A Thermodynamic Performance Analysis of Triple Effect Vapour Absorption Refrigeration System Using LiBr-H2O

Being an eco-friendly system and a cheaper way to produce cooling effect absorption refrigeration system (ARS) is becoming more popular as it can produce higher cooling capacity than vapor compression refrigeration systems, and it can be powered by other sources of energy (like waste heat from gas and steam turbines, or can utilizes renewable source of heat by sun, geothermal, biomass) other than electricity. In the recent years, the interest in absorption refrigeration system is growing because these systems have environmentally friendly refrigerant and absorbent pairs. In this study, a detail energetic analysis of triple stage LiBr-H20 absorption system using First law of thermodynamics is done. An Energy Equation Solver code are used to simulate the computer program is developed for the cycle and results are validated with past studies available is also done. Mass, energy and exergy balance equations and the various complementary relations constitute the simulation model of the triple effect refrigeration system. Further, the effect of exit temperature of generator, absorber, condenser and evaporator on COP, solution concentration and other parameters are studied. It was found in the study that COP increases with increasing the generator exit temperature keeping the absorber exit temperature constant but when the absorber exit temperature is increased COP tends to decrease and the concentration of weak solution leaving HP generator (Xw3), MP generator (Xw2) and LP generator (Xw1) also increases with increase in generator exit temperature, while it decreases with increase in condenser exit temperature. Keywords: Absorption Refrigeration System (ARS), LiBr + H2O, COP, solution concentration, Energy Equation Solver code, energetic analysis, triple effect refrigeration system.

Numerical study of a double inlet chamber counter flow vortex tube with insulation

The present study intends to improve the performance of the Ranque-Hilsch counter flow vortex tube, analysed using computational fluid dynamics. In the axisymmetric 3-D, steady-state, compressible, and turbulent flow vortex tube, the air has been used as the working fluid. The ANSYS17.1 FLUENT software has been used with the standard º-ε turbulent model for different mass fraction of cold fluid and inlet pressure in the numerical simulation and validated with the experimental results. It is observed from the study that as the inlet chambers number increases from 1 to 2, there is a decrease of 7.8 % in the cold exit temperature of the vortex tube. However, insulating the double chamber vortex tube leads to a further reduction of 4.2% in the cold exit temperature. Therefore, it indicates that the overall decline in the cold exit temperature from one chamber non-insulated vortex tube to double chamber insulated vortex tube is 9.6%. In terms of cold exit temperature, it can be concluded that using a double inlet chamber vortex tube with insulation yields the optimum results.

Preliminary thermal characterisation of an active latent thermal energy storage system using PCM

Preliminary results of energy charging/discharging processes in a latent thermal energy storage system are reported. A novel design of a rotative scrapper heat exchanger has been studied. Paraffin RT44HC is employed as a phase change material. A Coriolis flowmeter is employed for measuring the mass flow through the prototype, and PT100 temperature sensors are used for measuring the inlet and exit temperature of the heat transfer fluid.

Effect of Pad Material, Copper Vs. Steel, On the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions

The paper presents measurements of performance conducted on a copper pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads' backing material, copper vs. steel. The journal diameter D=102 mm, and a bearing has five pads with length L=0.4D, nominal radial clearance 0.064 mm. The bearings operate at four shaft speeds ranging from 6 krpm to 14 krpm and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. At the highest load (on pad) and low speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads' peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ~ 5% lower drag power loss than that in the C-PB. From dynamic load test results, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB.

Numerical Simulation of the Exit Temperature Pattern of an Aircraft Engine Using a Temperature-Dependent Turbulent Schmidt Number

This paper presents a numerical simulation for predicting the combustor exit temperature pattern of an aircraft engine, developed using the commercial fluid simulation software Ansys Fluent, which assumes a shape probability density function for the instantaneous chemistry in the conserved scalar combustion model and the standard k-ε model for turbulence. We found the compliance of the radial and circumferential non-uniformities of the exit temperature with the experimental data to be insufficient. To achieve much more accurate result, the mixing intensity was enhanced with respect to the initial calculation due to using the reduced value of the turbulent Schmidt number Sc. Numerical simulation was performed for values of the turbulent Schmidt number from Sc = 0.85 (default) up to Sc = 0.2, with results confirming the reduction of radial and circumferential non-uniformities of exit temperature. However, correlation between radial and circumferential non-uniformities is not admissible for these cases. Therefore, we propose to use a temperature-dependent formulation of the turbulent Schmidt number Sc, accounting for the increase in Sc number with increasing gas temperature. A user defined function (UDF) was used to implement the Sc number temperature dependence in Ansys Fluent. The numerical results for the proposed Schmidt number Sc temperature dependence were found to be in acceptable agreement with the experimental data both for radial and circumferential non-uniformities of the exit temperature pattern.

Effect of Pad Material, Copper vs. Steel, on the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions

High temperature operation limits the life of fluid film bearings; hence the need to quantify the effect of pad material on the performance of tilting pad journal bearings (TPJBs). The paper presents measurements of performance conducted on a copper-pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads’ backing material, copper vs. steel, and slightly in the assembled cold clearance. The journal diameter D = 102 mm, and a bearing has five pads with length L = 0.4D, nominal radial clearance 0.064 mm, and pad preload of 0.42. The pads are 12.3 mm in thickness and have a 50% offset pivot, ball-in-socket type. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s surface speed) to 14 krpm (74 m/s) and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. ISO VG 32 oil, at a supply temperature of 49 °C, lubricates a test bearing configured with end seals (flooded bearing). At the highest load (on pad) and low shaft speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads’ peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ∼ 5% lower drag power loss than that in the C-PB. Drag power in both bearings increases with shaft speed and is largely independent of applied load. From dynamic load tests with multiple excitation frequencies to 250 Hz, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB. Both bearings, however, show symmetry in the damping coefficients, i.e., CXX ∼ CYY. Virtual mass coefficients (MXX, MYY) are significant in magnitude though having a large uncertainty. A computational physics model predicts the TPJB performance under identical conditions. The exhaustive comparison conducted with a sound dimensional characterization of parameters reveals that predictions agree well with measurements of journal eccentricity, oil exit temperature, pad surface temperatures, and stiffness and damping force coefficients. The differences amount to 20% or less. The model relies on specifying the material properties for pads and pivots and the operating (hot) clearance to produce accurate thermo-mechanically induced deformations that affect bearing performance at high loads and high surface speed operation.

Optimization of Fuel Nozzle Diameter in a Novel Cross Flow Lean Direct Injection Burner

Lean Direct Injection (LDI) concept proves to be an ultra-low NOx combustion scheme for future gas turbine combustors because of its ability to operate at very lean conditions. For LDI burners, the Fuel Nozzle Diameters (FND) play a vital role in deciding a balance between the various performance criteria demanded by the gas turbine industry like efficient usage of fuel, a wide range of flame stability, uniform exit temperature distribution and very low overall emissions. This paper attempts to find the optimum FND in terms of some key combustion parameters, for a novel multi-swirl LDI burner having a cross-flow mixing between fuel jets and swirling air. At first, lean blow out limits were detected from experiments with different FND using two different fuels, methane and liquefied petroleum gas, within a range of air flow rates. It was observed that with the decrease in FND the flame extinguished at a higher equivalence-ratio. Then their performances were compared through CFD simulations with two different combustion models, namely, Eddy Dissipation and PDF Flamelet. The combined results of cold and hot flow simulations showed that with the decrease in FND the fuel jet was able to penetrate deeper into the air swirl by overcoming the air momentum, which resulted in enhanced mixing leading to more efficient utilization of fuel and also uniform exit temperature distribution resulting in lower pattern factor. Thus the findings of this research work should be resourceful in the development of modern cross-flow LDI combustors.

Study on Spectral Radiative Heat Transfer Characteristics of a Windowed Receiver with Particle Curtain

In this paper, a windowed receiver with a particle curtain is numerically simulated under full-spectrum conditions. The discrete phase model (DPM) is used to model the particle flow and interactions between the particle phase and the air phase. The scattering, absorption of the particle curtain and quartz glass window are considered in detail. The spectral characteristics of glass have an important influence on the heat transfer characteristics and the receiver efficiency. The results show that the quartz window can reduce the convective heat loss and the cavity re-radiation heat loss. Under the same conditions, the receiver efficiency of a windowed receiver with a particle curtain is increased by 11.9% compared with an aerowindow receiver with a particle curtain. Under the same mass flow, the particle curtain thickness and particle size have a non-negligible influence on the flow pattern and temperature distribution of the particle curtain. When the particle curtain thickness is low, the flow stability of the particle curtain is high; as the particle curtain thickness increases, the volume fraction of the particle curtain decreases, and the flow stability of the particle curtain decreases, which affects the shape of the curtain. The scattering and absorption characteristics of the particles are different, resulting in different net fluxes of incident radiation under the reflection of the particle curtain and the back wall. As the particle curtain thickness increases, the particle average exit temperature and the receiver efficiency show a trend of first increasing and then decreasing. When d = 30 mm, the incident radiation (G) at the position of the particle curtain is larger, the particle average exit temperature reaches 1156.72 K, and the receiver efficiency reaches 74.4%. Therefore, different particle sizes also have a significant impact on the flow pattern of the particle curtain and the radiation distribution inside it. In the range of 250–750 μm particle size, the particles average exit temperature reaches above 1150 K, and the receiver efficiency is above 72.6%. As the particle size increases, the particle average exit temperature, and the receiver efficiency show a trend of first decreasing and then increasing. When the particle size is 500 mm, the particle average exit temperature reaches 1175.8 K, and the receiver efficiency reaches 79.4%.

New Correlations for Flow and Conjugate Heat Transfer with Surface Radiation Characteristics of a Real-Scale Infrared Suppression System with Conical Funnels

The consistent and accurate prediction of fluid flow and heat transfer characteristics in an infrared suppression (IRS) device is challenging due to the complex nature of the flow features. The cool ambient air intake and subsequent mixing of hot exhaust gas from the engine in the cargo/naval ships are done inside the IRS system. The objective is to propose correlations for mass entrainment and outlet temperature of IRS device with conical funnels stacked one above the other. The mass intake rate and funnel exit temperature are determined by a set of relevant operating and geometric parameters, such as Reynolds number, nozzle exhaust temperature, the number of funnels, and funnel overlap. In this study, the funnel walls are conducting with finite wall thickness, and the surface radiation is taken into consideration. Numerical simulations are performed for the real-scale IRS unit by solving the mass, momentum, energy, and radiation equations in the computational domain surrounding the system. Non-linear regression analysis of the data is carried out using the Levenberg and Marquest (L-M) method to achieve an empirical correlation of mass intake ratio and outlet temperature ratio. The proposed correlation for mass intake ratio is valid within ±6%, and that of outlet temperature is valid within ±5% of the numerical data. The valid ranges for correlations are: 6×?10?^5= Nozzle Reynold number 3×?10?^6; 2 = Number of funnel = 5;-0.325 = funnel overlapping height = 0.25;1.33 = Nozzle exit temperature = 2.