Cylindrical Pin Fins Research Articles

Design and development of a heatsink for thermo-electric power harvesting in aerospace applications

In recent years, the growing interest of aerospace companies in wireless structural health monitoring (SHM) systems has led to the research of new energy efficient sources and power harvesting solutions. Among available environmental power sources, temperature gradients originated at different locations of the aircraft can be used by thermo-electric generators (TEGs) to create electrical voltage. TEGs are lightweight, provide high-energy conversion and do not contain movable parts. Thermal diffusion systems, commonly known as heatsinks, can be combined with TEGs to enhance their performance by increasing heat dissipation from a high temperature surface to the ambient air. This paper focused on the enhancement of TEG performance by developing an air-cooled heatsink for low-power wireless SHM applications. The design, manufacturing and testing of the proposed thermal diffusion system was investigated by evaluating the increase of the temperature gradient between the opposite surfaces of a commercial TEG element. The thermal performance of the heatsink was assessed with numerical finite element thermal simulations and validated with experimental tests. Experimental results revealed that the proposed thermal diffusion system provided higher temperature differences and, therefore, higher output power in comparison with traditional cylindrical pin-fin heatsinks. A hybrid heat diffusion system composed by copper heatsinks and highly oriented pyrolytic graphite layers was also here proposed in order to allow TEG reaching wireless SHM operative power requirements of tens of mW and, at the same time, adapt the assembly to the complexity of aerospace SHM arrangements. Experimental results revealed that the proposed heatsink-TEG arrangement was able to generate an output power over 25 mW.

Improved Photovoltaic Panel Performance Using a Cylindrical Pin Fins as a Heat Sink

In this work, the photovoltaic panel performance has been investigated theoretically and experimentally where using an array of pin fins as a cooling system. Trying to satisfy the ideal operation conditions of the solar panel, heat sink was fixated on the back of the PV panel to use as a passive technique. An Analytical thermal model based on the steady state and one dimension analysis condition was built to transfer the excess heat from PV panel with the heat sink existing to predict the operation temperature of PV panel. Theoretical results were compared with experimental results of solar panels cooled by heat sink, in order to validate the suggested thermal model. Also, the effect of the solar cells temperature on the panel performance has been studied experimentally. The results displays that using pin fins array as a cooling technique led to drop in the average panel's temperature nearly 5.9°C and an enhancement of the average output power nearly 13.5%.

Numerical Study of Transient and Steady-State Anisotropic Cylindrical Pin Fin Thermal Behavior

This paper deals with the transient thermal analysis of two-dimensional cylindrical anisotropic pin fin that contains tip convection and subjected to a prescribed temperature at the fin base. The heat conduction equation contains a dual second-order derivation, which precludes solving the equation by direct application of common exact methods. Therefore, an appropriate canonical mapping is selected as a solution to cancel the dual derivation of temperature in the mapped equations. The alternating-direction implicit finite difference method (ADI) performs the integration of the mapped equations in the novel space, which involve a complicate geometry. Applying the inverse spatial transformation provides transient temperature profile in the real geometry for full-field configuration. The established numerical code has been validated successfully with the analytical solutions of the usual fins (orthotropic and isotropic). The anisotropy effect is investigated by means of various contour plots of the temperature profile as well as heat transfer rate from the fin base and the effectiveness for different parameters of study (kr/kz, krz/kz , and Bir) in transient and steady-state heat conduction. The numerical code allows the study of the thermal behavior of anisotropic, orthotropic, and isotropic cylindrical pin fin according to the geometrical and physical parameters, as well as the thermal conditions to which the pin fin is subjected. A parametric study is performed in view to compare the thermal behavior of the various pin fin kinds submitted to the same conditions.

Filmwise Condensation of Steam on Pin Fin Arrays Fabricated by Selective Laser Melting

In this study, nine vertical flat plates of pin fin arrays were fabricated by selective laser melting to investigate the possible enhancements of external condensation. These specimens are cylindrical pin fins of the same fin diameter of 300 μm but are of different fin heights (l) and fin pitches (p) from 300 μm to 900 μm. Experiments were conducted in a condensation chamber with near quiescent vapor to simulate free-convection condensation. The aim is to investigate the effects of fin pitch and fin height on the condensation heat transfer performance of the surfaces. The results of this study show that the increase in fin height and the decrease in fin pitch lead to a systematic increase in the condensation heat flux (q''). At the same fin pitch, the increase in fin height from 600 μm to 900 μm resulted in a more significant increase in q'' as compared to the increase in fin height from 300 μm to 600 μm. On the other hand, at the same fin height, a larger increase in q'' is observed when the fin pitch is reduced from 900 μm to 600 μm as compared to the reduction in fin pitch from 600 μm to 300 μm. It can be deduced that increasing the fin height enables the fins to protrude out of the thick condensate film and increases the effective heat transfer area of the surfaces. However, when the fin density is large, it impedes the condensate drainage path and limits the enhancement in q''. The enhancement factor (η), which is the ratio of the average condensation heat flux of a pin fin surface to that of a plain surface, was computed for each specimen. The highest η value of 1.72 was achieved with the specimen of 900 μm fin height and 300 μm fin pitch. Finally, a relationship between η and the dimensionless fin pitch-to-height ratio (p/l) is proposed.

Effect of variation of cylindrical pin fins height on the overall performance of microchannel heat sink

Numerous researches are performed to take account of the heat transfer in the microchannel heat sink, due to its high efficiency and application in various fields of microelectronics. An attempt has been made to numerically investigate the effects of variation of cylindrical pin fin height, entrenched on bottom wall of microchannel. Three cases of microchannel heat sink are prepared: case 1: plain rectangular channel; case 2 and case 3 with decreasing pin fin height and with increasing pin fin height in the direction of flow, respectively. Also, diameter of pin fin is varied to obtain effects of any underlying flow feature on heat transfer augmentation. The analysis is performed for single-phase fluid deionized ultra-filtered water with temperature-dependent properties, for low Reynolds number range of 150–300. Higher Nusselt number is obtained for case 2, whereas lower pressure drop is obtained in case 3. The overall thermal performance of case 3 with increasing pin fin height outperforms the corresponding case 2 with decreasing pin fin height for the same pin fin diameter, due to the velocity distribution and reduced pressure drop in the downstream region in microchannel, which shows that the downstream region of microchannel heat sink has a significant impact in terms of the overall efficiency while establishing pressure drop as essential characteristics.

Energy, exergy, economic and enviroeconomic (4E) analyses of solar distillation system using different absorbing materials

In this study, the energetic, exergetic, economic and enviroeconomic (4E) analyses of single slope solar still using steel mesh fibers (a new porous medium) and hollow cylindrical pin fins as absorbing materials are investigated. Three cases are considered, case 1: traditional solar still, case 2: with hollow cylindrical pin fins, case 3: with steel wool fibers. The performance of the three cases is experimentally evaluated under the same meteorological situations. The results show that the total daily cumulative yield of distillate water in cases 2 and 3 enhanced by 16% and 25%, respectively in comparison with case 1. Also, the maximum energy efficiencies of cases 1, 2 and 3 are 42%, 45.5%, and 52.5%, respectively. It is observed that the modified stills (cases 2 and 3) exhibit an increment of the average daily exergy efficiency of 14% and 23%, respectively. Furthermore, economic analysis findings revealed that the costs per liter per square meter for the cases 1, 2 and 3 are 0.0427$, 0.0416$, and 0.0343$, respectively. Eventually, it was observed that the proposed systems (Cases 2 and 3) achieved an annual reduction of 14.4 and 15.6 tons of CO2 emissions, respectively.

An experimental study on the performance of single slope solar still integrated with a PCM-based pin-finned heat sink

The objective of this study is to improve the heat transfer characteristics of PCM storage unit, applicable to solar still system, using hollow cylindrical pin fins embedded in PCM. Hollow cylindrical pin fins act as thermal conductivity enhancer (TCE). In view of this, three cases are considered namely, Case 1: without PCM (conventional solar still), Case 2: solar still with PCM, Case 3: solar still with pin fins heat sink embedded in the PCM. The performance of the three cases is experimentally evaluated and compared to each other under the same climate conditions. The results revealed that the presence of PCM negatively affects the daytime freshwater productivity with a significant increment in the overall freshwater yield of the still. Also, solar still with PCM-based pin finned (Case 3) achieves the best thermal performance compared to conventional still (Case 1) and solar still with only PCM (Case 2). It is perceived that the total daily cumulative yield of distillate water of Case 3 is higher than those of case 1 and case 2 by 17 % and 7 %, respectively. Finally, the findings indicated that inclusion of PCM in the solar still systems for cases 2, 3 extends the production of fresh water after sunset by approximately 5h and 7h, respectively.

An experimental work on the performance of single slope solar still incorporated with latent heat storage system in hot climate conditions

The limit production of freshwater is considered the main problem of solar still. So, the objective of this work is studying the performance of single slope solar still coupled with phase change materials as a thermal storage unit and its effect on the still productivity. In view of this, different cases are considered namely, Case 1: solar still without phase change material (conventional solar still), Case 2: solar still coupled only with phase change material attached to the still base, Case 3: solar still with hollow cylindrical pin fins imbedded in the phase change material, case 4: solar still with phase change material and steel wool fibers in the still basin and case 5: solar still with only steel wool fibers in the still basin. The performance of the solar still for the five cases is experimentally evaluated and compared to each other's under the same climate conditions of New Borg El-Arab City, Egypt (Longitude/Latitude: E 029°42′/N 30°55′). The results revealed that the presence of phase change material negatively affects the daytime freshwater productivity with a significant increment in the overall freshwater yield of the still. Also, solar still with phase change material-based pin finned (Case 3) achieves the best thermal performance compared to conventional still (Case 1) and solar still with phase change material (Case 2). It is perceived that the total daily cumulative yield of distillated water of Case 3 is higher than those of case 1 and case 2 by 17 and 7%, respectively. Additionally, placing steel wool fibers in the basin accompanied with phase change material significantly enhances the daytime freshwater productivity with a considerable reduction in overnight productivity and an increase of the overall day productivity. Moreover, using steel wool fibers in the basin with a phase change material based solar still (case 4) enhances the total daytime freshwater productivity by 14% with a drop in the overnight productivity by 80%, compared to case 2. Among all tested configurations, case 5 achieves the highest accumulated daily freshwater productivity (approximately 25% an enhancement in the daily productivity compared to case 1) and thermal efficiency with minimum cost.

Filmwise condensation of steam on sinusoidal pin fin arrays: Effects of fin height and fin pitch

An experimental investigation on the use of sinusoidal pin fins to enhance filmwise condensation of steam on vertical plates was carried out. Nine surfaces with pin fin arrays were fabricated by Selective Laser Melting (SLM) and tested in a condensation chamber. The pin fin arrays have the same fin base diameter (db) but are of different fin heights (l) and fin pitches (p). At the same fin pitch (p = 1.25 mm and 1.67 mm), the heat flux (q″) and condensation heat transfer coefficient (h) increase as l increases from 1.25 mm to 1.66 mm. However, with further increment in l from 1.66 mm to 2.49 mm, reductions in q″ and h were observed. At the same fin heights of l = 1.25 mm and 1.66 mm, an increase in p from 1.25 mm to 1.67 mm has negligible effects on q″ and h. However, with further increment in p from 1.67 mm to 2.50 mm, significant reductions in q″ and h were observed. Visualization studies of the static condensate retention height (Have) show that two distinct flooding regions can be identified for sinusoidal pin fin surfaces. The static condensate retention height of both regions decreases with increasing p but remains unchanged with varying l. A fin analysis was performed to determine the average heat transfer coefficients (ht) which considers the total heat transfer areas (At) of the enhanced surfaces. Our results show that the highest thermal enhancement factor (η) of 1.86 is achieved with Specimens S4 and S5 whereas Specimens S3 has the highest average heat transfer coefficient (ht). In comparison with cylindrical pin fin surfaces, the sinusoidal pin fin surfaces show better heat transfer performances at the same p/l ratio.

Experimental investigation of heat transfer from different pin fin in a rectangular channel

ABSTRACTIn this study, the effect of both hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) into the rectangular channel on heat transfer augmentation, Nusselt number and friction factor were experimentally investigated. In planning of the experiments, different Reynolds number, pin fin array, pin fin geometry and the ratio of the distance between pin fin spacing (s) to the pin fin hydraulic diameter (s/Dh) were chosen as the design parameters. Air was used as the fluid. The Reynolds number, based on the channel hydraulic diameter of the rectangular channel, was varied from 3188 to 19531. In the experiments, the heating plate was made of stainless steel foil. The foil was electrically heated by means of a high current DC power supply to provide a constantly heated flux surface. The heat transfer results were obtained using the infrared thermal imaging technique. The heat transfer results of the hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) are compared with those of a smooth plate. Best heat transfer performance was obtained with the hexagonal pin fins. The maximum thermal performance factor ((Ƞ), was obtained as Re = 3188, staggered array, s/Dh = 0, Ƞ = 2.28.

Constructal operation cost minimization for in-line cylindrical pin-fin heat sinks

Second-law-based minimum operation cost optimization is performed based on constructal theory for in-line cylindrical pin-fin heat sinks (PFHS). With the minimum operation cost which is based on the entropy generation rate (EGR) as the objective, the optimal values of diameter, height to diameter aspect ratio and quantity of cylindrical pin-fin are achieved by combining the analytical and numerical method, the effects of fin-material fraction (FMF), heat transfer load (HTL) of the PFHS, fluid velocity (FV) and cost ratio on variations of the operation cost of the PFHS with the diameter of pin-fin are analyzed. The results indicate that when the single freedom degree optimization is performed, the minimum operation cost and the optimum constructs are various under various FMF, the HTL, the FV and the cost ratio in the research range of parameters; when the double freedom degree optimization is carried out, the operation cost of the PFHS increases with the height to width aspect ratio of the PFHS increasing.

The Second Law Analysis of Thermodynamics for the Plate–Fin Surface Performance in a Cross Flow Heat Exchanger

In this paper, a particular heat exchanger is designed and analyzed by using second law of thermodynamics. The heat exchanger operates with the cross flow forced convection having cylindrical, square, and hexagonal pin fins (tubular router) placed in the rectangular duct. The pin fins are installed periodically at the top and bottom plates of the duct perpendicular to the flow direction, structured in-line, and staggered sheet layouts. The entropy generation in the flow domain of the channels is calculated to demonstrate the rate of irreversibilities. To obtain the efficiencies, irreversibility, thermal performance factor, and entropy generation number (EGN), the heat exchanger is operated at different temperatures and flow rates by using hot and cold fluids. Optimization of the design parameters and winglet geometry associated with the performance are determined by entropy generation minimization. The variation of the EGN with Reynolds number for various tubular routers is presented. The Reynolds number is determined according to the experimental plan and the performance is analyzed with the method of effectiveness—number of transfer unit (NTU). Based on particular designs, it was determined that the increment in fluid velocity enhances the heat transfer rate, which in turn decreases the heat transfer irreversibility.

Hotspot thermal management using a microchannel-pinfin hybrid heat sink

An energy-efficient micro heat sink is presented for the thermal management of microprocessors with heterogeneous power distributions. The performance of the proposed microchannel-pinfin hybrid heat sink was evaluated numerically and compared with that of a simple microchannel heat sink. The hybrid heat sink was designed with two separate zones: rectangular microchannels were used over the low-heat-flux zone (background area), and an array of cylindrical pinfins were incorporated over the high-heat-flux zone (hotspot area) of the heat sink. Conjugate heat transfer analysis was performed by solving the three-dimensional Navier-Stokes and energy equations with the temperature-dependent thermophysical properties of the fluid. The thermal resistance, pumping power, temperature non-uniformity, and maximum temperature rise at the hotspot were selected as the performance parameters. The hybrid heat sink exhibited remarkable improvement in the thermal performance compared to the non-hybrid heat sink with a reasonable increase in the pumping power.

Parametric Study of Finned Surfaces Using a Graphical User Interface Developed in Matlab

The use of heat exchangers on extended surfaces has obtained high importance in the last years due to their high implementation in industrial processes, computer systems, refrigerators, electronic equipment, etc. It implies the use of computer technology to have a better comprehension of the phenomena that involve heat transfer in finned surfaces to design new prototypes with high efficiency. There are lots of parameters to consider when designing fins such as their geometry and the type of material making the design highly complex. Also, a selection of adequate fins requires knowledge of temperature distributions through them, which will depend on the properties of the fin material. In this article, it is presented the study of the energy transfer and effectiveness in Extended Surfaces using an educational graphical user interface developed in Matlab as a pedagogical strategy to promote the significant learning in engineering. The program uses the most important experimental correlations reported in the literature for solving real problems. The systems studied were Straight Rectangular Fins, Straight Triangular Fins, Cylindrical Pin Fins, and Straight Parabolic Fins, all the cases with air as refrigerant and Aluminum, Copper, Iron, and Stainless Steel as the fin working materials. Three case studies were made, the total heat transfer of the fins as a function of air velocity for different geometric configurations and materials of the fins to see the effect of the natural and forced convection, the effect of convection in the efficiency of the fins, and the effectiveness as a function of thermal conductivity of the fins for the geometrical configurations mentioned above. It was found that the configuration with the highest removal of heat was the straight rectangular fin. The cylindrical fin presented the highest efficiency, and the best working material was the copper.

Lattice Boltzmann Numerical Investigation of Inner Cylindrical Pin-fins Configuration on Nanofluid Natural Convective Heat Transfer in Porous Enclosure

Lattice Boltzmann Numerical Investigation of Inner Cylindrical Pin-fins Configuration on Nanofluid Natural Convective Heat Transfer in Porous Enclosure

Optimum Dimensions of Longitudinal Rectangular Fins and Cylindrical Pin Fins with a Prescribed Tip Temperature

ABSTRACTThis paper deals with constant-area, longitudinal fins with rectangular and circular cross-sections for the condition of prescribed tip temperature. For these fin geometries, the optimum aspect ratios for maximum heat transfer per unit volume have been determined analytically in the literature for the cases of adiabatic tip and convective tip using a one-dimensional analysis. For the case of prescribed tip temperature, a numerical two-dimensional analysis was reported for rectangular fins. In the present study, the temperature distribution and rates of heat transfer at the base and tip of both fin cross-sections were determined using one– and two-dimensional analyses. The ranges of independent parameters within which the one-dimensional solution was within 1% from the two-dimensional solution were determined, and simple analytical formulae for the optimum aspect ratios were derived based on the one-dimensional solution. An example is given showing the application of the results in design.

Flow boiling of R245fa in a microgap with staggered circular cylindrical pin fins

In this study, flow boiling of refrigerant R245fa is investigated in a microgap of height 200 μm populated with a staggered pin fin array of diameter 150 μm and spacing 200 μm. For heat fluxes up to 498 W/cm2, mass flux values up to 7896 kg/m2 s, and inlet temperatures of 13 °C and 18 °C, average two-phase heat transfer coefficient up to 60 kW/m2 K are measured. High speed flow visualizations at frame rate of 2229 fps elucidate the flow boiling patterns inside the microgaps, including bubbly and foggy that are generated in the pin finned area. Surface temperatures are measured for heat fluxes up to 498 W/cm2 which enable determination of heat transfer characteristics.

Effect of an axial hole on natural convection heat transfer from a cylindrical pin fin attached to a horizontal plate

Heat transfer under laminar natural convection from a hollow cylindrical fin mounted on a horizontal base plate has been numerically studied. The flow outside the fin is much stronger than that inside the hole and as a consequence the rate of heat transfer from a hollow fin is primarily due to the contribution by the outer surface of the fin. Fortunately, the rate of heat transfer is not negatively affected by the presence of the hole at the fin centre. On the contrary, when the Grashof number is higher or the hole diameter is bigger, the inside surface contributes marginally to the heat transfer. A hollow fin saves material and weighs less compared to a solid fin. So, this feature may be exploited.

Effects of Geometry, Spacing, and Number of Pin Fins in Additively Manufactured Microchannel Pin Fin Arrays

The demand for higher efficiency is ever present in the gas turbine field and can be achieved through many different approaches. While additively manufactured parts have only recently been introduced into the hot section of a gas turbine engine, the manufacturing technology shows promise for more widespread implementation since the process allows a designer to push the limits on capabilities of traditional machining and potentially impact turbine efficiencies. Pin fins are conventionally used in turbine airfoils to remove heat from locations in which high thermal and mechanical stresses are present. This study employs the benefits of additive manufacturing to make uniquely shaped pin fins, with the goal of increased performance over conventional cylindrical pin fin arrays. Triangular, star, and spherical shaped pin fins placed in microchannel test coupons were manufactured using direct metal laser sintering (DMLS). These coupons were experimentally investigated for pressure loss and heat transfer at a range of Reynolds numbers. Spacing, number of pin fins in the array, and pin fin geometry were variables that changed pressure loss and heat transfer in this study. Results indicate that the additively manufactured triangles and cylinders outperform conventional pin fin arrays, while stars and dimpled spheres did not.

Comparison of heat sink and water type PV/T collector for polycrystalline photovoltaic panel cooling

Abstract Cylindrical pin fin heat sinks are not used to cool a panel, which we have done so in the present work and tested it's performance against a traditional single-channel PV/T collector. An older 20 Watt polycrystalline solar cell photovoltaic panel with a standard efficiency of 11.7% is elevated to a high temperature by indoor halogen light of intensity 1378.4 W m−2 in this study. The temperature of 81.7 ± 2.3 °C temperature at the front and 88.6 °C at the rear under at 0 m2 s−1 wind speeds are lowered using a cylindrical pin fin heat sink (fin density 1.22 fin cm−2). A channel of aspect ratios α* = 0.08 was attached to the rear of the panel as the collector configuration. Temperatures dropped to 58.4 °C with heat sink and 47.9° using the collector. The analysis suggests that heat flux of 667.2 W m−2 at the rear of the bare panel with no cooling is enhanced by 30 and 41.5% by the heat sink and PV/T collector by natural methods. We strongly urge exploration of using the cylindrical pin fin heat sinks to cool the panel under stagnant wind conditions.