A numerical and experimental study has been conducted to enhance the thermal performance of the thermosyphon system. The enhancement response focused on the temperature of both the working fluid within the system loop and water inside the tank. To achieve this, three models were investigated to increase the surface area of the riser pipe without changing the amount of the working fluid. The first one (model A) involved increasing the diameter of the riser pipe and inserting a closed tube inside it to maintain the same amount of working fluid. The second method (model B) involved adding toroidal fins around the riser pipe. However, the third model (model C) combined both models (A and B). The thermal performance of the thermosyphon system for the conventional model has been compared experimentally. Furthermore, numerical simulations for all cases have been done using commercial computational fluid dynamics, ANSYS R 19.3 software. The results show that there is good agreement between the experimental and numerical results. Furthermore, it is found that the thermal responses of models A and B are approximately equal and both are higher than that of the traditional model. Moreover, the thermal performance of model C is found to be higher than those of all the other models under study.
In areas with very hot weather conditions (50 to 60℃), the temperature and pressure of the airconditioning condenser are increased considerably. This causes a decrease in the cooling capacity of the cycle and also causes an increase in the power consumption due to increased pressure ratio. In this work, an experimental and theoretical investigation has been done to improve the evaporator outlet fluid temperature through enhancing condenser performance. For this purpose, several modifications on the refrigeration system have been developed and tested to solve this hot weather problem. The air-side modifications include adding Spray Water above condenser (SW), wet Pad before condenser (Pad), and water Vapor Nozzle in the condenser air flow (VN). The refrigerant-side modification includes adding a pair of Heat Exchangers (HE) for exchanging heat between condenser exit and evaporator exit by using water-antifreeze mixture as a working fluid. A Water-Refrigerant(W-R) evaporator has been designed, manufactured, and compared with original Air-Refrigerant(A-R) evaporator performance. All air and refrigerant-side modifications have been investigated using both types of evaporators. The results indicate that the (SW) modification for enhancing condenser performance is the best method for COP improvement. The COP of (SW) system is found to increase at rate of (44.5 %) and (102.1%) as compared to system without modifications for (A-R) and (W-R) evaporators respectively. The outlet cooling temperature from evaporator has been found to reduce by about (30.3%) for (A-R) evaporator and (23.6%) for (W-R) evaporator. However, (HE+Pad) modification has been found as the best method for improving air side Nusselt number of condenser with an increase of about (4.7) times that of system without modifications. Ten new Nusselt number correlations have been predicted for each type of modifications under investigation by using both Engineering Equation Solver (EES) software and the experimental data. Cost-Benefit analysis in terms of life cycle cost, net present value, cost-benefit ratio, and payback period have been conducted. From the analysis, it can be concluded that using (SW) system will save a significant amount of energy with a payback period of less than five years.
The performance of thermal solar systems can be enhanced by extending its operational time by the aid of thermal energy storage. In the present work, the transient behavior of packed bed thermal energy storage (TES) was investigated experimentally and numerically. An experimental setup was designed and fabricated to simulate the charging and discharging operational modes of the system. 101 spherical capsules were filled with wax paraffin as PCM and packed in cylindrical container bed of 105 mm diameter and 420 mm long. The processes of the experimented storage system were simulated mathematically and solved numerically by finite difference technique. The analyses were carried out at two different mass velocity of the working fluid. The numerical model described the transient behavior of the system and it was in acceptable agreement with the experimental results. The transient period in the charging mode of the tested storage was around 30 min, while the energy recovery period in the discharging mode was around 60 min. The achieved results demonstrated that the tested TES could be used to enhance the performance of the thermal solar systems. The proposed packed bed thermal energy storage is easy to implement with low cost.
The thermal performance enhancement of a thermo-syphon system has been studied by many researchers. However, according to the best knowledge of the authors, the impact of the amount of the working fluid on the performance of thermo-syphon has not hitherto been studied. In the present work the impact of inserting a closed tube inside the riser pipe and effect of increase and decrease the amount of the working fluid on the thermal performance have been investigated. Several cases have been considered and tested. To ensure the validity of the theoretical results, an experimental work has been conducted and results compared with numerical results. The results show good match between numerical and experimental results. In particular, the maximum difference between experimental and numerical results is found 14.52% and 11.23% for water temperature inside tank and working fluid at outlet of the riser pipe respectively. As well as, the numerical results have been demonstrated that the amount of the working fluid within the thermos-syphon loop has a noticeable impact on the thermal performance of the regarding system. Furthermore, it is found that the (case-A-) is the best case among all cases under consideration regarding system the thermal performance of thermos-syphon. Moreover, a correlation equation to predict water temperature within the storage tank has been established. The accuracy of this equation around 95.6%.
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