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D. Nevrala - One of the best experts on this subject based on the ideXlab platform.

  • heat transfer correlations for an immersed finned heat exchanger coil transferring heat from a Hot Water Store
    Applied Energy, 1993
    Co-Authors: L.p. Chauvet, D. Nevrala, S.d. Probert
    Abstract:

    Natural-convection heat transfers, to a finned-tube heat-exchanger coil immersed in a Hot-Water Store, have been investigated. Cold Water was passed through the pipe of the heat-exchanger in order to extract heat rapidly from the Hot Water in the Store. Natural convection currents in the Stored Water were created by buoyancy forces, which were induced by the temperature gradients that developed as a result of the heat-extraction process. A heat-transfer correlation in terms of Nusselt and Rayleigh numbers has been deduced in order to predict the natural convection heat-transfer coefficient on the outside surface of the heat exchanger. This correlation, which is valid for heat entering the fins, to within an accuracy of better than 4%, is: Nu=0·280 Ra0·293 for 100 < Ra < 1500

  • influences of baffles on the rate of heat recovery via a finned tube heat exchanger immersed in a Hot Water Store
    Applied Energy, 1993
    Co-Authors: L.p. Chauvet, D. Nevrala, S.d. Probert
    Abstract:

    Abstract The heat transfer at the external wall of the heat exchanger occurs primarily by buoyancy-driven natural convection in the surrounding Water. An analysis of the effects of the presence of a rectangular duct on this heat-transfer process is presented. Small improvements in the rate of heat recovery were obtained repeatedly when a horizontal plate was located in the middle of the Store.

  • heat recovery from a Hot Water Store effect of parts of the immersed heat exchanger s pipe being thermally insulated
    Applied Energy, 1992
    Co-Authors: R Mote, Douglas Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat exchanger was employed to extract heat rapidly, from a 90-litre Hot-Water charged tank, the Water being initially at approximately 80°C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (which was totally immersed in the Store) occurred as a result of mains supply cold Water (at 20°C) being forced internally through the pipe. The axis of the heat-exchanger's coil is oriented horizontally, and the heat-exchanger's inlet is arranged to be at its lowest level. The effect of insulating short lengths of the heat-exchanger's pipe upon the rate of heat recovery was investigated. The purpose of this ‘insulation’ strategy for the heat exchanger was to prevent some of the heat gained by the Water as it passes through the heat-exchanger's pipe being unintentionally returned to the Store. Judicious positioning of the insulation has the effect of increasing the heat transfer rate along the exposed lengths of pipe, thereby enhancing the heat-exchanger's effectiveness. Irrespective of the flow rate of Water forced through the heat-exchanger's pipe, the best performance of the heat exchanger was achieved when using a 150-mm length of rubber-foam pipe insulation (of 40 mm o.d. including the heat-exchanger's external diameter) at the lowest level of the heat exchanger and near the vertical centre-line of the tank, i.e. in the path of the descending cooled stream of Water in the Store. The improvement then achieved in the heat-exchanger's effectiveness is approximately 2%.

  • rate of heat recovery from a Hot Water Store influence of the aspect ratio of a vertical axis open ended cylinder beneath a submerged heat exchanger
    Applied Energy, 1992
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat-exchanger was employed to extract heat rapidly, from a 90-litre Hot-Water charged tank; the Water being initially at a temperature of approximately 80°C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (immersed in the Store) occur as a result of initially-cold Water (at 20°C) being forced internally through the heat-exchanger's pipe. The axis of the heat-exchanger coil is orientated vertically, and the heat-exchanger's inlet is arranged to be at its lowest level. The influence of a smooth, vertical-axis cylindrical PVC baffle located symmetrically beneath the heat-exchanger upon the rate of heat recovery via the heat-exchanger was investigated. Irrespective of the flow rate of Water through the heat-exchanger's pipe, the greatest rate of heat recovery was achieved using the baffle index (a function of the height, diameter and depth of the baffle within the thermal Store as well as the latter dimensions) equals 1·70±0·05. The improvement in the heat-exchanger's effectiveness is approximately 2·5 to 3%. Increasing the rate of Water flow through the heat-exchanger's pipe resulted in a reduction of the heat-exchanger's quality-effectiveness, but a rise in the thermal Store's recuperation effectiveness. The latter was due to the reduced amount of mixing between the ascending warm-streams and the descending colder-streams of Water in the tank. The experimental, two-dimensional radial temperature-distribution can be employed to predict (to ±5·0%) the cumulative amount of heat recovered from the thermal Store.

  • free convective flows within a Hot Water Store induced by a submerged relatively cold heat exchanger
    Applied Energy, 1991
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat exchanger was employed to extract heat rapidly, at temperatures in excess of 30° C, from a 90-litre Hot-Water charged tank; the Water being initially at a temperature of approximately 80° C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (immersed in the Store) occur as a result of initially-cold Water (at ∼ 20° C) being forced internally through the heat exchanger's pipe. For the most rapid rate of heat extraction, the axis of the heat exchanger coil should be oriented horizontally, and the heat exchanger's inlet arranged to be at the lowest level. Increasing the rate of Water being passed through the heat exchanger's pipe resulted in a reduction of the heat exchanger's quality effectiveness, but a rise in the thermal Store's recuperation effectiveness. The latter was due to the reduced level of mixing between the ascending warm streams and the descending colder streams. The development of the thermal boundary layer adjacent to the tank's wall was beneficial in deflecting the centrally descending stream of relatively colder Water (which comes off the heat exchanger's pipe) to drive the ascending warmer Water onto the heat exchanger, which is located near the surface of the Water in the tank.

S.d. Probert - One of the best experts on this subject based on the ideXlab platform.

  • heat transfer correlations for an immersed finned heat exchanger coil transferring heat from a Hot Water Store
    Applied Energy, 1993
    Co-Authors: L.p. Chauvet, D. Nevrala, S.d. Probert
    Abstract:

    Natural-convection heat transfers, to a finned-tube heat-exchanger coil immersed in a Hot-Water Store, have been investigated. Cold Water was passed through the pipe of the heat-exchanger in order to extract heat rapidly from the Hot Water in the Store. Natural convection currents in the Stored Water were created by buoyancy forces, which were induced by the temperature gradients that developed as a result of the heat-extraction process. A heat-transfer correlation in terms of Nusselt and Rayleigh numbers has been deduced in order to predict the natural convection heat-transfer coefficient on the outside surface of the heat exchanger. This correlation, which is valid for heat entering the fins, to within an accuracy of better than 4%, is: Nu=0·280 Ra0·293 for 100 < Ra < 1500

  • influences of baffles on the rate of heat recovery via a finned tube heat exchanger immersed in a Hot Water Store
    Applied Energy, 1993
    Co-Authors: L.p. Chauvet, D. Nevrala, S.d. Probert
    Abstract:

    Abstract The heat transfer at the external wall of the heat exchanger occurs primarily by buoyancy-driven natural convection in the surrounding Water. An analysis of the effects of the presence of a rectangular duct on this heat-transfer process is presented. Small improvements in the rate of heat recovery were obtained repeatedly when a horizontal plate was located in the middle of the Store.

  • rate of heat recovery from a Hot Water Store influence of the aspect ratio of a vertical axis open ended cylinder beneath a submerged heat exchanger
    Applied Energy, 1992
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat-exchanger was employed to extract heat rapidly, from a 90-litre Hot-Water charged tank; the Water being initially at a temperature of approximately 80°C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (immersed in the Store) occur as a result of initially-cold Water (at 20°C) being forced internally through the heat-exchanger's pipe. The axis of the heat-exchanger coil is orientated vertically, and the heat-exchanger's inlet is arranged to be at its lowest level. The influence of a smooth, vertical-axis cylindrical PVC baffle located symmetrically beneath the heat-exchanger upon the rate of heat recovery via the heat-exchanger was investigated. Irrespective of the flow rate of Water through the heat-exchanger's pipe, the greatest rate of heat recovery was achieved using the baffle index (a function of the height, diameter and depth of the baffle within the thermal Store as well as the latter dimensions) equals 1·70±0·05. The improvement in the heat-exchanger's effectiveness is approximately 2·5 to 3%. Increasing the rate of Water flow through the heat-exchanger's pipe resulted in a reduction of the heat-exchanger's quality-effectiveness, but a rise in the thermal Store's recuperation effectiveness. The latter was due to the reduced amount of mixing between the ascending warm-streams and the descending colder-streams of Water in the tank. The experimental, two-dimensional radial temperature-distribution can be employed to predict (to ±5·0%) the cumulative amount of heat recovered from the thermal Store.

  • free convective flows within a Hot Water Store induced by a submerged relatively cold heat exchanger
    Applied Energy, 1991
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat exchanger was employed to extract heat rapidly, at temperatures in excess of 30° C, from a 90-litre Hot-Water charged tank; the Water being initially at a temperature of approximately 80° C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (immersed in the Store) occur as a result of initially-cold Water (at ∼ 20° C) being forced internally through the heat exchanger's pipe. For the most rapid rate of heat extraction, the axis of the heat exchanger coil should be oriented horizontally, and the heat exchanger's inlet arranged to be at the lowest level. Increasing the rate of Water being passed through the heat exchanger's pipe resulted in a reduction of the heat exchanger's quality effectiveness, but a rise in the thermal Store's recuperation effectiveness. The latter was due to the reduced level of mixing between the ascending warm streams and the descending colder streams. The development of the thermal boundary layer adjacent to the tank's wall was beneficial in deflecting the centrally descending stream of relatively colder Water (which comes off the heat exchanger's pipe) to drive the ascending warmer Water onto the heat exchanger, which is located near the surface of the Water in the tank.

  • the performance of a coiled finned tube heat exchanger submerged in a Hot Water Store the effect of the exchanger s orientation
    Applied Energy, 1991
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled-pipe exchanger was employed to extract heat rapidly at relatively high temperatures from a 90-litre Hot-Water charged tank, the Water being initially at a temperature of approximately 80°C. The free-convective movements of the Water around the outside of the coiled pipe (immersed in the Store) were due to buoyancy forces induced by colder Water being forced through the heat-exchanger's pipe. For the heat-exchanger orientations tested, the maximum effectiveness, with respect to the quality of the heat extracted was achieved (i) by having the axis of the coiled heat-exchanger arranged horizontally with its inlet at the lowest level; and (ii) with the lower rate tested (=6·6 litre/min) of Water being passed through the heat-exchanger's pipe, partly because this led to a lower rate of disruption of the stratification of the Water within the Store.

R Mote - One of the best experts on this subject based on the ideXlab platform.

  • heat recovery from a Hot Water Store effect of parts of the immersed heat exchanger s pipe being thermally insulated
    Applied Energy, 1992
    Co-Authors: R Mote, Douglas Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat exchanger was employed to extract heat rapidly, from a 90-litre Hot-Water charged tank, the Water being initially at approximately 80°C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (which was totally immersed in the Store) occurred as a result of mains supply cold Water (at 20°C) being forced internally through the pipe. The axis of the heat-exchanger's coil is oriented horizontally, and the heat-exchanger's inlet is arranged to be at its lowest level. The effect of insulating short lengths of the heat-exchanger's pipe upon the rate of heat recovery was investigated. The purpose of this ‘insulation’ strategy for the heat exchanger was to prevent some of the heat gained by the Water as it passes through the heat-exchanger's pipe being unintentionally returned to the Store. Judicious positioning of the insulation has the effect of increasing the heat transfer rate along the exposed lengths of pipe, thereby enhancing the heat-exchanger's effectiveness. Irrespective of the flow rate of Water forced through the heat-exchanger's pipe, the best performance of the heat exchanger was achieved when using a 150-mm length of rubber-foam pipe insulation (of 40 mm o.d. including the heat-exchanger's external diameter) at the lowest level of the heat exchanger and near the vertical centre-line of the tank, i.e. in the path of the descending cooled stream of Water in the Store. The improvement then achieved in the heat-exchanger's effectiveness is approximately 2%.

  • rate of heat recovery from a Hot Water Store influence of the aspect ratio of a vertical axis open ended cylinder beneath a submerged heat exchanger
    Applied Energy, 1992
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat-exchanger was employed to extract heat rapidly, from a 90-litre Hot-Water charged tank; the Water being initially at a temperature of approximately 80°C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (immersed in the Store) occur as a result of initially-cold Water (at 20°C) being forced internally through the heat-exchanger's pipe. The axis of the heat-exchanger coil is orientated vertically, and the heat-exchanger's inlet is arranged to be at its lowest level. The influence of a smooth, vertical-axis cylindrical PVC baffle located symmetrically beneath the heat-exchanger upon the rate of heat recovery via the heat-exchanger was investigated. Irrespective of the flow rate of Water through the heat-exchanger's pipe, the greatest rate of heat recovery was achieved using the baffle index (a function of the height, diameter and depth of the baffle within the thermal Store as well as the latter dimensions) equals 1·70±0·05. The improvement in the heat-exchanger's effectiveness is approximately 2·5 to 3%. Increasing the rate of Water flow through the heat-exchanger's pipe resulted in a reduction of the heat-exchanger's quality-effectiveness, but a rise in the thermal Store's recuperation effectiveness. The latter was due to the reduced amount of mixing between the ascending warm-streams and the descending colder-streams of Water in the tank. The experimental, two-dimensional radial temperature-distribution can be employed to predict (to ±5·0%) the cumulative amount of heat recovered from the thermal Store.

  • free convective flows within a Hot Water Store induced by a submerged relatively cold heat exchanger
    Applied Energy, 1991
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled finned-pipe heat exchanger was employed to extract heat rapidly, at temperatures in excess of 30° C, from a 90-litre Hot-Water charged tank; the Water being initially at a temperature of approximately 80° C. Free-convective buoyancy movements of the Water around the outside of this coiled pipe (immersed in the Store) occur as a result of initially-cold Water (at ∼ 20° C) being forced internally through the heat exchanger's pipe. For the most rapid rate of heat extraction, the axis of the heat exchanger coil should be oriented horizontally, and the heat exchanger's inlet arranged to be at the lowest level. Increasing the rate of Water being passed through the heat exchanger's pipe resulted in a reduction of the heat exchanger's quality effectiveness, but a rise in the thermal Store's recuperation effectiveness. The latter was due to the reduced level of mixing between the ascending warm streams and the descending colder streams. The development of the thermal boundary layer adjacent to the tank's wall was beneficial in deflecting the centrally descending stream of relatively colder Water (which comes off the heat exchanger's pipe) to drive the ascending warmer Water onto the heat exchanger, which is located near the surface of the Water in the tank.

  • the performance of a coiled finned tube heat exchanger submerged in a Hot Water Store the effect of the exchanger s orientation
    Applied Energy, 1991
    Co-Authors: R Mote, S.d. Probert, D. Nevrala
    Abstract:

    Abstract A coiled-pipe exchanger was employed to extract heat rapidly at relatively high temperatures from a 90-litre Hot-Water charged tank, the Water being initially at a temperature of approximately 80°C. The free-convective movements of the Water around the outside of the coiled pipe (immersed in the Store) were due to buoyancy forces induced by colder Water being forced through the heat-exchanger's pipe. For the heat-exchanger orientations tested, the maximum effectiveness, with respect to the quality of the heat extracted was achieved (i) by having the axis of the coiled heat-exchanger arranged horizontally with its inlet at the lowest level; and (ii) with the lower rate tested (=6·6 litre/min) of Water being passed through the heat-exchanger's pipe, partly because this led to a lower rate of disruption of the stratification of the Water within the Store.

Harald Druck - One of the best experts on this subject based on the ideXlab platform.

  • demonstration of an overground Hot Water Store in segmental construction for district heating systems
    Energy Procedia, 2018
    Co-Authors: Thorsten Urbaneck, Jan Markus Mucke, Fabian Findeisen, Markus Gensbaur, Stephan Lang, Dominik Bestenlehner, Harald Druck, Robert Beyer, Konrad Pieper
    Abstract:

    Abstract Thermal energy Stores can significantly improve the efficiency and environment-friendliness of the heat supply by storing heat surpluses and supply heat to the consumer if necessary. Therefore, a high demand for cost-effective storage technologies with low energy losses exists. For Hot Water storage tanks using the displacement principle significant optimization potentials exist regarding currently at the market available storage technologies, in particular pressure vessels and flat-bottom tanks. A new tank design eliminates disadvantages and offers numerous benefits. A demonstrator with a new design was already built in cooperation with scientific and industrial partners as part of the OBSERW project in Nortorf (Germany). The demonstrator is a small-scale Hot Water storage tank with a volume of approx. 100 m³. It allows numerous tests with low energy and time effort. The main novelty of the construction is an indoor floating ceiling, with the loading device (e. g. a radial diffuser) attached directly to it. A flexible connection allows the free movement of the floating ceiling between a top and bottom dead centre. This work describes the function of the storage tank and presents first operation experiences.

  • development of a combined Hot Water and sorption Store for solar thermal systems
    Energy Procedia, 2014
    Co-Authors: Rebecca Weber, Henner Kerskes, Harald Druck
    Abstract:

    Abstract The motivation for the development of a combined Hot Water and sorption Store is to complement the advantages and to reduce the disadvantages of the two particular storage technologies. Hot Water Stores offer high heat supply rates but are particularly suitable for short term storage due to heat losses whereas for a sorption Store the power drain is low but it shows the advantage of a high storage density and long-term heat storage almost without losses. The combined Hot Water and sorption Store has been developed using the example of a solar thermal system for domestic Hot Water preparation. The Store consists of a radial stream adsorber integrated in a Hot Water Store. Adsorption and desorption experiments in laboratory have been conducted with a prototype Store in full-scale. A numerical model of the combined Store has been developed and annual simulations of a solar thermal system including a combined Hot Water and sorption Store have been conducted. The thermal performance has been compared to those of reference Hot Water Stores. The results of the experimental and numerical investigations will be presented in this paper and the benefit of a combined Hot Water and sorption Store applied for solar thermal systems will be discussed.

L.p. Chauvet - One of the best experts on this subject based on the ideXlab platform.