Changes In Heat Load Research Articles

Boundary Layer Flashback Limits of Hydrogen-Methane-Air Flames in a Generic Swirl Burner at Gas Turbine-Relevant Conditions

AbstractOperating stationary gas turbines on hydrogen-rich fuels offers a pathway to significantly reduce greenhouse gas emissions in the power generation sector. A key challenge in the design of lean-premixed burners, which are flexible in terms of the amount of hydrogen in the fuel across a wide range and still adhere to the required emission levels, is to prevent flame flashback. However, systematic investigations on flashback at gas turbine relevant conditions to support combustor development are sparse. The current work addresses the need for an improved understanding with an experimental study on boundary layer flashback in a generic swirl burner up to 7.5 bar and 300 °C preheat temperature. Methane-hydrogen-air flames with 50 to 85% hydrogen by volume were investigated. High-speed imaging was applied to reveal the flame propagation pathway during flashback events. Flashback limits are reported in terms of the equivalence ratio for a given pressure, preheat temperature, bulk flow velocity, and hydrogen content. The wall temperature of the center body along which the flame propagated during flashback events has been controlled by an oil heating/cooling system. This way, the effect any of the control parameters, e.g., pressure, had on the flashback limit was decoupled from the otherwise inherently associated change in heat load on the wall and thus change in wall temperature. The results show that the preheat temperature has a weaker effect on the flashback propensity than expected. Increasing the pressure from atmospheric conditions to 2.5 bar strongly increases the flashback risk, but hardly affects the flashback limit beyond 2.5 bar.

Projected changes in heat load in Carpathian Basin cities during the 21st century

In this study the changes in the nighttime heat load in Carpathian Basin cities during the 21st century were examined. To quantify the heat load, the tropical night climate index was used. The MUKLIMO_3 local scale climate model was used to describe the urban processes and the land use classes were defined by the local climate zones. The expected change was examined over three periods: the 1981–2010 was taken as reference period using the Carpatclim database and the 2021–2050 and 2071–2100 future periods using EURO-CORDEX regional model simulation data for two scenarios (RCP4.5 and RCP8.5). To combine the detailed spatial resolution and the long time series, a downscaling method was applied. Our results show that spectacular changes could be in the number of tropical nights during the 21st century and the increasing effect of the urban landform is obvious. In the near future, a slight increase can be expected in the number of tropical nights, which magnitude varies from city to city and there is no major difference between the scenarios. However, at the end of the century the results of the two scenarios differ: the values can be 15-25 nights in case of RCP4.5 and 30-50 nights in case of RCP8.5. The results show that dwellers could be exposed to high heat load in the future, as the combined effect of climate change and urban climate, thus developing various mitigation and adaptation strategies is crucial.

Projected changes in heat load in Carpathian Basin cities during the 21st century

In this study the changes in the nighttime heat load in Carpathian Basin cities during the 21st century were examined. To quantify the heat load, the tropical night climate index was used. The MUKLIMO_3 local scale climate model was used to describe the urban processes and the land use classes were defined by the local climate zones. The expected change was examined over three periods: the 1981–2010 was taken as reference period using the Carpatclim database and the 2021–2050 and 2071–2100 future periods using EURO-CORDEX regional model simulation data for two scenarios (RCP4.5 and RCP8.5). To combine the detailed spatial resolution and the long time series, a downscaling method was applied. Our results show that spectacular changes could be in the number of tropical nights during the 21st century and the increasing effect of the urban landform is obvious. In the near future, a slight increase can be expected in the number of tropical nights, which magnitude varies from city to city and there is no major difference between the scenarios. However, at the end of the century the results of the two scenarios differ: the values can be 15-25 nights in case of RCP4.5 and 30-50 nights in case of RCP8.5. The results show that dwellers could be exposed to high heat load in the future, as the combined effect of climate change and urban climate, thus developing various mitigation and adaptation strategies is crucial.

Influence of field-dependent critical current on harmonic AC loss analysis in HTS coils for superconducting transformers supplying non-linear loads

There are two main obstacles in front of the development of high temperature superconducting (HTS) technology for electric power network applications; tape price and cooling cost. In order to reduce cooling cost, it is vital to evaluate AC transport current loss of the tapes precisely and then reduce it by some design innovative approaches. In addition, AC transport current loss in HTS material is a critical design variable for large-scale power network applications such as HTS transformers, superconducting fault current limiters, and power cables, since they are continuously carrying the network/load current during their operating life. In existing power networks, harmonic production sources are commonly used and thus, currents are distorted. Therefore, the effect of nonsinusoidal current on the critical apparatus in the network such as transformer must be studied. In this paper, AC transport current loss of a single-turn 2G YBCO HTS coil was modeled and numerically calculated under nonsinusoidal transport current using finite element method. Furthermore, influence of dependency of critical current density to magnetic field on the AC transport current loss of HTS coil when carries distorted currents was considered. It was observed that nonsinusoidal current causes excessive losses in HTS coil. On the other hand, a case study on an HTS transformer supplying non-linear load was considered to study the loss increment as well as heat load change. It was observed that current harmonics increases the AC loss, and heat load of transformer and decreases the efficiency, consequently.

Double-feedback control with stepless variable speed driving technology by sensing refrigerant pressure and indoor temperature applied to air conditioning system

An energy-saving strategy of variable refrigerant volume (VRV) is proposed for air conditioning systems by using the stepless variable speed driving technology. This control technology is applied to the air cooled packaged water chiller unit (ACH) according to the change of environmental heat load to achieve the best amount of refrigerant in real time. This study designs a double feedback Stepless Variable Frequency and Variable Refrigerant Output (DFSVFVRO) for controlling ACH. The double feedback variable frequency control uses both temperature and the pressure sensors as feedback signals to the control board and the frequency of the compressor is regulated by the inverter. Experimental results indicate that the proposed variable frequency control method has a lower energy consumption compared with the conventional normal mode (N). In addition, the proposed double feedback mode (DF) has a lower energy consumption, and thus, it is with better energy efficiency. Furthermore, in the various experiments of proposed DFSVFVRO by comparing the cumulative energy consumption of DF mode with N mode, the DF mode shows an energy saving rate of at least 25%. It also verifies that the double feedback variable frequency control method has a better energy-saving benefits than that of the single feedback frequency.

Research on Variable Operating Characteristics of Condenser Considering Vacuum Tightness

Considering the effect of vacuum tightness on the performance of condensers, the influence of various operating parameters on condenser pressure and terminal difference was studied by establishing a calculation model of variable operating conditions of condensers. The results show that the change of heat load has a greater impact on the vacuum, and the effect is more pronounced when the initial temperature of the cooling water is higher. Therefore, it is necessary to strictly control the internal leakage of the valve, reasonably adjust the steam parameters of the shaft seal, and minimize the additional heat load on the condenser. The cooling water flow and initial temperature directly affect the condenser vacuum and have a greater impact. The initial temperature of the cooling water is not easy to control. When the initial temperature is high, most power plants use a method of increasing the flow to increase the condenser vacuum. The cleaning coefficient and air leakage have a great impact on the quality of the vacuum. Therefore, regular operation of the rubber ball cleaning system and timely vacuum leak detection are necessary measures to ensure the vacuum of the unit, which can effectively improve the economic efficiency of the unit.

Analysis of the reliability of heat supply from hybrid energy source based on WPP and CHPP

The paper is devoted to the problem of the reliability analysis the functioning of the hybrid energy source based on the wind power plant (WPP) and the combined heat and power plant (CHPP). The main effect of the proposed technology is substituting a part of the fossil fuel used at CHPP (or other heat sources) for the production of electricity and thermal energy. At the same time, CHPP operates according to the heat schedule, i.e. in accordance with changes in the heat loads of consumers. In this regard, the attention in the study is focused on the problem of the reliability analysis of the heat supply (heating) from a hybrid energy source. To assess the reliability of heat supply, one of the main complex reliability index (RI) is used - the availability factor (AF), and the system of equations of a stationary markov process is used as a mathematical model of the states evolution of the studied object. Calculation of AF is made in accordance with seasonal changes in heat loads (annual heat load schedule); the heat storage effect of consumers (thermal inertia) and the factor of a possible decrease in wind speed are also additionally taken into account. Case study is carried out on a test circuit of the hybrid energy source (WPP+CHPP), as a result of which some analytical characteristics are obtained.

Phytoplankton of the cooling waterbody of the Lukoml state district power station under changing anthropogenic load

The paper presents the results of long-term research of phytoplankton of the cooling waterbody of the Lukoml state district power station (Belarus). The dynamics of abundance, biomass, community structure, and composition of the dominant phytoplankton species for the period of 1972 – 2019 were analyzed. The stages of development of the plankton algae community are determined, due to changes in the intensity and direction of anthropogenic factors. The response of phytoplankton to changes in heat load and dependence on the development of the population of Dreissena polymorpha Pallas is shown. The influence of the fish rearing complex on the developmental intensity and phytoplankton structure was revealed. Since 2004, the periods of intensive vegetation of algae alternate with a significant decrease in abundance and biomass, which indicates the unstable state of the ecosystem of the cooling waterbody. The succession of the dominant complex in 2019 was characterized by the loss of the species Aphanizomenon flos-aquae Ralfs ex Bornet & Flahault (family Nostocaceae) and the inclusion of the species Planktothrix agardhii (Gomont) Anagnostidis & Komárek (family Oscillatoriaceae).

Experimental investigation on operating behaviors of loop heat pipe with thermoelectric cooler under acceleration conditions

An experimental study was carried out in this article to investigate the transient operating performance of a Dual Compensation Chamber Loop Heat Pipe (DCCLHP) with Thermoelectric Cooler (TEC) under acceleration conditions and ammonia was selected as the working fluid. For the purpose of comparison, experimental work was conducted under terrestrial gravity. Sensitivity analysis was performed to explore the effect of several control parameters such as the heat load, acceleration magnitude and TEC assist on the startup and operating performance of the DCCLHP. Experimental results indicate that the DCCLHP can get to a steady-state operation when the heat load changes from 25 W to 300 W under terrestrial gravity. While under acceleration conditions, the DCCLHP can work at a high operating temperature or even fail to operate, which shows the acceleration effect plays a significant impact on the loop operation. The TEC assist with power of 10 W can improve the operating performance and reduce the operating temperature for the case of small heat load and acceleration magnitude. When the acceleration exceeds 3g at large heat load, the effect of TEC assist on the operation at large heat load can be ignored.

Comparative study of two loop heat pipes using R134a as the working fluid

In order to promote future commercial applications of loop heat pipe (LHP) especially in the civil fields, environmentally friendly R134a is considered a good candidate working fluid to replace the commonly used anhydrous ammonia. In this work, two sets of LHPs with R134a as the working fluid were designed and fabricated, one with a nickel wick, and the other with a stainless steel wick. Their thermal performance, mainly including the startup, the power increment test, the thermal resistance and the heat transport capability, were experimentally studied, evaluated and compared. Based on the experimental results, it is found that both of the R134a LHPs present excellent startup performance, achieve a maximum heat transfer capacity greater than 100 W, and exhibit good response characteristics to stepwise change of heat load. The R134a LHP with a nickel wick shows good anti-gravity capability; however, the one with a stainless steel wick is quite sensitive to the adverse elevation. The physical mechanisms responsible for the experimental results mentioned above have been analyzed and discussed. This work contributes to a better understanding on the operating performance and characteristics of the R134a LHPs, providing good design guidance and reference for its future applications.

Performance and emissions of pre-mixed and post-mixed combustion systems with a casting aluminum-silicon alloy (CASA) condensing gas boiler

Condensing gas boilers are widely employed for their high heat efficiency, which attributes to their ability to use the recoverable sensible heat and latent heat in flue gas. In this paper, the optimal excess air rate of a novel condensing gas boiler is investigated experimentally. With the change of excess air rate, the pre-mixed and post-mixed systems were used to study the performance, the thermal efficiency and emissions of the boiler. The CO emission reduces firstly then increases regardless of which premixed system, when the excess air rate is from 1.15 to 1.4. The NOx emission decrease from 64 ppm to 10 ppm and the efficiency decreases from 64 ppm to 19 ppm as the excess air rate increases from 1.15 to 1.4. The efficiency decreases from 102.05% to 98.7% and the efficiency decreases from 100.9% to 97.6% as the excess air rate increases from 1.15 to 1.35. Considering both NOx emission and thermal efficiency, the optimum excess air rate is 1.23. With the change of heat load, the emission, the fan speed and the thermal efficiency of the two system were compared. The concentration of CO increases from 7.5 ppm to 65.5 ppm when the pre-mixed system heat load changes from 8 kW to 24 kW. The efficiency of post-mixed system decreases from 106.5% to 97.5% and the efficiency of pre-mixed system decreases from 106.9% to 96.8% as the heat load increases from 9 to 26 kW. The variation of thermal efficiency and condensate volume with various heat load in the post-mixed system with different return water temperature are also studied. The efficiency decreases from 107% to 98.5% as the heat load increases from 9 to 24 kW at the inlet of return water is 30 °C. And the vapor condensation ratio ω decreases from 105% to 97.5% as the heat load increases from 9 to 24 kW at the inlet of return water is 40 °C. In summary, post-mixed system is more suitable for the development of small condensing boilers. The lower the return water temperature and heat load, the higher the thermal efficiency of boiler.

ХОЛОДОПРОДУКТИВНІСТЬ СИСТЕМИ КОНДИЦІЮВАННЯ ЗОВНІШНЬОГО ПОВІТРЯ ЗА ПОТОЧНИМ ТЕПЛОВИМ НАВАНТАЖЕННЯМ

The efficiency of the outdoor air conditioning systems application depends on how full the installed cooling capacity is applied, that is, with a more complete load and for as long as the possible yearly duration in actual climatic conditions. The production of cold is taken as a criteria of a quantitative evaluation of the efficiency of applying the cooling capacity of air conditioning systems – the amount of cold produced in accordance with its current demand for air conditioning, which in turn depends on the current consumption of cooling capacity and its duration and equals to their multiplication. It is obvious that the maximum value of the current amount of cold produced/consumed indicates an effective application of the installed cooling capacity. However, since the current demands of cooling capacity and their duration, that is, the amount of cold produced/consumed, depending on the changing current climatic conditions, they are characterized by significant fluctuations, which makes it difficult to choose the installed cooling capacity of the air conditioning system. Obviously, if we determine the amount of cold produced/consumed by its current values and summarized during the year, it is possible to significantly simplify the choice of the installed cooling capacity. At the same time, the current amount of cold produced/consumed causes a change in the rate of increment of the annual cold production with a change in the installed cooling capacity, and the maximum rate corresponds to the installed cooling capacity, which provides its efficient use. Proceeding from a different rate of increment of annual cold production with an increase in the installed cooling capacity of the air conditioning system due to a change in heat load in accordance with current climatic conditions during the year, the value of design heat load on the air conditioning system (installed cooling capacity) that provides maximum or close to it the rate of increment of the annual production of cold, and hence the maximum efficient use of installed cooling capacity is chosen

Assessment of heat-to-power ratio in a bio-oil sorption enhanced steam reforming and solid oxide fuel cell system

A solid oxide fuel cell (SOFC) is a high-efficiency technology for combined heat and power (CHP) generation. Heat and power production can be varied according to changes in heat and power loads, which affect the electrical and thermal efficiencies. This study analyzes changes in heat and power production rates of a bio-oil sorption enhanced steam reforming (SESR) and SOFC system. The variations in the stack-to-burner ratio (bio-oil split fractions), fuel utilization factor (Uf), and recirculation ratio (R) are investigated. The effect of heat-to-power ratio on the system performance and CO2 capture efficiencies is also studied. Moreover, the benefit of the implementation of a bio-oil SESR and SOFC system over a conventional operation to match the energy demand for an industrial case is evaluated. The results reveal that an increase in Uf decreases the operating range of the heat-to-power ratio. On the other hand, the anode gas recirculation ratio affects such a parameter when the system performs at the high stack-to-burner ratio. A higher heat-to-power ratio increases the stack electrical and thermal efficiencies, leading to a higher CHP efficiency. The heat-to-power ratio of the proposed system varies between 0.05 and 7.5. However, to attain a CO2 capture efficiency higher than 50%, the heat-to-power ratio should be lower than 1.5. By comparing the two operational strategies: fixed heat-to-power ratio, and variable heat-to-power ratio, it is found that the heat-to-power ratio is an important factor for energy management. The primary energy saving is enhanced when the system is operated to satisfy the rates of heat and power demand.

Integrating carbon capture into an industrial combined-heat-and-power plant: performance with hourly and seasonal load changes

The present work aims to map the variations in process gas and available excess heat of an integrated steel mill and to investigate the effects of these variations on the performance of a chemical absorption CO2 plant. Two time-scales are considered for the variations: seasonal and hourly changes. Dynamic process simulations are used to investigate the dynamic interactions between the steel mill and the capture unit. This includes the effect that periodic variations in the reboiler heat duty have on the performance of the capture plant and the effect of implementing a control strategy. The mapping of the operation of the steel mill reveals numerous variations on an hourly basis that are important for the design and operation of the capture plant, including decreases in the blast furnace gas (BFG) flow to 0% on approximately 10 occasions per year and variations of ±30 MW in the available heat more than 40 times per year. The simulations show that the capture unit responds very differently depending on the season, with a generally slower response during winter operation due to a lower level of circulation of the solvent. The capture unit shows also non-linearity in its response to changes in heat load - the deviation from the steady-state value is more pronounced when the heat is increased than when it is decreased. Thus, the simulation results indicate that implementing CO2 capture with chemical absorption in an integrated steel mill requires flexible operation of the capture plant. Dynamic simulations over a two-week period with historical (hourly) boundaries demonstrate that the capture process can operate in the presence of the steel mill variations. Implementation of a decentralized control strategy increases the amount of captured CO2 by 1.2%.

МЕТОДОЛОГИЧЕСКИЙ ПОДХОД К ЭНЕРГОСБЕРЕГАЮЩЕМУ ХЛАДОСНАБЖЕНИЮ СИСТЕМ КОНДИЦИОНИРОВАНИЯ ВОЗДУХА АДАПТАЦИЕЙ К ТЕКУЩИМ КЛИМАТИЧЕСКИМ УСЛОВИЯМ

The methodological approach was suggested to define a rational heat load of the air conditioning system (ACS) with taking into consideration the current climatic conditions of operation. The proposed approach is based on the hypothesis of sharing the current changeable heat load on the relatively stable share as the basic one for choosing installed (designed) refrigeration capacity of the refrigeration machine, operating with high energy efficiency in nominal or similar modes, and unstable heat load, corresponding to ambient air precooling at changeable current temperatures. To prove the methodological approach to defining a rational heat load of the ACS was carried out the analysis of current values of heat loads of the refrigeration machine ACS during cooling ambient air from its changeable current temperature to the temperature of 10, 15 and 20 ºС . It is shown that due to the different rates of annular refrigeration capacity production increment to cover the current heat loads with increasing the installed refrigeration capacity of the refrigeration machine, caused by the changes in heat load according to current climatic conditions during all the year round, it is necessary to choose a such heat load on the refrigeration machine of ACS (its installed refrigeration capacity), that provides a maximum or similar annular refrigeration capacity production at relatively high rates of its increment. Therein, the value of heat load for ambient air precooling is calculated according to remained principle as the difference between the rational total heat load and its basic relatively stable share. The proposed method is useful for defining a basic installed refrigeration capacity of the refrigeration machine of ACS with the accumulation of excessive (unapplied) refrigeration capacity at lowered current heat loads on ACS and its application for ambient air precooling, that is for covering unstable heat load share on ACS

Study on Temperature Rise Modeling of Main Motor of Hot Rolling Mill Based on Support Vector Machines

Along with the ongoing process of the adjustment of industrial structure in China, overcapacity of the traditional heavy industry has become an issue of deep concern, and the direct consequence of overcapacity is energy waste. Tandem rolling mill is the typical equipment whose designed capacity is greater that the current real need. In many steel mills the practical work load of tandem rolling mill is far below the rated, while its forced-air cooling motor still runs at full capacity regardless of any change of heat load or season, leading to energy waste. Adjusting drive frequency of the air cooling motor according to its heat load is a practical and feasible measure for energy saving. As one of the important aspects of variable speed control of the air-cooling motor, to establish a precise temperature rise model for the object is critical. This research focuses on the temperature rise modeling of the main motor of hot rolling mill. The temperature rise mechanism of the main motor is first analyzed, and then the support vector machines regression algorithm is used for parameter identification of the model. To ensure the security and reliability of the production line, different penalty coefficients are adopted for positive error and negative error. Long term workshop data are collected and used for comparison with the predicted data. Comparison results demonstrate the feasibility of the established model.

Experimental study of an ammonia loop heat pipe with a flat disk-shaped evaporator using a bimetal wall

A loop heat pipe (LHP) with a flat disk-shaped evaporator 40mm in diameter and 18mm in thickness has been developed and tested. The device was made of stainless steel and equipped with a main nickel biporous wick and a secondary wick made of a porous material with a low thermal conductivity. The flat evaporator wall being heated was made of a “stainless steel – copper” bimetal. The working fluid was ammonia. The LHP thermal characteristics were investigated at different orientations with slopes from −90° to +90° and heat sink temperatures in the range from 0 to 40°C. A maximum heat load of 300W (23.9W/cm2) at an evaporator temperature of no more than 80°C was achieved at both a favorable and a horizontal orientation of the LHP. A minimum thermal resistance of the evaporator of 0.067°C/W was obtained at a heat load of 220W. The corresponding value of the LHP thermal resistance was equal to 0.084°C/W. It has been found that under changes of orientation in the whole range of slopes the maximum heat load changes no more than 30%. It is shown that a heat source temperature not more than 85°C can be ensured in all test conditions at heat loads up to 140W.

Spallation target cryogenic cooling design challenges at the European Spallation Source

The European Spallation Source (ESS) project is a neutron spallation source research facility currently being designed and built outside of Lund, Sweden. A linear accelerator delivers a 5 MW, 2.0 GeV, 62.5 mA proton beam to a spallation target to generate fast neutrons. Supercritical hydrogen circulates through two moderators surrounding the target, and transforms the fast neutrons emitted into slow neutrons, which are the final form of useful radiation. The supercritical hydrogen is in turn cooled from a helium cryogenic plant operating at 15-20 K. The supercritical cryogenic hydrogen circuit is a dynamic system, subject to significant changes in heat load. Proper pressure control of this system is critical to assure safe operation. The interaction between the hydrogen system and helium cryoplant poses unique challenges. This paper investigates the impact of the hydrogen system constraints on operation and control of the helium cryoplant, and suggests design options for the helium circuit.

RF heat load compensation with electrical heater for XFEL accelerator - measurements at CMTB, AMTF and FLASH

A superconducting linac will provide electron bunches of 17.5 GeV beam energy for the operation of the European X-ray Free Electron Laser (XFEL) at DESY. 800 superconducting niobium 1.3 GHz nine cell cavities and 100 superconducting magnet packages will be cooled in a liquid helium II cooling bath at 2.0K temperature. Liquid helium II bath cooling at 2.0K is established by means of a 4 stages cold compressor system. For the stable operation of cold compressors sudden load changes should be avoided. Electrical heaters in the helium II bath will compensate dynamic heat load changes caused by the radio frequency (RF) operation of the cavities in the XFEL linac. The complementary load operation of electrical heaters is studied at the existing facilities at DESY. Measurements performed at Cryo Module Test Bench (CMTB), Accelerator Module Test Facility (AMTF) and FLASH accelerator are reported.

A confidence index for Toxicity Reference Value to inform risk assessors and managers about the quality of the value

Based upon an existing building and heating system with thermostatic radiator valves (TRVs), an integrated model is developed for simulating the thermal and hydraulic behavior of the heating system under various operation cases. According to the simulation results, the effectiveness of TRVs in reducing overheating has been studied. The results indicate that when the set value of the TRV is kept at 2–3, its effectiveness in reducing the overheating phenomena caused by an excessive water flow rate is less than 60%. If the overheating phenomena is caused by an excessive supply water temperature and radiator area, the effectiveness of the TRV can reach about 80%; the TRV's effect becomes more obvious with increasing overheating degree; however, about 20%–40% of overheating loss still needs to be resolved by improving improper operation adjustment and design. Considering these results, a control strategy is proposed, in which the supply water temperature is adjusted daily according to the flow performance of the system, and the pump is operated with frequency conversion and constant pressure difference. Further simulation indicates that, under the new control strategy, the variation of the heat supply quantity of the system can match the heat load change, and the flow rate of the system can be controlled at an appropriate range.