Numerical Studies on Geometric Features of Microchannel Heat Sink with Pin Fin Structure

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The manifold microchannel (MMC) heat sink is an effective method of electronic device cooling featured by the advantages such as low thermal resistance, compact structure, low flow rate and uniform temperature distribution along the flow direction. To improve the performance of MMC, numerical studies on geometry features of pin fin microchannel were carried out and the characteristics of flowing and heat transfer in two types of MMC structures which are respectively optimized through porosity with different pin-fin distribution and pin-fin located angle were investigated. Numerical results indicated that there are apparent influences of both above geometry features on the characteristics of flowing and heat transfer in MMC. Based on cooling performance factor, an optimum value of porosity with specific pin-fin distribution was obtained. Moreover, better effect on heat transfer could be achieved at a 30 degree around of rectangular pin fin located angle in our work

A Multiscale Thermo-Fluid Computational Model for a Two-Phase Cooling System

In this paper, we describe a mathematical model and a numerical simulation method for the condenser component of a novel two-phase thermosyphon cooling system for power electronics applications. The condenser consists of a set of roll-bonded vertically mounted fins among which air flows by either natural or forced convection. In order to deepen the understanding of the mechanisms that determine the performance of the condenser and to facilitate the further optimization of its industrial design, a multiscale approach is developed to reduce as much as possible the complexity of the simulation code while maintaining reasonable predictive accuracy. To this end, heat diffusion in the fins and its convective transport in air are modeled as 2D processes while the flow of the two-phase coolant within the fins is modeled as a 1D network of pipes. For the numerical solution of the resulting equations, a Dual Mixed-Finite Volume scheme with Exponential Fitting stabilization is used for 2D heat diffusion and convection while a Primal Mixed Finite Element discretization method with upwind stabilization is used for the 1D coolant flow. The mathematical model and the numerical method are validated through extensive simulations of realistic device structures which prove to be in excellent agreement with available experimental data

Design and operation of the air-cooled beam dump for the extraction line of CERN's Proton Synchrotron Booster (PSB)

A new beam dump has been designed, built, installed and operated to withstand the future proton beam extracted from the Proton Synchrotron Booster (PSB) in the framework of the LHC Injector Upgrade (LIU) Project at CERN, consisting of up to 1E14 protons per pulse at 2 GeV, foreseen after the machine upgrades planned for CERN's Long Shutdown 2 (2019-2020). In order to be able to efficiently dissipate the heat deposited by the primary beam, the new dump was designed as a cylindrical block assembly, made out of a copper alloy and cooled by forced airflow. In order to determine the energy density distribution deposited by the beam in the dump, Monte Carlo simulations were performed using the FLUKA code, and thermo-mechanical analyses were carried out by importing the energy density into ANSYS. In addition, Computational Fluid Dynamics (CFD) simulations of the airflow were performed in order to accurately estimate the heat transfer convection coefficient on the surface of the dump. This paper describes the design process, highlights the constraints and challenges of integrating a new dump for increased beam power into the existing facility and provides data on the operation of the dump

Multi-objective design optimization of a micro heat sink for Concentrating Photovoltaic/Thermal (CPVT) systems using a genetic algorithm

An optimization methodology for a microchannel, plate-fin heat sink suitable for the cooling of a linear parabolic trough Concentrating Photovoltaic/Thermal (CPVT) system is applied in this study. Two different microchannel configurations are considered, Fixed (FWμ) and stepwise Variable-Width (VWμ) microchannels respectively. The performance evaluation criteria comprise the thermal resistance of the heat sink and the cooling medium pressure drop through the heat sink. Initially, the effect of the geometric parameters on the heat sink thermal and hydrodynamic performance is investigated using a thermal resistance model and analytical correlations, in order to save computational time. The results of the 1-D model enable the construction of surrogate functions for the thermal resistance and the pressure drop of the heat sink, which are considered as the objective functions for the multi-objective optimization through a genetic algorithm that leads to the optimal geometric parameters. In a second step, a 3-D numerical model of fluid flow and conjugate heat transfer for the optimized FWμ heat sink is developed in order to investigate in detail the flow and thermal processes. The overall analysis demonstrates that microchannel heat sinks achieve very low values of thermal resistance and that the use of variable-width channels can significantly reduce the pressure drop of the cooling fluid. Furthermore, it is proven that the 1-D model is capable of providing a good estimate of the behavior of the heat sink

Optimization of Heat Sinks in a Range of Configurations.

In this study, different heatsink geometries used for electronic cooling are studied and compared to each other to determine the most efficient. The goal is to optimize heat transfer of the heat sinks studied in a range of configuration based on fin geometry. Heat sinks are thermal conductive material devices designed to absorb and disperse heat from high-temperature objects (e.g. Computer CPU). Common materials used in the manufacturing of heat sinks are aluminum and copper due to their relatively high thermal conductivity and lightweight [1]. Aluminum is used as the material for the heatsinks studied in this research project. To start, experimental results from a wind tunnel test conducted were compared to numerical results generated to establish a validation case. Best practices in running numerical simulations on heat sinks along with suitable models for simulating real-world conditions were determined and analyzed. The two main thermal performance-evaluating parameters used in this project are pressure drop (ΔP) and thermal resistance (R). Thirteen numerical CFD simulations were run on different heatsink fin extrusion geometries including the traditional rectangular plate, arc plate, radial plate, cross pin, draft pin, hexagonal pin, mixed shape pin fin, pin and plate, separated plate, airfoil plate, airfoil pin, rectangular pin, and square zig-zag plate heat sinks. It was observed that different fin geometries and dimensions affect the performance of heat sinks to varying extents. The square zig-zag plate heat sink from results obtained had the lowest thermal resistance of 0.25 K/W with the separated plate having the lowest pressure drop of 11.94 Pa. This information is relevant in the selection of fan type, size, and model of heat sink for electronics cooling. Also, another important conclusion drawn from this project is the existence of no definite correlation between the thermal resistance (R) and pressure drop (ΔP) parameters when evaluating heatsink performance

Design and optimization of a micro heat sink for concentrating photovoltaic/thermal (CPVT) systems

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.An optimization methodology for a microchannel heat sink suitable for the cooling of a parabolic trough CPVT system is presented in this study. Two different microchannel configurations are considered, Fixed (FWμ) and stepwise Variable-Width (VWμ) microchannels respectively. The performance evaluation criteria comprise the thermal resistance of the heat sink and the cooling medium pressure drop through the heat sink. Initially, the effect of the geometric parameters on the heat sink thermal and hydrodynamic performance is investigated using a thermal resistance model in order to save computational time. The results of the 1-D model enable the construction of surrogate functions for the thermal resistance and the pressure drop of the heat sink, which are considered as the objective functions for the multiobjective optimization process that leads to the optimal geometric parameters. In a second step, a 3-D numerical model of fluid flow and conjugate heat transfer in the optimized FWμ heat sink is developed in order to investigate in detail the flow and thermal phenomena. The overall analysis demonstrates that microchannel heat sinks achieve very low values of thermal resistance and that the use of variable-width channels can significantly reduce the pressure drop of the cooling fluid. Furthermore, it is proven that the 1-D model is capable of providing a good estimate of the behavior of the heat sink

Hybrid Ground Vehicle Thermal Management System Using Heat Pipes—Model and Control

The development of Hybrid Electric and Unmanned Ground Vehicles (HEV and UGV) offer various benefits including improved vehicle performance, compatibility with high level control systems, reduced fuel consumption, and less environmental pollution. According to the International Energy Agency (IEA), the number of HEVs and EVs is expected to reach 20 million by the year 2020 (Green Car Congress, 2017). Compared with traditional Internal Combustion (IC) engines, hybrid powertrains are more complicated due to additional electronics including the electric motor, battery pack, and control units. However, these additional components introduce new challenges for the powertrain thermal management system design since they have different operating temperature requirements and modes of heat generation. In a hybrid vehicle, the modes of heat generation, apart from the IC engine, include the electric motor, battery pack, and some electrical subsystems, which lead to a more demanding thermal control system. A traditional vehicle cooling system is composed of a mechanical water pump, radiator fan(s), hoses, and other mechanical actuators such as a thermostat valve. In recent times, however, computer-controlled actuators such as an electric water pump, variable speed fan(s), and smart valve(s) are being used for higher efficiency and performance. This approach, although effective and efficient for the common IC engine, may pose problems when it comes to the hybrid powertrains owing to limited space, different operating conditions, heat generation rates, etc. In this dissertation, several innovative designs, optimizations, and control strategies using heat pipes in the thermal management system targeted to hybrid powertrain applications will be analyzed. First, an integrated electric motor air cooling system based on radial heat pipes was designed and the performance was explored through computer simulations. A reduced order electric motor thermal model was introduced to simulate the motor’s internal temperatures. Heat pipes were modeled based on the vapor flow and heat transfer processes, and also selected as the cooling system thermal bus to efficiently remove heat. Mathematical models for the thermal cradle and heat exchanger were developed to complete the cooling system. A series of simulation tests based on the Urban Assault and Convoy Escort driving cycles were used to test the cooling system performance. Numerical results show that the proposed cooling system saves up to 52.1kJ of energy within a 1,800s simulation in comparison to a traditional liquid cooling design (e.g., 67.8% energy saving). Second, an electric motor liquid hybrid cooling system, for HEV applications, using integrated heat pipes and traditional liquid was designed and simulated. The innovative design features two parallel heat transfer pathways allowing optimal heat removal. Detailed mathematical models were developed for the electric motor, heat pipes, liquid cooling system, and heat exchanger. A classical controller was designed for the heat pipe heat transfer pathway while the liquid cooling pathway was adjusted using a nonlinear controller. Cooling performance was again evaluated based on the Urban Assault driving cycle for various road grades and ambient conditions. Results show that the electric motor temperature can be maintained around the target value of 70°C with 399kJ cooling system energy consumption compared to approximate 770kJ energy consumption with the conventional liquid cooling system (e.g., 48% energy saving). Third, a smart HEV battery pack thermal management system using heat pipes as a thermal bus to remove heat efficiently was developed. The battery cooling system couples a standard air conditioning (AC) system with traditional ambient air ventilation. A lumped parameter battery thermal model was created to predict the battery core and surface temperatures. A nonlinear model predictive controller (NMPC) was developed to maintain the battery core temperature about the reference value. The system performance and power requirements were investigated for various driving cycles and ambient conditions. Results showed that the proposed thermal management system can maintain the battery core temperature within a small range (maximum tracking error of 2.1°C) using a suitable cooling strategy based on the ambient temperature conditions and battery heat generation rate. Furthermore, the system showed the ability to remove up to 1134.8kJ of heat within the 1200s simulation. Fourth, a holistic thermal management system for an Unmanned Autonomous Ground Vehicle (UAGV) with a series hybrid powertrain was developed. The use of heat pipes combined with advanced controllers for the vehicle’s electric motors, battery pack, and engine generator set cooling was examined. A series of mathematical models were developed to describe the dynamics and thermal behavior for these elements. Controllers were designed to maintain the components temperatures about their reference values and minimize energy consumption by regulating multiple actuators (e.g., pump, radiator fan, smart valve, blower, and compressor). A vehicle level simulation was conducted which combines the cooling system power consumption with the vehicle power bus. An Urban Assault driving cycle with various road grades and ambient conditions were used for the simulation to show the robustness of the proposed cooling system. Results show that the component temperatures were maintained around their reference values with small errors (2.1°C) and up to 2,955kJ cooling system energy was saved over the 1,800s simulation using heat pipes and the proposed controllers (e.g., 19.8% energy saving). Overall, this research has developed the basis for the holistic control of HEV powertrain thermal management systems. A suite of model-based advanced controllers was used to simultaneously regulate the cooling actuators for the battery, e-motors, and IC engine. For electronics, heat pipes were introduced to reduce the cooling system energy consumption due to their high effective conductivities. Numerical studies have been conducted using vehicle model under various driving cycle, road grade, and ambient conditions to show the advantages of heat pipes and the proposed controllers. The next generation of thermal management system will feature multiple heat transfer pathways to help reduce energy consumption for a better use of fossil fuel and electric power resources