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This paper presents a review of the previous studies and papers about various thermodynamic cycles working for high temperature power generation procedures, in these cycles the highest temperature is not lower than 700 K. Thermodynamic cycles that working for power generation are divided into two broad categories, thermodynamic cycle model study and working fluid analysis. Thermodynamic cycle contains the simple cycle model and the complex cycle model, emphasis has been given on the complex thermodynamic cycles due to their high thermal efficiencies. Working fluids used for high temperature thermodynamic cycles is a dense gas rather than a liquid. A suitable thermodynamic cycle is crucial for effectively power generation especially under the condition of high temperature. The main purpose is to find out the characteristics of various thermodynamic cycles when they are working in the high temperature region for power generation. As this study shows, combined cycles with both renewable and nonrenewable energies as the heat source can show good performance. [ABSTRACT FROM AUTHOR]

Abstract: In the last years, there has been a rapid growth of research and development activities on high temperature molten salts for nuclear and non-nuclear applications. The study of their heat transfer characteristics is a key issue in the current development of the molten salt reactor (MSR) that is one of the innovative nuclear reactors proposed by the Generation IV International Forum. The MSR is a sort of circulating fuel reactor (CFR), which adopts a molten halide salt mixture containing the fissile material and playing the distinctive role of both fuel and coolant. In a thermal-neutron-spectrum MSR, the reactor core is composed by a graphite matrix (neutron moderator), through which the liquid nuclear fuel flows and leads to a strong and intrinsic coupling between thermo-hydrodynamics and neutronics. This peculiar feature requires a suitable and qualified multi-physics simulation environment for a proper description of the system (fuel/coolant+graphite) behaviour. With reference to such complex and non-linear system, the present work is intended to give two different but linked contributions, in the perspective of a multi-physics modelling able to accurately describe the synergy of the involved different physical phenomena (e.g., by means of software). [(I)] On one hand, this work is aimed at establishing a useful validation framework for the assessment of computational fluid-dynamics (CFD) analyses of liquids with internal heat generation. For this purpose, an analytic approach for both fluid velocity and temperature fields in a circular pipe surrounded by a solid region has been developed. It is an extension of the approach elaborated for pipe flow in (Di Marcello, V., Cammi, A., Luzzi, L., 2010. A generalized approach to heat transfer in pipe flow with internal heat generation. Chemical Engineering Science 65, 1301−1310), in order to take into account the heat conduction in the solid domain (represented by the graphite matrix in the specific case of interest). [(II)] On the other hand, the paper presents a preliminary investigation of the thermal-hydraulic behaviour occurring in a typical graphite-moderated MSR core channel. The developed analytic approach has been conveniently applied to this case study: (i) by testing the capabilities of to evaluate the heat transfer characteristics and the hydrodynamic behaviour of such system; and (ii) by investigating the applicability of correlations for the Nusselt number to fluids with internal heat generation. For a deeper insight into the numerical solutions provided by COMSOL, a code-to-code comparison has been also carried out, adopting a dedicated CFD finite volume software (i.e., FLUENT®). As a result, a satisfactory agreement has been found between the analytic solution and the numerical computations provided by COMSOL and FLUENT for a wide range of Reynolds numbers. As concerns the Nusselt number evaluation, the correlations usually adopted for molten salts have been proved as unsuitable for the analysed system, whereas the correlation advanced in the above mentioned paper (that explicitly takes account of the internal heat source) appears more appropriate. The results of the present work are thought to be useful because they provide: (i) a “generalized” analytic approach to the heat transfer that is applicable in a more general context; (ii) an insight into the heat transfer characteristics of the considered graphite-moderated MSR core channel; and (iii) a preliminary assessment of computations that is essential in view of the adoption of multi-physics tools (like COMSOL) for more complex and representative simulations of the dynamic behaviour of the molten salt reactor, and more in general of other kinds of CFRs. [Copyright &y& Elsevier]

High temperature heat pipes offer an efficient way of heat removal in nuclear reactors under both normal operation and postulated accidental scenarios. Heat pipes with sodium as a working fluid has been proposed to be used in Compact High Temperature Reactor (CHTR), 233 U-Thorium fuelled reactor being designed to operate at 1000 °C. High temperature heat pipes can also be used for decay heat removal from dump tanks of molten salt breeder reactor and heat removal from first wall of fusion reactors. High temperature heat pipes of special construction can also be used for heat removal from core without use of coolant. Thus, reliable and long term operation of heat pipes is essential for the safe working of the reactor. In this respect, computer codes have been developed for design and simulation of high temperature heat pipes. To assist in the design stages, codes have been developed, which incorporate performance limits based on correlations and having a user friendly GUI. For system level studies, simplified heat transfer model is developed using a FEM model. For a detailed study of the heat pipe, the vapour flow behavior and interface evaporation condensation phenomena using a full CFD analysis is essential. This has been done by using a commercial CFD code by incorporating user defined functions (UDFs) which address the saturated nature of the vapour phase and the vapour wick interface conditions. A three dimensional transient numerical model has been developed to predict the vapour core, wall temperatures, vapour pressure, and vapour velocity in the screen mesh wick of sodium heat pipe. The results have been compared using a sodium heat pipe developed in-house. This paper will give an outline of all the developed models and compared the predicted results against the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Sorption enhanced methane reforming (SER), employing a CaO-based solid as a high temperature CO2 sorbent, is generally considered to be a promising route for H2 production. In this paper we present a dynamic pseudo-homogeneous model to describe the operation of a packed bed reactor in which the SER reaction is carried out under adiabatic conditions. This reactor can be implemented according to several process schemes, including a novel Ca/Cu looping process for hydrogen generation with inherent CO2 capture. The proposed SER model is based on the well-established principles of gas–solid contact and heat transfer in fixed-bed reactors and on the kinetic expressions published in the literature that describe the main reactions involved in the process. The resulting model describes the transient performance of the SER reaction and confirms the theoretical viability of this critical reaction stage in a large scale H2 production facility. It is demonstrated that the SER process can yield a CH4 conversion and H2 purity of up to 85% and 95%, respectively, under operating conditions of 923K, 3.5MPa, a steam/carbon ratio of 5 and a space velocity of 3.5kg/m2 s. [Copyright &y& Elsevier]

Abstract: The vacuum solar receiver is the key component of a parabolic trough solar plant, which plays a prominent role in the gross system efficiency. Recently, China’s first high temperature vacuum receiver, Sanle-3 HCE, has been developed and produced by Southeast University and Sanle Electronic Group. Before being utilized in China’s first parabolic trough solar plant, accurately estimating the thermal properties of this new receiver is important. This paper first establishes and optimizes a 1-D theoretical model at Matlab program to compute the receiver’s major heat loss through glass envelope, and then systematically analyzes the major influence factors of heat loss. With the laboratorial steady state test stand, the heat losses of both good vacuum and non-vacuum Sanle-3 receivers were surveyed. Comparison shows the original 1-D model agrees with the ends covered test while remarkably deviating from end exposed test. For the purpose of identifying the influence of receiver’s end to total heat loss, an additional 3-D model is built by CFD software to further investigate the different heat transfer processes of receiver’s end components. The 3-D end model is verified by heating power and IR temperature distribution images in the test. Combining the optimized 1-D model with the new 3-D end model, the comparison with test data shows a good accordance. At the same time the heat loss curve and emittance curve of this new receiver are given and compared with those of several other existing receivers as references. [ABSTRACT FROM AUTHOR]

• Inverse method used to improve original T-history method equations to determine PCMs latent heat. • The method shown to be suitable method to calculate latent heat of low thermal conductivity bulk PCMs. • New transient modelling is more suitable for calculating latent heat with cooling rates than using original equations. High temperature phase change materials (PCMs) are being proposed as thermal energy storage media in concentrated solar power plants. The thermophysical properties of PCMs, such as the latent heat of fusion/solidification need to be defined to enable system design and evaluate system performance and cost analysis. Several methods have been used to measure the latent heat of fusion/solidification of PCMs including the T-history method. The original assumption of the T-history method is the Biot number should be less than 0.1 where the lumped capacitance method is applicable. However, when the Biot number is more than 0.1 then the original equations are not applicable to estimate the latent heat of PCM. This paper demonstrates how a one-dimensional heat transfer mathematical model can be used by applying an inverse method to overcome the limitation of the lumped capacitance method in the original T-history method to determine the latent heat of PCMs. The mathematical model demonstrates that variation of the temperature distributions inside the samples for the discharge curves. Furthermore, this model shows the errors in the latent heat values if the T-history method is used. It is evident from the discharge curves of low thermal conductivity PCMs that the original simplified equations used for interpreting the T-history test results are not applicable for calculating the latent heat at different ambient temperature. [ABSTRACT FROM AUTHOR]

• Mathematical models can describe the industrial anaerobic solid-state fermentation. • The models describe product concentrations and predict temperature. • The models predict overheating in large fermenters and at higher soil temperatures. • Our findings can be useful to improve traditional anaerobic solid-state fermentations. Traditional solid-state fermentation processes can give fluctuating product quality and quantity due to difficulties in control and scale up. This paper describes an engineering study of an industrial-scale anaerobic solid-state fermentation process for Chinese liquor (Baijiu) production, aimed at better understanding of the traditional process, as an initial step for future optimization. This mixed-culture fermentation is done in 0.44-m3 vessels embedded in the soil. At this scale, the fermentation is limited by product inhibition. We developed mathematical models based on the Han-Levenspiel equation for product inhibition, with parameters derived from measured data. The models accurately predicted the concentrations of starch and dry matter. A model with radial conduction into a small soil volume around the fermenter and consecutive vertical conduction into the underlying soil accurately predicted the pit temperature in the heating and cooling phases. This model is very sensitive to the values used for the enthalpies of combustion, meaning that direct measurement of the heat production rate would be preferable. In the industry practice, the fermenter volume can be from around 0.20 to 15.00 m3. The model predicts that overheating will occur not only in larger fermenters, but also in the 0.44-m3 fermenters when the soil temperature is high in summer. Our model predictions are consistent with observed behavior in the industry. Our findings can be used to improve this traditional process, as well as similar systems. [ABSTRACT FROM AUTHOR]

The problem of ignition of a condensed substance by single particles heated up to high temperatures is solved within the framework of the two-dimensional heat-transfer model. Numerical studies are performed for typical materials: polyvinyl nitrate and carbonic particles. Regimes of ignition of a condensed substance by a single particle at relatively low temperatures are adequate in terms of the ignition delay to regimes of heating of the condensed substance by a gas flow without particles; at high temperatures, they correspond to regimes of heating by a metal plate with a fixed temperature. In a certain (rather narrow) range of particle temperatures, the use of the two-dimensional heat-transfer model yields ignition-delay values substantially different from other regimes. [ABSTRACT FROM AUTHOR]