Thermal Technologies (United States)

A novel multi-objective optimization scheme is implemented to enhance the heat transfer characteristics and to reduce pressure drop of heat exchanger in this article. The heat transfer efficiency and pressure drop of the finned heat exchanger are considered as the optimal objective function through the fine-tuning of the heat exchanger’s fin spacing and fin angle. Numerical simulations of the prototype heat exchanger well agree with the experimental findings. The fin spacing and fin angles of the heat exchanger are manipulated as the optimization variables to attain the maximum Nusselt number and the minimum pressure drop. The nonlinear fitting of the data is performed using an Artificial Neural Network (ANN) to obtain the establishment of two predictive models. The models are optimized using a multi-objective Non-dominated Sorting Genetic Algorithm-II (NSGA-II), ultimately yielding a Pareto frontier curve. Two excellent optimization schemes can be obtained for heat exchanger. The Nusselt number of the optimized model rises as much as 4% when the pressure drop is almost consistent with the heat transfer of the original heat exchanger. The pressure drop of the optimized model reduces as much as 9% when the Nusselt number is well consistent with the drag force of the original heat exchanger. The energy efficiency is effectively improved by the optimization models of these two types of heat exchangers and the energy-saving goals are achieved through multi-objective optimization using NSGA-II.

Validated CO2 ejector models are essential for developing high-performance refrigeration and heat pump cycles. This study focuses on assessing the Homogeneous Equilibrium Model’s applicability to simulate a CO2 flashing ejector at a reduced pressure of 0.47. The model was implemented in FLUENT, integrating a user-defined real gas model. Simulation results with different boundary condition options were compared to experimental data. The analysis was carried out to evaluate the predictive capabilities of the model and assess the experimental data quality. The results indicate that the developed model accurately estimated the motive mass flow rate, with a maximum relative error of 5.7%, showing better performance than previously reported data. The entrained flow rate, assuming double choking operation, was significantly higher than the experimental measurement, and the CFD-predicted wall static pressure underestimated the experimental profile, suggesting single-choked ejector operation. In contrast, the outflow density was better predicted under the same assumption, with an average error of 8.6%. Nevertheless, the simulated temperature profiles showed good agreement with the experimental data, especially when using the experimental entrained mass flow rate as a boundary condition.

<div class="section abstract"><div class="htmlview paragraph">This paper provides information on the comparison of numerical simulations with experimental data for an electrothermal ice protection system with a focus on Appendix O [<span class="xref">1</span>] Freezing Drizzle (FZDZ) and Freezing Rain (FZRA) conditions. The experimental data is based on a test campaign with a 2D NACA23012 wing section in the RTA Icing Wind Tunnel in Vienna. 22 icing runs (all either unheated or in anti-ice mode) were performed in total and all residual ice shapes were documented by means of high-resolution 3D scanning. Unheated FZDZ and FZRA reference as well as heated cases with different heater configurations are presented. The experimental results are compared to numerical predictions from two different icing codes from AeroTex GmbH (ATX) and the University of Applied Sciences FH JOANNEUM (FHJ) in Graz. The current capabilities of the codes were assessed in detail and regions for improvement were identified. Overall, the codes were able to predict the ice shapes of both the unheated and heated cases with reasonable accuracy but both codes overestimated the thickness of the runback ice ridges throughout all cases. The biggest deviations in terms of the position of the ice accretions were seen on the lower surface; on the upper surface a better match was observed.</div></div>

View Video Presentation: https://doi.org/10.2514/6.2022-3457.vid This paper provides information on the generation of validation data for electrothermal ice protection system numerical tools, based on testing on a 2D wing section at the RTA test facility in Vienna. Updates to the RTA calibration capability are provided, including for the Freezing Rain, MVD > 40 microns regime. Latest developments in ice shape scanning and post-processing are shown, including for runback ice generated from heated cases. Some preliminary comparisons to the measured data are provided using different simulation tools, including unheated ice shapes.

Adsorptive heat transformer is a promising technology for waster heat recovery and global energy conservation. A novel cyclic adsorption heating system based on direct contact heat exchange method has been established for the purpose of high-temperature steam generation from hot water. Pre-adsorption is originally proposed before generation phase to enhance the system performance with composite zeolite 13X and MgSO4 in the open-loop adsorption heating system. Composite zeolite is prepared by impregnation method. Experimental results show steam with temperature higher than 200°C is generated from inlet water at 72.0°C. During regeneration phase, dry air at 130°C and relative humidity of 7.37% is employed. Gross temperature lift is 95.0°C to 103°C for different pre-adsorption conditions. The effective steam generation time with pre-adsorption temperature at 90.0°C is prolonged by 27.4%. Meanwhile, the mass of steam is elevated by 16.2% compared with the cycle without pre-adsorption. Exergy coefficient of performance is upgraded by 14.7% and specific heating power for steam generation is increased by 16.0%. The pre-adsorption operation achieved the goal of recovery of low-grade waste steam on adsorbents to enhance the subsequent high-temperature steam generation. After pre-adsorption operation, the packed bed reaches adsorption and thermal equilibrium more quickly during generation phase. Thus, dynamic steam generation is significantly intensified and then system performance is improved correspondingly.

Synthesis of biofuels is an important step in the phase out of fossil fuels in the transportation sector, especially in long-distance sea, air and road transport where direct electrification seems unfeasible. Integration of renewable electricity enables efficient electricity storage as well as an increased utilization of the biomass carbon, which lowers the biomass demand. This paper presents a flexible system for the conversion of biomass and electricity to methanol. The system is based on the deep integration of a Two-Stage gasifier and solid oxide cells (SOC). The integration enables efficient production of a nitrogen-free high-quality syngas, suitable for methanol production. This study focuses on the system in electrolysis mode, and analyzes the effects of recirculating CO2 from the gas conditioning and methanol synthesis process back to the SOC, as well as the effects of pressurized operation of the gasifier and increased H2O content in the gasifier. Thermodynamic modeling shows that CO2-recirculation allows an increase in conversion of the carbon in the biomass to methanol from 80 % up to 92 %, with an energy efficiency of 71 %. Only a slight pressurization seems feasible, as an increase in pressure beyond ~3 bar results in significant methane formation inside the SOC.

Many system configurations of large-­scale heat pumps (HP) are applicable to a district heating system, and choosing the right HP technology may be a challenge. In this study, thermodynamic models of eight different HP configurations are used to compare the Coefficient of Performance (COP) and Lorenz efficiency, for a range of sink and source outlet temperatures. Furthermore, for a specific case the total volume flow rate for each configuration was compared. The results revealed that a configuration with two two-­stage cycles with low stage desuperheat heat exchangers in most operating conditions was superior in terms of COP. However, for all considered operating conditions at least three configurations obtained a COP which was less than 3 % lower than the best one. Comparing the volume flow rates among the configurations a combination of a one-­stage cycle and a two-­stage cycle with low stage desuperheat heat exchanger holds the lowest needed volume flow rate.

Many industrial processes require both cooling and heating of process streams. The use of a cogeneration heat pump system enables the simultaneous production of both utilities within one single, electrically driven unit. Within this work, the addition of a tank system at the hot end of different heat pump systems was investigated. The tank system consists of a stratified storage tank for the storage of hot water and a smaller charge tank, which allows for multiple circulations of the water through the condenser. This leads to a gradual heating of the water, leading to a higher COP compared to heating in one step. Using numerical modelling and simulation, a screening was carried out investigating the influence of different working fluids and heat pump configurations, different temperature glides in the heat sink and different temperature lifts on the performance of the heat pump system. The largest improvement, compared to a conventional heat pump, was achieved with a one-stage heat pump with R600a, increasing the COP by 35 %.