Silicon photoconductive semiconductor switches (SiPCSS) are suitable for high power high voltage applications, however, the large amount heat gains may result in the degradation of the switch. The SiPCSS is slender with a trapezoidal cross section and has dimensions of 70mm long and 2.5mm wide at the small side of the trapezoid and also has rounded ends. This roughly 175mm² area is the base of the SiPCSS. The SiPCSS is connected in a circuit and is actuated via a laser. The switch acts as an insulator until energy is provided from the laser, after which current is allowed to pass through the switch. The laser pulses are 500 picoseconds in duration with a repetition rate in the order of microseconds.  In these pulse events, the SiPCSS will receive a significant amount of energy that is to be dissipated into heat. While there is no upper bound for heat extraction, a goal of maintaining the switch temperature at no higher than 80 °C, which is the temperature where the switch breaks down, is required for continuous operation. Therefore, it is vital to create a cooling system that can keep the switch below this threshold. The system constraints necessitate that the SiPCSS is oriented in such a way that the heat generated can only conduct through the 175 mm² base as well as only utilize low-viscosity silicone oil at 10°C as a coolant. The geometric constraints of the model limit the cooling system design to an approximate volume of 28cm³. There are number of studies that compare various methods of single-phase liquid cooling techniques. Two commonly mentioned methods are microchannel cooling and jet impingement cooling. Preliminary analysis involved a cooling block with laser-cut microchannel fins through which the coolant flowed. This cooling system offered too many thermal resistors and did not provide enough cooling performance to keep the SiPCSS below the 80°C threshold. Microchannel cooling has a greater number of studies about its performance when compared to jet impingement cooling due to the microchannel systems high surface area and relatively low flow rates.  However, jet impingement cooling can achieve higher heat transfer coefficients when compared to microchannel cooling, is the main reason that this study investigates a novel design of jet impingement cooling system. The simulation is performed in ANSYS Fluent 19.2 where the jet impingement cooling was chosen for its high heat transfer coefficient as well as the ability to be directly integrated into the current system. The jet impingement model uses a series of 11 nozzles configured in a single row. The nozzles will be 1mm in diameter, spaced 7mm apart and impinge normal to the surface of the copper plate from a distance of 5mm. The nozzles are to be trained on the centerline of the switch. With the proposed jet impingement cooling system, two thermal resistors are eliminated and the heat transfer coefficient is greatly increased. The results from simulation analysis show the maximum heat extraction rate of 662 W while keeping the switch temperature below the threshold value. It can be concluded that by creating a powerful low-volume cooling system which is designed in this study, the rapid reuse of photoconductive switches will be allowed in high-power applications.

Keywords: Silicon photoconductive semiconductor switch, computational fluid dynamics, jet impingement cooling, microchannel cooling, heat transfer improvement.


Thermal Design and Development of Cooling System for Silicon Photoconductive Semiconductor Switches

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
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