Twist-flow, spiral-flow, helicalliy coiled, high heat flux, critical heat flux
The cooling of high heat flux is becoming increasingly important in technical applications. This is on the one hand due to the fact that the available installation space is becoming smaller and smaller due to progressive miniaturization, on the other hand to the ever-increasing performance, which has to be taken away in technically demanding processes such as Inconel machining. In order to meet this challenge, a new type of evaporator, the swirl evaporator, was developed. The swirl evaporator is a screw-shaped cylindrical evaporator with an internal diameter between 1 – 3 mm, which is inserted as a blind hole in components with high heat generation. The refrigerant is fed into the blind hole via a concentrically oriented capillary, deflected by 180° in the drilling base and flows out of the evaporator again in a helical way (twist flow) against the inflow direction. The evaporator's design allows a compact size to be achieved, making it suitable for a wide range of technical applications. To enable a design for industrial needs, a 1-D simulation of the process had been conducted. The simulations showed ideal results for a hydraulic diameter of 2.05 mm and an evaporator length of 15 – 20 mm. According to the simulations an improvement of the energy efficiency of up to 19 % is possible when the mass flow is kept constant for R32. Based on the results of these simulations a design of the test-rig had been developed which allows different screw inserts to be tested with a variable length. Former experimental studies with R404A show that the average critical heat flux density of spot evaporators with a twist geometry increases by up to 33 % compared with spot evaporators without twist generation. The spot evaporators with swirl flow generation have a distinct, stable overheating zone with high heat flux (Humpfer, 2013).