The performance of a liquefier is governed by the effectiveness of its heat exchangers. Coiled finned tube heat exchangers are used in medium capacity helium liquefiers based on Collins cycle. Experimental and theoretical analysis of the first heat exchanger in helium liquefaction cycle is presented in this work. The objective of this study is to design, optimize and test the heat exchanger to achieve the desired effectiveness and therefore the drop in the temperature of the gas on the hot side. A transient numerical model is employed to optimize the geometrical configuration and operating parameters of the coiled finned tube heat exchanger. Effect of variable physical properties, axial conduction and radiative heat transfer of the outer shell is also considered. The numerical model is validated with experimental results found in open literature. The numerical model is then used for deriving the optimum geometrical configuration of the coiled heat exchanger. Experimental observations from the tests carried out on a fabricated prototype are also reported in this work. Finally, results of the numerical model are also compared with the experimental results obtained in this study.