A.B. Russell

Experimental and numerical analysis of the temperature transition of a suspended freezing water droplet

Abstract The objective of this study was to develop a simple experimental and numerical method to study the temperature transition of freezing droplets. One experimental approach and several numerical methods were explored. For the experimental method, a droplet was suspended in a cold air stream from the junction of a thermocouple. The droplet’s temperature transition was able to be accurately measured and the freezing of the droplet observed. The numerical models developed were able to predict the temperature transition and the freezing time of the droplet. Of the numerical methods, a simple heat balance model was determined to be an accurate means of predicting the freezing time of the droplet.

Simulation and experiment of the unsteady heat transport in the onset time of nucleation and crystallization of ice from the subcooled solution

Abstract Heat transfer is an unsteady process in the initial period of ice nucleation or phase transition from aqueous solution. During this period the latent heat of freezing increases the temperature in bulk solution monotonously until the system reaches equilibrium. Meanwhile heat can transfer from the solution to the environment or vise versa. The analysis of this unsteady heat transfer process leads to the establishment of a mathematical model, which is represented by two simultaneous differential equations. Using the Laplace transform and inverse transform, and incorporating the initial condition of ice nucleation, we obtained an analytical solution of this model. Further discussion of the model’s fitness by comparing to the experimental data leads to a recognition that ice fouling (or ice adhesion) on the cooler wall should be highlighted in estimating the heat transfer resistance at the very beginning of the ice formation. The model fits to the experimental data satisfactorily.

An experimental study of an NaClO generator for anti-microbial applications in the food industry

Abstract A pilot scale sodium hypochlorite (NaClO) continuous generator is described in this paper, which was used for anti-microbial applications, basically for cleaning-in-place (CIP) or sterilizing-in-place (SIP), in food industry. The electrolytic cell was constructed as a tubular electrochemical reactor with a nylon net membrane between the electrodes and with a layer of rare-earth metallic oxide, RuO 2 , as catalytic coating on the titanium-anode surface. The performance of this sodium hypochlorite continuous generator was analyzed from a reaction engineering view point. The electric current efficiency was above 82% and the consumption of sodium chlorine was 2.7 kg for producing 1 kg of available chlorine (Cl 2 ). The sterilizing water production rate ranged from 810 to 1080 l per hour with an available chlorine concentration of 200–150 ppm.

Ice fouling on a subcooled metal surface examined by thermo-response and electrical conductivity

Freeze concentration is an excellent alternative to evaporation and reverse osmosis for pre-concentration of many liquid foods. However, the build-up of an ice layer on the cooler surface, which is known as ice fouling, is unavoidable even at a low degree of supercooling, e.g. around 0.2 °C. This significantly reduces the heat-extraction rate and increases the cost of freeze concentration. In this study, we found that the onset time of ice fouling on the subcooled metal surface can be indicated by the step increase of the surface temperature due to the release of the latent heat of fusion. We also developed a method to indicate the ice fouling induction time on the cooler surface according to an increase of the AC impedance between the solution and the cooler surface. A mathematical model is presented which correlates the fouling induction time to the degree of supercooling. Factors influencing the ice fouling are studied and discussed in this paper.