This study is concerned with the potential use of the spray evaporator in the development of a new system for making ice slurry. This system could have many advantages in comparison with conventional refrigeration technologies. For example, this technology can utilize water as a refrigerant, decreasing the possibility of harm to humans as well as to the environment. In addition, this system can produce an ice slurry that is easily transported by conventional pipelines for heating.
If water is sprayed into a tank at pressures as low as 5 kPa, some of it vaporizes at a temperature of 0°C and the remainder of the water spray droplets are converted to an ice-slurry state by loss of the heat of evaporation. This water-spray technology will be a key component of the proposed ice-slurry system.
In the present study, we investigate spray characteristics such as the droplet size distribution and number density of the spray in order to obtain the design data for an ice slurry making system [I]. Generally, the main reason to use a spray in this kind of system is to enhance the evaporation of liquid by enlarging its surface area . In the present study, we require that sufficient vaporization takes place from the surface of a droplet to chill the remaining part of the droplet before it falls onto the surface of the ice slurry. The mean droplet diameter needs to be less than 100 μm. For this purpose, we used a pressurized-type swirl nozzle injector, with nozzle holes 0.15 - 0.4 millimeters in diameter. The flow rate of the spray from a nozzle ranges from 2 to 20 liters per hour at the injection pressure of 7 kgf/cm2, and the Sauter mean diameter of the spray is between 60 and 120 μm. The desired refrigeration capacity of the ice slurry making system is ten kilowatts, so that the rate of generation of water vapor needs to be approximately 5.0 grams per second [3,4]. Assuming this represents about 10% of the total spray flow, the flow rate of the spray system will be 180 L/h, and it is therefore necessary to use nine nozzles in the system. The mean diameter of the overlapping sprays from the multiple nozzles was increased by collisions between droplets, and the shape of the size distribution could change.
In the present study, a relatively simple twin spray was studied experimentally to investigate the droplet size distribution and the velocity of droplets in the overlapping spray region.