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/m(2) with a gap of 0.4 KW/m(2) 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/m(2) for PCM volume fraction 0.83. Afterwards, RT-44HC/Copper foam reveals maximum temperature reduction of 24% for 1.6 KW/m(2). RT35HC/Copper foam is least efficient at 2.4 KW/m(2) 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 degrees C and 60 degrees C for respective composites. (C) 2018 Elsevier Ltd. All rights reserved.