Effect Of Variable Specific Heat Research Articles

Thermal Modelling and Multi Decision Making Optimization of EDM of Non Conductive SiC-CNT Ceramic Composite Used for Li-ion Battery and Sensor

In this research work the thermal modeling of a nonconductive Silicon carbide Ceramic matrix composite (CMC) machined by Die Sinking Electric Discharge Machining (EDM) has been done. Though SiC is a non-conductive material but the presence of CNT makes it a conductive material which can be machined with EDM. The modeling procedure carried out by considering some realistic approach like Gaussian heat Flux, Specific Discharge Energy, Variable Latent heat etc. For this analysis a 2D continuum has been designed as work domain. By simulating the work domain model by a Finite Element Analysis (FEA) Software (COMSOL), material removal rate (MRR) has been estimated with variable thermal properties. Parametric analysis of effect of Variable Specific heat on MRR by considering different current, Voltage and Pulse-On time has been performed. The effect of different input parameters (peak current and Pulse-on time) on Crater geometry has been done. A new concept of Specific discharge energy has been introduced during modelling to make it a more realistic model which can also be used as electrode support for electrochemical energy devices as Polymer Electrolyte Membrane Fuel Cells on Li-ion battery. Desirability analysis has been done to get an optimize set of input parameters for I= 3A, V=30V, Ton= 75 µs for machining ceramic matrix composite by EDM. The optimized MRR at this setting is 7.25 mm3/min whereas PFE is 87%. The experimental analysis has been also performed to strengthen the thermal and mathematical modelling.

Comparative study of Reynolds stress budgets of thermally and calorically perfect gases for high-temperature supersonic turbulent channel flow

To study the Reynolds stress budgets, direct numerical simulations of high-temperature supersonic turbulent channel flow for thermally perfect gas and calorically perfect gas are conducted at Mach number 3.0 and Reynolds number 4800 combined with a dimensional wall temperature of 596.30 K. The reliability of the direct numerical simulation data is verified by comparison with previous results ( J Fluid Mech 1995, vol. 305, pp.159–183). The effects of variable specific heat are important because the vibrational energy excited degree exceeds 0.1. The viscous diffusion, pressure–velocity gradient correlation, and dissipation terms in the Reynolds stress budgets for TPG, except the streamwise component, are larger than those for calorically perfect gas close to the wall. Compressibility-related term decreases when thermally perfect gas is considered. The major difference for both gas models is mainly due to variations in mean flow properties. Inter-component transfer related to pressure–velocity gradient correlation term can be distinguished into inner and outer regions, whose critical position is approximately 16 for both gas models.

Effects of variable specific heat on energy transfer in a high-temperature supersonic channel flow

ABSTRACTAn energy transfer mechanism in high-temperature supersonic turbulent flow for variable specific heat (VSH) condition through turbulent kinetic energy (TKE), mean kinetic energy (MKE), turbulent internal energy (TIE) and mean internal energy (MIE) is proposed. The similarities of energy budgets between VSH and constant specific heat (CSH) conditions are investigated by introducing a vibrational energy excited degree and considering the effects of fluctuating specific heat. Direct numerical simulation (DNS) of temporally evolving high-temperature supersonic turbulent channel flow is conducted at Mach number 3.0 and Reynolds number 4800 combined with a constant dimensional wall temperature 1192.60 K for VSH and CSH conditions to validate the proposed energy transfer mechanism. The differences between the terms in the two kinetic energy budgets for VSH and CSH conditions are small; however, the magnitude of molecular diffusion term for VSH condition is significantly smaller than that for CSH condition. The non-negligible energy transfer is obtained after neglecting several small terms of diffusion, dissipation and compressibility related. The non-negligible energy transfer involving TIE includes three processes, in which energy can be gained from TKE and MIE and lost to MIE. The same non-negligible energy transfer through TKE, MKE and MIE is observed for both the conditions.

Heat and mass transfer and fluid flow in cryo-adsorptive hydrogen storage system

Compared to room temperature adsorption, cryo-adsorptive hydrogen storage capacity has been greatly improved, and has become the central issue of the hydrogen storage research. Accurate simulation and optimization for cryo-adsorptive hydrogen storage has important guidance and application value to the experimental research, and the finite element software Comsol Multiphysics™ and system analysis software Matlab/Simulink™ can be used to simulate the cryo-adsorptive hydrogen storage. However, the computational fluid dynamics (CFD) software Fluent™ can provide more information on the heat and mass transfer and the fluid flow than above softwares. Based on the mass, momentum and energy conservation equations, this paper uses the modified Dubinin–Astakhov (D–A) adsorption isotherm model, linear driving force (LDF) model and dynamic thermal boundary condition which are implemented by means of CFD software Fluent to simulate the hydrogen adsorption processes of charging and dormancy in the case of liquid nitrogen cooling. We study the variations of temperature and pressure during the processes of charging and dormancy. The results show that the experimental data is in good agreement with the simulation results. We also analyze the effect of variable specific heat and anisotropic thermal conductivity on the heat and mass transfer and the fluid flow in cryo-adsorptive hydrogen storage system.

The Effects of Variable Specific Heats of Working Fluid on the Performance of Irreversible Reciprocating Brayton Cycle

The mathematical model for thermokinetic characteristics of an irreversible reciprocating Brayton cycle has been analyzed. The analytical formulas of the specific work and the actual cycle thermal efficiency are derived, taking the variable specific heats of working fluid and the irreversibility in the compressor and the turbine into account. The model mentioned above has carried on the numerical calculus under typical circulation performance parameters. The results show that the variable specific heat and the internal efficiency of both the compressor and the turbine have an obvious influence on the cycle performance, and the internal efficiency of both the compressor and the turbine have more remarkable influence on the cycle performance. The results obtained in this paper may provide a theoretical guide for the assessment and improvement of the performance of actual gas turbine engines.

The effects of variable specific heat on the stability of hypersonic boundary layer on a flat plate

The gas temperature within hypersonic boundary layer flow is so high that the specific heat of gas is no longer a constant but relates to temperature. How variable specific heat influences on boundary layer flow stability is worth researching. The effect of the variable specific heat on the stability of hypersonic boundary layer flows is studied and compared with the case of constant specific heat based on the linear stability theory. It is found that the variable specific heat indeed has some effects on the neutral curves of both the first-mode and the second-mode waves and on the maximum rate of growth also. Therefore, the relationship between specific heat and temperature should be considered in the study of the stability of the boundary layer.

Unified thermodynamic description and optimization for a class of irreversible reciprocating heat engine cycles

A unified description of a class of generalized irreversible reciprocating heat engine cycles is given in this paper. The model cycle consisting of two heating branches, two cooling branches, and two adiabatic branches with heat transfer, friction, and variable specific heats of working fluid is established. The thermodynamic performance of the universal cycle is analysed and optimized by using finite time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific heats of the working fluid and cycle process on cycle performance are analysed and the major differences of cycle performance are compared when the specific heats of the working fluid are constant and variable respectively. The results obtained herein include the performance characteristics of endoreversible and irreversible reciprocating Diesel, Otto, Atkinson, Brayton, Braysson, Carnot, dual, and Miller cycles with constant and variable specific heats of the working fluid. They can provide some new guidelines for the design practice of real internal combustion engines.

Performance of reciprocating Brayton cycle with heat transfer, friction and variable specific heats of working fluid

SYNOPSIS The performance of an irreversible air-standard reciprocating simple Brayton cycle with heat transfer loss, friction-like term loss and variable specific heats of working fluid is analysed by using finite-time thermodynamics. The relationships between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relationship between the power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific heats of the working fluid and the friction-like term loss on the irreversible cycle performance are analysed. The results show that the effects of variable specific heats of the working fluid and friction-like term loss on the irreversible cycle performance are obvious, and they should be considered in practical cycle analysis. The results obtained in this paper may provide guidelines for the design of practical reciprocating Brayton engines.

Effects of heat transfer, friction and variable specific heats of working fluid on performance of an irreversible dual cycle

The thermodynamic performance of an air standard dual cycle with heat transfer loss, friction like term loss and variable specific heats of working fluid is analyzed. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle, are derived by detailed numerical examples. Moreover, the effects of variable specific heats of the working fluid and the friction like term loss on the irreversible cycle performance are analyzed. The results show that the effects of variable specific heats of working fluid and friction like term loss on the cycle performance are obvious, and they should be considered in practical cycle analysis. The results obtained in this paper may provide guidance for the design of practical internal combustion engines.

The effects of variable specific heats of working fluid on the performance of an irreversible Otto cycle

The performance of an air-standard Otto cycle with variable specific heats of working fluid and heat resistance and friction irreversible losses is analysed by using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific heats of working fluid on the irreversible cycle performance are analysed. The results show that the effects of variable specific heats of working fluid on the cycle performance are obvious, and it should be considered in practice cycle analysis. The results obtained in this paper may provide guidance for the design of practice internal combustion engines.

The effect of variable specific heat of the working fluids on the performance of counterflow heat exchangers

The effectiveness of counterflow heat exchangers using normal hydrogen at cryogenic temperatures has been evaluated by a numerical method.

Paper 34: Effects of Variable Specific Heats and Gas Composition on Unsteady Flow Calculations

A numerical method has been developed for the solution of one-dimensional non-steady flow problems including the effects of friction, gradual area change, heat transfer between the gas and the pipe wall, longitudinal variations, and discontinuities in gas composition and entropy. The fluid considered obeys the perfect gas equation of state, but the specific heats may vary with temperature. The method is not intended for use when shocks are present, but will give an approximate solution if shocks occur. The accuracy of the new method has been checked against existing methods for more simple cases, and although the new method has been found to be slightly superior it is more complicated, much slower, and the boundary conditions are more difficult to develop. For this reason, it is suggested that the new method be used to check on the adequacy of the existing simpler methods for each new application. The methods have been compared for the case of a typical diesel engine exhaust system and it has been found that the earlier methods are adequate for all practical purposes.

Flame temperatures in engines

After considering the most likely factors which may influence the measurement and calculation of gas temperatures in an engine during combustion and expansion, there appears to be reasonable agreement between measured and calculated results if (1) temperatures are measured by means of the line-reversal method with suitable corrections for the effect of temperature gradients in the gases, and (2) temperatures are calculated on the basis of thermodynamic analysis, assuming thermal and chemical equilibrium, including the effects of variable specific heat of the gases and dissociation, based on the most recent thermal and chemical data, and correcting for heat loss during combustion.

LIX. The effect of variable specific heat of gases on the quantities involved in heat transmission between liquids and gases

LIX. The effect of variable specific heat of gases on the quantities involved in heat transmission between liquids and gases

LXX. The critical pressure-ratio for gases as affected by variable specific heat

Summary In a previous paper in the ‘Philosophical Magazine’ for March 1922, the analysis involving the effect of variable specific heat on the discharge of gases through orifices or nozzles was given, and certain important conclusions were drawn therefrom. In the present note the critical pressure-ratio determining the maximum discharge condition under variable specific heat conditions has been deduced. The result obtained shows that this critical pressure-ratio is higher the higher the temperatures involved, and is also higher than under constant specific heat conditions.

LXIX. The effect of variable specific heat on the discharge of gases through orifices or nozzles

LXIX. <i>The effect of variable specific heat on the discharge of gases through orifices or nozzles</i>