Effect of fouling resistance in heat exchanger and the crystal form of CaCO3 in hard circulating cooling water with electrostatic field and alternating current electric field

The effect of high voltage electrostatic field and high voltage alternating current electric field on the heat exchanger surface fouling under the condition of hard water was investigated. The Ca2+ concentration in two water conditions was 12 mmol/L. The Mg2+ concentration was 10 mmol/L and 12 mmol/L respectively. The concentration changed with the Mg2+ concentration. X-ray diffraction and Scanning electron microscope results confirmed that the main crystal phases of the scale samples consist of calcite and aragonite. The high voltage electrostatic treatment can promote scale growth under both water quality conditions. However, the high voltage alternating current electric field treatment shows a good scale inhibition effect under both water quality conditions, and the scale inhibition effect is best when both Ca2+ and Mg2+ concentrations are 12 mmol/L, and the average scale inhibition rate reaches 47.58%. When the calcite content of the scale sample is significantly higher than that of aragonite, Mg2+ affects the growth and solubility of crystals. On the other hand, the high voltage alternating current electric field treatment can effectively extend the fouling induction period of the adherent scale on the heat exchanger surface, which is favorable for heat exchanger fouling.

Modeling on the Effect of Heat Exchanger Submersion on Controlling Spontaneous Combustion in A Coal Pile

Spontaneous combustion of coal has been well-known as a problem faced by coal industries, especially in storing and trans-shipping processes. The negative impacts of this phenomenon have led to several hazardous incidents and degrading product quality. Several methods have been researched to minimize the impacts; one of the proposed ways is immersing heat exchangers inside the coal stockpile. An experiment was conducted to analyze the cooling effect of an immersed simple heat exchanger made of a copper coil. By varying the number of windings, the experiment showed a significant decrease in pile temperature due to the immersed heat exchanger. This work continues exploring the possibility of applying the method by observing and analyzing the simulation model. COMSOL Multiphysics was used to model the physics phenomena that occur within the coal reactor. The effect of the heat exchanger surface area was studied from the model to observe the heat propagation within the coal reactor. The vast reach of heat propagation from the heat exchanger through the coal pile on the simulation was promisingly showing that this method was useful to limit the occurrence of spontaneous fire in coal piles.

Investigation on ash fouling formation of induced fan blade and heat exchanger surface in a 1000MW coal-fired power plant

The control of fouling deposition on the main equipment has always been an im-portant issue concerned by scientific research and industrial application. How-ever, severe fouling deposits on the induced fan blade and the low temperature economiser were found in a 1000 MW coal-fired power plant with ultra-low emission. The deposit samples were collected and analysed through X-ray dif-fraction spectrometer, X-ray fluorescence, elemental analyser and SEM with en-ergy dispersive spectrometers. The result shows that the deposits are mainly composed of tschermigite (NH4)Al(SO4)2 ? 12H2O, letovicite (NH4)3H(SO4)2, cal-cium sulphate CaSO4, and quartz SiO2. The ammonium sulphate is the main component of the fouling deposits. It acts as an adhesive and makes an important contribution to the deposition. The analysis shows that the ammonia slip from denitrification system and the unreasonable temperature setting are the main reasons for fouling deposition. It is suggested that the high concentration of am-monium slip at denitrification system and the rapid condensation of the sulphuric acid mist at heat exchanger should be paid more attention in coal-fired power plants.

Investigation Heat Transfer Parameters for a Helical-Coil Heat Exchanger in a Two-Phase Medium

The paper focuses on hydrocarbon fuel cooling in launch vehicles, specifically considering experimental technique and results obtained during investigation of one of the primary heat exchanger parameters, that is, heat transfer coefficient of the heat exchanger surface. We present a model of efficient hydrocarbon fuel cooling by means of intensifying heat transfer on the external heat exchanger surface due to nitrogen sparging causing active motion in the liquid heat carrier. We obtained quantitative data regarding heat transfer on the external surface of a helical-coil heat exchanger located in a two-phase medium consisting of antifreeze and nitrogen, in the temperature range of 243--293 K. We derived a similarity equation for calculating heat transfer coefficient on the external heat exchanger surface, which is required to determine the heat exchanger surface area and to compute heat transfer from hydrocarbon fuel to the two-phase medium consisting of antifreeze and nitroge.

Multi-Dimensional Performance Evaluation of Heat Exchanger Surface Enhancements

Enhanced heat transfer surfaces allow more energy-efficient, compact and lightweight heat exchangers. Within this study, a method for comparing different types of enhancement and different geometries with multiple objectives is developed in order to evaluate new and existing enhancement designs. The method’s objectives are defined as energy, volume, and mass efficiency of the enhancement. They are given in dimensional and non-dimensional form and include limitations due to thermal conductivity within the enhancement. The transformation to an explicit heat transfer rate per dissipated power, volume, or mass is described in detail. The objectives are visualized for different Reynolds numbers to locate beneficial operating conditions. The multi-objective problem is further on reduced to a single-objective problem by means of weighting factors. The implementation of these factors allows a straightforward performance evaluation based on a rough estimation of the energy, volume, and mass importance set by a decision maker.