2D thermal resistance of pile heat exchangers

Structural foundation piles are being used increasingly as heat exchangers to provide renewable heat for new buildings. To design such energy systems a steady state is assumed within the pile, which is conventionally characterised by constant thermal resistance. However, there has been little research regarding pile resistance and there are few published case studies. Numerical modelling results are presented here to provide typical values of pile resistance, depending on the details of the heat exchange pipes. Analysis suggests large diameter piles may take several days to reach steady state; in these cases a transient design approach may be more appropriate

A new modelling approach for piled and other ground heat exchanger applications

Pile heat exchangers have an increasing role to play in the delivery of renewable heating and cooling energy. Traditionally the thermal design of ground heat exchangers has relied upon analytical approaches which take a relatively simple approach to the inside of the heat exchanger. This approach is justified while the heat exchanger diameter remains small. However, as larger diameter piled foundations are used as heat exchangers, the transient heat transfer processes operating within the pile become more important. To increase our understanding of these processes and ultimately lead to improved thermal design approaches for pile heat exchangers it is important to examine the heat transfer within the pile in detail. To accomplish this, a new numerical approach has been implemented within the finite element software ABAQUS. Coupling of the convective heat transfer due to fluid flow within the heat transfer pipes and the heat transfer by conduction within the pile concrete is the most important facet of the model. The resulting modelling approach, which is ready to generalise to other geothermal applications and to assess thermo-mechanical couplings, has been validated against a multi-stage thermal response test carried out on a test pile in London Clay

An Essential Role for Interleukin 10 in the Function of Regulatory T Cells That Inhibit Intestinal Inflammation

A T helper cell type 1–mediated colitis develops in severe combined immunodeficient mice after transfer of CD45RBhigh CD4+ T cells and can be prevented by cotransfer of the CD45RBlow subset. The immune-suppressive activities of the CD45RBlow T cell population can be reversed in vivo by administration of an anti-transforming growth factor β antibody. Here we show that interleukin (IL)-10 is an essential mediator of the regulatory functions of the CD45RBlow population. This population isolated from IL-10–deficient (IL-10−/−) mice was unable to protect from colitis and when transferred alone to immune-deficient recipients induced colitis. Treatment with an anti–murine IL-10 receptor monoclonal antibody abrogated inhibition of colitis mediated by wild-type (WT) CD45RBlow CD4+ cells, suggesting that IL-10 was necessary for the effector function of the regulatory T cell population. Inhibition of colitis by WT regulatory T cells was not dependent on IL-10 production by progeny of the CD45RBhigh CD4+ cells, as CD45RBlow CD4+ cells from WT mice were able to inhibit colitis induced by IL-10−/− CD45RBhigh CD4+ cells. These findings provide the first clear evidence that IL-10 plays a nonredundant role in the functioning of regulatory T cells that control inflammatory responses towards intestinal antigens

Thermal Conductivity of Simulated Soils by the Needle Probe Method for Energy Foundation Applications

Soil thermal conductivity is an important parameter in the design of ground source heat pump and energy foundation systems. A laboratory method for measuring the soil thermal conductivity is the needle probe method. Earlier, analysis of the needle probe test data has been simplistic, relying heavily on human judgment and rules of thumb. This article presents an alternative method of analyzing the needle probe data with the aid of MATLAB, which is a technical programming language and computing environment. Four agar–kaolin specimens of varying densities were prepared to resemble simple soils. These were tested using the needle probe for a range of heating times and heating powers, to see what effect these parameters would have on the results. The repeatability when keeping the heating time and heating power constant was within ±2%. When the heating time and heating power were varied, the variation in results from the average for a given specimen ranged from ±4% to +10%/–8%. This range is significantly higher than the repeatability. Possible reasons for this are discussed in this article

Mechanisms of root reinforcement in soils:An experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation

Vegetation on railway or highway slopes can improve slope stability through the generation of soil pore water suctions by plant transpiration and mechanical soil reinforcement by the roots. To incorporate the enhanced shearing resistance and stiffness of root-reinforced soils in stability calculations, it is necessary to understand and quantify its effectiveness. This requires integrated and sophisticated experimental and multiscale modelling approaches to develop an understanding of the processes at different length scales, from individual root-soil interaction through to full soil-profile or slope scale. One of the challenges with multiscale models is ensuring that they sufficiently closely represent real behaviour. This requires calibration against detailed high-quality and data-rich experiments. This study presents a novel experimental methodology, which combines in situ direct shear loading of a willow root reinforced soil with X-ray computed tomography to capture the 3D chronology of soil and root deformation within the shear zone. Digital volume correlation (DVC) analysis was applied to the computed tomography (CT) dataset to obtain full-field 3D displacement and strain information. This paper demonstrates the feasibility and discusses the challenges associated with DVC experiments on root-reinforced soils

Defining the microbial transcriptional response to colitis through integrated host and microbiome profiling

The gut microbiome is significantly altered in inflammatory bowel diseases, but the basis of these changes is not well understood. We have combined metagenomic and metatranscriptomic profiling of the gut microbiome to assess modifications to both bacterial community structure and transcriptional activity in a mouse model of colitis. By using transcriptomic analysis of colonic tissue and luminal RNA derived from the host, we have also characterised how host transcription relates to the microbial transcriptional response in inflammation. In colitis, increased abundance and transcription of diverse microbial gene families involved in responses to nutrient deprivation, antimicrobial peptide production and oxidative stress support an adaptation of multiple commensal genera to withstand a diverse set of environmental stressors in the inflammatory environment. These data are supported by a transcriptional signature of activated macrophages and granulocytes in the gut lumen during colitis, a signature that includes the transcription of the key antimicrobial genes S100a8 and S100a9 (calprotectin). Genes involved in microbial resistance to oxidative stress, including Dps/ferritin, Fe-dependent peroxidase and glutathione S-transferase were identified as changing to a greater extent at the level of transcription than would be predicted by DNA abundance changes, implicating a role for increased oxygen tension and/or host-derived reactive oxygen species in driving transcriptional changes in commensal microbes

Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C

The Glasgow photon tagging spectrometer at Mainz has been upgraded so that it can be used with the 1500 MeV electron beam now available from the Mainz microtron MAMI-C. The changes made and the resulting properties of the spectrometer are discussed.Comment: 20 pages, 12 figure

The Thermal Behaviour of Three Different Auger Pressure Grouted Piles Used as Heat Exchangers

Three auger pressure grouted (APG) test piles were constructed at a site in Richmond, Texas. The piles were each equipped with two U-loops of heat transfer pipes so that they could function as pile heat exchangers. The piles were of two different diameters and used two different grouts, a standard APG grout and a thermally enhanced grout. Thermal response tests, where fluid heated at a constant rate is circulated through the pipe loops, were carried out on the three piles, utilising either single or double loops. The resulting test data can be used to determine the surrounding soil thermal conductivity and the pile thermal resistance, both essential design parameters for ground source heat pump systems using pile heat exchangers. This paper uses parameter estimation techniques to fit empirical temperature response curves to the thermal response test data and compares the results with standard line source interpretation techniques. As expected, the thermal response tests with double loops result in smaller thermal resistances than the same pile when the test was run with a single loop. Back analysis of the pile thermal resistance also allows calculation of the grout thermal properties. The thermally enhanced grout is shown to have inferior thermal properties than the standard APG grout. Together these analyses demonstrate the importance of pile size, grout thermal properties and pipe positions in controlling the thermal behaviour of heat exchanger piles