T2=Ts+(T1-Ts)exp(-UA) is one commonly used equation.
T2 is outlet temperature, Ts is surrounding temperature, T1 is inlet temperature, U is the overall heat transfer coefficient.
A is the relaxation distance which is a function of mass flow rate, area of pipe, heat capacity and overall heat transfer coefficient.
How would the heat capacity be used for a natural gas composed of C1 to C6? Would Cp or Cv value be used for a natural gas pipeline?
How would these values be taken into consideration when phase changes occur (occurring both as liquid and gaseous phases) and at what temperature would the heat capacity values be used at?