Performance comparisons of desiccant wheels for air dehumidification and enthalpy recovery

Numerical modelling and thermal simulation of PCM–gypsum composites with ESP-r

UV laser ablation of polymers was discovered 20 years ago.1,2 This effect has many fascinating applications in lithography, micromechanics, and medicine. For the last 20 years, more than 103 papers describing this phenomenon were published (see, e.g., comprehensive reviews, refs 3-7). Despite the high research activity, the nature of UV laser ablation of polymers is still far from being fully understood, e.g., one can find contradictory interpretations of the same results in different papers. Originally, UV laser ablation of polymers was believed to be a pure photochemical effect, resulting from the direct bond breaking by UV photons.8-10 Gradually, investigators obtained evidence that laser heating of materials is significant and a pure thermal nature of laser ablation was considered.11-13 Here we use the term “photothermal”7 for the process resulting from laser heating of material. Polymers are complex materials; therefore, laser ablation of polymers is also a complicated phenomenon. In this paper, we will focus on the models of laser ablation. In addition, we inevitably have to answer the question of what are the specific features of laser ablation of polymers that distinguish them from the laser ablation of other materials (metals, semiconductors, inorganic dielectrics, molecular solids). There are several approaches to modeling of polymer ablation. The authors of this paper represent one of the “schools”; thus, our view of the problem is somewhat subjective. Despite the complex nature of laser ablation, we prefer to develop simplified models (e.g., “pure” photochemical or “pure” photothermal), and analyze them in detail to be able to assign specific features, which are experimentally observed for a particular ablation mechanism. We start with the photochemical model. In fact, the first consideration of laser ablation10 employed a very simple but constructive idea that takes into account the specific feature of polymer materials. This idea is that polymers consist of long molecular chains with strong, covalent, bonds inside. At the same time, molecules belonging to different chains interact weakly. Therefore, polymer material becomes simple molecular solid (i.e., easily removed material), if we break the long polymer chains into small pieces by direct photochemical effect (UV photons are considered to have energy pω exceeding the energy of * Corresponding author, e-mail: bit@appl.sci-nnov.ru. † Institute of Applied Physics Russian Academy of Sciences. ‡ Data Storage Institute. 519 Chem. Rev. 2003, 103, 519−552

/pdf/models-for-laser-ablation-of-polymers-491ojmuzxp.pdf

Models for laser ablation of polymers.

[1] Global climate models (GCM) are frequently used to understand and predict future climate change, but most GCMs do not attempt to represent permafrost dynamics and its potentially critical feedbacks on climate. In this paper, we evaluate the Community Land Model (CLM3), which is a land-surface scheme, against observations and identify potential modifications to this model that improve fidelity of permafrost and soil temperature simulations. These modifications include increasing the total soil depth by adding new layers, incorporating a surface organic layer, and modifying the numerical scheme to include unfrozen water dynamics and more realistic phase change representation.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007GL029525

Improved modeling of permafrost dynamics in a GCM land-surface scheme

In the solid desiccant wheel air-conditioning system, the performance of the desiccant wheel is critical to the capability, size and cost of the whole system. Constructing mathematical model is an effective method for analyzing the performance of the rotary wheel as well as the system. The model can also be used to guide system operation, interpret experimental results and assist in system design and optimization. The overall objective of this paper is to provide a review of various efforts that researchers have made to mathematically model the coupled heat and mass transfer process occurring within the wheel. The paper first briefly describes desiccant wheel including fundamental principle, heat and mass transfer mechanism and the method of model establishment. Then various models consisting of ideal assumptions, governing equations, auxiliary conditions, solution methods and main results are presented. The models can be classified into two main categories: (1) gas-side resistance (GSR) model; (2) gas and solid-side resistance (GSSR) model which can be further subdivided into pseudo-gas-side (PGS) model, gas and solid-side (GSS) model and parabolic concentration profile (PCP) model. It shows that GSSR models are higher in precision and more complex compared with GSR models. In addition, the simplified empirical models based on measured data are briefly discussed. This review is useful for understanding the evolution process and status quo of the mathematical model and highlighting the key aspects of model improvement such as taking account of pressure loss or air leakage.

A. A. Samarskiĭ

Papers

Computational heat transfer