Mixed Storage Tank Research Articles

Discharge of a thermal storage tank using an immersed heat exchanger with an annular baffle

A number of solar domestic hot water systems and many combined space and water heating systems have heat exchangers placed directly in the storage fluid to charge and/or discharge the tank. Operation of the heat exchanger produces a buoyancy-driven flow within the storage fluid. With a view toward controlling the flow field to increase heat transfer, a cylindrical baffle is inserted in a 350 l cylindrical storage tank. The baffle creates a 40 mm annular gap adjacent to the tank wall. A 10 m-long, 0.3 m 2 copper coil heat exchanger is placed in the gap. The effects of the baffle on the transient heat transfer, delivered water temperature, heat exchanger effectiveness, and temperature distribution within the storage fluid are presented during discharge of initially thermally stratified and fully mixed storage tanks. The baffle increases the storage side convective heat transfer to the heat exchanger by 20%. This increase is attributed to higher storage fluid velocities across the heat exchanger.

A dynamic model of Ostwald ripening in ice suspensions

A computer-based dynamic model of Ostwald ripening in ice suspensions in a storage tank containing crystal growth kinetics, population, mass and energy balances has been developed to simulate the development of ice crystal size distributions during adiabatic ice slurry storage. The model assumed a homogeneously mixed storage tank with neither inlet nor outlet of mass. Growth and melting of ice crystals were caused by differences in equilibrium temperatures between differently sized crystals and crystal growth kinetics were based on heat and mass transfer. Validation with experimental results for different types and concentration of solutes, different ice fractions and different mixing rates showed that the model is able to predict the development of the average crystal size in time. Especially, the former two parameters have a strong effect on the ripening process, while the effect of the latter two is small. A difference between experimental and simulation results was found for the shape of the crystal size distribution curve after storage, which had a slightly longer tail during the experiments.

Transition time effects in collector systems coupled to a well mixed storage

Using analytical methods it is shown how transition times of fluids in collector arrays and system piping affect energy collection in solar systems with a well mixed storage tank. To a very good approximation this effect can be accounted for by a reduction factor multiplying the collector heat removal factor, F R . The effect is important especially for systems with a small ratio of storage volume flow rate to collector area, systems with a large fluid volume in the collectors and system with long connecting pipes. These all can be characterized by fluid transition times through collectors or piping which are not negligible relative to the fluid transition time in the storage tank. Such systems may appear as viable candidates in Industrial Process Heat applications.