Lower Coolant Flow Rates Research Articles

Numerical research for the influence of cylindrical ribs and inclined mainstream on double wall cooling configurations

Gas turbine operates in high temperature environment, cooling technologies are applied for reducing the temperature of turbine blade, double wall cooling configuration is an effective cooling method. This paper proposed an investigation on double wall cooling configurations by computational fluid dynamics (CFD). Different cylindrical ribs were arranged on the different plates. Their cooling performances and flow field were analyzed, what's more, new rib arrangement, hole arrangement and spacing arrangement were proposed in the base of original arrangement, their cooling performances were compared. Finally, inclined mainstream is added for simulating gas impacting the inclined blade surface in real engine condition, the inclined angles were 30°, 45°, 60°. According to the results, ribs brought limit influence on the cooling effectiveness. More holes consumed extra 54 % coolant but only increase cooling effectiveness by 15 % under high blowing ratio. The inclined mainstream decreases cooling effectiveness by 67 % maximally. Under low coolant flow rate, cubic polynomial describes the correlation between cooling effectiveness and inclined angle, and under high coolant flow rate, linear polynomial is more suitable. Besides, offset arrangement shows better cooling performance under the inclined mainstream.

Enhancement of battery thermal management system using a novel structure of hybrid liquid cold plate

Battery thermal management system (BTMS) is a crucial component of electric vehicles (EVs) as it ensures optimal operating temperature of battery cells, which is critical for battery safety and performance. Among various cooling methods, liquid cooling is the most reliable owing to its high heat transfer coefficient and low power consumption. In this study, a liquid cold plate (LCP) suitable for different ambient conditions was developed, with optimized power consumption and without pre-cooling the coolant. We investigated six different microchannels, including straight, wavy walls, and metal foam-embedded microchannels, in three different ambient conditions (20 °C, 25 °C, and 35 °C) at various coolant mass flow rates (ranging from 2.5 to 17 kg/s). Our results showed that the wavy walls microchannel reduced the maximum temperature by 4–6 °C, depending on the wave amplitude. Additionally, using fully embedded metal foam microchannels resulted in a 14 °C decrease in the maximum temperature compared to that of straight microchannels, while the temperature difference of the battery module remained within an acceptable range. We also found that a thick layer of metal foam in the vicinity of the microchannel walls decreased the battery module temperature by up to 4 °C while reducing the pumping power, especially at low coolant flow rates. Deploying the wavy microchannel reduced the pumping power between 50 and 73%, while a thin layer of metal foam caused a 50% decrease in pumping power.

Numerical study of three-dimensional microchannel using the Constructal Law

In this work it was performed a numerical study about the design of the fins geometry of a microchannel heat sink. The study was based on the Constructal Theory and proposes to develop a methodology to predict, in a deterministic way, the positioning and size of the heat sink fins. The method uses a construction function, which is dependent on velocity and temperature fields, to “guide” the construction. Main goal is to obtain arrangements with the lowest possible thermal resistance. The OpenFOAM software was used to solve the model equations using the Finite Volume method. The geometries were built from an empty domain to which fins were added. A total of 12 geometries were generated and best results were obtained with the geometries that better combined a large fins occupation area with a low coolant flow rate. It was also showed that there is a correct amount of solid which leads to the best thermal performance. Observing the best obtained configurations, it is clear that there is a limit to the material addition in the channel; flow restriction causes a drop in the flow rate which is not compensated by the increase in the heat sink solid volume.

Теплосъём и термостабилизация высокотемпературных поверхностей диспергированным потоком теплоносителя

The effectiveness of stabilizing the surface temperature by a dispersed coolant flow is experimentally studied on a bench simulating energy intensive elements of thermonuclear installations A test section in which the maximum heat flux density can be obtained when being subjected to high-frequency heating was developed, manufactured, and assembled. The test section was heated using a VCh-60AV HF generator with a frequency of not lower than 30 kHz. A hydraulic nozzle with a conical insert was used as the dispersing device. Techniques for carrying out an experiment on studying a stationary heat transfer regime and for calculating thermophysical quantities were developed. The experimental data were obtained in the stationary heat transfer regime with the following range of coolant operating parameters: water pressure equal to 0.38 MPa, water mass flow rate equal to 5.35 ml/s, and induction heating power equal to 6--19 kW. Based on the data obtained, the removed heat flux density and the heat transfer coefficients were calculated for each stationary heat transfer regime. The dependences of the heat transfer coefficient on the removed heat flux density and of the removed heat flux density on the temperature difference have been obtained. High values of heat transfer coefficients and heat flux density at a relatively low coolant flow rate were achieved in the experiments.

Research of the Influence of External Conditions on the Optimal Value of the Valves Hydraulic Resistances of Heating Devices Installed in a Heating Indoor Area

The article substantiates the relevance of the use of artificial intelligence methods for energy saving problems and provides examples of such works, including using the method of mathematical optimization. Several examples of topical optimization problems are given. The necessity of studying the landscape of the objective function when optimizing the hydraulic regime of the heating system of buildings is substantiated. The formulation of the problem of this study, including the formula for calculating the objective function, is given. A brief description of the optimization algorithms used (genetic algorithm and directed search algorithm) is given. A description of a computational experiment is given, during which the results of optimization of thermohydraulic modes of heated rooms under different conditions were investigated: outside air temperature, temperature and coolant flow rate. This study revealed that the optimal value of the hydraulic resistances of the valves of heating devices generally decreases with a decrease in the outside air temperature, as well as the temperature and flow rate of the heat coolant. Deviations from this pattern are observed under extreme conditions: too low outside air temperature, at low (for these conditions) coolant temperature or low coolant flow rate.

An Experimental Investigation on the Fluid Distribution in a Two-Phase Cooled Rack Under Steady and Transient Information Technology Loads

Abstract Increasing power densities in data centers due to the rise of artificial intelligence, high-performance computing, and machine learning compel engineers to develop new cooling strategies and designs for high-performance information technology (IT) equipment. Two-phase cooling is a promising technology that exploits the latent heat of the coolant which is significantly more effective in removing high heat fluxes than when using the sensible heat of the fluid. Also, utilizing the latent heat allows operating at lower coolant flow rates and implies more uniformity in the temperature of heated surfaces. Despite the benefits of two-phase cooling, the phase change adds complexities to a system when multiple evaporators (exposed to different heat fluxes potentially) are connected to a single coolant distribution unit. In this article, a commercial coolant distribution unit is used to investigate pumped two-phase cooling in rack scale. Seventeen two-rack unit servers from two distinct models are retrofitted with 34 impinging jet evaporators and deployed in a rack. Four case studies are presented to provide insights into the complex behavior of a pumped two-phase cooling system with several evaporators. The flow rates and pressure distribution across the rack are studied in various filling ratios. Also, investigated is the transient behavior of the cooling system due to a step change in the IT workload. Finally, a control system is designed to regulate the temperature of the supplied coolant in response to the step change in the IT workload and is tested.

Heat spreading performance of SiC-based power module with bonded vapour chamber for electric powertrain integration

After evolving side by side over the past three decades, insulated gate bipolar transistors (IGBTs) and metal–oxide–semiconductor field-effect transistor (MOSFETs) become two main options in high power semiconductor market of Hybrid Electric Vehicle (HEV) or Battery Electric Vehicle (BEV) systems. Recent improvements on high power performance are focused on the reduction of power losses and the enhancement of system reliability. Power losses of Si-based semiconductor are dissipated in the form of heat, which must be transferred away from the switching junction effectively. In this paper, we evaluate the new vapour chamber wick design and its heat spreading performance on a SiC-based MOSFETs, the results could be used as guides in order to provide a solution to tackle with thermal imbalance incurred by switching current. The selected cases showed that Silicon carbide (SiC) based MOSFETs could operate at more uniform temperature gradient with minimum 1.4 °C temperature difference across the whole bonding interfaces, and hotspots can be constrained below 120 °C by means of phase changing cooling methods. In addition, the replacement of conventional baseplate by vapour chamber could further reduce overall thermal resistance from junctions to coolant fluids. The simulation results show that wicks design with sintering methods could perform better than groove and mesh design in such high power application. At last, under low coolant flow rate chanlleges at 0.5 l/min, an integrated vapour chamber with ellipse pin–fin 16 × 20 is preferred with achieved temperature at 123.3 °C.

A comparison of temperature distribution in PEMFC with single-phase water cooling and two-phase HFE-7100 cooling methods by numerical study

Thermal management has been considered as one of the critical issues in proton exchange membrane fuel cell (PEMFC). Key roles of thermal management system are maintaining optimal operating temperature of PEMFC and diminishing temperature difference over a single fuel cell and stack. Severe temperature difference causes degradation of performance and deterioration of durability, so understanding temperature distribution inside a single fuel cell and stack is crucial. In this paper, two-phase HFE-7100 cooling method is suggested for PEMFC thermal management and investigated regarding temperature change inside a fuel cell. Also, the results are compared to single-phase water cooling method. Numerical study of temperature distribution inside a single PEMFC is conducted under various conditions for the two different cooling methods. Fuel cell model considering mass transfer, electrochemical reaction and heat transfer is developed.The result indicates that two-phase HFE-7100 cooling method has an advantage in temperature maintenance and temperature uniformity than single-phase water cooling method, especially in high current density region. It is also revealed that the cell temperature is less dependent on system load change with two-phase cooling method. It indicates that the fuel cell system with two-phase cooling method has high thermal stability. In addition, the effect of coolant flow rate and coolant inlet pressure in two-phase HFE-7100 cooling method are discussed. As a result, two-phase cooling method showed reliable cooling performance even with low coolant flow rate and the system temperature increased as coolant pressure rose.

A Novel Approach to the Thermal Management of Internal Combustion Engines

The paper presents a novel control architecture developed with the aim to satisfy the requirements of the cooling system of an ICE, by means of an electric pump and of an ad-hoc developed control module. The developed controller is based on the Robust Model Predictive Control and is designed with the purpose to satisfy the input and output constraints and to reject the external disturbances, by adopting a lumped parameter model of the engine cooling system, which predicts the coolant temperature, the average wall temperature and the heat transfer regime including nucleate boiling. Given that the proposed methodology is valid for each condition, in the present paper the focus is on the engine operating under fully warmed conditions, with the aim to keep the wall temperature into the prescribed limits, with the lowest possible coolant flow rates. This goal is achieved by properly defining the controller parameters. Different control strategies are proposed and their effectiveness is evaluated in terms of engine wall temperature, coolant temperature, coolant flow rate and heat transfer regime in response to step-wise variations in fuel flow rate. The region of stability of the controller is also discussed. Results show that the control algorithm is robust in terms of disturbance rejections and ensures effective and safe cooling with much lower coolant flow rates if compared to the ones provided by the use of the standard crankshaft driven pump.

Detecting the onset of nucleate boiling in internal combustion engines

The use of an electric pump instead of the standard crankshaft-driven one in Internal Combustion Engines, gives the possibility of controlling the coolant flow rate independently of engine speed, allowing therefore, the use of much lower coolant flow rates than usually adopted and the development of nucleate boiling flow regimes within the engine cooling system. In order to take advantage of nucleate boiling and of the associated high heat transfer coefficients, the onset of this heat transfer regime must be correctly identified. This work presents the results of an experimental campaign, which was carried out on a small displacement spark ignition engine (1.2dm3, 60kW) with the aim of detecting the occurrence of nucleate boiling within the engine cooling system. The test rig was properly instrumented in order to measure coolant temperatures at engine inlet and outlet, coolant pressure at several locations in the circuit, coolant flow rate and engine metal temperatures. Operating conditions involving different coolant flow rates were selected in order to enforce both the usual single-phase heat transfer regime and nucleate boiling conditions. Several experimental quantities were analyzed with the aim of establishing the coolant flow rates ranges where the nucleate boiling occurs. The agreement in the trend of coolant temperature and pressure and engine wall temperature provides hints to identify experimentally the onset of nucleate boiling.

An experimental study of density ratio effects on the film cooling injection from discrete holes by using PIV and PSP techniques

An experimental study was conducted to investigate the performance of film cooling injection from a row of circular holes spaced laterally across a flat test plate. While a high-resolution Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the dynamic mixing process between the coolant jet stream and the mainstream flows, Pressure Sensitive Paint (PSP) technique was used to map the corresponding adiabatic film cooling effectiveness on the surface of interest based on a mass-flux analog to traditional temperature-based cooling effectiveness measurements. The cooling effectiveness data of the present study were compared quantitatively against those derived directly from the temperature-based measurements under the same or comparable test conditions in order to validate the reliability of the PSP technique. The effects of the coolant-to-mainstream density ratio (DR) on the film cooling effectiveness were investigated by performing experiments at fixed blowing ratios by using either Nitrogen (DR=0.97) or CO2 (DR=1.53) as the coolant streams for the PSP measurements. An accompanying analysis of scaling quantities, such as the coolant-to-mainstream momentum flux ratio, I, and bulk coolant-to-mainstream velocity ratio, VR, in addition to the most-commonly used blowing ratio (i.e., the coolant-to-mainstream mass flux ratio), M, was also conducted to illuminate the extent to which the flow scenario can be described using purely kinematic or dynamic means. It was found that the scaling quantities that give more weight to density ratio (i.e., blowing ratio, M, and then momentum ratio, I) have more success to collapse measurement data from varying density ratio of the coolant flows for the cases with relatively low coolant flow rates, while the coolant-to-mainstream bulk velocity ratio, VR, may be used with some success to scale the film cooling effectiveness for the cases with higher coolant flow rates.

Effects of coolant flow rates on cooling performance of the intermediate pressure stages for an ultra-supercritical steam turbine

The effects of the coolant flow rates on the thermal and flow fields of the first two intermediate pressure (IP) stages of an ultra-supercritical steam turbine was numerically investigated using the Conjugate Heat Transfer (CHT) method, and the un-cooled case was also simulated for comparison. The three-dimensional Reynolds-Averaged Navier–Stokes (RANS) solution was utilized to analyze the flow field and temperature distributions of the first two IP stages. The numerical results show that the steam cooling system has proved its ability to cool down the high temperature components, even in the case with the low coolant flow rate. The cooling performance can be improved with increased coolant flow rate, however, great flow losses would be induced and make the stage efficiency reduce by 1.23%. The different coolant flow rates also lead to great differences in the flow field in the front cavity of the first stage: ingress dominated flow condition with the low coolant flow rate and egress dominated flow condition with the high coolant flow rate. The negative influence of the ingested hot main steam on the cooling effect was also described.

Experimental Studies of the Thermal Performance of Gas-Cooled Plate-Type Divertors

The helium-cooled plate-type divertor can reduce the number of divertor modules while accommodating heat fluxes q” up to 10 MW/m2 incident on tungsten-alloy armor. Dynamically similar experimental studies were performed to evaluate the thermal performance of variants of this divertor design at conditions that spanned the prototypical operating Reynolds number Re of 3.3 × 104. In the studies, a jet of air issuing from 0.5 mm and 2 mm wide slots impinged on and cooled a heated planar surface 2 mm away from the slot, then flowed through either a 2 mm wide channel or an array of cylindrical pin fins. The studies indicate that the fins, which increase the cooled surface area by a factor of 3.76, increase the effective heat transfer coefficient (HTC) by as much as 160% at a relatively modest increase in pressure drop of less than 40%.These experimental results were used to determine the thermal performance of the actual plate design with helium cooling under prototypical conditions. Although the benefit of the fins is reduced because the fin efficiency decreases as the HTC increases, the predictions suggest that the fins could increase the maximum q” that can be accommodated by this design to ˜18 MW/m2. Alternatively, for a given heat flux (e.g. 10 MW/m2), adding fins could allow operation of the divertor at lower coolant flow rates, and hence pumping powers.

Effect of Radial Location of Nozzles on Heat Transfer in Preswirl Cooling Systems

This paper investigates heat transfer in a rotating disk system using preswirled cooling air from nozzles at high and low radius. The experiments were conducted over a range of rotational speeds, flow rates, and preswirl ratios. Narrow-band thermochromic liquid crystal (TLC) was specifically calibrated for application to experiments on a disk, rotating at ∼5000 rpm and subsequently used to measure surface temperature in a transient experiment. The TLC was viewed through the transparent polycarbonate disk using a digital video camera and strobe light synchronized to the disk frequency. The convective heat transfer coefficient h was subsequently calculated from the one-dimensional solution of Fourier's conduction equation for a semi-infinite wall. The analysis was accounted for the exponential rise in the air temperature driving the heat transfer, and for the experimental uncertainties in the measured values of h. The experimental data was supported by “flow visualization,” determined from CFD. Two heat transfer regimes were revealed for the low-radius preswirl system: a viscous regime at relatively low coolant flow rates, and an inertial regime at higher flow rates. Both regimes featured regions of high heat transfer where thin, boundary layers replaced air exiting through receiver holes at high radius on the rotating disk. The heat transfer in the high-radius preswirl system was shown to be dominated by impingement under the flow conditions tested.

3D study on the effect of process parameters on the cooling of polymer by injection molding

AbstractPlastic injection molding (PIM) is well known as a manufacturing process to produce products with various shapes and complex geometry at low cost. Determining optimal settings of process parameters critically influence productivity, quality, and cost of production in the PIM industry. To study the effect of the process parameters on the cooling of the polymer during injection molding, a full three‐dimensional time‐dependent injection molding analysis was carried out. The studied configuration consists of a mold having cuboids‐shaped cavity with two different thicknesses and six cooling channels. A numerical model by finite volume was used for the solution of the physical model. A validation of the numerical model was presented. The effect of different process parameters (inlet coolant temperature, inlet coolant flow rate, injection temperature, and filling time) on the cooling process was considered. The results indicate that the filling time has a great effect on the solidification of the product during the filling stage. They also show that low coolant flow rate increases the heterogeneity of the temperature distribution through the product. The process parameter realizing minimum cooling time not necessary achieves optimum product quality and the complete filling of the cavity by the polymer material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Experimental Studies on the Influence of Operational Parameters on the Cold Start of a 2 kW Fuel Cell

AbstractIn this paper, experimental investigations on the influence of operational parameters on PEM fuel cell cold start are presented. The effect of current density, stack impedance at 1 kHz prior to start, as well as gas flow rate, gas pressure, coolant flow rate and surrounding subfreezing temperature are studied. The experimental apparatus is briefly described. It includes a main unit at room temperature and a smaller separate unit in a climatic chamber. Low current density, high impedance prior to start, moderate subfreezing temperature (–5 °C), high gas flow rate, low gas pressure and low coolant flow rate are found to have a positive impact on the cold start performance. Combining these parameters, self start‐up of the fuel cell without additional energy is achieved at –5 °C in 30 min. The whole set of observations leads to the following hypotheses on freeze mechanism: in the first phase, dry membranes and low current lead to a transient phase of membrane humidification. Then, in the second phase, ice clogging of the active layers occurs. In the third phase, a variable quantity of the produced water reaches the gas diffusion layers and channels.

Spray cooling heat transfer: Technology overview and assessment of future challenges for micro-gravity application

Advanced on-board flight systems for future NASA space exploration programs consist of components such as laser-diode arrays (LDA’s) and multi-chip modules (MCM’s). Thermal management of these systems require high heat flux cooling capability (⩾100 W/cm 2), tight temperature control (approx. ±2 °C), reliable start-up (on demand) and long term stability. Traditional multiphase thermal control technologies for space flight (e.g., loop heat pipes, capillary pumped loops, etc.) satisfy the temperature control, start-up and stability requirements, but their heat flux removal capabilities are limited. Spray cooling can provide high heat fluxes in excess of 100 W/cm 2 using fluorinerts and over 1000 W/cm 2 with water while allowing tight temperature control at low coolant fluid flow rates. Spray cooling has been flight proven in an open loop configuration through the Space shuttle’s flash evaporator system (FES). However, several closed system issues require investigation to further advance the technology to a technology readiness level (TRL) appropriate for closed system space flight application. This paper provides a discussion of the current status of spray cooling technology as well as NASA’s goals, current direction, and challenges associated with the implementation and practice of this technology in the micro-gravity environment.

A Linear Stability Analysis of Supercritical Water Reactors, (I)

This paper summarizes the analysis results of the thermal-hydraulic stability of a high-temperature reactor cooled and moderated by supercritical-pressure light water (SCLWR-H). A linear stability analysis code in the frequency domain was developed to study the thermal-hydraulic stability of SCLWR-H at constant supercritical pressure. The analysis method is based on linearization by perturbation of numerically-discretized one-dimensional single-channel single-phase conservation equations. The effect of water rods on stability is considered. The thermal-hydraulic stability of SCLWR-H for full-power and partial-power normal operations was investigated by frequency domain method. Our analysis reveals that though SCLWR-H has low coolant flow rate and large density change in the core, the thermal-hydraulic stability can be maintained both at normal operation and during power raising phase of constant pressure startup by applying an orifice pressure drop coefficient at the inlet of the fuel assemblies. A parametric study was also carried out to determine the parameters affecting the stability.

Influence of Fluid Dynamics on Heat Transfer in a Preswirl Rotating-Disk System

Modern gas turbines are cooled using air diverted from the compressor. In a “direct-transfer” preswirl system, this cooling air flows axially across the wheel space from stationary preswirl nozzles to receiver holes located in the rotating turbine disk. The distribution of the local Nusselt number Nu on the rotating disk is governed by three nondimensional fluid-dynamic parameters: preswirl ratio βp, rotational Reynolds number Reϕ, and turbulent flow parameter λT. This paper describes heat transfer measurements obtained from a scaled model of a gas turbine rotor-stator cavity, where the flow structure is representative of that found in the engine. The experiments reveal that Nu on the rotating disk is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations have been measured. At the higher coolant flow rates studied, there is a peak in heat transfer at the radius of the preswirl nozzles associated with the impinging jets from the preswirl nozzles. At lower coolant flow rates, the heat transfer is dominated by viscous effects. The Nusselt number is observed to increase as either Reϕ or λT increases.

A Linear Stability Analysis of Supercritical Water Reactors, (I) Thermal-Hydraulic Stability

This paper summarizes the analysis results of the thermal-hydraulic stability of a high-temperature reactor cooled and moderated by supercritical-pressure light water (SCLWR-H). A linear stability analysis code in the frequency domain was developed to study the thermal-hydraulic stability of SCLWR-H at constant supercritical pressure. The analysis method is based on linearization by perturbation of numerically-discretized one-dimensional single-channel single-phase conservation equations. The effect of water rods on stability is considered. The thermal-hydraulic stability of SCLWR-H for full-power and partial-power normal operations was investigated by frequency domain method. Our analysis reveals that though SCLWR-H has low coolant flow rate and large density change in the core, the thermal-hydraulic stability can be maintained both at normal operation and during power raising phase of constant pressure startup by applying an orifice pressure drop coefficient at the inlet of the fuel assemblies. A parametric study was also carried out to determine the parameters affecting the stability.