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Heat Transfer Analysis on the Expedition of Temperature Distribution and Bubble Behavior from Nucleation to Critical Heat Flux during Pool Boiling
(Indian Institute of Tehcnology, Jodhpur, 03-07-2023) Kothadia, Hardik B.
The phase change heat transfer processes are widely implemented for heat extraction as they utilise both sensible and latent heat (Rohsenow and Griffith, 1955). The capability to remove the higher magnitude of heat at low wall superheats, and the lack of moving parts makes pool boiling appealing (Memmott and Manera, 2011). Pool boiling is economical, simple, and prevalent among all available cooling schemes. The utilization of the aforementioned technique is widely implemented for thermal management in nuclear industries and in microelectronic devices. Conventional air cooling systems cannot handle these devices cooling requirements which may be due to their low heat transfer performance. In such instances, pool boiling, and droplet evaporation techniques can be implemented. Nowadays, the nuclear industries, renewable energy sectors, and power plants are implementing compact heat exchangers as preheaters, regenerators, and intermediate heat exchangers (Pattanayak et al., 2022) (Pattanayak and Kothadia, 2020). These compact heat exchangers are basically of tubular or plate-type. Therefore it gives the urge to study the heat transfer characteristics of those heat exchangers and analyse the methodologies that can enhance the heat transfer from the surface of tubes and plates (Pattanayak et al., 2022).
The lack of qualitative theories, quantitative data, and explanations in the area of critical heat flux (CHF) in tube and plate makes it an interesting domain of research. There is limited research explaining the effect of high, substrate and liquid temperatures, on droplet evaporation. There is a scarcity of research in analysing the heat transfer coefficient during the evaporation process (Pattanayak et al., 2021) (Pattanayak and Kothadia, 2022). The research highlights the critical heat flux (CHF) studies on mini-channels, micro-channels, and plates during pool boiling under uniform heat flux conditions. Identification of the tube and plate length and diameter beyond which CHF becomes independent of the dimensions is discussed. The effect of tube and plate orientations and pool subcooling on CHF has been analysed. Different regimes of pool boing under uniform heat flux conditions are discussed based on bubble behavior. The instantaneous heat transfer coefficient during droplet evaporation is analysed. The CHF data are used to derive an empirical correlation that includes the impact of subcooling, orientation, and dimensions (Pattanayak et al., 2023). In the case of the analysis of compact heat exchangers, SS 304 tubes and plates are used. The orientation is changed from 0ᵒ to 90ᵒ for tubes and 0ᵒ to 180ᵒ for plates. The length and diameter of tube is varied from 50 mm to 1000 mm and 1.2 mm to 9 mm, respectively. The water pool is kept at 30°C, 50°C, 75°C, and saturation temperature. The length of the plate is varied from 50 mm to 300 mm. The width of the plate ranges from 10 mm to 20 mm. The pool is maintained at 25℃ and saturation temperature corresponding to ambient pressure. It has been noted that the severity of CHF lessens as pool temperature rises. For a particular pool temperature, the shortest length has a higher magnitude of CHF. As tube diameter and width expand, CHF values decrease. In the case of tubes, the CHF value is larger for horizontal orientation than vertical orientation.In the case of the analysis of compact heat exchangers, SS 304 tubes and plates are used. The orientation is changed from 0ᵒ to 90ᵒ for tubes and 0ᵒ to 180ᵒ for plates. The length and diameter of tube is varied from 50 mm to 1000 mm and 1.2 mm to 9 mm, respectively. The water pool is kept at 30°C, 50°C, 75°C, and saturation temperature. The length of the plate is varied from 50 mm to 300 mm. The width of the plate ranges from 10 mm to 20 mm. The pool is maintained at 25℃ and saturation temperature corresponding to ambient pressure. It has been noted that the severity of CHF lessens as pool temperature rises. For a particular pool temperature, the shortest length has a higher magnitude of CHF. As tube diameter and width expand, CHF values decrease. In the case of tubes, the CHF value is larger for horizontal orientation than vertical orientation.In the case of the analysis of compact heat exchangers, SS 304 tubes and plates are used. The orientation is changed from 0ᵒ to 90ᵒ for tubes and 0ᵒ to 180ᵒ for plates. The length and diameter of tube is varied from 50 mm to 1000 mm and 1.2 mm to 9 mm, respectively. The water pool is kept at 30°C, 50°C, 75°C, and saturation temperature. The length of the plate is varied from 50 mm to 300 mm. The width of the plate ranges from 10 mm to 20 mm. The pool is maintained at 25℃ and saturation temperature corresponding to ambient pressure. It has been noted that the severity of CHF lessens as pool temperature rises. For a particular pool temperature, the shortest length has a higher magnitude of CHF. As tube diameter and width expand, CHF values decrease. In the case of tubes, the CHF value is larger for horizontal orientation than vertical orientation.The study demonstrates that for horizontally oriented tubes, CHF fluctuation is negligible beyond a length of 500mm, regardless of diameter. According to the study performed for vertical channels, CHF fluctuation is negligible for tubes with a diameter more than 2.5 mm beyond a length of 200 mm. The vertical orientation of the plates results in a higher CHF magnitude as compared to the horizontal upward and downward orientations respectively (Pattanayak and Kothadia, 2020), (Pattanayak et al., 2021), (Pattanayak et al., 2023). The hydrophobic surface of copper electrodeposited tubes exhibits a lesser CHF magnitude than the uncoated surface and is efficient for phase change heat transfer applications in lower heat flux regimes. Furthermore, the analysis of heat transfer during droplet evaporation is conducted to study the effect of surface and liquid temperature on the instantaneous heat transfer coefficient. It is observed that the evaporation rate is higher for copper than aluminum. The instantaneous heat transfer coefficient increases with the temperature of droplet evaporating on a given substrate and is higher for copper. When substrate temperature increases for a given droplet temperature, the instantaneous heat transfer coefficient increases (Pattanayak and Kothadia, 2021) (Pattanayak et al., 2022). The regimes from natural convection to CHF limit in a subcooled pool of water maintained under uniform heat flux conditions are studied for SS 304 upward-facing plates of different dimensions (Clifton and Chapman, 1969) (Pattanayak et al., 2022). During the heat transfer process, the temperature distribution along the plate is examined. The Nusselt number is seen to be independent of aspect ratio (Pattanayak et al., 2022) (Pattanayak and Kothadia, 2022). The Nusselt number rises when the plate length and width are independently increased. The study is also carried out in saline water of solutions with varying salinity from 0%, 0.2%, 0.5%, and 2%, and is observed that beyond salinity 0.2%, the heat transfer coefficient decreases (Pattanayak et al., 2022).
Open Volumetric Air Receiver based Solar Convective Furnace System
(Indian Institute of Tehcnology, Jodhpur, 30-06-2023) Chandra, Laltu
Electrical energy from fossil fuels or gas-fired systems is commonly used as a heat source for industrial process heating, such as the heat treatment of metals, which leads to harmful emissions. Freely available solar energy is a viable option for transitioning to a net zero carbon economy and reducing emissions. For instance, harnessed solar energy with a concentrated solar thermal (CST) system may be utilized, for example, in the melting, coating, and joining of metals. Recently, a novel, retrofitted solar convective furnace (SCF) system was developed for the heat treatment of Aluminum using hot air from a heliostat-based CST system. The developed SCF system comprises an open volumetric air receiver (OVAR), two pebble-bed sensible thermal energy storage (TES) systems, viz. primary and secondary, and the furnace itself. The OVAR produces hot air using the concentrated solar irradiance onto its aperture. The generated hot air is transported to the SCF directly or indirectly via the primary TES. The secondary TES is utilized for waste heat recovery from hot air at the furnace outlet. The feasibility assessment of the SCF system is performed using a two-step approach: (1) experiments are performed for each of the sub-systems and the integrated system, and (2) mathematical models are developed for scaling of OVAR, each of the sub-systems, and the integrated system analysis. The details are described as follows: Parametric experimental investigations are performed with primary TES for charging and discharging processes to evaluate its thermal evaluation. The experimental investigations for primary TES showed that the time-averaged charging and discharging efficiencies are 65-70% and 72-75%, respectively. Further analyses revealed the exergy efficiencies for charging and discharging are 45-50% and 58-60%, respectively. Experiments are performed to investigate heat transfer in the retrofitted solar convective furnace. These experiments include a provision for external heating for SCF. Experimental results of SCF, such as temperature profile and heating process, show the capability of heat treatment of metal-ingot via forced convection. For the numerical design, OVAR size (a key component of SCF) is selected based on a preliminary calculation for 0.58 MW capacity Aluminum furnace, with direct normal irradiance (DNI) of 220 W/m2 and a concentration ratio of 600. The modelling of unsteady heat transfer in OVAR is done by considering multiple zones of the receiver, viz. central, intermediate, and peripheral zones. The model was validated with experimental data and a two-zone model, which demonstrated the model's prediction capability within ±7%. A parametric investigation is carried out for the planned scale up OVAR design. An unsteady heat transfer model is developed for the TES. Analysis revealed that the deviation between the computed and experimental temperature is within ±15%. Also, a one-dimensional mathematical model is developed to analyze the unsteady heat transfer process for the retrofitted SCF. The calculations show a deviation of about ±15% from the experimental data. Finally, a mathematical model is developed for the installed lab-scale SCF system, including OVAR, connecting pipes with insulation, and TES. Findings demonstrate the potential of using the developed CST-based SCF system for the heat treatment of metal. However, the integrated model needs to be refined for better results and may be addressed in future.
Dynamics of the Homographic Ricker-like maps
(Indian Institute of Tehcnology, Jodhpur, 29-02-2024) Chandramouli, V.V.M.S.
In nature, the number of individuals of a species or a community of species varies over time within a region or territory. To address challenges in studying living systems due to these variations, mathematical modeling plays a crucial role in the development of an integrative point of view. Mathematical modeling of the population deals with the growth of the species and intrinsic interactions between each organism and its environment. The population modeling was pioneered by Verhulst in the 19th century with the introduction of the Logistic model. Among the several single-species models, one of the crucial population models is the Ricker population model, which was proposed to mathematically represent the stock and fisheries. The Ricker map and its various modified forms have been reviewed by several researchers [Ricker, 1954; Elaydi and Sacker, 2010; Liz, 2018; Rocha and Taha, 2020]. When the growth function of the Ricker map is defined by the Holling type II functional response, then the resulting map is a Homographic Ricker map. The nonlinear dynamics and bifurcation structure of the Homographic map have been discussed by L. Rocha in [Rocha et al., 2020]. The aim of the thesis is primarily to investigate the diverse dynamical properties of the q-deformed Ricker map, the q-deformed Homographic map, the 2D Homographic Ricker map, and the delayed 2D Homographic Ricker map. This study mainly focuses on the various dynamical aspects of these models, which involves the analysis of their nonlinear dynamics, singularities, intersections of different fold and flip bifurcation curves using bifurcation theory, and the exploration of the transition from periodic to chaotic attractors. In the first part of the thesis, we apply a deformation scheme [Jaganathan and Sinha, 2005; Tsallis, 1988] to the classical Ricker map and obtain a q deformed Ricker map, namely the q-Ricker map. We show that the q-Ricker map proclaims many exciting phenomena that are remarkable in one-dimensional dynamical systems, such as the presence of coexisting attractors, physically non-observable chaos, hydra paradox, bubbling effect, and extinction. We prove that the intersection of the fold and flip bifurcation of the curve gives a singular point of codimension greater than two, and that singular point merges with its associated cusp point. Finally, we show that a certain amount of deformation in the system can keep it in equilibrium; however, excessive deformation causes extinction [Aishwaraya et al., 2022]. Next, we discuss the analytical study of the q-deformed Homographic map (q-Homographic map).The notions of false derivative and the generalized Lambert W function of the rational type are useful in estimating the upper bound on the number of fixed points of q-Homographic map. Further, we explore the process of chaotification of the q-deformed map to enhance its complexity which involves incorporating the residue obtained from multiple scaling of the map’s value for the subsequent generation through the utilization of the multiple remainder operator [Moysis et al., 2023]. After the chaotification, the q-Homographic map shows high complexity and the presence of robust chaos, which has been theoretically and graphically analyzed using various dynamical techniques. In addition, we use the feedback control technique [Din, 2017] to control the period-doubling bifurcation and chaos in the q-Homographic map. In the second part of the thesis, we apply the Holling type - II functional response as a growth function in the classical two-dimensional Ricker map and propose a discrete-time competition model, namely the two-dimensional (2D) Homographic Ricker map. We discuss the boundedness of the solutions and the uniqueness of the coexisting fixed point of the proposed map. With the help of critical curves and singular points, we explain the geometry of the map and prove that all the points in the domain of the 2D Homographic Ricker map are either regular, fold, or cusp in nature. Furthermore, we use the centre manifold theory to explain the local stability of the fixed points of the proposed map. Using bifurcation theory, we derive some conditions under which the map exhibits the flip bifurcation [Aishwaraya and Chandramouli, 2023]. We further introduce a delayed 2D Homographic Ricker map by incorporating the delay terms in survival functions and small leak terms in the competing populations. We analyze the persistence, boundedness, invariance, and asymptotic behavior of the proposed map. Additionally, numerical simulations are employed to elucidate the stability and bifurcation analysis of the competing population. In the final part of the thesis, we study the combinatorial tools, namely the Hofbauer tower and the kneading map for a class of symmetric bimodal maps. We discuss the construction, various properties, and geometrical interpretation of these tools. Further, with the help of the Hofbauer tower, we define the cutting times associated with the bimodal map and propose an algorithm to compute the cutting times. Finally, we describe the splitting and co-splitting of the kneading invariants using the cutting and co-cutting times, respectively.
Physical Layer Security and Performance Evaluation of Power Line Communication Systems
(Indian Institute of Tehcnology, Jodhpur, 01-10-2024) Mathur, Aashish
Power line communication (PLC) is an information and communication technology (ICT) that enables two-way digital communication over existing electric wires or power distribution networks [1]. In recent years, PLC has been the subject of significant interest from researchers, industry, regulatory authorities, and standardization organizations owing to its inherent advantages and applications [2]. Specifically, PLC offers universal network coverage due to the omnipresence of wired infrastructure from urban to rural or remote areas. As a result, PLC has low installation and maintenance costs. Additionally, PLC is capable of delivering high-speed data rates, as demonstrated in the HomePlug Powerline Alliance (HomePlug) and IEEE P1901 standards for home networking [2]. Due to these aforementioned advantages, PLC is contemplated as the most suitable ICT for smart grid communications, smart homes and buildings, smart vehicles, and smart cities [2]. Despite these benefits, PLC suffers from some challenges, such as varying impedance, strong branching effect, frequency and distance dependent attenuation, and non-gaussian noise [4]. On the other hand, PLC channels are intrinsically broadcast and ubiquitous in nature thereby widening the potential of an intrusion and making them more vulnerable to eavesdropping and jamming [5]. Therefore, offering unbreachable data security is always a significant issue in the PLC networks. Recently, physical layer security (PLS), also known as information-theoretic security, has been extensively studied by researchers in wireless and wired communication systems, where the randomness of the communication channels is exploited in the physical layer to prevent data leakage [3]. PLS is proclaimed as a complimentary approach to safeguard the data instead of entirely relying on traditional cryptographic algorithms. In this research, we investigate the PLS performance of a differential chaos shift keying (DCSK)-based PLC system by utilizing a novel Farlie-Gumbel-Morgenstern (FGM) Copula approach, where a wiretap power line channel model is analyzed to compute the secrecy between the main channel and the wiretap channel [6]. Both PLC channels are considered to be correlated Log-normally distributed while the Bernoulli-Gaussian model characterizes the PLC channel noise [7]. Further, the PLS performance is numerically expressed in terms of secure outage probability (SOP) and strictly positive secrecy capacity (SPSC). To obtain useful insights into the PLC system’s secrecy performance, the asymptotic SOP analysis is conducted. Furthermore, an algorithm is proposed to maximize the secrecy throughput under SOP constraints. Finally, meaningful observations are obtained by analyzing the impact of different system parameters through numerical results. Next, we analyze the PLS performance of PLC systems against multiple eavesdroppers by employing DCSK modulation scheme [8]. A wiretap power line channel model is investigated by considering two different cases: 1) when all the channels are assumed to be independent and identically distributed (IID) following Log-normal distribution; and 2) the wiretap channels are considered to be identical but correlated Log-normally distributed and independent of the main channel. Contemporaneously, the Bernoulli-Gaussian random process models the PLC noise. A comprehensive PLS study of the considered PLC system is characterized in terms of the average secrecy capacity (ASC), SOP, and SPSC. We also propose an algorithm to maximize the secrecy throughput under security and reliability constraints. Moreover, to obtain essential insights, we reveal the impact of various parameters onto the secrecy performance of the proposed PLC system. After studying the secrecy performance of the considered PLC system, this dissertation further evaluates the performance of the PLC systems under random pulse jamming attacks assuming M-ary phase shift keying modulation (MPSK) [9]. Herein, the PLC channel is assumed to follow Log-normal channel gain and the Bernoulli-Gaussian random process describes the nature of PLC noise. Additionally, the state of the jammer is characterized by the Bernoulli random variable. Conditioned upon the jamming activity, we evaluate the probability density function (PDF) of the instantaneous signal-to-jamming-plus-noise ratio (SJNR) and the instantaneous signal-to-noise ratio (SNR). Capitalizing on the statistical characterization of the SJNR and SNR, we derive the series-based expressions of the average symbol error rate (ASER) and outage probability (OP) for the considered PLC system. Further, the asymptotic ASER analysis is performed in terms of the coding gain and diversity order in the high SNR regime. In order to gain more insights into ASER and OP analysis of the considered PLC system, we demonstrate the effect of the different system parameters through the numerical results.
Enhanced Edge Processing in Noisy Images: Leveraging noise-informed analysis for image denoising and edge detection
(Indian Institute of Tehcnology, Jodhpur, 21-09-2024) Chouhan, Rajlaxmi
This thesis aims to advance the research and development in image processing with a focus on edges of a noisy image by leveraging the noise itself. Edges occur where there is an abrupt change in the intensity in an image, and they act like boundaries or demarcations separating distinct objects in an image. Further, edges help enunciate the inner detailing present within an object. Since the very nature of edges is separating the boundary between two objects, it is highly desirable that the edges are definite and pixel-level accurate. Handling edges is challenging not only for developing an algorithm but also for extraction of ground truth. Some major contributions of this thesis include edge-preserving image denoising, enhanced edge detection, and modular plug-and-play edge post-processing. This thesis has also attempted to open new avenues by presenting how to analyze discontinuities (corners, lines, and edges) in real noisy environments, and how the noise (which is considered undesirable) can be used to improve the performance of a system at hand. The various analyses presented in this thesis go to the pixel-level details, with the objective to gain better insights that can be extended to diverse applications. Our first contribution deals with edge-preserving image denoising. It is well known that denoising through averaging typically reduces the sharpness of the edges and the details present in the denoised image. We proposed an edge-preserving image denoising algorithm where we extend the non-local means (NLM) algorithm by enhancing its most crucial part—the similarity weights. These similarity weights are enhanced, or in other words, rearranged, using the concept of stochastic resonance (SR). This iterative SR-based processing ensures that weights of similar patches are high and those of dissimilar patches are low. Through the lens of image attributes, the proposed work can be understood as iterative processing, and thereby enhancing, the similarity weights in a non-linear fashion using the modified and discretized Duffing’s equation. The proposed algorithm is tested for a wide range of AWGN noise, and benchmarked on the popular SET12 and BSD68 datasets. For a high noise (sd 50), the cumulative effect is reflected as an improvement (in PSNR) of 14.5% and 12.1% over that of NLM for SET12 and BSD68 datasets. As compared to the NLM, the proposed algorithm produces images with better visual quality, better edge preservation, and negligible artifact generation, especially at high noise. Our second contribution deals with discontinuity detectors and the noise behavior in real smartphone images. As smartphone cameras are the most popular photography devices in today’s era, we analyze how the discontinuity detectors like corner, line, and edge detectors behave when the image is corrupted by the real smartphone noise. On deeper analyses, it is observed and demonstrated that these discontinuity detectors exhibit SR in cameraphone noisy environment. The behavior of these detectors with changing noise as well with changing threshold is demonstrated. The pixel-level demonstrations presents how these detectors can take advantage of the presence of noise. Our third contribution is an application derived from the previous contribution and deals with improvement of popular Canny Edge Detector. Even the latest popular DL-based edge/boundary detectors produce thick grayscale edges (instead of thin binary edges), and struggle to achieve high pixel-level accuracy. Canny is a popular edge detector that gives thin binary edges, but it suffers from two major problems—broken edges and noisy structures. We propose an enhanced edge detector (SR-TW-CED) that improves the core of the Canny using SR-guided threshold maneuvering and window mapping. The whole image is partitioned into. windows, and mapped according to the underlying content, which decides how the threshold is to be maneuvered to obtain better edges. The proposed edge detector jointly addresses the two-fold problem of broken edges and noisy structures of the Canny edge detector. We also propose a novel measure of efficient edge detection; a unique, efficient way of edge content extraction and its combination for various channels; and a framework to handle repercussion of the randomness of the noise. Benchmarking on the BIPED dataset gives the human-level performance (F1 score 0.79), which is appreciable considering that it is a non-DL–based algorithm. Our fourth contribution is an application that derives its premise from the edge detection measures proposed in the previous contribution and does not directly use iterative SR processing. Most of the edge detectors in the research community are stand-alone edge detectors. With this contribution, we propose a post-processing filter that can simply be plugged in at the output of essentially any edge detector to suppress the detection of false edges, improve accuracy, and boost the precision of detection. A traditional edge detector suffers highly from false-positive edge detection, and the problem is so prevalent that the falsely detected edges often outnumber the true-positive detected edges. While this significantly limits the capabilities of non-DL–based edge detectors for typical images, it also creates a serious bottleneck in the performance of DL-based edge detectors particularly for images that contain texture or mesh. To address this, we have designed a novel framework, called the ’triple-window patch-debias broken-hysteresis’ framework. We also use the eigen-based measures as the filtering units in this framework to create a precision-boosting filter, called PBEdgeFilter. The proposed filter is a modular filter that requires minimum or, in most cases, no external inputs, and can be used in a plug-and-play manner. When tested on the BIPED dataset, PBEdgeFilter is observed to boost the precision of Canny by 89%, SMED by 102%, and LoG by 93.5%. When applied over the latest DL-based edge detector, DexiNed, the precision is observed to be boosted by 57.7% for the specific case of input images having mesh regions. The thesis includes image processing algorithms derived directly from or informed by the concept of SR or noise-enhanced iterative processing. While the first contribution, i.e. SR-enhanced NLM, directly utilizes the noise-aided iterative processing in a noisy environment, other contributions are broadly informed by the dynamics of signals (edges, in this case) in noisy and non-noisy environments. These contributions do not directly utilize SR-based processing but are designed with the rationale of signal behavior in different image regions. With the above contributions, an attempt has been made to contribute towards the knowledge base of edge processing in noisy environments.