• loop Heat Pipe
• natural circulation

The work analyse the Closed Loop Two-Phase Thermosyphons (CLTPT): these systems have a lot of industrial and engineering applications such as cooling system and waste heath recovery from process equipment where they are a consolidated technology and heat transport and thermal control where they are not completely developed.
In the majority of applications the CLTPT work with imposed heat flux and try to maximize the heat exchange in the evaporation section but, in some cases particularly analysed in the present work, they operates between fixed temperatures and the connection between mass flow and heat transfer is very important in order to optimize the performance of the system.
This work studies the connection between mass flow and heat transfer, the parameters which influence it and try to provide the elements necessary to predict the behaviour of a small system designed to environment applications.
To hit the mark, a numerical analysis of the problem is first performed using two numerical models. After that an experimental investigation on the evaporator is carried out and finally a new experimental device have been set up.
Results have been analysed and show that boiling process, and consequently the circulation in the loop, strongly depend on geometric parameters and fluid physical properties. The flow condition can only be determined by integral effect of these processes along the entire loop. Therefore, in order to develop meaningful similarity criteria, it is necessary to consider these integral effects through some simplified solutions.