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  • 1.
    Acuña, José
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Mogensen, Palne
    Palm, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Distributed Thermal Response Tests on a Multi-pipe Coaxial Borehole Heat Exchanger2011Inngår i: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 17, nr 6, s. 1012-1029Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a distributed thermal response test, distributed temperature measurements are taken along a borehole heat exchanger during thermal response tests, allowing the determination of local ground thermal conductivities and borehole thermal resistances. In this article, the first results from six heat injection distributed thermal response tests carried out on a new, thermally insulated leg type, multi-pipe coaxial borehole heat exchanger are presented. The borehole heat exchanger consists of 1 insulated central and 12 peripheral pipes. Temperature measurements are carried out using fiber-optic cables placed inside the borehole heat exchanger pipes. Unique temperature and thermal power profiles along the borehole depth as a function of the flow rate and the total thermal power injected into the borehole are presented. A line source model is used for simulating the borehole heat exchanger thermal response and determining local variations of the ground thermal conductivity and borehole thermal resistance. The flow regime in the peripheral pipes is laminar during all distributed thermal response tests and average thermal resistances remain relatively constant, independently of the volumetric flow rate, being lower than those corresponding to U-pipe borehole heat exchangers. The thermal insulation of the central pipe significantly reduces the thermal shunt to the peripheral pipes even at low volumetric flow rates.

  • 2.
    Sandberg, Mats
    KTH Research School University of Gävle, Department of Indoor Environment.
    Whole-field measuring methods in ventilated rooms2007Inngår i: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 13, nr 6, s. 951-970Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The occupied zone of a ventilated room constitutes a large volume, and the temperature, velocity, and concentration cannot be mapped simultaneously over a whole field with standard point (local) measuring techniques. The situation is improving due to the introduction of whole-field measurement techniques. Whole-field techniques are relatively new and under development; therefore, this paper describes the principles behind the techniques and their pros and cons. All techniques are optical techniques in the sense that pictures are taken by an array of sensors responsive to different wavelengths of light depending on the application. The velocity components can be recorded with particle image velocimetry (PIV) or particle streak velocimetry (PSV). Both methods are based on adding tracer particles, which ideally follow the air motions; a digital camera records their displacement during a specified time interval. Recording the displacement corresponds to the Lagrangian formulation of fluid mechanics. With PIV, the displacement of groups of particles is recorded, in contrast to the PSV method, where the displacement of a single particle is recorded. PIV can provide high-resolution information over small regions, whereas the PSV method can cope with large areas. The two-dimensional concentration distributions of certain contaminants can be obtained by using tomography. The attenuation of light along a bundle of lines (rays) directed in a certain direction (view) and crossing the region with the contaminant is recorded. The measurements are repeated for several other angles. Based on the one-dimensional information in the form of attenuation of light along rays running in different directions, the two-dimensional concentration can be reconstructed by a reconstruction algorithm. The temperature distribution can be recorded and visualized with an infrared camera and a measuring screen that ideally attains the room air temperature. New development of the classical Schlieren technique has made it possible to visualize the air temperature distribution over large fields.

  • 3. Shao, D. W.
    et al.
    Granryd, Eric G.
    KTH, Tidigare Institutioner                               , Energiteknik.
    Flow pattern, heat transfer and pressure drop in flow condensation part I: Pure and azeotropic refrigerants2000Inngår i: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 6, nr 2, s. 175-195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study concerns the flow pattern, heat transfer, and pressure drop for flow condensation. The experimental results are recorded in tests with a smooth horizontal tube of 6 mm inner diameter and 2 to 10 m long. This manuscript, which is part I of a two part series, focuses on pure and azeotropic fluids. Part II describes results with non-azeotropic refrigerant mixtures. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with pure and azeotropic fluids in this work. However, the Froude number is found to be a good additional indicator to identify transition between annular and wavy flows. The transition occurs mostly at Fr = 15 to 20 for both pure and azeotropic fluids. In the case of pure and azeotropic fluids, the hear transfer coefficient was found to be independent of the mass flux in wavy flow regions, but increased with an increasing mass flux in the annular flow regions. For pure and azeotropic fluids, a modified Tandon et al. correlation agreed best with experimental data from tests with R-12, R-22, R-134a, and R-502. For the local pressure drop it is correlated within +/-15% by using the Lockhart-Martinelli parameters. The experimental data for pure and azeotropic refrigerants can be predicted by using a correlation for overall pressure drop.

  • 4. Shao, D. W.
    et al.
    Granryd, Eric G.
    KTH, Tidigare Institutioner                               , Energiteknik.
    Flow pattern, heat transfer and pressure drop in flow condensation part II: Zeotropic refrigerants mixtures (NARMs)2000Inngår i: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 6, nr 2, s. 197-209Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper, which is parr II of a study on flow condensation is focused on zeotropic (or non-azeotropic) refrigerant mixtures (NARMs) In the experiments, condensation in a horizontal tube of inner diameter 6 mm and 10 m length were studied with fluids R-404A, R-407C, and three mixtures of R-32 and R-134a. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with NARMs studied in this work. Most tests recorded are in the annular or semi annular flow region. The Froude number is, however, found to be an additional indicator to identify transition between annular and wavy flows. The transition in the experiments occurs mostly at Fr = 15 to 20 for the fluids tested. For NARMs with a small temperature glide (e.g. R-404A), as observed in the case of pure and azeotropic fluids, the hear transfer coefficient is independent of the mass flux in wavy flow regions, and increases with an increasing mass flux in annular flow regions. For other NARMs tested, the hear transfer coefficient (starting from a lower level) always increases with an increasing mass flux within the tested ranges. The heat transfer data from the tests with R-404A, R-407C, and R-32/R-134a mixtures can be predicted reasonably well by a modified Tandon et al. (1985b, 1995) equation with a correction proposed by Granryd (1989)for NARMs. The classical correlations for the pressure drop do nor work well. Instead, the data for local pressure drop are correlated within +/-15% by means of the same correlation as for the pure and azeotropic fluids. A simple correlation for the overall pressure drop based on the experimental data for pure and azeotropic fluids is good also for R-404A (with a small glide), but overpredicts the pressure drop (by up to 50%)for NARMs with glide, such as R-407C.

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