## 4 **Introduction**  
Litchi (_Litchi chinensis_), a perishable fruit, is loved by people worldwide, and China contributes 60% of the world's production [1]. Litchi mainly matures in summer and has high-temperature flesh and skin, which contain large amounts of field heat after harvest [2]. In the postharvest environment, water lost from litchi due to transpiration is not well replenished, causing rapid deterioration [3]. Loss of litchis occurs due to a lack of proper and timely postharvest treatment [4]. Applying a cold treatment during postharvest can effectively lessen respiration, inhibit microbial growth, and reduce enzyme activity in fruits and vegetables [5, 6]. Precooling is the initial step to rapidly cooling down the harvested products to the desired temperature by using a low-temperature medium to extract heat. As such, precooling is required immediately after harvest to eliminate field heat, to significantly extend the shelf life, and to improve commodity quality [7]. There are four methods commonly used for the precooling of various fruits and vegetables [8, 9]. Forced-air cooling requires several hours and can easily lead to the formation of hot spots and water loss [10]. Ice cooling can cause uneven cooling, insufficient cooling, frostbite, soft pots on products, and increase transportation costs [11, 12]. Vacuum cooling leads to water loss and is not suitable for products with a low surface-to-volume rate [13; 14]. Hydrocooling could reduce water loss, avoid skin softening of crops, and is about 2-15 times faster than forced-air cooling under similar conditions [15; 16]. Litchi, apple, cherry, sweet corn, radiishes, Barhee dates, and carrots are precooled successfully using hydrocooling [8; 17; 18; 19]. At present, postharvest litchi precooling treatment is inadequate [20]. After being picked, most litchis are transported and sold with ice bags. However, litchi lose their commercial value by browning and decaying quickly [21]. Few litchis are transported to litchi processing enterprises while immersed in ice water or cold water for precooling. Precooling facilities are generally far away from litchi production [20]. Due to the costs of transportation and processing, litchi precoding costs are high. In addition, ice water immersion precooling is prone to overcooling or undercooling [22]. In China, the existing precooling equipment in litchi producing regions is limited to laboratory research. There is no precooling equipment that can precool litchis timely and quickly and meet the precooling demand of the litchi producer. TES systems can store either heat or cold energy [23]. Energy can be charged, stored, and discharged on a daily, weekly, seasonal, or annual basis [24]. It can shift energy usage from the peak to the off-peak periods and shift the energy to areas faced with a shortage. A wet precooling system for fruit and vegetables with TES has strong applicability, easily realizes a low-temperature stable environment, and has a large application space during precooling [25]. TES of slurry ice can be used for precooling in the fish industry to reduce energy consumption, accelerate precooling, reduce microbial growth, and improve shelf life [26]. TES of slurry ice is the most effective technology that is relevant to increases in the shelf life of various chilled aquatic food products because of subzero storage temperature, fast chilling rates, and less physical damage caused by microscopic spherical particles [27]. In this study, a spray hydrocooling device using TES technology was newly designed and fabricated. The use of direct evaporative TES provides a cooling source for precooling fruits and vegetables, and melting ice is used for precooling litchi, enabling rapid release of cooling capacity. The use of TES not only allows energy storage but also facilitates energy transfer in space, meeting the precooling needs of fruit and vegetable production areas.