Thermomechanical transient stresses in compact heat exchangers: Experimental and numerical study

Abstract

Compact heat exchangers (CHEs) can operate at high pressures and temperatures, requiring an adequate design of the geometric parameters to withstand these conditions. Therefore, they must have good thermo-hydraulic performance while withstanding high thermo-mechanical stresses. However, most works on CHE focus on thermal hydraulic performance or study thermal and mechanical stresses separately. To the best of our knowledge, this is the first study that analyzed transient thermomechanical stress, experimentally and numerically, in CHE fabricated with additive manufacturing (AM). A prototype was produced via AM with 46 channels and circular geometry. An experimental setup capable of applying high pressure (200 bar) and differential temperature (ΔT = 20 °C) was used, and a total of 40 tests under different conditions were carried out. A strain gage was positioned on the sample surface to measure the strain and estimate the stress. The stresses in the inside regions of the prototype were evaluated through a numerical model. The numerical model presented an average error of 2.7 % compared to the experimental data of thermomechanical stress. The stresses reached 36.9 MPa and 184 MPa on the surface and inside the sample, respectively. The validated model was utilized for higher temperature and pressure conditions, similar operation conditions of compact heat exchanger (P = 213.3 bar and ΔT = 100 °C). Transient stresses reach 527 MPa in the channel walls closer to the inlet region. The results showed that thermomechanical stress levels are higher than yield stress and close to the ultimate tensile strength of the stainless steel AISI 316L.