Power plants using air-cooled condensers suffer a 5 -10% plant-level efficiency penalty compared to plants with once-through cooling systems or wet cooling towers. In this study, a model of a representative air-cooled condenser (ACC) system is developed to explore the potential to mitigate this penalty through techniques that reduce the air-side thermal resistance, and by raising the air mass flow rate. The ACC unit model is coupled to a representative baseload steam-cycle power plant model. It is found that water-cooled power-plant efficiency levels can be approached by using enhanced ACCs with a combination of significantly increased air flow rates (+68%), reduced air-side thermal resistances (−66%), and air-side pressure losses near conventional levels (+24%). Emerging heat-transfer enhancement technologies are evaluated for the potential to meet these performance objectives. The impact of ambient conditions on ACC operation is also examined, and two hybrid wet/dry cooling system technologies are explored to improve performance at high ambient temperatures. Results from this investigation provide guidance for the adoption and enhancement of air-cooled condensers in power plants.
The diffusion absorption refrigeration (DAR) cycle offers a potentially fully thermally activated cooling technology. However, most implementations operate with high source temperatures, forced liquid cooling, or elevated evaporator temperatures ( 5°C). Additionally, few component design resources are available in the literature. In Part I of this investigation, a fully passive DAR design is proposed. Reduced temperature operation is enabled with alternate working fluids (NH 3-NaSCN-He), a distributed heated bubble-pump generator (BPG), and an enhanced absorber. Detailed models are formulated for the BPG, condenser, evaporator, absorber, and gas circulation loop. These are integrated to yield an overall system model. System behavior is evaluated over a range of operating conditions. With the necessary and reasonably expected component performances, refrigeration COPs of 0.11-0.26 can be achieved at design conditions (T amb = 24°C) with low source temperatures (110-130°C) and passive air cooling. In the accompanying paper (Part II), this refrigeration system is experimentally demonstrated, and the proposed models are evaluated.
Numerous investigations have been conducted to extend adiabatic liquid-gas VOF flow solvers to include condensation phenomena by adding an energy equation and phase-change source terms. Some proposed phase-change models employ empirical rate parameters, or adapt heat transfer correlations, and thus must be tuned for specific applications. Generally applicable models have also been developed that rigorously resolve the phase-change process, but require interface reconstruction, significantly increasing computational cost and software complexity. In the present work, a simplified first-principles-based condensation model is developed, which forces interface-containing mesh cells to the equilibrium state. The operation on cells instead of complex interface surfaces enables the use of fast graph algorithms without reconstruction. The model is validated for horizontal film condensation, and converges to exact solutions with increasing mesh resolution. Agreement with established results is demonstrated for smooth and wavy falling-film condensation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.