Study On Flow Friction And Characteristics Of Heat Transfer Of Liquid Nitrogen Boiling Two-Phase In Vertical Circular Tube

Liquid nitrogen, as an excellent low-temperature cooling medium, is widely used in various industrial fields taking the advantage of safe, reliable, inexpensive, abundant, sta-ble performance, etc. With China's rapid economic development, the demand of liquid ni-trogen continues to rise. So far, many domestic and foreign thesis related two-phase flow boiling of liquid nitrogen have been reported. Many different researchers have come to different points of view based on the corresponding empirical relationships. However, ac-curacy of these relationship and applicability to different problems needs to be further ve-rified. The main purpose of this paper is to do a system of research and theoretical analysis about two-phase flow boiling of liquid nitrogen of friction and heat transfer characteristics under low mass velocity and utilize the experimental data to validate several classical em-pirical relationships,coming to adapt to formula of liquid nitrogen the friction pressure drop and heat transfer under the low mass velocity on the basis of designing and building a two-phase flow and heat transfer experimental rig. The main tasks research is as follow-ing:Firstly, the test-rig was designed and constructed on the basis of reference and review about many relevant documents. After the completion of the test system, we did repeated test and inspection of the temperature measurement device, pressure measurement and gas tightness, pressure resistance, vacuum degree of test system, until meet experimental con-ditions.Secondly, liquid nitrogen in the vertical tube was also tested. We measured the para-meters of temperature, pressure drop, heat input at different flow, pressure and heating power. Thirdly, flow friction and characteristics of heat transfer characteristics of liquid ni-trogen boiling two-phase in Vertical circular tube is systematic studied and theoretical analyzed, obtaining relationship of the friction pressure drop with heat flux, mass flow rate and system pressure changes. The results show that: the friction pressure drop has in-creased with the heat flux, mass flow rate and system pressure increasing. After comparing experimental data with the more classic with existing empirical relationships, homogene-ous model prediction is relatively good within the experimental range.Fourthly.the outside temperature distribution and heat transfer characteristics on the vertical tube wall along the axial direction is studied and theoretical analyzed coming to the rules between tube wall temperature and local heat transfer Coefficient variation along the flow direction: wall temperature increases at first, decreases, and then increases again. Coefficient of heat transfer is the opposite. Relationship of the local heat transfer coeffi-cient with mass flux, heat flux and system pressure is obtained. Results show: with the mass flow rate, heat flux and system pressure increasing, coefficient of the heat transfer is increased. Comparing the experimental data of this paper with more classic with existing empirical relationships, prediction of Klimenko and Shan empirical relationships is rela-tively accurate. However, the error is still large. By means of fitting the experimental data in the paper, calculating relationship of the liquid nitrogen flow boiling heat transfer coef-ficient is proposed within experimental data.