Review On Indirect Evaporative Cooling

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International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)

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ISSN (Print): 2319-3182, Volume -6, Issue-1-2, 2017 23

Review On Indirect Evaporative Cooling

1A. M. Kamble, ²H. Darokar

1,2Department of Mechanical Engineering, (H.P.), I.C.E.M., Parandawadi, Pune, Maharashtra, India.

Abstract—Evaporative cooling is an environmentally friendly and energy efficient method for cooling in hot and dry region. Evaporative cooling operates using water and air as working fluids it consist in water evaporation, through the passage of an air flow, thus decrease the air temperature. There are mainly two types of evaporative technology, in which direct and indirect evaporative cooling take place. In case of direct evaporative cooling the air is exposed to water directly which allow it to cool and then get moist by sensible heat to latent heat of vaporization of water, with the heat and mass transfer phenomenon. But in case of indirect evaporative cooling the system effected by means of water evaporation without making any direct contact with the air flow, but through the channel or a media of non-porous wall. The paper present actual knowledge concerning the indirect evaporative cooling (IEC)this cooling technology is promising to develop in the future due its very low energy consumption and high efficiency in its range of application.in this paper various types of indirect cooling methods are review to understand the various way to attend cooling by this method

Keywords— Evaporative cooling, heat and mass transfer, air flow rate, sensible heat,latent heat

I. INTRODUCTION

Now a days energy availability is essential for everyday life and welfare all over the world. Therefore population and economic growth is expected to involve a faster increase in energy consumption, despite the rise in fossil fuel price. Taking these into account, many problems such as dependency on sources, increased cost or the environmental impact of energy use and transformation are to be faced. Thus new legislation to ensure sustainable energy provision at an affordable price is needed. This technology mainly depends on two criteria i.e decrease in humidity and increase in temperature of surrounding. Therefore in hot and dry tropical region the evaporative cooling technology can be used for saving large amount of energy with air cooling. There are two main evaporative cooling systems. Where in direct evaporative cooling system a cellulose medium with the water contact surface where air is passed is thorough to it at an uniform rate, and the another evaporative cooling system is indirect evaporative cooling system which uses a heat exchanger through which air is passes and it cool the air indirectly.

II. PRINCIPAL OF INDIRECT EVAPORATIVE COOLING

In case of indirect evaporative cooling system water evaporates in a secondary air stream which exchanges sensible heat with the primary one in heat exchanger.in this way the outdoor air

Stream is cooled when keeping into contact with the surface through which the heat exchange is produced, without modifying its absolute humidity; whereas at the other side of the surface secondary air stream is being evaporative cooled. Thus this process is called indirect evaporative cooling and it is mainly used in those applications where no humidity addition is allowed in the supply air as well as no risk of contamination, as no mass exchange is permitted between the two air stream.

Figure 1 indirect evaporative cooler [1]

Indirect Evaporative cooling systems are of two types:

1. Indirect system with tubular heat-exchanger:

The first reference to this kind of system comes from 1908, from a patent of a German inventor called Elfert.

Subsequently, models made of a window air cooler have been developed, which permitted obtaining outdoor air that passed inside a bank of fine horizontal tubes with the aid of a fan, while water was sprayed on the outer walls.

More modern designs of these systems used plastic tubes that resisted corrosion better. Figure 2 shows the operation configuration of this kind of devices.

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Figure 2 Tubular indirect evaporative cooler[1]

2. Indirect systems with a plate heat-exchanger:

This is undoubtedly the most used indirect evaporative system. The first reference known to this system comes from 1934, and that design suggested two stages. In the first stage return air is cooled in two spray humidifiers (direct evaporative cooling). Afterwards, this air is used in a plate heat-exchanger to cool outdoor air which will be supplied into the cooled room. Humid air is thrown outdoors. One advantage of this system is that water does not take into contact with the exchange surface, thus not originating incrustations. However, these are really large devices, and heat-exchange between gas mediums requires great areas of transference, so they are not used.

Figure 3 Configuration of a Plate indirect Evaporative Cooler[1]

III. PRINCIPLE OF WORKING

Figure 4 Flow arrangement inside cooler[1]

A. Advantages

1. The main advantages of evaporative coolers are there low cost and high effectiveness.

2. They can be specially applied in dry and hot climates as the minimum cooling temperature for air depend on its wet bulb temperature.

3. Evaporative air coolers have considerable low energy consumption compared to refrigeration system.

4. Applicable in domestic as well as industrial application .

5. Components are available in local market.

6. Its installation and operation is easy.

7. It can be easily maintained.

B. Dissadvantages

1. In hot and dry tropical region water resources is one of the critical issue

2. Evaporative cooling pads required continuous water supply.

3. Power consumption is more and result is less effective due to which it has found limited application in industries.

IV. STUDY OF INDIRECT EVAPORATIVE COOLER

Many researcher performed work on the indirect evaporative cooling successfully Eloy Velasco Gomez develop model of IEC to determine thermal effectiveness and cooling capacity of the indirect evaporative cooling system. They made the prototype of IEC which operates in two operating modes. For experiment purpose they use cross flow plate heat exchanger made up of polycarbonate. After performance they conclude that the temperature drop and the thermal effectiveness are improved by higher outdoor air temperature at the inlet as well as for a lower air volume flow. The cooling capacity improves with higher air flow rates, as it consider the amount of air treated by the system.[02]

Aftab Ahmad had investigate the performance of a indirect evaporative cooler under controlled environmental conditions for a different air flow rates (631 to 2388 m3/h). They found out that the intake air energy efficiency ratio of the cooler varied from 7.1 to 55.1 depending on test condition and air flow rate. The result indicated that intake air energy efficiency ratio was directly proportional to the wet bulb depression.[03]

Marijke Steeman present a simulation methodology focusing on the interaction between the thermal performance of IEC system and the heat and moisture

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balance of building. They found that the effectiveness is independent of the air inlet conditions.[04]

G.P. Maheshwari had define a methodology for the technical evaluation of an IEC, accounting for reduction in cooling capacity, peak power requirement and seasonal energy saving has been developed. The results of an engineering analysis are compared with a conventional PU for pre cooling the outdoor air used for ventilation. Performance & benefits offered by IEC are strongly site related as the outdoor conditions differ from place to place. They conduct an analysis for a Kuwait city.they found that ICE operate in the interior can achieve nearly 30% more reduction in cooling capacity of the conventional A/C system; 40% reduction in the peak power demand & nearly 100% more seasonal saving of electricity compared with the same system.[05]

The author Ghassem Heidarinejad, Mojtaba Bozorgmehr , Shahram Delfani , Jafar Esmaeelian (2008) has been done experimental investigation of cooling performance of two stage indirect/direct evaporative cooling system in various climatic condition in Iran. For this purpose they design an experimental set up of two stage evaporative cooling consist of an indirect evaporative cooling followed by direct evaporative cooling. Due to the wide variety of climatic conditions in Iran, two air simulators were provided to simulate outdoor design condition of different cities in primary and secondary air streams. They found that under various outdoor conditions, the effectiveness of IEC stage varies over a range of 55–61% and the effectiveness of IEC/DEC unit varies over a range of 108–111%.[06]

M. Shariaty Niassar, N. Gilani (2009) has done an Investigation of Indirect Evaporative Coolers, IEC With Respect to Thermal Comfort Criteria. In this work, the effects of air stream direction in the channels of indirect evaporative cooler (IEC) on system performance have been investigated. In addition, the dependence of system performance on outdoor air temperature and relative humidity has been studied to determine the allowable conditions for proper operation of the system, with respect to thermal comfort criteria. For this; the different types of IECs were investigated using the CFD technique. The calculated results show that when the air relative humidity is lower than 70%, the system can prepare a good indoor condition even at 50oC, and a higher performance is achieved by using the IEC with counter current configuration. The results showed that IECs can be successfully used in hot and humid climates to fulfill the indoor thermal comfort conditions. [07]

Aim of the paper “Experimental characterisation of an indirect evaporative cooling prototype in two operating modes” is to describe the experimental study developed to characterise an indirect evaporative cooling system made of polycarbonate as well as to introduce the main results obtained. For that purpose Eloy Velasco Gómez,

Ana Tejero González, Francisco Javier Rey Martínez (2011) has made a The prototype which is characterised by a total heat exchange area of 6 m², and is installed in a heat recovery cycle in the experimental setup constructed in the laboratory. Two operating modes are performed. In the first one, exhaust air from the climate chamber, in comfort conditions, goes through one side of the heat exchanger, producing heat transfer from the outdoor air stream through the plastic walls of the system. In the second case, an evaporative cooling mode is implemented by supplying water to the exhaust airstream. Results obtained show that heat transfer through the heat exchanger polycarbonate wall improves in the evaporative cooling mode. Furthermore, both cooling capacity and thermal effectiveness of the system also increase in the second case. Finally it is conclude that higher outdoor air temperatures imply better cooling capacities and thermal effectiveness. [08]

Two equally-sized cross-flow heat-exchanger prototypes have been designed by Ana Tejero-González, Manuel Andrés-Chicote, Eloy Velasco Gómez, Francisco Javier Rey Martínezwith in the year 2012 they made a heat exchanger having total area of 6 m2 and 3 m2 respectively, which is constructed by polycarbonate hollow panels of different cross section. They have been experimentally characterised in two operating modes in order to determine how evaporative cooling improves heat recovery in each case. They focus on the influence of modifying the constructive characteristics. Results are studied considering how constructive issues, outdoor air volume flow rate and temperature, as well as operating mode influence on the performance. Entering outdoor air temperature determines cooling capacities.

Improvements introduced by larger heat exchange areas compensate with their corresponding smaller cross sections, which hinder water air distribution on the exhaust air side of the heat exchanger. [09]

In the paper “Theoretical study of the basic cycles for IEC ” the author Sergey Anisimov , Demis Pandelidis (2014) has done a numerical study of heat and mass transfer in indirect evaporative air coolers with four air flow patterns: parallel-flow, counter-flow, cross-flow and regenerative The numerical simulation was performed on the basis of original two-dimensional heat and mass transfer models It was observed , that heat and mass transfer processes in the wet channels of counter-flow, cross-flow and regenerative indirect evaporative coolers are characterized by creation of two particular heat and mass transfer zones. They proposed a theoretical method for estimating the Lewis factor. Using the developed models the thermal performances of the conventional designs of indirect evaporative air coolers were analysed numerically and preferable climatic zones for considered heat exchanger were established.[10]

Standardized fin geometries for various fin types adds discrete aspects to an already complicated design problem. In this paper Kunpeng Guo, Nan Zhang, Robin

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Smith (2014) has design a new algorithm which is proposed to address this issue. By treating basic fin geometries such as plate spacing, fin pitch, fin length and fin thickness as continuous variables for all the fin types, different fin types are characterised based on the work published by different researchers. Then by taking into account thermal hydraulic performance of different fin types, optimal fin types and their corresponding design parameters can be obtained simultaneously by minimising the total volume of heat exchanger. The design parameters can be rounded to the nearest standardised fin parts for a feasible design.[11]

Stefano De Antonellisa,, Cesare Maria Joppoloa, Paolo Liberatib, Samanta Milania(2016),has done “an Experimental analysis of a cross flow indirect evaporative cooling system” In this work an indirect evaporative cooling system based on a cross flow heat exchanger has been widely tested. The system has been designed in order to minimize water consumption, with water mass flow rate between 0.4% and 4% of the secondary air one. On the whole, 112 experiments have been carried out in different working conditions of data centres. The effects of variation of water flow rate, humidification nozzles setup and secondary air temperature, humidity and flow rate have been widely investigated. Results put in evidence that performance is slightly dependent on nozzles number and size but it is strongly influenced by the water flow rate. In addition, nozzles in counter flow arrangement perform better than in parallel flow configuration. Depending on working conditions and equipment setup, the wet bulb effectiveness varies between 50%and 85% [12]

V. CONCLUSION

From the whole review paper above we come to conclusion that;

1. The temperature drop and thermal effectiveness are improved by higher outdoor air temperature.

2. Intake air energy ratio is directly proportional to the wet bulb depression.

3. The effectiveness of IEC depend on the various outdoor conditions.

4. The flow arrangement in the heat exchanger play an important role in improvement of effectiveness.

5. Plate type heat exchanger is more suitable for evaporative cooling purpose.

REFERENCES

[1] Dr.C.R.PATIL, K.G.HIRDE, “The Concept of Indirect Evaporative cooling” IJESIT Volume 2, Issue 5, September 2013

[2] Eloy Velasco Gomez, “Experimental characterisation of an indirect evaporative

cooling prototype in two operating mode” Paseo del cauce n. 59, 47011 valladolid, Spain.january 2012

[3] Aftab Ahmad , “Performance evaluation of an indirect evaporative cooler under controlled environmental conditions” king Fahd University of Petroleum and minerals, Dhahran-31261, Saudi Arabia March-2013.

[4] Marijke Steeman, “Performance evaluation of indirect evaporative cooling using whole- building hygrothermal simulation”- Pietersnieuwstraat 41, B-9000 Gent,Belgium February 2009.

[5] G.P.Maheshwari, “Energy saving potential of an indirect evaporative cooler” Kuwait institute for scientific research,PO Box 24885, 13109 Safat,Kuwait. November 2000.

[6] Ghassem Heidarinejad, Mojtaba Bozorgmehr, Shahram Delfani, Jafar Esmaeelian

“Experimental investigation of two-stage indirect/direct evaporative cooling system in various climatic conditions”-2009.

[7] M. Shariaty-Niassar, N. Gilani, “An Investigation of Indirect Evaporative Coolers, IEC With Respect to Thermal Comfort Criteria”-2009.

[8] Eloy Velasco Gómez, Ana Tejero González, Francisco Javier Rey Martínez “Experimental characterisation of an indirect evaporative Cooling prototype in two operating modes”- 2011.

[9] Ana Tejero González, Manuel Andrés Chicote, Eloy Velasco-Gómez,Francisco Javier Rey Martínez “Influence of constructive parameters on the performance of two indirect evaporative cooler prototypes”-2012

[10] Sergey Anisimov, Demis Pandelidis “Theoretical study of the basic cycles for indirect evaporative air cooling”-2014.

[11] Kunpeng Guo, Nan Zhang, Robin Smith

“Optimisation of fin selection and thermal design of counter-current plate-fin heat exchangers”-2014.

[12] Sergey Bolotin, Borys Vager, Vladimir Vasilijev

“Comparative analysis of the cross-flow indirect evaporative air coolers”-2015.

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