1. MODEL AND COMPUTER PROGRAM FOR HEAT TRANSFER ANALYSIS IN STRIP BRUSH PROTECTED RAILROAD SWITCH SYSTEMS Pavan Ravulaparthy and Ernesto Gutierrez-Miravete Rensselaer at Hartford

2. Heated Railroad Switch Systems

3. Strip Brush Protected Railroad Switch

4. Mathematical Model Concept Thermal energy introduced into the switch by the heating system is transported first across the narrow air gap that separates the brush from the switch, then through the brush bristles and finally through the snow layer and into the surrounding environment. The latent heat of melting of the snow is taken into account.

5. Boundary and Initial Conditions For boundary conditions, at the rail boundary we assume that, for safety reasons, the temperature of the switch cannot be allowed to fall below a preselected, well-defined value. On the external surface of the snow, heat is exchanged with the environment through the action of a suitably selected heat transfer coefficient. Regarding the initial condition of the problem, a reasonable temperature profile across the multi- layer system is assumed.

6. Heat Conduction with Change of Phase: Governing Equations and Approximation Method ρ C p,eff ∂ T/∂t = k ∇ 2 T C p,eff = C p,eff (T) T n+1 j = T n j + (Δt k j / ρ j C pj ) (T n j-1 – 2 T n j + T n j+1 )/ Δx 2

7. SnowProtec.f Inputs for the program include the physical properties and dimensions of all materials involved (air, brush bristles, snow), as well as the temperature of the surrounding environment and the power of the switch heating unit. The program computes the temperature profile across the air gap-brush-snow layer system as a function of time.

8. Computed Temperature History

9. Computed Temperature Profiles: Air Gap-Brush-Snow Pack

10. Conclusions The SnowProtec system provides mechanical and thermal isolation of the switch from the surrounding environment that results in savings in the energy required for the maintenance of the proper operating condition of the switch system. A mathematical model of the SnowProtec system provides additional evidence about the protective mechanism provided by the brush seal.