Varying Flow and Enthalpy

Hi,

The requirements for the injection are such that an enthalpy value is normally assigned. Given a process of surface system heat transfer, the enthalpy of injection must vary with the production temperatures. In this case, how do others specify the injection enthalpy without accepting the error between assumed production fluid temperature after the initial condition?

To simplify the explanation, imagine a scenario with a constantly changing flow rate (hourly). This hourly flow rate may force thermal breakthrough. The constant enthalpy assumption from the initial condition of the model become irrelevant because this value is a direct reflection of the production fluid temperature (assuming a constant dT). How do you handle this with TOUGH?

Thanks!