Relations for steam power plant condenser performance in off-design conditions in the function of inlet parameters and those relevant in reference conditions

•Two equations for cooling water outlet temperature were proposed.•The equations are functions only of inlet and reference parameters.•The proposed equations were verified against simulator and measurement data. In the classical approach, the effectiveness of a steam power plant condenser, being a surface-type steam–water heat exchanger, can be given as a function of an overall heat transfer coefficient, heat transfer surface area, cooling water mass flow rate, and the specific heat of water. The calculation of the overall heat transfer coefficient requires additional equations to determine the overall heat transfer coefficient from steam and water as well as Nusselt, Reynolds, and Prandtl similarity numbers. Basic geometric data of the condenser, such as tube diameter, tube wall thickness, heat exchanger length, and pitch of the tubes, also have to be taken into account. Complete geometric data of a heat exchanger are not always available, which raises further difficulties in developing a model. Hence, it is justified to provide a single equation for the steam power plant condenser effectiveness in off-design conditions (without any additional heat transfer equations) as a function of three independent parameters, such as cooling water temperature at the inlet, cooling water mass flow rate, and steam temperature, along with corresponding reference parameters (relevant under nominal operating conditions). The paper formulates two simplified equations for the steam power plant condenser effectiveness and the cooling water outlet temperature as functions of the parameters and reference conditions mentioned above. The proposed relations were verified against data obtained using a steam condenser simulator (written in Fortran), actual measurement data from a power plant, and measurement data available in the literature. One of the proposed relations is explicit but its use is limited to the range of NTU (number of transfer units) between 0.5 and 1.5. The other one is not limited to any range of NTU, but is an implicit function and has to be solved in an iterative process. The data obtained using the steam condenser simulator, actual measurement data, and data available in the literature allow the conclusion that the proposed equations provide good accuracy.