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1.
Integration of an absorption chiller to a process applying the pinch analysis approach
Andreja Nemet, Zdravko Kravanja, Miloš Bogataj, 2022, original scientific article

Abstract: In addition to the consumption of hot utilities, there is also a significant cost associated with the consumption of cold utilities when there is a high demand for cooling. A promising solution for cooling is an absorption chiller (AC), which uses heat instead of electricity for cooling. A thermodynamic approach for evaluating AC integrated with a process is presented in this work. A model for assessing the properties and duties of an AC cycle was developed. The integration of a combined process-AC system was evaluated using the Grand Composite Curve. Three different options of integration were analyzed: (i) above the Pinch, (ii) below the Pinch, and (iii) across the Pinch. AC represents the combined effect of a heat engine and a heat pump, as the generator together with the absorber and condenser has the function of a heat engine, while the evaporator combined with the absorber and condenser mimics the function of a heat pump. The comparison between the non-integrated and integrated process-AC systems has revealed that the proper placement of AC is across or below the Pinch and the improper is above the Pinch. If AC was entirely integrated below the Pinch, the integration would result in a complete (100%) reduction in the consumption of hot utility for the operation of AC. The most suitable placement of AC with double reduction of hot utility consumption and complete reduction of both hot and cold utility to operate AC is across the Pinch due to the pumping of heat through AC from below to above the Pinch.
Keywords: absorption chiller, Pinch analysis, heat integration, low-temperature heat
Published in DKUM: 15.05.2025; Views: 0; Downloads: 1
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2.
The effects of hedgerows shading on soil temperature and gravimetric soil water content
Andreja Borec, Tina Lešnik, Tadeja Kraner Šumenjak, Mateja Muršec, 2023, original scientific article

Abstract: This study sets out to examine the effects of hedgerow shading on soil physical properties, specifically soil gravimetric water content and soil temperature. Analyses of both soil parameters were conducted at two locations with different shade proportion. The aim of the study was to address the links between hedgerow shading and basic physical soil properties which could be significant both for agricultural production and for ecological processes in agroecosystems. At both locations, soil samples and measurements were taken at different distances from hedgerow and in different time intervals. Diurnal shading variation at certain distances from the hedgerow on Location 1 and 2 was calculated with the software toll for Arboriculturists. At Location 1 shading is consistently high throughout the year, ranging from 76 to 100%. In contrast, shading at Location 2 varies from 1 to 25%. The results reveal that hedgerows at Location 1, do not have a statistically significant impact on gravimetric soil water content and soil temperature across the entire plot surface. Additionally, the percentage of shading is only marginally decreases with distance. Conversely, Location 2 exhibits an increase in soil temperature and a slight but (non-significant) decrease in soil gravimetric water content as the distance from the hedgerow increases., The total mean shading at Location 2 is considerably lower compared to Location 1, and the shading percentage declines more at the distance from the hedgerow increases. Overall, lower soil temperatures and higher gravimetric soil water content where observed at the more shaded Location 1. The research outcomes are helpful in agricultural production planning as well as in the evaluation of hedgerows for the needs of agricultural policy.
Keywords: soil water content, soil temperature, hedgerow, sunlight
Published in DKUM: 11.04.2025; Views: 0; Downloads: 4
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3.
Multiple quartz crystals connected in parallel for high-resolution sensing of capacitance changes
Vojko Matko, 2022, original scientific article

Abstract: We present a new highly sensitive, low-value capacitance sensor method that uses multiple quartz crystals connected in parallel inside the oscillator. In the experimental setup, the measured (sensible) reactance (capacitance) is connected in parallel to the total shunt capacitance of the quartz crystals, oscillating in the oscillator. Because AT-cut crystals have a certain nonlinear frequency– temperature dependence, we use the switching mode method, by which we achieve a temperature compensation of the AT-cut crystals’ frequency–temperature characteristics in the temperature range between 0–50 ◦C. The oscillator switching method also compensates for any other influences on the frequency of the oscillator, such as ageing of the crystals and oscillator elements, supply voltage fluctuations, and other parasitic impedances in the oscillating circuit. Subsequently using two 50-ms-delayed switches between the measuring and reference capacitors, the experimental error in measuring the capacitance is lowered for measurements under a dynamic temperature variation in the range of 0–50 ◦C. The experimental results show that the switching method, which includes a multiple quartz connection and high-temperature compensation improvement of the quartz crystals’ characteristics, enables a sub-aF resolution. It converts capacitance changes in the range 10 zF–200 fF to frequencies in the range 4 kHz–100 kHz.
Keywords: multiple quartz crystals in parallel, quartz capacitive sensing method, temperature compensation, switching mode method
Published in DKUM: 01.04.2025; Views: 0; Downloads: 3
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4.
Experimental and numerical investigation of Rayleigh-Benard convection in rectangular cavity with motor oil
Predrag Živković, Mladen A. Tomić, Sadoon Ayed, Cristian Barz, Drago Sever, 2023, original scientific article

Abstract: Naturally flows have been the scope of the scientific research for centuries, Rayleigh-Benard convection being one of the leading. Many researchers have considered the flow patterns, boundary conditions, various cavities, nanofluids, theoretically, numerically, and experimentally. The flow was investigated in atmosphere and in nanofluids, in air, water, molten metals, non-Newtonian fluids. Almost all research focuses on 2-D or 3-D analysis of flow in laterally unlimited enclosures, as parallel plates or coaxial cylinders. In technical practice, only limited enclosures exist. This paper presents numerical and real experimental results for the test chamber with ratio 4×2×1 in x-, y-, and z direction, respectfully. The measurements were taken at fifteen different positions on the faces of the tank. Probes used are PT100 elements. As the chamber is limited in all directions, the results have shown strong influence of the lateral walls. The results are compared with the those obtained by IR camera. Various fluids were tested, and results for motor oil will be presented.
Keywords: Rayleigh-Bénard convection, temperature profile, PT100 probe, motor oil, numerical simulation
Published in DKUM: 27.03.2025; Views: 0; Downloads: 1
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5.
Study on the compression effect of clothing on the physiological response of the athlete
Marianna Halász, Jelka Geršak, Péter Bakonyi, Gabriella Oroszlány, András Koleszár, Orsolya Nagyné Szabó, 2022, original scientific article

Abstract: The study aimed to analyze whether the high compression of unique, tight-fitting sportswear influences the clothing physiology comfort of the athlete. Three specific sportswear with different compression were tested on four subjects while they were running on a treadmill with increasing intensity. The compression effect of the sportswear on the body of the test persons, the temperature distribution of the subjects, and the intensity of their perspiration during running were determined. The results indicate that the compression effect exerted by the garments significantly influences the clothing physiology comfort of the athlete; a higher compression load leads to more intense sweating and higher skin temperature.
Keywords: clothing physiology, tight-fitting sportswear, running test on a treadmill, thermal comfort, skin temperature, perspiration
Published in DKUM: 21.03.2025; Views: 0; Downloads: 2
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6.
High resolution short response time fiber-optic temperature sensor
Nermin Sinanović, Simon Pevec, Matej Njegovec, Vedran Budinski, Denis Đonlagić, 2025, original scientific article

Abstract: This article presents an all-silica microwire optical sensor designed for both fast response time and high-resolution temperature detection. The sensor consists of a thin optical microwire created at the tip of an optical fiber, configured as a temperature sensitive Fabry–Perot interferometer (FPI). For the purposes of achieving rapid response times, the sensing section of the sensor has a diameter of 11 µm. Experimental bench tests were set up to evaluate the sensor’s static and dynamic performance. The results indicate a sensor system resolution of about 5 mK and demonstrate a bandwidth of 38 Hz that corresponds to a response time of 4 ms in still air. The sensor’s functionality is shown through a basic periodic gas compression method detecting small temperature fluctuations. In addition, the sensor was demonstrated for operation up to 600 ◦C.
Keywords: Fabry-Perot, high-resolution temperature sensor, micromachining, microwire optic sensor, optical fibers, short response time
Published in DKUM: 12.02.2025; Views: 0; Downloads: 9
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7.
A short-range quasi-distributed strain and temperature sensing system utilizing a standard telecom laser diode
Jure Javornik, Denis Đonlagić, 2025, original scientific article

Abstract: This article presents a short-range fiber-optic quasi-distributed sensing device suitable for strain and temperature measurement. The sensing assembly consists of an fs laser inscribed reference mirror and a sensing array of equidistantly positioned mirrors. Utilization of the reference mirror and proper sensor geometry selection provides the possibility for a high-resolution spectral interrogation of the sensing array while relying on an ordinary, cost-effective distributed feedback (DFB) telecom laser diode. Beside the telecom DFB diode, the entire interrogation system includes only an additional detector, optical coupler, analog interface and a microcontroller. Measurement resolution better than 1 µε was demonstrated experimentally at a sampling rate exceeding 65 samples per second, while utilizing a sensing device with a typical length of 50 mm and spatial resolution of approximately 2 mm. To demonstrate the application potential of the proposed measuring device, a few different packages and sensor configurations were demonstrated and tested, including a system for tactile sensing applications and a short-range quasi-distributed temperature measurement probe.
Keywords: optical fiber sensors, short-range quasi-distributed fiber-optic sensor, strain/temperature sensing device, cost-effective interrogation system, tactile sensing, phase subtraction
Published in DKUM: 03.02.2025; Views: 0; Downloads: 10
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8.
Long-term temperature prediction with hybrid autoencoder algorithms
Jorge Pérez-Aracil, Dušan Fister, C. M. Marina, César Peláez-Rodriguez, L. Cornejo-Bueno, P. A. Gutiérrez, Matteo Giuliani, A. Castelleti, Sancho Salcedo-Sanz, 2024, original scientific article

Abstract: This paper proposes two hybrid approaches based on Autoencoders (AEs) for long-term temperature prediction. The first algorithm comprises an AE trained to learn temperature patterns, which is then linked to a second AE, used to detect possible anomalies and provide a final temperature prediction. The second proposed approach involves training an AE and then using the resulting latent space as input of a neural network, which will provide the final prediction output. Both approaches are tested in long-term air temperature prediction in European cities: seven European locations where major heat waves occurred have been considered. The longterm temperature prediction for the entire year of the heatwave events has been analysed. Results show that the proposed approaches can obtain accurate long-term (up to 4 weeks) temperature prediction, improving Persistence and Climatology in the benchmark models compared. In heatwave periods, where the persistence of the temperature is extremely high, our approach beat the persistence operator in three locations and works similarly in the rest of the cases, showing the potential of this AE-based method for long-term temperature prediction.
Keywords: autoencoder, temperature prediction, hybrid models, heatwave
Published in DKUM: 29.01.2025; Views: 0; Downloads: 3
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9.
Regulator temperature s krmilnikom pid : diplomsko delo
Miha Jerebic, 2024, undergraduate thesis

Abstract: Učinkovito vzdrževanje želene temperature je bistveno za zagotavljanje udobja, varnosti in optimalnega delovanja različnih sistemov. V ta namen se uporabljajo regulatorji temperature, ki omogočajo natančen nadzor nad temperaturo in zagotavljajo stabilno delovanje. V nalogi opišemo različne vrste regulatorjev temperature, njihove uporabe ter s tem povezano elektroniko na splošno. Posebno pozornost v nalogi namenjamo regulatorjem s proporcionalno-integracijsko-diferencialnimi krmilniki in kot praktični primer opišemo postopek načrtovanja v programu Altium Designer in izdelavo končnega izdelka v fizični obliki. Delovanje izdelka preverimo tudi z meritvami s pomočjo oscilatorja, ki nam ponudijo vpogled v pomanjkljivosti izdelanega regulatorja in njegove potencialne izboljšave.
Keywords: regulator temperature, temperatura, tiskanina, PID
Published in DKUM: 14.10.2024; Views: 0; Downloads: 15
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10.
The importance of thermally abnormal waters for bioinvasions - a case study of Pistia stratiotes
Nina Šajna, Tina Urek, Primož Kušar, Mirjana Šipek, 2023, original scientific article

Abstract: Thermally abnormal waters represent safe sites for alien invasive plants requiring warmer conditions than provided by the ambient temperatures in the temperate zone. Therefore, such safe sites are frequently inhabited by tropical and sub-tropical plants. By performing a literature review we assessed that at least 55 alien aquatic plant taxa from 21 families were found in thermally abnormal waters in Europe. The majority of these taxa are submerged or rooted macrophytes. Six taxa are listed as quarantine pests according to EPPO. Among these, Pistia stratiotes is present in seven European countries, most of the records of this presence being recent. We studied P. stratiotes in a thermally abnormal stream where a persistent population was able to survive harsh winters. Models showed that the optimum temperature for P. stratiotes biomass was 28.8 ± 3.5 ◦C. Here, we show that air temperatures had a higher influence on the photosynthetic efficiency of P. stratiotes, estimated by chlorophyll fluorescence measurements, than did water temperatures. Generally, growth, and consequently surface cover for free-floating plants, cannot be explained solely by thermally abnormal water temperatures. We conclude that even though the majority of thermophile alien plant occurrences resulted from deliberate introductions, thermally abnormal waters pose an invasion risk for further deliberate, accidental, or spontaneous spread, which might be more likely for free-floating macrophytes.
Keywords: macrophytes, alien invasive plants, chlorophyll fluorescence, plant mass, temperature gradient
Published in DKUM: 05.06.2024; Views: 158; Downloads: 32
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