# Study on the Dynamic Generation of Subcooled Water Using a Compact Heat exchanger
## 1 Introduction  
In a state where the saturation pressure corresponds to the saturation temperature, the temperature of water will be below the freezing temperature and still in the liquid phase, thus being called subcooled water [1]. Ice or ice slurry form after the subcooled water is released, possessing the characteristics of a high latent heat and quick release of the cold temperature. In ice storage air conditioning, food preservation, and medical fields, this process is widely utilized [2; 3]. The ice slurry formed by subcooled water, also known as pumpable ice or binary ice, is a kind of ice-water mixture that is easy to transport, has a large contact area, and can cool substances evenly and quickly. Heat exchangers play a crucial role in the dynamic generation of subcooled water systems [4; 5] which, currently, are mainly modified double-tube heat exchangers or plate heat exchangers used to dynamically generate subcooled water for ice storage. However, ice blockage can occur randomly and disrupt the generation of subcooled water [6; 7]. When ice blockage occurs, the process must be stopped and can only restart after the ice melts. This disruption through stopping and restarting again leads to an increased amount of energy consumed. Between 0 and 2 \({}^{\circ}\)C, subcooled water is commonly used in dynamic ice storage systems to for cold storage, and the ice storage tank has an ice packing factor (IPF) in the range of only 30-40% [8; 9], and this results in space wastage. Only a minor fraction of the subcooled water is converted into ice after the release through subcooling because of the small subcooling degree [1; 10]. This process requires constant water circulation in the ice storage tank for recooling to increase the ice storage capacity [3; 11]. Since the thermal resistance of a double-tube or plate heat exchanger is high, it is imperative to keep the inlet water temperature at 0-0.5 \({}^{\circ}\)C in order to keep the cooling source temperature at a highlevel for energy saving purposes [7; 12]. However, this inlet water temperature requires the installation of a front heater to eliminate the ice crystals that may be contained in the water, complicating the system setup and control. A greater subcooling degree of subcooled water leads to the release of more energy. A more powerful subcooling process allows for easier the generation of ice or ice slurry, which saves time in ice making and can expand its range of applications, such as indoor snowmaking, seafood preservation, and more. The causes of ice blockage are complex and are mainly related to the heat exchanger and the aqueous solution used for ice making. The materials of heat exchangers determine the minimum temperature of the subcooled water. Stainless steel and copper are the most common metallic materials in subcooling heat exchangers [11; 13]. The channel lengths and hydraulic diameters of the heat exchangers that are currently used are generally above 2000 mm and 5 mm, respectively, while the inner wall surface of the heat exchanger should also possess a high degree of finishing work to achieve the dynamic generation of subcooled water [7; 11]. For example, the authors of [6] achieved a minimum temperature of \(-3.3\)\({}^{\circ}\)C of subcooled water at a specific time using a specialized double-tube heat exchanger that was 3000 mm long with a hydraulic diameter of 8 mm, using pure water as the working fluid. Still, it was necessary to keep the cold source at approximately \(-15\)\({}^{\circ}\)C. The authors of [14] achieved \(-2.1\)\({}^{\circ}\)C subcooled water with a double-tube heat exchanger of 3800 mm in length and 10.5 mm in hydraulic diameter using non-freezing liquid (NFL) and water (test water) as the working fluid.