A slender rod of length L, diameter d (L >> d) and thermal

A slender rod of length L, diameter d (L >> d) and thermal conductivity k₁ i s joined with another rod of identical dimensions, but of thermal conductivity k 2, to form a composite cylindrical rod of length 2L. The heat transfer in radial direction and contact resistance are negligible. The effective thermal conductivity of the composite rod is

As per question, heat transfer in radial direction and contact resistance are negligible. In series connection,
(R_th) _eq = R₁ + R₂

	2L	=	L	+	L
	Ak_eq		AK₁		AK₂

	2	=	1	+	1
	K_eq		K₁		K₂

⇒ R_eq =	2K₁K₂
	K₁ + K₂