Comprehensive numerical studies of thermal management of data centers were presented by several
investigators for different geometric and operating conditions of data centers. In the present work, a technical note regarding the effect of the computer room air conditioning (CRAC) units layout arrangements is
presented. Two arrangements of CRAC units layouts are investigated; namely locating CRACs units in line
with the racks row and locating the CRACs units perpendicular to the rack row. Temperature distributions, air flow characteristics particularly air recirculation and bypass and thermal management in data
centers are evaluated in terms of the measureable overall performance parameters: supply/return heat
indices (SHI/RHI) and return temperature indices (RTI). The results showed that locating CRAC units perpendicular to the racks row has the following effects: (i) enhances the uniformity of the air flow from the
perforated tiles along the rack row, (ii) reduces the hot air recirculation at the ends racks of the row and
the cold air bypass at the middle rack of the row and (iii) enhances the data center performance parameters RTI, SHI and RHI.