Current CFD simulation studies of large data centers cannot model the detailed geometries of the perforated tiles due to grid size limitation. These studies often assume that the tile flow can be modeled as constant velocity based on a fully open tile. In this case, mass flux is enforced at the expense of under-predicting momentum flux; the error in momentum flux can be as high as a factor of four for a 25% open perforated tile. Since jet entrainment is a strong function of its initial momentum flux, this error can be significant with respect to predicting the mixing of the surrounding room air into the tile flow. Combined experimental and computational studies were carried out to quantify the importance of the detailed tile geometry, and it was found that proper prediction of the mixing process must account for the tile opening patterns. Suggestions of how to model the floor perforated tiles in data center CFD simulations are then presented.

An improved CFD model is presented to predict the thermal field in a small data center test cell. CFD analysis reported in an earlier paper tended to exaggerate hot and cold spots in a small data center test cell as a result of the inability of the CFD model to predict the correct level of mixing of the cold air emanating from the perforated floor tiles and the warmer room air. The same can be said about the mixing of the hot air stream exiting the rack and the surrounding room air. The overall RMS error in the earlier study was 4°C between numerical results and test data. Another indication of low mixing in the CFD results is illustrated in the comparison of the temperature profile along a vertical line in front of the rack between CFD results and test data. While the temperature of the cold flow from the under floor plenum entering the data center was measured to be 12.8°C, temperature measurement at the same location via a temperature mapping tool showed that it is 15°C at 6" above the floor and rising quickly to 17°C at a height of 4 ft. The present investigations yield several improvements to the CFD model, including modeling of the perforated tile flow and rack exhaust flow to conserve both mass and momentum, inclusion of the effects of buoyancy, and an improved thermal boundary condition for the floor. With these improvements, the overall RMS error was reduced to 2°C between numerical results and the same test data reported in.

There is a need in the IT industry for CFD models that are capable of accurately predicting the thermal distributions in high power density open-aisle air-cooled data centers for use in the design of these facilities with reduced cooling needs. A recent detailed evaluation of a small data center cell equipped with one high power rack using current CFD practice showed that the CFD results were not accurate. The simulation results exhibited pronounced hot/cold spots in the data center while the test data were much more diffused, indicating that the CFD model under-predicted the mixing process between the cold tile flow and the hot rack exhaust flow with the warm room air. In this study, a parametric study was carried out to identify CFD modeling issues that contributed to this error. Through a combined experimental and computational investigation, it was found that the boundary condition imposed at the perforated surfaces (e.g., perforated tiles and rack exhaust door) as fully open surfaces was the main source of error. This method enforces the correct mass flux but the initial jet momentum is under-specified. A momentum source model proposed for these perforated surfaces is found to improve the CFD results significantly. Another CFD modeling refinement shown to improve CFD predictions is the inclusion of some large-scale geometrical features of the perforated surfaces (e.g., lands/gaps) in the CFD model, but this refinement requires the use of grids finer than those typically used in practice.

The aim of the present study is to numerically investigate the thermal performance of a heat exchanger tube fitted with vortex generator inserts. In the present paper, three configurations of vortex generators—straight, double-curved, and triple-curved—are proposed to achieve the optimum configuration design that provides the highest thermal performance. The thermal performance results of the tubes fitted with the proposed vortex generators are compared with those fitted with a classical twisted tape and a plain tube. The triple-curved vortex generator, which is tested at four different pitch ratios (5, 4, 3, and 2), exhibits the highest thermal performance at a low Reynolds number. The numerical results indicate that the thermal performance increases as the pitch ratio decreases. Compared with the twisted tape, if the triple-curved vortex generator is employed at a pitch ratio of 2, the thermal performance can improve by approximately 24%. Using the numerical results of the current study, dimensionless correlations for the triple-curved vortex generator are developed and presented in this paper.

In this research, the impact of integrating solar still with thermal energy storage material and flat plate solar collector (FPSC) on the freshwater productivity was experimentally investigated. The experiments were conducted on three types of similar-sized solar stills under climate conditions of Saudi Arabia. The first type was a conventional solar still (CSS), without any modifications. The second type was a modified solar still (MSS-1), CSS integrated with natural stones in the still basin. The third type was a modified solar still (MSS-2), CSS integrated with both natural stones and FPSC. Three types of natural stones with same quantity were selected and individually tested in the MSS-1 and MSS-2 simultaneously (each stone type on one day). The corresponding experimental results of MSS-1 showed a 11–32% increase in the daily freshwater yield, compared to CSS, indicating a minimal effect of natural stones utilization on the freshwater productivity. The MSS-2 showed a 155–183% increase in the daily freshwater yield, compared to CSS, indicating a significant effect of basin water heating on the freshwater productivity. The total dissolved solids (TDS) level was measured at 112 ppm, which complies with the permissible limits for drinking water quality standards. The economic analysis revealed that the cost to produce one liter of freshwater is 0.028, 0.022, and 0.027 $ from CSS, MSS-1, and MSS-2, respectively. Additionally, the benefit–cost ratio (BCR) analysis demonstrated the economic feasibility of the constructed solar still, with a BCR value of 2.1.

The aim of this study is to experimentally investigate the impact of several design parameters on the performance of an active solar still that is typically used to produce desalinated water. Thus, a solar still with 1 × 1 m² basin area and 1 m height has been designed and constructed to carry out the experiments. This solar still was integrated with a photovoltaic unit to generate electricity to power two circulation pumps (CPs) and one electric heater (EH). These CPs and EH were immersed in the water basin to increase the turbulence intensity and temperature of the water molecules in the still basin and hence increase the water productivity. The impact of varying the water depth, circulating the basin water via CPs, and heating the basin water via EH on the solar still performance has been evaluated in a conventional solar still (CSS), an active solar still (CSS with CPs), and another active solar still (CSS with CPs and EH). The experimental results revealed that the water productivity increases as the water depth decreases: the daily productivity of the CSS with CPs increased by approximately 10% when the water depth was decreased from 6 to 3 cm. Moreover, compared to that of CSS at a water depth of 3 cm, the daily water productivity increased approximately 20% and 24% in cases of CSS with CPs and CSS with CPs and EH, respectively. Finally, an economic study was carried out to confirm the feasibility of the solar still. This study illustrated that the constructed solar still is economically feasible, and the estimated benefit-cost ratio is 4.1.