分离式热管（也称为环路热虹吸管）是一种高效能的导热元件。相比于金属材料，其导热能力更加优异。相比于闭式热虹吸管，分离式热管蒸发段和冷凝段互相分离，可以实现远距离传热。充液率和充注工质是分离式热管两个比较重要的影响因素。因此，本文以分离式热管的充液率和工质种类对换热性能的影响作为切入点，研究分离式热管的流动和换热特性，并进一步认识分离式热管工作原理。本文的工作主要有以下四个部分：（1）针对典型的分离式热管进行了充液率实验。实验采用定温差边界条件。实验结果提出了最佳充液率出现条件的理论假设，并给出了充液率影响换热能力的原因。（2）利用可视化流动换热试验台研究充液率对换热能力的影响与换热极限（蒸干极限和泛滥极限）。针对换热极限，结合可视化试验台，我们拍摄给出了蒸发端出口的流型，从流动特性上进一步解释了换热极限出现的原因和条件。（3）本文专门针对不同工质的对流换热特性通过可视化试验台进行了进一步研究。这些工质包括环保制冷剂R744（二氧化碳），新型制冷剂R410A，R134a和传统制冷剂R22。该研究采用测量蒸发换热系数和流动可视化相结合的方式，比较了不同工质的流动和换热特性。（4）本文针对不同的换热模型与实验结果进行了比较研究。这些模型有针对分离式热管的，有针对闭式热虹吸管的也有针对大空间池沸腾的核态沸腾部分的。模型有理论推导的也有根据实验结果回归拟合的。本文比较了各个模型的优缺点以及适用范围，并提出了适合本实验结果的经验公式。通过本文的研究，对分离式热管的换热机理有了进一步的认识，研究结果也表明，二氧化碳工质在分离式热管中有着很好的应用前景。

Separated heat pipe system (Also called loop thermosiphon) is a kind of heat transfer equipment with high thermal conductivity. Its heat transfer ability is even much higher than metal. Compared with traditional two phase closed thermosiphon, the condenser and evaporator of the separated heat pipe system is separated from each other and such system can transfer heat for long distance. Filling ratio and coolant type are the most two important factors for heat pipe system. Thus, this paper will study the relation between the coolant type, filling ratio and heat transfer characters including the flow pattern and heat transfer coefficient, in order to understand the operation principle thoroughly. There are mainly four parts of this paper:(1) The paper studied influence of the filling ratio for the separated heat pipe system. The boundary condition is the constant temperature. A theoretical assumption of the best filling ratio has been made according to the experiment results. (2) The paper studied the boiling heat transfer coefficient, flow pattern and heat transfer limit of the separated heat pipe system by the visualization experiment system (The heat transfer limit contains the dry up limit and flood limit). As for heat transfer limit, we have taken lots of photos at the exit point of the evaporator in order to know the flow pattern. By analyzing the flowing pattern, the reason and condition of heat transfer limit has been given. (3) This paper has also studied the heat transfer coefficient and flow pattern for different coolants, including R744 (new type coolant), R134a, R410A (environment friendly coolant) and R22 (traditional coolant). In this paper, not only the boiling heat transfer coefficient is measured but the flowing patterns of each coolant have also be compared. By analyzing the boiling heat transfer coefficient and flowing patterns, the heat transfer characters of each coolants have been compared.(4) This paper has compared our experiment results and the experimental formula in other papers. Among these experimental formulas, some of them are for two phase closed thermosiphon and some of them for separated heat pipe system. There are also some of them for nucleate boiling in pool boiling process. Some of these formulas are derived in theoretical while some of them are derived by linear regression. This paper has compared the advantages and disadvantages between these experimental formula, and obtained new formulas based on the experiment results. By the research of this paper, the principle of heat transfer character of separated heat pipe has been further understood. The results have also show that R744 coolant has good application prospect in the heat pipe system.