Louis Gosselin

A review of thermal response test analysis using pumping test concepts.

The design of ground-coupled heat pump systems requires knowledge of the thermal properties of the subsurface and boreholes. These properties can be measured with in situ thermal response tests (TRT), where a heat transfer fluid flowing in a ground heat exchanger is heated with an electric element and the resulting temperature perturbation is monitored. These tests are analogous to standard pumping tests conducted in hydrogeology, because a system that is initially assumed at equilibrium is perturbed and the response is monitored in time, to assess the systems properties with inverse modeling. Although pumping test analysis is a mature topic in hydrogeology, the current analysis of temperature measurements in the context of TRTs is comparatively a new topic and it could benefit from the application of concepts related to pumping tests. The purpose of this work is to review the methodology of TRTs and improve their analysis using pumping test concepts, such as the well function, the superposition principle, and the radius of influence. The improvements are demonstrated with three TRTs. The first test was conducted in unsaturated waste rock at an active mine and the other two tests aimed at evaluating the performance of thermally enhanced pipe installed in a fully saturated sedimentary rock formation. The concepts borrowed from pumping tests allowed the planning of the duration of the TRTs and the analysis of variable heat injection rate tests accounting for external heat transfer and temperature recovery, which reduces the uncertainty in the estimation of thermal properties.

Combined “heat transfer and power dissipation” optimization of nanofluid flows

This letter exercises the importance of maximizing the thermal performance of nanofluid flows under appropriate constraints. Laminar and turbulent boundary layer flows in forced and natural convection are considered. The objective is to maximize the heat transfer rate removed from a warm plate by the nanofluid. In forced convection, the power dissipation is constrained to highlight the competing effects of the thermal conductivity and viscosity variations due to the presence of the particles. In natural convection, the competition is intrinsic to the problem formulation. The amount of particles is optimized in each case.

Thermal Resistance Minimization of a Fin-and-Porous-Medium Heat Sink with Evolutionary Algorithms

This article presents a conceptual design of a heat sink combining a porous medium whose matrix is highly conductive and a fin. A simplified model is presented to estimate the performance of the system, relying on Darcy law and local thermal equilibrium. The objective is to minimize the hot-spot temperature under global mass constraint by using an optimization procedure based on genetic algorithms. The design variables are the porosity and material of each layer of the porous medium, the fin material, height, and width, the aspect ratio of the heat sink, and the shape of a weightless upper corner deflector which reduces the width of the inlet and outlet air slots while removing the less useful mass. Results show that the optimal porous layers were generally of copper, independent of the mass constraint. However, the fin is mostly beneficial for heavier designs, while the deflector becomes more important when lightness is required. These two special features show their efficiency by allowing a mass reduction of 95% with a decrease of only 24% in the cooling performance.

Emergence of asymmetry in constructal tree flow networks

In this paper, we demonstrate that asymmetry in fluid distribution tree networks emerges from power requirement minimization, under global volume constraint. We have discovered several levels of asymmetry in optimal trees: different pipe lengths at the same level of branching, different mass flow rates at junctions or bifurcations, and different main branches to build the optimal dendrite. The emergence of asymmetry in optimal tree networks (man-made or natural) is a result of the optimization: it is not an assumption or a modeling feature. The constructal method that we used to discover asymmetry is predictive, and this distinguishes it from descriptive methods such as fractal geometry.

Evolutionary Placement of Discrete Heaters in Forced Convection

This article aims to maximize the global conductance (C) of a symmetrical, discretely heated channel in forced convection, where the fluid flow is sustained by a fixed pressure difference given by the Bejan number. The maximization of C is obtained by determining the optimal arrangement of the discrete heaters along the channel and the optimal channel breadth with the help of a genetic algorithm (GA) that is fully coupled with the finite-element methods used for solving the conservation equations. The number of independent variables considered in the optimization process varies between N + 1 and 2N + 1, where N is the number of heat sources (1 ≤ N ≤ 20) and the extra unit represents the channel height. The numerical results agree with the available literature, showing that increased values of C are obtained with designs that do not use equally spaced heaters. The results show that a larger number of discrete heaters can provide higher values of global conductance when compared with fully optimized simpler designs (i.e., a small number of discrete heaters), which is also in agreement with previous studies. Designs with heaters of variable heat strength are also considered, to study the optimal allocation of the total heat input through the N heaters. This family of designs leads to even higher performance.

Utilization of Artificial Neural Networks in the Context of Materials Selection for Thermofluid Design

In this article, we use artificial neural networks (ANNs) to approximate the design space of heat transfer problems involving several choices of materials. The approximations provided by ANNs are used with genetic algorithms (GAs) to optimize the systems. Three test cases with multilayer structures are studied: 1) layered porous media heat sink, 2) finned heat sink, and 3) exterior building wall. Important computational time savings are reported compared to optimizations with GAs that rely on direct simulations. Optimal or nearly optimal designs have been identified in each case.

Heat Transfer and Airflow Analysis in the Upper Part of Electrolytic Cells Based on CFD

A CFD model of the top part of an electrolytic cell used in the primary aluminum industry is presented. The model is used to determine average heat transfer coefficients on the main surfaces, under different ventilation rates. Correlations have been developed for the heat transfer coefficient and pressure drop versus pot draft condition. Nonuniformity of the heat transfer coefficient is studied. Finally, the relative importance of natural convection versus forced convection is revealed by the analysis. The knowledge developed in this article is useful for the heat transfer design and analysis of electrolytic cells, which is crucial in this industry.

The Numerical Optimization of a Neumann-Type Boundary for the Graetz Problem

The main goal of this study is to numerically determine a converged optimal heating pattern for the Graetz problem in a two-dimension channel subjected to a discrete heating profile. The heat input is provided by multiple independent heaters, while considering the following conditions: symmetric and asymmetric heating without a conductive wall and symmetric heating with a conductive wall. The optimization process, which was based on the genetic algorithm, shows a strong dependence of the cooling performance on the heating profile which is especially affected at relatively low flow speeds if the wall conduction is not present. If conduction through the wall is considered, the importance of the heating pattern is reduced for relatively thick walls. Results also indicate that asymmetric heating conditions are not recommended when compared with symmetric patterns.

Constructal microchannel networks of rarefied gas with minimal flow resistance

In this article, we answer the question of how to optimally design a rarefied gas distribution network from a source point to a given number of equidistant users such that the diameters of the pipes used to carry the fluid fall in the microscale. A slip boundary condition is used to take into account the effects introduced by the smallness of the pipes. By specifying the overall pressure drop across the network, we maximize the total mass flow rate through the dendritic structure under global volume constraint using an evolutionary algorithm. Four complexity levels are considered, nbif=0, 1, 2, and 3, where nbif is the number of levels of bifurcation present in the structure. The results show that the version of Murray’s law originally proposed in order to determine the optimal diameters of the pipes is not valid when rarefaction is present, since the power-law exponent varies significantly with the number of outlet users N. Additionally, the results show that the bifurcation angles decrease in the presen...

Heat transfer and banks formation in a slag bath with embedded heat sources

A study was conducted for the heat transfer and the formation of solid banks inside a bath of molten slag. This study is motivated by the need to predict the formation of a protective thermal barrier for the refractory brick walls inside smelting furnaces. A mathematical model for natural convection dominated solid liquid phase change with embedded heat sources is presented. A scale analysis is conducted yielding algebraic expressions for the steady-state minimal side bank thickness and location, molten volume fraction and average Nusselt number at the surface of the bath in terms of the Rayleigh number. The predictions of the scale analysis are validated with numerical results and their range of application are delineated.