Natural Convection Cooling Research Articles

Thermal performance of serpentine channel immersion cooling for lithium-ion battery 18650 with HFE-7100

This paper presents Serpentine Channel Immersion Cooling (SCIC) as a new design for battery immersion cooling applications using HFE-7100 dielectric fluid. The main objective of this research is to analyze the temperature generation characteristics of Li-ion batteries with the performance of natural convection (NC) and Serpentine Channel Immersion Cooling (SCIC) with HFE-7100 liquid. The depth of discharge (DoD) is carried out at 80% of the battery capacity during the discharge process with variations in C-rates of 1 C, 1.5 C, and 2 C. The results show that the C-rate has a greater value, the temperature value released by the battery will also be greater. The negative pole, intermediate battery, and positive pole exhibit the characteristics of the battery pack’s surface temperature in order from highest to lowest throughout the discharge process. At the negative pole of the battery, the highest temperature in NC cooling is 30.1°C, 32.3°C, and 33.3°C can reduce this temperature to 28.8°C, 29.73°C, 31.8°C by SCIC with HFE-7100 liquid at DoD 1 C, 1.5 C, and 2 C respectively. Battery surface temperature characteristics based on channel position from highest to lowest using NC in the order of 6-3-2-4-5-1 and SCIC in the order of 6-5-4-3-2-1.

Axial Ventilation and Blade Row Effects on Transient Natural Convective Shutdown Cooling in a Gas Turbine

Abstract As a large civil gas turbine is cooling down, natural convective flows cause components to cool asymmetrically – the bottom sector cools faster than the top. This can lead to a number of issues that have the potential to damage engine components and affect operability. The ability to predict this cooling cycle of a gas turbine has proven to be extremely difficult, owing to the complex nature of natural convective flow and its dependency on a considerable number of design parameters. An experimental and numerical investigation into the impact of axial ventilation (interaction between the annulus and the external air) and blade rows on the natural convective flow in a large civil gas turbine high-pressure compressor has led to some key discoveries. Axial ventilation caused a 70% increase in the peak top-to-bottom temperature difference in the cooling cycle, when compared to the baseline sealed case. The combinations of four blade rows and axial ventilation caused a 130% increase in peak temperature difference over the baseline case. Numerical simulations illuminated that the root cause of this was the cold air drawn into the lower section of the annulus led to a relatively high heat flux, coupled with a blockage effect on the natural draft in the upper section of the annulus. This study has highlighted the importance and inter-dependency of these effects in defining the level of rotor bow that is observed. Therefore, it is imperative that they are included and sufficiently captured in order for a shutdown.

Natural Convection Cooling of a Heat Source Placed at the Bottom of a Square Cavity Filled with Water-Based Nanofluid

The present work deals with the cooling process of a heat source, placed in the center of the bottom wall of a square cavity. A numerical resolution using finite volume method was carried out. The cavity is filled with a water-based Nanofluid, where four different types have been assumed. The vertical and top walls are under low temperature TC. Two thermal conditions were assumed at the source (q-imposed or T-imposed), while the remaining parts of the same wall are isolated. The effects of Rayleigh number (Ranf), source length (SL), volume concentration of nanoparticles (Φ) and their types were analyzed. The case of pure water (Φ = 0%), studied first, served as a reference case. The results obtained for this case, showed the increase of disturbances in the dynamic and thermal fields, in addition to the average rate of heat transfer (Nu) when Ra increases and SL decreases. SL = 1.0 case showed exception. These effects are more important for the T-imposed case than the other. Subsequently, the Al2O3-Water Nanofluid is considered with 0 <Φ≤ 10%. An increase in circulation intensity with improvement of local (Nu) and average (Nu) heat exchange rates have been recorded when Φ increases, although mentioning that its effect is significantly stronger for the q-imposed case. In the last part of the work, three other types of Nanofluids were assumed, where the obtained results showed the main improving effect of higher thermal conductivity on the heat transfer intensity. An important result which can be summed up in the great rapprochement of the heat exchange intensities for strong Ranf and Φ for SL close to 1.0, for the two heating types. In other words, the condition on the source loses its importance for such considerations.

Scaling of Transient Natural Convection Cooling in Side-Cooled Cavity: The Effect of Variable Viscosity

The transient natural convection of variable and constant viscosity fluids in a side cooled cubical cavity is studied experimentally. The convective flow in the cavity is visualized by the shadowgraph technique. The fluid was initially preheated and enough time is allowed to assure uniform temperature distribution. Temperature difference is introduced by a sudden cooling of the two side walls. The results indicate that the transient flow development is characterized by the following distinct processes: the initial growth of the vertical boundary layer and horizontal intrusions, the interaction of the horizontal intrusions and the stratification. New scaling relations are introduced to include the effect of the viscosity variation with temperature. The new suggested scalings showed good agreement with the measurements based on the shadowgraph images.

A Free-Standing, Silent, Micro/Mesoscale Combustion-Powered Thermoelectric Generator Based on Natural Convection Cooling

Abstract In recent years, the world has become increasingly interested in power generation using thermoelectric generators (TEG) because of the advantage of converting heat directly to electricity. In this work, experimental studies have been carried out on micro/mesoscale combustor-powered thermoelectric generators (MCP-TEG) to evaluate the influence of different types of heat sinks on the cold side of MCP-TEG. The micro/mesoscale combustor was connected with Bi2Te3 based TEG1-12708 thermoelectric modules from both sides along with a heat sink on the cold side of the modules. The system uses natural convection cooling with a flat-plate aluminum heat sink. The MCP-TEG generates electrical power of 0.242 W with an overall efficiency of 0.3% at a hot-end temperature of 351 K. Power load feature and time history tests are conducted to evaluate the performance of the MCP-TEG system and comparisons of various related studies were made.

A NUMERICAL STUDY ON MULTI-OBJECTIVE DESIGN OPTIMIZATION OF HEAT SINKS FOR FORCED AND NATURAL CONVECTION COOLING OF IMMERSION-COOLED SERVERS

A NUMERICAL STUDY ON MULTI-OBJECTIVE DESIGN OPTIMIZATION OF HEAT SINKS FOR FORCED AND NATURAL CONVECTION COOLING OF IMMERSION-COOLED SERVERS

Proposed Modeling of Natural Convection Cooling Heat Pipe

Proposed Modeling of Natural Convection Cooling Heat Pipe

Natural Convection Cooling of Aircraft Wingbox Structures During Turnaround Period

Natural Convection Cooling of Aircraft Wingbox Structures During Turnaround Period

The Effect of Wall Thermal Boundary Condition on Natural Convective Shutdown Cooling in a Gas Turbine

Abstract As a civil gas turbine cools down, asymmetric natural convective heat transfer causes the bottom sector of the rotor to cool faster than the top; this circumferential thermal gradient can potentially cause the shaft to deflect – a phenomenon called thermal or “rotor” bow. Rotor bow is tremendously difficult to predict due to its dependence on a number of engine design parameters, in addition to the complex nature of natural convective flows. A novel experimental facility has been developed to gain further understanding into shutdown cooling of a gas turbine. The scope of this paper is to quantify the effect of basic design features on natural convective cooling in an engine annulus during shut-down; specifically the influence of the thermal boundary wall conditions and the annular diameter ratio. In addition to this, a low-cost, robust thermocouple probe has been developed and validated, which allows for accurate temperature measurements in a natural convective boundary layer. An extensive experimental campaign has been completed. The key finding is that the local radial wall temperature difference was found to be the most influential parameter on the local heat transfer. Non-isothermal walls did not alter the overall distribution of the inner wall equivalent conductivity. This was true for both cylindrical and conical sections. An appropriate characteristic length for use in the Rayleigh number definition for both the concentric cylinder and conical sections have been validated. The conical inner section (5 deg hade angle) did not affect the overall heat transfer in the range of conditions tested. Therefore, the mean surface heat transfer for non-isothermal inner and outer profiles, within the range −0.4<ΔRa/RaLc<0.4, where the thermal gradient is negative in the clockwise from top-dead-center, can be predicted using isothermal correlations for RaLc<5.0×105 and Dr < = 1.5.

Best Practices for Thermal Modeling in Microelectronics with Natural Convection Cooling: Sensitivity Analysis

A detailed sensitivity study was carried out on various key parameters from a high precision numerical model of a microelectronic package cooled by natural convection, to provide rules for the thermal modeling of microelectronic packages subjected to natural convection heat transfer. An accurate estimate of the junction temperature, with an error of less than 1˚C, was obtained compared to the experimental data for the vertical and horizontal orientations of the test vehicle in the JEDEC Still Air configuration. The sensitivity study showed that to have an accurate estimate of the temperature, the following elements should be present in the thermal model: radiation heat transfer in natural convection cooling; a computational fluid dynamics analysis to find realistic convection coefficients; detailed models of the high conductivity elements in the direction of the heat flow towards the environment; and finally precise values for the thicknesses of layers and the thermal properties of the substrate and the printed circuit board.

Natural Convection Cooling of a Heat Source Placed at the Bottom of a Square Cavity. Effect of Source Length, Position, Thermal Condition and Prandtl Number

Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means of natural convection has been studied numerically in this work. Two thermal conditions have been assumed at the source (q-imposed or T-imposed). The effects of Rayleigh number (Ra=10+3→10+6), source length (SL=0.1→1.0), source position (D) compared to left side, in addition to the effect of the number of Prandtl (Pr=0.71→10+2) were analyzed with ample details. For a source at the center of the bottom side, results showed an increase of flow and temperature disturbance with increasing Ra and/or SL, with an enhancement of both local and mean Nusselt numbers. Particular exceptions were noticed for high Ra values for the second heating type. For all considerations, the case of SL=0.1 makes an exception where a very good heat exchange rate is recorded. When the source is no longer centered, Clearer difference between this case and the previous one was recorded, especially for small D values. Very good heat exchange rate is recorded for D=0.0 for all considerations, with remarkable amount of difference compared the closest one to it, followed by a progressive decrease until the case of source at the center. Finally, Prandtl number (Pr) effect analysis showed an increase of the heat transfer rate with a clear amount from Pr=0.71 until Pr=5.0, followed by a slight increase for higher Pr values until stabilization for Pr>50.0. The good exploitation of the intervening parameters’ parameters, allows ensuring the best cooling of the source.

A Numerical and Experimental Study of a Novel Heat Sink Design for Natural Convection Cooling of LED Grow Lights

Light-emitting diode (LED) grow lights are increasingly used in large-scale indoor farming to provide controlled light intensity and spectrum to maximize photosynthesis at various growth stages of plants. As well as converting electricity into light, the LED chips generate heat, so the boards must be properly cooled to maintain the high efficiency and reliability of the LED chips. Currently, LED grow lights are cooled by forced convection air cooling, the fans of which are often the points of failure and also consumers of a significant amount of power. Natural convection cooling is promising as it does not require any moving parts, but one major design challenge is to improve its relatively low heat transfer rate. This paper presents a novel heat sink design for natural convection cooling of LED grow lights. The new design consists of a large rectangular fin array with openings in the base transverse to the fins to increase air flow, and hence the heat transfer. Numerical simulations and experimental testing of a prototype LED grow light with the new heat sink showed that openings achieved their intended purpose. It was found that the new heat sink can transfer the necessary heat flux within the safe operating temperature range of LED chips, which is adequate for cooling LED grow lights.

Porosity Manipulation in Bottom-Enclosed Vertical Porous Structure to Improve Natural Convection Cooling Efficacy: A Computational Study

Abstract Flow acceleration by imposing flow channelization structures like chimneys and/or solid barriers to improve natural convection cooling in pure fluids, is a well-known technique and a thoroughly investigated topic in thermal engineering. However, accelerating flow through porous media, by using such a passive technique, is challenging due to restriction imposed by the solid matrix to the erection of such structures. This study is a unique investigation into a passive method to accelerate flow in natural convection cooling through a bottom-enclosed porous medium with a vertical heated structure at the center, a configuration that is commonly encountered in industry. The porous domain is divided into distinct zones varying in porosity while retaining the average porosity of the original system, to ensure enough structural stability to the vertical heating element. Employing computational fluid dynamics (CFD) analyses, the study shows that the method has the potential to significantly improve natural convection cooling by accelerating flow in tall porous structures while at the same time improves mechanical stability of such structures.

Natural Convection Cooling of PCB Equipped with Perforated Fins Heat Sink including Inclination and Vibration Effects

Natural Convection Cooling of PCB Equipped with Perforated Fins Heat Sink including Inclination and Vibration Effects

Analytical Thermal Model of Natural-Convection Cooling in Axial Flux Machines

In this paper, an analytical approach is proposed in developing a lumped parameter thermal model for the stator coils of naturally cooled axial-flux tooth-coil permanent magnet machines. The model comprises one tooth, the coil around it, and the air channels between coils and the teeth supporting structure; each component is subdivided into cuboidal or arc subelements. An expression of the convective exchange coefficient is proposed to take into account the radial position of each tooth. Experimental results validate the proposed model, which can also be used in the design stage of a machine.

Water-Based Nanofluids for Natural Convection Cooling of a Pair of Symmetrical Heated Blocks Placed Inside a Rectangular Enclosure of Aspect Ratio Two

Water-Based Nanofluids for Natural Convection Cooling of a Pair of Symmetrical Heated Blocks Placed Inside a Rectangular Enclosure of Aspect Ratio Two

135 Relationship between Natural Convection Cooling Performance and Tilt Angle of Thin Enclosure

135 Relationship between Natural Convection Cooling Performance and Tilt Angle of Thin Enclosure

Optimized Finned Heat Sinks for Natural Convection Cooling of Outdoor Electronics

A series of analysis has been conducted previously to analyze the finned heat sink thermal performance. The analysis is first performed to optimize the fin spacing of a vertical continuous finned heat sink. Both empirical and CFD methods are utilized to obtain the optimal fin spacing of a given heat sink. The results from both methods are in very good agreement. The analysis was then extended to optimize the fin configurations. Three types of fin configurations, namely continuous fins, staggered fins and in-line fins are under consideration. The results from the CFD analysis indicate that the continuous fin configuration is the most effective thermally. Later, the effects of the cover or shrouds at various distances on the heat sink thermal performance are also analyzed. The heat sink with the cover in a direct contact with the fin tips performs best in the heat rejection. For tower or poled mounted electronics, the heat sink weight is extremely important. Therefore, the extrusion fin heat sink is replaced by the plain fin heat sink for weight reduction. This study is aiming at the development of newly developed light weight finned heat sink and its thermal performance under natural convection for cooling of electronics.

Experimental study of radiation dose rate at different strategic points of the BAEC TRIGA Research Reactor

The 3MW TRIGA Mark-II Research Reactor of Bangladesh Atomic Energy Commission (BAEC) has been under operation for about thirty years since its commissioning at 1986. In accordance with the demand of fundamental nuclear research works, the reactor has to operate at different power levels by utilizing a number of experimental facilities. Regarding the enquiry for safety of reactor operating personnel and radiation workers, it is necessary to know the radiation level at different strategic points of the reactor where they are often worked. In the present study, neutron, beta and gamma radiation dose rate at different strategic points of the reactor facility with reactor power level of 2.4MW was measured to estimate the rising level of radiation due to its operational activities. From the obtained results high radiation dose is observed at the measurement position of the piercing beam port which is caused by neutron leakage and accordingly, dose rate at the stated position with different reactor power levels was measured. This study also deals with the gamma dose rate measurements at a fixed position of the reactor pool top surface for different reactor power levels under both Natural Convection Cooling Mode (NCCM) and Forced Convection Cooling Mode (FCCM). Results show that, radiation dose rate is higher for NCCM in compared with FCCM and increasing with the increase of reactor power. Thus, concerning the radiological safety issues for working personnel and the general public, the radiation dose level monitoring and the experimental analysis performed within this paper is so much effective and the result of this work can be utilized for base line data and code verification of the nuclear reactor.

Natural Convection Cooling of an Array of Flush Mounted Discrete Heaters Inside a 3D Cavity

AbstractAn investigation of natural convective flow and heat transfer inside a three dimensional rectangular cavity containing an array of discrete heat sources is carried out. The array consists of a row and columnwise regular arrangement of identical square shaped isoflux discrete heaters and is flush mounted on a vertical wall of the cavity. A symmetrical isothermal sink condition is maintained by cooling the cavity uniformly from either the opposite wall or the side walls or the top and bottom walls. The other walls of the cavity are maintained adiabatic. A finite volume method based on the SIMPLE algorithm and the power law scheme is used to solve the conservation equations. The parametric study covers the influence of pertinent parameters such as the Rayleigh number, the Prandtl number, side aspect ratio of the cavity and cavity heater ratio. A detailed fluid flow and heat transfer characteristics for the three cases are reported in terms of isothermal and velocity vector plots and Nusselt numbers. In general it is found that the overall heat transfer rate within the cavity for Ra=107 is maximum when the side aspect ratio of the cavity lies between 1.5 and 2. A more complex and peculiar flow pattern is observed in the presence of top and bottom cold walls which in turn introduces hot spots on the adiabatic walls. Their location and size are highly sensitive to the side aspect ratio of the cavity and hence offers more effective ways for passive heat removal.