Experimental Investigations On Characteristics Of Laminar Enhanced Heat Transfer Of Double-component Microencapsulated Phase Change Suspension In A Circular Tube

Microencapsulated phase change material suspension (MPCMS) is a novel kind of enhanced heat transfer and storage media, which can not only markedly enhance convective heat transfer performance, but also can be used as an energy storage media in cold or thermal energy storage system, therefore MPCMS can serve as both energy storage media and heat transfer media. MPCMS has many important applications in energy storage and energy saving systems.In this thesis, the characteristics of laminar enhanced heat transfer for both the single component and the double-component microencapsulated phase change material suspensions in circular tube are experimentally investigated. The experimental results are compared with the numerical results, and the differences between them are analyzed. The detailed works in this thesis are as follows:The background of the MPCMS research is introduced, and the recent literatures in this research area are reviewed. The research methods and contents for this thesis are confirmed.The calculating methods and the values for physical properties of MPCMS are stated.The experimental apparatus are reconstructed roundly since there are some shortcomings for the previous experimental apparatus. The experimental system and the data reduction are introduced. The validation test with water were firstly performed before experiments with MPCMS.The characteristics of laminar enhanced heat transfer of the single-component microencapsulated phase change material suspension in a circular tube are investigated experimentally. The results show that the modified Nusselt number Nux* of MPCMS is 50% and 150% more than the Nux* of water when the mass concentration of MPCMS is between 5%-10%, Reynolds number of MPCMS is between 400-600, and Stefan number is between 3.8-11.8. The mass concentration and the Reynolds number are the most important influencing factors in heat transfer enhancement. When the Stefan number is less, its effect on heat transfer enhancement is great, and when it is higher, its effect is very weak. The differences between the experiment results before and after reconstructing experimental apparatus is less than about 12%, which indicates that the reproducibility of experiments is relatively better, and the reason for the difference is analyzed. The temperature profile and Nux* of MPCMS for laminar flow in circular tube with constant heat flux condition are simulated numerically. The numerical results are favorably in accordance with the experimental results within departure for the modified Nusselt numbers only about 10%, which is the smallest difference between experiment and numerical simulation in the published available literatures. The reason caused the difference is analyzed. The primary influencing factors of heat transfer enhancement of MPCMS with laminar flow in circular tube are analyzed in terms of field synergry principle.The characteristics of laminar enhanced heat transfer for the double-component microencapsulated phase change material suspension in circular tube are also investigated experimentally. The experimental results show that additive particulates without phase change in MPCMS augment the concentration of suspended particles, the micro-convection effect is reinforced, that makes the apparent thermal conductivity increasing, the heat transfer performance of MPCMS is therefore improved. The increasement of phase change temperature range,induced by usage of double-component phase change material, does not weaken heat transfer enhancement of MPCMS observably (theoretically it does weaken heat transfer enhancement). Since the dimensionless phase change temperature range MR is not very wide in the experiment, the change of phase change temperature range does not affect the heat transfer enhancement of MPCMS remarkably.