Condensation heat exchanger for passive cooling systems
The storage of spent fuel elements in actively cooled water pools, e.g. by pumps, is common practice in nuclear power plants. A promising approach to enhance the reliability of power plants is a two-phase, passive heat transfer system. Since this concept works without active components like pumps, water pools can be cooled even in beyond-design-basis accidents, e.g. station black out. In such systems a primary heat exchanger is located in the water pool and a coolant evaporates on the inside. By buoyancy the steam flows through a piping system to a secondary heat exchanger located in ambient air. At the secondary heat exchanger the coolant steam get condensed and flows back to the primary heat exchanger by gravitational force.
The heat transfer performance of such a system depends, among others, on the performance of the components. For that reason the reduction of the single heat transfer resistance improves the overall system.
The project focuses on optimization of the secondary heat exchanger located in the infinity heat sink air. A substantial part of the overall thermal resistance occurs by convective air side heat transfer. Cooling by natural convection was characterized and optimized by numerical methods. Based on this analysis an innovative tube-fin-design was developed and studied under application-oriented experiments in a flow channel.
A preliminary design of an oval finned tube heat exchanger under natural convection was done by CFD-Simulations. Thereby the temperature of the finned tubes was varied to represent different water pool conditions. Furthermore geometrical parameters were modified to optimize the thermal performance.
On the basis of these results a new tube-fin-design was developed and experimental investigated in a flow channel. At different positions along the heat exchanger the temperature was measured by thermocouples to describe the heat transfer of the new fin design. Temperature- and flow velocity distribution was measured in the wake flow region of the finned tube by an anemometric sensor. The experiments on the new fin-tube-design show a higher heat transfer performance of 10 % to 30 % compare to the conventional design.
- S. Unger, D. Sarker, U. Harm, U. Hampel
Enhanced drainage during condensation in passive safety systems for spent fuel pools by SAM coating.
Proceedings 47th Annual Meeting on Nuclear Technology (AMNT), 10.-12.05.2016, Hamburg, Germany
- S. Unger, R. Oertel, U. Hampel
Numerical Investigation of Passive Heat Transfer to Ambient for Cooling of Nuclear Spent Fuel Pools
Proceedings 48th Annual Meeting on Nuclear Technology (AMNT), 16.-17.05.2017, Berlin, Germany
- S. Unger, E. Krepper, U. Hampel
Numerical analysis of heat exchanger designs for passive spent fuel pool cooling to ambient air
Nuclear Engineering and Design, 2017. Submitted