Impacts of Double V-Rings in the Heat Exchanger Duct on Heat Transfer and Flow Behaviors: A Numerical Study

The impacts of the double V-rings (DVR) in the heat exchanger duct (HED) on heat transfer and flow structures are numerically analyzed. The general configuration of the DVR is called “type I,” while the discrete DVR can be split into two structures, which are called “types II and III.” The influences of the DVR sizes, DVR types and flow directions on heat transfer rate, friction loss, and thermohydraulic performance are considered. The Reynolds numbers in the range around 100–2000 (laminar regime at the entrance condition) are selected for the present investigation. The numerical problem of the HED installed with the DVR is solved with the finite volume method (a commercial code). The flow structure, heat transfer mechanism, and performance analysis in the HED that fitted the DVR are reported. The flow and heat transfer profiles in the HED fitted with the DVR are an important knowledge to develop the thermohydraulic performance of compact heat exchangers. As the numerical results, it is seen that the heat transfer ability of the tested duct improves around 1.05–16.62 times upper than the smooth duct. Additionally, the greatest value of the thermal enhancement factor in the HED fitted with the DVR is seen to be around 4.17 at a/H = 0.025, b/H = 0.10, Re = 2000, and V-upstream direction for the type I.

A Review on the Thermal-Hydraulic Performance and Optimization of Compact Heat Exchangers

Heat exchangers play an important role in power, the chemical industry, petroleum, food and many other industrial productions, while compact heat exchangers are more favored in industrial applications due to their high thermal efficiency and small size. This paper summarizes the research status of different types of compact heat exchangers, especially the research results of heat transfer and pressure drop of printed circuit heat exchangers, so that researchers can have an overall understanding of the development of compact heat exchangers and get the required information quickly. In addition, this paper summarizes and analyzes several main working fluids selected in compact heat exchangers, and puts forward some discussions and suggestions on the selection of working fluids. Finally, according to the existing published literature, the performance evaluation indexes of compact heat exchangers are summarized and compared, which is convenient for developers and researchers to better grasp the design direction.

A Heuristic for Designing Hybrid Compact Heat Exchangers for Nuclear Applications

Hybrid compact heat exchangers (HCHEs) are a potential source of innovation for intermediate heat exchangers in nuclear industry, with HCHEs being designed for Gen-IV nuclear power applications. Compact heat exchangers are commonly fabricated using diffusion bonding, which can provide challenges for HCHEs due to resultant non-uniform stress distributions across hybrid structures during bonding, leading to variations in joint properties that can compromise performance and safety. In this paper, we introduce and evaluate a heuristic for determining whether a feasible set of diffusion bonding conditions exist for producing HCHE designs capable of meeting regulatory requirements under nuclear boiler and pressure vessel codes. A diffusion bonding model for predicting pore elimination and structural analyses are used to inform the heuristic and a heat exchanger design for 316 stainless steel is used to evaluate the efficacy of the heuristic to develop acceptable diffusion bonding parameters. A set of diffusion bonding conditions were identified and validated experimentally by producing various test coupons for evaluating bond strength, ductility, porosity, grain size, creep rupture, creep fatigue and channel deviation. A five-layer hybrid compact heat exchanger structure was fabricated and tensile tested demonstrating that the bonding parameters satisfy all criteria in this paper for diffusion bonding HCHEs with application to the nuclear industry.

Pressure Losses at Moderate Reynolds Numbers in Diamond-Shaped Cylinders Arrays: Application to Microregenerators

Cylinders with an elliptical, oblong, lenticular, sinus, or diamond transveral shape are very interesting geometries for the design of compact heat exchangers. This work investigates the role of the porosity and of the apex angle of diamond-shaped cylinders networks on the pressure losses, at moderate Reynolds numbers, inside microheat regenerators. The design of the geometry under test has been chosen so that the cross section of the flow remains almost constant along the path of the flow between cylinders. Experiments have been performed at 1 ⩽ Re ⩽ 30 and a porosity range 0.40<ε<0.90 for an apex angle of α=33deg. Numerical simulations have been conducted using the same Reynolds and porosity ranges but varying the apex angle 33deg ⩽ α ⩽ 90deg. Experimental measurements and dimensional analysis have shown that the friction factor can be affected by the porosity. Two-dimensional numerical simulations confirmed that the friction factor increases with the porosity but also with the apex angle. An analysis at the scale of a channel flanked by adjacent cylinders has provided an original correlation able to describe easily the evolution of the Poiseuille number and the collective effects on the drag coefficient as a function of α and ε. Such a diamond-shaped design is found to induce much lower Poiseuille numbers than those expected from conventional stacked spheres, woven wires, and circular cylinders arrays. The findings of this study can help for better understanding the optimization of low pressure drop regenerators and how to reduce associated hydraulic power.