ملخص البحث :

This paper aims to investigate and analyze the thermal performance of a double-pass solar air heater using multiple rectangular capsules filled with paraffin wax-based on a phase change material PCM. An indoor projector simulator was used to test a new system during the charge/discharge process. In order to verify the accuracy of these readings, a mathematical model based on finite-volume scheme SIMPLE algorithm was applied to solve the three-dimensional forced convection turbulent flow in the double-pass solar heater. The computational results were in reasonable agreement with the experimental readings. The investigations were carried out at various airflow speed of (0.6, 0.9, 1.2, 1.5, and 1.8) kg/min and three solar irradiance intensities of 625, 725, and 825 W/m2. The results showed that the increased airflow rate leads to delay in the melting period and decrease melting temperature of the paraffin during the melting period. Furthermore, it can be detected that the optimal discharging period and the air temperature rise of the heater were reached of: 3hr with (17.95–3) °C, 2 h with (14–3) °C, and 1.25 h with (11–2.5) °C, for various solar intensity of 825, 725, and 625 W/m2 at the same airflow speed of 0.6 kg/min, respectively.

ملخص البحث :

Two numerical models are accomplished to predict thermal effectiveness of a novel solar heater with and without paraffin-based on the latent heat storage. The conservation equations with enthalpy transforming method of phase change material (PCM) are analyzed using finite-volume with an explicit scheme. The influence of the main parameters is investigated such as; airflow rate ranging of (0.6≤m˙a≤1.8) kg/min, and heat flux ranging of (625 ≤ Is ≤ 825) W/m². The results found that the air temperature rise is proportionate to the airflow rate inversely, during the charge/discharge processes. It was concluded that the useful power and the thermal performance are significantly depended upon the solar flux with airflow rate in both models. Moreover, the thermal effectiveness of the collector without and with paraffin was approximately (33.8 – 73.15)%, and (31.3 – 66.77)%, respectively, under the range of the studied parameters. It was noted that the decreased thermal efficiency is (5–7)% with PCM by absorbing the stored energy and releasing it to the system during sunset. To verify the accuracy of experimental and numerical results under the same operating conditions with a mean error of effectiveness with and without PCM was identified of ±6.4% and ± 8.6%, respectively, and the results were acceptable.

ملخص البحث :

Numerical modeling based on finite-volume method (FVM) SIMPLE algorithm was established to analyze the 3D-turbulent flow in the wavy two-pass solar collector is proposed. This model is used to analyze and simulate the performance of a V-grooved absorbent collector. The main parameters of an air velocity ranging of(1, 1.5 and 2 ) m/sec, and solar radiation values of(400, 600 and 800)W/m2 are studied. The results presented in terms of temperature and velocity distribution along the system, outlet air temperature, and air temperature rise of the two-pass solar collector’s with wavy absorbent. Also, it is found that the outlet temperature and temperature difference of air is proportionate to the airflow velocity inversely. Further, the temperature difference of air is gained across the wavy absorbent collector. It was approximately 20.7 °C, 19.1 °C and 18.1 °C for 800 W/m2 of heat flux and different air velocities range 1, 1.5 and 2 m/sec, respectively. It was concluded that the collector performance is significantly be influenced by the heat flux and air velocity in the collector.

ملخص البحث :

The problem studied in this paper consists of forced fluid flow inside a horizontal channel involving two semi-cylinders and two flexible baffles attached alternatively to the lower and upper walls of the channel. A phase change material fills the semi-cylinders, which are being heated by constant temperature. Cold air is forced through the channel to induce the contributions of convective and conductive heat transfers, fluid–structure interaction and the melting of phase change material. The prevailing mathematical equations of these physics are normalized and solved using the finite element method with the ALE scheme. The influential parameters are: dimensionless time , the elasticity modulus of the baffles and the Reynolds number . The most important results show a retardation of melting volume fraction with increasing Reynolds number and decreasing the elasticity modulus of the flexible baffles. It is found that elevating Re from 10 to 500 and E from 5 x 10^4 to 5X10^6, the melting volume fraction MVF at reduces by 4.15% and increases by 5.2%, respectively. The flexible baffles having a lower modulus of elasticity augment the Nusselt number very slightly (0.9%), while the pressure drop along the channel decreases notably.

ملخص البحث :

The FSI-mixed convection heat transfer in a lid–driven vented cavity is studied in the present work. The heat source is set partially on the base of the cavity; the left flexible wall is cold, while the remaining walls are adiabatic. The top wall of the cavity moves in different cases depending on its movement; stationary wall (case 0), moving to the left (case I) and moving to the right (case II). The arbitrary Lagrangian-Eulerian formulation and finite element method are utilized to solve the governing equations. A two-dimensional incompressible laminar flow with an unsteady-state condition is used in the present model. The effects of relevant factors like the Richardson number 0.01≤ Ri ≤ 100 and the ratio of the velocities of moving top wall to that of the air entering the cavity, which is governed by Reynolds numbers ratio 1 ≤ Rer ≤ 4 have been studied. The outcomes demonstrate the feasibility of using a flexible wall and a special movement of the top wall. The percentage increase of the Nusselt number due to the flexible wall alone is about 4.5% while when the top wall moving to the left (case I), the augmentation rises to 28%.

ملخص البحث :

Boosting the mixed convection in vented cavities using a moving wall results in a disturbed strongcirculation. This study investigates the mitigation of the disturbed circulation to promote the transfer ofheat by providing additional size to the circulation. The use of deformable walls with different thicknesses,lengths and modulus of elasticity is suggested for this problem. The top wall of the cavity is adiabatic andmoves in the positive direction, and four speeds were studied; 0.5, 1, 2 and 4 times the fluid velocity at theinlet vent. The ratio of the natural to forced convection is controlled by ranging Richardson number by 0.01≤ Ri ≤ 100. Three aspect ratios are studied; AR = 0.5 (horizontal cavity), 1 and 2 (tall cavity). The problem istreated numerically using the finite element method. Results indicate that the fluid flow inside the ventedsquare cavity changes from major single vortices into multi vortices at high (Ri = 100). Results affirm that aflexible wall yields a higher Nusselt number than the rigid wall, it's about 12 %, and 20 % for Ri = 0.01 and 10,respectively. A thicker flexible wall augments the Nusselt number for Ri ≤ 10. For specified conditions, theNusselt number of the horizontal cavity is 17.7 % greater than the tall cavity. The lid speed of u = 4 u exhibits a competent role in raising the Nusselt number for low Richardson number