The developed world has shown great interest in nuclear power in space owing to its great potential in providing nuclear power for various space operations. Space nuclear reactors generate waste heat that is vital in keeping the space thermal equilibrium. Considering the nature of the environment, liquid droplet radiators have been identified as potential candidates for meeting the thermal equilibrium requirement. These low weight radiators comprise of circulating pump, droplet collector, droplet generator and heat exchanger. They are easier to deploy in orbits as compared to other radiators.
The heated fluid from the droplet generator is ejected to form a droplet sheet consisting of numerous tiny droplets. The performance of the liquid droplet radiator is depended on the heat transfer characteristics of the droplet sheet. Although the heat transfer of the droplet sheet is a three-dimensional transient problem with each droplet bearing temperature gradient, they make the analysis more complicated and time-consuming. To enhance the calculation accuracy, researchers have proposed an analysis of the heat transfer characteristics of the droplet sheet based on the characteristics of the individual droplets.
Researchers at Harbin Engineering University: Chen Zeng, Dr. Sichao Tan, Dr. Shouxu Qiao, Fulong Zhao, and Tao Meng developed a new model for analyzing the heat transfer characteristics of the droplet sheet by estimating the characteristics of individual droplets. The main objective was to enhance the accuracy of the thermal characteristics of the rectangular liquid droplet radiator analysis. Their work is currently published in International Journal of Heat and Mass Transfer.
In the new model, the overall performance of the thermal characteristics was considered as a three-dimension problem. Additionally, a combination of the geometry method and basic heat transfer principles were used to verify the shape factors of two and three droplets. The above shape factor matrix based on the superposition rule was beneficial in determining the effect of the surrounding droplets during the analysis of the heat transfer of the droplet sheet.
The research team observed that the shape factors of the two droplets highly depended on the ratio of the distance between the two droplets to their radii. On the same width-thickness, however, the calculated temperature difference among the droplets was negligible with no considerable effects on the analysis. Based on this uniform temperature distribution, a simplified model for calculating the thermal performance of the droplet sheet was developed. The characteristics of the simplified model were compared to that of the initial model. Interestingly, the simplified model recoded a relative error of less than 0.35% as compared to the original model. This confirmed the potential of using the simplified model for analyzing the thermal characteristics of rectangular droplet radiators.
As a proof of the concept, the Harbin Engineering University scientists further analyzed the heat transfer characteristics of the droplet sheet taking into account additional parameters and factors: optimal radius of the droplets, the maximum initial temperature of the droplets, the optimal velocity of the droplets and the optimal distance in the velocity direction between two close droplets. Based on the calculation results, the proposals presented a general idea and guideline for the design of rectangular liquid droplet reactors.
Zeng, C., Tan, S., Qiao, S., Zhao, F., & Meng, T. (2019). A simplified method for calculating the heat rejection from a rectangle droplet sheet. International Journal of Heat and Mass Transfer, 132, 762-771.Go To International Journal of Heat and Mass Transfer