Design of multifunctional lattice-frame materials for compact heat exchangers

Abstract

Structured porous materials show great potential as extended surfaces in heat-exchange applications that also require design for load-bearing capability. In particular, lattice-frame materials (LFM) are known for their superior strength-to-weight ratio; this work presents a comprehensive experimental and numerical study of fluid flow and heat transfer in porous LFMs. Flow through a periodic unit cell of the material is simulated to characterize the forced-convection performance under hydraulically and thermally fully developed conditions. The performance of LFMs with a tetrahedral ligament configuration is characterized as a function of Reynolds number in the laminar regime (150 < Re < 1000) in terms of Nusselt number and friction factor; the effect of porosity is studied by changing the ligament diameter. Experiments are performed for a subset of porosities to validate the numerical approach. A method is demonstrated for utilizing the simulation results, which assume perfect surface efficiency, to predict the performance of LFMs with non-ideal surface efficiency, based on the conduction resistance of the ligaments. It is shown that the thermal behavior of the ligaments closely matches that of cylindrical fins in cross flow and that this analogy can be used to calculate the overall surface efficiency. The implications of the current results on the design of compact heat exchangers using LFMs is assessed using several conventional performance metrics. Our analysis illustrates the challenges in defining any one universal performance metric for compact heat exchanger design; an appropriate performance metric must be selected that accounts for the particular multifunctional performance characteristics of interest. LFMs are shown to provide the benefits of high-porosity and high surface area-to-volume ratio of materials such as metal foams, while also incurring lower pressure drops and displaying higher structural integrity. This makes them ideal for heat exchangers in aerospace and other applications demanding such multifunctional capabilities. The characterization provided in this study readily allows LFM designs for heat exchanger applications with combined heat-transfer and pressure-drop constraints.

Evaluation of Active Heat Sinks Design under Forced Convection—Effect of Geometric and Boundary Parameters

“…According to Ho et al [ 55 ], pressure drop and Nusselt number of Rhombi-Octet lattice structures increased with decreasing unit cell size and the highest Nusselt number was obtained with the lattice structure with the smallest ligament width. The same conclusion was obtained by Son et al [ 60 ].…”

Robust topology optimization of multi-material lattice structures under material and load uncertainties

“…At the microscale, for example, lattice metamaterials have been designed for negative Poisson's ratio [1][2][3], acoustic manipulation [4,5] and energy absorption [6]. Mesoscale lattice structures have also been embedded into global structures to achieve multifunctional heat exchangers [7,8], and parts with high energy absorption [9][10][11][12] and low weight [13,14]. In particular, lattice structures are exceptionally popular in the biomedical field due to their porosity, which allows biocompability with organic tissue, high performance-toweight ratio, and ease of customization [15][16][17].…”

Compact potential of exhaust heat exchangers for engine waste heat recovery using metal foams

“…There are many investigations regarding compact heat exchangers through new materials, innovative structure, and so on. Considering the operating conditions, the exhaust heat exchanger needs the ability to work long term in a corrosive and high temperature (≥750 K) environment .…”