Artur Rusowicz

Determining the Optimum Inner Diameter of Condenser Tubes Based on Thermodynamic Objective Functions and an Economic Analysis

The diameter and configuration of tubes are important design parameters of power condensers. If a proper tube diameter is applied during the design of a power unit, a high energy efficiency of the condenser itself can be achieved and the performance of the whole power generation unit can be improved. If a tube assembly is to be replaced, one should verify whether the chosen condenser tube diameter is correct. Using a diameter that is too large increases the heat transfer area, leading to over-dimensioning and higher costs of building the condenser. On the other hand, if the diameter is too small, water flows faster through the tubes, which results in larger flow resistance and larger pumping power of the cooling-water pump. Both simple and complex methods can be applied to determine the condenser tube diameter. The paper proposes a method of technical and economic optimisation taking into account the performance of a condenser, the low-pressure (LP) part of a turbine, and a cooling-water pump as well as the profit from electric power generation and costs of building the condenser and pumping cooling water. The results obtained by this method were compared with those provided by the following simpler methods: minimization of the entropy generation rate per unit length of a condenser tube (considering entropy generation due to heat transfer and resistance of cooling-water flow), minimization of the total entropy generation rate (considering entropy generation for the system comprising the LP part of the turbine, the condenser, and the cooling-water pump), and maximization of the power unit’s output. The proposed methods were used to verify diameters of tubes in power condensers in a200-MW and a 500-MW power units.

Air purification in industrial plants producing automotive rubber components in terms of energy efficiency

Abstract In automotive industry plants, which use injection molding machines for rubber processing, tar contaminates air to such an extent that air fails to enter standard heat recovery systems. Accumulated tar clogs ventilation heat recovery exchangers in just a few days. In the plant in which the research was conducted, tar contamination causes blockage of ventilation ducts. The effect of this phenomenon was that every half year channels had to be replaced with new ones, since the economic analysis has shown that cleaning them is not cost-efficient. Air temperature inside such plants is often, even in winter, higher than 30°C. The air, without any means of heat recovery, is discharged outside the buildings. The analyzed plant uses three types of media for production: hot water, cold water at 14°C (produced in a water chiller), and compressed air, generated in a unit with a rated power consumption of 180 kW. The aim of the study is to determine the energy efficiency improvement of this type of manufacturing plant. The main problem to solve is to provide an air purification process so that air can be used in heat recovery devices. The next problem to solve is to recover heat at such a temperature level that it would be possible to produce cold for technological purposes without air purification. Experimental studies have shown that air purification is feasible. By using one microjet head, a total of 75% of tar particles was removed from the air; by using 4 heads, a purification efficiency of 93% was obtained. This method of air purification causes air temperature to decrease from 35°C to 20°C, which significantly reduces the potential for heat recovery. The next step of the research was designing a cassette-plate heat exchanger to exchange heat without air purification. The economic analysis of such a solution revealed that replacing the heat exchanger with a new one even once a year was not cost-efficient. Another issue examined in the context of energy efficiency was the use of waste heat from the air compressor. Before any changes, the heat was picked up by a chilled water system. The idea was to use the heat for cold generation. Temperature of oil and air in the compressor exceeds 65°C, which makes it a perfect heat source for an adsorption refrigeration device. This solution reduced the cooling demand by 147 kW, thus reducing power consumption by 36.75 kW. This study shows that even in factories where air is heavily polluted with tar, there are huge potentials for energy recovery using existing technical solutions. It is important to note that problems of this kind should always be approached individually.

The Developmental Trends in Heat Spraying of Ceramic Coating

In the paper development of used ceramic materials and ways of their production with the aid of heat spraying is presented. According to a needness of continuous increase of coating’s mechanical resistance (high wearability, low brittlesness), corrosion resistance and profitable thermal and electric properties, current ceramic materials characterized by more and more attractive useful properties are described. Also a role of flame and plasma spraying including developmental trends towards prodution of coatings are underlined. The paper contains the own solution of plasma spraying of coatings consists in operation of the process under atmospheric pressure with gaseous ring-shaped protective jet. Additionally, proper choice of spraying’s parameters and some interesting characteristics of coatings are presented along with the examination of their structure (i. e. a rate of fusion, an oxidation of granules in a coating). Moreover the applications of coatings on machine parts (i. e. mechanical seal of impeller pumps, blades of turbines) are mentioned.Copyright

The Plasma Spraying of Nitride Coatings

Ceramics without oxides (i.e. nitrides) are vulnerable to oxidation in the presence of plasmagenic gases or oxygen from atmosphere during plasma spraying. Initially there were two ways of oxidation’s avoidance: first, modification of powder material and second, limitation of an oxygen’s stream flowing into plasma. The modification of the powder material consisted in covering of ceramic granules with material limiting contact with oxygen or usage of easily oxidizing material getting oxygen away (i.e. a graphite thin layer over carbide’s granule). This method seemed to be less economic due to additional increase in powder’s price. Eventually the second conception of limiting of oxidation was considered as worth developing. Originally the process of spraying was carried out in vacuum (VPS – Vacuum Plasma Spraying). Then application of atmosphere under control was examined (CAPS – Controlled Atmosphere Plasma Spraying). It includes process of spraying with application of different gaseous controlled atmospheres under different pressure (decreased, normal and increased). There are three kinds of atmosphere: neutral (argon, nitrogen), reductive (carbon monoxide, methane) and acting with spraying material. Eventually the process was carried out under atmospheric pressure with gaseous ring-shaped protective gas jet. Moreover the experiments with spraying of nitrides were described (AlN, TiN, Si3 N4 ). The most suitable characteristics of the process was chosen and some properties of coatings were examined as well.© 2002 ASME