Modeling heat exchangers under consideration of manufacturing tolerances and uncertain flow distribution

Small dimensions found in modern and novel heat exchanger (HX) designs encounter very challenging manufacturing issues. With current manufacturing techniques HXs in small dimensions will exhibit large tolerances relative to design variables. Hence, the anticipated variation in performance is a concern. Furthermore, small flow channel dimensions are very susceptible to severe fouling and even blockage. Therefore, flow distribution would be uncertain. These uncertainties in dimensions and flow distribution should be accounted for during the design and performance evaluation of new HX geometries with focus on ultra-compact designs.This paper outlines an effort to theoretically evaluate the performance of an air-to-water HX, assembled from tubes with non-conventional heat transfer surfaces. Vertical spacing within this HX is subject to a predefined statistical distribution compounded with uncertainty in water flow rate through each flow path (i.e., tube). A new implementation technique for ɛ-NTU is proposed in order to accommodate different air conditions on both tube sides. A Monte Carlo simulation approach is used to estimate the HX performance distribution. This approach is applied to three HX designs showing the performance degradation subject to geometrical and flow uncertainties. The simulation results under uncertainty provided useful insights into the reasons for the performance degradation and showed great impact to the uncertainty distribution. Overall, the proposed HX design with the smallest dimensions showed the least performance degradation due to manufacturing and operating conditions uncertainty.