Abstract: This invention relates to a process for cooling a product in a heat exchanger, the process comprising: flowing a refrigerant through a set of first microchannels in the heat exchanger; flowing a refrigerant through a set of second microchannels in the heat exchanger, the refrigerant flowing through the set of second microchannels being at a lower temperature, a lower pressure or both a lower temperature and a lower pressure than the refrigerant flowing through the set of first microchannels; and flowing a product through a set of third microchannels in the heat exchanger, the product exiting the set of third microchannels having a cooler temperature than the product entering the set of third microchannels. This process is suitable for liquefying gaseous products including natural gas.