Heat Leak Research Articles

К использованию тепловизоров в решении актуальных задач теплофизики на металлургическом предприятии

This paper formulates and substantiates the list of topical problems of thermal physics in relation to hazardous production facilities that constantly arise and require prompt solutions at a metallurgical enterprise. Many problems can be successfully solved using optoelectronic equipment, such as a thermal imager. Thermal imager allows to scan the entire object completely without contact. Topical tasks that can be solved with the help of a thermal imager: monitoring and evaluation of the probability of trouble-free operation of the steel ladle lining during its heating, wear resistance of the converter during oxygen purging of the metal melt, spills of the metal melt from the converter, damage of the exit edges of the nozzles of gas-air burners, determination of the surface temperature of the walls of various furnaces, etc. In the converter, electric steel-making and other workshops, with the help of a measuring thermal imager or pyrometer, it is possible to monitor heat leaks from the production premises, to obtain the distribution of the local heat transfer coefficient on various parts of the thermal surface. It is also possible to predict the temperature condition in emergency situations, confirm the requirements for the thermal mode of the operated object, identify and control ingots and billets with regard to their grain size and uniformity in the ingot cross-section, etc. Paper presents the examples of thermograms obtained both for the steel ladle and for other objects. Formulated list and experimentally confirmed solutions of thermal problems clearly show that with the help of a thermal imager it is possible to quickly, efficiently, and reliably solve the complex problems of heat exchange and heat transfer in the subdivisions of a metallurgical enterprise.

Optimization of Kiloampere Peltier Current Lead Using Orthogonal Experimental Design Method

Reducing heat leakage is crucial for the development of practical superconducting devices. In this work, orthogonal experimental design method is first used to optimize the design of hundred-ampere and kiloampere Peltier current leads (PCLs). Geometry and arrangement of Peltier materials and conductive materials of the current lead are analyzed. Through our simulation, we find that the coupling effect between the radius of Bi2Te3 (r2) and the length of Bi2Te3 (L2) has the greatest effect on the heat leakage of PCLs at the cold end for both PCLs. Furthermore, numerical simulations suggest that the lowest heat leakage at the cold end (approximately 30.0 W/kA) is at the same level for both hundred-ampere and kiloampere PCLs. If taking the heat dissipation area at the hot end into account, multiterminal solutions are better solutions for kiloampere current leads.

Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases.

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

Thermodynamic analysis of partially filled hydrogen tanks in a wide scale range

• Thermodynamic behaviors in liquid hydrogen tanks covering a wide scale range. • The pressurization rate was lower under microgravity for small tanks. • Tank size significantly affects the pressurization rate in small scale range. • An empirical correlation between the pressurization rate and tank diameter. • Weights of the three causes of self-pressurization. The primary challenge for the long-term storage of cryogens in space is evaporation and consequent pressurization due to heat leakage. This study innovatively presents the scale effects on pressurization covering a wide range of tank volume from 6.37 × 10 - 3 to 208 m 3 , under normal gravity and microgravity. A computational fluid dynamic model based on the volume-of-fluid method is constructed to predict the thermodynamic behaviors in partially filled hydrogen tanks. The geometric scale is found to play a significant role in influencing the pressurization rate only for tanks in the small-scale range, especially under normal gravity. The pressurization rate is lower under microgravity than under normal gravity for small tanks. However, the opposite is observed when the tank size exceeds a critical value. An empirical correlation is originally presented to relate the real pressurization rate to the tank diameter and the pressurization rate based on homogeneous model. According to a thermodynamic analysis, the direct sensible energy input of vapor, the mass transfer on the liquid-vapor interface, and the liquid thermal expansion are the three causes of self-pressurization, which are all related to the geometric scale. The conclusions can be used for the pressurization prediction of various emissions in the aerospace applications.

Design and test of a flat capillary pump with ceramic wick

<p indent=0mm>A novel flat capillary pump was designed to solve the problem of heat leakage from the evaporator to the accumulator in flat capillary pumps. The materials used to obtain the porous wick and main shell were silicon nitride and low-thermal conductivity titanium alloy, respectively. The size of the resulting capillary pump was <sc>82.0 mm</sc> × <sc>53.0 mm</sc> × <sc>16.0 mm,</sc> and eight cylindrical silicon nitride porous wicks were arranged inside the pump. The pore size, porosity, and heat conductivity of the porous wick were <sc>0.5 µm,</sc> 70%, and 2.7 W/(m K), respectively. Experimental results showed that the flat evaporator loop heat pipe can be started quickly and that no obvious overheating occurs in the evaporator under a heat load in the range of <sc>5.0–20.0 W</sc> when the angle of the capillary pump is 0°. The time required to start the flat evaporator loop heat pipe remarkably increased and the temperature increment evidently increased under a <sc>5 W</sc> start load when the angle of the capillary pump was increased. However, when the start load was increased to <sc>20 W,</sc> the starting characteristics of the pipe improved. The heat-transfer ability of the flat evaporator loop heat pipe, equilibrium temperature of the accumulator, and thermal resistance of the pipe were subsequently tested, and results revealed that the heat transfer and heat flux limits are <sc>400.0 W</sc> and <sc>26.3 W/cm²,</sc> respectively. The equilibrium temperature of the accumulator changed with the heat sink and load, and this is consistent with the typical running characteristic of the loop heat pipe. The minimum thermal resistance tested was 0.018°C/W. Finally, the back heat leakage from the evaporator to the compensation chamber was estimated from the energy balance of the compensation chamber.

Modeling and Performance Optimization of Double-Resonance Electronic Cooling Device with Three Electron Reservoirs

Abstract In this paper, a new model of the three-electron reservoir energy selective electronic cooling device applying double-resonance energy filters is proposed by using finite time thermodynamics. The analytical formulas of the main performance parameters for the double-resonance three-electron reservoir cooling device are derived. The optimal cooling load and coefficient of performance of the cooling device varying with major structure design parameters are explored and the optimal operation regions are further determined. Moreover, detailed analyses are conducted to reveal the influences of center energy level difference, chemical potential difference, energy level width, energy spacing and the phonon transmission induced heat leakage on the optimal performance characteristics of the cooling device. Finally, a performance comparison is made between the double-resonance and single-resonance three-electron reservoir electronic cooling devices. It is shown that through reasonable structure design, the optimal performance characteristics of the double-resonance device can be controlled to be much higher than those of the single-resonance cooling device.

Measurement of apparent thermal conductivity of regenerator materials in 4–20 K temperature range

The axial heat leakage between the cold and hot ends of the regenerator caused by the huge temperature difference is an important part of the cryocooler loss, where the apparent thermal conductivity of regenerator materials is the key parameter that determines the heat leakage. At present, only the apparent thermal conductivity of stainless steel wire mesh, lead and copper sphere above 80 K can be obtained, while measurement results for lower temperatures or other materials are currently not available. A low-temperature apparent thermal conductivity measurement apparatus for regenerator materials has been developed, and the apparent thermal conductivities of sphere-type material (GOS, HoCu2, Er3Ni, and lead), mesh-type material (stainless steel wire mesh), and helium-4 under various pressures have been measured. When the regenerator is in a vacuum state (below 10-4 Pa), the experimental results show that the thermal conduction factors (the ratio of the apparent thermal conductivity of the filled regenerator to that of the material itself) are 0.02 for GOS in 4–10 K temperature range, 0.28 for HoCu2, 0.43 for Er3Ni in 4–20 K temperature range, 0.005 for lead sphere and 0.13 for stainless steel wire mesh in 10–40 K temperature range, respectively. However, when the regenerator is filled with helium-4, the thermal conduction factor values increase by one order of magnitude.

NUMERICAL STUDY ON THERMAL DESTRATIFICATION IN LARGE SCALE HYDROGEN PROPELLANT TANK IN SPACE BY JET INJECTION UNDER ZERO GRAVITY CONDITION1)

Liquid Hydrogen plays a vital role in the future energy system as a space propellant, but it is sensitive to heat leakage from the environment because of its low boiling point and easy evaporation. On the other hand the buoyancy convection in the space microgravity environment is significantly reduced. When there is local heat leakage on the wall of the propellant tank, temperature stratification arises around the heat leakage source causing local overheating. It seriously affects the multiphase heat and mass transfer in the propellant tank which induces the tank pressure rise and jeopardize the structural safety of the system. To prevent the tank pressure from rising above the design of limits, venting or active pressure control techniques must be implemented. The cryogenic jet mixing is an effective means to suppress temperature stratification. The cryogenic fluid is mixed with the fluid inside the tank through a jet nozzle to reduce the local high temperature and achieve uniform temperature. In present paper, the thermal stratification phenomenon caused by the local heat leakage under microgravity condition was numerically simulated by using a fully filled two-dimensional large scale tank model. This paper mainly analyzes the suppression and elimination of local thermal stratification caused by heat leakage near the bottom of the storage tank and the outlet connecting section. The influence of different cryogenic jet mixing conditions on eliminating the temperature stratification effect is analyzed. The results show that the position of jet nozzle has no obvious effect on the elimination of thermal stratification inside the tank when the circular jet nozzle is used and the cryogenic jet condition is the same. When the jet nozzles are located in the same relative position inside the tank and the incident flow rate is the same, the circular jet nozzles have more concentrated flow direction, the flow field in the tank evolves faster, so the thermal stratification elimination effect is better than the hemispherical jet nozzles.

Power and Efficiency Characteristics of a Hybrid Electrochemical-ICE Cycle

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Power and efficiency characteristics of a hybrid cycle combining an electrochemical device (Fuel-Cell) and an internal combustion engine (ICE) were analyzed using the low-dissipation model. The low-dissipation model links energy dissipation with the energy transfer rate through the cycle. In the considered cycle, the electrochemical device transforms chemical potential of the fuel to electrical work, and the ICE uses the heat rejected by the electrochemical device and its exhaust effluent for mechanical work production. The cycle efficiency was calculated as a function of the hybridization level. The latter is defined as the electrical work fraction in the total cycle work. The results of the study show that the cycle efficiency is growing with the electrical work fraction increase. On the other hand, maximum power of the cycle is attained at an intermediate hybridization level. Moreover, power to weight ratio and power density of the cycle have maxima at different hybridization level. Cycle cooling losses are modeled as heat leak to the ambient that depends on the temperature and the duration of the cycle. Cooling losses are found to be the most influential parameter in optimization of the hybridization level for maximum power. In the extreme case of zero cooling losses, maximum power could be attained with ICE operation alone without the electrochemical reaction. The latter finding might be of interest for aerial propulsion systems. However, if efficiency is more important - for example for ground propulsion systems - the hybrid cycle is beneficial.&lt;/div&gt;&lt;/div&gt;

On miniaturisation of spirally wound tubular heat exchanger

Spirally coiled multilayer, Giauque-Hampson type heat exchangers, the classical examples of early generation cryogenic heat transfer devices, are best known for their unique and favourable features. These exchangers are capable of handling multiple fluid streams in different phases in a single unit, typically meant for high Ntu applications, operational over a wide range of temperature and pressure with minimum thermal stress development. On the negative part, they belong to the non-compact class of heat exchangers. As the trend of miniaturisation is gradually diffusing into almost every engineering discipline, the development of a compact system is the call of the present era. While probing the prospect of miniaturising multilayer spirally wound tubular (Giauque-Hampson) heat exchangers satisfying the compactness criteria, this article presents the design, fabrication, and testing of a miniature, compact, laboratory-scale prototype. Initially, the pros and cons of miniaturisation have been studied based on the ‘goodness factors’. Subsequently, a step-by-step methodology is proposed to design a compact and miniature heat exchanger geometry, subjected to design constraints. Description of critical fabrication steps is followed by the experimental performance evaluation of the prototype. The heat exchanger effectiveness is calculated based on the steady-state experimental data. Performance degradation is linked to the prevailing non-ideal operating conditions causing external heat ingress. The analysis including heat leak shows good agreement between the experimental results and theoretical predictions.

Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine.

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.

Determination of thermal conductivity of hollow glass microspheres (HGM) using graph theory and matrix approach

The method named ”Graph Theory and Matrix Approach” has been well used in numerous research studies to carry out decision-making when the problem becomes perplexed form or when the relative importance of one parameter over another is quite high. In such instances, the said Theory of graphical and matrix approach offers very suitable and fruitful solutions to efficiently render the decision. Using combined application of theoretical graph method findings coupled with certain artificial intelligence-inspired logics and practises like fuzzy logic, artificial neural network, etc., more developments and outcome enhancement can also be disclosed. Such method’s relevance and applicability in large fields of technology, engineering, and analysis are also proven. Today, our industrial industries are upgrading by artificial intelligence applications and other software-based directions. In this research, graph theory is used to test hollow glass microspheres (HGM) performance by evaluating thermal conductivity based on pressure, evaporation rate and heat leakage. 16 Tests were conducted with four samples A, B, C and D with four different pressure variations.

Performance optimization of thermionic refrigerators based on van der Waals heterostructures

In this paper, an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite time thermodynamics. The basic performance characteristics of the refrigerator are obtained. The effects of key factors, such as bias voltages, Schottky barrier heights and heat leakages, on the performance are studied. Results show that cooling rates and coefficients of performances (COPs) can attain the double maximum with proper modulation of barrier heights and bias voltages. Increasing cross-plane thermal resistance as well as decreasing electrode-reservoir thermal resistance and reservoir-reservoir thermal resistance can enhance the performance of the device. The optimal performance region is the interval between the maximum cooling rate point and the maximum COP point. By modulating the bias voltage, the working state of the device can fall into the optimal performance region. The optimal performance of the refrigerator when using single layer graphene and a few layers graphene as electrode material is also compared.

Modeling of Loop Heat Pipe Thermal Performance

The present work deals with the heat transfer performance of a copper-water loop heat pipe (LHP) with a flat oval evaporator in steady-state operation. Modeling the heat transfer in the evaporator was particularly studied, and the evaporation heat transfer coefficient was determined from a dimensionless correlation developed based on experimental data from the literature. The model was based on steady-state energy balance equations for each LHP component. The model results were compared to the experimental ones for various heat loads, cooling temperatures, and elevations, and a good agreement was obtained. Finally, a parametric study was conducted to show the effects of different key parameters, such as the axial conductive heat leaks between the evaporator and the compensation chamber cases, the capillary structure porosity and material, and the groove dimensions.

New methods of testing heat leak in cryogenic vessels

The heat leak in a cryogenic vessel is currently analyzed using a standard test based on measuring loss product. The test requires 72 h to complete; in addition, it requires that gas is discharged from the vessel to equalize the vessel pressure with the atmospheric pressure before the test can be performed. Therefore, the test is ineffective and wastes gas. In this study, new methods using constant pressure, constant flow rate, and self-pressurization are proposed to resolve the limitations posed by the standard test. Based on the heat leak transfer process and energy equations for cryogenic vessels, all factors, including temperature, pressure, latent heat, that influence the heat leak in cryogenic vessels are determined and analyzed. For a given cryogenic vessel, according to the equation between heat leak, temperature, and pressure, new test methods are proposed. Tests were conducted applying the new methods. The test results of each method showed that the heat leak in the cryogenic vessel was calculated accurately. We concluded that the new methods are effective and save significant amount of gas compared with the standard method.

Airtightness of High-Rises in the North

For the Republic of Sakha (Yakutia), effective thermal insulation of buildings is imperative for human comfort and for reducing the leakage of heat through the envelope. To design such insulation, one needs to duly consider the microclimatic specifics in the context of an extreme continental climate. Climate-induced leakage of heat through the envelope results in heat and electricity waste; such leakage is non-acceptable by modern standards. Demand for energy-efficient housing is rising. Thus, improving the thermal insulation of structures is a relevant issue.

Application of Precision Thermal Control Techniques in Taiji-1 satellite

In order to detect gravitational waves in space, the Chinese Academy of Sciences has drawn up the Taiji plan. The first step of the Taiji plan is to verify the key techniques of the core payload through the Taiji-1 satellite in low Earth orbit. Because the temperature stability directly affects the measurement accuracy of the interferometer ranging and acceleration, the temperature control index of (<italic>T</italic>± 0.1) K with high precision and high stability is proposed for the Taiji-1 satellite. Based on this requirement, an efficient thermal control scheme was designed. In the scheme, the thermal control from the selection of thermal components to the application of stand-alone equipment was controlled according to high indicators. At the same time, in the process of thermal implementation, in order to ensure the efficiency of the scheme, detailed control was also carried out. The thermal control scheme adopts the constant temperature cage as the design concept, adopts the means of three-stage temperature control, and combines the principle of active and passive. Finally, the high stability index of on-orbit flight temperature control of (<italic>T</italic>±0.005) K is obtained. Through the application research of high precision and high stability technology, it is found that thermal control heating scheme, heat leakage control, single resolution of temperature controller, temperature measuring circuit, control algorithm, control precision, temperature measuring resolution of temperature measuring element are still the important factors that restrict high precision temperature control technology.

A solar thermal storage power generation system based on lunar in-situ resources utilization: modeling and analysis

Continuous energy supply is crucial to the crew and assets of lunar outposts during the darkness lunar night of 350 h in the long term lunar exploration. A solar energy storage power generation system based on in-situ resource utilization (ISRU) is established and analyzed. An efficient linear Fresnel collector is configured for solar concentration. The thermal energy reservoir (TER) coupling with Stirling power generator is designed using the fuel tanks of descent module and lunar regolith. A comprehensively theoretical model based on finite time thermodynamics is developed to analyze the energy flow and efficiency of thermal storage power generation system, and the major irreversibilities are taken into account. The results show that the designed system can produce an average power of 6.5 kW during the lunar night with 19.6% utilization efficiency of collected solar energy in the daytime. The evaluated launch mass of designed power system has a competitive advantage than those of nuclear reactor power and photovoltaic-battery power systems. The influences of major heat transfer processes including heat leakage of TER, heat exchange capability of Stirling engine and radiator are also discussed, which provides physical insight for optimal design of future power generation system based on ISRU.

Numerical study of the boil-off gas (BOG) generation characteristics in a type C independent liquefied natural gas (LNG) tank under sloshing excitation

In this paper, a numerical model considering phase change and external heat leakage is established to study the thermodynamic and hydrodynamic of a type C LNG tank under sinusoidal sloshing excitation. The volume of fluid (VOF) method, coupled with the mesh motion treatment, is adopted to predict the movement of the vapor-liquid interface. The sinusoidal sloshing excitation is realized by a user-defined function (UDF). Compared with related fluid sloshing experiments, the feasibility of the numerical model is verified. The numerical results show that the sloshing excitation has great influences on the thermophysical process and the BOG generation of the LNG tank. The effects of different sloshing frequencies and amplitudes on the thermodynamic characteristics of the LNG tank are studied. In addition, the partial damage of the insulation system is also studied, and it is found that the sloshing has little effect on the critical superheat of the tank wall where the insulation layer is partial damaged, but it will delay the increase of the tank wall temperature. This study is significant to deeply understand the thermal behavior of the LNG sloshing and the characteristics of the BOG generation under sloshing condition during the actual marine transportation of LNG ships.

Design of Internal Supports for Double-Walled Liquefied Natural Gas Road Tanker

Transport and storage of liquefied natural gas (LNG) requires special double-walled cryogenic tanks. To provide a liquid state of LNG throughout entire storage time a temperature inside the tank should be equal −160 °C under the pressure of around 7 bar. Maintaining these parameters requires a vacuum insulation system and internal supports designed to minimize heat leakage into the tank. Additionally, the internal supports must be able to transfer complex mechanical loads that may occur during the operation of the tanker. Combinations and values of directional mechanical loads and thermal loads, to be accepted in designing mobile cryogenic tanks, are determined by proper vessels standards. In this article, we proposed the construction of internal supports for 25 m3 road tanker, which structure allows to reduce heat leakage into the internal tank, while transferring the complex mechanical loads. Tests of the presented solutions were carried out applying both mechanical and thermal finite element analysis using ANSYS software.