Precise nanoinjection molding through local film heating system

Wall temperature significantly affects stability and receptivity of the boundary layer. Changing the wall temperature locally may therefore be an effective laminar flow control technique. However, the situation is complicated when the wall temperature distribution is nonuniform, and researchers have experimentally found that local wall cooling may delay the onset of transition. We attempt to clarify the physical mechanisms whereby the local wall temperature affects the transition and the stability of a hypersonic boundary layer. A numerical investigation of the disturbance evolution in a Mach-6 sharp cone boundary layer with local wall heating or cooling is conducted. Direct numerical simulation (DNS) is performed for the single-frequency and broadband disturbance evolution caused by random forcing. We vary the local wall temperature and the location of heating/cooling, and then use the e N method to estimate the transition onset. Our results show that local wall cooling amplifies high-frequency unstable waves while stabilizing low-frequency unstable waves, with local heating amplifying all unstable waves locally. The disturbance amplitude and second-mode peak frequency obtained by DNS agree well with the previous experimental results. Local cooling/heating has a dual effect on the stability of the hypersonic boundary layer. For local cooling, while it effectively inhibits the growth of the low-frequency unstable waves that dominate the transition downstream, it also further destabilizes the downstream flow. In addition, while upstream cooling can delay the transition, excessive cooling may promote it; local heating always slightly promotes the transition. Finally, recommendations are given for practical engineering applications based on the present results.

At substations of district heating systems, water is heated and transferred by pumps through piping networks to the buildings of each local heating system. When they were designed, the operational parameters and system characteris tics of the local heating system were selected to provide thermal comfort in all the buildings served by the local heating system. After several years of opera tion, however, these parameters and characteristics change and, as a result, thermal comfort may be expected to deteriorate. This study investigates one strategy to mitigate this problem; that of retrofitting the local heating system with additional circulation pumps to provide greater system control and, thereby, improved thermal comfort. Using a steady-state, bottom-up ap proach, heat transfer in the local heating system is described by a system of equations that are then linearized. Mixed integer linear programming is then applied to these equations, implemented in the program PUMP, and used to optimize system characteristics. The results indicate that pump-placement optimization strategy is more effective in overcoming changes in hydraulic resistance than variations in radiator and building heat transmittance result ing from aging of the local heating system.

In the present study, local condensation heat transfer coefficients of the R1234ze(E) inside a vertical plate heat exchanger (PHE) were investigated experimentally. In the experiment, three vertical flow channels are formed in the test section where refrigerant flows downward in the middle channel and cooling water flows upward in other two channels. The test section consists of eight plates: two of them form a channel of chevron type PHE for refrigerant flow channel, other two flat plates are set for heat transfer measurements, and another consist on cooling water flow channel. Down flow of the condensing refrigerant R1234ze(E) in the center channel releases heat to other channels of cooling water. In order to measure local heat transfer characteristics, a total of 60 thermocouples were set at middle of flow direction and also in the right and left sides of plates in test section. Experiments were conducted for mass fluxes ranging from 10[Formula: see text]kg/m2s to 50[Formula: see text]kg/m2s. The measurement results show that local heat transfer coefficients decrease with increase of wetness with different values in horizontal direction. Further, characteristics of local heat flux and wall temperature distribution as a function of distance from inlet to outlet of refrigerant channel were explored in detail.

The optimized design of one-side-heated plasma-facing components (PFC) is dependent on knowing the local distribution of inside wall heat flux in the flow channels. The local inside wall heat flux can be obtained from selectively chosen local PFC wall temperatures close to the inside boundary of the flow channel. To this end, three-dimensional thermal measurements for a one-side-heated monoblock were made and show: (1) the three-dimensional variation of the wall temperature close to both the heated and fluid-solid surface boundaries, (2) the resultant effects of local subcooled flow boiling on the 3-D wall temperature/outside heat flux relationship – one of which is the 3-D wall temperature profile is almost unchanged in the vicinity for incident heat flux levels between the onset to fully developed boiling and CHF, and (3) the occurrence of local CHF and local post-CHF. The monoblock has a 180.0 mm heated length, has a 10.0 mm inside diameter, and has a circular-like cross-section with a 30.0 mm nominal outside diameter.

High heat flux removal from a single-side heated monoblock using flow boiling

Local heat transfer coefficients at the inlet of an annular flow passage

Two-phase flow wax deposition is a flow-pattern-dependent phenomenon. The thickness and hardness of the deposit vary along the pipe circumference. In this work, two-phase gas-oil stratified flow wax deposition experiments at various liquid and gas flow rates have been conducted systematically using Garden Banks condensate and natural gas in a 2-inch I.D. multiphase flow loop under the pressure of 350 psi. Both deposit mass and wax content increased as superficial gas and liquid velocities increased. The local deposits were observed to be thinner but harder at the sides compared to the bottom of the pipe. Meanwhile, the cross-sectional deposits were crescent-shaped with an increasing local wax mass flux along the circumferential direction. The local multiphase hydrodynamic and heat transfer characteristics are known to play an essential role in the wax deposition process, and the temperature gradient is critical for establishing the concentration gradient. Thus, it is paramount to have a proper understanding of the local momentum and heat transfer to predict wax deposition in multiphase flow accurately. Therefore, numerical simulations with an SST (Shear Stress Transport) k∼ω turbulent model was implemented to understand local heat transfer in two-phase gas-oil stratified flow. After each simulation, the ANSYS CFD-Post was used to export, visualize, and analyze the simulated results. A total of 19 locations were selected for circumferential sampling to analyze the local heat transfer in the model. Detailed information on liquid volume fraction, shear stress, and temperature were analyzed. It has been observed that the local shear stress, temperature gradient, and inner wall temperature decrease with increasing θ. The thickness of the thermal boundary layer increases as θ increases due to reduced Nuθ. The comparison between the localized Nuθ and Nu from unified heat transfer model has revealed that variation in Nuθ is critical in the circumferential heat transfer calculation and wax deposition modeling.

Experiments on the influence of intake conditions on local instantaneous heat flux in reciprocating internal combustion engines

Experimental studies on local and average heat transfer characteristics in helical pipes with single phase flow

Improving the detection of thermal insulation in buildings –which includes the development of models for heating and ventilation processes and fabric gain - could significantly increase building energy efficiency and substantially contribute to reductions in energy consumption and in the carbon footprints of domestic heating systems. Thermal insulation standards are now contractual obligations in new buildings, although poor energy efficiency is often a defining characteristic of buildings built before the introduction of those standards. Lighting, occupancy, set point temperature profiles, air conditioning and ventilation services all increase the complexity of measuring insulation efficiency. The identification of thermal insulation failure can help to reduce energy consumption in heating systems. Conventional methods can be greatly improved through the application of hybridized machine learning techniques to detect thermal insulation failures when a building is in operation. A three-step procedure is proposed in this paper that begins by considering the local building and heating system regulations as well as the specific features of the climate zone. Firstly, the dynamic thermal performance of different variables is specifically modelled, for each building type and climate zone. Secondly, Cooperative Maximum-Likelihood Hebbian Learning is used to extract the relevant features. Finally, neural projections and identification techniques are applied, in order to detect fluctuations in room temperatures and, in consequence, thermal insulation failures. The reliability of the proposed method is validated in three winter zone C cities in Spain. Although a great deal of further research remains to be done in this field, the proposed system is expected to outperform conventional methods described in Spanish building codes that are used to calculate energetic profiles in domestic and residential buildings.KeywordsFeature SelectionHeating SystemMachine IntelligenceImprove Energy EfficiencyIndoor TemperatureThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Thermal analysis of a new solar kang system

The decentralisation of existing district heating systems by network separation is a promising approach for district heating transformation. A district heating network is separated into several smaller district heating network structures that can be individually adapted, e.g. in relation to the existing network structure or concerning the properties of the local buildings supplied, such as the temperature requirements of their heating systems. In this work, an approach for the optimal separation of existing district heating networks is expanded, which enables the decentralisation of a specific district heating system and the partial transformation of the separated network depending on the heat source utilised and the local district heating system conditions. The approach first identifies coherent network areas through community detection and aggregation, then optimises network separation and the installation of heat pumps, and finally evaluates the arising district heating network systems through district heating network simulations. The individual steps of this approach are adapted to be applicable to large district heating network structures, e.g. to handle the great number of separation options. The approach is applied to two existing district heating systems with over four thousand buildings supplied. Two types of utilised waste heat sources are investigated, a sewage plant with fluctuating temperatures and an electrolyser with a dynamic operation schedule. The results show favourable transformation alternatives for existing district heating networks, as the separated network areas are transformed by reducing supply temperatures depending on the heat source potential utilised and the temperature requirements of the buildings supplied. • Separating district heating networks facilitates the utilisation of heat sources. • An optimisation model reveals the optimal separation of district heating networks. • The network separation considers available heat capacity and temperature level. • Heat pumps are installed in the separated network to utilise low-temperature heat. • A subsequent simulation evaluates the separated district heating networks.

Fundamental character of forced convection heat transfer to the endwall surface of a gas turbine passage can be simulated by using a 90° turning duct. Elevated operating temperatures in gas turbines require a thorough understanding of the turbulent thermal transport process in the three-dimensional end-wall boundary layers. The current study uses an in-house developed three-dimensional viscous flow solver to computationally investigate the heat transfer character near the endwall surfaces. Extensive heat transfer experiments also illuminate the local heat transfer features near the endwall surface and form a baseline data set to evaluate the computational method used. Present experimental effort at Re=342,190 employs a prescribed heat flux method to measure convective heat transfer coefficients on the end-wall surface. Local wall temperatures are measured with liquid crystal thermography. Local convective heat flux is determined by solving the electric potential equation with constant uniform potential that is applied along the inlet and exit boundaries of the endwall. The viscous flow and heat transfer computation algorithms are based on the same methods presented in Part I. The influence of the two primary counter-rotating vortices developing as a result of the balance of inertia and pressure forces on the measured and computed endwall heat transfer coefficients is demonstrated. It is shown that the local heat transfer on the endwall surface is closely related to the structure of the three-dimensional mean flow and the associated turbulent flow field. A comparison of the molecular/ turbulent heat diffusion, wall shear stress, visualization of local turbulent kinetic energy are a few of the tasks that can be performed using a numerical approach in a relatively time efficient manner. The current numerical approach is capable of visualizing the near wall features that can not be easily measured in the flow field near the end-wall surfaces.

This paper reports an experimental study on nanofluid convective boiling heat transfer in parallel rectangular minichannels of 800 μm hydraulic diameter. Experiments are conducted with pure water and silver nanoparticles suspended in water base fluid. Two small volume fractions of silver nanoparticles suspended in water are tested: 0.000237% and 0.000475%. The experimental results show that the local heat transfer coefficient, local heat flux, and local wall temperature are affected by silver nanoparticle concentration in water base fluid. In addition, different correlations established for boiling flow heat transfer in minichannels or macrochannels are evaluated. It is found that the correlation of Kandlikar and Balasubramanian is the closest to the water boiling heat transfer results. The boiling local heat transfer enhancement by adding silver nanoparticles in base fluid is not uniform along the channel flow. Better performances and highest effect of nanoparticle concentration on the heat transfer are obtained at the minichannels entrance.

Ventilation Control of Pig-Houses During Winter Period