MIST: Medical Image Segmentation Transformer with Convolutional Attention Mixing (CAM) Decoder

One of the common and promising deep learning approaches used for medical image segmentation is transformers, as they can capture long-range dependencies among the pixels by utilizing self-attention. Despite being successful in medical image segmentation, transformers face limitations in capturing local contexts of pixels in multimodal dimensions. We propose a Medical Image Segmentation Transformer (MIST) incorporating a novel Convolutional Attention Mixing (CAM) decoder to address this issue. MIST has two parts: a pre-trained multi-axis vision transformer (MaxViT) is used as an encoder, and the encoded feature representation is passed through the CAM decoder for segmenting the images. In the CAM decoder, an attention-mixer combining multi-head self-attention, spatial attention, and squeeze and excitation attention modules is introduced to capture long-range dependencies in all spatial dimensions. Moreover, to enhance spatial information gain, deep and shallow convolutions are used for feature extraction and receptive field expansion, respectively. The integration of low-level and high-level features from different network stages is enabled by skip connections, allowing MIST to suppress unnecessary information. The experiments show that our MIST transformer with CAM decoder outperforms the state-of-the-art models specifically designed for medical image segmentation on the ACDC and Synapse datasets. Our results also demonstrate that adding the CAM decoder with a hierarchical transformer improves segmentation performance significantly. Our model with data and code is publicly available on GitHub.Comment: 10 pages, 2 figures, 3 tables, accepted for publication in WACV 202

Experimental investigation of flow and forced convection heat transfer, in fully filled rectangular duct using porous media

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.An experimental study was performed to investigate the heat transfer characteristics of the convection flow through a rectangular air duct with aspect ratio of 10 (a/b=10) which is filled with metallic porous materials. All four walls of the duct are subjected to a constant and uniform heat flux. The Reynolds number based on the hydraulic diameter has been kept between 500-2000 in order to ensure the laminar flow through the duct. The effect of different parameters such as variable porosity and density of porous layers have been investigated. For different porous layers configuration, heat flux at the walls, wall temperatures and air mass flow rate has been measured and the Nusselt number has been calculated. The results are compared with the clear flow case where no porous material was used. It can be concluded that higher heat transfer rates can be achieved in porous media flow case at the expense of a reasonable pressure drop. Based on the experimental data new empirical correlations for both Nusselt number and friction factor have also been developed for such air duct, which gives a good agreement between predicted values and experimental values of Nusselt number and friction factor.dc201

Effects of Fin Spacing and Gas Radiation on Heat Transfer in Utility Boiler Economizers

The aim of this paper is to estimate fin spacing and gas radiation effects on heat transfer in utility boiler economizers to achieve the highest feed water temperature, and the biggest amount of heat transferred from flue gases to economizer tubes. This study is carried out for five different cases including a bare tube economizer and four finned-tube economizers with different fin spacing values. A finite volume method is employed to discretize and solve the governing equations for all cases in 3D. As a result, for verification purpose, the present numerical result is compared to the experimental outputs and it shows that the average Nusselt number difference is 15%. The finned-tube economizer with fin spacing value of 21mm absorbs the biggest amount of heat, and it has the highest outlet feed water temperature; therefore, it has the best thermal performance among the other cases. It is also concluded that radiation heat transfer mechanism has a minor effect on heat exchange in utility boiler economizers

Simulation of double diffusive convection in fluid-saturated porous media by lattice Boltzmann method

The research on double diffusive convection in porous media is important to deepen our insights into sustainable development and environment protection. A lattice Boltzmann (LB) model for REV (representative elementary volume) scale simulation of double diffusive convection in fluid-saturated porous media is proposed in the present work. It can work well not only for porous media with uniform porosity but also for non-uniform porous media. Several benchmark tests are adopted to validate its capability. The good agreement with previous publications demonstrates its applicability. It can provide an alternative numerical tool for modelling complex heat and mass transfer in fluid-saturated porous media beyond double diffusive convection, such as heat and moisture transfer in multi-layer building materials

Improving the melting performance of PCM thermal energy storage with novel stepped fins

Numerical investigation on latent heat thermal energy storage (LHTES) systems with phase change materials (PCMs) vertically heated from one side with novel stepped fins is presented. Transient numerical simulation by using the enthalpy-porosity method is performed to investigate the heat transfer rate and melting behaviors, while the natural convection is considered. To improve the PCM melting process, different upward and downward stepped fins with the step ratios (b/c) of 0.66, 1, 1.5, 2.33 and 4 are employed. The melt fraction and temperature contours by consideration the natural convection effects are presented. The results show that at the beginning of the melting process, the fins in the downward direction with b/c=0.66 improve the PCM melting rate than the other cases, as the part of the heat is well transferred to the bottom of container along the fins and heat is trapped between the heated wall and the fins. The results show that the melting process in all of the tested stepped fins is faster than the conventional horizontal fins. The results show that by using downward stepped fins (b/c=0.4) instead of conventional horizontal fins, the melting process could be enhanced up to 56.3% at t=800sec and 65.5% at t=3600sec