A Novel Organic Rankine Cycle System with Improved Thermal Stability and Low Global Warming Fluids

This paper proposes a novel Organic Rankine Cycle (ORC) system for long haul truck application. Rather than typical tail pipe heat recovery configurations, the proposed setup exploits the gaseous streams that are already a load on the engine cooling module. The system uses dual loops connected only by the Exhaust Gas Recirculation (EGR) stream. A water blend study is conducted to identify suitable mixtures for the High Temperature (HT) loop, while the Low Temperature (LT) loop utilises a Low Global Warming (GWP) Hydrofluoroether

Effect of Channel Aspect Ratio on Flow Boiling Characteristics within Rectangular Micro-passages

In the present paper, a fundamental analysis on the effect of the channel aspect ratio on the bubble dynamics and heat transfer characteristics for the early transient stages of the bubble growth within confined microchannels of rectangular cross-section, under saturated flow boiling conditions, is conducted, utilising high resolution, 3D, transient, conjugate heat transfer simulations. The open-source toolbox OpenFOAM is applied for the simulations, utilising a custom, user-enhanced, diabatic Volume OF Fluid (VOF) solver. Two different series of numerical simulations are performed, focused on a single nucleation event from a single nucleation site and a single nucleation event from multiple, arbitrarily located, nucleation sites, respectively. In each series, three different values of channel aspect ratio are considered, corresponding to a narrow, a square, and a wide microchannel. For the first series, the simulations are performed for a low, a medium, and a high value of applied heat flux and mass flux. For the second series, only the lower values of applied heat flux and mass flux are used for each channel aspect ratio, since this constitutes the worst-case scenario from the overall heat transfer performance point of view, amongst the cases examined in the first series of simulations. The micro-passage aspect ratio has a significant effect in the generated bubble dynamics during the onset of the nucleate boiling regime, as the bubbles grow within the confined liquid crossflow. This alteration of the generated interfacial dynamics, in effect, regulates the size and position of the contact areas of the generated bubbles with the microchannel walls, with a direct effect in the individual contribution and therefore, the balance between the contact line and the liquid film evaporation mechanisms. Moreover, the work presents the quantification of the effect of the solid domain thermal inertia on the whole process and in particular on the local Nusselt numbers. It is evident that considering conjugate heat transfer in numerical simulations of flow boiling is compulsory in order to predict the physical processes in a correct form

COMPARISON BETWEEN DIFFERENT BATTERY THERMAL MANAGEMENT SYSTEMS DURING FAST CHARGE CYCLES

Aiming to improve on fast charge timings, all-electric range and to reduce costs and complexity, a Battery Thermal Management System (BTMS) with Loop Heat Pipes (LHPs) and graphite sheets is proposed. The LHP placed at the bottom of a prismatic cell module will transfer heat from the cells to a chiller, already part of the HVAC system of the vehicle (hence reducing complexity). Graphite, due its woven structure, provides excellent heat transfer in one direction, and insulation from cell to cell. LHPs do not need pumps or moving parts, nor they need additional energy sources to transfer heat, contrarily to an active forced convection system using fans or pumps. This work investigates the performance between the passive BTMS proposed by the Authors, another passive cooling method (free convection) and an active BTMS (liquid cold plate), thanks to a previously validated code. It resulted that free convection, compared to the LHP-based and cold plate BTMS, can contain maximum cell temperature at low values of C-rates, but is not able to reduce the temperature once the vehicle returns to normal driving conditions. Furthermore, results showed potential for the LHP BTMS to contain the cell temperature below 50°C at 5C fast charge conditions (7 minutes) and to reduce the maximum cell temperature by 7.9ºC compared to free convection and even by 2ºC compared to the active liquid cold plate

A Novel Loop Heat Pipe Based Cooling System for Battery Packs in Electric Vehicles

A novel cooling method for Electric Vehicles battery modules by means of Loop Heat Pipe and graphite sheets is proposed. The Loop Heat Pipe is a passive two-phase system and as such it reduces the parasitic power consumed by the EV thermal management. A validated lumped parameter mathematical model has been created describing the thermo-fluid-dynamic problem and used to simulate the performance of the cooling system during highway driving and ultra-fast charging conditions. The numerical predictions show a clear potential to contain the cells’ temperature below 40°C even during ultra-fast charging, with a 3.3K peak temperature reduction in comparison to a conventional liquid cooling method. Moreover, this system adds only 8% of the battery pack mass and it shows potential parasitic power reductions of one order of magnitude

Numerical investigation on a combined loop heat pipe and graphite sheets cooling system for automotive applications

An innovative Battery Thermal Management System for a 3-cell Electric Vehicle module is proposed, involving Loop Heat Pipes and graphite sheets, with the particular aim of fast charging and reacting to automotive requirements. The design feasibility is verified through a Lumped Parameter Model, which has been validated comparing the data from an experimental demonstrator which included a copper/copper flat plate Loop Heat Pipe running ethanol. Results show that this solution is able to maintain the maximum temperature below 32°C after a 10 min fast charge cycle. System performance with a standard working fluid such as ethanol are compared with the system performance using a novel fluid, Novec™ 649, which has desirable features for the automotive industry, such as non-flammability, non-toxicity, below-zero freezing point and outstanding environmental properties (GWP = 1, ODP = 0). Nevertheless, comparison between the results with the two fluids reported no significant difference in thermal performance showing no contraindication in the use of the novel working fluid. Moreover, the model was used to estimate the effect of the Loop Heat Pipe building material, resulting in no sensible difference between the utilization of copper and aluminium, de facto justifying the choice of the lighter material for future applications

Wettability Effect On Flow Boiling Characteristics Within Micro- passages

A numerical investigation on the effect of wettability characteristics on a single bubble growth during saturated flow boiling conditions within a microchannel, is conducted in the present paper. The numerical simulations are conducted with the open-source toolbox OpenFOAM, utilising a user-enhanced Volume OF Fluid (VOF) solver. The proposed solver enhancements involve a treatment for spurious velocities dampening (a well-known defect of VOF methods), an improved dynamic contact angle treatment to accurately account for wettability effects as well as the implementation of a phase-change model in the fluid domain, accounting for conjugate heattransfer with a solid domain. The predictions of the simulations show that the local Nusselt number (Nu) is more depended on wettability characteristics for low heat fluxes, and less dependent on higher heat fluxes. In more detail, it seems that the local, instantaneous heat transfer coefficient is higher for super-hydrophilic cases in comparison to hydrophilic. However, as the applied heat flux increases, hydrophilic and super-hydrophilic cases show a similar heat transfer enhancement with respect to the single-phase heat transfer in the considered micro-channel. Finally, superhydrophobic cases, show lower heat transfer performance with respect to the single-phase case.This is due to the fact that a vapour blanket is rapidly formed immediately after the nucleation, acting as an insulator of the heated solid surface