Blower Power Research Articles

Heat transfer enhancement and development of correlation for turbulent flow through a tube with triple helical tape inserts

Influence of triple helical tapes inserted for turbulent flow through a tube on heat transfer enhancement was studied experimentally. The triple helical tapes made of mild steel with different helix angles, α = 9°, 13°, 17°, and 21° were examined for Reynolds number ranging from 22,000 to 51,000. The experiment showed that the Nusselt number, effectiveness and friction factor for the inserts were found to be up to 4.5, 3.45 and 3.0 times, respectively, over the plain tube. The highest enhancement efficiency achieved was 3.7 for the inserts based on constant blower power. Finally, new correlations for predicting heat transfer and friction factor for turbulent flow through a circular tube fitted with the inserts were proposed.

Experimental study on air bubbling humidification

A new process of solar humidification–dehumidification (HD) desalination by air bubbling humidification is designed. The studies are focused on the air humidifying experiments. The test-bed of air bubbling humidifier with a sieve plate is set up. The main factors affectinf air humidification are studied separately. The results show that the air relative humidity reaches 100% by humidifying in the range of the experiments. As the air flow rate increased, the quantity of air humidification, the pressure drop of air passing though the holes and the water level above sieve plate were all increased; as the temperature of air and water in the humidifier increased, the quantity of humidifying air increased significantly; as the height of water level above the sieve plate increased, the resistance of air passing though the humidifier increased, so that the blower power increased too; when the way of cooling air is improved, the GOR of the system can be enhanced and the cost of freshwater can be decreased. The stu...

SPRAY CHARACTERISTICS OF AN AIR-DRIVEN ROTARY ATOMIZER WITH A DOUBLE-LAYER CUP FOR USE IN AN INDUSTRIAL OIL BURNER

An experimental investigation of spray characteristics in a rotary burner with an air-driven double-layer cup atomizer is reported. The air stream generated by a centrifugal blower was used to rotate a vane propeller attached to the double-layer cup, and to assist disintegration of liquid sheets formed from the rim of the double-layer cup at the air nozzle exit. As the blower power increased, the rotational speed of the cup and the gas-to-liquid mass ratio (GLR) increased, and the atomizing crossflow velocity at an annular slot increased as well. For some given operating conditions, the effect of the crossflow velocity on the spray quality was investigated by varying the outer diameters of the air nozzle (88, 83, and 79.5 mm). The spray cone angles were measured by analyzing stroboscopic images. As the air velocity at the annular slot increased, the spray cone angle decreased. The spray radial and streamwise dispersion distributions were obtained by two liquid-collecting devices. The crossflow velocity at the annular slot, the GLR, and the diameter of air nozzles had an impact on the drop sizes and size distribution. The drop sizes of the spray were obtained using laser diffraction spectroscopy. The spray performance was described in terms of Sauter mean diameter (SMD), maximum drop diameter, relative span factor, and some representative drop diameters such as D0:9, D0:5, and D0:1. The SMD and maximum drop diameter were correlated with liquid Weber number (WeL) only. The atomization quality was improved with increasing GLR and crossflow velocity at the annular slot.

Battery Thermal Management Design Modeling

Battery thermal management is critical in achieving performance and the extended life of batteries in electric and hybrid vehicles under real-driving conditions. Appropriate modeling for predicting thermal behavior of battery systems in vehicles helps to make decisions for improved design and shortens the development process. For this paper, we looked at the impact of cooling strategies with air and direct/indirect liquid cooling. The simplicity of an air-cooling system is an advantage over a liquid-cooling system. In addition to its intrinsically lower heat transfer coefficient, another disadvantage of air cooling is that the small heat capacity of air makes it difficult to accomplish temperature uniformity inside a cell or between cells in a module. Liquid-cooling is more effective in heat transfer and takes up less volume, but the added complexity and cost may outweigh the merits. The surface heat transfer coefficient, h, and the blower power for air cooling are sensitive to the hydraulic diameter of the cooling channel (Dh). However, because of the added thermal resistances, h evaluated at cell surface is not as sensitive to the variation of Dh in an indirect (water/glycol jacket) cooling system. Due to the high heat transfer coefficient at small Dh, direct liquid cooling using dielectric mineral oils may be preferred in spite of high pressure loss in certain circumstances such as in highly transient large heat generating battery systems. In general, air-cooling should be considered first, as the power demand increases with heavier vehicles and more aggressive driving, water/glycol jacket cooling should be considered next. Results of computational fluid dynamics model simulation imply that capturing the internal heat flow paths and thermal resistances inside a cell using a sophisticated three-dimensional cell model is important for more accurate prediction of cell/battery thermal behaviors. This paper identified analyses and approaches that engineers should consider when they design a battery thermal management system for vehicles.

Evaluating and Comparing Aeration Blower Power Requirements

Evaluating and Comparing Aeration Blower Power Requirements

Experimental investigation and modelling study of long stick wood gasification in a top lit updraft fixed bed gasifier

We present results of an experimental study on long stick wood gasification, in an attempt to reduce wood gathering for gasification. This paper presents the results from experiments and the analyses of gasification using sticks with length ∼68 cm and diameter ∼6 cm. The moisture content of the wood was 25%. This top lit updraft gasifier operates with 180 W of blower power air supply to produce 9–10 kW of thermal energy, an energy yield of ∼50/1. Results were obtained for various flow conditions with airflow rates ranging from 25 to 45 m 3/h. For modelling, the flaming pyrolysis time for long stick wood in the gasifier is calculated to be 2.1 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 37 cm and 36 cm respectively. The turn down ratio for the gasification is around 2. The rate of feed was between 9 and 10 kg/h and the gasifier operated continuously for 5 h in two runs to study the gasifier reliability. The performance studies in specific gasification rate, equivalence ratio, turn down ratio, superficial velocity, airflow, and gas flow are analyzed. The temperature ranged from 1185 K in the combustion zone to 400 K in the drying zone. The gas and airflows can be converted to the Air/Fuel equivalence ratio, the most important aspect of gasifier operation. The equivalence ratio shows operation in a combustion mode (6.3) at start up; in a flaming pyrolysis mode (1.2) for the middle part of the run; and in the charcoal gasification mode (5.7) at the end of the run. Measurement of the equivalence ratio is a simple way of analyzing the behaviour of the gasifier. From the results of present investigation, it is revealed that the top lit updraft gasifier is more suitable for long stick wood as feed when compared to conventional updraft gasifier.

Indoor pollutant mixing time in an isothermal closed room: an investigation using CFD

We report on computational fluid dynamics (CFD) predictions of mixing time of a pollutant in an unventilated, mechanically mixed, isothermal room. The study aims to determine: (1) the adequacy of the standard Reynolds Averaged Navier Stokes two-equation ({kappa}-{var_epsilon}) turbulence model for predicting the mixing time under these conditions and (2) the extent to which the mixing time depends on the room airflow, rather than the source location within the room. The CFD simulations modeled the 12 mixing time experiments performed by Drescher et al. (Indoor Air 5 (1995) 204) using a point pulse release in an isothermal, sealed room mechanically mixed with variable power blowers. Predictions of mixing time were found in good agreement with experimental measurements, over an order of magnitude variation in blower power. Additional CFD simulations were performed to investigate the relation between pollutant mixing time and source location. Seventeen source locations and five blower configurations were investigated. Results clearly show large dependence of the mixing time on the room airflow, with some dependence on source location. We further explore dependence of mixing time on the velocity and turbulence intensity at the source location. Implications for positioning air-toxic sensors in rooms are briefly discussed.

Heat transfer and pressure loss characteristics of very compact heat sinks with plate fins cooled by jets

High-performance and very compact heat sinks have been developed for effective cooling of VLSIs with high heat-generation densities. Their heat transfer and pressure loss characteristics in air-jet cooling have been experimentally studied. The highly compact heat sinks were plate-fin arrays with a very small fin pitch of 0.4-2.0 mm. The rectangular jet nozzle width that gave the highest cooling performance was 30 to 40% of the streamwise length of the heat sinks. The influence of fin height on heat transfer became weak when the ratio of the height to the thickness of the fin exceeded approximately 35. When the air flow rate was constant, the thermal conductance increased as the fin pitch decreased. For a constant fin pitch, heat sinks with smaller fin thickness showed larger thermal conductance at a given blower power consumption. In our experimental range, the heat dissipation rate per unit heat sink volume increased as the base plate area of the heat sink became small.

Development and Evaluation of a Blower for Chopped Water Hyacinth

A blower was developed, fabricated and evaluated for blowing of chopped water hyacinth. The diameter, width and thickness of the casing of the blower were 0.70 m, 0.23 m and 3 mm respectively. Six radial blades of 4 mm thickness were fixed with blades arm of 0.275 m long, 38.1 x 6.35 mm angle bar. These angle bar were bolted to the back plate of thickness 20 mm. A conveyor was used to feed the material directly into the blower. Blowing operation was done at different speeds and feed rates. Regression analysis of total no-load power for operating the blower and total power for blowing chopped hyacinth were done. The capacity of the blower was 10.8 tons/hour at 180 kg/min feed rate and 1002 RPM. The total power consumption in blowing was 7.23 kW with equivalent amount of energy of 0.67 kWh/ton. The overall efficiency of the blower was 20.35 percent.

Experimental Study of Impingement Cooling of Heat Sinks for LSI Packages with Pin-Fin Arrays.

This paper describes an experimental study of impingement cooling characterisitics of heat sinks with pin-fin arrays. The experiments are performed with a variety of pin-fin arrays. For enhancing impingement cooling, one inlet orifice over the center of the heat sink is found to be the best geometric structure. The optimum orifice diameter is about 1/3 of the heat sink width. The optimum pin-fin diameter is about 0.5 mm for low blower power, and increases to 1.0 mm as the blower power increases. When the pin-fin diameter and the pin-fin number are constant, the heat transfer rate increases with increasing pin-fin height, but becomes almost constant when the pin-fin height is 10 mm or more. If the heat sink area or the pin-fin number is constant, the heat transfer rate reaches an optimum value when the ratio of the pin pitch to the pin-fin diameter reaches approximately 2∼2.5. By increasing the total surface area of the heat sink, the heat transfer rate per unit blower power increases, with a maximum value of about 5 to 6 times the fin base heat transfer rate without a heat sink.

Drying paper by impinging jets of superheated steam. Part 2: Comparison of steam and air as drying fluids

AbstractThe behavior of superheated steam and air as drying fluids during the constant rate period of drying paper under impinging jets was compared in the jet temperature range 20 ≤ Tj 465°C for jet Reynolds numbers of l000 ≤ Rej ≤ 12000. At equal mass flux, steam drying is faster than air drying above the inversion temperature of 175°C. Also, the specific blower power for steam drying is much lower than for air drying at temperatures in the range of industrial importance. Superheated steam impingement drying can therefore lead to important capital investment and energy cost reductions, relative to air drying.

Heat Transfer and Pressure Drop Characteristics of an Assembly of Partially Segmented Plates

The heat transfer and pressure drop characteristics of an assembly of plates in a rectangular duct, with part of each plate segmented transversely and the segments inclined at 25 deg to the flow, have been investigated experimentally in the range of Reynolds numbers between 900 and 4000. The segmented-to-total width ratios β were 0.81 and 0.61. Mass transfer measurements of naphthalene were made to obtain the heat transfer coefficient. A new spray technique is described for preparing the mass transfer models, which are so complex that previously reported techniques cannot be applied. The mass transfer models simulate louvered fin surfaces used currently in industries. The heat transfer coefficient is found to be a strong function of the segmented-to-total plate width ratio β, and it decreases as β decreases. The heat transfer coefficient of an existing louver fin heat exchanger whose geometries are in close proximity to one of the model configurations was compared with that of the model, and good agreement was obtained between the two. The pressure drop (through the plate assembly) measurements showed that the pressure drop is mainly due to inertia loss in the experimental range of the present work, and that the streamwise, per-row pressure drop coefficient Kp is a function of only β and independent of the Reynolds number NRe,Dh. It was found, for a fixed blower power, that there exists an optimum Reynolds number (NRe,Dh)opt for maximum Nusselt number at a given segmented-to-total width radio β. A similar trend is also found for a fixed pressure drop.

Impingement Heat Transfer Within Arrays of Circular Jets: Part 1—Effects of Minimum, Intermediate, and Complete Crossflow for Small and Large Spacings

An experimental study of the effects of three jet-induced crossflow schemes on impingement heat transfer was made. The schemes, referred to as minimum, intermediate, and maximum crossflow correspond, successively, to unrestricted flow of spent air away from the target surface, restriction of the flow to leave through two opposite sides, and through one side of a rectangular impingement surface. The study covered jet Reynolds number, jet-to-surface spacing, and open area of 1000–21,000, 2–16 jet hole diameters, and 1–4 percent, respectively. The best heat transfer performance is obtained with the minimum scheme, intermediate and complete crossflow being associated with varying degrees of degradation. For a given blower power, heat transfer can be enhanced markedly by having greater number of jets over a fixed target area; notably when working with the minimum scheme at narrow jet-to-target spacings.

A regenerable carbon dioxide removal and oxygen recovery system for the Japanese experiment module

The Japanese Space Station Program is now under Phase B study by the National Space Development Agency of Japan in participation with the U.S. Space Station Program. A Japanese Space Station participation will be a dedicated pressurized module to be attached to the U.S. Space Station, and is called Japanese Experiment Module (JEM). Astronaut scientists will conduct various experimental operations there. Thus an environment control and life support system is required. Regenerable carbon dioxide removal and collection technique as well as oxygen recovery technique has been studied and investigated for several years. A regenerable carbon dioxide removal subsystem using steam desorbed solid amine and an oxygen recovery subsystem using Sabatier methane cracking have a good possibility for the application to the Japanese Experiment Module. Basic performance characteristics of the carbon dioxide removal and oxygen recovery subsystem are presented according to the results of a fundamental performance test program. The trace contaminant removal process is also investigated and discussed. The solvent recovery plant for the regeneration of various industrial solvents, such as hydrocarbons, alcohols and so on, utilizes the multi-bed solvent adsorption and steam desorption process, which is very similar to the carbon dioxide removal subsystem. Therefore, to develop essential components including adsorption tank (bed), condensor, process controller and energy saving system, the technology obtained from the experience to construct solvent recovery plant can be easily and effectively applicable to the carbon dioxide removal subsystem. The energy saving efficiency is evaluated for blower power reduction, steam reduction and waste heat utilization technique. According to the above background, the entire environment control and life support system for the Japanese Experiment Module including the carbon dioxide removal and oxygen recovery subsystem is evaluated and proposed.

Production Rate Optimization in Continuous Fluidized Bed Freezers

A model for predicting freezing times of individual particles is adapted to operating conditions of fluidized beds. The equation is linked to a model for movement of solids along the continuous fluidized bed which includes longitudinal mixing. The equations obtained allow the design and optimization of fluidized bed freezers. Calculations are performed for beds of green peas. Maximum values in the production rate are found in terms of bed dimensions and operating conditions. A nomogram is provided to facilitate equipment design under conditions of maximum production rate and minimum blower power consumption.

Analysis and Design of Hybrid Double-Absorption Cooling Systems for Low Grade Thermal Energy Applications

A hybrid double-absorption system using LiCL-H2O solution as a working fluid is proposed in this paper. This system can operate at low source temperature (55–80°C), requires lower blower power than a desiccant system, and has a higher system C.O.P. A modification of this system, a double absorption-evaporation system that provides even higher C.O.P. is also proposed. Both closed and open regeneration of the working fluid are considered in the system design. Performance equations for these hybrid systems are presented. A computer code HYBRID is written to do parametric analyses for these systems under steady-state conditions. The operating range and optimum design conditions are determined through both theoretical analysis and computer simulation. It is shown that these hybrid absorption systems have definite advantages over conventional absorption and desiccant systems for low grade thermal energy applications.

A track-laying air cushion vehicle

Almost no previous research has dealt with the design of a track-laying air cushion vehicle. Preliminary estimates indicated that the total power requirement would be high, so means of reducing the likely power consumption were studied. An analysis of the behaviour of three track layouts made it possible to compare their power efficiencies under a wide range of operating conditions. A two track articulated configuration was generally the most efficient. To minimize loss pressurised air the exit gap height between track and side skirt must be small, but an unstable heave motion is prone to develop under these conditions. The heave motion characteristics of a plenum air cushion were, therefore, investigated theoretically and guidelines for design established. These were used in the design of a 3 4 scale model of one track of a 20,000 N air track vehicle. The model incorporated a new type of side skirt assembly which can react automatically to vertical motion of the lower track run. The new skirt was stable in heave and was reasonably effective in avoiding local closure of the air exit gap when the track belt was raised on small simulated bumps. It was confirmed that the original estimates of blower power required by an air cushion track were of the right order.

Contact-slit face seal for impellers in centrifugal-flow machines

The serv ice life of the components and the efficiency of centrifugal-flow compres so r s depends to a great extent on the design of the ro to r impel ler seal. Conventional floating-type contac t f ree seals loaded with elast ic steel springs cannot be used in the blowers on mainline gas ducts at compres so r stations. End whip of the ro tor is experienced in these blowers because of the high rotation speed (n ~8000 rpm), which sets the seal r ing vibrating. A s l i t type face seal backing up the radia l labyr in th seal great ly improves the blower efficiency and reduces the axial force acting on the thrust bearing [1]. However this type of seal also has its shor tcomings. Gas f rom the delivery cavity leaks through the slit into the intake cavity imnorma l operation. Under surge conditions, the ro to r is set vibrating at a high frequency in the axial direction, and its cover disk s t r ikes its end face against the seal ring and wreaks havoc with the latter. After a surge lasting no more than 3-5 sec, the sys tem will still function as a whole, but it will have to be taken off s t r eam in o rder to replace the ring in the mechanical shaft seal. If the ro tor is shifted axially toward the intake site in an accident because of wear on the thrust bearing, the braking torque on the shaft brought about by the frict ion force of the ro to r on the fixed seal r ing will be so formidable that the reduction gear train in the blower power drive will be hopelessly ruined.

Muffle-free electric furnace for gas nitriding

1. Large muffle-free furnaces can be used for gas nitriding in batch operations; the hardness and depth of the case are not inferior to those produced in muffle furnaces. 2. Muffle-free electric furnaces are lined with standard refractories and insulating materials with a low humidifying capacity. 3. With sufficient blower power no reverse of the blower or the gas flow is necessary. 4. Fairly rapid and dependable stabilizing of the gas composition during nitriding can be achieved under the following conditions: reliable sealing of the furnace; refractory and insulating materials with a low humidifying capacity; complete chemical reduction of the lining in the start up period; low humidity of the gas supplied to the furnace; no long intervals between nitriding cycles; keeping the lining temperature at 100–120°C at the lowest.

Optimizing a reactor coolant channel for minimum blower power

Equations are given for the calculation of the optimum coolant cross-sectional area in the active part of a nuclear reactor and the optimum degree of surface extension of the fuel element walls, when the entrance temperature of the coolant and the admissible clad temperature are fixed. The problem is solved from a purely thermodynamic point of view. The results may be applied especially to reactors with a high flow resistance in the non-active part of the primary circuit. The introduction of some dimensionless numbers allows presentation in generally valid diagrams.