One-dimensional Heat Transfer Analysis Research Articles

Nonlinear transient heat transfer analysis of multilayered thermal protection systems by incremental differential quadrature element method

As a first attempt, the incremental differential quadrature element method (IDQEM) is used for the one-dimensional nonlinear transient heat transfer analysis of multilayered thermal protection systems (TPSs) under time-dependent aerodynamic heating. All thermophysical properties are considered to be temperature-dependent (TD). Based on the IDQEM, the multilayered TPS is divided into several spatial sub-domains along the layer interfaces, and the entire heating process is also divided into several temporal sub-domains. For each temporal sub-domain, the governing equations are discretized by the differential quadrature method and then solved by the Newton-Raphson method. The initial condition of each temporal sub-domain is defined by the temperature results at the end of the previous sub-domain. The temperature profile of the TPS during the entire heating process can be obtained by repeating the calculation procedure from the first temporal sub-domain to the last one. Convergence and accuracy of the method are confirmed. Numerical examples are carried out to show the effects of TD thermophysical properties, thermal boundary, and layer thickness on the temperature profile of a three-layer TPS. The results show that the temperature dependency of thermophysical properties is worthy of consideration in predicting the temperature profile of the TPSs.

Simplified Modeling and Analysis of Surface Temperature Distribution in Electrically Heated Catalyst for Diesel Urea-SCR Systems

Impending emission regulations of diesel engines for construction machineries would regulate nitrogen oxide emissions strictly in cold operating conditions. The urea-based selective catalytic reduction (urea-SCR) system coupled with the electrically heated catalyst (EHC) has been considered as a potential measure to meet the strict emission regulations by promoting evaporation and thermal decomposition of urea–water solution in cold operating conditions. Analyzing the thermal conditions in the EHC is crucial for the optimized operation and control of EHC-based urea-SCR systems under various engine operating conditions. In the current study, we introduce a simple one-dimensional analysis scheme to characterize the surface temperature distribution in the EHC based on energy conservation and the theories of forced internal convection. Since the EHC has a complicated internal structure with fine flow cells inside it, a flow cell in the EHC is extracted for the one-dimensional heat transfer analysis. EHC operation parameters such as exhaust gas flow rate and supplied electric power to the EHC are scaled to be applied for the flow cell analysis. The adequacy of the analysis scheme is then validated by surface temperature measurement results at the EHC outlet. The validation results showed over 95% prediction accuracy of the 1D analysis scheme in the operating conditions of a heavy-duty diesel engine. Based on proven reliability, the effects of geometric and operation parameters on the surface temperature distribution in the EHC were analyzed and discussed using the analysis results.

The performance evaluation for thermal protection of turbine vane with film cooling and thermal barrier coating

• An expression of temperature-independent overall cooling effectiveness is obtained. • The external convective heat transfer is effected by the internal cooling flow. • Increasing convective heat transfer can increase overall cooling effectiveness. • Four parameters need to be similar when conducting heat transfer experiments. When conducting wind tunnel heat transfer test to evaluate the cooling performance of the turbine, it is difficult and costly to simulate the extremely high temperature gas of the real working conditions, and small temperature difference and room temperature test is usually used instead. In order to evaluate the cooling performance under real working conditions from the experimental results at room temperature, the corresponding evaluation method needs to be studied. In this paper, a turbine vane with film cooling and thermal barrier coating (TBC) is used as the study object. By introducing an improved driving temperature and adopting one-dimensional heat transfer analysis, an improved analytical expression of overall cooling effectiveness, which is independent of temperature, is derived and analyzed. Through numerical calculation, the overall cooling effectiveness defined by different reference temperatures are compared. The results show that the heat transfer of the turbine vane with film cooling and TBC is complicated. The influence of the internal cooling should be considered when calculating the external convective heat transfer. The temperature-independent overall cooling effectiveness on the TBC surface and the superalloy surface are obtained, respectively. The improved overall cooling effectiveness is more sensitive to the thermal resistance of the superalloy compared with the thermal resistance of the TBC. The overall cooling effectiveness can be improved by increasing the internal or external convective heat transfer coefficient. In order to obtain an accurate overall cooling effectiveness (dimensionless wall temperatures), it is necessary to satisfy similarities of four dimensionless parameters, including the Biot numbers ( B i TBC , B i w ), the ratio of external and internal convective heat transfer coefficients ( h e / h i ) and the ratio of gained convective heat transfer coefficient and external convective heat transfer coefficient ( h e , i / h e ).

Thermal Design of a Biohydrogen Production System Driven by Integrated Gasification Combined Cycle Waste Heat Using Dynamic Simulation

Utilizing biological processes for hydrogen production via gasification is a promising alternative method to coal gasification. The present study proposes a dynamic simulation model that uses a one-dimensional heat-transfer analysis method to simulate a biohydrogen production system. The proposed model is based on an existing experimental design setup. It is used to simulate a biohydrogen production system driven by the waste heat from an integrated gasification combined cycle (IGCC) power plant equipped with carbon capture and storage technologies. The data from the simulated results are compared with the experimental measurement data to validate the developed model’s reliability. The results show good agreement between the experimental data and the developed model. The relative root-mean-square error for the heat storage, feed-mixing, and bioreactor tanks is 1.26%, 3.59%, and 1.78%, respectively. After the developed model’s reliability is confirmed, it is used to simulate and optimize the biohydrogen production system inside the IGCC power plant. The bioreactor tank’s time constant can be improved when reducing the operating volume of the feed-mixing tank by the scale factors of 0.75 and 0.50, leading to a 15.76% and 31.54% faster time constant, respectively, when compared with the existing design.

Model order reduction of three-dimensional transient heat transfer analysis to one-dimensional by using Krylov-subspace concerning cooling effect of air

In semiconductors packages, heat generation density is increasing due to miniaturization. Since heat generation is caused by voltage input at the packages, electronic components are usually cooled by air. In recent years, electrification is widely spread among many engineering products like motor vehicles, and the amount of semiconductors packages installed in those products as well. To make the electronic components more densely installed, co-simulation of heat transfer analysis and electrical circuits is needed at designing products. In this paper, by using the Krylov-subspace model order reduction method, the accuracy of one-dimensional heat transfer analysis model concerning cooling effect of air is evaluated. By using the method, co-simulated with electrical circuits is possible.

Coupling Simulation of Thermal Response to Exhaust Gas at External Nozzle

This paper examines thermal response behind the high-Mach integrated control (HIMICO) experiment’s engine. In this experimental aircraft, instruments must be protected from heat load due to exhaust gas; therefore, a coupling calculation between the fluid and the wall is conducted to confirm the performance of HIMICO’s thermal protection system (TPS). First, the validity of the coupling calculation is confirmed through comparison with aerodynamic heating on a hollow cylinder. The present calculation result can reproduce the surface temperature distribution on the cylinder better than previous work has managed because we consider the turbulence effect. Second, one-dimensional heat-transfer analysis is conducted on the external nozzle, and the appropriateness of the calculation result is confirmed through comparison with the ramjet-engine experiment. Finally, a coupling calculation between the fluid and the wall is conducted to investigate the local temperature distribution. The calculation result indicates that the temperature increase easily meets design requirements and that TPS performance is sufficient.

A Theoretical Model for Wearable Thermoelectric Generators Considering the Effect of Human Skin

Wearable thermoelectric generators (w-TEGs) are attracting interest due to their ability to self-power miniaturized electronic devices by converting human body heat into electricity. However, the harvested power density utilizing w-TEGs is in the range of microwatts to milliwatts per square centimeter, which is not sufficient for powering wearable sensors and electronics. In this paper, a theoretical model for w-TEGs considering the human skin effect is developed based on one-dimensional heat transfer analysis. Human skin is geometrically modeled as a multilayer structure consisting of fat, dermis and epidermis, and metabolic heat generation and blood perfusion in skin tissues are taken into account. The influence of load resistance, skin effect, thermal contact resistance at the skin/w-TEG interface, fill factor, thermal conductivity of fill material and heat convection of the spreader on the performance of w-TEG are investigated. Numerical results show that the effect of metabolic heat generation can be negligible, but the heat transfer by blood perfusion in dermis should be considered for the power analysis of w-TEG. The simplified solutions with high accuracy which are more convenient for engineering application of w-TEGs are obtained through rigorous mathematical analysis. The closed-form optimal expressions of load resistance, fill factor and leg height corresponding to maximum power output are provided, and these results can be used to explore the design criteria of w-TEGs. The proposed model considering the effect of human skin is extremely helpful in the actual design of w-TEG devices.

A time-saving method to evaluate the thermal insulation performance of cryogenic vessels

Equivalent mass loss is a critical index used to evaluate the thermal insulation performance of cryogenic vessels. The current test standards for measuring the thermal insulation performance of cryogenic vessels in different countries require a long testing time and waste a considerable amount of working medium. In this study, a method that can shorten the test time of the thermal insulation performance of cryogenic vessels is established. Different from the current test methods that rely entirely on experiments, the method proposed in this paper is a semi-experimental and semi-analytical calculation method. The proposed method is based on the one-dimensional heat transfer analysis of a cryogenic vessel and short-term experimental test data, and it can be used to predict the mass loss over a long period of time. Moreover, the method can predict the mass loss of a cryogenic vessel at a high liquid level when the mass loss at a low liquid level is known. When this method is used to predict the mass loss, the comparison with the experimental data shows that the maximum relative error of the instantaneous mass flow is 21.1% and the relative error of the cumulative mass flow is less than 8%. When this method is used for the calculation of heat leakage between different liquid levels, the results show that the larger the difference between the two liquid levels, the greater the error of leakage heat, and the maximum is 18.9%.

Engineering aspects and thermal performance of molten salt transfer lines in solar power applications

Concentrating solar thermal power coupled with thermal energy storage is considered as one of the leading technologies to address the decarbonization of the energy sector. The use of molten solar salt (60–40% b.w. NaNO3-KNO3) as heat transfer fluid and thermal storage medium is the current commercial practice, with alternative salt mixtures being under evaluation for the next-generation higher-temperature systems. The main drawback of the molten salts is their high freezing temperature; active means are required for preheating of- and to prevent salt from freezing in- the transfer lines.In this article we present experiences from the PROTEAS facility, where heating tapes as opposed to heating cables are used. The thermal energy losses from the transfer lines are evaluated and compared to those predicted by a one-dimensional heat transfer analysis. Thermal losses between 43 and 100 W/m are found at operating temperatures from 300 to 500 °C. A joint optimization of the capital and operational expenditure for heating tapes and insulation is performed, leading to the optimal insulation thickness and installed heat tracing capacity. Increasing the installed heat tracing capacity with respect to the minimum required to overcome thermal losses, leads to a reduction of the preheating time and, therefore, a reduction in the overall operational expenses of the system. In some situations, this was found to also lead to a reduction in the necessary insulation thickness. Simulations indicate that if the optimal insulation was used, a decrease of 10 and 15% in thermal losses and O&M expenditures, respectively, could be achieved.

One dimensional liner temperature prediction in a tubular combustor

Liner cooling can be optimized in the preliminary design phase by using one-dimensional heat transfer analysis in scope of the gas turbine combustor liner durability. So it is important to understand heat transfer process in the combustor liner for an effective prediction of liner wall temperatures. In this study, one –dimensional liner wall temperature predictions of an experimental tubular combustor have been performed for different operating conditions. Experimental tests have been obtained by the combustor atmospheric rig tests over a range of inlet temperature from 400 to 475 K and inlet mass flow rates of 0.035–0.050 kg/s at 6 different axial locations representing the primary zone, film cooled area, secondary zone and dilution zone. A tubular type combustor with air-blast fuel injections has been used for the experimental study. By the help of this architecture, it was possible to get more axially symmetrical temperature distribution compared to an annular combustor. Predictions shows that a maximum 85 K error in primary zone. It has been predicted more accurate results in the other zones.

Thermal Modeling and Performance Analysis of U-Tube Evacuated Solar Collector using CO2

This study deals with the thermal modeling of U-tube evacuated solar collectors to investigate the heat transfer and performance characteristics. The U-tube evacuated solar collectors are integrated into solar-assisted new generation experimental organic Rankine cycle working with environmentally friendly supercritical CO2. For the modeling, one-dimensional heat transfer analysis is applied to the U-tube collectors for determining the heat transfer characteristics of the collectors as well as the CO2 exit temperature from the collectors for the steady heat transfer process. Additionally, heat loss coefficient and overall heat transfer coefficients are determined for the experimental U-tube collectors. The obtained results are also compared with the results of the experimental study.

Effects of wall thickness and material property on inverse heat conduction analysis of a hollow cylindrical tube

In this study, we examined the effects of a hollow cylindrical tube’s thickness and material properties on estimated time delay and waveform distortion in a one-dimensional inverse heat transfer analysis model using the thermal resistance method and an input estimation algorithm. Results indicated a persistent time delay for various heat flux amounts applied to different tube thicknesses. As the tube thickness increased, the numerically determined temperature data also experienced a time delay, which affected the inverse heat transfer response curve. Results also indicated that the transient heat flux waveform estimated for different material properties showed higher levels of distortion for materials having relatively low thermal conductivity. These materials also exhibited greater time delays. To address these issues, we applied a Fourier number (a dimensionless number representing the tube’s thickness and material properties) and proposed an equation to calculate sharpness, which can subsequently be used to predict probable time delays and heat flux waveform distortion. In conclusion, a correction is required when a low Fourier number is used in inverse heat transfer analysis.

Transient Thermal Behavior of Annular Thermoelectric Cooling System

The transient thermal behavior of an exoreversible thermodynamic model of an annular thermoelectric cooler has been studied by one-dimensional unsteady-state heat transfer analysis. Unlike the flat plate geometry of thermoelectric coolers, which have equal heat transfer area at their hot and cold sides, an annular thermoelectric cooler has a higher heat transfer area at its hot side than its cold side. The temperature variations with time at the hot and cold sides of an annular thermoelectric cooler have been predicted for different cooling loads, current flow, variable thermocouple length and with different heat transfer coefficients at its hot side. Finally, the transient thermal behavior of an annular thermoelectric cooler has been compared with a flat plate thermoelectric cooler. It was found that, for typical operating conditions with zero cooling load, the annular thermoelectric cooler can maintain a 2.3-K lower temperature than the flat thermoelectric cooler. It was also found that when the cooling load is 0.055 W/cm2 with the hot side heat transfer coefficient of 0.010 W/cm2 K, the coefficient of performance of the annular thermoelectric cooler is 2.32% higher than the flat thermoelectric cooler.

Investigating the collector efficiency of silver nanofluids based direct absorption solar collectors

A one-dimensional transient heat transfer analysis was carried out to analyze the effects of the Nanoparticle (NP) volume fraction, collector height, irradiation time, solar flux, and NP material on the collector efficiency. The numerical results were compared with the experimental results obtained by silver nanofluids to validate the model, and good agreement was obtained. The numerical results show that the collector efficiency increases as the collector height and NP volume fraction increase and then reaches a maximum value. An optimum collector height (∼10mm) and particle concentration (∼0.03%) achieving a collector efficiency of 90% of the maximum efficiency can be obtained under the conditions used in the simulation. However, the collector efficiency decreases as the irradiation time increases owing to the increased heat loss. A high solar flux is desirable to maintain a high efficiency over a wide temperature range, which is beneficial for subsequent energy utilization. The modeling results also show silver and gold nanofluids obtain higher photothermal conversion efficiencies than the titanium dioxide nanofluid because their absorption spectra are similar to the solar radiation spectrum.

An approximate analytical method for nonlinear transient heat transfer through a metallic thermal protection system

Metallic thermal protection system (MTPS) is being investigated more popular in present. In preliminary design, the MTPS can be simplified as a multilayer plate, and a one-dimensional transient heat transfer analysis is commonly used to size the thickness of MTPS. A novel approximate analytical method based on separation of variables and orthogonal expansion technique is presented for temperature prediction through MTPS subjected to convection and radiation boundary conditions, which considers the effects of temperature-dependent thermal material properties. The proposed method applies a set of linear functions with space-variable to describe the distribution of thermal diffusivity through the thickness direction, and it adopts a numerical solution dividing the whole process of heat transfer into a chosen number of time steps to solve the problem of boundary conditions variation with time. An advanced linearized approximation for radiation boundary condition is developed for modified use with the analytical model. Implementation of the proposed method is demonstrated by applying it to determine the problem of nonlinear transient heat transfer through a MTPS made of Titanium 6-4 and Saffil, and a good agreement is presented by comparing with the finite element method (FEM) results.

Selection of Materials and Design of Multilayer Lightweight Passive Thermal Protection System

A methodology has been established aiming to design a lightweight thermal protection system (TPS), using advanced lightweight ablative materials developed at the NASA Ames Research Center. An explicit finite-difference scheme is presented for the analysis of one-dimensional transient heat transfer in a multilayer TPS. This problem is solved in two steps, in the first step, best candidate materials are selected for TPS. The selection of materials is based mainly on their thermal properties. In the second step, the geometrical dimensions are determined by using an explicit finite-difference scheme for different combinations of the selected materials, and these dimensions are optimized for the design of lightweight TPS. The best combination of material employs silicone impregnated reusable ceramic ablator (SIRCA), Saffil, and glass-wool for the first, second, and third layer, respectively.

Calibration Procedures for Multidimensional Heat Transfer Models Based on On-site Experimental Data

An experimental and numerical approach to the characterization of thermal bridges is presented, based on on-site taken measurements. Commonly on-site applied numerical thermal assessments perform one-dimensional heat transfer analysis over planar elements such as façades. However, it is well known that within thermal bridges in a building one-dimensional heat transfer analysis cannot be applied.A procedure is proposed, based on the creation of a numerical 2D thermal model which is calibrated against experimental data from several temperature and heat flux sensors which are located at specific points in the thermal bridge elements. Results of one particular implementation of this method are discussed.

Performance study of counter-flow indirect evaporative air coolers

This paper numerically investigates the performance and heat and mass transfer processes that occur in counter-flow indirect evaporative air coolers. Different types of counter-flow air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger, a regenerative unit and a novel modified exchanger, proposed by authors. Additionally the paper investigated impact of location of the perforated holes in the channel plate of regenerative air cooler. The numerical model is based on a one-dimensional heat and mass transfer analysis that was validated against existing experimental data. The results obtained from the simulation reveal the high effectiveness of the presented units. It was established that selected arrangements of the presented exchangers are characterized by the different efficiency in different air-conditioning applications.

Initial Analysis on the Novel Spiky Central Receiver Air Pre-heater (SCRAP) Pressurized Air Receiver

Abstract A combined cycle (CC) concentrating solar power (CSP) plant provides significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A CC CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The small number of pressurized air receivers demonstrated to date have practical limitations, when operating at high temperatures and pressures. As yet, a robust, scalable and efficient system has to be developed and commercialized. A novel receiver system, the Spiky Central Receiver Air Pre-heater (SCRAP) concept has been proposed to comply with these requirements. The SCRAP system is conceived as a solution for an efficient and robust pressurized air receiver that could be implemented in CC CSP concepts or standalone solar Brayton cycles without a bottoming Rankine cycle. The presented work forms part of an initial analysis intended to provide an answer to whether the proposed SCRAP concept can effectively absorb the concentrated solar radiation and transfer the captured heat into a pressurized air stream in a robust and cost-effective manner, while maintaining an acceptable pressure-drop. A ray-tracing study was executed to identify the sensitivity of the SCRAP receiver to optical plant parameters, such as the heliostat size. A one-dimensional heat transfer analysis was initiated to develop initial understanding of the thermal system behavior and generate a tool for rapid geometry optimization.

Conjugate heat transfer analysis of the effects of impingement channel height for a turbine blade endwall

Advancements in cooling for applications such as gas turbines components require improved understanding of the complex heat transfer mechanisms and the interactions between those mechanisms. Critical cooling applications often rely on multiple thermal protection techniques, including internal cooling and external film cooling in gas turbine airfoils, to efficiently cool components and limit the use of coolant. Most research to quantify the effectiveness of such cooling technologies for gas turbine applications has isolated internal and external cooling in separate experiments. The research presented in this paper uses a conjugate heat transfer approach to account for the combined effects of both internal and external cooling. The geometry used for this study is a turbine blade endwall that includes impingement and film cooling as well as the relevant conduction through the endwall. Appropriate geometric and flow parameters were scaled to ensure engine relevant dimensionless temperatures were obtained. Using the conjugate heat transfer approach, the effect of varying the height of the impingement channel was examined using spatially resolved external wall temperatures obtained from both experiments and simulations. A one-dimensional heat transfer analysis was used to derive the average internal heat transfer coefficients from the experimental results. Both experiments and simulations showed good agreement between area averaged cooling effectiveness and impingement heat transfer coefficients. The cooling effectiveness and heat transfer coefficients peaked for an impingement channel height of around three impingement hole diameters. However, the heat transfer coefficients were more sensitive than the overall effectiveness to the changes in height of the impingement channel.