Designing a cost-effective phase change thermal storage system involves two challenging aspects: one is to select a suitable storage material and the other is to increase the heat transfer between the storage material and the heat transfer fluid as the performance of the system is limited by the poor thermal conductivity of the latent heat storage material. When used for storing energy in concentrated solar thermal power plants, the solar field operation temperature will determine the PCM melting temperature selection. This paper reviews concentrated solar thermal power plants that are currently operating and under construction. It also reviews phase change materials with melting temperatures above 300 °C, which potentially can be used as energy storage media in these plants. In addition, various techniques employed to enhance the thermal performance of high temperature phase change thermal storage systems have been reviewed and discussed. This review aims to provide the necessary information for further research in the development of cost-effective high temperature phase change thermal storage systems.

Review on storage materials and thermal performance enhancement techniques for high temperature phase change thermal storage systems

Study of working fluid selection of organic Rankine cycle (ORC) for engine waste heat recovery

Review of organic Rankine cycles for internal combustion engine exhaust waste heat recovery

The focus of this study is to review the latest developments and technologies on waste heat recovery of exhaust gas from internal combustion engines (ICE). These include thermoelectric generators (TEG), organic Rankine cycle (ORC), six-stroke cycle IC engine and new developments on turbocharger technology. Furthermore, the study looked into the potential energy savings and performances of those technologies. The current worldwide trend of increasing energy demand in transportation sector are one of the many segments that is responsible for the growing share of fossil fuel usage and indirectly contribute to the release of harmful greenhouse gas (GHG) emissions. It is hoped that with the latest findings on exhaust heat recovery to increase the efficiency of ICEs, world energy demand on the depleting fossil fuel reserves would be reduced and hence the impact of global warming due to the GHG emissions would fade away.

Technologies to recover exhaust heat from internal combustion engines

Internal combustion (IC) engines are the major source of motive power in the world, a fact that is expected to continue well into this century. To increase the total efficiency and reduce CO2 emissions, recently exhaust heat recovery (EHR) based on thermoelectric (TE) and thermal fluid systems have been explored widely and a number of new technologies have been developed in the past decade. In this paper, relevant researches are reviewed for providing an insight into possible system designs, thermodynamic principles to achieve high efficiency, and selection of working fluids to maintain necessary system performance. From a number of researches, it has been found the Rankine cycle (RC) has been the most favourite basic working cycle for thermodynamic EHR systems. Based on the cycle, various different system configurations have been investigated. Accepting a certain design and manufacture cost, a system based on heavy duty vehicle application can increase the total powertrain efficiency by up to 30% (based on NEDC driving condition). To achieve the highest possible system efficiency, design of systemic structure and selections for both the expander and the working fluid (medium) are critical.

A review of researches on thermal exhaust heat recovery with Rankine cycle

Theoretical Analysis of Waste Heat Recovery from an Internal Combustion Engine in a Hybrid Vehicle

This paper investigates the sensitivity of the long-term performance simulations of solar energy systems to the degree of stratification in both liquid and packed-bed storage units. The degree of stratification is controlled by the number of nodes used in a finite-difference approximation of the storage system temperature distribution. Short- and long-term simulations of typical water heating and solar thermal power plant systems are conducted. The results indicate that the long-term performance of these systems is far less sensitive to the number of nodes used to represent the degree of stratification than expected based on short-term simulations or experimental data. An explanation is offered for this non-intuitive result. Copyright © 2007 John Wiley & Sons, Ltd.

Sensitivity of long‐term performance simulations of solar energy systems to the degree of stratification in the thermal storage unit

A concentrating solar power plant utilizes two heat transfer fluids. A first heat transfer fluid is heated in a field of concentrating solar collectors. A second heat transfer fluid is heated through a heat exchanger using heat imparted from the first heat transfer fluid. The second heat transfer fluid is then further heated, for example in a second field of concentrating solar collectors, and power is generated utilizing thermal energy extracted from the second heat transfer fluid. The second heat transfer fluid may be a solar salt, and may thus have a higher working temperature than the first heat transfer fluid. The power plant may realize the power generation efficiency improvements offered by utilizing a high temperature working fluid, while at least some of the plant does not require backup heating to protect against freezing events.

Hybrid solar field

This paper presents the development of an automatic coupling between the component-based system simulation program TRNSYS and the general-purpose CFD package FLUENT. Due to the nature of the iterative solution strategy in TRNSYS, the coupling can be considered as a fully-dynamic coupling, as the CFD component iterates with all of the other components in the system in order to obtain a converged solution at each time step. The connection between the two programs takes place by running the CFD program from TRNSYS through a script file written by TRNSYS during the simulation. The results from the CFD simulation are then used by other component model within TRNSYS to simulate the behavior of the rest of the system.

http://ibpsa-usa.org/index.php/ibpusa/article/download/189/176

Advances on the coupling between a commercial cfd package and a component-based simulation program

This work presents a complete model of the carburetor for small engines. It extends the previously published models by incorporating a detailed review of two-phase flow pressure drop, the effect of the fuel well on the control of airbleed flow, and unsteady flow. The homogenous two-phase flow model, which is commonly used in carburetor modeling, was compared with an empirical correlation derived from experiments in small pipes and found to be in poor agreement. In order to assess unsteady flow conditions, the model was extended by solving instantaneous one-dimensional Navier-Stokes equations in single-phase pipes. This strategy proved successful in explaining the mixture enrichment seen under pulsating flow conditions. The model was also used to derive a sensitivity analysis of geometries and physical properties of air and fuel.

Diego A. Arias

Papers

Theoretical Analysis of Waste Heat Recovery from an Internal Combustion Engine in a Hybrid Vehicle

Sensitivity of long‐term performance simulations of solar energy systems to the degree of stratification in the thermal storage unit

Hybrid solar field

Advances on the coupling between a commercial cfd package and a component-based simulation program

Numerical and Experimental Study of Fuel and Air Flow in Carburetors for Small Engines