Ice Slurry System Research Articles

Cold storage with ice slurries

The storage of ‘cold’ with ice slurries—a special type of thermally multi-functional fluids or phase change slurries (PCS)—is discussed. At first an example of a calculation of a thermal energy storage tank in an ice slurry system with a peak load demand is presented. Then a new concept of ice slurry storage without mixing is introduced. It leads to ice particle stratification and front propagation in the storage vessel. The stratification of ice particles in ice slurry is theoretically described by multi-component multi-phase fluid dynamics. The resulting stratification process is calculated and front propagation times are compared with experimental results; they compare fairly well. Copyright © 2007 John Wiley & Sons, Ltd.

Superheating of ice slurry in melting heat exchangers

One of the main components of an ice slurry system is the melting heat exchanger, in which ice slurry absorbs heat resulting in the melting of ice crystals. Design calculations of melting heat exchangers are mainly based on heat transfer and pressure drop data, but recent experimental studies have shown that superheating of ice slurry should also be considered. This paper presents ice slurry melting experiments with a tube-in-tube heat transfer coil. The experimental results indicate that operating conditions such as ice slurry velocity, heat flux, solute concentration, ice fraction, and ice crystal size determine the degree of superheating. The various influences are explained by considering the melting process as a two-stage process consisting of the heat transfer between wall and liquid and the combined heat and mass transfer between liquid and crystals. Bigger ice crystals and higher solute concentrations decrease the rate of the second stage and therefore increase the degree of superheating.

Ice slurry: Pressure drop and deposition velocity

Ice slurries are used in indirect refrigeration systems. The storage tank of ice slurry systems decreases the maximum required cooling capacity of the equipment and smooths down the installation consumption. An advantage of ice slurry systems compared to chilled water systems is the higher cooling energy that can be delivered to customers using the same installed pipes. This paper gives a complete investigation of ice slurry pressure drops and deposition velocity. A model for the friction factor, obtained by empirical and semi-empirical approximation, is discussed. A new simple and efficient method is introduced to find the deposition velocity in an ice slurry fluid flow. Finally a variety of experimental results and some theoretical calculations of ice slurry flow patterns are shown.

Comparison of the performance of different ice slurry types depending on the application temperature

The ice slurry medium type used in a refrigeration application could influence the performance of an ice slurry system. For this reason and depending on the refrigeration application, the user has to usually carry out a judgemental selection of the ice slurry mixture type, which should take into account the solute type and its concentration. This article compares the performance of several commonly used organic and inorganic ice slurry secondary refrigerants. This study was based on thermophysical assessments carried out at different operating temperatures. The calculation method that was used to determine the ice slurry properties is first presented. Then, in order to describe the thermophysical efficiency of mixtures at various operating temperatures (−5, −20 and −35 °C), three performance criteria were compared, namely, the volume enthalpy drop, the temperature at the inlet of the application and the relative viscosity of the ice slurry. The results showed that inorganic mixtures are good selection candidates, except for situations where low temperatures and high ice concentrations are encountered at the inlet of the application. Methyl alcohol came out as a good performance candidate for all refrigeration applications, although NH 3 was the best choice based on the current thermo-physical property assessments.

Melting of ice slurry in a tube-in-tube heat exchanger

One of the main components of a closed ice slurry system is the heat exchanger in which ice slurry absorbs heat resulting in the melting ice crystals. Design calculations of heat exchangers are mainly based on heat transfer coefficient and pressure drop data. But experiments presented in this paper show the effect of ice slurry mass flux on heat transfer rate and heat transfer coefficient during melting. For the experiments, ice slurry was made from 6.5% ethylene glycol–water solution, flowing through a 16.91mm internal diameter, 1500mm long horizontal copper tube. The ice slurry was heated by hot water circulated at the annulus gap of the heat exchanger. Experiments of the melting process were conducted with changing the ice slurry mass flux and the ice fraction from 800 to 3500kgm−2s−1 and 0 to 25%, respectively. During the experiment, it was found that the measured heat transfer rates increase with the mass flow rate and ice fraction; however, the effect of ice fraction appears not to be significant at high mass flow rate. At the region of low mass flow rates, a sharp increase in the heat transfer coefficient was observed when the ice fraction was more than a certain value. Experiments were also conducted to investigate the effect of hot water temperature on the heat transfer coefficient. Copyright © 2006 John Wiley & Sons, Ltd.

05/02763 Performance of components of ice slurry systems: pumps, plate heat exchangers, and fittings

05/02763 Performance of components of ice slurry systems: pumps, plate heat exchangers, and fittings

The control of ice slurry systems: an overview

This article outlines some typical control strategies for the basic components of an ice slurry system. From this review it became apparent that the control of terminal units is not fundamentally different from the control of classical single-phase secondary cooling systems, except from the fact that it must be based on the use of local pumps and the ON–OFF operation of actuators to avoid ice plugging problems. The safe control of the ice generator can be ensured with a simple thermostat, although the resulting ice concentration control would be approximate. It was also demonstrated that any ice accumulation in the storage tank would not prevent the ice slurry system from functioning safely. As a final precaution, it was not recommended to operate an ice slurry generator at low solute concentrations and temperatures greater than −3/−4 °C due to the risk of plugging up the distribution loop and causing mechanical wear to the ice generator.

Performance of components of ice slurry systems: pumps, plate heat exchangers, and fittings

In recent years, a lot of important work has been carried out in order to gather knowledge of the fundamental behaviour of ice slurry in piping systems and heat exchangers. The scope of this work has been to bring ice slurry one step closer to practical application, i.e. to provide a basis for selecting distribution pumps and investigating flow in piping system components. The performance of different multiple-stage centrifugal pumps has been measured with ice concentrations in the range from 0 to 30 wt% of ice. It was found that the pump operation is reliable in the entire range of ice concentrations. The pump performance decreases with increasing ice concentration due to the increasing viscosity of the ice slurry. The viscosity model proposed by Hansen [Viscosity of ice slurry. Second IIR Workshop, Paris, France (2000)] has been applied to compare the manufacturer data on the viscosity dependency. From the results, it cannot be concluded whether the pump performance is entirely determined by the increasing viscosity or whether the solid particles have an additional effect. The flow behaviour of ice slurry has been investigated in a test rig with transparent pipes to allow visual observation of flow patterns in various single components such as fittings, valves and heat exchangers. Finally, pressure loss coefficients in selected fittings have been measured to reveal the dependency of ice concentration.

Time-dependent behavior of different ice slurries during storage

One of the main advantages of ice slurry as secondary refrigerant is the possibility of cold storage, which enables load shifting and peak shaving. During cold storage, ice crystals are subject to mechanisms as attrition, agglomeration and Ostwald ripening causing changes in the crystal size distribution, which are of great importance for ice slurry systems since they influence other parameters such as pressure drop and heat transfer characteristics. Storage experiments with ice crystals in aqueous solutions of sodium chloride, ethylene glycol, ethanol and propylene glycol show that Ostwald ripening is the most important mechanism inducing an increase in average crystal size. The ripening rate strongly decreases as the solute concentration increases and the type of solute and the mixing regime also play an important role. The different ripening rates are caused by the fact that crystal growth and dissolution by means of Ostwald ripening are mainly limited by surface integration kinetics at low concentrations and by mass transfer at high solute concentrations.

CO2 Hydrates in Refrigeration Processes

Global warming concerns have led the refrigeration industry to seek and develop new refrigeration systems with a reduced impact on the environment. The use of two-phase secondary refrigerants generated by a primary closed refrigeration circuit is a promising solution. Solid−fluid secondary refrigerants are known for their higher energy efficiency compared to single-phase fluids, because of the additional latent heat of the solid phase. The objective of the present work is to investigate experimentally the latent heat of CO2 hydrate−ice mixture systems in comparison to that of ice slurry systems. By using a new DTA apparatus, the CO2 hydrate−ice mixture was shown to offer a dissociation enthalpy of 507 kJ/kg that is higher than that of ice (333 kJ/kg). Artificial tuned CO2 hydrate−fluid systems appear to be an environment-friendly alternative for refrigeration and air-conditioning systems that can be used in a wide range of applications.

Control of molecular-level ice crystallization using antifreeze protein and silane coupling agent

To obtain acceptable ice-slurry characteristics for low-temperature energy storage and transport systems, methods for preventing ice recrystallization must be developed. Antifreeze proteins (AFPs) are known to be an effective additive in ice-slurry systems, making ice slurries resistant to recrystallization, and thereby improving flowability. However, AFPs are expensive and easily degrade. Therefore, we investigated the use of silane coupling agents (SCAs) as substitutes for AFPs. To determine the SCA's ability to control crystallization, in this study we observed free growth of ice crystals in SCA solutions, and found that SCAs that form long-chain molecules in water are effective for crystallization control. Then we analyzed ice crystal surfaces containing AFPs and SCAs by using scanning tunneling microscopy (STM) to investigate the mechanism of crystallization control with these additives. STM observation of ice crystal surfaces showed that the AFP molecules are adsorbed onto the ice crystal surface on the {202̄1} planes along the 〈011̄2〉 directions, preventing further crystal growth from the site where the AFP molecules are adsorbed. Furthermore, we found that long-chain SCA molecules are adsorbed onto ice crystal surfaces, preventing crystal growth from the site where the long-chain SCA molecules are adsorbed.

Investigation of the Characteristics of Ice Slurry Containing Antifreeze Protein for Ice Storage Applications.

Ice slurry systems have recently attracted much attention in Japan for their ability to reduce electricity peaks caused by high energy-consumption by air-conditioners in the daytime. While conventional storage systems involve compact ice generation, these days ice slurry systems are introduced for transporting flowable ice in pipelines. Even though seveal methods for dynamic ice formation have been researched and developed, there are still problems related to the recrystallization of ice crystals for realizing long-term storage and long-distance transportation. Antifreeze proteins (AFPs) strongly influence ice crystal growth by adsorption to the ice crystal surface. In this paper. we present results from investigations of ice slurry made from an AFP solution, and of its thermophysical properties such as thermal storage and flowability characteristics, as well as the results from observation of crystal growth and ice slurry flow. For ice storage applications, the benefits of this additive are the ability to create well-defined crystal structures and the inhibition of recrystallization.

Microscale Analysis of Crystals in Ice Slurry Made from an Antifreeze Protein Solution.

In order to clarify the crystal growth mechanism and to tealize the low-terperature heat transportation system of ice slurry made from an antifreeze protein (AFP) solution which consists of ice crystals resistant to recrystallization, a fundamental and microscale analysis has been conducted on the ice crystals. Since the thermophysical propertics of ice slurry used for ice storage applications, such as energy storage ability and flowability, depend on the shape and size of individual crystals, crystal growth patterns were experimentally investigated by changing the local supercooling temperature while neglecting the influence of heat flux. At low temperatures, when supercooling exceeded a certain transition value, dendritic crystals were generated, which were apparently unaffected by the existence of AFP. In between the transition terperature and the freezing point, needle-like crystals were observed to grow rapidly in the c-axis direction. If these needle-like crystals were held at terperatures within the hysteresis gap (between the freezing and the melting point), bipyramidal crystals within a maximum tip angle of approximately 30° were formed. Since protein adsorption to the ice crystal surface will strongly affect the crystal growth, the surface of crystals was investigated by using a Scanning Tunneling Microscope (STM) in order to determine the influence of AFP on the microscale surface struture. A systematic groov/ridge pattern that was aligned 65° (±5°) to the hexagonal side on one bipyramidal plane was observed. The grooves' length and width were similar to the length and width of AFP, indicating adsorption of single protein molecules to ice with an orientation corresponding to the alignment angle. Their depth, ranging from 2 nm to 10 nm, gives information about the surface curvature. Knowledge from microscale analysis can be used in order to create cost-effective artificial additives for ice slurry systems.

Ice thermal storage: Application to demand-side management in the United Kingdom†

The paper investigates the use of ice storage technology as a demand side management tool. A theoretical study of a dairy application is described in which the costs of running an ice storage installation under a traditional maximum demand tariff are compared with those under a pool-based contract. The paper also describes a new dynamic ice slurry system currently under development.