Thermal performance of mixed electroosmotic-pressure driven flows in microtubes with constant wall temperature

A numerical analysis is performed to explore the heat transfer characteristics of mixed electroosmotic and pressure-driven flows in a microtube with constant wall temperature. Thermally fully-developed flow with Joule heating is considered. The Joule heating is generated by imposed voltage gradient and can be regarded as volumetric heat source. The analysis combines energy equation with overall energy balance equation for a control element to generate a nondimensional governing equation. Of interest are the effects of the relative duct radius a (ratio of the duct radius to Debye length), the pressure gradient parameter P (ratio of pressure gradient to electroosmotic forces) and the Joule number S (ratio of heat generation due to Joule heating to heat transfer at the wall) on the temperature distribution and the local heat transfer rate. The results indicate that the Nusselt number increases with an increase in the relative duct radius and the Joule number or a decrease in the pressure gradient parameter. The resulting solution due to the conditions of energy unbalance in the flow is also discussed.     

Joule heating effect on electroosmotic flow and mass species transport in a microcapillary

This study presents a numerical analysis of Joule heating effect on the electroosmotic flow and mass species transport, which has a direct application in the capillary electrophoresis based BioChip technology. A rigorous mathematic model for describing the Joule heating in an electroosmotic flow including the Poisson-Boltzmann equation, the modified Navier-Stokes equations and the energy equation is developed. All these equations are coupled through the temperature-dependent liquid dielectric constant, viscosity, and thermal conductivity. By numerically solving the aforementioned equations simultaneously, the double layer potential profile, the electroosmotic flow field, and the temperature distribution in a cylindrical microcapillary are computed. A systematic study is carried out to evaluate the Joule heating and its effects under the influences of the capillary radius, the buffer solution concentration, the applied electric field strength, and the heat transfer coefficient. In addition, the Joule heating effect on sample species transport in a microcapillary is also investigated by numerically solving the mass transfer equation with consideration of temperature-dependent diffusion coefficient and electrophoresis mobility. The simulations reveal that the presence of the Joule heating could have a great impact on the electroosmotic flow and mass species transport.     

Comparative analysis of Cu/blood and Cu–CuO/blood nanofluids on a peristaltic flow governed by an asymmetric channel

Contraction and expansion play a crucial role in biomedical applications, such as heart pumping, ovum in the feminine fallopian vessel, blood fluid transport, and so forth. Inspired by these features, the present effort concentrates on the consequences of a thermal slip in the peristalsis of Cu/blood and Cu–CuO/blood nanofluids in asymmetric flow formation. Hence, the microrotation influence of blood flow is considered here. Heat transported through the channel due to perpendicular flow buoyancy effects is also studied. The special effects of thermal radiation, nanoparticle shape, and heat source/sink parameters on the flow are studied in the proposed model. The MATLAB BVP4c condition is utilized to achieve the numerical solutions of the transformed system of nonlinear coupled differential equations. The most important outcome of the present analysis is an enhancement in the evaluation study of the Cu/blood and Cu–CuO/blood nanofluids on the axial velocity, axial spin velocity, pressure gradient, and temperature distributions in the asymmetric channel. Also, another important outcome is observed that the Cu–CuO blood nanofluid strongly has dominated the Cu/blood nanofluid in axial spin velocity.     

Flow patterns and thermal drag in a one-dimensional inviscid channel with heating or cooling

In this paper investigations on the flow patterns and the thermal drag phenomenon in one-dimensional inviscid channel flow with heating or cooling are described and discussed; expressions of flow rate ratio and thermal drag coefficient for different flow patterns and its physical mechanism are presented.     

实现煤粉气流点火的几种电加热途径分析

对煤粉气流实现电加热无油点火的几种重要的技术途径,进行了全面的分析。电热体(纯金属、合金和非金属)用于煤粉气流点火,可适用两种情况：一种是制造价格低廉的煤粉点火器;一种是制造用于点燃低挥发分难燃煤的点火器。感应加热用于煤粉气流点火,由于可加热异型金属,因此,方便了点火器设计,可采取一些稳燃技术;加热速度相对较快。等离子体用于煤粉气流点火,具有较快的响应速度。     

An experimental feasibility study of vanadium oxide films on metallic bipolar plates for the cold start enhancement of fuel cell vehicles

An experimental study of vanadium oxide polycrystalline films deposited onto 316L stainless steel bipolar plates as an efficient Joule heating source for fuel cell vehicles was conducted by carefully modulating the negative temperature coefficients of the electrical resistance of the films at subzero temperatures. To fabricate the thin films, a well-mixed precursor solution of vanadium alkoxide and organic cosolvent was prepared by the hydrolytic sol-gel route and then coated on the pre-cleaned flat surface of 316L stainless steel plates with natural passive oxide layers by a dip-coating method. Subsequently, the variation of the nonlinear electrical resistance of the thin film was measured simultaneously over a wide temperature range of −20 to 80 °C, allowing direct detection of the surface temperature of the thin films. In addition, the adhesion, microstructures, compositions, and morphologies of the vanadium oxide thin films were investigated using the ASTM D3359 method, XRD, FE-SEM, and XPS analyses. A remarkable result from this study was that a temperature increase of 41.65 °C was induced by significant Joule heating of the vanadium sesquioxide films on metallic bipolar plates, i.e. approximately 1.8-folded more than the minimum requirement of Joule heating, at a current density of 0.1 A·cm⁻² at −20 °C. Thus, it was concluded that thermal dissipation from the resistive vanadium oxide films with a negative temperature coefficient can be effectively used as a self-heating source to melt frozen water at subzero ambient temperatures, particularly for fuel cell vehicles.     

基于Trnsys的电锅炉供暖系统蓄热控制优化研究

以某展览馆为例,基于Trnsys软件建立模型且验证其准确性,模拟实际工况,分析运行状态,以期提高电锅炉加蓄热模块的运行效率。针对当前运行状态,提出3种优化蓄热控制方法：方案1为利用蓄热模块蓄热状态,控制锅炉的蓄热时间;方案2根据蓄热模块放热结束后回水温度,控制锅炉是否需要蓄热;方案3为基于室内热负荷需求,分阶段控制供暖流量。结果表明,相比原系统,方案2节能16.6%,且提高蓄热效率;方案3节能18.2%,且减少在极端天气时室内不满足设计温度的天数。     

Joule Heating and its Implications on Crack Detection/Arrest in Electrically Conductive Circular Cylindrical Shells

Distribution of Joule heating and the corresponding electromagnetic field in the vicinity of the crack in a thermo- and electro-conductive thin-walled shell carrying a non-stationary electrical current is investigated. Specifically, a circular cylindrical shell with one finitely long crack that is perpendicular to the current direction is considered. The crack is free of mechanical loads. The underlying boundary-value problem is addressed via the use of Fourier series expansion and the solution reduces to that of a singular integral equation with Hilbert-type singular kernel. The influence of the presence of crack, and the effect of non-stationarity of the current on the distribution of current and Joule heating in the shell are investigated and pertinent conclusions are drawn. The results are instrumental toward crack detection and active arrest of crack propagation in structures made of electro-conductive materials or aged structure components in aerospace industry.