Category Archives: Particle Image Velocimetry (PIV)


Dunkle’s equation was originally applied in SOLSTILL to calculate the convective heat transfer between the basin water and the cover. This is in accordance with the approach used by the majority of previous researchers. The predicted temperature of the water in the still and the measured values are shown in Figure 3 while the predicted and measured distillate produced is shown in Figure 4. As shown in Figure 3, the predicted water temperature closely follows the trends in the measured data. The maximum discrepancy is 8 0C in the

most overcast day (i. e., the second day of testing), while the differences recorded for the rest of the days were up to 5 0C. Similar results were obtained for the predicted distillate from the still. The simulation model over-predicted the experimental result every day with a maximum error of 34 % on the cloudiest day. With the use of Dunkle’s equation, the model overpredicted the cumulative distillate by 14.7% over the 7 day period of testing.

Figure 4. The predicted distillate using the Dunkle model and measured distillate from the

standard still.


Manuel Collares-Pereira, INETI — Instit. Nac. Tecnologia e Engenharia Industrial — DER Joao Farinha Mendes, INETI — Instituto Nac. Tecnologia e Engenharia Industrial — DER Pedro Horta, INETI — Instituto Nacional de Tecnologia e Engenharia Industrial — DER

Water desalination is an important idea to alleviate potable water scarcity all around the World and there are already many commercial solutions. An important challenge still persists if one wants to use solar energy as the energy input to the system, thereby taking advantage of the fact that often this problem arises in areas of the world with abundant sunshine and little other energy resources.

The ongoing AQUASOL project [3] is one more attempt at putting solar energy to use in this context, with the objective of improving the economical and environmental performance of a MED desalination plant [1]. Within this project, reported elsewhere, an advanced solar dryer is being studied, allowing for brine concentration and/or ultimate salt recovery from the MED brine effluent. The idea is to add economical value to the investment in a MED plant, by providing one more product — salt — using the fact that the effluent of the MED plant has a higher salt concentration already and that the whole system might be integrated in a classical Saltworks, as one more step in the process.

1. Introduction

In recent decades, an increasing exploitation of water resources has lead to several forms of water shortage in many European regions (and elsewhere in the World), a problem assuming more alarming levels especially in semi-arid climate areas, where water, for human or agricultural consumption is either not supplied or supplied with scarcity and/or lack of quality. Often, in such areas, abundance of sea water and solar irradiation could use desalination as means for a medium-term sustainable process for potable water production. Yet, taking into account the proximity of sensible environments such as marine/tidal ecosystems, eventual negative impacts related with desalination effluent discharges must also be considered.

In light of the arguments above, the undergoing AQUASOL project [3] aims first at the development of a lower cost MED desalination technology with improved energy and environmental performance, promoting the use of solar energy both in the desalination and in the effluent treatment processes. The reduction of energy consumptions in the MED process, together with the exploitation of NaCl as a sub-product resulting from the effluent treatment process through brine concentration in a solar passive dryer, constitute likely means to accomplish a lower water cost objective. This will hopefully increase the competitiveness of MED technology when compared with the more common RO process. The present paper addresses the effluent treatment issue, taking into account the specificities of NaCl production. After development of a new concept of a passive solar dryer, based in the study of a numerical model describing dryer operation under given yearly climate conditions, a prototype is under test, allowing a deeper knowledge of the design and identification of further evaporation enhancement strategies.

The paper is organized as follows: in 2. a description of the dryer prototype is made; in 3. an overview of preliminary evaporation results, as well as comparison with simulation results, after the original numerical model, is presented; in 4. results analysis and numerical model correction is addressed; in 5. a brief idea is given of further prototype developments; in 6 a simulation of yearly results for the corrected numerical model is presented, and in 7 conclusions are presented.

Advanced Storage Concepts for Solar Combisystems

H. Druck, W. Heidemann, H. Mtiller-Steinhagen

Universitat Stuttgart, Institut fur Thermodynamik und Warmetechnik (ITW) Pfaffenwaldring 6, D-70550 Stuttgart Tel.: 0711/685-3536, Fax: 0711/685-3503

email: drueck@itw. uni-stuttgart. de, Internet: http://www. itw. uni-stuttgart. de

Using a typical single family house in Germany as an example, the influence of the solar collector area and the store volume on the energy savings is determined by means of numerical system simulations. Based on these results it is outlined how the system performance can be increased by using advanced storage concepts.

In particular the following storage concepts are investigated:

• hot water stores with improved thermal insulation (e. g. with vacuum insulation)

• stores using phase change materials (latent heat stores)

• thermochemical energy stores (e. g. based on sorption)

In addition to the primary energy savings that can be achieved with the different heat storage technologies and system concepts, the resulting solar thermal heat prices and the energy payback times are discussed.

1 Introduction

Thermal solar systems for domestic hot water preparation and space heating, so-called solar combisystems, are already introduced to the market, and their market share is increasing continuously. Today standardised solar combisystems consist of a solar collector with an area between 10 m2 to 20 m2 and a hot water storage tank with a volume in the range of 0.7 — 1.5 m3. If such systems are installed in a „typical" middle European single family house, they can save approximately 20 — 30 % of the primary energy required for domestic hot water preparation and space heating. In order to increase the energy savings, larger collector areas and/or store volumes are required.