**2. System structure**

.

O absorption cycle, get-

million tons, accounting for sixth place in the world. However, per capita water resources in the global rankings are 108 in China, and China is one of the most water-short countries in 21 poor countries in the world, and water per capita fresh water is only <sup>1</sup>⁄4 times the word average per capita. And in 2010, the total water demand was 730 billion tons in China, but the water supply was only 6200~6300 billion tons. By 2030, the water deficit will be higher than 100 billion cubic meters in 2010, and the amount of water per capita will fall to 1760 *m*<sup>3</sup>

The most severe water shortage is in the coastal industrial cities, where the per capita water

Scholars have done a lot of the work on water purification and other aspects, but the principle of the method is not the same, and new methods and new technologies continue to emerge. For example, Sevda et al. [2] use microbial respiration to purify the water, and they have made the single seawater desalination room volume increased from 3 ml to 15 L. There are also a lot of traditional researches on the distilled water by evaporation pipe, for example, Hegazy [3] collected the water through a vacuum evaporator to collect steam condensation, and the energy consumption is about 1.8 Kwhr/kg; Mahkamov [4] studied a new type of small and dynamic solar desalination device, where the piston converter was driven by solar energy and with periodic changes in volume and pressure, in which the purified water can be collected in evaporation tube. There are also many scholars who used membrane technology to produce distilled water. For example, Deshmukh et al. [5] studied the desalination by forward osmosis, and they summed up quantitative results between the structure parameters of the support layer with reduced film area in a certain range, thereby saving cost. In the direct contact membrane distillation process, Duong [6] optimized the thermal efficiency of the brine, so that the water recycling rate ranges from 20 to 60% and the energy consumption can be reduced by more than half. Khalifa [7] and other studies have used air gap membrane distillation to produce distilled water, and the influence of feed temperature and air gap width on the system performance was obtained. In addition, solar energy as a clean energy was also widely used to produce distilled water, for example, Reif et al. [8] used solar energy to desalination. Comparing with the conversion of solar energy into electricity, they pointed out that it was more effective and attractive for the system to be converted into heat energy. Sahoo et al. [9] used solar energy for desalination of sea water and polygeneration, reducing the cost and greenhouse gas emissions. Combination of distilled water and refrigeration system has been researched in depth by scholars. For example, Wang [10] studied a high-efficiency

combined desalination and refrigeration system based on the LiBr-H2

ting more high energy utilization rate and lower operating costs. Nada [11] et al. studied the water production rate of distilled water in the process of desiccant air conditioning. Houa et al. [12] used simulation method to verify the feasibility of marine cooling system with seawater cooling and seawater desalination. Chiranjeevi [13] studied the combination of the two-stage seawater desalination and refrigeration system to improve the energy utilization coefficient. Scholars have studied other methods for producing distilled water, for example, Rommerskirchen [14] produced distilled water by using the single module electrode capacitor. Compared to the traditional capacitive de ionized, it can produce distilled water continuously. Zhang [15] studied the influence of salt, anionic polyacrylamide, and crude oil on the membrane fouling in the process of polymer flooding. Comparing with the effect of silica gel

, which belongs to the severe water shortage area.

resource is much lower than 500 *m*<sup>3</sup>

78 Desalination and Water Treatment

The vacuum heat pump system is shown in **Figure 1**.

The structure of system is divided into two parts: the refrigeration cycle system and the water cycle system.

The principle of refrigeration cycle system is that the high-temperature and high-pressure gas from compressor releases heat when it enters into the vapor generator and auxiliary con-

**Figure 1.** System structure of distilled water. 1, compressor; 2, vapor generator; 3, auxiliary condenser; 4, capillary; 5, condensate absorber; 6, vent valve; 7, gas–liquid separator; 8, water intake; 9, water outlet; 10, high-pressure diaphragm pump; 11, ejector.

denser, and then the gas turns into low-temperature and low-pressure liquid when it flows through the capillary. The liquid will get in the condensate absorber to transfer heat with water vapor. At the end, the low-pressure gas will be back to the compressor after the liquid passing through the gas-liquid separator. In this cycle, the condensing heat of refrigerant is used to produce water vapor by vapor generator, and the evaporative cooling is used to capture water vapor and produce distilled water in condensate absorber.

**2.2. Application of capillary in system**

**3. Design and simulation**

results were shown in **Figure 3**.

**3.1. Design and simulation of the ejector**

lary tubes.

in **Table 1**.

Dt = 4 mm.

The selection of capillary tubes plays an important role in the system's energy-saving optimization, it is the component for throttling in the system. The refrigerant is pressurized by a compressor and congealed by a condenser. And it becomes a highpressure liquid and then flows into the capillary tube. Because the inner diameter of the capillary tube is very small, the flow of the refrigerant causes great resistance, and the pressure of the refrigerant is gradually reduced. When the pressure is reduced to the gasification pressure at the temperature of the

Distilled Water Production by Vacuum Heat Pump http://dx.doi.org/10.5772/intechopen.76839 81

In this chapter, CFD simulation and experimental test are performed on the matching of capil-

For the ejector, in order to get a low suck pressure for the vapor generator, the spreading ratio (SR) defined as the ratio of the throat area to the tube area should be very small, and the velocity should be very high according to energy conservation. So selecting one optimized ejector to obtain a good performance of the vacuum heat pump system is very important; we designed three ejectors with different spreading ratios, of which the ratios were 0.0156, 0.0532, and 0.0946, respectively, and the throat diameters were 1.5, 3, and 4 mm, respectively, shown

(A) SR = 0.0156 and Dt = 1.5 mm; (B), SR = 0.0532 and Dt = 3 mm; and (C), SR = 0.0946 and

The performance of the above three ejectors were analyzed by FLUENT software. The fluid was the water, the inlet pressure was 0.6 MPa, and the inlet velocity is 1.6 m/s. The simulated

**Table 1.** Physical structure of three different ejectors 3-a:SR=0.0156,Dt=1.5mm, 3-b:SR=0.0532,Dt=3mm, 3-c:SR=0.0946,Dt=4mm.

refrigerant throttling, after the metastable process, the refrigerant is gasification.

The work principle of water cycle system is that the water from condensate absorber is sucked by high-pressure diaphragm pump into the ejector, and then the water will be mixed with the vapor sucked by ejector entrainment from vapor generator. After ejector diffuser, the mixture of the vapor and the water returns to the condensate absorber, where the vapor is cooled into distilled water.

#### **2.1. Application of ejector in system**

From the working principle of the vacuum heat pump to produce the distilled water, we can find that the function of ejector is of vital importance in this system. The pressure of vapor generator is determined by the sucking pressure resulted from the injecting pressure and velocity of the water. When the injecting pressure is lower, the temperature of the vapor generator is low, so the condensation temperature of the refrigeration system will be reduced and the system efficiency is improved. While the temperature of the condensate absorber is higher, which means a higher temperature of the evaporation temperature of the refrigeration system, it also provides a higher performance of the refrigeration system. **Figure 2** shows the relationship between the water boiling temperature in vapor generator and induced pressure.

It can be seen from **Figure 2**, if a lower water vapor temperature is needed, the lower the induced pressure. When the temperature of water vapor is 30°C, the pressure is 4.25 kPa, and the induced pressure is 7.38kPa at 40°C, which means a very low pressure in vapor generator, so a very good ejector is necessary to obtain an excellent performance of the vacuum heat pump.

**Figure 2.** Induced pressure vs. boiling temperature in vapor generator.

#### **2.2. Application of capillary in system**

denser, and then the gas turns into low-temperature and low-pressure liquid when it flows through the capillary. The liquid will get in the condensate absorber to transfer heat with water vapor. At the end, the low-pressure gas will be back to the compressor after the liquid passing through the gas-liquid separator. In this cycle, the condensing heat of refrigerant is used to produce water vapor by vapor generator, and the evaporative cooling is used to cap-

The work principle of water cycle system is that the water from condensate absorber is sucked by high-pressure diaphragm pump into the ejector, and then the water will be mixed with the vapor sucked by ejector entrainment from vapor generator. After ejector diffuser, the mixture of the vapor and the water returns to the condensate absorber, where the vapor is cooled into

From the working principle of the vacuum heat pump to produce the distilled water, we can find that the function of ejector is of vital importance in this system. The pressure of vapor generator is determined by the sucking pressure resulted from the injecting pressure and velocity of the water. When the injecting pressure is lower, the temperature of the vapor generator is low, so the condensation temperature of the refrigeration system will be reduced and the system efficiency is improved. While the temperature of the condensate absorber is higher, which means a higher temperature of the evaporation temperature of the refrigeration system, it also provides a higher performance of the refrigeration system. **Figure 2** shows the relationship between the water boiling temperature in vapor generator and induced pressure. It can be seen from **Figure 2**, if a lower water vapor temperature is needed, the lower the induced pressure. When the temperature of water vapor is 30°C, the pressure is 4.25 kPa, and the induced pressure is 7.38kPa at 40°C, which means a very low pressure in vapor generator, so a very good ejector is necessary to obtain an excellent performance of the vacuum heat pump.

ture water vapor and produce distilled water in condensate absorber.

distilled water.

80 Desalination and Water Treatment

**2.1. Application of ejector in system**

**Figure 2.** Induced pressure vs. boiling temperature in vapor generator.

The selection of capillary tubes plays an important role in the system's energy-saving optimization, it is the component for throttling in the system. The refrigerant is pressurized by a compressor and congealed by a condenser. And it becomes a highpressure liquid and then flows into the capillary tube. Because the inner diameter of the capillary tube is very small, the flow of the refrigerant causes great resistance, and the pressure of the refrigerant is gradually reduced. When the pressure is reduced to the gasification pressure at the temperature of the refrigerant throttling, after the metastable process, the refrigerant is gasification.

In this chapter, CFD simulation and experimental test are performed on the matching of capillary tubes.
