Neural Degradation Representation Learning for All-In-One Image Restoration

Existing methods have demonstrated effective performance on a single degradation type. In practical applications, however, the degradation is often unknown, and the mismatch between the model and the degradation will result in a severe performance drop. In this paper, we propose an all-in-one image restoration network that tackles multiple degradations. Due to the heterogeneous nature of different types of degradations, it is difficult to process multiple degradations in a single network. To this end, we propose to learn a neural degradation representation (NDR) that captures the underlying characteristics of various degradations. The learned NDR decomposes different types of degradations adaptively, similar to a neural dictionary that represents basic degradation components. Subsequently, we develop a degradation query module and a degradation injection module to effectively recognize and utilize the specific degradation based on NDR, enabling the all-in-one restoration ability for multiple degradations. Moreover, we propose a bidirectional optimization strategy to effectively drive NDR to learn the degradation representation by optimizing the degradation and restoration processes alternately. Comprehensive experiments on representative types of degradations (including noise, haze, rain, and downsampling) demonstrate the effectiveness and generalization capability of our method

Mutual-Guided Dynamic Network for Image Fusion

Image fusion aims to generate a high-quality image from multiple images captured under varying conditions. The key problem of this task is to preserve complementary information while filtering out irrelevant information for the fused result. However, existing methods address this problem by leveraging static convolutional neural networks (CNNs), suffering two inherent limitations during feature extraction, i.e., being unable to handle spatial-variant contents and lacking guidance from multiple inputs. In this paper, we propose a novel mutual-guided dynamic network (MGDN) for image fusion, which allows for effective information utilization across different locations and inputs. Specifically, we design a mutual-guided dynamic filter (MGDF) for adaptive feature extraction, composed of a mutual-guided cross-attention (MGCA) module and a dynamic filter predictor, where the former incorporates additional guidance from different inputs and the latter generates spatial-variant kernels for different locations. In addition, we introduce a parallel feature fusion (PFF) module to effectively fuse local and global information of the extracted features. To further reduce the redundancy among the extracted features while simultaneously preserving their shared structural information, we devise a novel loss function that combines the minimization of normalized mutual information (NMI) with an estimated gradient mask. Experimental results on five benchmark datasets demonstrate that our proposed method outperforms existing methods on four image fusion tasks. The code and model are publicly available at: https://github.com/Guanys-dar/MGDN.Comment: ACMMM 2023 accepte

An investigation on cooling performance of air-cooled heat exchangers used in coal seam gas production

This paper reports an investigation into a practical cooling issue on a type of fan-forced finned-tube heat exchangers used in Queensland's coal seam gas (CSG) industry. CSG compression facilities in some production sites suffered underproduction in recent summers because of frequent automatic engine shutdowns. The problem is not expected by the manufacturer's design. However, it is suspected of being related to the control systems on the compression facilities triggering the overheating-protection shutdowns due to possible deficiencies in one or some water/gas cooling loops in the facilities’ air-cooled heat exchangers. Therefore, to understand which heat exchangers and what exact reasons cause the unexpected cooling issue, an investigation has been carried out on the cooler units of the gas compression facilities. A field instrumentation measurement on one operating cooler unit has been done, followed by an analysis using a one-dimensional analytical model and a three-dimensional computational fluid dynamics model. The experimental results are used to validate both the models. Then the cooling performance of the cooler unit under the summer peak condition is predicted by the verified models. The prediction suggests that the water inlet temperature in one particular cooler section is higher than its upper limit defined by the manufacturer, due to poor cooling at high ambient temperatures. The lower cooling performance is caused by large reductions in the cooler air speed and total heat transfer coefficient, which are related to less efficiency of the cooler fans, more airflow resistance, and fouling on both sides of the finned tubes

Simulation of the UQ Gatton natural draft dry cooling tower

Natural draft dry cooling tower (NDDCT) is an effective cooling technology which can be utilized in most of geothermal and concentrated solar thermal (CST) power plants. The experimental studies of the full scale cooling tower, especially the small size NDDCTs, are still not extensive. To fill this gap, Queensland Geothermal Energy Centre of Excellence (QGECE) at The University of Queensland has built a 20m high NDDCT. In this paper, the 1D analytical model and the 3D CFD model of this cooling tower were developed and its cooling performance was investigated at different ambient temperatures, hot water temperatures and velocities of cross wind. The result shows that the small size NDDCT is suitable for 2~3MW CST power plants. The cooling performance decreases with the increase in the ambient temperature and the decrease in the hot water temperature. In terms of the cross wind, the heat rejection ratio decreases with the increase of the cross wind velocity when cross wind velocity is low. However, when velocities of the cross wind become large enough, the heat dumped at the bottom of the tower can compensate some loss caused by cross wind. The results found in the present paper give reference for planed future experiments

Influence of ambient conditions and water flow on the performance of pre-cooled natural draft dry cooling towers

A simplified heat and mass transfer model in cellulose medium was developed to predict the air outlet temperature and humidity after evaporative cooling. The model was used to simulate the operation of pre-cooled Natural Draft Dry Cooling Towers (NDDCTs) by a validated MATLAB code. The effects of supplied water flow rate to the media, ambient temperature and humidity on the performance of pre-cooled NDDCTs were investigated. It was found that the effect of the selected water flow rates on tower performance is negligible. Both ambient temperature and humidity affect the tower performance

A study on cooling performance of air-cooled heat exchangers for CSG production

This paper reports a study on a real cooling issue in the heat exchangers used in Queensland’s coal seam gas (CSG) industry. CSG gas compression facilities in some production sites suffer underproductions in recent summers because of frequent automatic engine shutdowns. The cause of the issue was suspected that the control systems on the compression facilities trigger the overheating-protection shutdowns due to the possible deficiencies in one or some water/gas cooling loops in the facilities’ air-cooled heat exchangers. However, it is unknown which heat exchangers or what exact reasons cause the unexpected cooling issue which is not expected by the manufacturer’s design. Therefore, an investigation has been carried out on the cooling performance of the cooler units in the gas compression facilities. A field instrumentation measurement on one operating cooler unit has been done, followed by an analysis using a 1-dimensional analytical model. The experimental results are used to validate the 1D model. Then the cooling performance of the cooler unit under the summer peak condition is predicted by the verified analytical model. The prediction suggests that the water inlet temperature in engine water cooler section is higher than its upper limit defined by the manufacturer due to poor cooling at high ambient temperatures. The lower cooling performance is caused by large reductions in the cooler air speed and total heat transfer coefficient. The former is a direct result of the less efficiency of cooler fans, while the latter is related to fouling on the finned-tube surfaces

Experimental investigation on spray cooling using saline water

Natural draft dry cooling towers (NDDCTs) are a type of cooling technology used in thermal power plants, including geothermal power plants. Interest from industry in this technology is increasing due to its water saving potential. However, the cooling performance of NDDCTs is inherently negatively impacted by high ambient temperatures. Among all existing solutions to this issue, inlet airflow precooling using water sprays is thought to be a good method to reduce the impact of high ambient temperature on the performance of NDDCTs. In previous studies, spraying of saline water obtained from water sources such as coal seam gas wells (as a by-product) was shown not only to save valuable freshwater resources but also to provide the further possibility of increasing the evaporation rate of water droplets, thereby shortening the wet length (distance) required for the spraying system. However, this benefit has not been verified. To address this knowledge gap, three different water sources were experimentally examined in the current study, viz. fresh, artificial simulated saline water, and real coal seam gas well water. Spraying using these three types of water was compared based on tests in a wind tunnel using a specific type of nozzle. The results confirmed an increase in the cooling efficiency of the spraying system when saline water was selected as the water source. However, the cooling efficiency may be more influenced by the nozzle orientation with respect to the airflow. On the other hand, spraying of saline water resulted in considerable deposition of solid particles from the water droplets in the airflow at 4.5\ua0m downstream of the nozzle after only 2\ua0h of spraying, although no significant nozzle clogging was observed even after the total of 50\ua0h of testing. This effect could potentially cause fouling and corrosion on heat exchanger surfaces

Development of small natural draft dry cooling towers for geothermal power plants

Current design methods for natural draft dry cooling tower (NDDCT) do not include the crosswind effect which is unfavorable to the performance of cooling towers. This effect of the crosswind will be even more unfavorable to the performance of small cooling towers since the percentage of the disturbed free air flow is considerably higher than for large NDDCT. Therefore, the validity of the current design methods is questionable for small NDDCT design. Analytical and numerical modeling has been carried to investigate the performance of small NDDCT under different crosswind conditions. The smallest sizes of natural draft cooling towers were derived based on current design methods. The effect of various crosswinds on the performance of small tower is demonstrated with a 3D CFD simulation. Preliminary results showed that the velocity and temperature distributions in the tower have been significantly influenced by the crosswinds

Experimental study on the effects of a tri-blade-like windbreak wall on small size natural draft dry cooling towers

Cooling efficiency of heat exchangers in conventional large natural draft dry cooling towers (NDDCTs) is often affected by crosswind. In the authors’ previous work, it was proved that the crosswind influence is more significant on short NDDCTs (height< 30 m) with horizontal heat exchangers than on large towers at a same wind speed, and a new triblade-like windbreak was proposed and analysed through CFD method only. The numerical models have not been validated by testing data yet. Therefore, an experiment on a 1:12.5 scaled NDDCT equipped with a novel round heat exchanger model was carried out and is presented in this paper. The study obtained the real measurements on the air temperatures and velocities as well as the heat rejection rates in the scaled cooling tower model with and without the windbreak wall. The influences of three wind attack angles (0°, 30°, and 60°) with respect to the windbreak wall were investigated. The angle was found sensitive to the overall heat transfer performance of the cooling tower. The study found that the cooling performance is improved most if the tri-blade-like windbreaks placed in the attack angle of 0°.The experiment results agreed with the predictions of the two 3D CFD models, the 15 mtall prototype and the 1.2 m-tall tower model, so that verified the validity of the previous CFD modelling