Simulation and Optimization of the Fluid Solidification Process in Brazed Plate Heat Exchangers

When a brazed plate heat exchanger is used as an evaporator,the working mass in the channel may undergo soli-dification,thereby hindering the refrigeration cycle.In this study the liquid solidification process and its optimi-zation in a brazed plate heat exchanger are investigated numerically for different inlet velocities;moreover,different levels of corrugation are considered.The results indicate that solidificationfirst occurs around the con-tacts,followed by the area behind the contacts.It is also shown that deadflow zones exist in the sharp areas and such areas are prone to liquid solidification.After optimization,the solidification area attains its smallest value when a corrugation spacingλ=4.2 mm is considered.

Optimizing Grids Demand Reduction through Enhanced Heat Transfer in Low-Temperature Waste Heat Driven ORC Systems

With increasing awareness of energy conservation and environmental protection, the Organic Rankine Cycle (ORC) system has gained significant attention. This technology enables the recovery of industrial waste heat, waste incineration heat, and renewable energy sources such as geothermal heat, biomass energy, and solar energy at lower temperatures. However, the low-grade heat source utilized in ORC systems faces a challenge to achieving high power generation efficiency and output power. Therefore, enhancing the power generation capacity of ORC systems is a key research focus in this field. An entranced heat exchanger ORC system with the screw expander driven by the low-temperature heat source is established to investigate the relevant performance. Hot water temperature from 77°C to 132°C is adopted for performance analysis, while the environmental temperature is approximately 25°C. Refrigerant R245fa is selected as the working fluid, and the screw expander is employed for power generation. It is worth noting that the entranced heat exchanger ORC system has significant potential for low-temperature heat recovery. Experimental results indicate that the maximum power output is 12.83 kW, which is obtained at around 105°C hot water inlet temperature. Correspondingly, the average power output remains 11.75 kW, revealing the system’s high stability for power generation. The implementation of a plate heat exchanger for enhanced heat transfer has enabled a 50% reduction in system size compared to traditional shell-tube type ORC systems. Besides, economic calculations demonstrate substantial benefits associated with the ORC system. The calculations indicate an internal benefit of 560,000 RMB/year, accompanied by notable external benefits such as an energy saving and emission reduction potential of up to 784 t CO2 per year. Moreover, the payback period is 2.23 years. It shows a remarkable improvement in terms of performance and excellent economic benefits. As a result, the novel ORC presents a promising alternative for low-grade heat utilization as compared to conventional small-scale ORC systems.

Estimation of ground heat flux and its impact on the surface energy budget for a semi-arid grassland

Three approaches, i.e., the harmonic analysis （HA） technique, the thermal diffusion equation and correction （TDEC） method, and the calorimetric method used to estimate ground heat flux, are evaluated by using observations from the Semi-Arid Climate and Environment Observatory of Lanzhou University （SACOL） in July, 2008. The calorimetric method, which involves soil heat flux measurement with an HFP01SC self-calibrating heat flux plate buried at a depth of 5 cm and heat storage in the soil between the plate and the surface, is here called the ITHP approach. The results show good linear relationships between the soil heat fluxes measured with the HFP01SC heat flux plate and those calculated with the HA technique and the TDEC method, respectively, at a depth of 5 cm. The soil heat fluxes calculated with the latter two methods well follow the phase measured with the HFP01SC heat flux plate. The magnitudes of the soil heat flux calculated with the HA technique and the TDEC method are close to each other, and they are about 2 percent and 6 percent larger than the measured soil heat flux, respectively, which mainly occur during the nighttime. Moreover, the ground heat fluxes calculated with the TDEC method and the HA technique are highly correlated with each other （R2= 0.97）, and their difference is only about 1 percent. The TDEC-calculated ground heat flux also has a good linear relationship with the ITttP-calculated ground heat flux （R2 = 0.99）, but their difference is larger （about 9 percent）. Furthermore, compared to the HFP01SC direct measurements at a depth of 5 cm, the ground heat flux calculated with the HA technique, the TDEC method, and the ITHP approach can improve the surface energy budget closure by about 6 percent, 7 percent, and 6 percent at SACOL site, respectively. Therefore, the contribution of ground heat flux to the surface energy budget is very important for the semi-arid grassland over the Loess Plateau in China. Using turbulent heat fluxes with common corrections, soil heat storage between the surface and the heat flux plate can improve the surface energy budget closure by about 6 to 7 percent, resulting in a closure of 82 to 83 percent at the SACOL site.

Heat Flux Characterization of DC Laminar-plasma Jets Impinging on a Flat Plate at Atmospheric Pressure

By using steady and transient methods, the total heat fluxes and the distributions of the heat flux were measured experimentally for an argon DC laminar plasma jet impinging normally on a flat plate at atmospheric pressure. Results show that the total heat fluxes measured with a steady method are a little bit higher than those with a transient method. Numerical simulation work was executed to compare with the experimental results.

NUMERICAL STUDY ON FLOW DISTRIBUTION IN PLATE-FIN HEAT EXCHANGERS

Objective To investigate the flow distribution in plate fin heat exchangers and optimize the design of header configuration for plate fin heat exchangers. Methods A mathematical model of header was proposed. The effects of the header configuration on the flow distribution in plate fin heat exchangers were investigated by CFD. The second header configuration with a two stage distributing structure was brought forward to improve the performance of flow distribution. Results It is found that the flow maldistribution is very serious in the direction of header length for the conventional header used in industry. The numerical predictions indicate that the improved header configurations can effectively improve the performance of flow distribution in plate fin heat exchangers. Conclusion The numerical simulation confirms that CFD should be a suitable tool for predicting the flow distribution. The method has a wide variety of applications in the design of plate fin heat exchangers.

EXACT FINITE ELEMENT METHOD

In this paper, a new method, exact element method for constructing finite element, is presented. It can be applied to solve nonpositive definite or positive definite partial differential equation with arbitrary variable coefficient under arbitrary boundary condition. Its convergence is proved and its united formula for solving partial differential equation is given. By the present method, a noncompatible element can be obtained and the compatibility conditions between elements can be treated very easily. Comparing the exact element method with the general finite element method with the same degrees of freedom, the high convergence rate of the high order derivatives of solution can be obtained. Three numerical examples are given at the end of this paper, which indicate all results can converge to exact solution and have higher numerical precision.

Heat Flux on EAST Divertor Plate in H-mode with LHCD/LHCD+NBI

Based on the surface temperature measured by the infrared camera on the experimental advanced superconducting tokamak （EAST）, the heat fluxes on the lower outer divertor target plate during H-mode with the lower-hybrid wave current drive （LHCD） only and with the LHCD combined with the neutral beam injection （NBI） are calculated by the DFLUX code and compared. The analyzed discharges are lower single null divertor configuration discharges. In the case with the LHCD only （Ip ~ 400kA, PLHCD ~ 2 MW）, ELM-free appears after L-H transition with the peak heat flux on the lower outer target plate less than 1 MW/m2. However, there is no ELM- free appearing after the L-H transition in the case with the LHCD＋NBI （Ip ~ 300 kA, PLHCD ＋ PNBI ~ 2 MW）. The results show that the peak heat fluxes on the lower outer target plate in the LHCD＋NBI H-mode cases are larger than those in the LHCD H-mode under the similar auxiliary heating power. This is because the heat flux profiles of the lower outer target plate as a function of plate location in ELMing with the LHCD＋NBI are narrower than those with the LHCD only. The results are consistent with the results in terms of the scrape-off layer width observed in the EAST.

Cooling System Design and Thermal Analysis of Modular Stator Hybrid Excitation Synchronous Motor

Hybrid excitation synchronous motor has the advantages of uniform and adjustable electromagnetic field, wide speed range and high power density. It has broad application prospects in new energy electric vehicles, wind power generation and other fields. This paper introduces the basic structure of hybrid excitation motor with modular stator, and analyzes the operation principle of hybrid excitation motor. The cooling structure of the water-cooled plate is designed, and the effects of the thickness of the water-cooled plate and the number of water channels in the water-cooled plate on the heat dissipation capacity of the water-cooled plate are analyzed by theoretical and computational fluid dynamics methods. The effects of different water cooling plate structures on water velocity, pressure drop, water pump power consumption and heat dissipation capacity were compared and analyzed. The influence of different inlet flow velocity on the maximum temperature rise of each part of the motor is analyzed, and the temperature of each part of the motor under the optimal water flow is analyzed. The influence of the traditional spiral water jacket cooling structure and the water-cooled plate cooling structure on the maximum temperature rise of the motor components is compared and analyzed. The results show that the water-cooled plate cooling structure is more suitable for the modular stator motor studied in this paper. Based on the water-cooled plate cooling structure, the air-water composite cooling structure is designed, and the effects of the air-water composite cooling structure and the water-cooled plate cooling structure on the maximum temperature rise of each component of the motor are compared and analyzed. The results show that the maximum temperature rise of each component of the motor is reduced under the air-water composite cooling structure.

Technological Perspectives for Propulsion on Nuclear Attack Submarines

This work aimed at proposing a new combination of technologies to improve military performances and reduce costs of nuclear attack submarines, without overlooking safety constraints. The last generation of nuclear attack submarines increased size to meet safety and operational requirements, imposing huge burden on costs side, reducing fleet size. The limitations of current Technologies employed were qualitatively discussed, explaining their limitations. There are new technologies (plate and shell heat exchangers) and architectural choices, like passive safety, and segregation of safety and normal systems, which may lead to reduction of costs and size of submarines. A qualitative analysis was provided on this combination of technologies, stressing their commercial nature and maturity, which reduced risks. The qualitative analysis showed the strong and weak points of this proposal, which adopted the concept of strength in numbers. Concluding, new Technologies enabled the existence of 3800 t nuclear attack submarines with powerful propulsion systems and good acoustic discretion.

SIMULATION AND ANALYSIS OF FLOW PATTERN IN CROSS-CORRUGATED PLATE HEAT EXCHANGERS

Using numerical methodology, the flow fields between two corrugated plates with different values of the corrugation inclination angle β were simulated. The simulation results directly indicate that β affects the flow pattern between corrugated plates, and the results are in good agreement with the experimental results reported by interrelated literature. The results show that the flow pattern between the two plates changes from ＂double cross-flow＂ to ＂zigzag flow＂ with the increase in β. The reason for the effect on the flow pattern between the two corrugated plates was discussed from the view of the variation of momentum in the direction of corrugation with the variation in β.

FLOW RESISTANCE AND HEAT TRANSFER CHARACTERISTICS OF A NEW-TYPE PLATE HEAT EXCHANGER

A new-type corrugation Plate Heat Exchanger （PHE） was designed. Results from both numerical simulations and experiments showed that the flow resistance of the working fluid in this new corrugation PHE, compared with the traditional chevron-type one, was decreased by more than 50%, and corresponding heat transfer performance was decreased by about 25%. The flow field of the working fluid in the corrugation PHE was transformed and hence performance difference in both flow resistance and heat transfer was generated. Such a novel plate, consisting of longitudinal and transverse corrugations, can effectively avoid the problem of flow path blockage, which will help to extend the application of PHEs to the situation with unclean working fluids.

Heat Transfer Performance of Microgroove Back Plate Heat Pipes with Working Fluid and Heating Power

Micro heat pipes(MHP) cooling is one of the most efficient solutions to radiate heat for high heat flux electronic components in data centers. It is necessary to improve heat transfer performance of microgroove back plate heat pipes. This paper discusses about influence on thermal resistance through experiments and numerical simulation with different working fluids, filling ratio and heat power. Thermal resistance of the CO2 filled heat pipe is 14.8% lower than the acetone filled heat pipe. In the meantime, at the best filling ratio of 40%, the CO2 filled heat pipe has the optimal heat transfer behavior with the smallest thermal resistance of 0.123 K/W. The thermal resistance continues to decline but the magnitude of decreases is going to be minor. In addition, this paper illustrates methods about how to enhance heat pipe performance from working fluids, filling ratio and heat power, which provides a theoretical basis for practical applications.

Utilisation of waste heat from exhaust gases of drying process

Nowadays a lot of low-grade heat is wasted from the industry through the off- and flue-gasses with different compositions. These gases provide the sensitive heat with utilisation potential and latent heat with the components for condensation. In this paper, process integration methodology has been applied to the partly condensed streams. A hot composite curve that represents the gas mixture cooling according to equation of state for real gases was drawn to account the gas-liquid equilibrium. According to the pinch analysis methodology, the pinch point was specified and optimal minimal temperature difference was determined. The location of the point where gas and liquid phases can be split for better recuperation of heat energy within heat exchangers is estimated using the developed methodology. The industrial case study of tobacco drying process off-gasses is analysed for heat recovery. The mathematical model was developed by using MathCad software to minimise the total annualised cost using compact plate heat exchangers for waste heat utilisation. The obtained payback period for the required investments is less than six months. The presented method was validated by comparison with industrial test data.

Numerical simulation and experimental research on heat transfer and flow resistance characteristics of asymmetric plate heat exchangers

The asymmetric plate heat exchanger(APHE)has the possibility of achieving balanced pressure drops on both hot and cold sides for situations with unbalanced flow,which may in turn enhance the heat transfer.In this paper,the single-phase water flow and heat transfer of an APHE consisted of two types of plates are numerically(400≤Re≤12000)and experimentally(400≤Re≤3400)investigated.The numerical model is verified by the experimental results.Simulations are conducted to study the effects of,an asymmetric index proposed to describe the geometry of APHEs.The correlations of the Nusselt number and friction factor in the APHEs are determined by taking and working fluids into account.It is found that an optimal exists where the pressure drops are balanced and the heat transfer area reaches the minimum.The comparison between heat transfer and flow characteristics of the APHEs and the conventional plate heat exchanger(CPHE)is made under various flow rate ratios of the hot side and the cold side and different allowable pressure drops.The situations under which APHE may perform better are identified based on a comprehensive index.

Optimal Heating in Heat-Treatment Process Based on Grey Asynchronous Particle Swarm Optimization

To ensure plate heating quality and reduce energy consumption in heat-treatment process, optimal heating for plates in a roller hearth furnace was investigated and a new strategy for heating procedure optimization was developed. During solving process, plate temperature forecast model based on heat transfer mechanics was established to calculate plate temperature with the assumed heating procedure. In addition, multi-objective feature of optimal heating was analyzed. And the method, which is composed of asynchronous particle swarm optimization and grey relational analysis, was adopted for solving the multi-objective problem. The developed strategy for optimizing heating has been applied to the mass production. The result indicates that the absolute plate discharging temperature deviation between measured value and target value does not exceed ± 8 ℃, and the relative deviation is less than ± 0.77%.

Comprehensive comparison of small-scale natural gas liquefaction processes using brazed plate heat exchangers

The brazed plate heat exchanger(BPHE)has some advantages over the plate-fin heat exchanger(PFHE)when used in natural gas liquefaction processes,such as the convenient installation and transportation,as well as the high tolerance of carbon dioxide(CO2)impurities.However,the BPHEs with only two channels cannot be applied directly in the conventional liquefaction processes which are designed for multi-stream heat exchangers.Therefore,the liquefaction processes using BPHEs are different from the conventional PFHE processes.In this paper,four different liquefaction processes using BPHEs are optimized and comprehensively compared under respective optimal conditions.The processes are compared with respect to energy consumption,economic performance,and robustness.The genetic algorithm(GA)is applied as the optimization method and the total revenue requirement(TRR)method is adopted in the economic analysis.The results show that the modified single mixed refrigerant(MSMR)process with part of the refrigerant flowing back to the compressor at low temperatures has the lowest specific energy consumption but the worst robustness of the four processes.The MSMR with fully utilization of cold capacity of the refrigerant shows a satisfying robustness and the best economic performance.The research in this paper is helpful for the application of BPHEs in natural gas liquefaction processes.