Fig. 2.
Effect of shape and surface area on precision and tunability of miniature heaters. (A) Design criteria of the miniature heater. We want the heater to be within 5 °C of precision and achieve tunable temperatures in the range of 37 °C to 65 °C (∆TRT = 12 °C to 40 °C). (B) Photographs of miniature heaters with star-shaped vs. circular inner channels in water. Star-shaped inner channels continuously heat the water while clearing hydrogen bubbles, while circular channels result in irregular heating due to lack of hydrogen bubble clearance. Scale of heater: 8 mm. (C) Thermal profile of star-shaped vs. circular channeled miniature heaters (n = 3). Star-shaped channels provide precise heating (<5 °C) while circular channels provide irregular heating (>5 °C). (D) Mechanism of the role of shape on precise heating. Sharper angled channels can retain more water at their angles and provide access to water despite hydrogen bubble generation. (E) Effect of channel surface area on tunability of temperature (n = 3). By varying the surface area of lithium accessing water, the final temperatures can be modulated. (F) Mechanism of effect of surface area on final temperatures. Higher surface areas provide larger masses of lithium accessing water to result in higher final temperatures. SALi = surface area of lithium; mLi = mass of lithium; TF = final temperature.