Analytical study of the heat transfer limits of a novel loop heat pipe system

✍ Scribed by Zhangyuan Wang; Xudong Zhao

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 248 KB
• Volume: 35
• Category: Article
• ISSN: 0363-907X
• DOI: 10.1002/er.1697

✦ Synopsis

A novel loop heat pipe system was designed for use in solar hot water heating and an analytical model was developed to investigate its thermal performance and determine six major limits to system operation, i.e. capillary limit, entrainment limit, viscous limit, boiling limit, sonic limit, and filled liquid mass limit. Relations among the limits and several associated parameters, i.e. the heat pipe operating temperature, wicks type, heat pipe diameter, and height difference between the absorbing pipes array and condenser (heat exchanger), were established through a comprehensive analyses. It was found that the levels of capillary, entrainment, viscous, sonic, and filled liquid mass limits increased with the increasing temperature; however, the boiling limit was in the adverse trend. It was also found that the mesh screen wicks were able to obtain a higher capillary limit than sintered powder wicks, whilst other limits remained same. Larger pipe diameters would lead to higher operating limits. The height difference between the condenser (heat exchanger) and absorbing pipes (absorber) was the most important factor impacting on heat transfer capacities of the system, and largely affected the capillary limit of the system. It was noted when the pipe (inner) diameter increased to 5.6 mm or above, the governing limit of the system switched from entrainment to capillary. Relationship between the system governing limit, i.e. capillary limit, and the above addressed parameters were analysed. Adequate system configuration and operating conditions were suggested, which were summarized as follows: 6 mm of pipe inner diameter with mesh screen wicks, 581C of heat pipe operating temperature, and 1.3 m height difference between absorber and condenser (heat exchanger).