Dependence Θwallmax = f (γ) for identical channels of different groups with ΔTi = idem: 1 – channels with ϕ = 15.88 mm, of the peripheral core area; 2 – channels with ϕ = 12.7 mm, of the peripheral core area; 3 – channels with ϕ = 15.88 mm, of the central core area; 4 – the maximum temperature of the channel walls with ϕ = 12.7 mm, of the central core area.