# Design of Novel Cooling Systems Based on Metal Plates with Channels of Shapes Inspired by Nature
###### Abstract
Microchannels provide efficient cooling and their applications typically operate with low fluid velocities, corresponding to a laminar flow, to avoid an undesired high pressure drop [6]. Consequently, the heat transfer improvement by utilization of small channels should be evaluated together with a pressure drop analysis for the fluid, to account for the pumping cost of the cooling fluid [7]. Therefore, channel-based cooling systems should find a compromise between a high heat dissipation across the solid and a low pressure drop for the fluid. Some techniques are reported in the literature to enhance thermal dissipation, focused on diminishing the thermal resistance and the pressure drop of the fluid flowing along the channel [8]. These techniques are generally devoted to studying the influence of the geometry of the heat sink microchannels [9] and the cooling fluid's properties, including the development of new fluids with better thermal properties. In this sense, some works related to microchannels technology are focused on increasing the thermal conductivity of the cooling fluid by introducing nanoparticles with higher thermal conductivity in the fluid, generating the so-called nanofluids. This enhancement of the heat transfer properties of the nanofluids implies an increment on the convective heat transfer coefficient, improving the heat dissipation [10; 11]. Nevertheless, the use of these fluids also produces an increment in the pressure drop due to the higher density and viscosity of nanofluids, penalizing the ratio of heat transfer dissipation to pumping power supply. Another problem associated with nanofluids is the sedimentation caused by a deficient mixing of the nanoparticles, which may generate agglomerates that could end up blocking the channels [12]. Recent studies show numerical simulations and analyses of the impact of employing hybrid nanofluids generated from mixtures of two different nanoparticles on heat transfer and hydrodynamics [13; 14]. Several research works have focused on studying the performance of cooling systems based on metal plates with channels through which cooling fluids circulate. For instance, in photovoltaic (PV) technology, the unused solar radiation induces an increment of the PV cell temperature, which results in a reduction in the photovoltaic efficiency. A reliable solution is the refrigeration of the PV cell with channels or serpentines that enhance the heat dissipation and homogenize the cell temperature, promoting an increase in the conversion efficiency [15; 16]. There exist several alternative applications of cooling plates with relevance in the last years, such as the necessity of controlling the operation temperature of lithium-ion batteries of electric vehicles and in fuel cells. In these systems, a common refrigeration method is based on indirect liquid cooling, such as a refrigeration plate with mini/micro channels to circulate a cold fluid [17; 18; 19]. The main advantage of these compact liquid-based refrigeration systems is that they can maintain a proper temperature of the battery, avoiding hot spots under extreme conditions, such as rapid charging and discharging at high atmospheric temperatures [20]. In most of these cooling applications, the reduction in the maximum temperature of the system is a relevant parameter, but also the homogeneity of temperature of the system plays a critical role, e.g., to improve the mismatch of PV cells [21]. The most widely studied configurations for the channelscomprise parallel conduits, serpentines, and combinations of both [22; 23; 24]. However, the shapes of the employed configurations are rarely optimized in these studies. Regarding the optimization of the shape of the channels, [PERSON] [25] reviewed the numerical approaches to optimize the design of industrial cooling applications, known as topology optimization. This technique is founded in complex mathematical expressions that minimize or maximize objective functions under several constraints.