An assessment of a flat plate double pass (DP) solar air heater (SAH) having V-corrugated absorber (C_SAH) and corrugated-perforated absorber (CP_SAH) via energy, exergy, economic and environmental approaches (4E) is presented experimentally. The study is performed at four different levels of air mass flow ratios inside the flat plate solar air heater with two levels of absorber plates i.e. C_SAH and CP_SAH. C_SAH and CP_SAH performance is compared with flat SAH (F_SAH) performance. The results show that F_SAH achieves the lowest daily energy efficiency values of 52.5%, 55.86%, 54.77%, and 56.7% while CP_SAH achieves the highest of 67.67%, 69.7%,71.85%, and 70.8% at SP, 1/3 DP, 2/3 DP, and DP conditions, respectively. Moreover, C_SAH and the CP_SAH achieve maximum daily efficiency of 70.58% and 71.85% at 2/3 DP condition. CP_SAH achieves average daily exergy efficiency of 0.78%, 0.89%, 0.97%, and 0.92% with percentage increments of 47%, 55%, 76%, and 54% compared to F_SAH at same previous conditions, respectively. F_SAH at SP condition achieves the maximum energy cost of 0.0427 $/kWh while CP_SAH at 2/3 DP condition achieves the minimum energy cost of 0.0324 $/kWh. The proposed CP_SAH at 2/3 DP condition is the most suitable from the studied cases.

An assessment of using different passive condenser designs of the solar distiller based on productivity, exergy, energy, energyeconomic, exergyeconomic, enviroeconomic is investigated experimentally. Five different condenser designs are considered; (i) glass plate condenser, GC (CSS), (ii) corrugated aluminum sheet heat sink condenser, CHS, (iii) aluminum heat sink condenser having vertical rectangular fins at its outer surfaces, RHS, (iv) aluminum heat sink condenser having pin fins at its outer surface, PHS, and (v) aluminum heat sink condenser having pin fins at its outer and inner surfaces, DPHS. The findings show that augmenting the rate of condensation by varying the condenser design increases the still yield to a limit and then decreases this yield at a higher condensation rate. CSS has the smallest freshwater yield and still with PHS has the maximum production with an increment of 54 % comparing with GC condenser. The maximum increase of the daily average energy and exergy efficiencies of the still is about 55.3 % and 73.1 %, respectively in case of PHS condenser compared with CSS. Still with DPHS condenser has the maximum production cost while the still with PHS or CHS condenser has the minimum. Distiller with PHS condenser is the best system in achieving CO₂ reduction benefits of 1.82 tons CO₂/year.

An experimental study on the performance of double pass Solar Air Heater (SAH) having a new designed absorber is performed. The new SAH absorber is constructed from conductive aluminum tubes adjacent to each other and installed in the same direction of the air flowing inside the SAH. The new SAH performance (called Tubular Solar Air Heater (TSAH)) is studied at various mass flow rates of air inside the SAH. Moreover, it is compared with the performance of Flat plate Solar Air Heater (FSAH) having the same dimensions and materials of the TSAH except the absorber design. Findings indicate that the TSAH has higher outlet air temperature, efficiency and net energy gain and lower top heat loss compared to FSAH. TSAH achieves maximum air temperature rise more than 6 °C compared to FSAH at 0.025 kg/s. TSAH efficiency is greater than FSAH efficiency by about 19.4%, 21%, and 40.3%, at inlet air flow rate of 0.075 kg/s, 0.05 kg/s and 0.025 kg/s, respectively. The outlet air temperature and top thermal energy loss of the TSAH decrease with increasing the air mass flow rate, while its efficiency, energy output, and pressure drop increase. Moreover, TSAH efficiency in case of double air pass is greater than single air pass. Despite the TSAH pressure drop is greater than FSAH pressure drop, but its value is very small to impact the TSAH net thermal energy gain. The designed TSAH performance is found greater than the performance of FSAH and previous designs of published SAHs.

In this work, experimental work is presented on the performance of a hybrid solar distiller comprising solar still (SS) combined with parabolic trough solar collector (PTSC) using direct heating of salty water by the collector. In this technique, the salty water supplied to the SS is heated by passing it directly through the parabolic receiver without using heat transfer mediums that reduce the system efficiency. The study is carried out at different salty water depths inside the SS basin under hot climate conditions of Upper Egypt. The system performance is compared with a previous system using oil as a heat transfer medium between PTSC and still (indirect heating). The advantages of this technique are its ability to reduce initial salty water depth in the basin and avoid using the pumping system and heat exchanger compared to the direct heating. The performance of the proposed system is evaluated based on productivity, energy payback time (EPBT), exergy, enviroeconomic, and exergoeconomic methodologies. Findings illustrate that the present system rises the energy efficiency by about 12%, 27.5%, and 46% and the system exergy efficiency by about 14%, 30%, and 49% at salty water depth 15 mm, 10 mm, and 5 mm in the basin compared with the indirect heating system. Moreover, using this technique of salty water heating reduces the production cost of freshwater by about 71% compared with the direct heating system. The exergoeconomic and enviroeconomic parameters of the direct heating mechanism are more effective compared with those of the indirect heating mechanism.

This work proposes an innovative statistical model by utilizing the response surface methodology (RSM) method to analyze a batch solar behaviour still. This investigation’s main goal is to study the impact of the input factors (solar radiation, ambient temperature, water depth, and thickness of insulation) most influencing water productivity. The polynomial regression model derived from a numerical balance energy model to predict the solar’s productivity still is established. The quadratic model is checked by a coefficient of determination (R2). An excellent fitting is attained between the forecasted results derived from the statistical model and the numerical simulation derived from the heat balance model. The results reveal that the importance of the influence in the order of impact on the amount of distilled water is water depth, solar radiation, ambient
temperature, and thickness of insulation. A simple polynomial statistical model is stated in this investigation to determine and maximize the amount of distilled water from solar still based on the four considered input factors. 

In this paper, an experimental investigation is performed on the impact of condensation rate of solar still condenser at different thermal energy storage materials on the performance of single slope passive solar still. The condensation rate is changed by installing different designs of the still condenser: (i) glass plate condenser, GC, (ii) corrugated aluminum sheet heat sink condenser, CHS, (iii) aluminum heat sink condenser having vertical rectangular fins at its outer surfaces RHS, (iv) aluminum heat sink condenser having pin fins at its outer surface, PHS, (v) aluminum heat sink condenser having pin fins at its outer and inner surfaces, DPHS. Two different thermal energy storage materials inside the still basin are used; sand and black wool fibers (BWF) plus pure saline water which yield different evaporation rates of the saline water. The findings show that increasing the heat transfer rate (HTR) by the condenser increases the still yield to a limit and then decreases this yield at higher rates. Moreover, increasing the evaporation rate by using thermal energy storage material reduces the negative
impact of high condensation rate. The still yield of GC is the minimum while the still yield in case of PHS has the maximum production. Solar still with PHS condenser achieves maximum yield increments of 54%, 63%, 76% in case of saline water only, sand, and BWF medium in the basin, respectively compared to the case of GC condenser
with saline water only (conventional still) in the basin. The conventional still has the minimum efficiency of 23.3% and the still with PHS condenser and BWF achieves the maximum still efficiencies of 40.7%. Moreover, enhancement of HTR through using of DPHS condenser reduces the still efficiency to 29.2%, 34.3%, and 37.5%
in case of pure saline water, sand, and BWF, respectively. Using PHS condenser with BWF in the still basin reduces the freshwater yield cost by about 21% compared to
conventional still

The influence of thermal energy storage (TEGS) of coupling new hybrid system of two phase change materials (PCMs) with air conditioning (A/C) unit on its cooling and heating performance in summer and winter, respectively is investigated. PCM RT 10 HC (PCM10HC) of 10-12 C phase change temperature and PCM type SP
24E (PCM24E) of about 24-25 ◦C phase change temperature suitable for working on winter and summer climate conditions, respectively are integrated as a hybrid system and coupled with the condenser/evaporator of the A/C unit. The performance of the A/C unit of this hybrid system is compared with the unit performance using only PCM24E system in summer and PCM10HC system in winter. The study is studied at two configurations of the
hybrid PCMs system. The studied physical systems are modeled by a complete mathematical model that is numerically solved by utilizing ANSYS-Fluent software. The solution numerically is validated by using an experimental setup which shows the high accuracy of the numerical solution. The findings based on the stated design conditions of Egypt demonstrate that the time of complete charging and discharging procedures is nearly the same for hybrid and single PCMs systems. The maximum increase of the A/C unit COP is about 88% for the hybrid system in summer while it is nearly 22% in winter. The percentage increase of the saving power for the single system, the hybrid system is about 6.85%, and 6.5%, respectively in summer and 3.9% and 2.8% in winter,
respectively compared to A/C without PCM units. Increasing the distance between the PCMs’ plates impacts negatively on the exit air temperature from PCMs plates and the saving power. The results demonstrate that the hybrid system has nearly the same merits on the A/C working as the single systems plus it can work during the hot and cold climate conditions.   

This study experimentally investigates the performance of solar still coupled with a parabolic trough solar collector (PTSC) at different cooling rates based on energy, exergy, exergoeconomic, and enviroeconomic standpoints. Different solar still systems are considered; conventional solar still (CSS), solar still with heat sink condenser (MSS)
and coupled with PTSC (MSS + PTSC), MSS having an umbrella and coupled with PTSC (MSS + PTSC + U), MSS with PTSC and condenser forced air cooling (MSS + PTSC + FA), and MSS + PTSC with condenser forced water cooling (MSS + PTSC + FW). Experiments are conducted under hot climate conditions of Sohag city, Egypt.
Results indicated that the freshwater yield of all studied systems in ascending order is as follow; CSS + PTSC, MSS + PTSC +U, MSS +PTSC, MSS +PTSC +FA, and MSS + PTSC +FW in summer with value of 7.74, 8.02, 8.68, 9.11, and 9.45 kg/m 2
, respectively. The maximum exergy efficiency of 1.34% in summer is achieved in case
of MSS + PTSC + FW system. The economic analysis shows that distilled water cost is minimum for MSS + PTSC + FW (~0.02 $/L), while it is maximum for MSS + PTSC + U (~0.022 $/L). It can be concluded that high freshwater production and less distilled water cost are making the enhanced solar desalination system feasible and competitive. Minimum exergy efficiency occurs in case of CSS +PTC with a value of 1.197% and MSS
has higher average daily exergy efficiency. MSS + PTSC achieves the best performance-based exergoeconomic approach. MSS + PTSC + FW is by far the best system in cutting down CO2 emissions.

A novel fractional model based on the Riemann Liouville fractional derivative to simulate the thermal performance of conventional solar still and show the effect of using hybrid nanofluid on the desalination system is presented. The results of the fractional model are compared with the results obtained from the classical model, then compared to real experimental data under various climate conditions of Upper Egypt. The theoretical results reveal a perfect agreement between the proposed fractional model and the experimental data of the still with a percentage of error reached 1.486% in summer and 3.243% in winter compared to an error percentage of 24.1 % and 20.08%,  in case of applying the classical. Moreover, the performance of the modified solar still after adding hybrid nanoparticles is also compared with the conventional solar still. The model is implemented using a hybrid nanofluid of alumina and copper oxide (Al₂O₃-CuO) with a concentration of 0.025% for each nanoparticle. The results show that using hybrid nanofluid raises the still daily productivity to 5.5239 kg/m².day in summer and 3.1079 kg/m².day in winter of an enhancement in the still output yield of 27.2% and 21.7% compared with still without nanoparticles. The average energy efficiency of the still in summer is also increased to 49.54% and 23.212% in summer and winter, respectively, with an augmentation of 12.6% and 11.85% in hot and cold climate conditions, respectively. In addition, the average exergy efficiency is raised by 22.5% in summer and 13.4% in winter by using hybrid nano.

This paper presents three-dimensional study on the enhancement of waste heat recovery from vertical chimney via  thermoelectric generators (TEG) by using heat spreader. The physical model composes of aligned  TEGs mounted on the chimney wall where each TEG is cooled at its cold side by rectangular finned  heat  sink. The  spreaders are installed on the generators’ cold sides between the generators and the  heat sinks’ bases. The studied model represents three of the TEGs installed on the chimney wall. Three dimensional model is  presented for the physical model coupling the governing equations of thermal, fluid flow  and electrical models and is solved by using ANSYS software. Results indicate that using spreader increases  total  output  generators  power by 17% and 42% at spreader length 40 and 140 mm, respectively and  pitch 140 mm. The increase of the TEGs power is about 17% and 21% due to using spreader length
of 40  and 80 mm, respectively at 80 mm pitch. Using heat spreader with maximum length of 140 mm, increases  the conversion efficiency of the lower, middle generator and upper TEGs by 22.2%, 18.8%, and 19.7%,  respectively, while the overall efficiency of the system rises by 20.4%. Using spreader with 140 mm reduces  the used generators and heat sinks numbers to approximately the half.