## 1 Introduction  
With the rising awareness of necessity of sustainable energy systems, power electronics (PE) technologies are increasingly becoming the key technology of various energy conversion systems. The insulated-gate bipolar transistor (IGBT) has been used as one of the key components in PE. Advances in PEs has led to the need for manufacturing of highly compact IGBTs, associated with high heat density generation. This trend stresses the necessity of studies regarding design of cooling systems and providing proper thermal management of the IGBT modules to avoid intense heating and even burn-out. An IGBT module can be seen in Figure 1.  
Figure 1: An unpacked IGBT module.  
As a solution to the problem of high heat density, heatsinks have been introduced as additional coolers for PE and they are widely used. A heatsink, which consists of several microchannels, is a promising approach to cool electronic chips with a high rate of heat generation. A heatsink with conventional straight microchannels can be seen in Figure 2a.  
The design and structure of microchannels have a significant impact on hydraulic and thermal performance of heatsinks. In the last 50 years, much effort has been devoted to enhance the heat dissipation ability of heatsinks in respect to the heatsink materials and fabrication methods [1; 2; 3], different arrangements of equipment in cooling loops and systems [4], optimization tools [5], different coolants [6], different phases of coolants [7; 8], combination of thermoelectric coolers and heatsinks [9], compact sandwiched press-pack SiC power module [10], using nanofluids [11], heat exchangers designs [12], using porous materials in heatsinks [13] and different channel shapes and designs [14].  
Different flow profiles are created by passing fluids through different heat sink configurations, causing different temperature profiles and different cooling abilities. A structure which is commonly used in heat exchangers and can improve the heat transfer rate is the U-turn (Figure 2b). Such a path creates centrifuge forces and prolongs the cooling path inside the heatsink, both of which contribute to the rising cooling efficiency.  
[PERSON] et al. [14] investigated different rectangular and parallel channel shapes including curvy microchannels (Figure 2c). Their simulation results show that the curvy microchannels will improve the heat transfer coefficient compared to the conventional straight microchannels.  
One of the high-performance configurations is offset strip fin (Figure 2d). For a given pressure drop and heat source base area, the offset strip fin heatsink offers a better thermal hydraulic performance than the conventional straight microchannels [15].  
In recent years, many studies have been conducted on offset strip fin configurations, investigating different structures (Z type and H type) [16; 17], the thermal and hydraulic behavior of single phase flow experimentally [18] and two phase flow [19; 20], predicting the thermo-hydraulic characteristics  
Figure 2: Schematics of a heatsink with (**a**) Conventional straight microchannels, (**b**) U-turn path, (**c**) Parallel curvy microchannels, (**d**) Offset strip fins.  
numerically [21], pressure drop and heat transfer correlations for single phase flow [22; 23] and two phase flow [19].  
The development of new generation of power devices, such as wide bandgap devices (WBG) and high-performance converter topologies leads to requiring of novel heatsink designs to overcome higher heat flux and making new designed components. In this paper, to follow the efforts for improving heat transfer rate of cooling systems and considering the advantages of offset design, curvy fins and U-turn path, a new and modified configuration based on mentioned heatsinks concept (offset strip fin, curvy fins and U-type design) is introduced and investigated. This new design is proposed to extend the current limitations of the heat transfer dissipation of conventional offset strip fin design.