A Novel Generator Design Utilised for Conventional Ejector Refrigeration Systems

Ejector refrigeration systems are rapidly evolving and are poised to become one of the most preferred cooling systems in the near future. CO2 transcritical refrigeration systems have inherently high working pressures and discharge temperatures, providing a large volumetric heating capacity. In the current research, the heat ejected from the CO2 gas cooler was proposed as a driving heating source for the compression ejector system, representing the energy supply for the generator in a combined cycle. The local design approach was investigated for the combined plate-type heat exchanger (PHE) via Matlab code integrated with the NIST real gas database. HFO refrigerants (1234ze(E) and 1234yf) were selected to serve as the cold fluid on the generator flowing through three different phases: subcooled liquid, a two-phase mixture, and superheated vapour. The study examines the following: the effectiveness, the heat transfer coefficients, and the pressure drop of the PHE working fluids under variable hot stream pressures, cold stream flow fluxes, and superheated temperatures. The integration revealed that the cold fluid mixture phase dominates the heat transfer coefficients and the pressure drop of the heat exchanger. By increasing the hot stream inlet pressure from 9 MPa to 12 MPa, the cold stream two-phase convection coefficient can be enhanced by 50% and 200% for R1234yf and R1234ze(E), respectively. Conversely, the cold stream two-phase convection coefficient dropped by 17% and 37% for R1234yf and R1234ze(E), respectively. The overall result supports utilising the ejected heat from the CO2 transcritical system, especially at high CO2 inlet pressures and low cold channel flow fluxes. Moreover, R1234ze(E) could be a more suitable working fluid because it possesses a lower pressure drop and bond number.

Analysis Of Three Layer Concentric Tube Heat Exchange Using Mathematic Modeling

A three-channel concentric pipes heat exchanger is a development or improvement of a two-channel concentric heat exchange apparatus. This study was conducted to determine the output temperature of each channel, and compare the results of theoretical calculations using mathematical modeling of experimental results conducted in the field. So that obtained difference of value between result of experiment to result of theory calculation. In this study have 3 variations of temperature data that is 50 °C, 55°C, and 60 °C with two streams namely CounterFlow and PararellFLow and discharge 2.5 l/minute, while cold fluid with 25 °C discharge 1.5 l/minute. From the above analysis it can be concluded that the temperature of the hot fluid coming out of the APK in the experiment tends to be higher than the temperature of the hot fluid coming out of the APK on theoretical calculations of mathematical modeling methods. Meanwhile, the cold cold fluid temperature coming out of the APK in experimental tends to be lower than the temperature of the cold fluid coming out of the APK on theoretical calculations of mathematical modeling methods.

Performance of Heat Exchanger with Nanofluids

The effect of adding nanomaterial of aluminum oxide (Al2O3), titanium oxide (TiO2) and zirconium oxide (ZrO2) in different concentrations of 0.25, 0.5, 0.75, 1.0, and 1.25 g/L to the cold fluid (water) turbulently flowing with different flow rates of 75, 100, 125, 150, and 175 L/min in tube side countercurrently to hot water flowing with a constant flow rate of 60 L/min in the shell side of shell and tube heat exchanger on the heat transfer rates and overall heat transfer coefficients are experimentally studied. It is found that the addition of nanomaterials gives rise to outlet cold (nano) fluids temperatures causing to enhancement averagely 7.74, 11.25, and 17.38 percent for ZrO2, TiO2, and Al2O3 respectively in heat transfer rate and averagely 12.72, 19.47, and 28.71 percent for ZrO2, TiO2, and Al2O3 respectively in overall heat transfer coefficients. The maximum enhancement values in heat transfer rates and in overall heat transfer coefficients are attained at a flow rate of 150 L/min of cold fluid.

Robust Design Approach to 2 Inch and 3 Inch Thermal Tees on 14 Inch Pipework for Hot and Cold Fluid Turbulent Mixing at the Branch-Run Interface

This paper presents a concept design methodology to establish robust designs against thermal fatigue of 2″ and 3″ thermal tee branch sizes on 14″ pipework, which are subjected to relatively hot and cold fluid turbulent mixing, for use in Pressurised Water Reactor Plant. Thermal tees can be subjected to extremely demanding thermal fatigue conditions, e.g. high temperature fluctuations causing high stress ranges where hot and cold fluid mix at the tee position from different branches of the system, these conditions ultimately limiting design life. Prior to conducting a full design justification to the ASME Section III code [1], which for these components Rolls-Royce has justified by a section NB3200 approach using finite element analysis and computational fluid dynamics, analysis/iteration time can be saved, and the likelihood of a robust design being found increased, by understanding the effect and significance of geometric features of the tees. Fundamentally, establishing which features have a greater influence on the thermal fatigue performance of the tee and setting maximum and minimum values for these features. This paper presents an approach that can be used in the concept design phase to understand the influence of variables such as: branch throat internal diameter, run versus branch reinforcement, inclusion of integral orifices and branch fluid flow rate, and also of how they interact with each other in relation to providing a code compliant design. The approach is also used to size such features so that they are away from ‘cliff edges’ in performance, i.e. away from values that are likely to produce high stress levels and reduce design life. The paper covers: the variables chosen to be investigated, the methodology including the associated stress models to understand the effect of variable change and positioning in the ‘design landscape’, and identifies which geometric features should be maximised or minimised in size to maximise thermal fatigue life.

FEA Analysis of Double Tube Heat Exchanger on Variable Baffle Pitch for Optimizing Thermal Efficiency

The main objective of this work is to compare different configurations of helical baffles in the cold fluid side of a double tube heat exchanger. For this analysis double pipe heat exchangers are divided into three different domains such as two fluid domains hot fluid in the inner tube and cold fluid in the outer pipe and a solid domain as helical baffles on inner tube of hot fluid. The hot water flows inside the heat exchanger tube, while the cold fluid flows in the outer side in the direction of counter flow. Mass flow rate cold fluid was varied from 0.1 kg/s to 0.3 kg/s while the flow rate in the inner tube i.e. hot water was kept constant at 0.1 kg/s. the inlet temperature of hot fluid taken as 40oC while Cold fluid inlet temperature taken as 15oC. The fluent software is used to calculate the fluid flow and heat transfer in the computational domains. The governing equations are iteratively solved by the finite volume formulation with the SIMPLE algorithm. Results show that that the maximum temperature drop of 10.9 oC for hot fluid and the maximum temperature rise of 11.9 oC for cold fluid are observed at 0.3 kg/sec mass flow rate for double pipe heat exchanger with double helical baffles. It has been also observed that the heat transfer coefficient increasing with the increasing in the mass flow rate of cold fluid. The overall heat transfer coefficients differ significantly by 20.4 % at same mass flow rate, because the considerable difference between heat transfer surface area on the inner and outer side of the tube resulting in a prominent thermal enhancement of the cold fluid.

Direct numerical simulation of particle Brownian motion in a fluid with inhomogeneous temperature field

In this work the fluctuating-lattice Boltzmann method was adopted to numerically investigate the Brownian motion of particles in a fluid with inhomogeneous temperature field. It has been found that the Brownian particles are preferential to randomly move into a cold fluid area. Once the particles go into the cold area, the boundary between the hot fluid and cold fluid acts like a temperature barrier, preventing the particles from going out. Most important of all, the Brownian particles can be captured or collected by the cold fluid area if the temperature of cold fluid is lower than a critical value. In addition, the dependence of this critical value on the fluid viscosity is studied.