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1.
The purpose of this article is to experimentally investigate the effect of different pore size distributions in bidisperse
wicks upon the heat transfer performance in a LHP. Three bidisperse wicks and one monoporous wick were tested in a loop heat
pipe. The pore size distributions of the bidisperse wicks were measured, and the results reflected the three different large/small
pore size ratios. The experiments showed that the maximum heat load of the monoporous wick reached about 400 W; and the three
bidisperse wicks showed improvements on the maximum heat load up to 570 W. For the monoporous wick, the evaporator heat transfer
coefficients of 10 kW/m2 K and total thermal resistance of 0.19°C/W were achieved at a high heat load of 400 W. For the better bidisperse wick, the
evaporator heat transfer coefficients could attain about 23 kW/m2 K and total thermal resistance of 0.13°C/W. The results also indicated that a smaller cluster size in a bidisperse structure
created a small pore size ratio. It was also found that the bidisperse wick with smaller clusters had a better enhancement
in terms of the evaporator heat transfer coefficient. 相似文献
2.
Investigation has been carried out on the thermal performance of sintered miniature heat pipes with 3 mm outer diameter.
In the theoretical analysis, the influence of wick structure parameters is determined by using the theory of capillary limitation.
As a result, the degree of importance is found to be as follows: porosity, powder diameter and thickness of wick structure.
In the experiments, heat pipes with sintered dendritic copper powder wicks were fabricated and tested. The maximum heat transfer
rate is about 13 W with an effective heat pipe length of 20 cm. By adopting the formulae developed for both sintered spherical
powder and fiber and adjusting their proportion, the agreement between experimental results and prediction is found to be
quite good in the tested operation temperature range.
Received on 26 February 2001 相似文献
3.
This paper deals with the evaporation heat transfer mechanism in thin biporous media that have two characteristic capillary
pore radii. The character of the two levels of pore sizes allows the liquid phase to easily occupy the void space of the small
pores and vapor phase to occupy the void space of the big pores. Compared with mono-porous media, biporous media increase
the number of small evaporating menisci with high heat transfer performance. Evaporation heat transfer in pores of porous
media is analyzed in detail. The results indicate that the average heat transfer coefficient increases with the capillary
pore size reduction. Under the assumption of the uniform structure of biporous media, a calculation method to predict heat
transfer performance for the evaporation in thin biporous media is given. The preliminary results reflect the behavior of
observed vaporization heat transfer in thin biporous media well.
Received on 22 February 2000 相似文献
4.
In order to evaluate characteristics of the liquid film flow and their influences on heat and mass transfer, measurements
of the instantaneous film thickness using a capacitance method and observation of film breakdown are performed. Experimental
results are reported in the paper. Experiments are carried out at Re = 250–10000, T
in = 20–50°C and three axial positions of vertically falling liquid films for film thickness measurements. Instantaneous surface
waveshapes are given by the interpretation of the test data using the cubic spline method. The correlation of the mean film
thickness versus the film Reynolds number is also given by fitting the test data. It is revealed that the surface wave has
nonlinear behavior. Observation of film breakdown is performed at Re = 1.40 × 103–1.75 × 104 and T
in = 85–95°C. From experimental results, the correlation of the film breakdown criterion can be obtained as follows: Bd = 1.567 × 10−6
Re
1.183 相似文献
5.
The exponential growth of component density in microelectronics has renewed interest in compact and high heat flux thermal
management technologies that can handle local heat fluxes exceeding 1 kW/cm2. Accurate and spatially resolved thermometry techniques that can measure liquid-phase temperatures without disturbing the
coolant flow are important in developing new heat exchangers employing forced-liquid and evaporative cooling. This paper describes
water temperature measurements using dual-tracer fluorescence thermometry (DFT) with fluorescein and sulforhodamine B in laminar
Poiseuille flow through polydimethyl siloxane-glass channels heated on one side. The major advantage of using the ratio of
the signals from these two fluorophores is their temperature sensitivity of 4.0–12% per °C—a significant improvement over
previous DFT studies at these spatial resolutions. For an in-plane spatial resolution of 30 μm, the average experimental uncertainties
in the temperature data are estimated to be 0.3°C. 相似文献
6.
A detailed numerical study is carried out to investigate fluid flow and heat transfer characteristics in a channel with heated
V corrugated upper and lower plates. The parameters studied include the Reynolds number (Re = 2,000–5,500), angles of V corrugated plates (θ = 20°, 40°, 60°), and constant heat fluxs (q″ = 580, 830, 1,090 W/m2). Numerical results have been validated using the experimented data reported by Naphon, and a good agreement has been found.
The angles of V corrugated plates (θ) and the Reynolds number are demonstrated to significantly affect the fluid flow and the heat transfer rate. Increasing the
angles of V corrugated plates can make the heat transfer performance become better. The increasing Reynolds number leads to
a more complex fluid flow and heat transfer rate. The numerical calculations with a non-equilibrium wall function have a better
accuracy than with a standard wall function for solving high Reynolds numbers or complex flow problems. 相似文献
7.
V. I. Melikhov O. I. Melikhov Yu. V. Parfenov S. E. Yakush 《Journal of Applied Mechanics and Technical Physics》2007,48(6):852-860
The temperature regime of a filtering unit being cooled after an accident at a nuclear power plant is considered. A mathematical
model is developed; the model is based on three-dimensional equations of thermohydrodynamics and takes into account heat-transfer
mechanisms (convection, heat conduction, and radiation). For the unit variants considered, the maximum value of temperature
in the sorbing module is less than 300°C, and the temperature reserve is 20–50°C.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 92–102, November–December, 2007. 相似文献
8.
Hideo Inaba Fujio Komatsu Akihiko Horibe Naoto Haruki Akito Machida 《Heat and Mass Transfer》2008,44(11):1305-1313
This paper describes heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a fin-tube
heat exchanger. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were
conducted under various conditions of air flow rate (0.5–1.0 m/s) and the temperature of brine (14–20°C) that was the heat
transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected
by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted.
Finally the average mass transfer coefficient of the organic sorbent coated on heat transfer surface of a fin-tube heat exchanger
is non-dimensionalzed as a function of Reynolds number and non-dimensional temperature, and it is found that the effect of
non-dimensional temperature on them is larger than Reynolds number . 相似文献
9.
Comparison between oxide-reduced and water-atomized copper powders used in making sintered wicks of heat pipe 总被引:2,自引:0,他引:2
Liu-Ho Chiu Chang-Hui Wu Pee-Yew Lee 《中国颗粒学报》2007,5(3):220-224
Oxide-reduced copper powder can be produced efficiently at low cost. The volume shrinkage, porosity, maximum pore size, permeability and thermal conductivity of wicks sintered from two oxide-reduced (OR) powders were compared with one from water-atomized (WA) powder. The green specimens were sintered at temperatures from 800 to 1000 ℃ in a tube furnace under a reduction stream of 10% hydrogen and 90% argon. The results show that the property variations of OR - 100 and WA wicks due to porosity changes have a similar tendency and range. Nine hundred degree celsius is a recommended sintering temperature for producing ideal wicks for use in heat pipes. A smaller maximum pore size can be obtained by increasing the green density.2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. 相似文献
10.
This paper presents the experimental results of condensation heat transfer coefficients of hydrocarbon (HC) refrigerants R-290
and R-600a, hydrochlorofluorocarbon (HCFC) refrigerant R-22, and hydrofluorocarbon (HFC) refrigerant R-134a in a horizontal
double-pipe heat exchanger having pipe inner diameters of 10.07, 7.73, 6.54, and 5.80 mm. The condensation process experiments
were conducted at mass flux of 35.5–210.4 kg/m2 s and condensation temperature of 40°C. The main results were summarized as follows: The average condensation heat transfer
coefficients of R-290 and R-600a were higher than those of R-22 and R-134a. The pressure drops of the four refrigerants were
in the order of R-600a > R-290 > R-134a > R-22. The pressure drops of R-600a, R-290, R-134a, and R-22 were approximately 6–15,
9.8–12.5, 4.3–6.7, and 2.1–4.6% higher, respectively, in the 10.7 mm diameter tubes compared to the 5.80 mm diameter tubes.
Comparing the condensation heat transfer coefficients of our experimental results with those of other correlations, our experimental
data in all the test tubes coincided best with that of Haraguchi et al. 相似文献
11.
Andrew J. Onstad Christopher J. Elkins Frank Medina Ryan B. Wicker John K. Eaton 《Experiments in fluids》2011,50(6):1571-1585
Open-celled foam geometries show great promise in heat/mass transfer, chemical treatment, and enhanced mixing applications.
Flow measurements on these geometries have consisted primarily of observations of the upstream and downstream effects the
foam has on the velocity field. Unfortunately, these observations give little insight into the flow inside the foam. We have
performed quantitative flow measurements inside a scaled replica of a metal foam, ϕ = 0.921, D
Cell = 2.5 mm, by Magnetic Resonance Velocimetry to better understand the fluid motion inside the foam and give an alternative
method to determine the foam cell and pore sizes. Through these 3-D, spatially resolved measurements of the flow field for
a cell Reynolds number of 840, we have shown that the transverse motion of the fluid has velocities 20–30% of the superficial
velocity passing through the foam. This strong transverse motion creates and dissipates streamwise jets with peak velocities
2–3 times the superficial velocity and whose coherence length is strongly correlated to the cell size of the foam. This complex
fluid motion is described as “mechanical mixing” and is attributed to the geometry of the foam. A mechanical dispersion coefficient,
D
M, was formed which demonstrates the transverse dispersion of this geometry to be 14 times the kinematic viscosity and 10 times
the thermal diffusivity of air at 20°C and 1 atm. 相似文献
12.
Correlations are presented to compute the mutual solubilities of CO2 and chloride brines at temperatures 12–300°C, pressures 1–600 bar (0.1–60 MPa), and salinities 0–6 m NaCl. The formulation
is computationally efficient and primarily intended for numerical simulations of CO2-water flow in carbon sequestration and geothermal studies. The phase-partitioning model relies on experimental data from
literature for phase partitioning between CO2 and NaCl brines, and extends the previously published correlations to higher temperatures. The model relies on activity coefficients
for the H2O-rich (aqueous) phase and fugacity coefficients for the CO2-rich phase. Activity coefficients are treated using a Margules expression for CO2 in pure water, and a Pitzer expression for salting-out effects. Fugacity coefficients are computed using a modified Redlich–Kwong
equation of state and mixing rules that incorporate asymmetric binary interaction parameters. Parameters for the calculation
of activity and fugacity coefficients were fitted to published solubility data over the P–T range of interest. In doing so, mutual solubilities and gas-phase volumetric data are typically reproduced within the scatter
of the available data. An example of multiphase flow simulation implementing the mutual solubility model is presented for
the case of a hypothetical, enhanced geothermal system where CO2 is used as the heat extraction fluid. In this simulation, dry supercritical CO2 at 20°C is injected into a 200°C hot-water reservoir. Results show that the injected CO2 displaces the formation water relatively quickly, but that the produced CO2 contains significant water for long periods of time. The amount of water in the CO2 could have implications for reactivity with reservoir rocks and engineered materials. 相似文献
13.
Experimental investigation on the sensible effectiveness of LiCl wheel is reported. The measurements were made for balanced
flow (C* = 1) for a wide range of rotational speed 0–10 rpm, regeneration temperature of 50–70°C and airflow rate 150–550 kg/h.
The results revealed that the operation rotational speed for LiCl wheel is about 5 rpm which is significantly lower that for
Silica gel wheel. It is also found that the sensible effectiveness is independent of the regeneration temperature. The experimental
results are also fitted to the existing correlation of Simonson et al. (ASHRAE Trans 106(1):301–310, 2000). For the range
of the applicability of the correlation, most of the experimental data fit the correlation within an error band of ±5%. 相似文献
14.
Edward T. Kopesky Stephen G. Boyes Neil Treat Robert E. Cohen Gareth H. McKinley 《Rheologica Acta》2006,45(6):971-981
Two distinct oligomeric species of similar mass and chemical functionality (M
w≈2,000 g/mol), one a linear methyl methacrylate oligomer (radius of gyration R
g≈1.1 nm) and the other a hybrid organic–inorganic polyhedral silsesquioxane nanocage (methacryl-POSS, r≈1.0 nm), were subjected to thermal and rheological tests to compare the behaviors of these geometrically dissimilar molecules over the entire composition range. The glass transition temperatures of the blends varied monotonically between the glass transition temperatures of the pure oligomer (T
g=−47.3°C) and the pure POSS (T
g=−61.0°C). Blends containing high POSS contents (with volume fraction φ
POSS≥0.90) exhibited enhanced enthalpy relaxation in differential scanning calorimetry (DSC) measurements, and the degree of enthalpy relaxation was used to calculate the kinetic fragility indices m of the oligomeric MMA (m=59) and the POSS (m=74). The temperature dependences of the viscosities were fitted by the free-volume based Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) framework and a dynamic scaling relation. The calculated values of the fragility from the WLF–VFT fits were similar for the POSS (m=82) and for the oligomer (m=76), and the dynamic scaling exponent was similar for the oligomeric MMA and the POSS. Within the range of known fragilities for glass-forming liquids, the temperature dependence of the viscosity was found to be similarly fragile for the two species. The difference in shape of the nanocages and oligomer chains is unimportant in controlling the glass-forming properties of the blends at low volume fractions (φ
POSS<0.20). However, at higher volume fractions, adjacent POSS cages begin to crowd each other, leading to an increase in the fractional free volume at the glass transition temperature and the observed enhanced enthalpy relaxation in DSC. 相似文献
15.
The influence of oil on nucleate pool boiling heat transfer 总被引:1,自引:0,他引:1
The influence of various oil contents in R134a is investigated for nucleate pool boiling on copper tubes either sandblasted
or with enhanced heating surfaces (GEWA-B tube). Polyolester oils (POE) (Reniso Triton) with medium viscosity 55 cSt (SE55)
and high viscosity 170 cSt (SE170) were used. Heat transfer coefficients were obtained for boiling temperatures between −28.6
and +20.1°C. The oil content varied from 0 to 5% mass fraction. For the sandblasted tube and the SE55 oil the heat transfer
coefficients for the refrigerant/oil-mixture can be higher or lower than those for the pure refrigerant, depending on oil
mass fraction, boiling temperature and heat flux. In some cases the highest heat transfer coefficients were obtained at a
mass fraction of 3%. For the 170 cSt oil there is a clear decrease in heat transfer for all variations except for a heat flux
4,000 W/m2 and −10.1°C at 0.5% oil content. The heat transfer coefficients are compared to those in the literature for a smooth stainless
steel tube and a platinum wire. For the enhanced tube and 55 cSt oil the heat transfer coefficients are clearly below those
for pure refrigerant in all cases. The experimental results for the sandblasted tube are compared with the correlation by
Jensen and Jackman. The calculated values are within +20 and −40% for the medium viscosity oil and between +50% and −40% for
the high viscosity oil. A correlation for predicting oil-degradation effects on enhanced surfaces does not exist. 相似文献
16.
The heat transfer, pressure drop and flow patterns during flow boiling of R407C in a horizontal microfin tube have been investigated.
The microfin tube is made of copper with a total fin number of 55 and a helix angle of 15°. The fin height is 0.24 mm and
the inner tube diameter at fin root is 8.95 mm. The test tube is 1 m long. It is heated electrically. The experiments have
been performed at saturation temperatures between −30°C and +10°C. The mass flux was varied between 25 and 300 kg/m2/s, the heat flux from 20,000 W/m2 down to 1,000 W/m2. The vapour quality was kept constant at 0.1, 0.3, 0.5, 0.7 at the inlet and 0.8, 1.0 at the outlet, respectively. The measured
heat transfer coefficient is compared with the correlations of Cavallini et al., Shah as well as Zhang et al. Cavallini’s
correlation contains seven experimental constants. After fitting these constants to our measured values, the correlation achieves
good agreement. The measured pressure drop is compared to the correlations of Pierre, Kuo and Wang as well as Müller-Steinhagen
and Heck. The best agreement is achieved with the correlation of Kuo and Wang. Almost all values are calculated within an
accuracy of ±30%. The flow regimes were observed. It is shown, that changes in the flow regime affect the heat transfer coefficient
significantly. 相似文献
17.
Marie Violay Benoit Gibert Pierre Azais Philippe A. Pezard Gérard Lods 《Transport in Porous Media》2012,91(1):303-318
Electrical resistivity soundings are used by geophysicists to determine the structure and composition of the Earth’s crust
and mantle and to explore natural resources (ore, oil, gas, water). Their interpretations in terms of composition and in-situ
physical conditions depend mainly on laboratory measurements of electrical conductivity of rocks at simulated crustal conditions
of temperature, pressure, saturation and pore pressures. These measurements present a numbers of limitations, in particular,
in the case where conductive pore fluids are present, as in the case of deep reservoir conditions, where temperature exceeds
250 °C. Here, we present a new cell capable of measuring electrical conductivity of large saturated samples at confining pressure
up to 200 MPa, pore pressure up to 50 MPa, and temperature up to 500 °C. The measurement cell has been developed in a commercial,
internally heated, gas pressure apparatus (Paterson press). It is based on the concept of “guard ring” electrode, which is
adapted to samples that are jacketed by a very conductive, metallic material. Numerical modeling of the current flow in the
electrical cell allowed defining the optimal cell geometry. Calibration tests have been performed on Fontainebleau sandstones
saturated with electrolytes of different conductivities, up to 350 °C. The resulting electrical formation factor and temperature
dependence of electrical conductivity are in very good agreement with previous studies. This new cell will improve the exploration
and exploitation of deep fluid reservoirs, as in unconventional, high enthalpy geothermal fields. In particular, the investigations
address possible effects of fluid-rock interactions on electrical resistivity of a reservoir host rock. 相似文献
18.
Several heat pipes were designed and manufactured to study the effect of the working fluids, container materials, and the wick structures on the heat transfer mechanism of the heat pipes. Also, the effect of the number of wick layers on the effective thermal conductivity and the heat transfer characteristics of the heat pipes have been investigated. It was found that the flow behavior of the working fluid depends on the wicking structures and the number of wick layers. The heat transfer characteristics and the effective thermal conductivity are related directly to the flow behavior. Increasing the number of wick layers (up to 16 layers) increases the heat flux with smaller temperature differences. The flattening phenomena of the thermal resistance was observed after 16 wicks layers due to the entrainment limit. 相似文献
19.
Ir. H. A. Waterman 《Rheologica Acta》1969,8(1):22-38
Summary The propagation of elastic waves (both longitudinal and transverse) through polyurethane rubbers filled with different amounts
of sodium chloride particles was studied at 0.8 MHz and 5 MHz. At a constant filler concentration (∼10% by volume), the velocity
of these waves appeared to be independent of filler size. On the other hand, both velocities were found to increase with filler
content. From the wave velocities, the effective modulus for longitudinal waves, L, bulk modulus, K, and shear modulus, G,
were calculated according to the relations for a homogeneous isotropic material. All three moduli appear to be monotonically
increasing functions of filler content, c, over the whole experimentally accessible temperature range (−80°C to +80°C for
L and K; −80°C to about −30°C for G) and they, moreover, reflect the glass-rubber transition of the binder. Poissons ratio,
μ, was found to decrease with increasing filler content and shows a rise at about −30°C as a result of the approach of the
glass-rubber transition.
The attenuation of the elastic waves was also measured in the temperature ranges mentioned. For filler particles beyond a
critical size both tan δL and tan δG in the hard region are independent of the filler content within the accuracy of the measurements. The critical size depends
on the type of wave and on its frequency. In the rubbery region, however, tan δL increases with particle size (at a constant content of 10% by volume) and even shows an enhancement with the smallest particles
(1–5 μ) at 0.8 MHz. Moreover, it is found that for the same filler size tan δL increases with filler content. In some cases an anomalous damping behaviour was found, such that in the rubbery region the
attenuation rises indefinitely with temperature. For filler particles larger than the above-mentioned critical size, tan δG and tan δL increase in the hard region as well. Finally, the experimental results are compared with existing theories on the elastic
properties of and wave propagation through composite media. 相似文献
20.
Heat transfer coefficients were measured on a horizontal platinum wire and converted to data on horizontal copper tubes. The
measurements spanned a large region of pressures p* = p/pcrit = 0.05–0.50 and heat fluxes of q = 103–1.5 × 105 W/m2. The preparation of the test equipment is described. The effects of pressure and concentration on the heat transfer coefficients
are shown. The mixture behaves very much like an azeotropic mixture; concentration has only a small effect, the heat transfer
coefficients can be obtained from the heat transfer coefficients of the pure components according to their molar fractions.
The conversion steps from wire- to tube-data are presented. A comparison of wire-data with correlations given in literature
is shown. It renders good agreement. 相似文献