Development and performance of steam ejector refrigeration system operated in real application in Thailand

This paper presents the design and construction of a prototype steam ejector refrigeration system which can be operated under the actual condition of Thai environment, which is rather hot and humid. The prototype refrigerator was designed to produce a cooling capacity of approximately 3 kW. Water was selected to be used as the working fluid. The steam boiler used was a vertical fire tube type and it was designed to be used with LPG compact gas burner. The condenser was cooled by water obtained from a conventional cooling tower. The prototype refrigerator was used to produce chilled water which was used to cool a small tested room. It was observed that the room temperature of 24.2 °C was obtained at the cooling load of 3000 W. The cooling water was supplied to the condenser at about 30 °C. The COP obtained was 0.45. This prototype refrigerator is proven to be practical and can be used in actual environment of Thailand.     

Vakuum in der Kältetechnik

Pressures below ambient are used for refrigeration purposes both indirectly for auxiliary processes for drying, suction removal and insulation purposes as well as directly for selected refrigeration cycles with refrigerant as water in steam jet, ab‐ and adsorption machines and in cold‐air machines according the Joule‐process with air as working fluid. Required pressures are in the low vacuum range down to 10° mbar. In the future the application of environmentally friendly working fluids will increase so that refrigeration cycles with vacuum processes will become of greater importance. Furthermore the refrigeration technique can be applied for the generation of clean vacuum.     

Uphill quenching to reduce residual stress in a heat treatable aluminium alloy

Three rectilinear blocks of the aluminium alloy 7449 were characterised using neutron and X-ray diffraction. One block was heat treated normally and two blocks were subject to uphill quenching from ?196°C to 100°C. Boiling water and steam were used to rapidly increase the temperature of the blocks to reverse the thermal gradients introduced by cold water quenching. It was possible to detect the beneficial influence of uphill quenching on residual stress using either fluid. The influence of steam was very effective but localised and limited to the surface in close proximity to the steam jet. For more uniform stress relief, multiple steam jets will be required to ensure the entire surface receives a significant thermal input.     

Wrought Ni‐Base Superalloys for Steam Turbine Applications beyond 700 °C

The development of a new steam turbine generation for use in advanced coal fired power plants with prospective operating temperatures beyond 700 °C and a projected thermodynamic efficiency of about 55 % requires, amongst other innovations, the partial substitution of ferritic steels by wrought Ni‐base superalloys. Although Ni‐base alloys are already widely used in the aerospace industry, they are faced with demands regarding component size and operation temperature, which by far exceed current aero‐engine requirements. In this article, the potential of selected alloys for 700 °C steam turbine applications is discussed with respect to their manufacturability and mechanical performance. Hereby, the focus is on the steam turbine rotor, which probably is the most critical component. It is concluded that material solutions are available for operation conditions around 600 °C but not for temperatures of 700 °C and above. Based on these results, alloy development strategies are suggested in order to close this gap and two new alloys, DT 706 and DT 750, are introduced.     

Characterisation and simulation of the creep behaviour of Nicrofer 6025HT wire material at 650 °C

Thermal efficiency of combined cycle power plants can be improved by increasing temperature and pressure in the steam turbine. Since typical power plant materials have presently reached their operation limit with higher steam temperature, the application of a new cooling system could reduce the material temperature to tolerable conditions. For this purpose, a new sandwich structure was developed comprising a woven wire mesh interlayer between two plane sheets. Cooling steam is fed into the interlayer where it can flow without severe losses. This sandwich structure is applied to the steam turbine casing as a wall cladding.Due to the combination of constant overpressure of cooling steam and high temperature exposure of hot steam, the structures are stressed parallel and perpendicular to the intermediate layer primarily by creep loads. To simulate the creep behaviour via the finite element method the exact knowledge of the creep behaviour of the constituents, the wire and the sheet, is essential. Therefore, creep tests at 650 °C on wire material, manufactured from the nickel base alloy Nicrofer 6025HT, were carried out to determine constitutive equations. The creep behaviour was simulated on the basis of the concept of the internal backstress, which was implemented in an adequate user subroutine of the commercial FEM-software Abaqus.     

Yields, solids loss and effluents generation during blanching and cooling of asparagus spears

Blanching and cooling of asparagus spears (two sizes) were compared for overall product yield, total solids loss, effluents generation and chemical oxygen demand (COD). Blanching was done using steam followed by cold water (2°C) cooling or air (static or forced) cooling. Steam blanching of 1 cm diameter asparagus produced a total solids loss of 1.04%, an effluent of 9.50 g/100 g of fresh asparagus, a COD of 0.061 g/100 g of fresh asparagus and a yield of 99.20%. Yields for cold water cooling, static air cooling and forced air cooling were, respectively, 99.8, 94.7 and 96.0%. Since cold water cooling produced a total solids loss similar to steam blanching, the combination steam blanching (IQB)-cold water cooling appears to be convenient for obtaining an excellent yield with low total solids loss of a high price vegetable like asparagus.     

ITO‐coatings by reactive low‐voltage ion plating: film properties and plasma analysis

Transparent conductive oxides (TCO) are widely used materials for multifarious applications. According to today's state of knowledge, indium‐tin‐oxide (ITO) still offers the best electrical properties among numerous TCOs. However, ITO films produced by ion plating have only rarely been reported to be investigated. For most coating processes, ITO films need to be deposited under high temperature conditions (some 100 °C substrate heating) or require post‐deposition heat treatment in order to obtain high film quality. In this study, reactive low‐voltage ion plating (RLVIP) was used, which allows ‐ due to plasma assistance during the coating process ‐ deposition of ITO films at temperatures below 100 °C. Essential film properties, i.e. resistivity and optical transmission, were optimised by variation of arc current, gas pressure and deposition rate. These quantities ‐ particularly arc current and gas pressure ‐ have huge influence on the characteristics of the supporting plasma. This was shown by analysing the plasma with a mass‐spectrometric plasma monitoring system and with a Langmuir probe. In comparison with formerly studied coating materials (Ta₂O₅,Nb₂O₅,HfO₂), different plasma compositions regarding the presence of metal oxide ions were determined, which could be attributed to elemental and molecular energy properties (ionisation and binding energies).     

Simulating the implications of oxide scale formations in austenitic steels of ultra-supercritical fossil power plants

Formation of steam-side oxide scale that can cause major failures in boilers is a large concern in fossil-fueled power plant operation. In this work, we attempt to simulate the implications of oxide scale formation and subsequently assumed exfoliation in the given length of an austenitic tube of ultra-supercritical (USC) fossil power plants under different presumed service conditions. The incremental procedures used to determine the average metal temperature and scale thickness over a period of time in superheater/reheater tubes at a specified steam temperature are presented. A number of simulation results for both formation and subsequent exfoliation of the oxide scales are presented and discussed. Based on the simulation results, the estimated scale growth and presumed exfoliation rate in austenitic steels at 650 °C seemed to be allowable. However, to run USC power plants with steam condition of around 650 °C, more detailed studies are required.     

Prozessberechnungen für eine CO<Subscript>2</Subscript>-Anlage zur Kälte- und Wärmeerzeugung für Supermärkte. Teil 2: Begrenzte bzw. keine CO<Subscript>2</Subscript>-Abkühlung durch Umgebungsluft

CO₂ processes are used in supermarkets for medium- and low-temperature refrigeration and by now even for room heating and hot tap-water preparation via heat recovery. Through systematic thermodynamic process calculations, the limits of the heat recovery and it’s influence on the refrigeration process as well as the complete system are investigated for a supermarket with 100 kW medium-temperature refrigeration capacity. This investigation focuses on the energy efficiency of the heat supply by the extended CO₂ plant. By using the medium-temperature refrigeration capacity as reference, the results for ambient temperatures between ??15?°C and +?10?°C are applicable for other supermarket sizes as well.In part 2, a plant is investigated with a ratio between low- and medium-temperature refrigeration capacity of 0.2 and of 0.4, and limited or no CO₂ cooling the ambient air. The contributions of refrigeration and heat supply are specified for a range of high-pressure values for sub-critical and for trans-critical operation of the CO₂ plant. Relevant data for design and operation of the CO₂ plant are made available: the supplied heating capacity (relative to the medium-temperature refrigeration capacity), the coefficients of performance and the exergy efficiencies of refrigeration (medium-temperature, low-temperature and total), of heating, and of combined refrigeration and heating. With this knowledge, optimal operation parameters for the CO₂ process can be chosen depending on the ambient temperature. Moreover, the decision is prepared, whether an additional heating system is required or the heat recovery from the refrigeration plant is sufficient.     

Prefabricated building elements based on FGD gypsum and ashes from coal-fired electric generating plants

Mixtures of fly ash, bottom ash and Flue Gas Desulphurized (FGD) gypsum, all solid wastes from coalfired electric generating plants, can be combined with lime and 10% of water to produce a damp powder which can be moulded at a pressure of 20–40 MPa and then steam-cured in less than 1 day at 35–80°C. The resulting building materials-in the form of bricks, blocks or slabs-produced by this Pressure Forming (PF) process, are stronger and sounder than the corresponding materials produced by a slip casting (SC) process. The physical and mechanical properties of the materials manufactured through the PF process are based on the reaction of amorphous silica and alumina of the ash with lime or lime and gypsum respectively, so that calcium silicate hydrate and ettringite are produced. When the temperature of the steam curing is as low as 35°C, the hardened material is sound in the air, but it swells and is quickly destroyed by the action of water. This effect can be ascribed to the formation of ill-crystallized ettringite. On the other hand, with thermal treatment at higher temperatures (60–80°C), the material is stronger and sound even in the presence of water in service. The well-crystallized ettringite fibers, favoured by the higher temperature of the steam curing treatment, are considered to be responsible for the better mechanical performances and the lower change in length. In general, the physical and mechanical properties of the ash-gypsym-lime cementitious system are better than those of the traditional clay-based ceramic products manufactured at temperatures as high as 1000°C. Therefore, this process based on steam curing at 60–80°C appears to be very useful for both the re-utilization of solid wastes and the saving of energy in the production of building materials.     

Microscopical investigation of steamside oxide on X20CrMoV121 superheater tubes

Abstract

X20CrMoV121 is a 12%Cr martensitic steel which has been used in power plants in Europe for many decades. Superheater tubes exposed for various durations up to 135,000 h in power plants in Denmark at steam temperatures varying from 450 to 575°C were investigated. Light optical and scanning electron microscopy was used to investigate steamside oxide morphologies. At all temperatures there is a double layered oxide, however, the inner:outer oxide thickness is not always equal. At the lower steam temperature range of <500°C, there is an internal oxidation zone at the oxidation front indicating that chromium is less mobile at these temperatures. At a higher steam temperature range of 540 – 575°C the inner oxide consists of chromium rich and chromium poor oxide running parallel to the oxidation front indicating that the chromium is more mobile within the steel. Both types of morphology have been observed in the laboratory, however, the internal oxidation is observed up to 600°C and the chromium rich oxide striation are observed at 700°C.     

Solar cooling with water–ammonia absorption chillers and concentrating solar collector – Operational experience

Concentrating solar collectors provide high efficiency at high driving temperatures favourable for thermally driven chillers. Therefore, they offer applications for hot climates and industrial process integration, especially in combination with NH₃–H₂O chillers that provide refrigeration temperatures below 0 °C. The presented solar cooling installation comprises a linear concentrating Fresnel collector that provides the driving heat for two NH₃–H₂O absorption chillers at temperatures up to 200 °C. Chilled water temperatures are produced in the range between −12 °C and 0 °C. Collector capacities reached up to 70 kW at peak times and the total cooling capacity of both chillers showed peak values up to 25 kW. For good operating conditions, the thermal system EER was 0.8 and an electrical system EER of 12 was easily achieved. The system showed a sound operating behaviour. The performance of different operation and control strategies was analysed, evaluated and enhanced within the two year operation phase.     

Studies on sky-therm cooling

Passive cooling by the sky-therm technique presents a very attractive prospect for environmental conditioning in India because of its inherent simplicity and low cost. Sky-therm control has been proposed for storage rooms for the sericulture industry (which is a major cottage industry in Karnataka State). The temperature within these rooms is to be kept at 25 ± 3°C throughout the year. A thermal model for buildings equipped with roof ponds and movable insulating covers as proposed in the sky-therm process has been developed. The thermal behaviour of a building has been simulated to study the influence of such parameters as the heat capacity, depth of water in the pond, roof thickness and its thermal conductivity, air infiltration rates etc. Experiments have been carried out to check which of the several commonly used empirical relations for the sky temperature is valid. A simple technique for measuring air infiltration has been developed. It has been found that even for the most severe cooling requirement in Bangalore (for April), sky-therm cooling alone is adequate to maintain a temperature below 28°C. In places where the requirements are more demanding, it may be necessary to augment sky-therm with evaporative cooling.     

Hydromechanisches Tiefziehen und Hochdruckblechumformung als Verfahren zur Herstellung komplexer Bauteile aus Magnesiumfeinblechen des Typs AZ31B‐0

Hydro Mechanical Deep‐Drawing and High Pressure Sheet Metal Forming as Forming Technologies for the Production of Complex Parts Made of Magnesium Sheet Metal AZ31B‐0 Semi ‐ finished sheet ‐ metal products made of magnesium alloys such as AZ31B are known as better deformable at temperatures in the range of 175 °C ‐ 240 °C. By means of hydroforming technologies, as there are hydro mechanical deep‐drawing and high pressure sheet metal forming, the influence of different forming parameters on the forming results has been investigated. A more complex experimental geometry was deformed applying forming temperatures of 175 °C, 200 °C, 225 °C and 240 °C and accordingly adjusted forces of the blank holder. Concerning the applied forming ‐ methods and experimental parameters the forming results have been evaluated and compared regarding the decrease of sheet thickness and the development of small radii. For some experimental parts, which have been deformed by means of high pressure sheet metal forming at temperatures of 175 °C and 225 °C, supplementary investigations have been carried out in order to determine the evolution of characteristic surface values in dependence on the forming operation. On the basis of these results practical recommendations for the limits of application of aforementioned forming technologies for AZ31B‐0 magnesium sheet metal are given.     

Einfluß von Spannungsfrei-Glühung und Abkühlungsgeschwindigkeit auf Mikrostruktur und Festigkeit von TiAl6V4

Influence of stress relieving of TiA16V4 The stress relieving of Ti6A14 V has been investigated by electron microscopy and by tensile tests. Partial recrystallization could be detected at 740 °C. The cooling rate from the stress relieving temperature exerts a marked influence on strength and elastic modulus. Slow cooling increases tensile strength, probably because of a higher volume fraction of alpha and because of an oxygen ordering reaction. It is concluded that after stress relieving, slow cooling down to a temperature of 300 °C is of advantage.     

Experimental and numerical analysis of an air-cooled double-lift NH3–H2O absorption refrigeration system

The prototype of an air-cooled double-lift NH₃–H₂O absorption chiller driven by hot water at low temperature is presented. The main objective of the study is to illustrate the experimental performances of the prototype under different operating conditions. A mathematical model of the cycle is developed, along with a procedure for the identification of otherwise difficult to measure data, with the purpose of providing the complete picture of the internal thermodynamic cycle. The combined experimental and numerical data allowed assessing the effects on the thermodynamic cycle with varying operating conditions. The unit operated steadily with chilled water inlet 12 °C, outlet 7 °C, air temperature between 22 °C and 38 °C, and hot water driving temperatures between 80 °C and 90 °C. The reference cooling capacity at air temperature of 30 °C is 2.5 kW, with thermal COP about 0.3 and electrical COP about 10.     

Studies in biogas technology. Part III. Thermal analysis of biogas plants

A thermal model for a conventional biogas plant has been developed in order to understand the heat transfer from the slurry and the gas holder to the surrounding earth and air respectively. The computations have been performed for two conditions : (i) when the slurry is at an ambient temperature of 20°C, and (ii) when it is at 35°C, the optimum temperature for anaerobic fermentation. Under both these conditions, the gas holder is the major “culprit” with regard to heat losses from the biogas plant. The calculations provide an estimate for the heat which has to be supplied by external means to compensate for the net heat losses which occur if the slurry is to be maintained at 35°C. Even if this external supply of heat is realised through (the calorific value of) biogas, there is a net increase in the biogas output, and therefore a net benefit, by operating the plant at 35°C. At this elevated temperature, the cooling effect of adding the influent at ambient temperature is not insignificant. In conclusion, the results of the thermal analysis are used to define a strategy for operating biogas plants at optimum temperatures, or at higher temperatures than the ambient.     

电动客车用余热回收型热泵的换热器优化及性能实验研究

本文针对热泵空调系统在冬季低温工况下制热能力衰减问题,通过换热器设计优化,研发出基于喷射补气的余热回收型热泵空调系统,并进行了性能实验研究.结果表明:研制的准二级压缩电动客车热泵空调系统在低温条件下具有较好的制热性能.在环境温度为-20℃,车内温度为20℃,余热量为1.8 kW的制热工况下,相比于无余热回收工况,系统制...     

LCA of strippable coatings and of steam vacuum technology used for nuclear plants decontamination

The application of strippable coatings is an innovative technology for decontamination of nuclear plants and for any decontamination project aiming at removing surface contamination. An adhesive plastic coating is applied on the contaminated surface. The strippable coating is allowed to cure for up to 24 h, after which it can be easily peeled. The coating traps the contaminants in the polymer matrix. Strippable coatings are non-toxic and do not contain volatile compounds or heavy metals. Since the coating constitutes a solid waste, disposal is easier than treating contaminated liquid wastes, produced by the baseline technology: steam vacuum cleaning, based upon superheated pressurized water in order to remove contaminants from floors and walls. A life cycle assessment (LCA) has been carried out with the purpose of comparing the strippable coating with the steam vacuum technology. The functional unit of the study is represented by a surface of 1 m² to be decontaminated. The results of LCA achieved using Sima Pro 5.0^® software confirm the good environmental performances of strippable coatings. Taking into account both LCA and environmental costs for liquid wastes, the advantages of strippable coatings will be more and more evident.     

Utilisation of the heat of condensation from medium capacity refrigerating units for heating waterL'utilisation de la chaleur de condensation de groupes frigorifiques de moyenne puissance pour le chauffage de l'eau

This paper is concerned with the utilisation of condenser heat rejected by a refrigerator cooling milk. The condenser pressure is raised so that hot water can be produced in a recuperator, any residual refrigerant vapour being passed to an air cooled condenser. The performance and control of such equipment with varying heat demand and ambient temperature are considered.To cool 1000 dm³ of milk from 35°C down to +5°C, the quantity of heat recuperation increases from 177 500 to 182 000 kJ when the ambient temperature drops from 20° to 10°C. However, this 2.5% gain in recoverable heat will result in a 33.3% increase in the running time of the compressor and an 8.6% increase in the power consumption.A higher capacity expansion valve can be fitted in order to improve the functioning of the refrigerating unit during cold periods, but this will entail adjustments to the valve during warm periods.Another method is to fit a constant pressure valve between the recuperator and the condenser to maintain the desired pressure in the recuperator and thus directly control the fluid flow volume. This will involve the fitting of a suitably sized accumulator and increasing the amount of refrigerant. It also brings control problems.A secondary study has analysed the difficulties arising when the heated water temperature is raised from 40°C to 50°C. For a flow of 1300 dm³ at 40°C an economy of 51 kWh was achieved. The latter temperature was found impossible to achieve, the maximum being 47.5°C and this required an additional power consumption of 31.9%.A properly designed installation will provide the daily cooling of 1000 l of milk with an annual saving of 16 000 kWh.