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Power Electronic Converters
Published in Iqbal Husain, Electric and Hybrid Vehicles, 2021
Junction Temperature: This is the temperature at the pn-junction of a power device. Since the temperature cannot be measured directly, but can only be determined by indirect means, the term ‘virtual’ is often used with junction temperature. The junction temperature during switching operation of semiconductors is the most relevant parameter for the thermal system design and is also the one to be used for estimating lifetime. The point where the product of the voltage and current, i.e., the power dissipation loss is the maximum, will be the hottest point which will be at the pn junction.
Principles of component characterization
Published in Kaveh Azar, in Electronic Cooling, 2020
The focal point of component thermal characterization is the control of junction temperatures. Since semiconductor reliability is adversely affected by higher junction operating temperatures, the determination of junction temperature is essential to developing and producing electronic systems free from thermally induced failures.
Limits of Air Cooling—A Methodical Approach
Published in Sung Jin Kim, Sang Woo Lee, for Electronic Equipment, 2020
Combinations of modeling and design temperature limits can provide us with the answers to the question of whether natural or forced convection by air can be used for cooling. We should also note that the modeling technique suggested here can also address the use of extended surfaces (heat sinks) typically used to reduce the junction temperature. The model allows for parameters such as heat transfer coefficient, areas or Q1 and Q2, section 5.2, to be altered such that they include either the heat sink or the effect of the heat sink. A typical example is to upgrade the value of heat transfer coefficient such that the effect of heat sink is included. Hence, the suitability of the cooling system can be determined by the use of a set of algebraic equations without the need to adhere to any unsubstantiated yard sticks.
Experimental investigation of rectangular mini channel array as an effective tool for energy efficient cooling of electronic gadgets
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Jitendra D Patil, B S Gawali, Umesh Awasarmol, Girish Kapse, Shivam R Patil
In both cases-1 & 2, with the increase in Re, for constant heat supply condition, the actual heat flux extracted by the cooling medium from the channel walls is increasing gradually and reaches to its maximum at 0.63 MW/m2 and 1.5 MW/m2 respectively, as shown in Figure 9. The actual heat extracted by the cooling medium from the heat source depends on the magnitude of two thermal resistances. The first one is thermal resistance between source of heat and cooling medium flowing through the channel (heat gain) and the second one is between source of heat and surrounding ambient air (heat loss). With the increase in Re for the same heat supplied, thermal resistance between heat source and cooling medium is decreasing and as a result of this, heat loss to the surrounding gradually decreases. The net result is an increase in heat flux dissipated through cooling medium and decrease in junction temperature as shown in Figure 9. Reduction in junction temperature results in increase of reliability and computational capabilities of electronic gadgets and reduction in thermal issues involved in design and developments of such devices. The range of junction temperature obtained in this study is 51.5°C (325.5 K) to 77°C (350 K) for case-1 and 51.6°C (324.6 K) to 77°C (350 K) for case-2, as against the 85°C (358 K) recommended by ITRS. The reduction in the junction temperature of 8°C (281 K) is equivalent to 40% increase in reliability (Zhou et al. 2020).
Understanding multi-domain compact modeling of light-emitting diodes
Published in Cogent Engineering, 2021
Junction temperature affects multi-domain LED performance parameters, as well as electrical power consumed. It is one of the most crucial output parameters of a compact model. For a proper thermal analysis of an LED, several temperatures need to be considered on an individual basis. These are junction, heat-sink and ambient temperatures. There is no direct way to measure junction temperature due to miniature size of the pn-junction and inability to access it in a non-destructive way. Heat-sink temperature is one of the most important boundary conditions for modeling, because major portion of the heat generated in LED is conducted towards the ambient via the heat-sink. Junction temperature is directly dependent on heat-sink and ambient temperature. Therefore, often it has to be implicitly estimated. Ambient temperature surrounding an LED and its system influence the thermal aspects of the LED. The two-diode Spice-like electro-thermal-optical model of LEDs with a serial resistor representing the light emission is proposed by Delphi4LED project (Hantos et al., 2017), instead of using two parallel diodes a single diode and an efficiency model can be derived. Further, for accurately measuring junction temperature, it is important to control driving current and forward voltage, significant inaccuracies in current and voltage measurements might result in as high variations in actual values of the LED junction temperatures (Onushkin et al., 2017).
Numerical visualization via heatlines for natural convection in porous bodies of rhombic shapes subjected to thermal aspect ratio-based heating of walls
Published in Numerical Heat Transfer, Part A: Applications, 2019
R. Anandalakshmi, Tanmay Basak, Leo Lukose
Natural convection in porous enclosures has gained special interest involving various transport processes and applications [15–31]. The fundamental understanding of convection patterns in fluid saturated porous enclosures requires analysis based on various factors involving fluid properties, mechanism of transport processes, geometric configurations, surface area of heat transfer, orientation of the enclosures, etc. For example, temperature becomes controlling factor in the system design for many electronic applications to achieve improved performance. Heating of the device beyond the maximum allowable junction temperature may lead to performance failure, breakdown, fire, etc. In addition, increase in junction temperature may lead to change in the quality of the devices and color of the LEDs [32]. Therefore, to design a good thermal management solution, the heat flow control should be determined. The efficient thermal performance also involves the placement of the components to improve convective cooling and to configure the components for maximization of heat dissipation. The efficiency of cooling can be reduced significantly as the air flow tends to be hindered by components at number of locations within enclosures during convection cooling process. Therefore, the permeability plays an important role to determine the flow characteristics for accurate design. In sum, the geometrical orientation of solid bodies at various porosities plays a role on convection. The heating pattern of walls induces convection and the intensity of convection is strongly dependent on various values of porosities.