Transcript Pavan.pptx

MODEL AND COMPUTER PROGRAM FOR
HEAT TRANSFER ANALYSIS IN STRIP BRUSH
PROTECTED RAILROAD SWITCH SYSTEMS
Pavan Ravulaparthy and
Ernesto Gutierrez-Miravete
Rensselaer at Hartford
Heated Railroad Switch Systems
Strip Brush Protected Railroad Switch
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.
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 multilayer system is assumed.
Heat Conduction with Change of
Phase: Governing Equations and
Approximation Method
ρ Cp,eff ∂ T/∂t = k∇2 T
Cp,eff = Cp,eff (T)
Tn+1j = Tnj + (Δt kj/ ρ j Cpj) (Tnj-1 – 2 Tnj + Tnj+1)/ Δx2
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.
Computed Temperature History
Computed Temperature Profiles:
Air Gap-Brush-Snow Pack
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.