Interphase matter transfer: an experimental study of condensation of mercury

1981 ◽  
Vol 378 (1774) ◽  
pp. 305-327 ◽  
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Vapour Pressure ◽  
Temperature Drop ◽  
Vertical Plane ◽  
Film Condensation ◽  
Interface Temperature ◽  
Condensation Coefficient ◽  
Condensation Rate ◽  
Matter Transfer

Comparisons between interphase matter-transfer theory and measurements have, in the past, been hindered by uncertainties about the ‘condensation coefficient’. Large experimental errors have often been misinterpreted as indicating low values of the condensation coefficient. Condensation experiments with metals are convenient for the study of interphase matter transfer since, owing to the high thermal conductivity of the liquid, the temperature drop across the condensate film is small and, particularly at low pressures and high condensation rates, the temperature discontinuity at the vapour-liquid interface is of measurable magnitude. Condensation rate, and vapour and condenser surface temperature measurements have been made during film condensation of mercury on a vertical, plane, square (side 40 mm), nickel-plated, copper surface. Thermocouples, accurately located and spaced through the copper condenser block, served to measure, by extrapolation, the temperature of the copper-nickel interface and, from the temperature gradient, the heat flux from which the condensation mass flux was determined. Special care was taken to ensure that the results were not vitiated by the presence in the vapour of noncondensing gases. The observations cover wider ranges of vapour pressure (temperature) and condensation rate (heat flux) than hitherto studied, i.e. 50-4300 Pa (378-493 K) and 0.2- 3.6 kgm ~2 s- 1 (56-1062 kW m -2 ) respectively. The results are considered to have enhanced accuracy. In particular, after the accuracy of calibration and positioning of the thermocouples, and th at of the thermoelectric measurements has been considered, it is estimated that the condenser surface temperature was measured to within around ± 0.1 K. Interface temperature discontinuities up to around 70 K have been observed at low vapour pressure and high condensation rate. The results lend support to recent theoretical studies and indicate that the condensation coefficient exceeds 0.9.

Fuel Drop Vaporization under Pressure on a Hot Surface

1969 ◽  
Vol 184 (1) ◽  
pp. 677-696 ◽  
Author(s):  
R. W. Temple-Pediani
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Saturation Temperature ◽  
Material Surface ◽  
Interface Temperature ◽  
Maximum Value ◽  
Peak Heat Flux ◽  
Initial Drop ◽  
Temperature And Pressure ◽  
Hot Surface

The evaporation lifetime of liquid fuel drops in contact with a hot surface is investigated at pressures of up to 69 atm. Modes of evaporation and drop behaviour at subcriticai and supercritical conditions of temperature and pressure are described. It is shown that at any subcriticai pressure the lifetime is a minimum at a surface temperature just above the saturation temperature; the lifetime at all supercritical pressures is a constant minimum when the surface temperature is 60 degC or more than the critical temperature of the liquid. The heat flux to a drop in the contact modes of evaporation has a maximum value comparable to the peak heat flux obtained in boiling heat transfer work. Subsidiary tests at atmospheric pressure investigate the influence of surface material, surface finish, and initial drop temperature upon the lifetime; the transient surface interface temperature during evaporation is also investigated. The application of the data to deposited fuel in engines is discussed.

Improving Biporous Heat Transfer by Addition of Monoporous Interface Layer

2009 ◽  
Author(s):  
Sean W. Reilly ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Thin Layer ◽  
Effective Thermal Conductivity ◽  
Double Layer ◽  
Temperature Drop ◽  
Single Layer ◽  
Heat Pipes ◽  
Interface Temperature

Biporous evaporator wicks, generated by sintering copper particles into semi-uniform clusters, were demonstrated to achieve high flux, heat transfer performance for use in heat pipes by Semenic (2007). The effective thermal conductivity of thick biporous wicks at high heat fluxes was found to be reduced because the region next to the wall dried out prematurely allowing the wall interface temperature to rise well above the saturation temperature. The region above the dried out portion of the wick continued to work with the large pores between the clusters being primarily occupied with vapor and the small pores between the particles being occupied with the liquid. In this work, we report our efforts to reduce the size of the wall-wick interface dry-out region by sintering a thin layer of uniform size particles on the wall as originally suggested in a thesis by Seminic (2007). The boiling curve for this “double layer” wick diverges from a standard “single layer” biporous wick at the point of nucleation by reducing the wall temperature, and concurrently the overall temperature drop across the wick needed to drive a given heat flux. The temperature drop across the wick is reduced because the thin layer of particles between the biporous wick and the wall reduces the wall-wick interface resistance and also provides additional capillary channels underneath the biporous wick. Experimental data supports this hypothesis by showing a clear divergence between measured wall temperatures for the double layer wick from its single layer counterpart. The presumed point of nucleation in both wicks is similar, with the heat flux increasing much more rapidly than the liquid superheat and it is clear that this slope is much steeper for the double layer wick. This finding has great potential to expand the performance capabilities of heat pipes and vapor chambers because the new double layered wick can transfer more heat with less superheat thereby increasing the effective thermal conductivity of the wick and decreasing the wall-wick interface temperature for a given heat flux.

On interphase matter transfer, the condensation coefficient and dropwise condensation

1987 ◽  
Vol 411 (1841) ◽  
pp. 305-311 ◽  
Keyword(s):  
Heat Transfer ◽  
General Theory ◽  
Water Molecule ◽  
Temperature Difference ◽  
Interface Temperature ◽  
Dropwise Condensation ◽  
Condensation Coefficient ◽  
Upper Limit ◽  
Approximate Nature ◽  
Matter Transfer

It is argued that heat-transfer measurements for dropwise condensation cannot be used to determine the condensation coefficient accurately. It is shown that, when recent data for dropwise condensation of steam are re-evaluated, taking account of polyatomicity of the water molecule in the calculation of the interface temperature difference, an upper limit for the value of the condensation coefficient is found to be 0.93 rather than 0.6, as reported earlier. In view of the approximate nature of the polyatomicity correction and uncertainties in the general theory of dropwise condensation, it is considered that these data do not show conclusively that the condensation coefficient is less than unity.

scholarly journals Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 180
Author(s):  
Asif Ali ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Linear Regression ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Surface ◽  
Regression Method ◽  
Thermal Transient

The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

High-output diesel engine heat transfer: Part 1 - comparison between piston heat flux and global energy balance

2021 ◽  
pp. 146808742110170
Author(s):  
Eric Gingrich ◽  
Michael Tess ◽  
Vamshi Korivi ◽  
Jaal Ghandhi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Diesel Engine ◽  
Surface Temperature ◽  
Fast Response ◽  
Temperature Data ◽  
Start Of Injection ◽  
Local Measurements ◽  
Surface Temperature Data ◽  
High Output

High-output diesel engine heat transfer measurements are presented in this paper, which is the first of a two-part series of papers. Local piston heat transfer, based on fast-response piston surface temperature data, is compared to global engine heat transfer based on thermodynamic data. A single-cylinder research engine was operated at multiple conditions, including very high-output cases – 30 bar IMEPg and 250 bar in-cylinder pressure. A wireless telemetry system was used to acquire fast-response piston surface temperature data, from which heat flux was calculated. An interpolation and averaging procedure was developed and a method to recover the steady-state portion of the heat flux based on the in-cylinder thermodynamic state was applied. The local measurements were spatially integrated to find total heat transfer, which was found to agree well with the global thermodynamic measurements. A delayed onset of the rise of spatially averaged heat flux was observed for later start of injection timings. The dataset is internally consistent, for example, the local measurements match the global values, which makes it well suited for heat transfer correlation development; this development is pursued in the second part of this paper.

scholarly journals Operating temperatures of oil-lubricated medium-speed gears: Numerical models and experimental results

2003 ◽  
Vol 217 (2) ◽  
pp. 87-106 ◽  
Author(s):  
H Long ◽  
A A Lord ◽  
D T Gethin ◽  
B J Roylance
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Rotational Speed ◽  
High Speed ◽  
Applied Load ◽  
Frictional Heat ◽  
Transfer Coefficients ◽  
Gear Teeth ◽  
Heat Transfer Coefficients

This paper investigates the effects of gear geometry, rotational speed and applied load, as well as lubrication conditions on surface temperature of high-speed gear teeth. The analytical approach and procedure for estimating frictional heat flux and heat transfer coefficients of gear teeth in high-speed operational conditions was developed and accounts for the effect of oil mist as a cooling medium. Numerical simulations of tooth temperature based on finite element analysis were established to investigate temperature distributions and variations over a range of applied load and rotational speed, which compared well with experimental measurements. A sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperatures was conducted and the major parameters influencing surface temperature were evaluated.

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