Effective cooling of a heat-generating micro-electromechanical system using dispersed nano-encapsulated phase change material in water

• Investigation on thermal performance of suspended nano-encapsulated phase change material in water inside a chamber with an oscillatory heat-generating cylinder. • Impact of radius and oscillation frequency of the cylinder on mixed convection phenomenon at different Reynolds ( Re ), Grashof ( Gr ) and Richardson ( Ri ) numbers. • A drastic increase in the average Nusselt number ( Nu av ) is observed beyond Ri = 1 at constant Re for a unity oscillation frequency. • A sharp change in Nu av is also observed with variations in Re at constant Ri. To regulate the cooling temperatures for heat-generating components such as computer chipsets, detectors, and solar collectors, nano-encapsulated phase change material (NEPCM) can offer an effective solution. This study investigates conjugate mixed convection in a square-shaped cavity containing a rotationally oscillating heat-generating cylinder. The enclosure boundaries are maintained at a cold temperature, and the fluid inside consists of water and a suspension of NEPCM at a volume fraction of 3.5%. The main objective of this study is to improve cooling performance by identifying optimal system parameters under different conditions. The fluid region within the system is modeled using the pressure–velocity formulation of the Navier-Stokes and heat energy equations. In contrast, heat transfer inside the cylinder is governed by the two-dimensional heat conduction equation. After obtaining non-dimensional governing equations, the Galerkin finite element method is used to resolve them with appropriate boundary conditions. This study’s parametric variations include three dimensionless sizes for the oscillating cylinder ( R/L = 0.20, 0.25, 0.30, where L is the chamber dimension), and two oscillation frequencies ( F = 0.1 and 1). The Nusselt number is determined at the boundary of the heat-generating cylinder at each time step, then averaged after the system reaches a quasi-periodic steady state. Three separate cases within the mixed convection regime are investigated by varying the Richardson number (0.1 ≤ Ri ≤ 10), Grashof number (9 × 10 3 ≤ Gr ≤ 9 × 10 5 ), and Reynolds number (50 ≤ Re ≤ 500). For each case, the optimal cylinder oscillation frequency and cylinder radius are determined. After meticulous examination, enlarging the cylinder’s radius to its maximum ensures effective cooling in all cases. Moreover, the lowest oscillation frequency is optimal, except under buoyancy-dominated conditions. Notably, the optimum Nusselt number is attained at a particular dimensionless fusion temperature of θ f = 0.0125.