Performance Characteristics of PTC Elements for an Electric Vehicle Heating System
A high-voltage positive temperature coefficient (PTC) heater has a simple structure and a swift response. Therefore, for cabin heating in electric vehicles (EVs), such heaters are used either on their own or with a heat pump system. In this study, the sintering process in the manufacturing of PTC elements for an EV heating system was improved to enhance surface uniformity. The electrode production process entailing thin-film sputtering deposition was applied to ensure the high heating performance of PTC elements and reduce the electrode thickness. The allowable voltage and surface heat temperature of the high-voltage PTC elements with thin-film electrodes were 800 V and 172 °C, respectively. The electrode layer thickness was uniform at approximately 3.8 μm or less, approximately 69% less electrode materials were required compared to that before process improvement. Furthermore, a heater for the EV heating system was manufactured using the developed high-voltage PTC elements to verify performance and reliability.
Effects of geometric parameters and operating conditions on the performance of a high-voltage PTC heater for an electric vehicle
Abstract To realize the maximum mileage of an electric vehicle per single charge in winter, improving the positive temperature coefficient (PTC) heater performance and reducing the power consumption of the heating, ventilation, and air-conditioning system is necessary. Therefore, a lightweight heater technology having good thermal performance characteristics and power density is required for the optimal design of PTC heater components. In this study, the geometric parameters of the heater were set for an experiment involving a comparison of the analysis results of the heater models for various radiation fins. The bead array fin heater exhibited an 11.8% higher heating capacity, 2.5% higher efficiency, 7.2% higher pressure drop, and an 11.7% higher power density than the plate fin heater. The bead-emboss fin heater showed 10.3% higher heating capacity, 1.2% higher efficiency, 0.4% higher pressure drop, and 23.7% higher power density than the plate fin heater. Furthermore, the air-side heat transfer and friction characteristics were investigated according to the high-voltage PTC heater operating conditions in an electric vehicle. In the bead-emboss fin heater, the j factor was 8.0% higher and f factor was 39.6% lower on average for 300
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.