SprayCool™ Thermal Management for Dense Stacked Memory

This paper presents the comparative studies on heat transfer coefficient for circular and non-circular duct like square, elliptical and triangular section using computational fluid dynamics simulation package. The forced convection with turbulent flow is very complicated and analyzed through CFD simulation. The geometry model developed for four cases and meshed processed using CFX13 software package for the given boundary conditions. CFD simulation is carried out with the constant heat flux on the wall to compute the heat transfer coefficient and compared with experimental and correlation method. It is concluded from the analysis elliptical cross section having more heat transfer co-efficient value of 153W/m2K when compared to circular having heat transfer coefficient value of 147W/m2K due to increase in the surface of the elliptical section when compared to circular.

Nowadays, heat exchange devices are becoming one of the essential components in complex engineering systems such as power plants and food processing industries. Especially in power plants, the surface condenser plays a crucial role in enhancing the thermal efficiency which works like shell and tube heat exchangers. Generally, the heat transfer coefficient and pressure drop of the surface condenser depend on baffle spacing. The baffle spacing significantly influences the heat transfer coefficient for the shell-side fluid. CFD simulations were carried out for different cases of single-pass shell and tube heat exchanger by varying the number of baffles at same operating conditions. The purpose of baffles is to support the tube bundle and directs the fluid to flow on the surface of tubes. In this study, four different cases by varying the shell diameter relative to baffle spacing and the number of baffles were considered to evaluate the heat transfer coefficients and pressure drops. It is observed that following the decrement in baffle spacing, the cross-flow area of shell-side region decreases; hence, there will be an increase in Reynolds number for shell-side fluid which results in enhanced heat transfer coefficients. Moreover, the segmental baffles are widely used in industrial applications where the purpose of enhancing heat transfer coefficient in surface condensers is to improve the condensation process of steam to liquid at faster rates.

The objective of this study is the thermal investigation of a typical spark-ignition (SI) engine combustion chamber with particular focus in determination of the locations where the heat flux and heat transfer coefficient are highest. This subject is an important key for some design purposes especially thermal loading of the piston and cylinder head. To this end, CFD simulation using the KIVA-3V CFD code on a PC platform for flow, combustion, and heat transfer in a typical SI engine has been performed. Some results including the temporal variation of the area-averaged heat flux and heat transfer coefficient on the piston, combustion chamber, and cylinder wall are presented. Moreover, the temporal variation of the local heat transfer coefficient and heat flux along a centerline on the piston as well as a few locations on the combustion chamber wall are shown. The investigation reveals that during the combustion period, the heat flux and heat transfer coefficient vary substantially in space and time due to the transient nature of the flame propagation. For example, during the early stages of the flame impingement on the wall, the heat flux undergoes a rapid increase by as much as around 10 times the preimpingement level. In other words, the initial rise of the heat flux at any location is related to the time of the flame arrival at that location.

Computational fluid dynamics (CFD) simulation is usually a computationally expensive, memory demanding, and time consuming iterative process. These drawbacks limit the use of CFD, especially when either spatiotemporal scales or geometry complexity increases. This paper presents the preliminary results from the assessment of an approximation model for predicting non-uniform steady turbulent flows in a 3D domain, utilizing deep learning (DL) algorithms. In particular, the artificial neural network (ANN) approach uses most important variables data from currently CFD simulation results to link multi-variable input spaces (e.g. input speed and direction, geometry configuration) with multi-variable output space (e.g. velocity magnitude, pressure gradient) to obtain an efficient and accurate approximation of the entire velocity field for given input flow field characteristics. The results demonstrated higher computational speed with a similar accuracy using DL algorithms versus CFD simulation. This integrated approach can provide immediate feedback for real-time design iterations for the entire computational domain at the early stages of design. Hence, designers and engineers can easily generate immense amounts of design alternatives without facing the time-consuming task of evaluation and selection.

This paper discusses about the effect of feeder height and heat flux on the heat transfer characteristics of horizontal tube falling film evaporation in the thermal regimes. In order to investigate this, a two- dimensional CFD model was developed to perform simulation and results were compared and validated with published data available in the literature. Heat transfer co-efficients in the thermal regimes were determined from the CFD simulation and the results were recorded, analyzed and validated with the mathematical models available in the literature. The novelty of the current study is to predict the commencement of the fully developed thermal region over the tube from the simulation model under varying feeder height and heat flux. An effort was also made to measure the liquid film thickness around the tube from the CFD model in the thermal regimes. It is observed that angle of thermally developing region contracts and fully developed thermal region extends with the increase of the feeder height and heat flux. It is observed from the study that increase of heat flux by 10 kW/m2 resulted in increase of heat transfer co-efficient value by 10–12% average in thermally developing region and 12–15% average in fully developed region. Thinnest liquid film thickness observed between 85 and 127°angle. Shifting of thinnest region of liquid film upward from the mid tube with the increase of the feeder height and heat flux is noted.

A coupling system was developed in the present study to simulate the heat transfer and physiological responses of the unclothed human body in hot and cold environments. This system included a computational thermal manikin controlled by a multi-node thermal model, which could dynamically respond to the environmental conditions. The computational thermal manikin was employed to determine the heat transfer between the human body and ambient environment as well as heat transfer coefficients at each body segment. The CFD simulation was then coupled with a multi-node thermal model to predict the heat transfer and human physiological responses in real time. The performance of coupling system was examined by comparing the simulated skin temperatures with the published measurements from human trials in hot and cold environments. The coupling system reasonably predicted the skin temperatures at local body segments with the maximum discrepancies between the observed values and simulated ones no more than 1.0 °C.

This paper deals with the experimental and numerical studies of aero-thermal characteristics of film cooling for turbine blade leading edge having three differently hole geometries. The hole geometries used in this study are called typeA and typeB. The purpose of this study is to sort out the most suitable hole geometry. Mainstream Reynolds number based on the cylinder diameter was 86,000. The effect of blowing rates (BR) was studied of various blowing ratios of 1.0 and 2.0. Transient techniques using thermochromic liquid crystal is used to measure film effectiveness and heat transfer coefficient. In addition, Detailed investigation of film cooling for leading edge is carried out using CFD simulations. RANS applying a Shear Stress Transport turbulence model is addressed to solve thermal convection. Results show that the typeA provide better film cooling performance on BR=1.0 than typeB.

A combined experimental and computational fluid dynamics study of single-phase liquid nitrogen flow through a microscale pin-fin heat sink is presented. Such cryogenic heat sinks find use in applications such as high performance computing and spacecraft thermal management. A circular pin fin heat sink in diameter 5 cm and 250 micrometers in depth was studied herein. Unique features of the heat sink included its variable cross sectional area in the flow direction, variable pin diameters, as well as a circumferential distribution of fluid into the pin fin region. The stainless steel heat sink was fabricated using chemical etching and diffusion bonding. Experimental results indicate that the heat transfer coefficients were relatively unchanged around 2600 W/m2-K for flow rates ranging from 2–4 g/s while the pressure drop increased monotonically with the flow rate. None of the existing correlations in literature on cross flow over a tube bank or micro pin fin heat sinks were able to predict the experimental pressure drop and heat transfer characteristics. However, three dimensional simulations performed using ANSYS Fluent showed reasonable (∼7 percent difference) agreement in the average heat transfer coefficients between experiments and CFD simulations.

Numerical and experimental thermo-fluid dynamic analysis of a power transformer working in ONAN mode

Effect of the number of orifices and operative variables on the heat and mass transfer in a hydrofluidization system with static spheres

PurposeThe purpose of this study is to numerically and experimentally survey the thermal efficiency of a block-type heat exchanger operated in different working conditions by using pure water and two nanofluids as heat transfer fluids.Design/methodology/approachAn aluminum block-type heat exchanger integrated with Peltier thermoelectric element was designed and installed to operate in a cycle, and the thermal performance of the heat exchanger, heat transfer rate, Nusselt and heat transfer coefficient variations were examined at different bath water temperatures by using recycled nanofluids. New generation surface-modified Fe3O4@SiO2-mix-(CH2)3Cl@Imidazol/water nanofluid was used as heat transfer fluid in the cycle. In addition, CFD simulation was performed using ANSYS/Fluent to investigate the temperature distribution and fluid flow structure in the used heat exchanger.FindingsExperiments were carried out by using numerical and experimental methods. In the experiments, the operating conditions such as flow rate, volume fraction of the nanofluid and water bath temperature were changed to find the effect of each parameter on the thermal efficiency. The Reynolds number varied depending on the test conditions, which was calculated in the range of approximately 100 < Re < 350. In addition, Nusselt number and heat transfer coefficient of test fluids were very close to each other. For 0.4% nanofluid, the maximum h value was obtained as 3837.1, when the Reynolds number was measured as 314.4.Originality/valueIn the scientific articles published in the field of heat exchangers operated by nanofluids, little attention has been paid to the stability of the nanofluids and sedimentation of particles in the base fluids. In addition, in most cases, experiments were implemented using an electrical resistance as a heat source. In this research, stable surface-modified nanofluids were used as heat transfer fluids, and it was found that the Peltier thermoelectric can be used as heat sources with acceptable efficiency in flat-type heat exchangers and even non-circular channels.

A correlation for U-value for laminar and turbulent flows in concentric tube heat exchangers

Closed loop steam has been chosen for cooling airfoils in heavy frame Advanced Turbine Systems (ATS) to improve efficiency. Enhanced cooling by the use of mist is considered to have potential to augment cooling by internal steam alone. Water droplets generally less than 10μm are added to 1.3 bar steam and injected through a row of four discrete round jets onto a heated surface. The Reynolds number is varied from 7500 to 22500 and the heat flux varied from 3.3 to 13.4 kW/m2. The mist increases the heat transfer coefficient along the stagnation line and downstream wanes in about 5 jet diameters. The heat transfer coefficient improves by 50 to 700 percent at the stagnation line for mist concentrations 0.75 to 3.5 percent by weight, depending on conditions. Off-axis maximum cooling occurs in most of the mist/steam flow but not in the steam-only flow. CFD simulation indicates that this off-axis cooling peak is caused by droplets’ interaction with the target walls.

Analysis and comparison of internal and external temperature measurements of a tubular oscillating heat pipe

Additive manufacturing (3D printing) is a promising approach to creating packings for laboratory-scale distillation columns. Current research focuses on experiments and simulations to tailor packing geometry regarding performance (e.g., pressure drop, fluid distribution). These performance benchmarks are, in large part, dependent on the wettability of the manufactured surface. Research shows that the 3D-printing process settings affect wetting significantly. This effect must be quantified to accurately assess the effectiveness of printed packing geometry. Due to the interdependence of wetting, surface roughness, and involved substances, the required experimental effort is not feasible. Sessile drop experiments show that analytical models underpredict the resulting wettability. In this study, a novel method to address this issue is introduced. The rough surface of a printed sample is reverse-engineered, and CFD simulations are performed to predict the static contact angle. The results show agreement between the computational model and experimental investigations.