# Condenser Design for On-Board ORC Recovery System
## 1 Introduction  
Since the 1970s, the importance of new means of providing energy has grown. In addition, the recent Paris Agreement highlighted the urgent need for energy efficiency initiatives, together with the potential reuse of waste energy [1]. The EU Sustainable Development Goals require major changes in current energy systems, aimed at increasing flexibility [2] and reducing the consumption of energy resources [3]. The Organic Rankine Cycle is widely studied thanks to its numerous and interesting applications. The ability to produce energy from a relatively low temperature heat source is the core of all applications [4]. The most common plants are biomass [5], geothermal, solar, desalination. The Organic Rankine Cycle can be used to recover energy from exhaust gases, such as electric trains and boats, improving fuel consumption and reducing their environmental impact [6]. The interesting, perhaps new, aspect is that in almost all cases, when researchers talk about ORC systems, they are talking about stationary configurations [5; 6; 7; 8; 9; 10]. Apart from that, there are a lot of works on small ORC systems. Some authors studied how to optimize--at these small rates--the heat exchangers [11]; others evaluated their technical and economic feasibility [12] and characteristic operating points [13]. In others, the feasibility of particular organic fluids and the use of volumetric expanders [14; 15] have been studied. In this case, the application is vehicular, trying not to excessively modify the car structure and not to vary (or to vary as little as possible) both the payload and the weight arrangements to ensure the car's stability. Another aspect is to use the exhaust gases of the ICE engine as an energy source. This source varies depending on the driving cycle. Thus, the study proposed here is focused on the process of optimizing the ORC system and its various componentsat the various engine speeds, accepting variations in performance (fixing them within a certain range, in our case 5%). The advantages of ORC are various. The organic substance used is usually characterized by a low boiling point, a low latent heat of evaporation and high density. These properties are preferable to increase the mass flow rate into the expander. Then, the specific heat of evaporation of the organic fluid is considered lower than that of water; this is the main reason why the organic fluids are used in place of water for heat recovery from sources in the low to medium temperature range. Another important factor that has contributed to the diffusion of the ORC is the possibility of adapting the same system for different heat sources with minor changes--the components used, in fact, can be derived from those of air conditioning, which have already reached full technological maturity. The favorable performance of ORCs in energy recovery, if adopted by industrial facilities, could ease electricity demand, simultaneously decreasing fossil fuel consumption and increasing the overall energy efficiency.  
The temperature and pressure of the exhaust gases, in this case 723 K and a pressure of 1 bar, set a limit to the use of organic fluid and the net power. Once the operating fluids have been chosen, the pump, turbine, and condenser characteristics (dimensions, input and output temperature, pressure ratio, etc.) are calculated and the \"nearly-optimal\" combination is sought.