Temperature control for biological experiments in an automated modular environment

In biological experiments, temperature control is required to maintain cell growth, inhibit cell activity, or to trigger bio-chemical reactions [1]. In manual experiments it is very common to obtain the constant temperature source from constant temperature water baths or buckets filled with a mixture of water and ice. While these devices are able to maintain certain pre-defined temperatures, they do not meet the needs of the automation of biological experiments. This paper presents combined heat source and sink which requires only electrical energy and is suitable for automated experiments that require different temperature levels. A thermoelectric cooling (Peltier element) is used as a heat sink while an electrical heating element serves as heat source. Water is used as the heat transfer medium. A variable speed peristaltic pump circulates the water from the two constant temperature sources to the point of interest, and the flow velocity is adjusted based on water bath temperature. To avoid unnecessary mixing of water and heat transfer between the two constant temperature sources, solenoid valves are used to isolate one tank while the other is in use. Experiments show that the system can adjust the temperature of an 80ml reservoir in the range of 5~45°C, and the accuracy is smaller than + 0.5°C, meeting the needs of biological experiments.