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Study on Thermal Flow Characteristics of Non-Newtonian Slurry Flow

Purpose

Recently, the realization of an energy-saving low-carbon society is required against environmental problems such as global warming. Heat energy sharing is effective for reducing the primary energy supply. A piping network system to share the heat (less than 100 ℃) exhausted from factories is proposed. In order to realize the system, it is required to decrease the temperature drop and to increase the heat transfer rate per mass flow rate. For the requirements, phase change material (PCM) slurry using latent heat of melting is expected for high efficient heat transport medium. Using the latent heat, the energy density per unit flow rate can be increased and the temperature drop during transportation can be suppressed. However, in the solidification process with heat radiation, there is a delay in latent heat supply due to a thermal resistance of the solidification layer. Therefore, fluid temperature may drop before the phase change completed. In a heat supply system using PCM slurry, the clarification of the heat transfer characteristics during during heating (heat storage) and cooling (heat release) is important issue.
The purpose of this study is to clarify the heat transfer characteristics of PCM slurry and to obtain the basic data for the heat exchanger design.

　

Research content

　

A PCM is packed in hard-shell microcapsules, and the microcapsules are dispersed in a surfactant solution. The hard-shell microcapsule is made of silica. Sodium acetate trihydrate is used for the PCM. Esocard is used for the surfactant. The fluid is non-Newtonian due to mixing the surfactant. PCM slurry is non-Newtonian microcapsule slurry.
Heat transfer coefficient and pressure drop are measured using a horizontal copper straight smooth tube with the inner diameter of 5 mm. The flow is heated by a silicon cord heater winded od the outer surface with the heating length of 805 mm. Wall temperatures are measured by thermocouple soldered on the outer surface at 7 points. Heat transfer and flow characteristics are compared among water, surfactant solution, microcapsule slurry with and without PCM. The influences of the dispersed microcapsules and non-Newtonian property on the heat transfer coefficient are investigated.


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