Investigating the heating of water through a double tube nonphase change heat pipe

Abstract

The heat pipe has been used extensively in modern day heat management due to its high thermal conductance and it is considered as the device of the 21st century. The heat pipe is capable of functioning at temperature as high as 1800°C to temperature as low as -230°C depending on its working medium. It is not dependent on the evaporation-condensation cycle (phase change) of the working medium but on the pressure response. The pressure response is dependent on the temperature difference when a fully filling state of the working medium in the heat pipe is attained. The NPC-HP's ability to conduct heat in the radial direction using a special configuration of the NPC-HP, i. e, the double tube NPC-HP was investigated in this research. Here, the heat pipe is constructed with an outer and inner shell, where the working medium is charged in the annulus between the larger and smaller tube. The surface temperature of the inner tube without any flow of water was found to be homogenous and the average temperature was 66.63 °C. A wavy pattern of temperature distribution was observed throughout the length of pipe geometry and it indicated that the working fluid would remain in phase change suppressed mode. The change of equivalent resistivity with heat transfer rate demonstrated that three distinct heat transfer mode, namely natural convection mode, phase change and pulsation mode and phase change suppressed mode occurred. At different heating and cooling condition, the double tube NPC-HP exhibits a different heat transfer characteristics and at high heat transfer rate, the resistivity of the double tube NPC-HP approaches a near constant value of 0.02K/W in radial direction which is not possible in a conventional simple wicked heat pipe. As NPC-HP can be operated in phase change suppressed mode at high heat transfer rate, hence it can be used to store energy temporarily and to act as a buffer. Moreover, it can be used to preheat heavy oil.