Istraživanje učinkovitosti dizalice topline s bušotinskim izmjenjivačem topline

The paper presents results of an optimal design process of a ground-source heat pump system including thermal modelling of the system and selection of optimal design parameters which affect the system performance and operational costs. An integrated building and system simulation program was built for this purpose. The results were compared with a predefined “reference” installation defining energy savings, environmental benefits and economical results. It was found that a primary energy saving and CO2 emission reduction of 31 % was obtained. Decreasing the borehole resistance leads to an increased natural cooling fraction of 48 % to 61 %. Operational costs were higher for the reference installation (86 %) than for the heat pump system (73 %). Over a lifetime, the ground source heat pump system is a far more economical choice.Ovaj rad predstavlja rezultate optimiranja rada dizalice topline s bušotinskim izmjenjivačem topline, te uključuje termodinamički model sustava, odabir optimalnih parametara koji utječu na učinkovitost sustava te njegovih pogonskih troškova. U tu svrhu izgrađena je simulacija cjelovite zgrade s prethodno navedenim sustavom. Rezultati su uspoređeni s ranije definiranom referentnom instalacijom, definirajući uštede energije, pozitivan utjecaj na okoliš, te ekonomske rezultate. Rezultati su pokazali da je ostvarena ušteda primarne energije i smanjenje CO2 emisije od 31 %. Smanjenje toplinskog otpora bušotine vodi do porasta udjela prirodnog hlađenja s 48 % na 61 %. Operativni troškovi su bili veći za referentni sustav (86 %) za razliku od sustava s dizalicom topline s bušotinskim izmjenjivačem topline.(73 %). Obzirom na vijek trajanja, dizalica topline s bušotinskim izmjenjivačem topline predstavlja ekonomski isplativiju opciju

Economic optimization of heat exchangers for corrosive environments

Heat exchangers play a key role in power generation and many industrial processes. In various applications, the construction material is however exposed to a corrosive environment. This requires the device to be made from expensive corrosion resistant materials, causing the cost of the heat exchanger to increase significantly. One alternative could be to use more readily available metals (e.g. carbon steel). Although it might have to be replaced several times over its lifetime, the material cost of the heat exchanger would be more economical. In order to investigate if this is a viable alternative, a model was made. This model calculates the total cost of ownership (TCO) of a heat exchanger, taking into account the investment costs, maintenance costs and operational costs. A corrosion model is implemented allowing to specify the behaviour of a certain material in the fluid it is exposed to. Furthermore, the model allows to optimize the design to achieve a minimal TCO for a specific case. As a demonstration, the model is applied to the design and selection of an 5 MW heat exchanger for a binary geothermal power plant in Belgium, where the (corrosive) geothermal brine is used to heat water for a district heating network and an organic Rankine cycle

Sorption heat storage for long-term low-temperature applications: A review on the advancements at material and prototype scale

Sorption heat storage has the potential to store large amounts of thermal energy from renewables and other distributed energy sources. This article provides an overview on the recent advancements on long-term sorption heat storage at material- and prototype- scales. The focus is on applications requiring heat within a temperature range of 30–150 °C such as space heating, domestic hot water production, and some industrial processes. At material level, emphasis is put on solid/gas reactions with water as sorbate. In particular, salt hydrates, adsorbents, and recent advancements on composite materials are reviewed. Most of the investigated salt hydrates comply with requirements such as safety and availability at low cost. However, hydrothermal stability issues such as deliquescence and decomposition at certain operating conditions make their utilization in a pure form challenging. Adsorbents are more hydrothermally stable but have lower energy densities and higher prices. Composite materials are investigated to reduce hydrothermal instabilities while achieving acceptable energy densities and material costs. At prototype-scale, the article provides an updated review on system prototypes based on the reviewed materials. Both open and closed system layouts are addressed, together with the main design issues such as heat and mass transfer in the reactors and materials corrosion resistance. Especially for open systems, the focus is on pure adsorbents rather than salt hydrates as active materials due to their better stability. However, high material costs and desorption temperatures, coupled with lower energy densities at typical system operating conditions, decrease their commercial attractiveness. Among the main conclusions, the implementation within the scientific community of common key performance indicators is suggested together with the inclusion of economic aspects already at material-scale investigations.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES

Energy density and storage capacity cost comparison of conceptual solid and liquid sorption seasonal heat storage systems for low-temperature space heating

Sorption heat storage can potentially store thermal energy for long time periods with a higher energy density compared to conventional storage technologies. A performance comparison in terms of energy density and storage capacity costs of different sorption system concepts used for seasonal heat storage is carried out. The reference scenario for the analysis consisted of satisfying the yearly heating demand of a passive house. Three salt hydrates (MgCl2, Na2S, and SrBr2), one adsorbent (zeolite 13X) and one ideal composite based on CaCl2, are used as active materials in solid sorption systems. One liquid sorption system based on NaOH is also considered in this analysis. The focus is on open solid sorption systems, which are compared with closed sorption systems and with the liquid sorption system. The main results show that, for the assumed reactor layouts, the closed solid sorption systems are generally more expensive compared to open systems. The use of the ideal composite represented a good compromise between energy density and storage capacity costs, assuming a sufficient hydrothermal stability. The ideal liquid system resulted more affordable in terms of reactor and active material costs but less compact compared to the systems based on the pure adsorbent and certain salt hydrates. Among the main conclusions, this analysis shows that the costs for the investigated ideal systems based on sorption reactions, even considering only the active material and the reactor material costs, are relatively high compared to the acceptable storage capacity costs defined for different users. However, acceptable storage capacity costs reflect the present market condition, and they can sensibly increase or decrease in a relatively short period due to for e.g. the variation of fossil fuels prices. Therefore, in the upcoming future, systems like the ones investigated in this work can become more competitive in the energy sector.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement Nº 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES

Design of an experimental set-up to determine the influence of corrosion on heat transfer

In the exploitation of geothermal energy, heat exchangers are essential to distribute heat to energy conversion systems (e.g. organic Rankine cycles) or district heating networks. The geothermal brine found in Belgium however has a high temperature and a high salinity which makes it extremely corrosive. In such environments, the classic solution is to construct a heat exchanger with a highly corrosion resistant metal such as titanium or nickel. However, since these metals are very expensive, alternatives are investigated. One such alternative is using heat exchangers made of less corrosion resistant materials, but where detailed information about the corrosion process is available. This information is then used during design and for predictive maintenance. An experimental set-up to determine the corrosion rate and the influence of corrosion on the heat transfer is designed.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

Corrosion in heat exchangers in geothermal power plants

In geothermal power plants that use low to medium temperature geothermal reservoirs, electricity is generated using an organic Rankine cycle or heat is provided to district heating networks. The energy in the geothermal fluid is recovered with a heat exchanger. Since the temperatures and pressures are relative high (100-150°C, 40 bar), metallic heat exchangers are preferred. These are however susceptible to corrosion in the aggressive geothermal environment, so highly corrosion resistant materials should be used or suitable coatings should be applied. This has an adverse impact on the financial viability of the project. Therefore, this research investigates the possibility to use cheaper materials that come in contact with the brine. First, a model is described to determine the total cost of ownership of the heat exchanger and to determine an optimal design. Additionally, an experimental setup is described. This setup will allow to calibrate the corrosion parameters implemented in the model, to determine the influence of corrosion on the performance of the heat exchanger and to assess the influence of the flowing conditions on the corrosion process. In this paper, the methodology and expected outcome are described

Corrosion and corrosion prevention in heat exchangers

In many industries and processes, heat exchangers are of vital importance as they are used to transfer heat from one fluid to another. These fluids can be corrosive to heat exchangers, which are usually made of metallic materials. This paper illustrates that corrosion is an important problem in the operation of heat exchangers in many environments, for which no straightforward answer exists. Corrosion failures of heat exchangers are common, and corrosion often involves high maintenance or repair costs. In this review, an overview is given of what is known on corrosion in heat exchangers. The different types of corrosion encountered in heat exchangers and the susceptible places in the devices are discussed first. This is combined with an overview of failure analyses for each type of corrosion. Next, the effect of heat transfer on corrosion and the influence of corrosion on the thermohydraulic performances are discussed. Finally, the prevention and control of corrosion is tackled. Prevention goes from general design considerations and operation guidelines to the use of cathodic and anodic protection

Perpendicular magnetic anisotropy of CoFeB\Ta bilayers on ALD HfO2

Perpendicular magnetic anisotropy (PMA) is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\CoFe(B) interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\Ta bilayer deposited on amorphous high-kappa dielectric (relative permittivity kappa=20) HfO2, grown by atomic layer deposition (ALD). PMA with interfacial anisotropy energy K-i up to 0.49 mJ/m(2) appears after annealing the stacks between 200 degrees C and 350 degrees C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350 degrees C coincides with the onset of interdiffusion in the materials. High-kappa dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA). The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-kappa dielectrics

Hysteresis and Fractional Matching in Thin Nb Films with Rectangular Arrays of Nanoscaled Magnetic Dots

We have investigated the periodic pinning of magnetic flux quanta in thin Nb films with rectangular arrays of magnetic dots. In this type of pinning geometry, a change in the periodicity and shape of the minima in the magnetoresistance occurs for magnetic fields exceeding a certain threshold value. This has been explained recently in terms of a reconfiguration transition of the vortex lattice due to an increasing vortex-vortex interaction with increasing magnetic field. In this picture the dominating elastic energy at high fields forces the vortex lattice to form a square symmetry rather than being commensurate to the rectangular geometry of the pinning array. In this paper we present a comparative study of rectangular arrays with Ni-dots, Co-dots and holes. In the magnetic dot arrays, we found a strong fractional matching effect up to the second order matching field. In contrast, no clear fractional matching is seen after the reconfiguration. Additionally, we discovered the existence of hysteresis in the magnetoresistance in the crossover between the low and the high field regime. We found evidence that this effect is correlated to the reconfiguration phenomenon rather than to the magnetic state of the dots. The temperature and angular dependences of the effect have been measured and possible models are discussed to explain this behavior.Comment: 1 Table, 5 Figure