Equilateral Triangular Pitch Research Articles

Optimization of temperature distribution in the novel power-to-heat matrix-in-batch OnePot© reactor

In this work, we assess the optimal temperature distribution inside a new automated, stand-alone, matrix-in-batch patented reactor, named OnePot©. This novel reactor is equipped with seven rotating hot rotating cylinders—here referred to as spots—which make it possible a precise tuning of fluid temperature. To conduct this investigation, we consider two radial layout of spots, here indicated as uniform configuration and alternate one, respectively. The former characterised by a single uniform equilateral triangular pitch, whereas the latter by two different equilateral triangular pitches alternated to form a double-triangle star. We consider two different fluids, water and argon, as representative of the behaviour of liquids and gases, respectively. Furthermore, the effect of viscosity is also taken into account by forcefully increasing that of water by 100 and 1,000 times. The optimization of the temperature distribution is performed obtaining velocity and temperature fields using a computational fluid dynamic (CFD) approach. As a sort of objective function to maximise, we defined a thermal mixing efficiency to provide a quantitative measure of the temperature distribution uniformity. As a remarkable result, we find an optimal value of pitch approximately equal to 36% of the vessel diameter for both liquid water and argon gas. As for the alternate configuration, we found that it provides a better temperature distribution than the uniform one, especially at high viscosity values. This is because the inner spots are able to prevent the formation of large colder “islands” around the centre. Furthermore, we estimate the overall heat transfer coefficient between thermal spots and fluid bulk, whose values are perfectly in line with the literature ones. The modularity of our novel fully-electric reactor allows for applications in a number of industrial contexts, especially pharmaceutical ones.

Bubble departure characteristics in a horizontal tube bundle under cross flow conditions

The visualization experiments for measuring departure diameter and frequency of vapor bubbles in the saturated nucleate boiling of distilled water have been carried out at atmospheric pressure. The experiments were carried out for an isolated single cylindrical tube and that for a tube bundle under pool and cross flow boiling conditions. The test setup was a stainless steel cuboidal tank of dimensions 400 mm × 200 mm × 180 mm provided with a 5 × 3 staggered tube bundle with an equilateral triangular pitch of 1.95. The departure diameter and frequency were measured using a high-speed camera to understand the parametric behavior of the bubble departure characteristics in a tube bundle under pool and cross flow condition. The range of operating conditions was: (1) heat flux q″=8−28kW/m2, (2) wall superheat ΔTsat=7−22K, (3) inlet mass fluxG=120−303.5kg/m2s. The departure diameter and frequency were found to increase with an increase in the heat flux, but decrease with an increase in the mass flow rate. The local departure diameter and frequency were observed to increase as the neighboring tubes in the bundle were successively heated. Empirical correlations have been developed for departure diameter and frequency for saturated nucleate boiling under cross flow conditions incorporating the effect of the tube bundle. The correlations were found to predict experimental data within acceptable limit.

Critical Power in 7-Rod Tight Lattice Bundle

The Reduced-Moderation Water Reactor (RMWR) has recently becomes of great concern. The RMWR is expected to promote the effective utilization of uranium recourse. The RMWR is based on water-cooled reactor technology, with achieved under lower core water volume and water flow rate. In comparison with the current light water reactors whose water-to-fuel volume ratio is about 2-3, in the RMWR, this value is reduced to less than 0.5. Thereby, there is a need to research its cooling characteristics. Experimental research on critical power in tight lattice bundle that simulates the RMWR has been carried out in Japan Atomic Energy Research Institute (JAERI). The bundle consists one center rod and six peripheral rods. The 7 rods are arranged on a 14.3mm equilateral triangular pitch. Each rod is 13mm in outside diameter. An axial 12-step power distribution is employed to simulate the complicate heating condition in RMWR. Experiments are carried out under G=100-1400kg/m2s, Pex=2-8.5MPa. Effects of mass velocity, inlet temperature, pressure, radial peaking factor and axial peaking factor on critical power and critical quality are discussed. Compared with axial uniform heating condition, the axial non-uniform heating condition causes an obvious decrease in critical quality. Arai correlation, which is the only correlation that has been optimized for tight lattice condition, is verified with the present experimental data. The correlation is found to be able to give reasonable prediction only around RMWR nominal operating condition.

Heat Transfer on Tube Bundles Embedded Horizontally in a Liquid-Fluidized Bed

Heat transfer on tube bundles embedded in a liquid-fluidized bed was investigated experimentally. In the experiment, 5 kinds of staggered tube bundles of equilateral triangular pitch, including single tube, were used. Tested particles were of glass and ceramics, and their diameter was from 2.1 to 6.0 mm. It was found, that the distribution of the local heat transfer coefficients around a tube depends on the tube pitch, and does not depend on the kind of particles, when a good fluidization is maintained. Based on the experimental data, a correlation was derived to predict average heat transfer coefficient, which could be applied for the tube bundles having a tube pitch to diameter ratio of 1.2 to infinity (single tube).

Nucleate Pool Boiling of a TURBO-B Bundle in R-113

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, copper TURBO-B tubes arranged in an equilateral triangular pitch, designed to simulate a portion of a flooded evaporator. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples. For increasing heat flux, the incipient boiling wall superheat of upper tubes decreased as lower tubes were activated. In the boiling region at low heat fluxes (≈ 1 kW/m2), the average bundle heat transfer coefficient was 4.6 times that obtained for a smooth tube bundle (under identical conditions) and 1.6 times greater than that obtained for a single TURBO-B tube; a similar bundle factor has been reported for a smooth tube bundle. At high heat fluxes (100 kW/m2), the average bundle heat transfer coefficient was 3.6 times that of a smooth tube bundle. Furthermore, there was still a significant bundle factor (1.22), contrary to a smooth tube bundle, where all effect of lower tubes was eliminated at high heat fluxes.

Heat transfer and hydrodynamic investigations of a baffled slurry bubble column

Heat transfer and hydrodynamic investigations have been conducted in a 0.108 m internal diameter bubble column at ambient conditions. The column is equipped with seven 19mm diameter tubes arranged in an equilateral triangular pitch of 36.5 mm. A Monsanto synthetic heat transfer fluid, Therminol-66 having a viscosity of 39.8 cP at 303 K, is used as a liquid medium. Magnetite powders, average diameters 27.7 and 36.6 µm, in five concentrations up to 50 weight percent in the slurry, are used. As a gas phase, industrial grade nitrogen of purity 99.6 percent is employed.

Nucleate Boiling Characteristics of R-113 in a Small Tube Bundle

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, smooth copper tubes arranged in an equilateral triangular pitch. The bundle was designed to simulate a portion of a refrigeration system flooded-tube evaporator. The outside diameter of the tubes was 15.9 mm, and the tube pitch was 19.1 mm. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples to obtain an average wall temperature and a resultant average heat transfer coefficient. All tests were performed at atmospheric pressure. The majority of the data were obtained with increasing heat flux to study the onset of nucleate boiling and the influence of surface “history” upon boiling heat transfer. Data taken during increasing heat flux showed that incipient boiling was dependent upon the number of tubes in operation. The operation of lower tubes in the bundle decreased the incipient boiling heat flux and wall superheat of the upper tubes, and generally increased the boiling heat transfer coefficients of the upper tubes at low heat fluxes where natural convection effects are important. The boiling data confirmed that the average heat transfer coefficient for a smooth-tube bundle is larger than obtained for a single tube.

Heat Transfer and Pressure Drop of Typical Air Cooler Finned Tubes

The heat transfer and pressure drop performance of heat exchangers fabricated from helically wrapped finned tubes with an equilateral triangular pitch arrangement are reported for one through five rows. Two finned tube types were tested, one with a “T” foot and the other with an overlapped “L” foot. The dimensions of both finned tubes were similar and were typical of those used in air-cooling applications. The tube diameter was 25.4 mm; the fin height was 15.87 mm; the fin number was 0.41/mm; and the fin-tip clearance was 6.35 mm. The fin base thickness was 0.38 mm and was tapered to half the base thickness at the fin outside diameter. No difference in the thermal performance of the two finned tube types could be detected. Both the heat transfer coefficient and pressure drop were found to increase with the number of tube rows. These results were then compared to other published data.

Optimal heat pipe heat exchanger design

A typical heat pipe heat exchanger with continuous planar fins and a staggered equilateral triangular pitch of the tubes is subject to optimization from the point of view of the ratio heat flow/weight and heat transfer effectiveness. Different optimization procedures are explained in detail and numerical results are given in the application. The procedures are as follows. 1. A. If hot and cold fluid mass flow velocities in the minimum free flow areas are given, one obtains the maximum of the ratio heat flow, Q /mass, M for optimal values of fin density and equilateral triangular pitch. The ratio of evaporator to condenser lengths observes a relation which allows Q/M to be permanently at its peak with respect to the dimensionless saturation temperature. 2. B.1. One obtains the maximum of the ratio heat flow/evaporator mass for optimal fin and triangular pitches. 2. One selects the cold fluid mass flow velocity G 2 so as to obtain equality between evaporator and condenser fin side heat transfer coefficients. The optimal pitches found at the evaporator also lead to the maximum of heat flow/condenser mass. 3. There is an optimal value of the ratio of evaporator to condenser lengths which ensures Q/M to be a maximum with respect to the dimensionless saturation temperature. 3. C.1. As B.1.2. G 2 remains variable. A condenser with maximal heat exchanger heat transfer effectiveness is “linked” to the optimized evaporator. One obtains the ratio of evaporator to condenser lengths and the ratio of hot and cold fluid heat capacities as optimal functions of G 2 . 4. D.1. As B.1.2. G 2 remains variable. The ratio of evaporator to condenser lengths is selected from the condition: Q/M maximum with respect to the dimensionless saturation temperature. It follows that this ratio becomes an optimal function of G 2 . The ratio of the heat capacities is derived as an optimal function of G 2 too. The heat flow value, the number of tubes in a row and the number of rows do not affect optimization results. The optimization procedures presented in this paper may be used, with adequate transformations, for other heat pipe heat exchanger configurations.

Prediction of Heat Transfer Coefficients in Gas Flow Normal to Finned and Smooth Tube Banks

A new method is presented to predict heat transfer coefficients for gas flow normal to smooth and finned tube tanks with triangular pitch. A transformation from the actual tube bank to an equivalent equilateral triangular pitch infinite smooth tube bank (ETP-I-STB) is made. A function of Ch(Ch = NSTNPR2/3NRe0.4) versus (Xt D0)Δ, ratio of transverse pitch to tube diameter for the ETP-I-STB, was developed. The Ch for the equivalent ETP-I-STP then applies to the actual tube bank. The method works with circular finned tubes, smooth tubes, continuous finned tubes, and segmented finned tubes with any triangular pitch. Also, fair predictions were made for in-line tubes with high Reynolds numbers.

Analytical study of heat transfer rates for parallel flow of liquid metals through tube bundles: II

AbstractA theoretical analysis of heat transfer to liquid metals in parallel flow through a tube bundle, following the method of Lyon, results in an equation which agrees within 10% with the calculated values. The conditions are fully developed turbulent flow, constant heat flux at the wall, and an infinite number of tubes arranged on an equilateral triangular pitch. The hexagonal flow area assignable to any tube is approximated by a circle of equal area, and the velocity distribution of Bailey for an annulus is assumed to apply from the inner wall to the circle of maximum flow. The range of conditions is: pitch‐to‐diameter ratio, 1.375 to 10; Reynolds number, 104 to 106; Prandtl number, 0 to 0.1; and Peclet number, 0 to 105. Laminar and slug flow Nusselt numbers are also determined.