Values Of Temperature Difference Research Articles

Investigation on the mechanisms of cluster formation and transition from adsorption to condensation

In order to understand the mechanism of cluster formation and transition from adsorption to condensation, a series of theoretical analysis based on the Zeta adsorption model and molecular dynamics simulations are hybrid to study the transition process of argon atoms adsorption on a solid surface. The influence of solid-fluid interaction strength and temperature difference are discussed. Results show that the interfacial adsorption dominates the density profiles in the near wall region. With the increase of temperature difference, the enlarged chemical potential difference drives the transition from adsorption to condensation. The critical temperature differences for the transition are determined. The smaller value of solid-fluid interaction induces a larger condensation resistance, which results in a bigger value of critical temperature difference. Meanwhile, the cluster formation and transition process are theoretically described based on the Zeta adsorption model, without singularity at saturation pressure. The predicted adsorption sites show a good agreement with the molecular dynamics simulations. Once the pressure ratio exceeds a certain value, the adsorption sites are occupied by homogeneous clusters, which initiates the liquid phase to wet the surface. The wetting condition is determined. Also, in terms of Gibbs equation, the surface tension is lowered from the solid surface tension without adsorption to the value at wetting. The critical temperature difference for the transition obtained by theoretical prediction coincides well with the molecular dynamics simulation.

Experimental and numerical study of flow and thermal transport in fractured rock

An experimental and numerical study was carried out to investigate matrix-fracture thermal transport in fractured rock. Two different synthetically fractured core plugs were used during the flow-through experiments while core plugs’ outer surface was maintained at two different constant temperatures. To investigate the matrix-fracture thermal transport, cold water was injected through the single fracture core plugs at different flow rates. A film type heat flux sensor was used in the fractured core plug to measure the fracture temperature and heat flux over the matrix-fracture interface. Experimental results showed that fracture temperature decreases with increasing flow rate while heat flux increases. At high flow rates, temperature difference over matrix-fracture interface increases due to large volume of water contacting the fracture at a given time. Water temperature decreased more in the case of fracture surrounded by rock matrix with low volumetric heat capacity and thermal conductivity. A numerical model calibrated using experimental values of the fracture temperature was developed to estimate thermal properties of rock matrix and to identify their importance on the matrix-fracture thermal transport. Using the calibrated numerical model, it has been shown that temperature in the fracture and fracture surface temperature are different contrary to previous studies assuming the same values for these two temperatures. Local and transient convective heat transfer coefficients were introduced with respect to local values of temperature difference and transient values of heat flux along matrix- fracture interface enabling accurate representation of matrix-fracture thermal transport.

Performance Assessment of Heat Exchangers for Process Heat Integration

Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries. In this approach, maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets. The thermal performance of a heat exchanger over its lifetime is however a concern to industries. Thermal performance of a heat exchanger is affected by many factors which include the physical properties of the shell and tube materials, and the chemical properties of the heat transfer fluid. In this study, thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated. The aim of this paper is to present predictions of thermal performances of shell and tube heat exchangers with different heat transfer fluids and geometries as they undergo fouling degradation. Engineering approaches based on thermodynamic analysis, heat balance and Kern Design equations, as well as what-if simulation modeling are used in this work. Shell and tube heat exchangers were designed to meet internal heat recovery targets for three process plants, A, B and C. These targets were published in a separate paper. The effects of degradation of the tubes-due to incremental growth of fouling resistance - on thermal performance of the exchanger were simulated using Visual Basic Analysis (VBA). Overall, it was found that growth in fouling reduces thermal efficiency of shell and tube heat exchangers with an exponential relationship. An increase of 100% of fouling resistance leads to an average reduction of 0.37% heat transfer. Higher values of logarithmic mean temperature difference (LMTD) and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers. The results of this work can be applied in pinch analysis, during design of heat exchangers to meet the internal heat recovery targets, especially in predicting how fouling growth can affect these targets. This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.

Thermo-economic analysis of heat-driven ejector system for cooling smelting process exhaust gas

This study presents a new solution for cooling the exhaust gas of an aluminum smelting process, thus increasing the efficiency of the Gas Treatment Center (GTC). High-temperature waste gas enters the GTC, where contaminants are removed before release to the atmosphere. After the smelting process, the gas temperature varies between 100 °C (in winter) and 150° (in summer). It should not exceed 135 °C at the GTC inlet to ensure good scrubbing process performance. A heat-driven ejector system is proposed for this purpose. Its main advantage is that it can produce a double effect cooling by utilizing waste heat from the exhaust gas. The peculiar feature of the proposed design is that both the generator and the evaporator of the ejector system are used to produce a cooling effect for the smelter exhaust gas. A simulation model of the proposed system is developed, and a two-step approach is applied to complete the thermo-economic analysis. At the first step, formulated as a thermodynamic evaluation, the total heat transfer area was minimized as a function of the generator temperature difference. In the second step, the optimum value of this parameter is used to design the heat exchangers and the ejector. The results show the existence of an optimum value for the generator temperature difference that minimizes the total heat transfer area. An economic analysis based on evaluating the Equivalent Uniform Annual Cost (EUAC) criterion concludes the investigation. It is shown that the new optimization strategy for an ejector system improves its viability as a potential solution for cooling smelting process exhaust gas. The proposed ejector system can reduce the total heat transfer area and the capital cost up to 34% and 57% compared to a commercially available cooling system.

A Comparison of 3D and 2D FE Frictional Heating Models for Long and Variable Applications of Railway Tread Brake.

The article proposes two 3D and 2D numerical FE models of frictional heating for the estimation of temperature distributions in railway tread brake in 1xBg configuration during repeated long-term braking. The results of computations were compared with the time courses of temperature measured using thermocouples throughout the duration of the tests on a full-scale dynamometer for two different brake shoe materials in combination with a steel wheel. The resulting temperature distributions calculated using the proposed models agreed well with the experimental measurements, and the maximum difference in temperature values does not exceed 20%. It has been proven that 2D FE model can be as efficient as 3D model to estimate the temperature distribution during long-term and variable braking in the considered friction node. The differences in the calculation of the temperature values using these models did not exceed 3%, and the calculation time for the 2D model, compared to the 3D model, was shorter approximately 85 times for the braking cycle lasting 5032 s, and approximately 45 times for the braking cycle lasting 3297 s.

Role of modeling approach on the results of thermodynamic analysis: Concept presentation via thermoeconomic comparison of biomass gasification-fueled open and closed cycle gas turbines

Thermodynamic analysis of various cycles (for single- or multi-generation systems) is a major topic on which lots of attention is paid in recent years. In such research activities, setting up an experimental rig is very time and money consuming, thus many of research works are conducted theoretically and the results are verified using the available data in literature. However, details of cycle modeling in component level has received little attention, albeit it has crucial effects on the obtained results from theoretical modeling and simulation. To demonstrate this issue in this paper, two different modeling approaches, which have been commonly used in previous literature to model the heat exchangers in thermodynamic cycles, are compared. To attain this goal, a biomass-fueled externally fired closed cycle gas turbine is proposed and its performance is compared with that of conventional open cycle gas turbine. To model the Intermediate Heat Exchanger (IHE), two approaches are considered: Approach (a): assuming a proper value for cold end temperature difference, and Approach (b): assuming a proper value for heat exchanger effectiveness. A comprehensive thermoeconomic analysis is conducted to evaluate the two considered systems’ performance via applying the two modeling approaches. The results revealed that, applying different modeling approaches brings about attaining conflicting outcomes, a conclusion which is not desirable from engineering perspective and reveals the crucial importance of applying appropriate modeling approach. It is found that, via applying approach (b) as the more rational approach, the closed cycle gas turbine yields a lower value of LCOE by 16.3% and a higher value of net output power by 13.5% than the conventional open cycle system.

Study on the body surface temperature variation patterns of the meridian acupoints related to the physiological status of the uterus

By observing the body surface temperature changes of different meridian acupoints located at the same or adjacent spinal segments of the uterus during the whole storing and releasing process of the uterus under normal physiological condition by the infrared thermal imaging technology, to explore the specific patterns that the functions of Zang-fu organs are reflected on the biophysical characteristics of acupoints, and to enrich the functional specificity theory of the meridian acupoints, thus to provide a reference for discussing the biophysical characteristics of meridian acupoints associated with the menstrual cycle in healthy female college students. Ninety healthy subjects were included. Infrared thermal imaging device was used to detect the body surface temperature of the Yuan-Primary points, the Xi-Cleft points, the crossing points, the non-specific points, the unrelated meridian acupoints and the non-meridian non-acupoint points of the three yin meridians of foot located at the same or adjacent spinal cord segment with uterus, during the menstrual phase, the follicular phase, the ovulation phase and the luteal phase. The absolute skin temperature difference between the left and right acupoints with the same name was used as the main outcome indicator. The temperature difference between left and right Diji (SP 8, the Xi-Cleft point of the Spleen Meridian) during the ovulation phase was significantly higher than that during the other 3 phases (all P 0.05); the absolute temperature difference value of each meridian acupoint was not statistically different from each other in the same phase (all P>0.05). The temperature of Diji (SP 8) specifically reflected the onset of ovulation, and the thermal characteristics of Diji (SP 8) specifically reflected the physiological changes of uterus. The meridian acupoints reflecting the performance of Zang-fu function is not only associated with the spinal cord segment innervating the acupoints, but also associated with the characteristics of the acupoints and the meridians to which the acupoints belong.

CFD analysis on flow and heat transfer characteristic in natural circulation system with subchannels under rolling conditions

The combination of advancement in nuclear technology and ship engineering is a new technology of nuclear application which can not only marine capability and provide power for remote islands, but also help solve the practical issues of high cost, high pollution and high pressure in cutting down emissions in the petroleum exploitation field. The CFD analysis in this paper focuses on the exploration of single-phase natural circulation flow and heat transfer characteristics for rod bundle under rolling conditions. The rolling version CFD tool is developed and compared with the calculated results by system code. The natural circulation system which consists of a 2 by 2 subchannel is established. This paper mainly focuses on the effect of different rolling parameters on natural circulation flow and heat transfer characteristics for rod bundle loop under rolling motion. The thermal–hydraulic performance varies periodically under rolling motion. The variation period equals to rolling period. The stronger the rolling intensity is, the greater the fluctuations of different thermal–hydraulic parameters are. The average values of mass flux and heating section temperature difference under rolling conditions are lower than those under non-rolling conditions, proving that rolling motion may enhance heat transfer. Meanwhile, the inlet temperature of heating section under rolling conditions is lower compared with that under non-rolling conditions. With increasing rolling intensity, the effect of heat transfer enhancement is greater.

Transient process optimization of battery cooling on heat transfer enhancement structure

Thermal management on lithium-ion batteries is a crucial method to improve performance and safety. This work describes L-shaped fins sandwiched between the battery cells. And they are cooled by the cold plate at the battery module level. The investigation is done about cooling performance and efficacy on the mitigation of thermal runaway. A 1D/3D model is developed to study the comparison between the aluminum alloy fin and graphite sheet fin. The results show that the graphite sheet fin has better performance than the aluminum alloy fin on battery cooling. Based on the graphite sheet fin in 0.2 mm, the linear cooling strategy is studied to improve the cooling effect. The influence factors include the cooling slope, initial temperature, and stable temperature. The results show that the cooling slope can improve the cooling efficiency in the cooling process and the temperature uniformity. Especially in a high discharge rate, a high cooling slope can ensure the temperature does not exceed the actual stable temperature and reduce the peak value of temperature difference. The large difference between the initial temperature and the stable temperature leads to a worse cooling effect.

Determination of Energy Efficiency Features of Oil Refinery Units and Their Complexes

The index of the process energy efficiency has been introduced to assess the energy efficiency of oil refinery units and their complexes. The index is calculated as the ratio of the payload difference of the hot utilities of the operational unit and the reference unit to the payload of the operational unit. As a reference unit, the examined unit is selected with a thermal energy recuperation system, which has a specified value of driving force for vertical heat transfer. This value of the minimum temperature difference of the heat transfer carrier in the heat-exchange equipment is selected using the best available technologies in heat transfer. Additionally, the energy efficiency index is calculated taking into account the elimination of heat losses to the environment. A simplified method for estimating heat losses from heated surfaces of oil refinery equipment has been developed for this purpose. It is shown that to determine the energy efficiency of a unit complex, it is possible to use the temperature Total Site profile. Indices of energy efficiency for crude oil unit, catalytic reforming with preliminary hydrotreating for the production of stable catalysis unit and hydrotreating of diesel fuel and kerosene unit, as well as their complex, are determined. Indices for economically optimal integration of these processes are decided. The introduced index of the energy efficiency potential of the process is an absolute value indicating the grade of the process perfection. The introduced index can be used to compare the energy efficiency of both individual units and plants.

Determination of Thermoelectric Cooling Modes of Heat-Loaded Electronics

A computational algorithm is presented for determining the modes of thermoelectric cooling that ensure the given temperature difference of the base of the heat-loaded element and the environment. The obtained analytical expressions make it possible to determine the power supply current of the thermoelectric module taking into account its operating characteristics, thermal resistance of the cooling system, and power of the heat-loaded element. The dependences of the current strength on the value of the given temperature difference are calculated and the parameters affecting the thermoelectric cooling modes are analyzed.

Оценка влияния радиуса изгиба при расчетах продольных напряжений длительно эксплуатируемых трубопроводов

Calculations of stress-strain state of pipelines are performed in accordance with the unified regulatory requirements, which do not take into account facilities operation. Thus, the limitation of minimal allowable bend radius with the value of 1000 pipe diameters (1000D) can be considered justified in relation to a new construction project, but the problem is that it is applied to all pipelines independently of its service life. At the same time the modern smart pigging technologies allow for obtaining precise data on bend radius of operated pipelines, and the diagnostics results indicate, that mandatory requirement for minimal value of 1000D frequently contradicts the actual technical condition of researched objects. The authors performed the analysis of standard formula for calculation of longitudinal stresses, considered the impact on the calculated value of its separate constituents: values of pressure, temperature difference and bend radius. The conclusion is made about the necessity for reassessment of the current regulations for scientific justification of acceptable values of pipeline longitudinal stresses. It is established, that the primary factor, which is responsible for forming the value of longitudinal stresses of the pipelines during long-term operation is the bend radius.

Design and evaluation of a parallel-connected double-effect mechanical vapor recompression evaporation crystallization system

This paper proposes a parallel-connected double-effect mechanical vapor recompression (MVR) evaporation crystallization system, which combines the falling film evaporator with the forced circulation evaporator. With the purpose of treating high salinity wastewater, the circulation process of the system was designed and mathematical models were established according to the mass and energy balance as well as thermodynamic properties in the heat transfer process. Model calculation was conducted using 5% sodium sulfate solution, based on which the effects of evaporation temperature, feed concentration, and temperature difference between saturated boiling solution and condensate on the system performance were analyzed by a parametric study. The results showed that the optimal values of evaporation temperature and saturation temperature difference could be determined based on a trade-off between power consumption and heat transfer area. After that, the performance of the proposed system was compared with that of a traditional multi-effect evaporation crystallization system, and it was revealed that the coefficient of performance (COP) and exergy efficiency of the proposed system were 21.4 and 49.1%, respectively, 82.2% and 51.5% higher than those of the traditional system under the same working condition. Meanwhile, the exergy destruction of the proposed system was 24.7% lower than that of the traditional system, indicating that the new system performs better regarding energy saving and thermodynamic perfection.

Battery space optimization to limit heat transfer in a lithium-ion battery using adaptive elephant herding optimization

Pure electric vehicles have a variety of benefits such as energy efficiency, zero environmental emissions, elimination in air pollution, and decreased carbon dioxide emissions. While it offers major benefits, it suffers from numerous battery-related issues, and, among them, heat dissipation is considered to be a major challenge, leading to significant performance degradation if not handled properly. In this present work, a battery thermal management system design is presented using ANSYS Fluent and adaptive elephant herding optimization algorithm for optimizing the battery spacing, reducing the heat dissipation, and ensuring a proper battery temperature in the lithium-ion battery pack. The adaptive elephant herding optimization algorithm provides an optimal battery spacing of (17, 23, 21, 0.23, 0.23, 0.174, 0.174), and the maximum temperature, minimum temperature, and temperature difference values observed are 298.3112 K, 292.9874 K, and 5.47 K, respectively. The research findings show that the adaptive elephant herding optimization algorithm works as an appropriate cost-effective strategy for depicting the influence of the battery spacing towards the battery temperature and results in a uniform cooling of the entire battery pack.

Effect of turbulator modifications on the thermal performance of cost-effective alternative solar air heater

Over the past years, there has been a huge growth in the solar energy research, development and progress, due to being a renewable, economical and non-polluting energy source. In this research, different design and placement of turbulators inside a cost-effective tube-type solar air heater (TSAH) has been analyzed to upgrade thermal performance. Both experimental and CFD analysis have been performed in order to survey the performance of solar heating systems. Numerical method has been done by utilizing Fluent program in order to simulate real models and also verified with experimental results. It is proposed to improve the thermal efficiency of TSAH by integrating turbulators in different modifications. According to the experimental outcomes maximum instantaneous heater efficiency was reached to 72.41%. Also, experimental and numerical average temperature difference values in TSAHs varied in the range of 9.16–14.54 °C and 9.50–14.95 °C, respectively. The experimental and numerical simulation results exhibited successful design of this simple and inexpensive alternative hot air generation system. Manufactured simple-structured TSAHs in the present work have acceptable thermal performance in comparison to more complex solar heaters in the literature. This type of solar heater could be used in different applications such as; drying, greenhouse heating, space heating and air preheating.

Conceptual design of small modular reactor driven by natural circulation and study of design characteristics using CFD & RELAP5 code

A detailed computational fluid dynamics (CFD) simulation analysis model was developed using ANSYS CFX 16.1 and analyzed to simulate the basic design and internal flow characteristics of a 180 MW small modular reactor (SMR) with a natural circulation flow system. To analyze the natural circulation phenomena without a pump for the initial flow generation inside the reactor, the flow characteristics were evaluated for each output assuming various initial powers relative to the critical condition. The eddy phenomenon and the flow imbalance phenomenon at each output were confirmed, and a flow leveling structure under the core was proposed for an optimization of the internal natural circulation flow. In the steady-state analysis, the temperature distribution and heat transfer speed at each position considering an increase in the output power of the core were calculated, and the conceptual design of the SMR had a sufficient thermal margin (31.4 K). A transient model with the output ranging from 0% to 100% was analyzed, and the obtained values were close to the Thot and Tcold temperature difference value estimated in the conceptual design of the SMR. The K-factor was calculated from the flow analysis data of the CFX model and applied to an analysis model in RELAP5/MOD3.3, the optimal analysis system code for nuclear power plants. The CFX analysis results and RELAP analysis results were evaluated in terms of the internal flow characteristics per core output. The two codes, which model the same nuclear power plant, have different flow analysis schemes but can be used complementarily. In particular, it will be useful to carry out detailed studies of the timing of the steam generator intervention when an SMR is activated. The thermal and hydraulic characteristics of the models that applied porous media to the core & steam generators and the models that embodied the entire detail shape were compared and analyzed. Although there were differences in the ability to analyze detailed flow characteristics at some low powers, it was confirmed that there was no significant difference in the thermal hydraulic characteristics' analysis of the SMR system's conceptual design.

Use of infrared thermography to control osteoreparative and integrative processes during implantation in animals

Thermography is an integral indicator which is formed by means such factors as the vasculature and the level of tissue metabolism. Infrared thermal imaging can be a tool for assessing the safety and effectiveness of implantation in bone tissue using various materials. The aim of the study was a comprehensive assessment of osteoreparative and integrative processes using thermography when implantation in dogs. The research objects were clinically healthy outbred dogs (n=16) at the age of 1 year and a live weight of 10-12 kg. Experimental implants coated with titanium dioxide had on their surface a polymer film of polyazolidinammonium modified with halogen hydrate ions with nanoaggregates of flavonoids according to the original author’s technique (Patent No. 2535067). Similar implants without coating were used as a control. According to the results of x-ray studies in the early and longterm after surgery, there were no foci of bone resorption in the peri-implant zone. Thermography showed a difference in temperature values in the peri-impalantant zone of experimental and control samples reaching 2°C during 1-4 weeks after implantation. On day 32, the temperature indicators for control and experimental samples were stabilized. Consequently, osteoreparative and integrative processes when using implants with author’s coating are accompanied by significantly less metabolic stress for the animal’s body, which was established using infrared thermography.

Electrical Performance Analysis of Thermoelectric Generating System with INC-MPPT Algorithm.

Thermoelectric Generator (TEG) is a new trend in renewable energy issues that utilize heat energy to produce electricity from various waste energy sources. These sources are available from natural sources like geothermal and solar heat and recovering from many industrial processes. In this paper, the electrical performance of a TEG system has been analyzed when the Incremental Conductance - maximum power point tracker (INC-MPPT) control algorithm has been applied to maximize the energy conversion efficiency. The TEG system has been simulated, implemented and tested at different values of temperature difference. Simulation and experimental results show that, the proposed control algorithm can be operated at the maximum power point (MPP) of the TEG module at any operating condition with good accuracy and low fluctuation around this point. Also, the experimental results show that, the harvested power has been duplicated by more than six times by applying the INC-MPPT algorithm (11.9W) in comparing with connection without MPPT (1.9W) at the same resistive load (16Ω), the same applied temperature and the same operating conditions.

Effect of temperature on tensile properties of reinforced thermoplastic pipes

This paper presents a study on the tensile properties of reinforced thermoplastic pipes (RTP) under the effect of temperature. A mechanical model of RTPs with an arbitrary number of reinforced layers under tensile action was constructed by combining the constitutive relationship of elastoplastic materials with the continuous displacement condition. The correctness of the mechanical model of RTPs was verified by experiments. On this basis, the temperature distribution of the pipeline was determined by the heat conduction equation, and thermal stress was introduced to the overall stress–strain relationship of the model to analyze the influence of temperature on the tensile properties of RTPs. The results showed that the temperature had an important influence, and the relationship between temperature and total tensile load was roughly inverse linear. The decrease in temperature increased the Polyethylene (PE) load and fiber load to some extent. The effect of temperature difference on the PE load was not significant whereas fiber load was sensitive to it. The larger the absolute value of temperature difference was, the greater the increase in fiber load was.

Performance evaluation of 10 W cooling power thermoacoustic refrigerator with spiral stacks using air and helium as working fluids

The current research work involves the effect of different operating parameters on the performance of the thermoacoustic refrigerator. The thermoacoustic refrigerator is fabricated by using Poly Vinyl Chloride (PVC), which reduces the conduction heat loss. Two spiral stacks have been used to study the performance of the thermoacoustic refrigerator by varying the gap between two spirals (0.33 mm and 0.38 mm). The variants of spiral stacks are made up of PVC sleeves and mylar sheets of thickness 0.12 mm. In this work, Air and Helium are used as working fluids. The experiments have been carried out for different drive ratios ranging from 0.6% to 1.6%, with operating frequencies of 200–600 Hz with a step of 100 Hz. Also, the mean operating pressure of 2 to 10 bar with a step of 2 bar and a cooling load of 2 to 10 W with a step of 2 W has been considered. The temperature difference between the hot end and cold end of the stack is recorded using RTDs and Bruel & Kjaer data acquisition system. The effect of different parameters on the performance of thermoacoustic refrigerator, such as operating frequency, cooling load, mean operating pressure and drive ratios have been studied. The TAR is modeled in DeltaEC environment, simulation of significant operating conditions are analyzed and found that the results are in good agreement with experimental results. The experimental result shows that the lowest temperature measured at the cold heat exchanger is 1.12 °C by maintaining the hot heat exchanger temperature at about 32 °C when helium is used as the working fluid. Also, 30.56 °C and 28.03 °C are the highest values of temperature differences (∆T) achieved for 0.33 mm and 0.38 mm spaced spiral stacks respectively, whereas 28.56 °C and 26.04 °C are the corresponding results with air as the working fluid.