## 1 Introduction  
In order to ensure sustainable energy generation and easy access to electricity and other forms of energy, there is increased interest in the study and development of power generation systems and devices. Moreover, pro-ecological technology has been driving the research in this area into effective and efficient solutions. Therefore, there is some increased interest in the investigation and development of waste heat recovery technologies [1; 2; 3] and the utilization of intermittent and fluctuating heat sources [4]. Recent studies on the utilization of intermittent and fluctuating heat sources involving thermal energy storage (TES) also indicate that thermal energy can be stored and used at any time to produce electricity. In this case, the Carnot battery offers a good solution that can be implemented to utilize and store the waste heat with the help of a heat engine, a heat pump, and TES [5]. A literature review shows that there are three possible types of Carnot battery technologies. These are methods based on the Lamm-Honigmann process, pumped thermal energy storage (PTES, also known as compressed heat energy storage (CHEST) [6]), and liquefied air energy storage (LAES) [5]. In the Carnot battery, the electric energy is stored as sensible or latent heat (i.e., charging schemes); it can then be recovered using several different heat engine technologies such as Rankine or Brayton cycles [7]. Due to their advantages, such as flexibility to adapt to different operating conditions and working fluids, easier integration of waste heat, relatively low investment and maintenance cost, and compact modular design, Rankine-based cycles are a promising approach for implementation in Carnot batteries. Therefore, our paper focuses on these cycles. A significant interest in the research related to Rankine-based cycles is visible in many investigations of the selection of a suitable working fluid [8]. In the classical Rankine cycle, water is applied as the working fluid, whereas the organic Rankine cycle (ORC) uses organic working fluid instead of water in a Rankine-based system. The ORC can utilize various working fluids, and its performance depends on the type of applied working fluid used. These fluids are conventionally classified as wet, dry, or isentropic; alternatively, these working fluids can also be classified by special points, A-C-Z-M-N [9], located on their \(T\)-s diagrams. The ORC system performance depends not only on the applied working fluid but also on the system architecture, which includes simple, cascaded, combined, reheated, and regenerative systems, and those integrated with two-phase expansion cycles [10]. Recent articles [11; 12] discussed the maximal efficiency of ORC and its gradual efficiency trendline in a simple design compared with the trilateral flash cycle (TFC) and the partially evaporated ORC (PE-ORC). This simple approach is a benefit for engineers in designing and operating a compact and efficient ORC system. By applying a recuperator, the efficiency of the ORC system in which dry working fluid is applied can be improved [13]. Since the Carnot battery can be implemented using a Rankine-based cycle, various design schemes exist depending on the employed expanders. Compared to turbines, volumetric expanders appear to be more promising for application in Carnot batteries as they can operate with relatively lower noise and vibration and under two-phase conditions (wetness). Therefore, many technical issues can be avoided, such as droplet condensation during expansion (which may lead to serious problems, i.e., blade erosion) [14; 15]. A recent preliminary study [16] discussed the possible application of various types of volumetric machines as two-phase expanders, such as the screw, scroll, and multi-vane systems. In the literature, a study [17] analyzed the Carnot battery with a Rankine-based system in which the heat pump and heat engine were designed as separate devices (that is, the design employed a compressor, a pump, an expander, and a throttle valve).