Some studies on ice slurry refrigeration system

Abstract

Compared to commonly used brines, the application of ice slurries in indirect refrigeration systems shows interesting advantages, such as the possibility of enhanced thermal storage and the reduction of transport friction losses due to the higher volumetric heat capacity. Among various ice slurry generation techniques, the scraped ice slurry generator is the most technologically developed and widely accepted ice slurry generation process. However, a widespread utilization of ice slurry systems has not taken place mainly attributed due to the high investment costs of commercially available ice slurry generators. In the present research work, a scraped surface ice slurry generator test rig has been designed, developed and fabricated with the help of cost effective manufacturing processes. Initially a scraped surface ice slurry generator test rig of five litre capacity has been developed. Based on the encouraging results a scraped surface ice slurry generator of 74 litre capacity has been designed, developed and fabricated successfully through commonly used cost effective manufacturing processes employed by small and medium scale industries with a focus on collection of experimental data related to ice slurry production using 10%, 20%, 30% and 40% concentrations of antifreezes (PG, MEG and DEG). R410A (refrigerant blend having zero ODP) is used as primary refrigerant in the primary refrigeration circuit. The lowest temperatures achieved were -20.7 0C, -25.6 0C and -19.9 0C respectively for PG, MEG and DEG for 40 % depressant concentration. The COP of present ice slurry generation test rig varies between 2.30 to 3.33. Thermophysical properties are significantly different as compared to the chilled water. Three distinct stages- cool down or chilling period, nucleation or unstable ice slurry generation period and stable ice slurry generation period were observed through historical time dependence curves. Experiments were conducted on a plate heat exchanger and heat transfer and pressure drop data were collected for water to water and ice slurry to water flow. The depressants use for ice slurry production are PG and MEG. Thermo-hydraulic modeling for PHE is validated with the experimental data. The parameters included in thermo-hydraulic modeling are overall heat transfer coefficient, cooling duty and pressure drop. It can be concluded that the present formulation provides the relationship to predict heat transfer based on the allowable pressure drops are reasonably matching with experimental data. The thermo-hydraulic model is useful for the design of individual PHEs. Keywords: Scraped surface ice slurry generator; Ice slurry; Depressants; Thermo- hydraulic modeling; Plate heat exchanger.