Search

Vortex generator can be used to enhance heat transfer as it is capable of providing better mixing. Vortex generator is easy to manufacture and install in heat transfer units without much additional cost. Present work is planned to investigate the effect of vortex generators on local heat transfer coefficient, critical heat flux (CHF) and pressure drop to ensure design and safety of heat transfer units with vortex generators. Experiments are carried out for three values of pitch 22, 32 and 41 mm and an angle of attack of 45° of vortex generators with horizontal configuration in a smooth tube of diameter 11.9 mm, length 1,000 mm and 0.4 mm wall thickness with R-123 as the working fluid. The effect of mass flux (175–681 kg/m2s) and heat flux (7.9 − 221.7 kW/m2) are studied. Both horizontal and vertical-oriented configurations of the vortex generator are tested. Local wall temperature measurement is carried out with Infrared thermography. Comparing results with plain tube shows the heat transfer coefficient and CHF enhancement. Horizontal orientation (HO) of the vortex generator gives better results than the vertical orientation (VO). Heat transfer coefficient, CHF and pressure drop penalty increase with a decrease in the pitch of the vortex generator. [ABSTRACT FROM AUTHOR]

The inclined impinging jets owing to higher efficiency are widely used to disperse concentrated and transient heat loads. The temperature and heat transfer characteristics of jet cooling vertical hot plate at different inclinations are experimentally investigated. Experiments are performed to investigate the area average heat transfer over a flat surface of 600 × 300 mm2 placed at different location (z) of 3−20 d from the jet. The investigation is employed for Reynolds number based on hydraulic diameter of 11.5 mm ranging from 10,000 to 75,000. The orientation of the jet varies from 15° to 75°. The study aims to investigate the influence of jet orientation at different area locations on the surface from the point of impingement. The effect in stagnation region with different jet tilt is investigated. The area average temperature variation and characteristic temperature contours with increasing surface area and inclination is delineated. The characteristics of heat transfer on the surface's periphery are studied. Heat transfer increases by 40% at lower tilt angle as the jet is displaced from 20 to 6 d, whereas the maximum average Nu occurs at higher inclination. The available Nusselt numbers in inclined jet are compared with present experimental results. A new empirical correlation is developed for a complete range of z/d, Re and large radial span. [ABSTRACT FROM AUTHOR]

Droplet impingement is one of the phase change techniques used for equipment cooling because of the proper utilization of sensible and latent heat. This study analyzes droplet evaporation on aluminum and copper substrate. The instantaneous heat transfer coefficient (HTC) during evaporation of 100 µl de-ionized water is studied. The infrared camera is used to visualize and analyze the evaporation mechanism. The effect of substrate and fluid temperature on droplet evaporation is analyzed. The surface temperatures of both substrates are varied from 105 °C to 165 °C. The test fluid is maintained at temperatures of 30 °C, 50 °C, 75 °C, and 99.4 °C. The droplets exhibited Leidenfrost behavior for temperatures beyond 145 °C with copper and 150 °C with aluminum surface. It is observed that the evaporation rate is higher for copper than aluminum. A user-friendly interface is developed for determining the instantaneous surface area of an evaporating droplet. The apparent peak in the area in copper is higher than aluminum for all cases due to surface tension gradient and Marangoni flow. HTC increases with the temperature of droplet evaporating on a given substrate and is higher for copper. When substrate temperature increases for a given droplet temperature, the instantaneous HTC increases. [ABSTRACT FROM AUTHOR]

Heat transfer over a heated plate positioned normal to the horizontal circular impinging jet is investigated experimentally. The area average and local heat transfer characteristics over a large plate impinged by jet of air are investigated for Reynolds numbers ranging from 10,000 to 45,000, with jet-to-plate distances of 3–20 d for a maximum range of 0 ≤ r/d ≤ 44. The experiment is carried out for two jet diameters of 5.88 mm and 11.5 mm on a plate of 600 × 300 mm2 impinged by a jet. The infrared (IR) thermal imaging method is used to find the temperature distribution over the heated plate. The combined heat transfer investigation of both local and area average gives a proper insight of the cooling phenomenon of the jet at any location over the plate. The investigation is effective in identifying areas with a greater rate of heat transfer. At various locations, the Nusselt number growth with increasing mass flow rate is studied. The area average heat transfer is discovered to be the highest at z/d = 3 for all Reynolds numbers in the A1 (0 < r/d < 2.17) region. However, for z/d = 6 and r/d = 0, the local Nusselt number is reported to be the highest. Reduction in area average heat transfer is reported in area A3, i.e., r/d = 6.5, and beyond this area, the profile of Nusselt number practically converges. [ABSTRACT FROM AUTHOR]

AbstractNumerical simulations were performed to investigate the thermal and aerodynamic characteristics of an annular jet impinging on a concave surface using the Realizable k-ε model. The study examined the significance of the blockage ratio (BR) from 0.3 to 0.7 and the jet exit Reynolds number (Re) from 5000 to 35000. The investigation uses an annular jet with a 10 mm outer diameter impinging on a concave surface with 150 mm radii. Three specific dimensionless distances from the nozzle exit to the target surface (z/do) were considered: z/do = 0.5 (initial merging zone), z/do = 3 (intermediate merging zone), and z/do = 6 (fully merged zone). Furthermore, the annular jet’s performance was compared to that of a conventional circular jet under analogous conditions. At small separation distances, a pair of counter-rotating vortices formed downstream of the jet outlet, inducing a reverse flow that extended to the heated surface. Vortices and flow reversals were also identified at intermediate separation distances. At large separation distances, the flow reattached to the domain axis, resembling a circular jet. The local Nusselt number (Nu) increases as the Reynolds number increases and the blockage ratio decreases. With increasing BR, the difference between the primary and secondary Nu peaks reduces. Additionally, the average Nu and turbulent kinetic energy increase with an increase in Re. [ABSTRACT FROM AUTHOR]

The study attempts to present the melting phenomena in a Latent Heat Thermal Storage System (LHTSS) where ice is used as Phase Change Material (PCM) with fins incorporated to advance the thermal performance. The PCM-based storage system finds vast potential in addressing the imbalance between energy supply and demand. Computations are carried out to find the optimum fin number to be incorporated in Heat Transfer Fluid (HTF) tube for improved heat transfer and minimum melting time. The effect of incorporating optimum fin number on different influential parameters such as HTF tube arrangement, diameter, and temperature on charging performance is evaluated. The physical phenomena occurring due to increased fin number is also explained. Criteria such as liquid fraction, mean temperature, heat transfer rate, and heat transfer coefficient are used to compare the system's performance under varying parameters. As the number of fins is augmented from 4 to 15, the generated liquid PCM is found to increase by 34.69% followed by a declination rate of 9.03% on further increment in the numbers. Geometrical alteration in the HTF tube arrangement from inline to staggered results in a better melting performance. Considering the HTF tube temperature parameter, it is found that 280 K HTF tube produces 2.08 times more liquid PCM as compared to 275 K case. Increasing HTF tube diameter is found to enhance the charging process with 20 mm diameter HTF tube system generating 2.68 times more liquid PCM as compared to that of 5 mm HTF tube. • Melting of ice as PCM in fin-incorporated LHTSS is studied. • Optimal geometric and thermal operating conditions for enhanced charging are found. • There is an optimal fin number beyond which melting efficiency of system reduces. • Increasing diameter and temperature of HTF tube reduces the melting time. [ABSTRACT FROM AUTHOR]