Charging and Discharging Characteristics of Spherical Ice Storage Capsule : Part 1-Visualization of Freezing Processes and Its Model

Abstract

Recently a heat storage tank using spherical ice storage capsules has been used because of high heat transfer rate and high density of stored heat. In order to design the ice storage tank of this type optimally and to operate it effectively, it is necessary to predict its charging and discharging characteristics with high accuracy. For the sake of this achievement, it is also necessary to investigate the model that reveals phase changing phenomena accurately to estimate heat transfer characteristics of a spherical ice storage capsule. In this paper, freezing processes inside the spherical capsule were visualized and measurements of its freezing rate were conducted. A freezing model considering the volume change caused by phase changing and inside air room to absolve it was proposed. Coefficient of Heat transfer rates calculated from the proposed model were compared with that measured. Good agreements were obtained between measured and calculated results. Furthermore the proposed model was compared with conventional ones. It was found that, at beginning of freezing, calculated heat transfer rates from conventional models are more than 20% higher than that from the proposed one.