## 3 Results and Discussion  
The number of grids has great influence on the time and precision of calculation. So we choose the number of grids considering both the precision requirements and computational time. Several appropriate grids that are suitable need to be designed. The number of grids was changed from approximately 33,655 to 3,876,420 nodes, and the numerical simulation results are summarized in Figure 3.  
As shown in Figure 3, the result is almost independent of grid numbers and there is no significant change of the pressure drop results for different grids. The results of pressure drop for the plate fin heat sink with the number of grids of 33,655 has a relatively large deviation, and the maximum error is nearly 2%. The results of pressure drop for the number of grids of 465,234 and 3,876,420 match quite well, the deviation is 1% which is relatively small. A grid of 465,234 nodes was chosen for the grid number of these numerical simulations considering computational time. The experiments of pressure drop for plate fin heat sinks in laminar regime with different inlet widths subjected to impinging air flow were conducted by [PERSON] and [PERSON] [3]. [PERSON] et al. [43] also made numerical simulations for pressure drop of plate fin heat sinks subjected to impinging air flow with the software ICEPAK produced by ANSYS Inc. Figure 4 compares the pressure drop for  
Figure 3: Grid independence verification results. plate fin heat sink subjected to impinging air flow obtained in the present study with that conducted by [PERSON] and [PERSON] [3] and [PERSON] et al. [43]. As shown in Figure 4, the pressure drop results obtained from the numerical simulation have a great consistency compared with those experimental data by [PERSON] and [PERSON] [3] and simulation results by [PERSON] et al. [43]. Numerical simulation pressure drop results obtained by [PERSON] et al. and the numerical simulations in the present study match well and the maximum error is within 15%. The agreement of pressure drop results between present numerical simulations and the experimental data obtained by [PERSON] and [PERSON] [3] is quite satisfying in view of the uncertainties of pressure drop measurements. The effectiveness of the results obtained in the present paper was validated well. In this paper, we also compare the pressure drop of number 1 plate fin heat sink for \(s=10\%\)\(L\) obtained from present numerical simulations with that obtained by experiments performed by [PERSON] and [PERSON] [3]. As shown in Figure 5, the error bars of 20% is sketched in this picture and the present results agree well with the experimental results by [PERSON] and [PERSON] [3]. All the points lie within the range of experimental uncertainties and the maximum deviation is no more than 18% which is fairly fulfilling in consideration of uncertainty. The results of pressure drop obtained from different research groups are shown in Figures 5 and 6. The numerical simulations are performed with different channel widths for \(b=1.44\) mm and \(b=2\) mm. The length and width used in this model are set to be 40 mm and 40 mm and the fin thickness is 0.5 mm, which is consistent with the model geometry parameters of [PERSON] et al. [6]. Figure 6 showed that the present results by numerical simulations are in great agreement with the experimental results obtained from [PERSON] et al. [6]. As shown in Figure 6, the maximum deviation of the present results and the experimental results obtained by [PERSON] et al. [6] is 19%. The results acquired from numerical simulations are in agreement with experimental data provided by [PERSON] et al. [6] in consideration of relatively large uncertainty for the experimental measurement. Figure 4: Comparison between the present results and experimental data by [PERSON] and [PERSON] [3] and simulation results by [PERSON] et al. [43]. This paper investigates the pressure drop of the plate fin heat sink subjected to impinging air flow with different inlet widths, fin heights, and the shapes of flow channels.