Background
With the continuous innovation and development of power battery technology, especially the cost of lithium ion batteries is greatly reduced, and the development speed of the global electric automobile industry is obviously accelerated.
The power of the electric automobile needs a large-capacity battery and high-current discharge, and a large amount of heat such as electrochemical reaction heat, current joule heat, polarization heat and the like can be generated in the working process of the battery, so that the temperature of the battery body is increased. The heating of the battery is a main safety problem of the lithium ion battery, the discharge performance and the cycle service life of the battery are affected by the overhigh or overlow temperature or uneven temperature of the battery, and even the explosion danger exists under extreme conditions, so that a heat management system with reasonable design and high efficiency for a power battery pack becomes more important.
The thermal management method using air as a medium is the most traditional method, has advantages in cost, complexity, maintenance, weight and the like, but is poor in thermal conductivity and not suitable for being used under conditions of high ambient temperature or high-rate battery discharge and the like, and under the conditions, the thermal management method using air as a medium cannot meet the heat dissipation requirement of the battery pack. Compared with the heat management method using air as a medium, the heat management method using liquid as a medium can increase the weight and the structural complexity, but is more effective in heat management of the battery. Although the potential problem of coolant leakage exists, with the increase of the demand of quick charging and the application of the power battery in a severe environment, the heat management method adopting liquid as a medium has wide application prospect. The biggest challenge of passive phase change material thermal management technology (PCM-BTMS) is to improve its thermal conductivity while considering the problem of latent heat recovery. In addition, integration of PCM systems necessarily increases space requirements, weight and cost.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the prior art, the power battery pack thermal management system based on the immersion boiling heat transfer is provided, and the requirements that the power battery pack in the prior art needs to dissipate heat under a high-temperature working condition and needs to be preheated under a low-temperature working condition are met.
The technical scheme is as follows: a thermal management system of a power battery pack based on immersion type boiling heat transfer comprises power batteries arranged in an aluminum barrel, heat insulation pads are arranged among the power batteries, foam is arranged between the power batteries and the aluminum barrel, the power batteries and the aluminum barrel are immersed in a low-boiling-point working medium in a sealing groove, a PTC heating film is arranged at the bottom of the sealing groove, and the sealing groove is vacuumized; the device also comprises a first circulating pipeline and a second circulating pipeline; a condenser is arranged on the first circulating pipeline, a heat exchanger is arranged on the second circulating pipeline, inlets of the first circulating pipeline and the second circulating pipeline are connected with the top of the sealing groove, and outlets of the first circulating pipeline and the second circulating pipeline are connected to the lower part of the side face of the sealing groove through a recovery pump; when the working temperature of the power battery is 40-50 ℃, a first circulation pipeline is started; and when the working condition temperature of the power battery is higher than 50 ℃, the second circulation pipeline is started.
Furthermore, a valve is arranged on the first circulating pipeline, and when the working temperature of the power battery is 0-20 ℃, the valve is closed.
Further, a gas flowmeter is arranged on the first circulating pipeline.
Furthermore, a safety exhaust valve is installed at the top of the sealing groove.
Further, the material of the sealing groove is steel.
Further, the material of the heat insulation pad is aerogel.
Has the advantages that: 1. the system can simultaneously meet the multiple functions of cooling, temperature equalization and preheating;
2. during the working period of the power battery, even if one power battery generates thermal runaway, a large amount of heat can be taken away immediately through boiling heat transfer, the thermal runaway is controlled in a single battery, and other batteries cannot be influenced;
3. the adopted working medium is non-conductive, and the boiling point of the working medium is very low, so that the working medium can easily reach a boiling state;
4. the heat management system can start different circulating pipelines under different working conditions, and further meets the requirement that the power battery works at the optimal temperature in real time.
Detailed Description
The invention is further explained below with reference to the drawings.
As shown in fig. 1 and 3, the power battery pack thermal management system based on immersion boiling heat transfer comprises power batteries 9 arranged inside an aluminum barrel 10, a heat insulation pad 8 made of aerogel is arranged between each power battery 9, foam 7 is arranged between each power battery 9 and the aluminum barrel 10, and the power batteries 9 and the aluminum barrel 10 are immersed in a low-boiling-point working medium 5 in a steel sealing groove 1. The bottom of the sealing groove 1 is provided with a PTC heating film 6, and the sealing groove 1 is vacuumized by a vacuum pump 3. Wherein the Fischer-Tropsch point of the working medium with low boiling point is less than 40 ℃, and the working medium is preferably an electronic fluorinated liquid, and can be hydrofluoroether, liquid ammonia, liquid propane and the like. When thermal runaway appears in a certain power battery 9, the heat insulation pad 8 can separate heat transfer, so that thermal runaway of a plurality of batteries is prevented, and the safety of the electric automobile is improved. The foam 7 arranged between the power battery 9 and the aluminum barrel 10 can avoid the safety problem caused by bulging and extrusion of the battery in the working process.
The system further comprises a first circulation line 13 and a second circulation line 15. The first circulation pipeline 13 is sequentially provided with a valve 2, a gas flowmeter 14 and a condenser 12, the second circulation pipeline 15 is provided with a heat exchanger 16, inlets of the first circulation pipeline 13 and the second circulation pipeline 15 are connected with the top of the sealing groove 1, and outlets of the first circulation pipeline 13 and the second circulation pipeline 15 are connected to the lower part of the side surface of the sealing groove 1 through a recovery pump 11. And a safety exhaust valve 4 is installed at the top of the sealing groove 1.
The system comprises high-temperature heat dissipation working condition control and low-temperature heating working condition control.
Wherein, the high temperature heat dissipation operating mode includes following step:
a1: the high-temperature heat dissipation working condition comprises a second high-temperature working condition and a high-temperature working condition, wherein the temperature range of the second high-temperature working condition is 40-50 ℃, and the temperature range of the high-temperature working condition is more than 50 ℃.
A2: when the power battery pack works, working media with low boiling point are heated, boiled and vaporized by the power battery pack, the first circulation pipeline 13 is opened, heat generated by the battery is taken away by the working media, the generated working media steam is conveyed into the condenser 12 to be condensed into liquid, and then the liquid is recovered into the sealing groove 1 by the recovery pump 11, so that the circulation of the working media is completed, as shown in fig. 2. When the power battery pack is in a sub-high temperature working condition, the condensing speed of the working medium is accelerated by increasing the rotating speed of the fan of the air-cooled condenser 12, so that more working medium steam is condensed, the saturation pressure of the liquid working medium in the sealing groove is reduced, the saturation temperature of the working medium is further reduced, namely the boiling point is reduced, and the temperature of the battery is at the optimal working temperature. The working medium 5 is non-conductive, the safety of the system can be guaranteed, the boiling phenomenon can be easily triggered by the system due to the low boiling point characteristic, and then heat can be quickly taken away.
A3: when the power battery pack is in a high-temperature working condition, the rotating speed of the condenser fan is adjusted to ensure that the battery can not be cooled to the optimal temperature, the first circulating pipeline 13 is closed, the second circulating pipeline 15 is opened, working medium steam and air conditioner refrigerant carry out efficient heat exchange through the heat exchanger on the second circulating pipeline 15, the condensation amount of the working medium is greatly increased, the pressure of the sealing groove is reduced, and the boiling point of the working medium is cooled to the optimal working temperature of the battery.
The low-temperature heating working condition mode comprises the following steps:
b1: the low-temperature heating working condition comprises a low-temperature working condition below zero and a low-temperature working condition above zero, wherein the temperature range of the low-temperature working condition below zero is less than 0 ℃, and the temperature range of the low-temperature working condition above zero is 0-20 ℃.
B2: when the electric automobile runs and the power battery pack is in a low-temperature working condition above zero, the valve 2 on the first circulation pipeline 13 is closed, the circulation volume of working medium steam is reduced, the steam in the sealing groove is increased, so that the internal pressure is increased, namely the saturation pressure of the working medium is increased, the boiling point of the working medium is further increased, and the temperature of the power battery is at the optimal working temperature.
B3: when the electric automobile is not started and the external environment temperature is lower than 0 ℃, namely the power battery pack is in a low-temperature working condition below zero, the preheating system in the sealing groove is started, namely the working medium is heated through the PTC heating film at the bottom of the sealing groove, so that the temperature of the power battery pack immersed in the working medium is quickly increased to the optimal working temperature, and the electric automobile can be safely started.
The battery thermal management system can simultaneously meet the multiple functions of temperature reduction, temperature equalization, preheating and the like, and can quickly take away the heat generated by the power battery pack by utilizing the boiling heat transfer of the working medium, so that the power battery always works in the optimal temperature range. The heat management system has the advantages of short thermal response time, strong heat exchange capability, high safety performance and the like.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.