Unlike conventional combustion engine vehicles, electric vehicles do not produce sufficient waste heat to heat the vehicle cabin. As such, they use a combination of a positive temperature coefficient (PTC) heater and a heat pump as a heat source [ 1 3 ]. High-capacity PTC heaters are needed to compensate for insufficient heat due to the reduction in heat pump performance caused by low outdoor temperatures during winter [ 4 6 ]. PTC heaters must also have a lightweight design to improve the single-charge traveling distance of electric vehicles. They must also use a radiation fin design that considers fragility and ease of manufacturing for mass production.
Many studies have been conducted on PTC heaters for heating the interiors of electric vehicles. Shin et al. studied a 5 kW class electric vehicle PTC heater with an integrated controller [ 7 ]. They performed experiments on heating performance according to heater design factors such as the maximum temperature of the PTC element, thermal conductivity of the insulator, radiator fin thickness, and radiator fin shape (plate and emboss). They also performed a numerical analysis on a 1/16 heater model that included the radiator fin and housing, and examined the distribution of temperature and pressure according to the increase in inlet flow. They analyzed a 1/12 heater that included a controller, and studied the cooling performance of the insulated-gate bipolar transistor within the controller. Based on the results of the heater design factor experiment and the numerical results of the small-scale heater model, a high-voltage PTC heater with a heating performance of 5.4 kW and a pressure drop of 40.5 Pa was built, and its reliability was verified through impact and dust tests. Shin et al. attempted to improve the surface uniformity and reduce the PTC material usage in the manufacturing processes of PTC elements used in electric vehicle PTC heaters [ 8 ]. Instead of employing the conventionally used screen printing method to manufacture the PTC element, a sputtering method was applied to obtain an electrode layer thickness of 3.8 μm. This method reduced the electrode materials by 69% compared to the conventional method. Park and Kim proposed a new heating performance experiment apparatus with a closed loop shape to measure the heating performance of 5 kW class PTC heaters [ 9 ]. A plate fin heater was used to test the heating performance according to PTC heater operational variables such as inlet air flow rate, inlet air temperature, and input voltage. Based on the measurement results and those of a numerical analysis on a 1/16 model, they proposed an emboss fin PTC heater with improved heat transfer performance and gravimetric power density. Park and Kim performed a numerical analysis and proposed bead array fin and bead-emboss fin shapes that are suitable for electric vehicles’ PTC heaters. PTC heaters of each fin design were built, and their heating performance was tested [ 10 ]. The heater that used the bead-emboss fin had a heating performance of 5.44 kW and an efficiency of 96.1%. These values were compared to those of a heater with a plate fin shape, and the results showed that it had an 8% higher j factor and a 39.6% lower f factor, confirming that the heater shape design was excellent. Kang et al. performed a numerical analysis on a lightweight design of a 6 kW class PTC heater using a plate fin. The PTC heater was analyzed according to changes in its design variables [ 11 ]. They presented a simulation model that includes one fin and considers the capability of the computer via a numerical analysis. User-defined functions were used to simulate the temperature as it changed according to the resistance of the PTC element. The numerical analysis results and the heating, ventilation, and air conditioning environment of the vehicle were considered, and a bigger PTC heater was proposed. Their study measured the uniformity and degree of mixing in the air heated by the heater, and aimed to improve the heating performance.
Most existing studies have focused on 5 kW class PTC heaters. Heaters with a higher capacity are needed to compensate for the reduction in heat pump performance during winter and to quickly satisfy passengers’ thermal comfort standards. So far, no study has experimentally evaluated the performance of high-capacity PTC heaters of 6 kW or more. Existing studies have also mainly focused on plate fins, and the few studies on modified fin shapes have been limited to bead and emboss shapes. Furthermore, the PTC heater elements reported in the literature have generated heat at up to 172 °C under standard conditions, but in order to create a high-capacity heater of 6 kW or more, it is necessary to conduct PTC heater studies using PTC heater elements that generate temperatures of 180 °C or more. This study used numerical analysis and experiments to develop a 6 kW class high-voltage PTC heater for electric vehicles. Numerical analysis of the heat flow according to the geometric design variables of the modified louver shape was conducted to develop a modified louver fin by considering heat transfer performance and ease of manufacturing. The developed modified louver fin was applied to a PTC heater, and a 6 kW class high-capacity PTC heater was built. Heating performance experiments were conducted under standard conditions, and a comparative analysis was performed.