Total Heat Transfer Area Research Articles

Thermodynamic, dynamic and flow friction analysis of a Stirling engine with Scotch yoke piston driving mechanism

This study concerns with the thermodynamic and dynamic analysis of an alpha type Stirling engine with Scotch-yoke piston driving mechanism. The thermodynamic aspect of the analysis is treated with a polytrophic nodal approximation. The pressure of nodal volumes is calculated with modified Schmidt formula which takes into account the pressure differences between nodal volumes caused by flow friction. The flow friction is calculated with adapted Darcy formula. The variation of the gas temperature in nodal volumes are calculated via the first law of thermodynamics given for unsteady open systems. The dynamic behavior of the engine is modeled via the motion equations of pistons and crankshaft. For a 2 kW nominal shaft power and 1400 rpm nominal speed, dimensions and working conditions of the engine were investigated by using realistic inputs. It was estimated that an engine having about 1.44 L swept volume, 1000 K hot source temperature, 400 K cold source temperature, 9050 cm2 total inner heat transfer area, 6 bar charge pressure, 2000 W/m2K inner heat transfer coefficient may produce more than 2 kW shaft power. For 142 rad/s average crankshaft speed the optimum thermal efficiency and torque of the engine were determined as 31% and 15.63 Nm respectively.

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.

Optimization of a separator assisted two-phase thermosyphon loop by using entropy generation analysis

In this paper, an optimization model is developed for a separator assisted two-phase thermosyphon loop and basic two-phase thermosyphon loop based on the entropy generation minimization method. The total entropy generation rate of the system is proposed as an optimization objective function and the total heat transfer area of evaporator and condenser is considered as a constraint. The model takes into account the irreversibility due to both irreversible heat transfer and pressure drop. The results show that there always exists minimum total entropy generation rate of the two systems when the heat transfer area ratio varies. The optimal heat transfer area ratios corresponding to the minimum total entropy generation rate also lead to the minimum total thermal resistance of the system and achieve the lowest temperature of the cooled object. Besides, the separator assisted two-phase thermosyphon loop can gain lower total entropy generation rate than the basic two-phase thermosyphon loop. Furthermore, the effects of the heat load, the total heat transfer area, the working fluid charge, the inner diameter of the separator and the height of two-phase tube on the minimum total entropy generation rate and the corresponding area ratio are also evaluated.

Energy, entropy and cost analysis of a combined power and water system with cascade utilization of geothermal energy

This paper proposed a novel combined system to achieve the cascade utilization of geothermal energy for joint power and water production. A regenerative organic Rankine cycle (ORC) is adopted as the top cycle, while a desalination system based on humidification dehumidification (HDH) principle with open-air architectures is applied to further utilize the geothermal energy. Based on the streams within the ORC and HDH units, the corresponding mathematical models with mass and energy conservation are established, and performance simulation according to thermodynamic laws is fulfilled. Furthermore, cost analysis of the combined system is also accomplished to reveal the correlations between the system economy and the involved parameters. The research results show that the actual peak values of net power, water production and gained-output-ratio (GOR) reach 42.68 kW, 236.81 kg h−1 and 1.42, and the total efficiency of the entire system is 31.19%. Based on the obtained thermodynamic performance, the bottom cost of the entire system is found as 4983.83$ with a total heat and mass transfer areas of 104.27 m2 at the balance condition of the humidifier. Furthermore, according to the influence analysis, an elevation of the evaporation temperature of the ORC, which is within the prescribed range, is beneficial to improve the thermodynamic performance and the relevant cost of the combined system.

Potential of the transcritical Rankine cycle using CO2-based binary zeotropic mixtures for engine’s waste heat recovery

The CO2 transcritical Rankine cycle has considerable potential for the waste heat recovery of engine, but its high operation pressure, harsh condensation condition and low thermodynamic performance are huge obstacle restricting the wide application of it. The purpose of this paper is to investigate the performance improvements of transcritical Rankine cycle using CO2 mixtures for the waste heat recovery of engine. A large number of refrigerants are discussed and then eight of them are selected as the candidate additives into CO2. The Peng-Robinson equations of states are applied to calculate the properties of CO2 mixtures in this study. Afterwards, thermodynamic, economic and miniaturization analyses are implemented. The results show that CO2 mixtures can enlarge the condensation temperature range of the transcritical Rankine cycle and the high operation pressure will also be improved. Moreover, based on transcritical Rankine cycle with optimal power output, CO2/R32 (0.3/0.7) performed best when the condensation temperature is lower than 40 °C, else the CO2/R161 (0.45/0.55) is a suitable selection among the CO2 mixtures. The optimal operation pressure will reduce by 36% and 35% respectively for the transcritical Rankine cycles with CO2/R161 (0.45/0.55) and CO2/R32 (0.3/0.7) compared with the CO2 transcritical Rankine cycle. Based on transcritical Rankine cycle with optimal total heat transfer area, the CO2/R32 (0.7/0.3) is the best selection. The optimal operation pressure of transcritical Rankine cycle with CO2/R32 (0.7/0.3) decreases by 1.4 MPa and net output power increases by 8.8% compared with CO2 transcritical Rankine cycle. The optimal total heat transfer area increment of CO2/R32 (0.7/0.3) will decrease by 29.4% compared with that of CO2/R32 (0.3/0.7).

Thermodynamic and dynamic analysis of an alpha type Stirling engine and numerical treatment

In this study, the nodal thermodynamic and dynamic analysis of an alpha type Stirling engine driven by Scotch-yoke mechanism is presented. The nodal thermodynamic section of the analysis is performed via 15 nodal volumes. The temperature variations in nodal volumes are calculated by means of the first law of the thermodynamics given for the open systems. The pressures in all of the nodal volumes are assumed to be equal and calculated via Schmidt relation. The momentary masses in nodal volumes are calculated via the perfect gas relation. The dynamic section of the analysis involves the motion equations of pistons and crankshaft. The motion equations are derived by means of the Newton method. In the derivation of the motion equations of pistons, the working fluid forces and friction forces are considered beside the inertia forces. In the derivation of motion equation of the crankshaft, moments of working fluid forces, moments of friction forces, the moment of external load and the moment of starter motor are considered as well as mass inertia moments. It is estimated that an engine having 1.8 L swept volume, 1000 K hot end temperature, 400 K cold end temperature, 3000 cm2 total inner heat transfer area, 5.1 bar charge pressure and 2000 W/m2 K inner heat transfer coefficient is capable of producing a shaft power above 2 kW. For these inputs and shaft power; the speed, speed fluctuation and torque are optimized as 138 rad/s, 16% and 14.9 N m respectively. The presented analysis is useful for engine development studies.

Thermodynamic analysis of compound cycle system for automotive waste heat recovery and air conditioning refrigeration

A compound cycle system, which integrates an automotive waste heat recovery (WHR) and air conditioning (A/C) refrigeration functions, is proposed in this paper. The models of this compound cycle system, independent organic Rankine cycle (ORC) system and independent A/C system are built by Aspen Plus software. R134a and R1234yf are selected as working fluids because of their common use in air conditioning system. R245fa is employed as working fluid for independent ORC system as a comparison. The targets of this analysis are more power output and smaller heat transfer area. Linear weighted method is applied to optimize this multi-objective problem using the working fluid flow rate and WHR evaporating pressure as variables. The simulation results indicate that the compound system behaves better than independent system both in the power output and heat transfer area with the same working fluid. The independent system with R245fa-R134a generates the most power output of 13.01 kW. The compound system with R1234yf shows the smallest total heat transfer area and total heat transfer area decreasing ratios (THTADRs) are 6.2–14.8% comparing with independent systems.

Optimal design of microtube recuperators for an indirect supercritical carbon dioxide recompression closed Brayton cycle

This paper presents a baseline design and optimization approach developed in Aspen Custom Modeler (ACM) for microtube shell-and-tube exchangers (MSTEs) used for high- and low-temperature recuperation in a 10 MWe indirect supercritical carbon dioxide (sCO2) recompression closed Brayton cycle (RCBC). The MSTE-type recuperators are designed using one-dimensional models with thermal-hydraulic correlations appropriate for sCO2 and properties models that capture considerable nonlinear changes in CO2 properties near the critical and pseudo-critical points. Using the successive quadratic programming (SQP) algorithm in ACM, optimal recuperator designs are obtained for either custom or industry-standard microtubes considering constraints based on current advanced manufacturing techniques. The three decision variables are the number of tubes, tube pitch-to-diameter ratio, and tube diameter. Five different objective functions based on different key design measures are considered: minimization of total heat transfer area, heat exchanger volume, metal weight, thermal residence time, and maximization of compactness. Sensitivities studies indicate the constraint on the maximum number of tubes per shell does affect the number of parallel heat exchanger trains but not the tube selection, total number of tubes, tube length and other key design measures in the final optimal design when considering industry-standard tubes. In this study, the optimally designed high- and low-temperature recuperators have 47,000 3/32 in. tubes and 63,000 1/16 in. tubes, respectively. In addition, sensitivities to the design temperature approach and maximum allowable pressure drop are studied, since these specifications significantly impact the optimal design of the recuperators as well as the thermal efficiency and the economic performance of the entire sCO2 Brayton cycle.

Experimental investigation of PCM thermal energy storage charge and discharge process with aperiodic (ramp) temperature inputs

In recent years, the use of storages filled with phase-change material (PCM) is increasingly considered. Such design is characterized by a higher density of thermal energy accumulation in comparison with water storages. However, the optimal use of the PCM storages requires a recognition of its dynamic characteristics during the loading and unloading process. This paper presents research aimed at understanding and dynamic description of the heat transfer process in a shell-and-tube thermal energy storage. The experimental test stand and the measurement and control system are described. The investigated storage had a form of a cylindrical tank of 40 dm3 volume in which a coil made of pipes with an external diameter of 3.35 mm was immersed in the PCM. The total heat transfer area was 9.4 m2. A lumped parameter model was used to describe mathematically the storage thermal dynamics. The PCM used was commercially available RT15 material with the heat capacity of 150 kJ/kg in the temperature range of 10–17°C. In the investigations, aperiodic (ramp) temperature inputs were used. The storage tests were carried out for low (12 h) and high (6 h) speeds of charging and discharging. The amplitude of the input signal and the liquid temperature at the storage inlet were set to include the phase transition interval of the PCM used. The obtained test results allowed to determine the enthalpy as a function of temperature for the whole storage. The experimental results were also used to validate 0D mathematical model of the heat storage.

The Design Of Grain Drying Oven Using Residual Exhaust Gas From Diesel Engine With Heat Transfer Analysis

The drying process plays an important role in the preservation of agricultural products. To this day, the drying process of rice grains harvested by the farmers in Semangga District, Merauke Regency, has always used sunlight. However, during rainy season, the farmers cannot dry their grains, and if such thing happens for a long time, it will cause decayed grains. The drying characteristics of a material are necessary in designing the dryers in use. The method used in this research was the design of grain dryers, which took the form of heating oven, by utilizing heat from the residual exhaust gas of diesel engine. The exhaust gas coming out of the exhaust manifold would be flowed through the heating pipe in the oven heating chamber, then through the convective heat transfer process, followed by conductive heat transfer, and then the heat flow conduction would be transmitted to the drying chamber. The objective of this research was to design grain dryers by using Diesel engine's residual exhaust gas, and to calculate the efficiency of grain dryer using heat transfer analysis. The bulk gas temperature in the exhaust gas section for hot fluid in the pipe is 371.55 K at a motor rotation of 2400 rpm, with the flow rate of the incoming exhaust gas heat mass of 0.01798031 kJ/s. The velocity of incoming exhaust gas mass is 36.75 kg/s, with the comprehensive heat transfer coefficient on the inlets of 92.7334404 W/ m2.oC. The heat transfer in the air section/ fluid section in the inner pipe is 351.1351 K, while the convective heat transfer coefficient in exit pipe is 8.010580984 W/m2.oC, thus obtaining Comprehensive heat transfer of 40.2312698 W/ m2.oC. The logarithmic mean temperature difference (LMTD) in the evaporator is 35.69590751oC with total heat transfer area of 084178 m2. With 2400 rpm motor rotation, the total heat transfer at the heat exchanger, which is the usable maximum heat, is equal to 0.226296111 kW; while the effectiveness of heat exchanger is at 60.95%. The energy used to evaporate the water and the amount of convective heat transfer from dry air to the product are 0.03696 kW, while the amount of air energy used is 0.05150 kW, obtaining the efficiency of the drying machine at 71%.

Numerical study of the geometrically graded micro-channel heat sink for high heat flux application

With the rapid development of the micro-scale and nano-scale electronic systems, the requirement of the operating temperature becomes more stringent to ensure good reliability and safety. Hence, thermal management technologies for dissipating the heat generated become an important agenda for researchers over the world. Micro-channel heat sink has been widely investigated by researchers and it is known that by increasing the total heat transfer area to volume ratio could enhance overall heat transfer performance. There are various types of micro-channel available such as straight channel, pin fin and wavy channel. Straight channel is the most common used of micro-channel in the market due to ease of manufacturing and low cost. There are several drawbacks associated with the straight channel design especially cooling performance is deteriorated along the flow direction. This will lead to the development of high temperature gradient from upstream to downstream and resulted uneven cooling performance which in turn shortens the device life expectancy. In this study, a novel geometrically graded micro-channel heat sink is introduced to improve the thermal performance of the conventional straight channel heat sink. Computational fluid dynamic simulations were conducted to investigate the performance of the novel fin micro-channel and straight channel heat sink. Under heat load of 2000 W, the geometrically graded micro-channel heat sink could reduce the average temperature to 69.6 °C and variation of temperature to 2.7 °C.

The power flow topology of heat transfer systems at supercritical conditions for performance analysis and optimization

Heat transfer processes with supercritical fluids are more complex than those with ordinary fluids due to the drastic variation of physical properties. In this study, with consideration of the changes of specific heat and heat transfer coefficient, the power flow topology of a multi-loop heat exchanger network is developed to investigate heat transfer processes at supercritical conditions. Simulation of a cooling process with supercritical CO2 validates the newly proposed method, where the maximum relative error of heat transfer rate is −2.72%. Meanwhile, optimization of a heat exchanger network discovers several design criteria for the optimal heat transfer performance. For instance, the mass charge of CO2 in the heat exchanger network influences its supercritical heat transfer performance significantly, which has the optimal value. Furthermore, the optimal mass charge nearly keeps constant with the heat transfer rate and the temperature boundaries, and increases linearly with the rise of the total heat transfer area, which indicates the optimal average density keeps constant. Substituting this constant density into the state equation of CO2 establishes the matching relation of the temperature range and the pressure for the optimal heat transfer performance.

A mechanical vapor compression desalination system coupled with a transcritical carbon dioxide Rankine cycle

In this paper, a desalination system in accordance with the running principles of mechanical vapor compression (MVC), in which the steam compressor is driven by a transcritical carbon dioxide (CO2) Rankine cycle (CRC), is suggested. The integrated mechanisms between the two subsystems are revealed and analyzed through the corresponding mass and energy conservation. The turbine parameters, comprising the inlet pressure and temperature, are first specified to explore the relevant influence impacts, and the obtained results are applied to accomplish the sensitivity analysis focusing on the top temperature of the seawater boiler, ambient temperature and terminal temperature difference (TTD) of the MVC heater. In combination with the entropy generation values of the components both within the MVC and CRC subsystems, all the calculated results are sufficient to prove the practicability and availability of the combined desalination system, producing freshwater. It is found peak values of the freshwater production, mc=1.29kgs−1 and gained output ratio (GOR), GOR=2.42, arise at the prescribed parameter range. Based on the results from the sensitive analysis, it is found a more prominent freshwater production and energy conversion efficiency can result from a higher top temperature, a lower ambient temperature and TTD of the MVC heater. Furthermore, based on the detailed simulations for the heat exchanger configurations, it is obtained that the total heat transfer area arrives at At=381.54m2 at Tt=353.15K, with a total cost of Ct=212,040.86¥.

Optimization design of heat recovery systems on rotary kilns using genetic algorithms

Heat loss from rotary kilns accounts for certain amounts of the total energy consumption in chemical and metallurgical industries. To reduce the heat loss, a parallel and a series-parallel heat recovery systems with nine heat recovery exchangers are proposed to preheat the cold water in this paper. Experimental measurements are carried out to determine the heat transfer coefficient equations of each heat recovery exchanger. Then, the heat recovery systems are analyzed to deduce the mathematic relation between the design parameters and the system requirements, i.e. the temperatures and heat transfer rates of the nine heat recovery exchangers. The total heat transfer area, the total power consumption and the entropy generation due to heat transfer and fluid flow are set as the objective functions in four multi-objective optimization (MOO) cases. With the aid of the genetic algorithm in the Matlab 2015, the optimized operational and structural parameters are obtained. Finally, the MOO results are compared with that of the single objective optimization (SOO) method and the original values. The optimization results show that the MOO method are more suitable for the operational parameters design of the heat recovery systems compared with the SOO method. The required total heat transfer area and the total power consumption are decreased by at least 12.1% and 13.7%, respectively. Besides, as the entropy generation due to heat transfer and fluid flow decrease in the MOO cases, the corresponding heat transfer area and power consumption of the heat recovery system decrease, respectively.

Performance and economic analysis of the distilled seawater desalination process using low-temperature waste hot water

In this paper two waste-heat-driven MED desalination processes (HW-MED and Boost-HW-MED) using waste hot water from petrochemical industry were developed. The thermodynamic model of the two MED systems was established based on the energy and mass balance equations. Taking the typical production capacity of 10,000m3/d as example the gained output ratio and total heat transfer area were selected as property indexes to compare the systemic performance of the two desalination processes based on the model calculation data. The effect of inlet temperature, outlet temperature and flow rate on the system performance were emphatically studied. Results showed that every 1°C increment in feed water temperature would increase the output of freshwater by approximately 438m3/d, and every 1°C increase in return water temperature would decrease the output by 417m3/d. Finally as the first recommendation, the investment and water-making cost of HW-MED process was investigated and compared with the common TVC-MED system. The operating cost of HW-MED system is only 2.354RMB/m3, which is 39.5% lower than that of TVC-MED system motived by commodity steam. The financial evaluation and sensitivity analysis on the cost was carried out. The results show that HW-MED process has a strong ability to resist fluctuations of the freshwater production price, raw material prices and the total investment. The conclusion provides data reference and theoretical support for desalinating seawater using waste heat from low-grade energy sources.

Thermo-flow characteristics of indirect dry cooling system with elliptically arranged heat exchanger bundles around a traditional circular cooling tower

In a traditional indirect dry cooling system, the heat exchanger bundles are circularly arranged around the circumference of a cooling tower, which suffers severely from ambient winds. In this paper, an elliptical arrangement of heat exchanger bundles, which surround a traditional circular cooling tower, is proposed to restrain the adverse impacts of ambient winds. Elliptically arranged heat exchanger bundles with four different minor to major axis ratios were investigated on the condition that the total heat transfer area is the same as the traditional indirect dry cooling system. The flow and temperature fields of cooling air in the absence/presence of ambient winds were obtained. The mass flow rate, heat rejection and outlet water temperature of the alternative indirect dry cooling systems were calculated and analyzed. The results show that the elliptically arranged heat exchanger with a small ratio of minor to major axis is superior in thermo-flow performance at high wind speed. It is recommended that indirect dry cooling system incorporating elliptically arranged heat exchanger bundles be applied in regions with strong prevailing winds to achieve better thermo-flow performance.

A practical approach to heat exchanger network design in a complex natural gas refinery

In this paper, a real-life case study of a complex natural gas refinery has been analyzed using the pinch technology concept, so that heat recovery as well as total hot and cold utilities have been improved for the main process units. This can be done by total heat transfer area and cost targeting, which called supertargeting. Two basic approaches to this analysis were developed, one for all hot and cold process streams simultaneously, without any restrictions and constraints, which was called “overall pinch method”, and the other for five divided areas in the plant, each consisting of some processing units, called “zonal targeting method”. Then the results were compared with each other and the potential of improvements was determined for each case. The result of this study showed that the retrofitted HEN using zonal targeting method improved total energy consumption and heat recoveries dramatically. Also, some modifications have been proposed, using grid diagrams to retrofit the existing HEN, in order to comply with energy recoveries determined from pinch analysis. Off course, this can be done by considering more investment (capital cost) for installation of new heat exchangers, in such a way that the operating costs can be remarkably reduced.

Cost-based design optimization of the heat exchangers in a parabolic trough power plant

This paper addresses two important concerns of the design of steam generators of parabolic trough power plants: cost minimization and component reliability. A thorough economic analysis of the heat exchangers of the steam generator and oil-to-salt heat exchangers of a 50 MWe parabolic trough power plant is presented. The heat exchanger design is realized following TEMA standards and optimized using a genetic algorithm. Two design strategies are compared: the minimization of the total heat transfer area and the minimization of the total annualized cost. It is seen that the second approach provides substantial savings over the lifetime of the plant.The economic analysis reveals a global optimum with an outlet temperature of the heat transfer fluid of 293 °C and an evaporator pinch point of 4.85 °C. The best design of the steam generator consists of a TEMA-H shell superheater and preheater and a TEMA-F shell reheater. The best design of the oil-to-salt heat exchangers includes six TEMA-F shell heat exchangers in series, with a log mean temperature difference of 7 °C and the molten salt on the shell-side. Lastly, a TEMA-X recirculation evaporator is proposed with a considerably reduced wall thickness when compared to a kettle evaporator.

Performance analysis of organic Rankine cycles using R600/R601a mixtures with liquid-separated condensation

Organic Rankine cycle (ORC) is a promising technology for power generation from medium to low temperature heat sources (<350°C). Although a zeotropic mixture can improve ORC efficiency, its large condenser heat transfer area is a crucial factor that impedes the broad application of ORCs using zeotropic mixtures. The liquid-separated condensation method is the process of separating the condensed fluid from the two-phase flow during condensation. This method has potential to effectively reduce the condenser heat transfer area of an ORC using a zeotropic mixture by increasing the condensation heat transfer coefficient and reducing the pressure drop. This study introduced the liquid-separated condensation into ORCs using R600/R601a mixtures. The effects of vapor quality at the liquid-separated unit inlet (xLSI) on the net power outputs, condensation heat transfer coefficients and heat transfer areas were analyzed. Results show that a xLSI below 0.3 maximizes the average condensation heat transfer coefficient for the R600/R601a mixture. The liquid-separated condensation can increase the average condensation heat transfer coefficient by 23.8% and reduce the condenser heat transfer area by 44.1% compared to the conventional condensation. Although the liquid-separated condensation may slightly reduce the maximized net power output for a low xLSI, the decrease of total heat transfer area is larger than that of the maximized net power output. Thus, the ratio of the total heat transfer area to the net power output can be reduced by 28.3%. The R600/R601a (0.9/0.1) mixture with xLSI=0.3 obtains the lowest electricity generation cost for the R600/R601a mixtures with single-stage liquid-separated condensation.

Convective heat transfer performance of airfoil heat sinks fabricated by selective laser melting

This paper presents the forced convective heat transfer performances of novel airfoil heat sinks produced by Selective Laser Melting (SLM). Heat sinks with staggered arrays of NACA 0024 and NACA 4424 airfoil shaped fins were investigated experimentally and the results were compared with conventional heat sinks with circular and rounded rectangular fins. In addition, NACA 0024 heat sinks with angles of attack (α) ranging from 0° to 20° were also fabricated and the effects of the angle of attack (α) on the heat sink thermal performances were examined. Experiments were conducted in a rectangular air flow channel with tip (CLt) and lateral (CLh) clearance ratios of 2.0 and 1.55 and with Reynolds numbers (Re) ranging from 3400 to 24,000. Numerical studies were first performed to validate the experimental results of the circular finned heat sink and reasonably good agreement between the experimental data and numerical results were observed. Comparison of the experimental results showed that the heat transfer performances of the airfoil and rounded rectangular heat sinks exceeded those of the circular heat sink. The experimental Nusselt numbers were computed based on the heat sink base area (Nub) and the total heat transfer area (Nut). In comparison with the circular heat sink, highest enhancements in Nub and Nut of the NACA 0024 heat sink at α = 0° were 29% and 34.8%, respectively. In addition, the overall heat transfer performances of the NACA 0024 heat sinks were also seen to increase with increasing α. The results suggest that the streamline geometry of the airfoil heat sink has low air flow resistance, which resulted in insignificant bypass effect and thereby improving the heat sink thermal performance. In addition, the increase in α further improves the heat transfer performance of the NACA 0024 heat sinks through the formation of vortices which enhanced fluid mixing. Finally, based on the above mechanisms proposed, a semi-analytical model was developed to characterize the heat transfer performances of the NACA 0024 heat sinks for the range of α and Re tested. In comparison with the experimental data, reasonably accurate predictions were achieved with the model where the deviations in Nub were less than 7% for Re ≥ 6800.