenser with gunny bag Acknowledgement which is 2.09 times higher compared to the conventional refrigerator with addition of distilled water output extracted from the low heat The authors would like to acknowledge with appreciation, ISHRAE, India and ISHRAE, Madurai Chapter for the financial support for this

(a) 544 kg/h (b) 544 kg/h

19.8 21.6 23.4 25.2 27 28.8 30.6 19.8 21.6 23.4 25.2 27 28.8 30.6 Mass flow rate of air, kg/h Mass flow rate of air, kg/h

Fig. 9. Effect of cone turbulator on COP and distillate.

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