Using Graywater in Spray Cooling

Work type: Dissertation chapter – Results
Academic level: Master’s
Subject or discipline: Engineering
Title: Result – Using Graywater in Spray Cooling
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Paper format: APA
# of pages: 5
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Paper details:
 Research Project ( Result and disscussion)

this order is to complete my project result. I already put the resutl in tables and I need the writer to present them in great academicc style.

 Research project: Use of Gray Water in Spray Cooling

  1. Introduction

    • Wastewater reuse

In a semi-arid and arid country such as Saudi Arabia, sustainable management of water is very crucial for socioeconomic development to be achieved. In fact, the comfort living of people in arid and semi-arid regions directly depends on effective water conservation and water reuse practices. Although large-scale wastewater reuse measures have been adopted such as use of treated municipal effluent to irrigate golf courses, gray water recycling is an important option that people can use to save wastewater in homes.


  • Gray water reuse

Gray water generally refers to the domestic untreated wastewater that has not been polluted by the toilet waste. Usually, it includes all the water that drains from the showers, laundry tubs, bathtubs, hand basins, washing machines, and floor wastes (World Health Organization, 2006). However, it excludes the wastes from dishwashers, garbage disposal units, and kitchen sinks. Since graywater does not contain fecal coliform or organic matter, it can be treated much easily than the black water from toilet and kitchens. According to a report by World Health Organization (2006), graywater constitutes 61% of the total wastewater generated by households. Certainly, if the gray water is managed responsibly without posing a threat to human health, it can significantly contribute to the sustainability of water resources. The reuse of gray water ensures that the load on wastewater treatment systems is decreased and therefore, the authorities save money spent on treatment of sewage. Besides, the lifespan of the wastewater treatment systems are prolonged and the demand of potable water by the public is reduced.

Generally, graywater can be reused in different areas such as landscaping, toilet flushing, car washing, garden watering, irrigation, and cooling purposes in industrial plants (World Health Organization, 2006).

The reuse of gray water in cooling has gained special attention recently with a several power plants in freshwater constraint areas adopting graywater in their recirculating water cooling systems. The primary challenges encountered when using gray water as a coolant is that it contains significant amounts of hardness, ammonia, phosphate, organic matter, and dissolved solids in comparison to fresh water (Li, Jason, Vidic, & Dzombak, 2011). The elevated quantities of these minerals coupled with high temperatures normally cause mineral deposition problems (scaling) both in the spray nozzle and on the surface being cooled.

In the meantime, air conditioning (AC) systems account for nearly 50% of power consumption in the Kingdom. In the residential sector alone, it is estimated that 70% of power consumption is due to AC systems. The problem is more serious in the summer, because the performance of air-cooled AC systems, such as window type and split case units, deteriorates considerably when the ambient air is hot. The reason is that heat needs to be rejected from the condenser of the AC system to the ambient air at extremely high temperatures and pressures, making the power consumption of the compressor very high. One way to improve the performance of an air-cooled AC system is to create a cool environment around the condenser such that the temperature of heat rejection is reduced, thereby reducing the power consumption of the compressor. This can be done by attaching an evaporative cooling system to the condenser of the air conditioner. Figure 1 shows an example of such a system.


Air Suction Grilles
Evaporative Cooling System Body
Condenser Body
Condenser Fan

Figure 1: Sketch of evaporative cooling system surrounding the condenser of an air conditioner

Depending on ambient conditions, the type of evaporative cooling system used, and the amount of water injected, a significant reduction in power consumption can be realized.

Certainly, adoption of gray water as an evaporative cooling medium for air conditioning can ensure that significant amounts of potable water are saved (Hou, 2014). The use of gray water in air conditioning also ensures that more businesses and homes in arid areas are more efficiently and effectively cooled (Heng 2011).

In particular, mosques are a great candidate for use of gray water for air conditioning. The main reason is that gray water effluent from mosques contains minimal pollutants since it is mostly the result of ablution. Therefore, the treatment needed can be simple filtration and minimal chlorination. Another reason is that the cooling load in mosques is huge due to their large sizes, making them a high priority for the use of evaporative cooling for air conditioning.

For the reasons above, this study will focus on the use of gray water effluent from mosques to cool the condensers of air conditioners evaporative.



1.3 Research Objectives

  1. To analyze gray water composition of an office building in Riyadh.
  2. To measure scale formation on the tip of a spray nozzle when gray water is used.
  3. To measure cone angle and spread diameter of the nozzle when gray water is used.





  1. Literature Review
    • Gray water use in Saudi Arabia

Due to the growing demand for water in the domestic, commercial, and industrial sectors in Saudi Arabia, the Ministry of Water and Electricity published a guide in 1429H explaining how gray water can replace potable-quality water in numerous applications, and how gray water systems should be installed. Al-Wabel (2011) described a simple system for handling and reuse of gray water resulting from ablution in mosques in Riyadh. He concluded that tertiary treatment quality water can be achieved by using sand filters, activated charcoal, and an ultraviolet unit. Abu-Rizaiza (2002) also suggested that gray water can be used for irrigation of public areas as well as for flushing toilets, and proposed the development of a plumbing system designed to collect, filter and disinfect ablution water to be used subsequently for other purposes.


  • Spray cooling

Essentially, spray cooling involves a liquid being forced from a small orifice and getting released as a dispersion of droplets which then impact on the surface to be cooled. According to a study by Grissom and Weirum (2012), there are three modes of operation in spray cooling. The first mode is that of a spray forming a thin liquid film on the surface of the material being cooled in what is commonly known as the flooded state. The droplets usually spread and then evaporate, retracting with them large quantities of energy due to latent heat of vaporization and creating a cooling effect. The second mode is that of the hot surface vaporizing all the impinging spray in a process called dry-wall state. The third mode is called Leiden frost state and involves the sprayed liquid forming an insulating vapor layer that prevents a material from heating rapidly (Jia & Qiu, 2013). The droplets may also puncture the entrapped vapor and thereby increase the rate of heat transfer. Spray cooling is normally preferred because cool liquid water gets much closer to the hot surface compared to other cooling methods such as pool boiling. However, its successful usage depends on numerous factors such as droplet velocity, droplet size distribution, the impact angle, gas content, droplet number density, and heater surface orientation. Besides, spray cooling is commonly used in electronic cooling, fire suppression, and coal gasification, and treatment of steel.

In a study of how suitable nanofluids could be used in spray cooling on copper blocks, Bansal and Pyrtle (2010) reported an enhanced heat transfer performance of the nanofluids compared to the pure fluids. Nanofluids are the fluids whose particles are less than 100 nm in size and are composed of particles of oxides, metals, carbides, and nitrides. Duursma et al (2013) noted that the fraction of a nanoparticle affects its spreading ratio, breakup, and the rebound of sprayed droplets which ultimately affected the heat transfer performance (Bellerova, Tseng, & Pohanka, 2012). A research by Tilton and Morgan (2012) revealed that the presence of non-condenser gas reduced the condenser performance and in fact, increased the surface temperature and the boiling temperature for fixed volume systems. They also established that dissolved gas increased the maximum heat transfer. Besides, Morgan and Tilton also realized that critical heat flux in spray cooling was due to liquid deficiency which was attributed by the droplet splashing, getting entrained, and nucleate bubbles explosion (Jia & Qiu, 2013). An experiment by Kiger and Kim (2011) showed that for temperatures slightly above or below the boiling temperature, the dissolved gas was noted to improve the heat transfer probably because of an increase in the circumference of the splat. Additionally, Kiger and Kim (2011) observed that when 1% weight of sodium hydrogen carbonate solution was added to water, it decayed into sodium carbonate and carbon dioxide when heated during cooling. The carbon dioxide produced caused the droplet to swell thereby increasing the size of contact area (Kim, Horacek, & Kiger, 2011). On the contrary, the precipitated sodium carbonate salt formed a nucleation site for scaling of particles.

In yet a different study on spray cooling, Chien et al (2009) noted an increase in the heat transfer performance when the liquid volume flow rate was increased.  Their data also indicated that the performance of heat transfer depended on the surface enhancement ratio Additionally, a research conducted by Bostanci et al. (2010) on the effect of using ammonia in spray cooling of structured surface revealed that heat transfer increased by 49% and 112% for surfaces with indentations and protrusions respectively compared to smooth surfaces (Hou & Tao, 2014). Recently, a new study on spray cooling revealed that the critical heat flux (CHF) for a large area (19.3 sq. cm) was 34% lower compared to that of a small area (2 sq. cm) when an eight-nozzle water spray was use (Horacek & Kiger, 2010). The authors suggested that multiple nozzle spraying resulted in accumulation of water on heated surface and caused the lower heat transfer in large surfaces.

  • Scale Formation

Past research has shown that the thickness and rate of scale formation on the cooled surface depended on the surface temperature and water chemistry. It has also been found that scale forms more quickly on higher temperature surfaces. According to a study by Nalepa et al. (1999), a key concern when using gray water for cooling is the need to control bio growth. Their study revealed that the use of chlorine as a biocide compromises the effectiveness of graywater as a coolant since it enhances mild steel corrosion due to its nature as a strong oxidant (Li, Jason, Vidic, & Dzombak, 2011). A different study by Eriksson et al (2007) revealed four ways of inhibiting scale formation when using gray water as a spray coolant. Firstly, adsorption of antiscalants is to be done on the surface to be cooled so as to prevent deposition of minerals on that surface during cooling. Secondly, antiscalants can be applied to ensure the minerals particles are dispersed in the aqueous solution and therefore cannot be deposited to cause scaling. Thirdly, antiscalants can be applied in order to react with a newly formed mineral nuclei and interrupt the crystallization process which ultimately inhibits the growth of precipitating particles (Li, Jason, Vidic, & Dzombak, 2011). The fourth mechanism for inhibiting scale formation is by adding antiscalants so as to increase the solubility of calcium and magnesium cations that often cause scaling. According to Metcalf and Eddy (2007), prior to use gray water for cooling or other purposes, it should be filtered through a 0.45 m sieve, and then evaporated at 40 degrees Celsius to reduce hardness caused by magnesium and calcium cations.




  1. Methodology
  2. Method of Work
  3. Several A samples of gray water from an office building in Riyadh will be collected over the period of a few weeks. The samples will be analyzed to understand the properties of gray water. Based on the analysis results, a suitable treatment method will be implemented.


  1. An experimental apparatus will be set up in order to run a long term test on a spray nozzle that uses the treated gray water. The purpose of the experimental campaign is to study scale formation with and without gray water. The experimental procedure is as follows:
  1. Examine the tip of a new spray nozzle under the microscope to ensure that it is free of any scaling.
  2. Spray regular tap water for 5-6 hours per day, for a period of 2-3 weeks.
  3. Re-examine the tip of the nozzle to characterize scale formation by looking at the average height of scale crusts.
  4. Examine the tip of another new spray nozzle under the microscope (as in Step a)
  5. Spray treated gray water for 5-6 hours per day, for a period of 2-3 weeks.
  6. Re-examine the tip of the nozzle to characterize scale formation with treated gray water.
  7. Compare scale formation in the two cases.


  1. Another set up will be used to measure the cone angle and diameter of coverage of the spray with and without treated gray water. The objective of this experiment is to determine whether the use of treated gray water (with the potentially excessive scale formation) causes nozzle tip to be partially blocked such that the nozzle’s performance will deteriorate with time as evidenced by the cone angle and diameter of coverage. The simple experimental setup will consist of a camera to measure the cone angle and hydrophilic paper to measure the spray diameter. The experimental procedure will be run in parallel to the experiment described in Part 2, and will consist of the following steps:
  2. On each day of the experiment in Part 2, photos of the cone leaving the nozzle tip will be taken.
  3. The photos will be studied to measure the cone angle.
  4. At the same time, hydrophilic paper will be placed at a fixed distance from the nozzle tip such that it is wetted by the water droplets.
  5. The cone diameter is measured and recorded.


  1. Materials
  2. High resolution camera
  3. Reservoir
  4. Spray nozzle
  5. Flowmeter
  6. Pump
  7. Treated gray water



No. Material Amount
1 High resolution camera SR 3000
2 Reservoir SR 500
3 Spray nozzle SR 500
4 Flowmeter SR 500
5 Pump SR500
6 Miscellaneous SR500
Total SR = 5500


  1. Bellerova, H., Tseng, A., & Pohanka, M. (2012). Spray Cooling by solid jet nozzles using alumina/water nanofluids. Journal of Thermal Sciences, 127-137.
  2. Horacek, B., & Kiger, K. (2010). Single nozzle spray cooling heat transfer mechanisms. International journal of heat and mass transfer, 1425-1438.
  3. Hou, Y., & Tao, Y. (2014). The effects of micro-structured surfaces on multi-nozzle spray cooling. Journal on applied thermal engineering, 613-621.
  4. Jia, & Qiu. (2013). Experimental. Journal on experimental thermal and fluid science, 829-838.
  5. Kim, J., Horacek, B., & Kiger, K. (2011). Spray cooling using multiple nozzles: visualization and wall heat transfer measurements. 1EEE transactions on device and materials reliability, 614-624.
  6. Li, H., Jason, M., Vidic, R., & Dzombak, D. (2011). Control of mineral scale deposition in cooling system using secondary-treated municipal wastewater. Journal on water research, 748-760.
  7. World Health Organization. (2006). Overview of graywater management considerations. Amman: WHO press.
  8. Al-Wabel, M, (2011). Simple system for handling and reuse of gray water resulted from ablution in Mosques of Riyadh City, Saudi Arabia, International Conference on Environment Science and Engineering, Singapore.




  1. Abu-Rizaiza, O. S,( 2002). Ablution Water: Prospects for Reuse in Flushing of Toilets at Mosques, Schools, and Offices in Saudi Arabia.King Abdul Aziz Univ. J.,14 (2):3- 28.



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