Unequal Temperature Distribution Research Articles

Thermal Performance Assessment for an Active Latent Heat Storage Tank by Using Various Finned-Coil Heat Exchangers

Paraffin-based latent heat storage has a higher thermal capacity than sensible heat storage. Despite that, the actual implementation of paraffin as an active latent heat storage (ALHS) system is limited due to low charging and discharging rate with unequal temperature distribution as the impact of mushy region formation. The present study evaluates the finned-coil heat exchanger for the ALHS tank to overcome the related problems. Three finned-coil configurations are tested experimentally: straight-fin, branched-fin and height-fin. The evaluation uses the ALHS arrangement to assess each configuration's charging/discharging rate. The branched fin provides an equal thermal distribution, promoting a higher final temperature of 112.3°C. It also achieves the highest power rate of 250.5 Watts. The height-fin minimizes the effect of void formation, which maintains a sufficient heat transfer rate during the discharging. However, the average power rate for each model is relatively low. The finding indicates that it is essential to provide adequate heat transfer for the center part of the tank, including adding a branched fin along with coil turn to provide a better heat transfer rate. It boosts the charging/discharging rate, making the system's response time desirable to achieve effective power during the operation.

Modeling and Design of Cookware for Induction Heating Technology With Balanced Electromagnetic and Thermal Characteristics

Improving the cooking experience of induction-heating users involves, among other factors, an optimized power distribution at the bottom of the cooking vessel. Conventional ferromagnetic cookware presents high efficiency but unequal temperature distribution with flat inductors, which subsequently leads to uneven cooking results. In this work, we propose an alternative to the traditional cookware arrangement by inserting some aluminum pieces in the ferromagnetic bottom of cookware. This arrangement combines the optimal inductive performance of the ferromagnetic iron an the high thermal conductivity of aluminum. The performance of the proposed arrangement is analyzed by means of a multiphysics tool including electromagnetic and heat transfer sub-models which is applied to predict both the equivalent electrical circuit and the temperature distribution in cookware. As a result, a balanced trade-off between efficiency and temperature distribution is evidenced with the proposed solution. Experimental results also corroborates the predictions of the proposed solution.

A model of micro lubrication between two walls with unequal temperature distribution based on kinetic theory

Micro lubrication of a gas between two walls with arbitrary and independent temperature distributions is studied on the basis of the Bhatnagar–Gross–Krook–Welander (BGKW) model of the Boltzmann equation. The BGKW equation is studied analytically using the slowly varying approximation. Following the author's previous study [T. Doi, “A model of micro lubrication between two walls with an arbitrary temperature difference based on kinetic theory,” Phys. Fluids 32, 052005 (2020)], the leading-order approximation, which ought to be the solution of the nonlinear heat transfer problem, is replaced by its free molecular solution. A lubrication model of the Reynolds-type equation is derived in closed form. A direct numerical analysis of the lubrication flow subject to localized heating or cooling of the walls is conducted for an assessment of the lubrication model. The lubrication lift calculated using the model agrees with that of the direct numerical solution within an error of 5% when the Knudsen number based on the gap size lies between 0.1 and 10. The result of the lubrication model agrees also with that of the Boltzmann equation for a variable hard sphere gas. A sharp peak arises in the pressure distribution for large Knudsen numbers owing to the effect of thermal creep flows induced by localized heating.

Investigation of Localized Skin Temperature Distribution Across the Transtibial Residual Limb.

Interventions to resolve thermal discomfort as a common complaint in amputees are usually chosen based on the residual limb skin temperature while wearing prosthesis; whereas, less attention has been paid to residual limb skin temperature while outside of the prosthesis. The objective of this study was to explore the localized and regional skin temperature over the transtibial residual limb (TRL) while outside of the prosthesis. Eight unilateral transtibial adults with traumatic amputation were enrolled in this cross-sectional study. Participants sat to remove their prostheses and rested for 30 minutes. Twelve sites were marked circumferentially in four columns (anterolateral, anteromedial, posteromedial, and posterolateral) and longitudinally in three rows (proximal, middle, and distal) over the residual limb and used for attachment of analog thermistors. Skin temperature was recorded and compared for 11 minutes. Furthermore, the relationship of skin temperature with participants' demographic and clinical characteristics was explored. The whole temperature of the TRL was 27.73 (SD=0.83)°C. There was a significant difference in skin temperature between anterior and posterior columns. Likewise, the distal row was significantly different from the proximal and middle rows. The mean temperature at the middle and distal zones of the anteromedial column had the highest and lowest skin temperatures (29.8 and 26.3°C, p<0.05), respectively. The mean temperature of the whole TRL had no significant relationships (p>0.05) with participants' demographic and clinical characteristics. An unequal distribution of temperature over the TRL was found with significantly higher and lower temperatures at its anterior column and distal row, respectively. This temperature pattern should be considered for thermoregulation strategies. Further investigation of the residual limb temperature with and without prosthesis, while considering muscles thickness and blood perfusion rate is warranted.

Improved method for aging assessment of winding hot-spot insulation of transformer based on the 2-FAL concentration in oil

2-furfuraldehyde (2-FAL) is widely accepted as a chemical marker to indicate the degradation of cellulose insulation in oil-impregnated transformers. However, the application of 2-FAL in the aging diagnosis of transformers in operation is ineffective. The excessive dispersion of 2-FAL concentration measured in transformers is caused by many influence factors. In addition, the 2-FAL concentration in oil cannot indicate the aging of the most serious point given the temperature distribution along the winding height, that is, the insulation at the hot spot of a winding. To optimize the assessment, an improved method for the hot-spot insulation assessment based on the 2-FAL concentration in oil is proposed in this work. The 2-FAL generation in cellulose chain scission is firstly analyzed theoretically, and a new linear relationship between (1/DPt-1/DP0) and 2-FAL total generation is obtained. Moreover, the 2-FAL partitioning between an insulation paper and mineral oil influenced by temperature, moisture, and aging status in total is considered. Second, by considering the linear relationship and the 2-FAL partitioning, an equation between the insulation at hot-spot temperature and the 2-FAL concentration in oil is established for the thermal aging under unequal temperature distribution condition. Finally, to verify the proposed method, a testing platform is introduced to conduct the thermal aging experiment with temperature gradients. The proposed method demonstrates better assessment results than the conventional thermal aging test at constant temperature.

Direct Utilization of Methane in Microtubular-SOFC

This paper analyzes the possibilities for application of micro-tubular SOFC (mSOFC) with partial oxidation catalyst (CPOX) located at the cell inlet for direct utilization of hydrocarbons. Applied system reduced coke deposition without integration into the cell structure and allowed application of traditional Ni:zirconia cermet for direct hydrocarbons utilization. The key problem in the proposed Microtubular Solid Oxide Fuel Cell (mSOFC) system is where the part of the cell is outside of the hot zone. This is caused by the temperature distribution (TD). Despite the good resistance to thermal shock, the long-term operation with unequal TD can cause cell damage. The TD was measured along and across the cell (internally and externally) under different operating conditions. H2 and CH4 were used as fuels in the first instance. Different mixtures of fuel and air and different forms of the catalyst were tested for the CPOX of hydrocarbons. Different forms/geometries of the catalyst were tested to optimize the system design. The paper mainly focuses on solving problems with temperature distribution along and across the mSOFC cell.

안동댐 유역 기상인자의 시공간분포 추정

This study investigates characteristics of time series spatial distribution on climate factors in Andong Dam basin by estimating precise spatio-temporal distribution of hydro-meteorological information. A spatio-temporal distribution by estimating Semi-Variogram based on spatial autocorrelation was examined using the data from ASOS and 7 hydro-meteorological observatories in Andong Dam basin of upper Nakdonggang River, which were installed and observed by NIMR(National Institute of Meterological Research). Also, temperature and humidity as climate variables were analyzed and it was recognized that there is a variability in watershed area by time and months. Regardless of season, an equal spatial distribution of temperature at 14 o'clock and humidity at 10 o'clock was identified, and nonequal distribution was noticed for both variables at 18 o'clock. From monthly spatial analysis, the most unequal distribution of temperature was seen in January, and the most equal distribution was detected in September. The most unequal distribution of humidity was identified in May, and the most equal distribution was seen in January. Unlike in forest, seasonal spatial distribution characteristics were less apparent;but temperature and humidity had respective characteristics in hydro-meteorology.

A New PWM Strategy for Grid-Connected Half-Bridge Active NPC Converters With Losses Distribution Balancing Mechanism

Photovoltaic systems technological development is driven by the request for higher efficiency and safety. These concerns influence also the choice of the power converter stage. Several topologies have been proposed and many of them are available commercially. Among them, the neutral point clamped (NPC) and derived topologies offers high efficiency, low leakage current, and low EMI. However, one main disadvantage of the NPC inverter is given by an unequal distribution of the losses in the semiconductor devices, which leads to an unequal distribution of temperature that can affect lifetime. By using the active NPC (ANPC) topology, where the clamping diodes are replaced by bidirectional switches, the power losses distribution problem is alleviated. The modulation strategy is a key issue for losses distribution in this topology. In this paper, two known strategies are discussed and a new PWM strategy, namely the adjustable losses distribution is proposed for better losses distribution in the ANPC topology. Simulations and experimental results help in evaluating the modulation strategies.

Direct Utilization of Methane in Microtubular-SOFC

Microtubular-SOFC (μSOFC) offer many advantages over planar SOFC systems. They offer greater resistance to thermal shock, allow rapid startup and shut down. They have high volumetric power density and the seals can be placed out of the high temperature zone. Liquefied natural gas (LNG) is receiving increased interest as a fuel for trucks. This is an ideal fuel for SOFC. In this paper we examine the use of LNG in μSOFC in a truck APU application and the issues associated with LNG fuel. The work mainly focuses on solving issues with temperature distribution along and across the cell. The key problem in the proposed system is the temperature distribution (TD). Despite the good resistance to thermal shock, the long-term operation with unequal TD can cause cell damage. The TD was measured along the cell (internally and externally) under different operating conditions. H2, CH4 and simulated LNG (individual gases mixed in the correct ratio of LNG) were used as fuels. CH4 and simulated LNG were converted into syngas using semi-internal catalytic partial oxidation catalyst (CPOX) located at the entrance of the cell. Different mixtures of fuel and air and several different catalysts were tested for the CPOX of hydrocarbons. The figure shows a typical result during OCV using H2 as a fuel at 700oC furnace temperature. It shows there was a difference of 200oC between the internal and external part of the tube at the fuel inlet, indicating research needs to be conducted into minimising this to ensure the durability of any SOFC APU system. Figure 1. Temperature distribution inside the μSOFC single cell. The results are part of the SAFARI project funded under Europe’s Fuel Cell and Hydrogen Joint Undertaking (FCH JU), Grant Agreement No.325323. The Consortium gratefully acknowledges the support of the FCH JU. Figure 1

Direct Utilization of Methane in Microtubular-SOFC

Liquefied natural gas (LNG) is receiving increased interest as a fuel for trucks. This is also an ideal fuel for SOFC. The work presented here is part of a project utilising LNG in microtubular SOFC (mSOFC) in a truck APU application and the issues associated with this fuel. The paper mainly focuses on solving problems with temperature distribution along and across the mSOFC cell. The key problem in the proposed system is the temperature distribution (TD). Despite the good resistance to thermal shock, the long-term operation with unequal TD can cause cell damage. The TD was measured along and across the cell (internally and externally) under different operating conditions. H2 and CH4 were used as fuels in the first instance. CH4 was converted into syngas using semi-internal catalytic partial oxidation catalyst (CPOX) located at the entrance of the cell. Different mixtures of fuel and air and different forms of the catalyst were tested for the CPOX of hydrocarbons.

Effect of Non-Uniform Temperature Distribution over the Cross-Section in Steel Frame Structure

The paper deals with the effect of non-uniform temperature over the cross-section in the steel frame structure under fire loading. The unequal temperature distribution causes additional bending moments in statically indeterminate structures. Numerical results of thermal and structural analysis from the commercial computer software ANSYS are compared with the experimental measurements on the steel frame exposed to high temperature.

A Study on Vibrational Viscometers Considering Temperature Distribution Effect

In viscosity measurement, temperature control is very important. In this study, the effects of temperature distribution on vibrational viscometers are investigated. Vibrational viscometers are preferred over other types of viscometers owing to their low cost, easy to use and efficacious continuous viscosity measurement capability. The study was conducted in two parts. In the first part, the challenge of unequal temperature distribution in vibrational viscometers was analyzed. The heat generated by a heater during continuous viscosity measurement disperses every part of a sample fluid and influences the fluid's viscosity. Therefore, the sample fluid may have inhomogeneous viscosity values because temperature distribution cannot be equal at every point in a fluid. This experiment is repeated several times with different temperature gradients for gaining a better understanding about the effect of unequal temperature distribution on fluid viscosity. Experimental outcomes show that under some conditions, viscosity measurement errors could reach 27.9%. This finding has been verified by mathematical calculations. In the second part of the research, for solving the unequal temperature distribution problem, the use of a magnetic stirrer for mixing up the fluid throughout the viscosity measurement with the aim of achieving homogenous temperature distribution is proposed.

Experimental investigation of embedding high strength reinforcements in extrusion profiles

Embedding reinforcement or functional wires in extruded profiles offers the potential to increase mechanical properties as well as the field of application. With improved strength and stiffness and an integrated function as deformation sensor or data transmitter the weight of space frame structures can be reduced substantially. To comprehend the general conditions when embedding the reinforcement and functional elements during the extrusion process, experimental extrusion investigations have been carried out for the analysis of significant process and tool geometry parameters. Extrusion with porthole dies, i.e. by feeding the elements over bridges inside the die in the aluminum base material flow, was studied to manufacture continuous reinforced, thin-walled, and hollow profiles. Special care was taken to ensure an accurate positioning in the transient material flow to prevent a loss of functionality by insufficient covering and loss of positioning caused by the die geometry or unequal temperature distribution inside the die. Studies on different reinforcement wires and wire ropes based on high strength steel are presented, showing an increasing process stability when using solid wires. General process restrictions are analyzed and process guidelines are presented based on exemplary extrusions.

Calculation of the power capabilities of HBT amplifiers based on a new physical HBT model

A novel model for the simulation of the microwave power capabilities of HBTs is presented. The model is based on physical analytical formulation of the terminal currents as functions of the base-emitter and base-collector voltages. It takes into account the unequal thermal distribution of temperature for multifinger HBT devices, the impact ionization, tunnelling, recombination currents, etc. From the simulation of multi-finger transistor structures it can be concluded that high thermal device resistances are detrimental for power performance, because of the unequal distribution of temperature and, hence, base current in the HBT structure. In can also be concluded that the input and output reflection coefficients are insensitive to temperature variation. Finally, it has been shown theoretically and experimentally that the breakdown voltage increases slightly with increasing operating temperature. © 1996 John Wiley & Sons, Inc.

8 熱応力撓角式の荷重項に就て

To calculate the thermal stresses of rigid frames by the slope deflection method, considering unequal distribution of temperature at any cross sections of the members, we must calculate the constant terms 〓_<AB>, 〓_<AB>, H_<AB> and H_<AB> which are called the "load-terms" of the slope deflection equations. In this report, the formulas of load-terms both in general and in special cases are presented. And the tables of d_<A(0)>, d_<B(0)>, and load-terms in various cases for linear distribution of temperature at the cross sections and for the axial direction of the members are indicated.

Studies on frost injury to wheat. I. Laboratory freezing tests in relation to the behaviour of varieties in the field

Factors influencing the reactions of different varieties of wheat to stem and ear frosting were studied under controlled conditions and in the field. Artificial freezing tests were successful in demonstrating varietal differences in resistance, but these were not always in agreement with behaviour under commercial cultivation. Thus, whereas the American winter wheat Cheyenne showed resistance superior to that of the Australian varieties Bencubbin and Gabo, the observed superiority of Bencubbin over Gabo in the field was not maintained under controlled conditions. A possible explanation for this anomaly lies in the unequal distribution of temperature which obtains within a crop. On several frosty nights the ears and stems of Gabo, owing to their more forward development, were observed to be in a colder zone than those of Bencubbin. These conditions were not reproduced in the freezing cabinet, and comparisons between plants at different stages of growth failed to show any marked change in resistance with age up to the time of ear emergence. The relationship between temperature of freezing and degree of injury was established under different sets of conditions. In one case interaction between the effects of temperature and variety showed that this factor may be of some importance in the interpretation of results of freezing trials.

The Effect of Unequal Temperature Distribution on the Maximum Pressure Developed in Explosions in a Closed Vessel

When a combustible gas mixture is exploded at the center of a spherical vessel, a temperature gradient is established at the moment of maximum pressure which rises from the wall to the center. The maximum pressure recorded is lower than would have been found had the temperature been equalized without heat loss. A method for calculating this difference in pressure is described. For ozone explosions it is shown to be less than 0.2 percent in weak mixtures and less than 0.5 percent in rich mixtures. For explosions of H2 and O2 with inert gases it amounts to 0.2 to 0.8 percent.

Scientific Serials

THE American Meteorological Journal for July contains the following articles:— On the appearance and progressive motion of cyclones in the Indian region, by W. L. Dallas. The object of the inquiry is to see whether the cyclones of the Indian Ocean originate from the unequal distribution of temperature over and above the earth's surface. The author favours the assumption that cyclones are a production of the upper atmosphere, and thinks that the evidence, although far from conclusive, goes to show that (1) cyclonic storms descend from and retreat to the superior layers of the atmosphere; (2) the whirl may travel along in the upper atmosphere, giving only faint indications of its presence at the earth's surface; (3) the movements of cyclones agree generally with what may be supposed to be the movements of a superior layer of the atmosphere.—S. A. Hill, a memoir, by Edna Taylor Hill.—The eye of the storm (conclusion), by S. M. Ballou. The cause of the clearness of the eye is attributed by the author to the deficiency of the air at the outer edge of the calm, owing to the deflective force of the earth's rotation and the upward and outward movements of the air before reaching the centre; the deficiency being supplied by a gradual settling of the air over the whole area, thus dissolving the cloud stratum and showing the blue sky. The author admits that the discussion of the subject shows the need of more observations concerning the phenomenon.—Recent efforts towards the improvement of daily weather forecasts, by H. Helm Clayton. Tne author states in a clear and interesting form the various rules which have hitherto been established, and draws attention to a law of averages discovered by Francis Galton, which might with advantage be used in weather forecasting, for, although only applied by Mr. Galton to heredity, it is probably universal. For example, if a storm during a given twelve hours has moved with a velocity below the average, the probability is that it will move with a velocity one-third nearer the average during the next twelve hours.—The other articles are—on the sea breeze, by W. C. Appleton, and temperature sequences, by H. A. Hazen, being an inquiry as to whether, if the temperature has been high or low for a certain period, we may anticipate the contrary condition shortly. The inquiry does not seem to have led to any result which could be turned to practical use.