In the power generation industry, panel heat exchangers (or panel radiators) are often used to cool electric transformers. The panel radiator consists of a row of vertical, flat hollow panels surrounded by air. Transformer oil coming from the core flows through the panels and is cooled. For most of its life the transformer operates in off-peak load conditions. The circulation of oil is driven by the conjugate natural convection between the cooling oil inside the radiator and ambient air. When the transformer operates at peak load condition, a fan forces air between the radiator panels in order to increase the heat transfer. In both operating regimes the oil motion through the panels is gravity-induced and does not require an external pumping system. This makes the panel radiator a convenient choice for power generation applications.
When the heat transfer is driven by conjugate natural convection, the fluids follow a specific pattern. Colder denser oil near the panel wall descends, entraining fluid from the quiescent region and developing into a downward free convective channel flow. Heat from the oil is transferred through the panel wall by conduction to the ambient air. Warmer, less dense air near the wall then rises vertically, inducing upward free convection channel flow between two adjacent panels. Then, the cooled oil flows back into the transformer tank where it is heated again by the copper winding of the core. In a steady-state regime, heat generation by the transformer core is balanced by the free convective heat exchange between oil and air, creating a steady circulation of oil from the heat exchanger to the transformer tank and back.
In this simulation example, we will learn to simulate conjugate heat transfer for a panel radiator and analyze the convection of oil and air in the process of cooling the transformer.
Download the Mesh file required for setting up the simulation and associated Case & Data files here. Follow the instructions below to set up this simulation in Ansys Fluent starting with the Mesh file. In case you face any issues setting up or running the simulation, refer to the corresponding initial and final Case and Data files.
Let’s now analyze the simulation results and understand the effects of conjugate natural convection in a panel radiator.