Middle Marsyangdi Hydropower Plant (MMHPP) in Nepal, has been currently facing a severe problem with the existing Cooling Water System (CWS) due to excessive silt which is coming with the flowing water in the open loop of CWS. Due to this, the existing system has been experiencing unexpected unit breakdown as well as frequent maintenance that ultimately cause a severe impact on the power generation. This problem could be overcome by introducing a close loop circuit along with an open loop circuit of cooling water supply which passes through a Tubular Heat Exchanger directly submerged into Draft Tube water where heat transfer could takes place. Based on the suitable design parameters, existing site conditions of the plant and ensuring its technical feasibility, a detailed design of proposed Tubular Heat Exchanger has been carried out.