Energy Performance Improvement of a Solar Still System Using Date and Olive Kernels: Experimental Study

Currently, solar distillation systems are used to contribute to solving the fresh water supply deficiency problem in some desert and rural areas. The present outdoor experimental work aims to improve the energy performance of a solar still installed in a semi-arid region. Experiments are performed using three solar distillers (a reference system, a distiller with date kernels, and one with olive kernels). The integration effect of two kernel types date and olive with different concentrations in the range of 300–600 g kernels per 5 L on the hourly and cumulus water production, and thermal and exergy efficiencies are analyzed. The results show that, for the same kernel mass concentration, the system with olive kernel is more effective than that with date kernels; moreover, compared to the reference system, cumulus water production of these systems at a mass concentration of 500 g kernels per 5 L is higher by ≈226% and 176%, respectively. At a concentration of 500 g kernels per 5 L, the average daily thermal efficiency of the solar still with olive kernels and that with date kernels is 38.01% and 30.7%, respectively, and their daily average exergy efficiency is 8.4% and 3.1%, respectively.     

Prediction of wave pressures on smooth impermeable seawalls

Simple prediction methods are proposed to estimate the wave induced pressures on smooth impermeable seawalls. Based on the physics of the wave structure interaction, the sloped seawall is divided into a total of five zones (zones 1, 2 and 3 during run-up (corresponding pressures are called as positive pressures) and zones 4 and 5 during run-down (corresponding pressures are called negative pressures)) (Fig. 1). Zone 1 (0<z<d−H_i/2), where the wave pressure is governed by the partial reflection and phase shift; Zone 2 (d−H_i/2<z<d), where the effect of wave breaking and turbulence is significant; Zone 3 (d<z<Run-up height), where the pressure is induced by the run-up water; Zone 4 (Run-down<z<d), where the wave pressure is caused by the run-down effect and Zone 5 (0<z<d-Run down), where the negative wave pressures are due to partial reflection and phase shift effects. Here d is the water depth at the toe of the seawall, H_i is the incident wave height and z is the vertical elevation with toe of the seawall as origin and z is positive upward. For wave pressure prediction in zones 1 and 5, the empirical formula proposed by Ahrens et al. (1993) to estimate the wave reflection and Sutherland and Donoghue's recommendations (1998) for the estimation of phase shift of the waves caused by the sloped structures are used. Multiple regression analysis is carried out on the measured pressure data and empirical formulas are proposed for zones 2, 3 and 4. The recommendations of Van der Meer and Breteler (1990) and Schüttrumpf et al. (1994) for the prediction of wave run-down are used for pressure prediction at zone 4. Comparison of the proposed prediction formulas with the experimental results reveal that the prediction methods are good enough for practical purposes. The present study also shows a strong relation between wave reflection, wave run-up, wave run-down and phase shift of waves on wave pressures on the seawalls.