## 1 Introduction
In industry, the cooling of manufactured elements is often done by placing the element on a long belt or by immersing the element in a cold liquid. However, such immersion in the coolant is often not possible due to the destruction of the manufactured product [11]. Methods of supporting air cooling are sought that will significantly shorten the cooling time without adversely affecting the properties and structure of the material. There is a lack of reports on ultrasonically assisted cooling in the literature. In this article, the problem of ultrasonic-assisted cooling is addressed. Such support can be particularly beneficial in the food industry due to the proven positive effect of ultrasound on food products. Often, the application of ultrasound is a separate technological process that improves the quality and stability of the product [14]. In the food industry, the effects of ultrasound can cause protein denaturation, which reduces the activity of enzymes that affect the decomposition of the product [15; 16; 17]. The impact of ultrasound, for example, on pork meat proteins, causes softening of meat tissues after a longer exposure time and the release of myofibrillar proteins, which in meat products result in better water binding capacity, tenderness, and cohesiveness [18]. [PERSON] et al. [19] stated the positive effect of ultrasound with a power of 29 W and a frequency of 37 kHz on the refrigerated quality of pineapple. [PERSON] and [PERSON] et al. [20] showed that the ultrasound could effectively inhibit microbial metabolism and improve the antioxidant capacity of protein compared to the reference products treated without ultrasound. The effect of ultrasonic with a power of 50 W and a frequency of 40 kHz on the quality of frozen bananas was studied by [PERSON] et al. [19]. The retention of the content of phenolic compounds and improved antioxidant capacity, thus maintaining better color and nutrition results, was proved in the ultrasonic treatment when compared with the untreated group obtaining significantly better results. Shear forces and rapidly changing pressure generated by ultrasonic waves are effective in destroying microbial cells, especially in combination with, e.g., heating. The mechanism of cell destruction and its effect on various microorganisms is the thinning and rupture of the cell membranes, which inactivates microorganisms [21; 22]. Ultrasound has been established to reduce the resistance of microorganisms to heat by physically damaging cellular structures caused by extreme pressure changes and disruption of cellular protein molecules and achieves the purpose of sterilization [23]. This makes them more sensitive to heat denaturation. Similar changes may partly explain the synergistic effect of ultrasound and heat on enzyme inactivation. The use of an external acoustic field, especially ultrasound, is widely discussed in the literature. [PERSON] et al. [24] present a review of the intensification of convective heat exchange using ultrasound. According to this review, the ultrasound in the low-frequency range, between 20 and 40 kHz usually is analyzed. Only a few research papers discuss the effects of ultrasound in the range above 100 kHz. This is because lower ultrasound frequencies are associated with higher wave energy [25]. As expected, the best results are obtained with ultrasound in the low-frequency range, between 20 and 40 kHz. However, the results of the research are not unambiguous because various authors obtained an increase in the convective heat exchange coefficient from 10% to several hundred percent [24]. Until now, about 100 articles have been published describing the enhancement of convective heat exchange by using ultrasonic waves. Most of these works report the results of convection studies in water [26; 27; 28]. In addition, other liquids have been used as a heat transport medium, such as milk [29], ethanol and acetone [30], brine and sugar water [31], coolant liquids [32], different aqueous solutions [33], and nanofluids [34; 35].