## 1 Introduction  
As the function of modern computers advances, the dissipating heat in electronic environment is increasing with power flux. Simultaneously, thermal dissipation in the electronic equipment is significantly difficult because of high heat load. The cooling method with impinging flow for heat sinks is interest of researchers for solving these problems. If one treats fins as a hot fluid, the fins and flow paths of heat sink could be considered as a type of heat transfer. The heat performance of a heat sink depends significantly on the flow-stream direction. Three fundamental one-dimensional flow forms of heat interchangers including counter-flow, cross-flow, and parallel-flow are widely used. Counter-flow has better potential to accomplish high heat removal. The thermal performance of impinged flow may precede that of cross flow since the flow type for a heat sink with impinging flow is in-between the counter-flow and cross-flow. So it has a better cooling capacity for impinging flow than for parallel flow because of its high cooling effectiveness [1]. Numerical studies were conducted by [PERSON] [2] to estimate a single isothermal channel pressure drop of impinging flow with variable inlet widths. [PERSON] numerically developed the correlation for pressure drop coefficient of heat sinks with different heat sink parameters in this work. However, the correlation was not validated experimentally. [PERSON] and [PERSON] [3] studied the pressure drop of an impinging air cooled plate fin heat sink and presented a simple model and conducted experiments to validate the approximated effectiveness of the model. [PERSON] et al. [4] numerically investigated the flow characteristics and made entropy generation analysis of Al\({}_{2}\)O\({}_{3}\)-water nanofluid in microchannel plate fin heat sinks. [PERSON] et al. [5] numerically investigated flow characteristics in hydrodynamic entrance region of rectangular microchannels with lattice Boltzmann method. [PERSON] et al. [6] studied the jet impingement thermal performance of plate fin and pin fin heat sinks through experiments and numeric analysis, and built a model with volume average method to investigate the pressure drop and thermal performance. They found that optimized pin fin heat sinks demonstrated relatively better thermal performance for low pumping power. [PERSON] et al. [7] investigated the turbulent flow and thermal transfer characteristics for the rotating and stationary pin-fin heat sinks subjected to impinging air flow by means of numerical solutions. The effects of fillet profiles setting at the bottom of channels on fluid flow and heat performance of an impinging flow plate fin heat sink were investigated numerically by [PERSON] and [PERSON] [8]. [PERSON] et al. [9] proposed an improved solution to investigate the distributions of velocity and temperature of a parallel-flow plate heat sink with uniform impingement. [PERSON] et al. [10] experimentally investigated the influences of cross flow area and pin fin shapes on the single-phase impingement point heat transfer coefficients for micro pin fins. [PERSON] et al. [11] made numerical simulations to analyze heat transfer characteristics of jet impingement with a novel single cone heat sink. It is found that the heat transfer capability of a cone heat sink with fluid impingement is better than that of a conventional plate fin heat sink. In order to analyze the effect of fin shapes on the heat sink property, [PERSON] et al. [12] investigated the distributions of the flow fields and temperature fields of heat sinks with short plate fins subjected to impinging flow. The pressure drop for three sets of fin shapes including rectangular, round-headed, and elliptic were studied in this paper. They found that the fin shapes have prominent influence on the secondary flow as well as flow separation. [PERSON] et al.