A new dimensionless thermal hydraulics parameter for the heat exchangers. (August 2018) - Ilyas, Muhammad
Highlights: Various types of heat exchangers are used in energy systems. A dimensionless number for thermal and hydraulics characterization (DITCH) is derived. DITCH can characterize heat exchangers based on thermal and hydraulic consideration. DITCH demonstrates the trade-off between heat transfer coefficient and pressure loss. DITCH is calculated for selected experimental data including various flow regimes. Abstract: Thermal and hydraulic considerations are crucial for the design of an efficient heat exchanger (HX) which allow boiling. Steam generator is one of the biggest and most expensive components of most nuclear power plants. Therefore, design perfections of heat exchangers can lead to improved design of steam generators. Two-phase heat transfer coefficient (HTC) strongly depends on the prevailing flow regime for a given surface pattern as well. The enhancement in HTC is associated with an increase in frictional pressure drop. A single parameter for characterization of heat transfer surfaces based on thermal and hydraulic consideration doesn't exist. A newdi mensionless number fort hermal and hydraulicsch aracterization (DITCH) of the heat exchanger surface has been derived for evaluation of heat transfer surfaces. It captures the hydraulic behavior of coolant due to phase change and wall friction. Its value characterizes different flow regimes of two phase flow. Analysis of a selected data reveals that DITCH increases with quality 'x' and the mass flow rate ' m ̇ '. A steep increase up to x = 0.4 is followed by lesser slope. It is also observed that bubbly flow regime has a least value of this parameter whereas slug flow regime has a value less than 1. This ratio is nearly equal to one or higher for the annular flow region. It is therefore concluded that in annular flow regime, compared to the other flow regimes, heat transfer coefficient is getting significant and pressure drop is getting insignificant.