Conference Year
2016
Keywords
heat exchangers, design, additive manufacturing
Abstract
The shortage of water supply in arid regions constitutes a challenge for cooling systems in power plants. Air is often used as a cooling fluid when water is scarce, but these air-cooled systems are typically less efficient and more costly than those that are water-cooled. One way of improving the performance of these heat exchangers is to incorporate non-conventional geometries to utilize phenomena that naturally increase heat transfer, such as rough surfaces and torturous flows. These geometries would go beyond the commonly used finned-tubes to be more efficient, thus requiring less space and material. Traditional manufacturing techniques currently limit the flexibility of design, but additive manufacturing demonstrates the potential to manufacture more complex features. Advances in filled polymers help to achieve a higher thermal conductivity (2 – 8 W/m-K) otherwise sacrificed by traditional 3D-printed plastic material (0.2 W/m-K). This paper focuses on the design and modeling techniques of 3D-printed air-cooled heat exchanger prototypes. A sub-scaled heat exchanger design was used to incorporate a flow arrangement similar to conventional air-cooled heat exchangers, where multi-pass hot-side channels are arranged in cross-flow with air channels. Airside convection was found to be the greatest source of thermal resistance and had the highest potential for improvement; geometric features would be most beneficially placed inside the air channels. The heat exchangers are modeled and analyzed using Engineering Equation Solver (EES) (Klein, 2015). The model is set up to solve for many performance characteristics that would be of interest about the heat exchanger. It implements ε-NTU method for the heat exchanger performance, utilizes internal and external flow correlations, and carries out optimization of certain parameters. Its main purpose is to calculate the required size of the heat exchanger to satisfy two desired performance characteristics: airside pressure drop and heat exchanger effectiveness ε based on given boundary conditions. Current and future work on the design of these heat exchangers integrates the demands of increasing heat transfer rate and decreasing pressure drops while accommodating to printability constraints. As geometric features become more refined and complex, common flow correlations will no longer be applicable, and some simulation will be done using computational fluid dynamics (CFD) software. With that analysis in conjunction with the EES model, performance of the heat exchanger will be compared to experimental data from an actual printed prototype.