The Effects of Working Fluid on the Heat Transport Capacity of a Microheat Pipe

The effects of the thermophysical properties of the working fluid on the performance of a microheat pipe of triangular cross section are investigated. For this purpose, five different working fluids are selected: water, hepthane, ammonia, methanol, and ethanol. For operating temperatures ranging from $20°Cto100°C$⁠, it is found that the behavior of the heat transport capacity is dominated by a property of the working fluid, which is equal to the ratio of the surface tension and dynamic viscosity $σ∕μl$⁠. This property has the same dimension as velocity and can be interpreted as a measure of the working fluid’s rate of circulation, which can be provided by capillarity after overcoming the effect of viscosity. Of the five working fluids selected, ammonia is preferable for operating temperatures below $50°C$ since it yields the highest heat transport capacity; however, water is the preferred working fluid for temperatures above $50°C$⁠.