Combined heat and mass transfer in laminar gas stream flowing over an evaporating liquid film

A numerical analysis was carried out to study the detailed heat and mass transfer characteristics in laminar gas stream flowing over a falling liquid water film by solving the respective governing equations for the liquid film and gas stream together. It was observed that the cooling of the liquid film is mainly caused by the latent heat transfer connected with the vaporization of the liquid film. Significant liquid cooling results for the system with a high inlet liquid temperature, high gas stream velocity or a low liquid flowrate. Additionally, the predicted Nusselt and Sherwood numbers were correlated.     

Solution processed amorphous InGaZnO semiconductor thin films and transistors

Amorphous indium gallium zinc oxide (a-IGZO) semiconductor thin films and transistors were deposited on alkali-free glasses by the sol–gel route. The atomic ratio of In:Ga:Zn in the solution was 0.7:0.3:1. In this study, the effects of annealing temperature on the structural, surface condition, optical transmittance, and electrical resistivity of a-IGZO semiconductor thin films were investigated. GIXRD measurements and TEM-NBD analysis indicated that all annealed IGZO thin films had an amorphous phase structure. The dried IGZO sol–gel films annealed at a temperature higher than 425 °C had a flat surface and exhibited high transparency (>89%) in the visible region. According to results from TGA, FT-IR and XPS, the residual organic compounds in the dried IGZO sol–gel films were completely removed at the annealing temperatures higher than 450 °C. Therefore, we chose the 450 °C annealed thin film as the active channel layer in the bottom-gate, bottom-contact (BGBC) thin-film transistor (TFT) in the present study. Current–voltage (I–V) characteristics of the 450 °C annealed a-IGZO TFT revealed that it operated in n-type behavior with a positive threshold voltage (enhancement mode).     

Enhancement of pool boiling heat transfer in a horizontal water layer through surface roughness and screen coverage

An experimental investigation was carried out to study the augmentation of heat transfer in saturated pool boiling of a liquid water layer on a heated horizontal stainless steel plate by roughing the surface and/or covering it with a single layer of stainless steel screen. The results were presented in terms of the boiling curves. Effects of various parameters – the surface roughness, liquid level and size of the stainless steel mesh on the boiling heat transfer were examined in detail. The measured data clearly indicated that a lowering of the liquid level from 60 to 5?mm in water depth causes heat transfer reduction. Roughing the surface was found to sig- nificantly enhance the heat transfer. Use a layer of metal screen to cover the heated surface was shown to substantially augment the heat transfer especially for a shallow water layer if the mesh size is comparable with the bubble departure diameter. Covering the rough surface with the metal mesh, however, reduced the heat transfer.     

Effect of dopants on the structural,optical and electrical properties of sol–gel derived ZnO semiconductor thin films

Undoped, Ga-, In-, Zr-, and Sn-doped ZnO transparent semiconductor thin films were deposited on alkali-free glasses by sol–gel method. 2-methoxyethanol (2-ME) and diethanolamine (DEA) were chosen as a solvent and a stabilizer, respectively. The doping concentration was maintained at 2 at.% in the impurity doping precursor solutions. The effects of different dopants on the structural, optical, and electrical properties of ZnO thin films were investigated. XRD results show that all annealed ZnO-based thin films had a hexagonal (wurtzite) structure. ZnO thin films doped with impurity elements obviously improved the surface flatness and enhanced the optical transmittance. All impurity doped ZnO thin films showed high transparency in the visible range (>91%). The Ga- and In- doped ZnO thin films exhibited higher Hall mobility and lower resistivity than did the undoped ZnO thin film.