태양광 발전용 인버터 방열에 사용되는 압입형 및 압출형 히트싱크의 방열 성능 평가

In a design competition by the mechanical engineering students at Carnegie Mellon University, which was the design of heat sinks for electronic cooling applications, twenty seven heat sinks were designed and tested for thermal performance. A heat sink with three rows of 9, 8, and 9 dimpled rectangular fins (staggered configuration) demonstrated the best performance in the test. This heat sink even had the least total volume (about 25% less than the set value). This paper reports on an effort made to verify and quantify the role of dimples on heat transfer enhancement of the heat sinks. This includes measurements and simulations of the thermal fluid properties of the heat sinks with and without dimples. Results of both the measurements and simulations indicate that dimples do in fact improve heat transfer capability of the heat sinks. Albeit, dimpled fins cause more pressure drop in air along the heat sink. Keeping the total volume of the heat sink and the height of the fins constant and changing the number of the fins and their arrangement show that there exist an optimum number of fins for the best performance of the heat sink. However, this number of fins is different for inline and staggered arrangements. To check the role of the roughness type on the heat transfer behavior of the fins, a heat sink with twenty-seven bumped fins with inline arrangement was also simulated. Results indicated that bumps increase both thermal resistance and pressure drop relative to that of the heat sinks with plain fins.

Evaluation of heat sink performance using PCM and vapor chamber/heat pipe

Statistical study on engine knock oscillation and heat release using multiple spark plugs and pressure sensors

Numerical modeling of natural convection heat transfer from radial branching heat sinks for LED cooling applications

Remotely deployed wireless devices such as tower-top active antenna arrays, remote radio heads, and pico or femto-cells are an increasingly prevalent feature of communications systems. Environmental standards which govern outdoor wireless equipment stipulate stringent conditions: high solar loads (up to 1 kW/m2), ambient temperatures as high as 55ºC and negligible wind speeds (0 m/s). These challenges result in restrictions on power dissipation within a given envelope, due to the limited heat transfer rates achievable with natural convection. There are two main objectives of this thesis; the first is to compare the results from a numerically modelled natural convection heat sink, representative of a remote radio head, with and without a solar shield subject to industrial standards and an environmentally defined worst case condition (a daytime condition in a hot location). The impact of solar shield length and location of the heat sink within the solar shield are investigated. The second main objective of this thesis is to segregate the components within a remote radio head across two heat sinks to improve the heat dissipation of the temperature sensitive components. The primary heat sink, representative of the temperature sensitive components, is experimentally and numerically investigated with and without a shield and without wind or solar loading. A secondary heat sink, representative of high power devices, is added to the shielded configuration in order to create a segregated structure. The secondary heat sink is investigated to determine the impact of the location and the number of fins to maximise the heat transfer on the primary heat sink. The deployment of a solar shield which is longer than the device that it contains was found to increase heat dissipation through a ‘chimney flow’ effect and it was determined that the heat sink should be located at the base of the solar shield. For a segregated structure, a secondary heat sink with a base plate temperature of 65°C above ambient was found to increase the Nusselt number of the primary heat sink by over 50 % in comparison to an unshielded case. The optimization of the number of fins on the secondary heat sink was found to offer an enhancement of 80 % over an unshielded heat sink. The findings of this thesis are of practical relevance for the thermal design of outdoor communications equipment: in particular, it is evident that the use of standard environmental conditions is conservative in comparison with a more comprehensive design process which references representative worst case data.

The FY13 NETL-RUA Turbine Thermal Management effort supported the Department of Energy’s (DOE) Hydrogen Turbine Program through conduct of novel, fundamental, basic, and applied research in the areas of aerothermal heat transfer, coatings development, and secondary flow control. This research project utilized the extensive expertise and facilities readily available at NETL and the participating universities. The research approach included explorative studies based on scaled models and prototype coupon tests conducted under realistic high-temperature, pressurized, turbine operating conditions. This research is expected to render measurable outcomes that will meet DOE’s advanced turbine development goals of a 3- to 5-point increase in power island efficiency and a 30 percent power increase above the hydrogen-fired combined cycle baseline. In addition, knowledge gained from this project will further advance the aerothermal cooling and TBC technologies in the general turbine community. This project has been structured to address: • Development and design of aerothermal and materials concepts in FY12-13. • Design and manufacturing of these advanced concepts in FY13. • Bench-scale/proof-of-concept testing of these concepts in FY13-14 and beyond. In addition to a Project Management task, the Turbine Thermal Management project consists of four tasks that focus on a critical technology development in the areas of heat transfer, materials development, and secondary flow control. These include: • Aerothermal and Heat Transfer • Coatings and Materials Development • Design Integration and Testing • Secondary Flow Rotating Rig.

Natural convection heat transfer enhancement in new designs of plate-fin based heat sinks

The objective of the present investigation is to perform a feasibility study of the working of a passive cooling device employing ferrofluid as a cooling medium and designing its heat sink. A computational study has been performed using COMSOL MultiPhysics, wherein a feasibility study was first done to check the working of a ferrofluid-based cooling device, and thereafter a design strategy was developed for selecting the number and height of annular fins for cooling of the ferrofluid in the closed channel. Ferrofluid was allowed to flow in the miniature cooling system in the presence of an external magnetic field produced by a permanent magnet. As ferrofluid flows through the loop, the thermal energy it absorbs should be dissipated so that colder ferrofluid is available for the next cycle of operation. Annular fins have been employed in the heat sink region to augment the heat dissipation rate. The effect of fin height and spacing on temperature drop across the heat sink has been studied, and it was found that the number of fins has a direct relation with the temperature drop across the heat sink. Fin height also contributes to the temperature drop, but, beyond a certain value, its effect was found to be insignificant.

The main objective of this study is to experimentally evaluate the effect of the air precooler heat transfer area on the effectiveness of a two-stage evaporative air cooler. To the best of our knowledge, this effect has not been studied before. In the experimental unit used, there were three identical heat exchangers to precool the ambient air prior to its flow into the direct evaporative cooling unit. These heat exchangers can work individually or be combined to control the total heat transfer area of the air precooler. In addition, the effectiveness of the two-stage system was measured as a function of the ratio between the mass flow rate of water flowing over the packing and the mass flow rate of the dry air passing through the packing; the effectiveness also depends on the mass flow rate of water flowing into the precoolers. The data obtained showed that there is an optimum value for the air precooler heat transfer area at which the thermal performance of the two-stage evaporative cooler has the maximum value. Moreover, the system effectiveness improved with the rate of flow of water into the first and the second precoolers. Note that the optimum value of the precooler heat transfer area should be determined accurately for each set of design and operating conditions.

Multi-objective topology optimization and thermal performance of liquid-cooled microchannel heat sinks with pin fins

Heat sinks have manifold applications, from micro-electronics to nuclear fusion reactors. Their performance expectations will continue to increase in line with the power consumption and miniaturisation of technology. Additive manufacturing enables the creation of novel, compact heat sinks with greater surface-to-volume ratios and geometrical complexities than standard pin/fin arrays and pipes. Despite this, there has been little research into the use of high surface area lattice structures as heat sinks. Here, the hydraulic and thermal performance of five surface-based lattice structures were examined numerically. Computational fluid dynamics was used to create useful predictive models for pressure drop and volumetric heat transfer coefficients over a range of flow rates and volume fractions, which can henceforth be used by heat transfer engineers. The thermal performance of surface-based lattices was found to be heavily dependent on internal geometry, with structures capable of distributing thermal energy across the entire fluid volume having greater volumetric heat transfer coefficients than those with only localised areas of high heat transfer and low levels of fluid mixing.

Computational Fluid Dynamics (CFD) for air/water-vapor and water-liquid two-phase flow mixing with condensation in a vertical inverted U-tube is presented in this paper. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in air/water-vapor and water-liquid mixing flow when condensation is considered. Water-liquid flows upward-downward through the inverted U-tube while the air/water-vapor mixture is extracted from a side-tube just after the flow oriented downward. The CFD simulation is carried out for a side air/water-vapor mixture volume fraction (αm) of 0.2–0.7, water-vapor mass fraction (Xv) of 0.1–0.5 in the side air/water-vapor mixture and water-liquid mass flowrate (mw) of 2,4,6, and 8 kg/s. The present results reveal that, at lower air mass flow rate, no significant effect of Xv on the generated static pressure at the inverted U-tube higher part. However, by increasing the air mass flow rates, ma ≥ 0.001 at mw = 2 kg/s, and ma ≥ 0.00125 at mw = 4 kg/s, we can infer that the lowest static pressure can be attained at Xv = 0.1. This may be attributed to the increased vapor and air mass flow rates from the side tube which results in shifting the condensation from the tube highest part due to air accumulation. This leads to increasing the flow pressure and decelerating the water-liquid flow. Raising mw from 2 to 4 kg/s at the same vapor mass ratio results in a lower static pressure due to more condensation of water vapor. The turbulent intensity and kinetic energy starts to drop approximately at ma = 0.002 kg/s, and αm = 0.55–0.76 at mw = 2 kg/s for all Xv values but no noticeable change at mw = 4 kg/s occurs. These findings estimate the operational values of air and water mass flow rates for stable air entrainment from the side-tube. Increasing the air and vapor mass ratio over these values may block the evacuation process and fails the system continuance. Likewise more air entrainment from the side-tube will decelerate the water flow through the inverted U-tube and hence the flow velocity will decrease thereafter. Moreover, this study reveals that the inverted U-tube is able to generate a vacuum pressure down to 55.104 kPa for the present model when vapor condensation is considered. This generated low-pressure helps to vent an engineering system from the non-condensable gases and water vapor that fail its function if these are accumulated with time. Moreover, the water-liquid mass flow rate in the inverted U-tube can be used to sustain the required operating pressure for this system and extract the non-condensable gases with a less energy consuming system. The present CFD model provides a good physical understanding of the flow behavior for air/water-vapor and water-liquid flow for possible future application in the steam power plant.

This study aims to optimize the thermal performance of pin fin heat sinks by minimizing the maximum temperature of the heat source. Using ANSYS ICEPAK, simulations were conducted for various design parameters, including the number of fins, inlet flow rate, and fin thickness, across circular fins in both inline and staggered arrangements. The circular staggered configuration with 36 fins (3 mm thick) and a flow rate of 6 CFM (Cubic Feet per Minute) achieved the lowest temperature of 34.96 °C, outperforming the inline arrangement. The Taguchi method helped strike a balance between heat transfer and pressure drop, revealing that flow rate has a greater influence when varied compared to the number of fins and fin thickness. An optimal configuration was identified with 36 fins and a flow rate of 4 CFM, which was less sensitive to operational variations. Analysis of Variance (ANOVA) revealed that inlet flow rate significantly impacts heat sink performance, while polynomial regression models demonstrated strong generalization capabilities, with Root mean square error (RMSE) of 8.92%. These findings provide reliable predictive tools and practical insights for optimizing heat sink designs in electronics cooling applications. By utilizing the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method, the coefficient of relative closeness (Cn*) is plotted as a main effect. Referring to the multi-objective optimization-based TOPSIS method, it is found that the attributes are partly from the inlet flow rate (Q) are 63.4% of the number of fins (Nf) (25.05%).

Optimization of tube arrangement and phase change material for enhanced performance of solar air heater- A numerical analysis

Three dimensional numerical models were developed to make prediction free convection heat transfer at steady state condition from radial flow heat sink. The air was considered as the medium of heat transfer. In radial flow heat sink, heat conducts through base in radial pattern and is uniformly transported to the fins. The Tagucy method was used to investigate the effect of several design parameters such as fin length, fin height, number of fins and heat sink base radius on heat transfer. There are five factors and four levels on each factor were chosen. Sixteen types of model were analyzed to obtain total heat transfer for each model. The result was used to estimate the optimum designed values of the parameters affecting the heat sink efficiency. The reproducibility of the optimum design value was verified. The average rate of heat transfer of optimum model was increased by more than 50 % than the reference model. Finally, the heat transfer data of radial flow heat sink were correlated of several outer radius by an equation.