Influence Of Thermal Resistance Research Articles

Thermoelectric performance study on a heat pipe thermoelectric generator for micro nuclear reactor application

Heat pipe cooled reactor is designed to meet the future energy demands with many unique advantages such as modularization, solid and static state, high reliability and passive safety. In the innovative nuclear reactor design, heat pipes are used to cool the reactor core and transfer the fission heat passively, thermoelectric generators (TEGs) are utilized to achieve static energy conversion. In this article, a finite element model is established to investigate the detailed TEG thermoelectric performance coupled with heat pipes. A temperature field and flow field coupling model is used to simulate the heat transfer performance of the potassium heat pipe including a heat pipe wall, wick and vapor region. A heat pipe TEG experimental setup is established and the steady-state experiment is conducted. The experimental setup is selected as the numerical simulation object and the simulated results are compared with the experimental data to verify the numerical model. The maximum simulation error is within 5%. Based on the verification and validation, the steady-state thermoelectric performances, the effect of contact thermal resistance and external load on the skutterudite TEG thermoelectric performances are investigated. The detailed heat flux distributions, temperature distributions and potential distributions are researched in the steady-state simulation. The temperature distributions of the TEG cross section are centrally symmetrical and the horizontal temperature difference is 26°C. The temperature difference introduced by thermal resistance at the TEG hot side increases from 33°C to 94°C with the increasing heat flux through TEG module. The influence of thermal resistance on TEG hot side is more significant than that on TEG cold side. The effect of external load on TEG output characteristics is investigated under different heat flux conditions. With the increase of heat flux from 60 to 166 kW/m2, the temperature difference of TEG module and p-n unit increase by 432°C and 348°C, the thermoelectric conversion efficiency is improved from 3.6% to 8.5%, and output power increases by 20 W, respectively. The research results are of guiding significance for exploring the application potential of TEGs in the static heat pipe cooled reactor. This work provides research foundations for the multiphysics coupling analysis of the micro heat pipe cooled reactor.

INFLUENCE OF THERMAL RESISTANCE OF AIR CONDENSER TUBES ON STEAM COOLING EFFICIENCY


 
 
 The research is carried out using a mathematical model of conditions and features of condensation processes with the influence of changes in internal and external thermal resistances of working bodies, which occur during contamination of outside and inside metal pipes of heat exchange surfaces of air condenser. capacitor. Particular attention is paid to the selection, detailing and determination of more than twenty basic parameters that characterize the operation of the direct cooling unit of the condensing unit for the summer, the conditions of heat transfer processes between the working bodies taking into account the finned outer surface of elliptical condenser tubes. The results of experiments on the mathematical model are analyzed and the influence of the incoming air velocity and ambient temperature on the output steam pressure in the condenser direct air cooling system within the change of internal and external thermal resistances in the range 0-0.001(m2·K)/W due to cooling tube contamination is determined. air condenser steam turbine installation. Conditions, character and features of influence of thermal resistance of pollution in cooling tubes on steam pressure at an exit from them are defined, the basic factors defining steam pressure at an exit, necessity of the organization of control of thermal resistance of pollution in a pipe during unit operation at variable operating conditions and expediency is substantiated. conducting test studies of operating modes while taking into account the influence of thermal resistance of external and internal pollution on the thermal efficiency of the cooling unit.
 
 
 
 Studies have shown that at a fixed value of the heat load of the exhaust steam, the pressure of the steam outlet increases with increasing ambient temperature and decreasing the speed of the incoming air.
 
 
 
 
 

Plane Thermoelastic Deformation of a Multilayer Foundation with Non-Ideal Thermal Contact between its Layers

We proposed the method of the compliance function for the solution of two-dimensional stationary problem of thermoelasticity for a multilayer foundation (stack of elastic layers coupled with a half plane) with a non-ideal thermal contact between its layers. We constructed the recurrence relations for the auxiliary functions and the compliance functions of neighboring layers of the foundation. We analyzed the influence of thermal resistance on the distribution of stresses and temperature at the points of the lower boundary of the upper layer for a two-layer foundation subjected to the action of thermal loads.

Dimensionless Mathematical Model of a Thermoelectric Cooler: ΔTmax Mode

The thermal resistances on the cold and hot sides substantially affect the output characteristics of thermoelectric devices. A dimensionless mathematical model of a thermoelectric cooler, which makes it possible to calculate device parameters, such as the optimal thermal resistance ratio on the cold and hot sides as well as the optimal current taking into account the influence of thermal resistances, is presented. The maximal temperature difference ΔTmax mode is considered. It is shown that the optimal cooler parameters are different for implementation of the ΔTmax and Qmax modes. The determining factor for the ΔTmax mode is the influence of the thermal resistance on the hot side, and the optimal current is 0.4–0.7 of the maximal current in most cases for the material with ZT = 1. It is shown that an additional increase in ΔTmax of a cooler is attained with a decrease in the thermal conductivity of the thermoelectric material due to a decrease in the influence of the thermal resistance on the hot side besides the effect from an increase in ZT. An increase in the length of thermoelectric legs has the same positive effect of an increase in ΔTmax of a cooler, while a decrease in the leg length negatively affects ΔTmax.

Безразмерная математическая модель термоэлектрического охладителя: режим Delta T-=SUB=-max-=/SUB=-

AbstractThe thermal resistances on the cold and hot sides substantially affect the output characteristics of thermoelectric devices. A dimensionless mathematical model of a thermoelectric cooler, which makes it possible to calculate device parameters, such as the optimal thermal resistance ratio on the cold and hot sides as well as the optimal current taking into account the influence of thermal resistances, is presented. The maximal temperature difference Δ T _max mode is considered. It is shown that the optimal cooler parameters are different for implementation of the Δ T _max and Q _max modes. The determining factor for the Δ T _max mode is the influence of the thermal resistance on the hot side, and the optimal current is 0.4–0.7 of the maximal current in most cases for the material with ZT = 1. It is shown that an additional increase in Δ T _max of a cooler is attained with a decrease in the thermal conductivity of the thermoelectric material due to a decrease in the influence of the thermal resistance on the hot side besides the effect from an increase in ZT . An increase in the length of thermoelectric legs has the same positive effect of an increase in Δ T _max of a cooler, while a decrease in the leg length negatively affects Δ T _max.

Performance of concrete-filled steel tubular column-wall structure subjected to ISO-834 standard fire: Experimental study and FEA modelling

This paper reports a full-scale fire testing of concrete filled thin-walled steel tubular (CFST) column-wall structure. All together eight specimens were designed and tested under axial compression load and subjected to ISO-834 standard fire. Load ratio, fire-exposure time and insulation scenarios were varied in the testing program. Cement mortar, aerated concrete block, and mineral wool were used as the insulation layer materials. Test results including temperature to time relations, axial deformation, and fire resistance as well as failure modes were described. A finite element analysis (FEA) model was established in order to simulate the thermal and structural behavior of CFST column-wall under fire. The FEA model was verified against test data and turned out to be reasonably accurate in predicting the temperature distribution, axial displacement, fire resistance and failure modes of CFST column-walls. Sensitivity studies were carried out to determine some major parameters in the FEA model. Discussion was made on the influence of thermal resistance, spalling of the insulation layer and confinement of inner concrete on the modelling of CFST column-wall structures.

Tuning Parameters of Pid Controllers for the Operation of Heat Exchangers Under Fouling Conditions

The present paper is an extension of the work presented by authors at SDEWES2015 conference, where changes in the dynamic behaviour of shell-and-tube heat exchangers induced by fouling build-up were studied. A mathematical model was proposed of transient heat exchange with the influence of thermal resistance of fouling taken into account. Next a mathematical model of the entire heat exchanger was implemented and simulations were carried out using Simulink in MATLAB environment. The model was validated using data records acquired during 3 years of operation of a heat exchanger network coupled with a Crude Distillation Unit (CDU). Using the validated dynamic model, one can simulate the behaviour of a heat exchanger together with its PID control loop and investigate the influence of fouling build-up on specific indexes of quality of operation. A simulation study was carried out on selected PID-controlled exchangers operated in a heat exchanger network coupled with a CDU rated 220 kg/s crude oil. For different periods of uninterrupted exchanger operation, that is, at different values of the thermal resistance of fouling, tuning parameters were determined using the Ziegler-Nichols method. It was found that the optimal values of tuning parameters changed when the thermal resistance of fouling was changed. However, oscillations remained in the characteristics of some controlled exchangers indicating that the new values of tuning parameters determined by the simple Ziegler–Nichols method were ineffective. In the present work, to improve the quality indices of the exchangers control under fouling conditions, a more advanced method of the optimization of controller tuning is presented using Signal Constraint block in MATLAB/SIMULINK.

Effect of Conjugated Heat Transfer Conditions on the Crystallization of the Composite Coating

This paper presents the thermophysical model of crystallization of the coating at the conditions of imperfect contact between the coating and sunstrate. The model takes into account the heat exchange of coating with the environment and with the substrate. The influence of thermal resistance of the interface and concentration of filler in the coating on the change of temperature during cooling is investigated.

The Influence of Thermal Resistances and Nonperfect Regenerative Losses on the Performance of a Ferroelectric Ericsson Refrigerator

Using the finite-time thermodynamics, the influence of thermal resistances and nonperfect regenerative losses on the optimal performance of a ferroelectric Ericsson refrigeration-cycle is analyzed. Based on the thermodynamics properties of ferroelectric materials and a linear heat-transfer law, the inherent regenerative losses in the cycle are calculated and the fundamental optimum relations and other relevant performance parameters are determined. The ecological optimization criterion of the refrigerator is derived. The results obtained here may reveal the general characteristics of the ferroelectric Ericsson refrigeration cycle.

Optimization of the rate of exergy output for an endoreversible Carnot refrigerator

By using finite-time thermodynamic theory, the optimal performances related to exergy of a Carnot refrigerator under the influence of thermal resistance are studied. The optimal relations between the rate of exergy output and the coefficient of performance and between the rate of exergy output and the rate of refrigeration are derived. Moreover, the main characteristics of the two optimal relations are discussed and some uses of the concept of exergy in finite-time thermodynamic theory are expounded. Some novel and useful results are obtained. Finally, it is pointed out that to extend the traditional exergy analysis using the theory of finite-time thermodynamics is quite important.

The effect of irreversibilities on the performance of a three-heat-source heat pump

An irreversible three-heat-source heat pump may be treated as a combined cycle of a finite-size irreversible Carnot heat engine driving an irreversible Carnot heat pump. The influence of thermal resistance and working fluid internal dissipation on the optimal performance of a three-heat-source heat pump is investigated by using a finite-time thermodynamic approach. The results obtained here are more realistic than those of classical thermodynamics.

The fundamental optimal relation and the bounds of power output and efficiency for an irreversible Carnot engine

By using the finite-time thermodynamic method, the optimal performances of a Carnot engine under the influence of thermal resistance, heat loss and other irreversibilities are studied and the fundamental optimal relation for the engine is derived. Thus, a new theory for irreversible Carnot cycles is established, together with some significant discussions. The results obtained here are more general and useful than those in the relevant literature.

Optimal heat-transfer areas for endoreversible heat pumps

The influence of thermal resistance on the performance of a heat pump operating with three heat sources is investigated by using an endoreversible cyclic model with continuous flow. The overall heat-transfer area of the heat pump is chosen as an objective function for optimization. For a specified COP and rate of heat pumping, the expression for minimum overall heat-transfer area of the heat pump is derived. This expression is used 1. (a) to discuss the optimal performance of an endoreversible heat pump operating with three heat sources and 2. (b) to deduce the optimal performance of a Carnot heat pump with continuous flow. The results obtained here may be useful for exploitation of heat pumps driven by low-grade heat from the sun, geothermal energy or waste heat and also for improvement of heat pumps driven by high-grade energy sources.

Influence of thermal resistance of condensate drops on heat and mass transfer in condensation of vapor from a vapor-gas mixture

Heat transfer to a solid wall during condensation of a vapor from a vapor-gas mixture in drops is discussed.