Direct Heating System Research Articles

Numerical simulation on the direct contact condensation in a steam-water two-phase ejector with non-condensable gas

The steam-water condensing ejector is widely used in many industrial fields and production processes. In the practical operation of ejectors in many systems such as nuclear reactors and underwater gas-ejection devices, the steam pressure is much higher than those in common direct heating systems or refrigeration systems. In addition, some non-condensable gas is inevitably mixed into steam jet. With the presence of non-condensable gas, the flow field and performance of ejector are significantly influenced by the changes in heat transfer characteristics. This paper presents a three-dimensional numerical simulation of the high-pressure steam-water condensing ejector with non-condensable gas based on inhomogeneous multiphase model. The steam inlet pressure, mass flow rate and non-condensable gas fraction are in the range of 0.70–2.40 MPa, 1019–3310 kg/(m2s) MPa and 0–0.05, respectively. The changes in steam plume shapes, distributions of thermal hydraulic parameters and pressure ratio are investigated under different boundary conditions. Numerical results show that the steam plume inside ejector transforms from ellipsoidal shape to divergent shape with the increase of steam inlet mass flow rate and the decrease of back pressure. The choking phenomenon in throat is found at divergent steam plume and the changes of flow field in diffuser do not spread upstream to the mixing chamber, so the thermal hydraulic parameters in mixing chamber and pressure ratio of ejector keep unchanged. In addition, the pressure ratio first increases from 1.08 to 2.34, then decreases to 1.99 with the increase of steam mass flux. As back pressure rises, the pressure ratio drops from 2.00 to 1.30 at low steam inlet mass flux; while first increasing linearly from 1.98 to 2.41 and then decreasing to 1.78 at high steam inlet mass flux. With the increase of non-condensable gas mass fraction, the pressure ratio slowly decreases from 1.48 to 1.39 at low steam mass flux while rapidly decreasing from 4.00 to 1.65 at high steam mass flux.

A Novel District Heating System Coupled with Reclaimed Water Source Heat Pump: Energy, Economic, Environmental, and Application Analysis

The large amount of low‐grade thermal energy from reclaimed water is not fully utilized. It can be used as a good heat supplement for district heating. A novel district heating system coupled with a reclaimed water source heat pump (RWSHP) is proposed in this article. The models of energy efficiency, economic feasibility, environmental benefits, and application suitability are established to analyze three typical systems including the traditional district heating system (TDHS), the direct heating system using RWSHP (D‐RWSHP), and the traditional district heating system coupled with RWSHP (T‐RWSHP). The results show that the energy consumption and operating costs of T‐RWSHP are lower than those of TDHS. T‐RWSHP can achieve longer distance heating than D‐RWSHP. Under design conditions, the annual energy consumption of T‐RWSHP can be reduced by 11.36% and the annual operating costs can be reduced by 5.8 CNY m−2 compared with TDHS. Taking the Yanqing wastewater treatment plant as an example, the heating area of D‐RWSHP is only 2% of that of T‐RWSHP. According to the sensitivity analysis, the energy consumption, operating costs, and CO2 emissions of the system decrease greatly with the increase of temperature difference between the influent and effluent reclaimed water of RWSHP.

Developing the new industrial flatbread baking system using numerical technique to increase the product quality

AbstractBread is one of the most important food sources for consumers, especially in developing and underdeveloped countries. Large quantities of bread are wasted every year because different factors affect the quantity of waste products include flour quality, bread production technology, and the storage condition of the bread. The objective of this study was to improve existing systems and developed the new flatbread industrial baking machine to increase product quality and product storability. Therefore, a rotary bread baking machine with an indirect heating system was designed, and the heat exchangers of the machine were simulated. The results of the simulation were utilized to investigate the uniformity of airflow velocity inside the exchanger and the distribution of heat on the dough on the baking bed. After achieving the most effective design, the exchangers were constructed and installed inside the baking machine. Bread baking experiments with the developed machine and the existing conventional machines were conducted to evaluate the instrumental, sensory, and staling characteristics of the produced flatbreads from different baking machines. The results indicated that the sensory qualities of the bread produced with the indirect heating system in the present study as well as uniformity of baking and sensory acceptability were superior compared to the bread produced from the conventional industrial machines with direct heating systems (with a total sensory score of 5.09 vs. 4.54).Practical ApplicationsIn this research, a superior flatbread baking machine with indirect heat was designed, constructed, and evaluated. The flatbread baked with the indirect heating system had better quality scores and a longer shelf life compared to the flatbread baked with the direct heating system. This type of the flatbread lasted more than 168 hr without mold and it was the best choice for longer‐term storage purposes and for the reduction of food waste. Also, bread prepared using the new machine was free of any contaminants such as polycyclic aromatic hydrocarbons.

Simultaneous Full-Field Strain and Temperature Measurements in Tensile Hopkinson Bar Experiments at Extreme Temperatures

Simultaneous full-field strain and temperature measurements were used to monitor tension Split Hopkinson Pressure Bar (SHPB) tests at elevated temperatures. A direct heating system was used to increase the specimen temperature up to 1350 °C. Digital Image Correlation (DIC) and Infrared Thermography (IRT) were used was used to simultaneously monitor the evolution of the full-field strain and temperature of the specimen. Data acquisition was synchronized using a function generator, a camera pinhole model was used to represent both strain and temperature on the same coordinate system, and the displacement vector field from DIC was used to represent both datasets on the same reference frame. The use of fullfield techniques was essential at elevated temperatures, as necking occurred soon after yielding and the usability of the data obtained from the SHPB after the onset of necking is debatable. The method was able to follow the full-field strain and the temperature evolution under extreme conditions. Some challenges were found in the development of the method and recommendations as well as future applications are also described in this paper. This experimental approach is versatile and can be applied to different materials at similar testing conditions but also different loading modes and testing setups.

Productivity, exergy, exergoeconomic, and enviroeconomic assessment of hybrid solar distiller using direct salty water heating.

In this work, experimental work is presented on the performance of a hybrid solar distiller comprising solar still (SS) combined with parabolic trough solar collector (PTSC) using direct heating of salty water by the collector. In this technique, the salty water supplied to the SS is heated by passing it directly through the parabolic receiver without using heat transfer mediums that reduce the system efficiency. The study is carried out at different salty water depths inside the SS basin under hot climate conditions of Upper Egypt. The system performance is compared with a previous system using oil as a heat transfer medium between PTSC and still (indirect heating). The advantages of this technique are its ability to reduce initial salty water depth in the basin and avoid using the pumping system and heat exchanger compared to the direct heating. The performance of the proposed system is evaluated based on productivity, energy payback time (EPBT), exergy, enviroeconomic, and exergoeconomic methodologies. Findings illustrate that the present system rises the energy efficiency by about 12%, 27.5%, and 46% and the system exergy efficiency by about 14%, 30%, and 49% at salty water depth 15 mm, 10 mm, and 5 mm in the basin compared with the indirect heating system. Moreover, using this technique of salty water heating reduces the production cost of freshwater by about 71% compared with the direct heating system. The exergoeconomic and enviroeconomic parameters of the direct heating mechanism are more effective compared with those of the indirect heating mechanism.

Modeling and Simulation Research of Wind Energy Heat Pump Direct Heating System Based on Geographic Information System

Modeling and Simulation Research of Wind Energy Heat Pump Direct Heating System Based on Geographic Information System

CFD modelling of biomass boilers - a review of the state of the art

Combustion is the main method of converting biomass to energy, either by direct heating systems or by boilers. By means of CFD models, it is possible to optimize the behavior of those systems and improve significantly its performance, without incurring the economic and environmental cost of experimental studies. However, modelling of biomass combustion is a complex process that requires a large number of sub-models and computational resources for a detailed description, therefore, different approaches have been developed which depend on the system and simulation objective. In this work, a review of the state of art of modelling of solid biomass combustion in the last years is presented, including classification, description and analysis of several of the main models about the subject.

Thermodynamic and exergoeconomic analysis of a novel CO2 based combined cooling, heating and power system

In this paper, a novel combined cooling, heating and power (CCHP) system consisting of a supercritical carbon dioxide (sCO2) power cycle, a transcritical carbon dioxide (tCO2) power cycle with a carbon dioxide based refrigeration cycle, and a direct heating (DH) system is proposed. In the novel system, the waste heat from sCO2 power cycle is recovered by the tCO2 power cycle to generate additional power and drive the CO2 based refrigeration cycle to provide cooling for users, and the DH system further recovers the waste heat from the sCO2/tCO2 power cycle and the refrigeration compressor outflow to feed heat for users. Mathematical models are developed to conduct the thermodynamic and exergoeconomic analysis of the proposed CCHP system, and parametric studies on the effects of different key parameters on the system performance are carried out. Besides that, the optimization and comparative researches are performed to find out and compare the maximum system exergy efficiency and minimum total product unit cost for the proposed CCHP system and the stand-alone sCO2 system. The results indicate that for different users’ demands, the proposed CCHP system can obtain the best improvement by 12.01% for the system exergy efficiency and 5.14% for the total product unit cost, and the worst improvement by 10.83% for the system exergy efficiency and 4.12% for the total product unit cost, compared with the stand-alone sCO2 power cycle. These results confirm the obvious superiority in thermodynamic and economic performance of the proposed CCHP system under different users’ demands.

Heat collection in an attached sunspace

The attached sunspaces are classic bioclimatic systems. Normally, they are used as solar passive techniques in buildings. However, it has been suggested that they could also be used as active systems in order to collect solar energy and harness it in the heating, ventilation and air conditioning (HVAC) equipment. This paper analyses the sunspace built during the ARFRISOL project, which has a validated simulation tool of its thermal behaviour, developed in a previous research. In this paper, this tool is applied to study the possibility of the energy collection. Although this energy is not enough to be used as direct heating system, it can pre-heat the air before entering the HVAC equipment. Two configurations have been studied: collecting the energy during the whole day or only at night to take advantage of the sunspace thermal inertia. Also, the results obtained with these configurations have been compared with the sunspace used in passive mode. For this analysis, several characteristic days with summer and winter climatic conditions have been considered. Finally, an economic evaluation of this innovative system –a solar active sunspace- is performed taking into account the results of the different configurations.

Coal drying study for a direct syngas fired supercritical CO2 cycle integrated with a coal gasification process

The Allam Cycle is a semi-closed, oxy-fuel, supercritical carbon dioxide (sCO2) Brayton power cycle fueled with natural gas or syngas derived from coal, biomass or other carbonaceous fuels, offering advantages over simple cycle and combined cycle arrangements. For the coal based Allam Cycle, a gasification system is required to convert coal to clean syngas for downstream power generation. These systems require heat input to dry as-delivered coal to certain specifications. Produced steam is typically used for this purpose, but since the Allam Cycle is based on use of sCO2, and not steam, it is preferable to utilize alternative methods for coal drying. An experimental study was carried out at Energy & Environmental Research Center (EERC) to determine the heat energy required for drying lignite coal down to moisture levels acceptable for the operation of different gasifiers (range of moisture levels inserted here), and to investigate the effect of the heat transfer medium (steam and/or N2) and heat transfer type (direct or indirect) on the lignite drying performance. The results show that optimal operating temperature of coal drying is 90 °C. For direct heating system, the result shows a relatively linear trend of drying energy versus the coal’s moisture content, and the drying data suggests that individual parameters of velocity, residence time, and bed temperature are of secondary importance compared to how they combine to determine energy transfer to the coal. When the results of the direct heating tests using different heat transfer medium were compared, they were in good agreement, in that they indicate an approximate heat of evaporation around 2791.2 kJ/kg moisture removed. The energy consumption of the indirect heating steam coil tests is about 4652–5815 kJ/kg moisture removed, which is much higher than direct heating test data since not all the steam can condense at the exit of the steam coil. All the test results are important for designing the lignite drying process for the Allam Cycle. In the coal based Allam Cycle power generation system, low grade energy at the temperature of 70–100 °C from the turbine exhaust stream is sufficient for the coal drying process. Nitrogen from air separation unit can be used via direct heating and coal fluidization medium. For an indirect heating coal dryer system, a closed loop high pressure water system can be designed to transfer low grade heat from turbine exhaust stream to the dryer to remove moisture from coal.

Hazardous gases (CO, NOx, CH4 and C3H8) released from CO2 fertilizer unit lead to oxidative damage and degrades photosynthesis in strawberry plants

CO2 boilers/direct heating systems used in greenhouses often lead to incomplete combustion, which results in the formation of hazardous gases, such as carbon monoxide (CO), nitroxide (NOX) and other hydrocarbons. In this study, strawberry plants that were grown on rockwool cubes were transferred to airtight bottles and treated with CO, NOX, CH4 and C3H8 gases for 1–48 hours. Oxidative damage due to hazardous gases was observed, as indicated by H2O2 and {{bf{O}}}_{{bf{2}}}^{{boldsymbol{-}}1} determination. Photosynthetic pigments were reduced, and stomatal guard cells were damaged and remained closed compared to the control. The activity of other photosynthetic parameters was negatively related to hazardous gases. Reduction in the expression of multiprotein complexes was highly observed under hazardous gas treatments. This study highlighted that hazardous gases (CO, NOX, CH4 and C3H8) emitted due to incomplete combustion of CO2 fertilization units/or direct heating systems resulted in the formation of ROS in shoots and limited photosynthetic metabolism. We predicted that major steps must be incorporated to improve the efficiency of CO2 boiler/heating systems to decrease the emission of these hazardous gases and other hydrocarbons and to reduce the observed risks that are key to the reduction of crops.

Increasing Solar Energy Usage for Dwelling Heating, Using Solar Collectors and Medium Sized Vacuum Insulated Storage Tank

This article describes a method for increasing the solar heat energy share in the heating of a dwelling. Solar irradiation is high in summer, in early autumn, and in spring, but during that same time, the heat demand of dwellings is low. This article describes a solution for storing solar heat energy in summertime as well as the calculations of the heat energy balance of such a storage system. The solar heat energy is stored in a thermally insulated water tank and used in the heating period. The heat is also stored in the ground if necessary, using the ground loop of the heat pump if the water tank’s temperature rises above a certain threshold. The stored heat energy is used directly for heating if the heat carrier temperature inside the tank is sufficient. If the temperature is too low for direct heating, then the heat pump can be used to extract the stored energy. The calculations are based on the solar irradiation measurements and heating demand data of a sample dwelling. The seasonal storing of solar heat energy can increase the solar heat energy usage and decrease the heat pump working time. The long-term storage tank capacity of 15 m3 can increase the direct heating from solar by 41%. The direct heating system efficiency is 51%.

Numerical simulation for treatment of hypothermia based on vascular interventional direct heating system

The treatment of hypothermia suffered by naval fighters owing to seawater immersion has been a focus of research in recent years. Currently, the treatment of hypothermia in China is limited to external rewarming, which is of low efficiency and is not effective for patients suffering moderate to severe hypothermia. We thus proposed a vascular interventional heating method which directly heats the blood flow via a minimally invasive heating needle for rewarming. And a numerical simulation using a compartment model based on finite difference method was conducted. A set of whole body heating treatment simulation was also developed. Appropriate treatment parameters and procedures can be set and adjusted based on patient physical parameters. Here temperature response curves of different heating modes were obtained and analyzed. It was demonstrated that the desired thermal response can be achieved by adjusting the heating power and heating time, ensuring controllable accuracy in the treatment of patients with severe hypothermia. The proposed treatment for hypothermia is a new and effective alternative, and further progress is expected in clinical trials.

Impact of direct and indirect heating systems in broiler units on environmental conditions and flock performance

This study compared the impact of three indirect heating systems to direct gas flame heaters on a selection of flock performance and environmental indicators in commercial broiler units. No statistically significant differences (P≥0.05) were found in flock mortality rates, bird weight, water consumption, stress response, carbon dioxide, ammonia, temperature, relative humidity, litter quality, within-flock Campylobacter levels or mean Campylobacter counts when flock data from any of the three indirect heating systems were compared to flocks reared in houses with direct heating systems. Differences in litter quality were observed between upper and lower litter layers in all houses, regardless of heating type, which may have implications for bird health and welfare. Carbon dioxide concentrations in houses with direct heating systems were significantly higher than those in houses with indirect heating systems during the first 10 days of bird life (P≤0.05). This was due to the increased use of heating systems during this period of the flock cycle. Differences in CO2 concentrations had no effect on flock performance, possibly due to the fact that concentrations did not exceed known safe levels. A statistically significant increase in stress response was observed in birds as a result of partial depopulation (thinning) within houses, irrespective of heating system type used (P≤0.05). Stress associated with thinning may have consequences for bird welfare and food safety. In conclusion, the results of our study suggest that indirect heating systems do not appear to negatively impact on flock performance, stress response, within-flock Campylobacter levels or mean Campylobacter counts and do not appear to significantly alter environmental conditions within broiler houses when compared to houses equipped with direct heating systems. Indirect systems are a viable alternative for heating broiler houses in terms of flock performance, bird welfare and food safety.

Hot incremental forming of magnesium and aluminum alloy sheets by using direct heating system

This article presents the use of an electrically assisted manufacturing method in the incremental sheet forming process to improve formability, surface quality, and geometric accuracy. This system utilizes a direct current source connected directly to a metal sheet through two electrodes at opposite edges to conduct heat based on Joule’s effect. The approach produces a homogeneous heating zone in the whole metal sheet with very short ramping time. In this work, the heating system is designed to serve the investigation of formability, geometric accuracy, and surface roughness of the hot incremental forming technology. Three main results expected from this system are the influence of the processing parameters on the formability, the ability to improve accuracy and formability, and the reduction or elimination of springback effects in the deformation of high-strength aluminum alloy sheets (AA5055) and magnesium alloy sheets (AZ31).

Extreme high-temperature treatment of milk with respect to plasmin inactivation

The thermal inactivation of plasmin in combination with the denaturation of β-lactoglobulin was studied using a newly developed Innovative Steam Injection (ISI) system, a direct heating system with a very short heating time combined with very high temperatures (0.2 s, 150–180 °C). The model for inactivation of plasmin was improved by integrating the effect of the formation of (partly) denatured β-lactoglobulin during pre-heating on the kinetics of plasmin inactivation. By applying these new kinetics, the heat load of milk by currently applied UHT-treatments can be reduced while obtaining a sufficient inactivation of plasmin (i.e., <1%). It turned out that it is possible to decrease the plasmin activity below 1% of the initial value and concomitantly to achieve >5.5 decimal reduction of Bacillus sporothermodurans while computer simulations showed the denaturation of β-lactoglobulin to be minimized.

A High-Temperature Catalytic Combustor With Starting Burner

A catalytic combustion system has high potential to achieve low NOx emission level. When this combustion system is applied to a gas turbine, the required combustor performance must be maintained over a wide range of operating conditions. These conditions range from cold starting to steady-state operation. Particularly during the initial stage of cold starting when the catalyst is not yet activated, the catalyst must be heated by some means. This study proposes a new concept of a catalytic combustor with a direct heating system using vaporizing tube for starting burner in order to downsize the combustor and reduce the warm-up time during cold starts. The effectiveness of this concept is experimentally verified. Furthermore, NOx, CO, and HC emissions during startup can be reduced to a low level so as to achieve ultra-low pollution of the catalytic combustion over a wide range of operating conditions from cold start to steady-state operation. This paper outlines the operation concept covering cold start, verification of the concept through the experiments with flame visualization in the combustor, spray characteristics, construction of the combustor, and combustion characteristics that show low pollution in various operating conditions of the catalytic combustor.

Stability of Cholesterol and Paprika Carotenoids in Egg Powders as Influenced by Dietary and Processing Treatments

The effects of dietary α-tocopherol and/or oleoresin paprika (OP) on cholesterol and carotenoid stability in egg powders during spray drying and subsequent storage were investigated. Cholesterol oxidation and loss of carotenoids in eggs dried with a direct gas-fired spray dryer were greater (P < 0.05) than in eggs dried using an indirect (electric) heating system. Dietary supplementation of α-tocopherol acetate (200 mg kg -1 feed) significantly increased (P < 0.01) the oxidative stability of cholesterol and carotenoids in eggs dried with the direct heating system. Supplementation of OP (7.5 μg g -1 egg lipids) through diet or by direct addition to liquid eggs did not affect the formation of cholesterol oxidation products (COPS) during storage. However, increased concentrations of OP in liquid eggs (15 and 30 μg g -1 lipids) suppressed the formation of COPS during processing and subsequent storage.

Stability of Cholesterol and Paprika Carotenoids in Egg Powders as Influenced by Dietary and Processing Treatments

The effects of dietary α-tocopherol and/or oleoresin paprika (OP) on cholesterol and carotenoid stability in egg powders during spray drying and subsequent storage were investigated. Cholesterol oxidation and loss of carotenoids in eggs dried with a direct gas-fired spray dryer were greater (P<0·05) than in eggs dried using an indirect (electric) heating system. Dietary supplementation of α-tocopherol acetate (200 mg kg−1 feed) significantly increased (P<0·01) the oxidative stability of cholesterol and carotenoids in eggs dried with the direct heating system. Supplementation of OP (7·5 μg g−1 egg lipids) through diet or by direct addition to liquid eggs did not affect the formation of cholesterol oxidation products (COPS) during storage. However, increased concentrations of OP in liquid eggs (15 and 30 μg g−1 lipids) suppressed the formation of COPS during processing and subsequent storage.

Process Systems Engineering. Heat Sterilization and Viscosity Change of Fresh Cream.

Heat sterilization causes evident viscosity change of fresh cream as well as a change in other physical properties due to heat denaturation. This experimental study shows that the viscosity changes can be summarized by using a C-value defined with the calculation method here, which is found to be commonly applicable to plate type indirect heating systems and two kinds of typical steam direct contact heating systems, showing the same tendency regardless of the heating system. It is suggested that the direct heating system is better in order to get a lower viscosity change with the same sterilization effect.