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

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

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

Performance of an Environmentally Friendly Alternative Fluid in a Loop Heat Pipe-Based Battery Thermal Management System

The present investigation aims to devise a thermal management system (TMS) for electric vehicles able to improve on limitations like charging time and all-electric range, together with the safety and environmental impact of the chosen thermal medium. A research gap is identified, as focus is often on addressing system thermal performance without considering that the thermal medium must not only provide suitable performances, but also must not add risks to both passengers and the environment. Thus, this work proposes an innovative cooling system including graphite sheets and a Loop Heat Pipe, filled with Novec™ 649 as working fluid, due to its exceptional environmental properties (GWP = 1 − ODP = 0) and safety features (non-flammable, non-toxic, dielectric). A three-cell module experimental demonstrator was built to compare temperatures when the proposed TMS is run with Novec™ 649 and ethanol. Results of testing over a bespoke fast charge driving cycle show that Novec™ 649 gave a faster start-up and a slightly higher maximum temperature (0.7 °C), meaning that the gains in safety and lower environmental impact brought by Novec™ 649 came without lowering the thermal performance. Finally, the TMS was tested under three different fast charge conditions (1C, 2C, 3C), obtaining maximum temperatures of 28.4 °C, 36.3 °C and 46.4 °C, respectively

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