62 research outputs found

    Improving intermittent waste heat recovery with ORC systems by integrating thermal energy storage

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    https://scholarlyworks.lvhn.org/progress_notes/1201/thumbnail.jp

    Development of a dynamic model for ice-on-coil external melt storage systems

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    Ice storage systems are commonly used to balance the intermittency of renewable energy and decrease the peak load by switching to off-peak hours. An adequate model is necessary to predict the behaviour of these systems. However, there is a scarce in detailed models available used to describe the performance of an ice storage evaporator and its use in a refrigeration cycle. Most existing models approximate the working principles with a steady analysis, not considering the sub cooling of ice and thickness distribution along the length. The developed model in this article uses a discretisation in length and radial direction together with an adapted thermal resistance matrix method to limit the calculation time. It has a great variability of boundary conditions and the ability to implement different types of refrigerants. The simulation results are in good agreement with the data of the manufacturer. The model shows that switching from R404A to R449A reduces the total electricity consumption

    Thermal analysis of a plastic helical coil heat exchanger for a domestic water storage tank

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    In the present study, the heat transfer coefficients of helically coiled corrugated plastic tube heat exchanger inside of the solar boiler vessel were investigated experimentally. The metal coil of the conventional solar boiler for domestic usage was replaced by a plastic tube and the results were compared with the numerical simulation and the technical documentation of the initial solar boiler. All the required parameters like inlet and outlet temperatures of tubeside and stratified temperatures, flow rate of fluids, etc. were measured using appropriate instruments. The test runs were performed for different temperatures inside the tank ranging from 30-60°C and different flow rates from which the heat transfer coefficients were calculated

    Optimal charging set point for a latent thermal energy storage for cold chain transport

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    Cold chain transport is a major contributor to greenhouse gas emissions worldwide. To reduce costs and failure rates, passive transport utilizing latent thermal energy storage can be applied instead of active transport containers. The energy storage needs to be pre-charged before transport and therefore an effective charging strategy is key. The present article discusses a thermal battery design and characterizes the charging time of the battery as a function of heat transfer fluid mass flow rate and temperature. Subsequently it discusses the optimum working point for charging the battery taking into account both the energy cost and the wage of idling workers during charging. The optimal point depends heavily on the size of the system, where small systems require minimizing idle time while larger systems require a balance between energy and time

    1D simulations of thermally buffered prismatic batteries through the application of PCMs

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    Thermal management of Li-ion batteries is critical for its performance and lifetime. Furthermore, when batteries are submitted to excessive temperatures by a bad thermal management system, thermal runaway can occur which can destroy the afflicted cell and the adjacent cells in a battery pack. Batteries are subject to cyclic behavior, charging and discharging, which is accompanied by a non-steady-state heat dissipation. Through thermal buffering, heat can be stored temporarily, which allows the heat transfer to the environment to be more evenly and thus reducing the maximal cooling load. Phase change materials or PCMs for thermal buffering are studied in this paper. By melting and solidifying, these substances take up and release a large amount of heat in a small volume and mass. To be able to design a thermal buffering system with PCMs, a one-dimensional transient model is developed to identify which influence design parameters have on the battery temperature. Simulations are performed for pure PCMs and for PCMs enhanced with three types of thermally conducting structures: metal foam, expanded graphite and carbon fibers. The results show that the effectiveness of thermal buffering is highly dependent on the cycle duration. For long cycles in the order of one day or more, thermal buffering can reduce peak temperature by around 4°C. For medium duration cycles in the order of several hours, peak temperatures can be reduced by around 13°C. For shorter cycles, heat buffering in the simulated cases was only slightly beneficial for the battery temperature. Furthermore, the simulations show that thermal buffering for battery packs requires a relatively small amount of PCM which results in short heat paths through the PCM. Enhancing the thermal conductivity by using thermally conductive structures slightly improves the thermal buffering performance, but might not be advisable due to the added complexity and cost

    Charging of a thermal battery composed of open-cell metal foam and phase change material for use in pharmaceuticals transport

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    Active coolers for pharmaceutical transport require maintenance significantly and present risks with movable parts. Passive coolers on the other hand have less components and do not require chilling units on board unlike their active counterparts. Phase change materials (PCM) have already been used in pharmaceutical logistics for the constant temperature provided thanks to the latent heat released during melting. However, before docking the gel packs require a significant amount of time for freezing due to their low thermal conductivities. In this study, the overall thermal conductivity of the enclosures of PCMs in a thermal battery is increased via combining them with open-cell metal foams. Experimental results on the thermal battery prototype show that the attempts for quickening the freezing process are promising for further research.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

    Plastic helical coil heat exchanger as an alternative for a domestic water storage tank

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    A reduction in weight and cost of a domestic hot water storage vessels is an interesting case for the industry, that can be reached by an alternative material of the helical coil heat exchanger inside them. The goal of the present study was to design a fully polymer solar boiler demonstrator and to explore its thermal performance in the low pressure and low temperature conditions. The metal coil of the conventional solar boiler for domestic usage was replaced by a plastic tube and the heat transfer behavior of helically coiled smooth plastic tube heat exchanger was investigated experimentally. The heat exchanger is placed in the middle of the tank in two parallel coils that fill almost whole height of the vessel in order to achieve maximal surface area. The water inside the tank was heated by circulating in closed loop with heater to achieve constant initial temperature across the whole volume of the vessel. When reached, the heating was stopped and a cold water of the tap temperature started to flow inside the polymeric tube. All the required parameters like inlet and outlet temperatures of tube-side and stratified temperatures in fifteen different points, flow rate of fluids and pressure drop were measured using appropriate instruments. The test runs were performed for different initial temperatures inside the tank ranging from 30-60°C from which the overall heat transfer coefficient and thermal resistances were calculated. The validity of obtained results was compared with the numerical simulation and the experimental results on the initial metallic tube.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

    Dynamic and steady state performance model of fire tube boilers with different turn boxes

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    The market for fire tube boilers is increasingly demanding custom designs from the manufacturers. For these new designs, a comprehensive thermal model is needed. In this article, both a steady state and dynamic thermal model is developed based on the plug flow furnace model with general experimental correlations. The steady state model allows optimizing (i.e. safely downsizing) boiler designs. This model has been verified with measurement reports. The dynamic model is used to estimate the peak load capability of a boiler. In the presented case, the fire tube boiler can produce up to 2.5 times the nominal steam flow rate for a period of 10 min. Special attention has been paid to the turn boxes and their specific placement, which other models in literature neglect. The efficiency penalty of a non-submerged turn box can reach up to 12% but can be reduced significantly by insulation. Turn boxes also affect peak load capability. If the total length of the boiler is constant, submerging the turn box has a positive effect on the peak load capability. This effect is mostly attributed to the increased water volume. Finally, the article includes a comparison between the plug flow furnace model the ε-NTU method and the ε-NTU method with inclusion of radiation to model the tube passes. The ε-NTU method with inclusion of radiation allows to significantly reduce the necessary number of control volumes without reduction in the model accuracy
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