Copper foam (with porosity 97 and pore density 35 pores per inch) based heat sink without phase change material (PCM) and copper foam/PCM composites heat sinks are investigated to observe the behavior of operational time of heat sinks with respect to specific temperature both for charging and discharging. Paraffin wax, RT-35HC, RT-44HC and RT-54HC are used as PCM. Investigations are performed at heat flux of 0.8�2.4 KW/m2 with a gap of 0.4 KW/m2 uniformly distributed. PCM volume fractions of 0.68 and 0.83 are used in composites. Results indicated that at the end of 90 min charging, maximum temperature reduction of 25 is noted for RT-35HC/Copper foam at 0.8 KW/m2 for PCM volume fraction 0.83. Afterwards, RT-44HC/Copper foam reveals maximum temperature reduction of 24 for 1.6 KW/m2. RT-35HC/Copper foam is least efficient at 2.4 KW/m2 which reduces the base temperature only by 5�7. Maximum enhancement ratio in operation time is noticed as 8 and 7.7 for RT-35HC/Copper foam and RT-44HC/Copper foam respectively at set point temperature (SPT) of 40 °C and 60 °C for respective composites. © 2018 Elsevier Ltd