Title: Numerical Analysis on Feasibility of Thermally Induced Pore Fluid Flow in Saturated Soils
The exact heat transfer mechanism in the soil media can be understood by analyzing the soil behavior surrounding the heat sources. In literature, heat conduction has been considered as a main heat transfer mechanism in soil, and less attention has been given to the natural heat convection in saturated soils. There is only limited research in the literature which shows the presence of thermally induced pore fluid flow in soil media. It has been observed that heat convection through pore fluid flow in sand facilitates heat transfer in the ground. Therefore, both heat conduction and heat convection must be considered to accurately model the heat transfer mechanism in soil. In this paper, the presence of natural convection of water in a 2D axisymmetric domain of soil with a vertical heat source has been numerically investigated in steady-state condition. The soil thermal response and heat transfer mechanism for different soil types are compared. Feasibility of thermally-induced pore fluid flow is analyzed for different soil types. The results determine the presence of thermally driven pore fluid flow in high permeability soil (e.g., coarse sand) and confirm that the effect of heat convection in low permeability silt and clay is negligible. more »« less
Huang, Ching-Wei; Srikanth, Vishal; Kuznetsov, Andrey V.
(, Proceeding of 5-6th Thermal and Fluids Engineering Conference (TFEC))
null
(Ed.)
The influence of microscale flow structures (smaller than the pore size) on turbulent heat transfer in porous media has not been yet investigated. The goal of this study is to determine the influence of the micro-vortices on convection heat transfer in turbulent porous media flow. Turbulent flow in a homogeneous porous medium was investigated using Large Eddy Simulation (LES) at a Reynolds number of 300. We observed that the convection heat transfer characteristics are dependent on whether the micro-vortices are attached or detached from the surface of the obstacle. There is a spectral correlation between the Nusselt number and the pressure instabilities due to vortex shedding. A secondary flow instability occurs due to high pressure regions forming periodically near the converging pathway between obstacles. This causes local adverse pressure gradient, affecting the flow velocity and convection heat transfer. This study has been performed for obstacles with shapes of square and circular cylinders at porosities of 0.50 and 0.87. Understanding the dominant modes that affect convection heat transfer can aid in finding an optimum geometry for the porous medium.
Saini, Satyam; Gupta, Gautam; Bansode, Pratik; Shahi, Pardeep; Simon, Vibin Shalom; Modi, Himanshu; Agonafer, Dereje; Shah, Jimil
(, American Society of Mechanical Engineers)
Abstract Data centers are critical to the functioning of modern society as they host digital infrastructure. However, data centers can consume significant amounts of energy, and a substantial amount of this energy goes to cooling systems. Efficient thermal management of information technology equipment is therefore essential and allows the user to obtain peak performance from a system and enables higher equipment reliability. Thermal management of data center electronics is becoming more challenging due to rising power densities at the chip level. Cooling technologies like single-phase immersion cooling allow overcoming many such challenges owing to their higher thermal mass, lower fluid pumping powers, and potential component reliability enhancements. It is known that immersion cooling deployments require extremely low coolant flow rates, and, in many cases, natural convection can also be used to sufficiently dissipate the heat from the hot server components. It, therefore, becomes difficult to ascertain whether the rate of heat transfer is being dominated by forced or natural convection. This may lead to ambiguity in choosing an optimal heat sink solution and a suitable system mechanical design due to unknown flow regimes, further leading to sub-optimal system performance. Mixed convection can be used to enhance heat transfer in immersion cooling systems. The present investigation quantifies the contribution of mixed convection using numerical methods in an immersion-cooled server. An open compute server with dual CPU sockets is modeled on Ansys Icepak with varying power loads of 115W, 160W and 200W. The chosen dielectric fluid for this single-phase immersion-cooled setup is EC-100. Steady-state Computational Fluid Dynamics (CFD) simulations are conducted for forced, natural, and mixed convection heat transfer in a thermally shadowed server configuration at varying inlet flow rates. A baseline heat sink and an optimized heat sink with an increased fin thickness and reduced fin count are utilized for performance comparison. The effect of varying Reynolds number and Richardson number on the heat transfer rate from the heat sink is discussed to assess the flow regime, stability of the flow around the submerged components which depends on the geometry, orientation, fluid properties, flow rate and direction of the flow. The dimensionless numbers’ influence on heat transfer rate from a conventional air-cooled heat sink in immersion versus an immersion-optimized heat sink is also compared. The impact of server orientation on heat transfer behavior for the immersion optimized heat sink is also studied on heat transfer behavior for the immersion optimized heat sink.
Gupta, Gautam; Nair, Vivek; Bansode, Pratik; Suthar, Rohit; Pundla, Sai Abhideep; Herring, Joseph; Lamotte-Dawaghreh, Jacob; Sivaraju, Krishna Bhavana; Agonafer, Dereje; Mynampati, Poornima; et al
(, American Society of Mechanical Engineers)
Abstract Data centers are witnessing an unprecedented increase in processing and data storage, resulting in an exponential increase in the servers’ power density and heat generation. Data center operators are looking for green energy efficient cooling technologies with low power consumption and high thermal performance. Typical air-cooled data centers must maintain safe operating temperatures to accommodate cooling for high power consuming server components such as CPUs and GPUs. Thus, making air-cooling inefficient with regards to heat transfer and energy consumption for applications such as high-performance computing, AI, cryptocurrency, and cloud computing, thereby forcing the data centers to switch to liquid cooling. Additionally, air-cooling has a higher OPEX to account for higher server fan power. Liquid Immersion Cooling (LIC) is an affordable and sustainable cooling technology that addresses many of the challenges that come with air cooling technology. LIC is becoming a viable and reliable cooling technology for many high-power demanding applications, leading to reduced maintenance costs, lower water utilization, and lower power consumption. In terms of environmental effect, single-phase immersion cooling outperforms two-phase immersion cooling. There are two types of single-phase immersion cooling methods namely, forced and natural convection. Here, forced convection has a higher overall heat transfer coefficient which makes it advantageous for cooling high-powered electronic devices. Obviously, with natural convection, it is possible to simplify cooling components including elimination of pump. There is, however, some advantages to forced convection and especially low velocity flow where the pumping power is relatively negligible. This study provides a comparison between a baseline forced convection single phase immersion cooled server run for three different inlet temperatures and four different natural convection configurations that utilize different server powers and cold plates. Since the buoyancy effect of the hot fluid is leveraged to generate a natural flow in natural convection, cold plates are designed to remove heat from the server. For performance comparison, a natural convection model with cold plates is designed where water is the flowing fluid in the cold plate. A high-density server is modeled on the Ansys Icepak, with a total server heat load of 3.76 kW. The server is made up of two CPUs and eight GPUs with each chip having its own thermal design power (TDPs). For both heat transfer conditions, the fluid used in the investigation is EC-110, and it is operated at input temperatures of 30°C, 40°C, and 50°C. The coolant flow rate in forced convection is 5 GPM, whereas the flow rate in natural convection cold plates is varied. CFD simulations are used to reduce chip case temperatures through the utilization of both forced and natural convection. Pressure drop and pumping power of operation are also evaluated on the server for the given intake temperature range, and the best-operating parameters are established. The numerical study shows that forced convection systems can maintain much lower component temperatures in comparison to natural convection systems even when the natural convection systems are modeled with enhanced cooling characteristics.
Roth, Mary J.; Caslake, Laurie F.
(, Geo-Congress 2019)
Growing biofilm in saturated sand has been shown to reduce the permeability of soil by one or more orders of magnitude and may be a viable approach to reducing seepage in the field; however, obtaining laboratory permeability results in soil samples where biofilm is being developed is difficult. Adding nutrients results in the formation of biofilm in the soil but also the formation of biofilm in the piping and other areas of the permeability testing apparatus. In addition, some bacteria produce gas as a product of metabolism and this gas can collect in the apparatus and interfere with fluid flow. This paper presents an approach to permeability testing that effectively minimized the growth of biofilm and the collection of gas in the testing apparatus for multiple sand samples treated with a nutrient solution over a period of more than 60 days.
Korba, David; Li, Like
(, Journal of Fluid Mechanics)
The study of thermal convection in porous media is of both fundamental and practical interest. Typically, numerical studies have relied on the volume-averaged Darcy–Oberbeck–Boussinesq (DOB) equations, where convection dynamics are assumed to be controlled solely by the Rayleigh number ( Ra ). Nusselt numbers ( Nu ) from these models predict Nu – Ra scaling exponents of 0.9–0.95. However, experiments and direct numerical simulations (DNS) have suggested scaling exponents as low as 0.319. Recent findings for solutal convection between DNS and DOB models have demonstrated that the ‘pore-scale parameters’ not captured by the DOB equations greatly influence convection. Thermal convection also has the additional complication of different thermal transport properties (e.g. solid-to-fluid thermal conductivity ratio k s / k f and heat capacity ratio σ ) in different phases. Thus, in this work we compare results for thermal convection from the DNS and DOB equations. On the effects of pore size, DNS results show that Nu increases as pore size decreases. Mega-plumes are also found to be more frequent and smaller for reduced pore sizes. On the effects of conjugate heat transfer, two groups of cases (Group 1 with varying k s / k f at σ = 1 and Group 2 with varying σ at k s / k f = 1) are examined to compare the Nu – Ra relations at different porosity ( ϕ ) and k s / k f and σ values. Furthermore, we report that the boundary layer thickness is determined by the pore size in DNS results, while by both the Rayleigh number and the effective heat capacity ratio, $$\bar{\phi } = \phi + (1 - \phi )\sigma$$ , in the DOB model.
Tamizdoust, Mohammadreza Mir, and Ghasemi-Fare, Omid. Numerical Analysis on Feasibility of Thermally Induced Pore Fluid Flow in Saturated Soils. Retrieved from https://par.nsf.gov/biblio/10104920. Eighth International Conference on Case Histories in Geotechnical Engineering . Web. doi:10.1061/9780784482124.009.
Tamizdoust, Mohammadreza Mir, & Ghasemi-Fare, Omid. Numerical Analysis on Feasibility of Thermally Induced Pore Fluid Flow in Saturated Soils. Eighth International Conference on Case Histories in Geotechnical Engineering, (). Retrieved from https://par.nsf.gov/biblio/10104920. https://doi.org/10.1061/9780784482124.009
Tamizdoust, Mohammadreza Mir, and Ghasemi-Fare, Omid.
"Numerical Analysis on Feasibility of Thermally Induced Pore Fluid Flow in Saturated Soils". Eighth International Conference on Case Histories in Geotechnical Engineering (). Country unknown/Code not available. https://doi.org/10.1061/9780784482124.009.https://par.nsf.gov/biblio/10104920.
@article{osti_10104920,
place = {Country unknown/Code not available},
title = {Numerical Analysis on Feasibility of Thermally Induced Pore Fluid Flow in Saturated Soils},
url = {https://par.nsf.gov/biblio/10104920},
DOI = {10.1061/9780784482124.009},
abstractNote = {The exact heat transfer mechanism in the soil media can be understood by analyzing the soil behavior surrounding the heat sources. In literature, heat conduction has been considered as a main heat transfer mechanism in soil, and less attention has been given to the natural heat convection in saturated soils. There is only limited research in the literature which shows the presence of thermally induced pore fluid flow in soil media. It has been observed that heat convection through pore fluid flow in sand facilitates heat transfer in the ground. Therefore, both heat conduction and heat convection must be considered to accurately model the heat transfer mechanism in soil. In this paper, the presence of natural convection of water in a 2D axisymmetric domain of soil with a vertical heat source has been numerically investigated in steady-state condition. The soil thermal response and heat transfer mechanism for different soil types are compared. Feasibility of thermally-induced pore fluid flow is analyzed for different soil types. The results determine the presence of thermally driven pore fluid flow in high permeability soil (e.g., coarse sand) and confirm that the effect of heat convection in low permeability silt and clay is negligible.},
journal = {Eighth International Conference on Case Histories in Geotechnical Engineering},
author = {Tamizdoust, Mohammadreza Mir and Ghasemi-Fare, Omid},
}
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