Heat pipe is a two-phase flow passive and reliable heat transfer device widely used in thermal systems . It is known that the thermal conductance of heat pipes is higher than any solid conductor due to the accompanying latent heat during the closed two-phase cycle. Moreover, heat pipes have many advantages compared to other heat exchangers: higher amounts of heat transferred over long distance, faster thermal response time, easier design and manufacturing, lower temperature difference, broad temperature range for applications, and easier control which allow transporting high rates of heat at various temperature levels. Also, as a passive device, no external power is required for its operation, and heat pipe is highly reliable and almost requires no maintenance. Because of the mentioned advantages, heat pipes are ideal for many applications. Heat pipe is considered as an effective thermal solution, particularly in high heat flux applications and in situations where there is a combination of nonuniform heat loading, limited airflow over the heat-generating components, and space or weight constraints.
After the introduction of heat pipes with the paper
2. Advances on heat pipes
The recent advances of heat pipes may include recent advances in working fluids (nanofluids, new refrigerants, etc.), wick structures (microgrooves, sintered, etc.), special types of heat pipes (VCHP, pulsating HP, rotating HP, electrokinetic force), and new applications (energy conservation and storage, reactors, spacecraft, renewable energy, food industries, cooling of electronic components, etc.) [3, 4, 5].