• Energy Research

A three-dimensional numerical model is established to predict heat transfer characteristics of a multi-vapor channel vapor chamber (VC) with novel composite wick. In order to validate the numerical model, the surface temperature of the VC is compared with the experimental results. The mass flow rate distribution of working fluid in the wick is obtained. And the effects of the height of the vapor channel on the velocity, pressure drop of the vapor and total thermal resistance are investigated at different heating powers. The velocity, pressure drop of the vapor and total thermal resistance have the same variation trend, which are all inversely correlated to the height of the vapor channel respectively. However, the reduction of the thermal resistance of the vapor decreases as the height of the vapor channel increase. At last, the conduction-based model for the vapor chamber is put forward and the effective thermal conductivity of the vapor channel is derived. The maximum relative error between the VC surface temperature prediction based on the conduction model and the experimental data is less than 5 %.

A three-dimensional numerical model is established to predict heat transfer characteristics of a multi-vapor channel vapor chamber (VC) with novel composite wick. In order to validate the numerical model, the surface temperature of the VC is compared with the experimental results. The mass flow rate distribution of working fluid in the wick is obtained. And the effects of the height of the vapor channel on the velocity, pressure drop of the vapor and total thermal resistance are investigated at different heating powers. The velocity, pressure drop of the vapor and total thermal resistance have the same variation trend, which are all inversely correlated to the height of the vapor channel respectively. However, the reduction of the thermal resistance of the vapor decreases as the height of the vapor channel increase. At last, the conduction-based model for the vapor chamber is put forward and the effective thermal conductivity of the vapor channel is derived. The maximum relative error between the VC surface temperature prediction based on the conduction model and the experimental data is less than 5 %.

The study of micro flame is very important for the design of an efficient, safe micro-burner. An experimental study of small jet diffusion flame was performed. Combustion tests under strong electric field were carried out in ceramic tube burners with the inner diameter of 1.0mm using liquid ethanol as fuel. The relationship between flame dimension and Reynolds number with the voltage was analyzed experimentally. The experiments were conducted with the voltage ranging from 0V to 10000V, and with different electrode spacing (3cm, 5cm, 7cm). The experimental results show that under electric field, the Reynolds number of ethanol vapor increases with increasing the voltage. And the Reynolds number may become instable when the electrode spacing is too large. A strong electric field can reduce soot emission from the flame.

The study of micro flame is very important for the design of an efficient, safe micro-burner. An experimental study of small jet diffusion flame was performed. Combustion tests under strong electric field were carried out in ceramic tube burners with the inner diameter of 1.0mm using liquid ethanol as fuel. The relationship between flame dimension and Reynolds number with the voltage was analyzed experimentally. The experiments were conducted with the voltage ranging from 0V to 10000V, and with different electrode spacing (3cm, 5cm, 7cm). The experimental results show that under electric field, the Reynolds number of ethanol vapor increases with increasing the voltage. And the Reynolds number may become instable when the electrode spacing is too large. A strong electric field can reduce soot emission from the flame.

In order to study the fundamental physical mechanisms of fluid flow and heat transfer in microchannels, many effects should be taken into account. The effect of axial heat conduction on heat transfer in microchannels is one of the hottest topics. Experimental investigation was carried out to analyze heat transfer characteristics of methanol flowing through microchannel heat sink, which consists of 10 parallel triangular microchannels. Experimental results show that the temperature distribution on the heated wall do not change linearly along the channel, which mainly caused by the axial heat conduction in the wall. The ratio of the power due to the axial heat flux to the Joule heating in the heater, and the axial heat conduction number were used to evaluate the heat conduction effect in the wall. Many factors play important roles in the axial heat conduction, including geometric configuration, material of the wall, and Reynolds number. The experimental study reveals that the axial heat conduction effect is gradually strengthened as the Reynolds number decreases.

In order to study the fundamental physical mechanisms of fluid flow and heat transfer in microchannels, many effects should be taken into account. The effect of axial heat conduction on heat transfer in microchannels is one of the hottest topics. Experimental investigation was carried out to analyze heat transfer characteristics of methanol flowing through microchannel heat sink, which consists of 10 parallel triangular microchannels. Experimental results show that the temperature distribution on the heated wall do not change linearly along the channel, which mainly caused by the axial heat conduction in the wall. The ratio of the power due to the axial heat flux to the Joule heating in the heater, and the axial heat conduction number were used to evaluate the heat conduction effect in the wall. Many factors play important roles in the axial heat conduction, including geometric configuration, material of the wall, and Reynolds number. The experimental study reveals that the axial heat conduction effect is gradually strengthened as the Reynolds number decreases.

Abstract The temperature gradient due to the battery cooling thermally drives the unbalanced discharging of a battery module, which is seldom discussed. The shortcoming of the previous modeling methodology of modules also limits the discussion. A multilayer electrochemical-thermal model considering parallel connected cells inside each battery is developed for a serially connected module to investigate the unbalanced discharging with the cooling incorporated. The unbalanced discharging intensifies significantly after the depth of discharge exceeds about 0.8. The unbalanced discharging is the most susceptible to the non-uniform cooling when the cooling performance exactly reaches to the stage of slight improvement. The discharging rate slightly aggravates the unbalanced discharging after 4 C. Reducing the initial temperature of the module exponentially aggravates the unbalanced discharging, which will increase by about 100% when the coolant temperature reduces by 5 °C. The local temperature difference of a battery aggravates the unbalanced discharging, especially when each battery has various local temperature differences. Increasing the cell number will reduce the unbalanced discharging and the reduction will be insignificant when the improvement of cooling performance becomes slight with the convective heat transfer coefficient increasing. The results are helpful to the design of cooling configurations, cooling control strategy and equalization method.

Abstract The temperature gradient due to the battery cooling thermally drives the unbalanced discharging of a battery module, which is seldom discussed. The shortcoming of the previous modeling methodology of modules also limits the discussion. A multilayer electrochemical-thermal model considering parallel connected cells inside each battery is developed for a serially connected module to investigate the unbalanced discharging with the cooling incorporated. The unbalanced discharging intensifies significantly after the depth of discharge exceeds about 0.8. The unbalanced discharging is the most susceptible to the non-uniform cooling when the cooling performance exactly reaches to the stage of slight improvement. The discharging rate slightly aggravates the unbalanced discharging after 4 C. Reducing the initial temperature of the module exponentially aggravates the unbalanced discharging, which will increase by about 100% when the coolant temperature reduces by 5 °C. The local temperature difference of a battery aggravates the unbalanced discharging, especially when each battery has various local temperature differences. Increasing the cell number will reduce the unbalanced discharging and the reduction will be insignificant when the improvement of cooling performance becomes slight with the convective heat transfer coefficient increasing. The results are helpful to the design of cooling configurations, cooling control strategy and equalization method.

Abstract The thermal and electrochemical performance is seldom discussed for a battery module using heat pipe cooling. A three dimensional battery module model, including conjugated heat transfer sub-model, multi-cell sub-models and heat pipe sub-model for a serially connected battery module using heat pipe cooling, is developed and experimentally validated. The electrochemical-thermal characteristic is correspondingly considered for each cell. The dynamics of temperature, local current density, Li+ concentration and voltage are studied in cooling process with different coolant temperatures. With coolant temperature reducing, the temperature difference of the module increases although the maximum temperature decreases. The cell near to the inlet has larger local temperature difference. Under different coolant temperatures, both the local current density and Li+ concentration initially show little variation. Subsequently, those under lower coolant temperatures changes more violently, forming a larger spatial gradient within a cell. Compared with that in anode, the gradient of solid phase Li+ concentration in cathode is more sensitive to the coolant temperature and dominates the loss of available capacity when reducing coolant temperature. The voltage of the battery module decreases and the available capacity decreases by about 0.88%–1.17% with reducing coolant temperature by 10 °C at 5C discharge.