Off-Design of a Pumped Thermal Energy Storage Based On Closed Brayton Cycles

The growth of renewable energy source requires reliable, durable and cheap storage technologies. In this field, the Pumped Thermal Energy Storage (PTES), is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e. the inventory control, is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the off-design operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase.

Off-Design of a Pumped Thermal Energy Storage Based on Closed Brayton Cycles

The growth of renewable energy source requires reliable, durable and cheap storage technologies. In this field, the Pumped Thermal Energy Storage (PTES), is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e. the inventory control, is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the off-design operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase.

Thermodynamic consequences of specific modified gravity on the apparent horizon

We discuss the thermodynamical behavior of homogeneous and isotropic universe (flat and non-flat) in the framework of [Formula: see text] gravity, where [Formula: see text] stands for Ricci scalar and [Formula: see text] signifies the trace of energy–momentum tensor of a scalar field [Formula: see text]. We follow through the first-order formalism that specifies the scalar field to the Hubble parameter which becomes [Formula: see text] By using Bekenstein–Hawking entropy, we analyze the validity of generalized second law of thermodynamics at apparent horizon for different values of [Formula: see text] and evaluate the equilibrium condition for all cases as well.

Thermodynamics of black holes with higher order corrected entropy

For analyzing the thermodynamical behavior of two well-known black holes, such as Reissner–Nordström – anti-de Sitter (RN-AdS) black hole with global monopole and f(R) black hole, we consider the higher order logarithmic corrected entropy. We develop various thermodynamical properties, such as entropy, specific heat, pressure, and Gibbs and Helmhotz free energies for both black holes in the presence of corrected entropy. A versatile study on the stability of black holes is made by using various frameworks, such as the ratio of heat capacities (γ), grand canonical and canonical ensembles, and phase transition in view of higher order logarithmic corrected entropy. It is observed that both black holes exhibit more stability (locally as well as globally) for growing values of cosmological constant and higher order correction terms.

Einstein–Gauss–Bonnet black holes with a perturbative nonlinear electrodynamics: Geometrical thermodynamics

Taking into account the perturbative corrections of Einstein (EN)–Maxwell gravity, we study thermodynamical behavior of the black holes in the context of geometrical thermodynamics (GT). We consider a quadratic Maxwell invariant as a correction of Maxwell theory in electromagnetic viewpoint and Gauss–Bonnet (GB) gravity as a correction of EN theory in gravitational point of view. We study thermodynamical phase transition and show that employing Weinhold, Ruppeiner and Quevedo approaches fails to produce desirable results. Next, Hendi–Panahiyan–Eslam Panah–Momennia (HPEM) metric will be employed in order to study GT of the solutions. We show that this metric is capable of matching all the divergence points of its thermodynamical curvature scalar with phase transition and bound points. Moreover, the effects of the variation of different parameters on phase transition points will be investigated.

Thermodynamic geometry of charged dilaton black holes in AdS spaces

It was shown that with the combination of three Liouville-type dilaton potentials, one can derive dilaton black holes in the background of anti-de-Sitter (AdS) spaces. In this paper, we further extend the study on the dilaton AdS black holes by investigating their thermodynamic instability through a geometry approach. First, we review thermodynamic quantities of the solutions and check the validity of the first law of thermodynamics. Then, we investigate phase transitions and stability of the solutions. In particular, we disclose the effects of the dilaton field on the stability of the black holes. We also employ the geometrical approach toward thermodynamical behavior of the system and find that the divergencies in the Ricci scalar coincide with roots and divergencies in the heat capacity. We find that the behavior of the Ricci scalar around divergence points depends on the type of the phase transition.

F(R)Gravity’s Rainbow and Its Einstein Counterpart

Motivated by UV completion of general relativity with a modification of a geometry at high energy scale, it is expected to have an energy dependent geometry. In this paper, we introduce charged black hole solutions with power Maxwell invariant source in the context of gravity’s rainbow. In addition, we investigate two classes ofF(R)gravity’s rainbow solutions. At first, we study energy dependentF(R)gravity without energy-momentum tensor, and then we obtainF(R)gravity’s rainbow in the presence of conformally invariant Maxwell source. We study geometrical properties of the mentioned solutions and compare their results. We also give some related comments regarding thermodynamical behavior of the obtained solutions and discuss thermal stability of the solutions.

Thermodynamical behavior of the variable Chaplygin gas

The thermodynamical behavior of the variable Chaplygin gas (VCG) model is studied, using an equation-of-state (EoS) like [Formula: see text], where [Formula: see text]. Here B0 is a positive universal constant, n is also a constant and V is the volume of the fluid. From the consideration of thermodynamic stability, it is seen that only if the values of n are allowed to be negative, then [Formula: see text] throughout the evolution. Again thermal capacity at constant volume cV shows positive expression. Using the best fit value of n = -3.4 as previously found by Guo and Zhang (Phys. Lett. B. 645 (2007) 326) gives that the fluid is thermodynamically stable throughout the evolution. The effective EoS for the special case of n = 0 goes to Λ Cold Dark Matter (ΛCDM) model. Again for n < 0, it favors phantom-like cosmology which is in agreement with the current SNe Ia constraints like VCG model. The deceleration parameter is also studied in the context of thermodynamics and the analysis shows that the flip occurs for the value of n < 4. Finally, the thermal EoS is discussed which is an explicit function of temperature only. It is also observed that the third law of thermodynamics is satisfied in this model. As expected, the volume increases as temperature falls during adiabatic expansions. In this case, for T → 0, the thermal EoS reduces to [Formula: see text], which is identical with the EoS for the case of large volume.

Investigation of Friction Power Losses in Automotive Journal Bearings

Journal bearings are used in a large number of critical positions in automotive internal combustion engines (ICE) and contribute a major contribution to the total friction power losses in these engines. These reasons motivate in addition the accurate and reliable simulation of the operating conditions and friction power losses in journal bearings. In this work the lubrication of journal bearings is investigated in detail using detailed rheological lubricant models that include the piezoviscous effect. To describe mixed lubrication realistically in the simulation, a sophisticated contact model is employed together with measured surface roughness data from journal bearings. Starting point is an extensive thermo-elastohydrodynamic (TEHD) simulation, which yields important insights into the thermodynamical behavior of the lubricant film in journal bearings. From these results, a powerful isothermal elastohydrodynamic (EHD) simulation model is derived that calculates the oil temperature for the simulation from two easily accessible experimental temperatures. The capabilities of the presented simulation methods are compared to extensive experimental measurements performed on a journal bearing test-rig, which show excellent agreement.