Thermal Balance Method Research Articles

Flammability limits of theoretical azeotropic mixtures consist of R1243zf, RE170 and flame retardants (R13I1, R134a, or R227ea)

3,3,3-trifluoropropene (R1243zf) is a low climate change effect refrigerant that has great development potential. However, R1243zf is flammable and its safety classification is A2 as per ISO standard 817. To reduce its risk of flammability, the method of using mixed refrigerants in practical applications is an effective approach. In this paper, an experimental system was established according to the ASHRAE standard 34 to measure the flammability limits of four azeotropic mixtures containing R1243zf. First, the critical suppression ratio (CSR) of R13I1/R1243zf was tested out that is 0.353. Further measurements were made to determine the lower flammability limits (LFLs) and critical suppression concentrations (CSCs) of three ternary mixtures consisted of R1243zf, thermodynamic performance enhancer (RE170) and flame retardants (R13I1, R134a or R227ea), at various compositions. The experimental non-flammable proportions of R1243zf/RE170/R13I1, R1243zf/RE170/R134a, and R1243zf/RE170/R227ea were 31.81 %, 5.49 %, and 22.42 %, respectively. Besides, a comparison was made between the experimental data and the predicted results by means of three different theoretical methods (the equal effect method, thermal balance method, and group contribution method). The fresh experimental results will provide practical guidance for the applications that utilize the R1243zf blends in low flammability risk.

Optimization of Arabinogalactan Sulfation in Process Scaling

To ensure the safety of the arabinogalactan sulfation process, the thermal effect of the reaction (148.26 kJ) was determined by the thermal flux balance method. The dependence of the dynamic viscosity of the reaction medium on the way of introducing the sulfating agent and on its particle size was studied by phase rheology. The stirring process was calculated to substantiate the optimum stirrer design and determine the quality parameters of stirring of the reaction medium. The data obtained allow optimization of the process for producing Agsular® substance in scaling of the production technology.

A thermal balance method for measuring thermal conductivity by compensation of electric cooling or heating based on thermoelectric modules

To achieve the accuracy and convenience of thermal conductivity measurement, a thermal balance method for measuring thermal conductivity by compensation of electric cooling or heating based on thermoelectric modules is proposed in this paper. In this method, the thermoelectric module is regarded as the compensation unit to achieve the thermal balance between the compensation and test sides. Using the balance principle, the sample's thermal conductivity to be measured can be obtained by knowing the thermal conductivity of the compensation side. According to theoretical and experimental research, the compensation model is divided into self-supply energy and energy supply modes, and the law of thermal conductivity changes in thermoelectric modules in the two supply modes is summarized. To verify the feasibility of the thermal balance method, the thermal conductivity of alumina ceramics and polymethyl methacrylate (PMMA) materials with large differences in thermal conductivity were measured. The experiment proved that the thermal conductivity of alumina ceramic is 19.23 W/mK, slightly smaller than the standard value. The average thermal conductivity of PMMA is 0.21 W/mK, consistent with standard values. Taking the experiment conditions and error into account, the data are effective, which verified the feasibility of this method.

Exergy and performance analysis of low GWP and Non-flammable HFO based refrigerant mixtures as alternatives to R134a

R1234yf and R1234ze(E) can be potential retrofits for the conventional refrigerants used in domestic refrigerator provided their flammability is controlled. In this study, the inerting effect of the dilutants R125, R134a, R227ea and R245fa on R1234yf and R1234ze(E) based ternary mixtures is studied theoretically. R152a, R161 and RE170 are used as the secondary refrigerants with R1234yf and R1234ze(E) based ternary mixtures. Minimum inerting concentration (most important parameter that decides the flammability of the mixture) is estimated with thermal balance method (TBM) and modified thermal balance method (MTBM) for the selected mixtures. The calculated MIC values are compared with 86 experimental data points (both binary and ternary) available in the literature. It is calculated that TBM and MTBM predicted the minimum inerting concentration values (for a majority of the mixtures) within ±30% and ±8% respectively when compared with the experimental data. The COP ratios of the non-flammable mixtures (that are proposed with MTBM) are estimated and is found to be maximum at a volumetric cooling capacity ratio close to 0.8. It is also calculated that the exergy efficiency varied between 0.54 to 0.64 for the low GWP mixtures (M1 to M5) proposed in this study.

Effect of dilutant concentration on the performance of environment-friendly mixed refrigerants used in domestic refrigerators.

This paper presents the environment-friendly mixture compositions of hydrocarbons (HC)- and hydrofluorocarbon (HFC)-based ternary mixtures that can be better alternatives for R134a in domestic refrigeration units. Combustible refrigerant HCs (R290, R600, R600a) and HFCs (R152a and R161) are used along with the dilutants R13I1, R245fa, R134a, R227ea, and R125 and their flammability studies were carried out theoretically. Minimum inerting concentration (MIC) is used to classify the flammable and non-flammable zones of the ternary mixtures. MIC points estimated with modified thermal balance method (MTBM) are compared with 62 experimental data points available in the literature. It was calculated that MTBM predicted the MIC values with in ±9%, for most of the working fluids selected in this study. R13I1 is used along with all the refrigerant (HC and HFC) combinations (as the first dilutant) while the effect of other dilutants on the system performance is carried out theoretically. It is predicted from the flammability diagram (developed in this study) that the inert effect of R227ea is higher than of R245fa, R134a, and R125. It is also observed that the drop in coefficient of performance (COP) is significant with R290/R13I1/R245fa (with increase in R245fa) mixture when compared to other combinations. Finally, mixtures R600a/R13I1/R245fa, R600a/R13I1/R227ea, R600a/R13I1/R134a, R600a/R13I1/R125, R161/R13I1/R134a, R290/R13I1/R125, R161/R13I1/R227ea, and R161/R13I1/R125 are identified as the best environment-friendly mixture compositions as alternatives to R134a. It is also calculated that the mixture R600a/R13I1/R125 possesses COP greater than 10% to R134a at the same working conditions.

Vascular and Transpiration Flows Affecting Apricot (Prunus armeniaca L.) Fruit Growth

Fruit growth is a biophysical process that depends mainly on the daily balance between vascular (xylem and phloem) and transpiration flows. This work examines the seasonal and daily behaviour of apricot fruit growth as well as their vascular and transpiration flows. Seasonal patterns of the shoot and fruit growth, as well as fruit surface conductance and dry matter accumulation, were monitored at regular times intervals during the season on “Farbela” and “Ladycot” cultivars. In addition, the daily courses of leaf and stem water potentials and leaf gas exchanges were monitored at 66 and 109 DAFB. On the cultivar “Farbela”, the daily patterns of phloem, xylem, and transpiration flow to and from the fruit were determined through precise and continuous monitoring of fruit diameter variations. Branch sap flow was also determined through the thermal balance method. Apricot fruit growth showed a double sigmoid pattern, typical of other drupaceous species. Stem and leaf water potential maintained values above the stress threshold, and in the last part of the season, the leaf photosynthetic rate increased. Leaves received higher sap flow in the morning and at midday, while a higher amount of xylem water was moved to the fruit in the late afternoon. Fruit showed high transpiration rates, which led to fruit shrinkage during the warmest hours of the day. High xylem inflows balanced the transpiratory losses, while phloem import was lower and occurred mainly during the mid-day hours. As a result, the fruit grew mostly in the late afternoon and night, and its growth was sustained mainly by xylem fluxes, which represented over 90% of the fruit’s total inflows. Later in the season, fruit transpiration and xylem flow decreased but did not stop even at harvest. Phloem import increased its importance throughout the season and, in the final stages, accounted for 36% and then 66% of the daily relative contribution to fruit growth. This knowledge represents a starting point to improving apricot orchard management in terms of irrigation and fertilisation.

Flammability and performance studies of eco-friendly ternary refrigerant mixtures used in vapour compression systems.

The present article analyses the refrigerant safety parameters flammability, global warming potential (GWP) and coefficient of performance (COP) for twenty-seven combinations that contain two flammable and one non-flammable (dilutant) component. The flammability of the flammable refrigerants R290, R600, R600a, R152a and R161 were investigated with different dilutants such as R245fa, R13I1 and R134a. To determine the minimum inerting concentration (which decides the flammable zone), two methods were used: thermal balance method (TBM) and the modified thermal balanced method (MTBM). The MICs estimated with both the methods are compared against the 50 experimental datapoints available in the literature (for different ternary mixtures). It was found that for all the ternary mixtures, majority of the MIC values estimated with MTBM are within ± 8% while with TBM are within ± 30%. Fifty-five ternary mixture compositions were identified (from the proposed twenty-seven mixture combinations) using the MICs predicted by MTBM. The COPs of the identified mixtures M1-M6, M8-M12, M14-M24, M26-M30, M34-M39 and M53-M54 are estimated to be less than 10% of the COP of R134a (at the same operating conditions). It is also estimated that the corresponding GWP value of the mixtures (M1 to M6, M8 to M12, M14 to M24, M26 to M30, M34 to M39, M53 and M54) are reduced by 91 to 99% when compared to R134a (GWP = 1300).

Optimal design of homogeneous ignition of biomass by pulse ignition technique

The volatile matters in biomass have an essential effect on their ignition stabilization. In the present work, the homogeneous ignition of seven kinds of biomass and eight kinds of coals is studied by the pulse ignition technique. At ignition, the flame brightness of biomass appears more faintly than that of coal. The flame color appears in bluish violet for biomass and yellowish red for coal. The homogeneous ignition temperature ranges from 270?C to 310?C for biomass and 390-500?C for coal, respectively, and it decreases with the decrease of the particle size. A theoretical model is established to predict the homogeneous ignition temperature by the thermal balance method and the thermal explosion theory. Based on the theoretical prediction, a quasi-linear model and a non-linear model are developed through the least square algorithm.

Research methods in the study of heat transfer coefficient during flow in minichannels

The paper presents the specification of research methods commonly encountered in the studies of heat transfer processes in minichannels. In particular the following methods have been emphasized: electrochemical limiting current method as well as the thermal balance method. In thermal balance method the mean heat transfer coefficient is determined by the set of experimental thermal measurements of the investigated heat exchanger. In turn, limiting current method is based on heat and mass transfer analogy. The discussed research methods have been implemented on two specially designed and constructed test facilities with compact minichannel heat exchangers, which have been presented and described in details. In order to validate the designed setup, the preliminary experimental measurements of two minichannel heat exchangers with hydraulic diameter of 2 mm and rectangular cross sections during single-phase liquid flows have been carried out. In further perspective it is planned to extend the experimental studies of minichannel heat exchangers and to compare the results obtained by both methods described.

Power Measurement Methodologies for Pool Nuclear Research Reactors

Redundancy and diversity are two important criteria for power measurement in nuclear reactors. Other criteria such as accuracy, reliability and response speed are also of major concern. Power monitoring of nuclear reactors is normally done by means of neutronic instruments, i.e. by the measurement of neutron flux. The greater the number of channels for power measuring the greater is the reliability and safety of reactor operations. The aim of this research is to develop new methodologies for on-line monitoring of nuclear reactor power using other reliable processes. One method uses the temperature difference between an instrumented fuel element and the pool water below the reactor core. Another method consists of the steady-state energy balance of the primary and secondary reactor cooling loops. A further method is the calorimetric procedure whereby a constant reactor power is monitored as a function of the temperature-rise rate and the system heat capacity. Another methodology, which does not employ thermal methods, is based on measurement of Cherenkov radiation produced within and around the core. The first three procedures, fuel temperature, energy balance and calorimetric, were implemented in the IPR-R1 Triga nuclear research reactor at Belo Horizonte (Brazil) and are the focus of the work described here. Knowledge of the reactor thermal power is very important for precise neutron flux and fuel element burnup calculations. The burnup is linearly dependent on the reactor thermal power and its accuracy is important in the determination of the mass of burned 235U, fission products, fuel element activity, decay heat power generation and radiotoxicity. The thermal balance method developed in this project is now the standard methodology used for IPR-R1 Triga reactor power calibration and the fuel temperature measuring is the most reliable way of on-line monitoring of the reactor power. This research project primarily aims at increasing the reliability and safety of nuclear reactors using alternative methods for power monitoring.

Modified thermal balance method for estimating minimum inerting concentraion of flammable refrigerant mixtures

R1234yf is considered as a better alternative for R134a (the conventional refrigerant) due to its low global warming potential value, while its usage is limited because of its flammability. The flammability of any flammable refrigerant can be reduced by adding dilutants that are inert. Two methods (group contribution method and thermal balance method) were used to estimate the minimum inerting concentration (which decides the flammability zone) of the binary mixtures (refrigerant + dilutant). It was observed that the group contribution method and the thermal balance method predicted minimum inerting concentration of the refrigerant mixture (refrigerant + dilutant) with an absolute error of more than 50% and 8%, respectively. Therefore, a modified thermal balance method is proposed in this study to estimate the minimum inerting concentration and found that the proposed method predicts the values with reasonable accuracy when compared with the available experimental data. Further, the minimum inerting concentration for the dilutants R125 and R245fa (that are not experimentally known) with R1234yf is estimated. The results indicated that R227ea has better inert effect with R1234yf when compared to other dilutants (R125, R134a and R245fa) considered in this study. It was also found that the critical inerting concentration for R1234yf is 36.5%.

The explosion parameters of methanol under variable pressures and 423 K

The high-temperature and high-pressure methanol one-step oxidation has been the primary process for the mass production of dimethoxymethane. However, the risk of explosion for this process is still not properly defined. This paper presents new results from the experimental study on the explosion characteristics, including the explosion pressure and the explosion limits for methanol/air mixtures with a variable oxygen level, under an initial pressure between 0.3 MPa and 0.75 MPa and at the initial temperature of 423 K. The upper explosive limits were found to increase along with the initial pressure. If the limits for normal air are known, the oxygen effect on flammability is predictable from the thermal balance method. With a correlation for the pressure effect and a method for the oxygen effect, we can have the flammable range predictable.

The safety improvement of VVER-1000 NPP against SBO accident using portable air-cooled diesel generator

The Fukushima accident demonstrated that the safety design of nuclear power plants should be assessed by installing additional backup sources of electrical power and cooling to cope with extreme natural events. It is supposed that both off-site and on-site AC power supply sources are lost during the station blackout accident (SBO). The probabilistic safety analysis (PSA) of VVER-1000/V-446 nuclear reactor shows that the core damage frequency (CDF) due to SBO is a dominant contributor to the total CDF of NPP. In this study, the installation of portable air-cooled diesel generator (PDG) is proposed to prevent severe core damage and maintain the safety functions during SBO accident in NPP. The scenarios to remove the residual heat of the core through primary and secondary cooling systems by deploying PDG are determined. The list of loads and sequence connection of safety systems are specified for each scenario. The capacity, type, and characteristics of PDG are determined based on the identified electrical loads and weather condition of the NPP site. The conceptual plans for connections of PDG into the electrical distribution of NPP to feed safety systems are represented as well. The suggested scenarios are justified by thermal balance method and assessment of reported thermal-hydraulic calculation of NPP. The PSA analysis is performed by SAPHIRE code as a reliability and risk assessment software to investigate safety improvement of NPP against SBO accident with considering PDG. The results show that the CDF due to SBO is reduced from 3.61E−06 (1/year) to 9.897E−009 (1/year).

Heat transfer coefficients during the impingement cooling with the use of synthetic jet

The paper presents experimental studies on heat transfer phenomena which occurs during the impingement cooling with the use of synthetic jet. The synthetic jet was created by a special actuator consisting in a plexiglass cavity and a loudspeaker. An air was a working fluid. The effect of synthetic jet actuator geometry and supply parameters on heat transfer enhancement has been investigated. The experiment was performed with the use of classical thermal balance method. Heat transfer coefficients at a stagnation point have been obtained. Measurements were carried out in the range of excitation frequency f = 5 ÷ 600 Hz and of root mean square voltage E = 1, 2, 3, 4, 6 V. Changes of actuator geometry included: orifice diameters d = 9, 15, 24 mm, orifice thickness t = 3, 5, 20 mm and cavity depth H = 20, 40, 60 mm. On the basis of measurements results the correlations for the stagnation point Nusselt number of an axisymmetric impinging synthetic jet characterized by large Reynolds numbers have been obtained. Nusselt number has been determined in the function on scaling parameters: Reynolds number, jet-to-surface spacing x/d and the dimensionless stroke length L0. Reynolds numbers were ranging from 3600 to 22950, x/d = 1 ÷ 20 and L0 = 0.84 ÷ 170.5. The scaling parameters have significantly extended the range of research so far. The obtained Nusselt number correlations provide heat transfer calculations at large Reynolds numbers and are expected to have practical applications.

Economic Analysis of Power Plants Under Different Loads Based on Structural Theory

The economy analysis of coal-fired power plants is usually based on traditional thermal balance method, which only considers the thermodynamic factors but ignores the economic factors such as cost. In this paper, to have a more comprehensive and accurate evaluation on the production performance and economical efficiency of thermal systems, the cost analysis method based on the Structural Theory of Thermoeconomic is applied to a 300MW thermal power generating unit in Yunnan province. The thermoeconomic model and the exergetic cost model for the plant based on the Fuel—Product concept have been defined to quantify the productive interaction between different devices. By calculating the thermoeconomic cost of four typical different working conditions and analyzing the distributions and change rules of generating cost, the Structural Theory of Thermoeconomic is proved scientific and useful and offers a set of feasible and reliable analysis method for the performance analyses and improvement of power plants.

The flammable resistance method for mixture flammability

Le Chatelier's rule is known for its inability to treat the contribution of a diluent in a flammable mixture. This is not true if we treat the diluent as a flammable resistor with a fictitious lower flammable limit as its signature resistance. Thus the diluent in the mixture can be treated consistently along with other fuels like electrical resistors in parallel. Strictly derived from the thermal balance method, this flammable resistance method has the principle of energy conservation embedded with each energy term additive in the denominator. Like an electrical circuit, the mixture flammable limit serves as the total resistance of a parallel circuit, thereby sharing a simple form with Ohm's Law. This method completes Le Chatelier's rule in dealing with mixtures of multiple fuels and diluents.

Theoretical Flammability Diagrams for Oxy-combustion

In order to utilize the low-calorific value gases, oxy-combustion technology is generally used to burn the diluted fuel mixture more efficiently, cleanly and safely. Here the thermal balance method is tailored to check the fuel mixture flammability with the help of theoretical flammability diagrams and non-dimensional HQR diagrams. Specifically, the contributions of diluent/oxidant/temperature are checked. Even with limited experimental data, they are found to be a powerful tool to understand the mixture flammability, since they are based on simple principles of energy conservation. This approach provides the foundation for fine-tuning safe operation parameters related to oxy-combustion technologies.

DEVELOPMENT OF METHODS FOR MONITORING AND CONTROLLING POWER IN NUCLEAR REACTORS

Power monitoring of nuclear reactors is normally done by means of neutronic instruments, i.e. by the measurement of neutron flux. The greater the number of channels for power measuring the greater is the reliability and safety of reactor operations. The aim of this research is to develop new methodologies for on-line monitoring of nuclear reactor power using other reliable processes. One method uses the temperature difference between an instrumented fuel element and the pool water below the reactor core. Another method consists of the steady-state energy balance of the primary and secondary reactor cooling loops. A further method is the calorimetric procedure whereby a constant reactor power is monitored as a function of the temperature-rise rate and the system heat capacity. Another methodology, which does not employ thermal methods, is based on measurement of Cherenkov radiation produced within and around the core. The first three procedures, fuel temperature, energy balance and calorimetric, were implemented in the IPR-R1 TRIGA nuclear research reactor at Belo Horizonte (Brazil) and are the focus of the work described here. Knowledge of the reactor thermal power is very important for precise neutron flux and fuel element burnup calculations. The burnup is linearly dependent on the reactor thermal power and its accuracy is important in the determination of the mass of burned 235U, fission products, fuel element activity, decay heat power generation and radiotoxicity. The thermal balance method developed in this project is now the standard methodology used for IPR-R1 TRIGA reactor power calibration and the fuel temperature measuring is the most reliable way of on-line monitoring of the reactor power. This research project primarily aims at increasing the reliability and safety of nuclear reactors using alternative methods for power monitoring.

Theoretical Flammability Diagram for Analyzing Mine Gases

Out of the thermal balance method, a method of presenting mine fire data is proposed in this work. By grouping fuels into a pseudo fuel, grouping nitrogen and oxygen into a pseudo air, and using carbon dioxide as the diluent, a diluted flammability diagram is reconstructed for this oxygen-modified environment. The flammability envelop is controlled by oxygen availability, while the operation point is controlled by fuel/diluent availability. The relative position between the envelop and the operation point shows the flammable state of this mixture. Coward’s explosive triangle is also applied using the limiting oxygen concentration derived from the diagram. Both are most useful in guiding the suppression operation for an underground coal mine fire.

Transpiration and canopy conductance of Caragana korshinskii trees in response to soil moisture in sand land of China

Caragana korshinskii is widely used in vegetation reestablishment programs to stabilize the shifting of sand on the Loess Plateau. This sand shifting of sand exerts pressure on the limited soil water and vice versa. However, detailed transpiration and sap flow studies that focus on water use in these stands remain limited. The hourly sap flows, along with successive soil water balance and meteorological measurements, on three trees were measured using the thermal heat balance method during the growing season period. Results showed that the midday sap flow and stand transpiration were significantly lower during the stress period (from May to July) compared with those at the beginning of August concurrently with high soil water content. The heat balance measurements underestimated the transpiration obtained from the soil water balance method. When the tree conductance was fitted with climatic variables and soil water content, the canopy conductance increased exponentially with above-canopy radiation, whereas it decreased logarithmically with decreasing vapor pressure deficit. In the absence of water stress, the tree conductance was unchanged when the relative extractable water remained above 0.4, whereas the conductance decreased linearly after the wilting point. The model was generally well fitted to the measured transpiration data in terms of the response during the dry and rainy seasons, thus demonstrating the feasibility of developing a quantity schedule for C. korshinskii transpiration on the Loess Plateau in the presence of a soil water stress.