comments and changes when checking bcc calculations

heatpipe.py

@@ -97,7 +97,8 @@ class HeatPipe:
 
     def calculate_bcc_properties(self, strut_diameter, unit_cell_size, material_conductivity=400): #need to verify this!
         """
-        Calculate properties for BCC lattice wick structure
+        Calculate properties for BCC lattice wick structure. Structure assumed to have 12/4 edge struts 
+        (12 edge struts shared by 4 unit cells) and 4 diagonal struts.
         
         Args:
             strut_diameter (float): Diameter of the struts in meters
@@ -107,6 +108,7 @@ class HeatPipe:
         Returns:
             dict: Updated properties for BCC lattice structure
         """
+        ## TODO: change default material from copper to user choice
         # Volume calculations
         V_unit_cell = unit_cell_size**3
         
@@ -133,7 +135,7 @@ class HeatPipe:
                        n_struts_edge * math.pi * strut_diameter * unit_cell_size)
         specific_surface = surface_area / V_unit_cell
         
-        # Kozeny constant for BCC lattice (typical range 4.5-5.5)
+        # Kozeny constant for BCC lattice (typical range 4.5-5.5, is this correct? I also saw this can be 2-3)
         K_kozeny = 5.0
         
         # Calculate permeability
@@ -143,16 +145,18 @@ class HeatPipe:
         # Assuming copper as base material and water as fluid
         k_fluid = self.fluid_properties["water"]["thermal_conductivity"]
         k_solid = material_conductivity
+        volume_fraction = 1 - porosity
         
         # Maxwell's model for effective thermal conductivity
-        num = k_solid + 2*k_fluid + 2*(k_solid - k_fluid)*porosity
-        den = k_solid + 2*k_fluid - (k_solid - k_fluid)*porosity
+        num = k_solid + 2*k_fluid + 2*(k_solid - k_fluid)*volume_fraction
+        den = k_solid + 2*k_fluid - (k_solid - k_fluid)*volume_fraction
         k_eff = k_fluid * (num/den)
         
         # Calculate effective pore radius
         # For BCC lattice, this is approximately the radius of the largest sphere
         # that can fit in the void space
-        pore_radius = (unit_cell_size - 2*strut_diameter) / 4
+        # pore_radius = (unit_cell_size - 2*strut_diameter) / 4
+        pore_radius = l_diagonal / 4
         
         # Update wick properties for BCC lattice
         self.wick_properties["bcc_lattice"].update({