The apparatus consists of fabricated SS shell, inside which SS tubes are fitted. Hot water passes to one end through the tubes and exit to another end. The cold water is admitted at the one end of shell, which passes over the hot-water tubes. The tubes are arranged in the shell so that the flow of cold and hot fluid crosses each other to make it cross flow. Valves are provided to control the flow rates of hot and cold water. Flow rates of hot and cold water are measured using Rotameters. A magnetic drive pump is used to circulate the hot water from a re-cycled type water tank, which is fitted with heaters and Digital Temperature Controller. Cold water is to be supplied by laboratory overhead tank by end user.