Plenum Air Research Articles

COMPUTATIONAL FLUID DYNAMICS MODELED AIR SPEED THROUGH IN-SHELL PEANUTS IN DRYING WAGONS COMPARED TO MEASURED AIR SPEED

Abstract.HighlightsPeanut drying wagon internal airflow simulation and visualization.Comparison of computer fluid dynamic (CFD) solutions to measured air speed.Modeling of airflow through masses of in-shell peanuts. Information is lacking about airflow through masses of drying in-shell peanuts in drying wagons because of the difficulties encountered in making direct measurements. Information about airflow is needed to improve efficiency of drying peanuts to make peanut crops more profitable. Computational Fluid Dynamics (CFD) modeled airflow through in-shell peanuts loaded in drying wagons was validated using actual airflow measurements. CFD models allow for the investigation of airflow within peanut loads and the air plenum of drying wagons. Airflow through a wagon load of in-shell peanuts treated as a solid mass with distributed resistance was modeled using airflow behavior following Darcy’s law. CFD model simulations were undertaken using measured air speed, wagon air plenum static air pressure, and fan performance curve data. CFD modeling was based on actual air speed measurements made at 40 locations on the top surface of wagon loads of in-shell peanuts. The 40 measurement locations represented the top center of 40 blocks which the peanut load was divided into to investigate air speed. To match actual measurements to CFD model results, CFD models were configured with the same 40 blocks as those of the actual measurements. In CFD models, the permeability of the peanuts in each of the 40 blocks could be varied in a trial-and-error fashion to increase or decrease the air speed at the top surface of the peanut load to match that of the actual air speed measured for each of the blocks. Model results reproduced the measured air speed to within the accuracy limits of the air speed measurements. The air speed and static air pressure distribution in the wagon air plenum was found not to be uniform even when all blocks had the same permeability. Model results revealed wagon air plenum air speed patterns and static air pressure distribution could explain the general air speed distribution of slower air speeds at the top surface of the peanut load near the wagon air inlet wall and the increasing air speed along the length of the wagon. Permeability variations within the peanut load were found to explain localized variations in air speed at the top surface of the peanut load. Keywords: Air speed, Airflow, Modeled results compared to measured, Computational fluid dynamics modeling, Drying wagon, In-shell Peanuts, Peanut bulk permeability, Peanut curing, Peanut drying .

Effect of Grain Inverters in Cross-Flow Dryers on Kernel Fissuring and Head Rice Yield Reduction

HighlightsGrain inverters minimized fissuring of rice kernels closest to the heated air plenum at plenum air temperatures =55°C.Grain inverters had no effect on rice kernel fissuring across a grain column at plenum air temperatures <55°C.Grain inverters decreased head rice yield reduction of samples dried at plenum air temperatures >55°C but had no effect on head rice yield reduction at plenum air temperatures =55°C.One or two grain inverters in a cross-flow dryer can help reduce kernel fissuring and minimize head rice yield reduction.Abstract. Industrial-scale cross-flow dryers are commonly equipped with grain inverters to facilitate uniform drying across the column thickness, but limited information is available on the effect of grain inverters on rice milling quality. In this study, lab-scale drying experiments were performed to investigate the effect of grain inverters on kernel fissuring and head rice yield reduction. Rice samples of long-grain cultivar Roy J were dried for 60 min at plenum air temperatures of 45°C, 50°C, 55°C, and 60°C. The number of grain inversions during a 60 min drying period were 0, 1, and 2. After drying, a portion of the sample was tempered at a final bulk-rice temperature (heated tempering), while the other portion was tempered at ambient room temperature (ambient tempering). At plenum air temperatures of 55°C or 60°C, grain inversion (1 or 2 inversions) minimized fissuring of kernels closest to the heated-air plenum compared to 0 grain inversion. At 45°C and 50°C, grain inversion did not affect kernel fissuring. Similarly, at plenum air temperatures greater than 55°C for both ambient tempering and heated tempering approaches, 1 or 2 grain inversions significantly minimized head rice yield reductions compared to 0 grain inversion. These findings may be valuable for designing cross-flow dryers by informing decisions on the number of grain inverters needed to reduce fissuring and minimize head rice yield reduction. Keywords: Column dryer, Milling yields, Reversed airflow, Rice quality, Tempering, Turnflow, X-ray imaging.

Experimental model for prediction of tip temperature of diesel injector nozzle in dual-fuel engines

Dual-fuel technology enables Diesel engines to use natural gas as fuel injected into the intake. Ignition is achieved through the injection of fuels with high cetane numbers. This technology offers a cleaner and more economical burning for commercial engines. However, this fuel change leads to an increase in the tip temperature of the injector nozzle, causing the formation of deposits and coking in this component. Here, experimental and numerical studies were carried out in an engine converted to operate in dual-fuel mode, with the aim of developing a model to predict the dome temperature of the diesel injector nozzle. The following relevant parameters were found: the rate of Diesel replacement by compressed natural gas, combustion center, air-fuel equivalence ratio, Diesel injection pressure, exhaust gases recirculation rate, plenum air temperature, and engine coolant temperature. The tip temperature results were analyzed and except for the Diesel injection pressure, every parameter was found to influence this temperature being optimized. The temperature obtained through a new model shows a good correlation with the values measured with a deviation of less than 2% when the amount of Diesel injected is varied, and less than 1% when the engine coolant temperature and combustion center are varied.

Enhancement of cooling capacity through open-type installation of cooling radiant ceiling panel systems

Cooling radiant ceiling panel (CRCP) systems have been increasingly applied to modern buildings, owing to high thermal comfort, energy-saving potential, and integration with building design. Currently, the cooling capacity of CRCP is generally evaluated for the closed-type CRCP, wherein the overall ceiling surface is covered with ceiling panels. However, there have been few previous studies on the evaluation of the cooling capacity for open-type CRCP, which are installed with openings (void areas) between adjacent ceiling panels. This study was conducted to verify the hypothesis that the open-type CRCP can enhance cooling capacity by utilizing the cooled plenum air moving through the opening. If the plenum air is cooled by the upper surface of ceiling panels and descends to the conditioned space, it can contribute to increasing the convective heat transfer and cooling capacity. A simulation model for open-type CRCP was developed and validated against the mock-up experiment. Using the simulation model, the cooling capacity of the open-type CRCP was evaluated with respect to the opening area and panel layout. The results showed that the open-type CRCP could provide 54–80% (average 64%) higher nominal cooling capacity than conventional closed-type CRCP. The enhanced cooling capacity may lead to reduction in construction costs and energy consumption, because panel installation area could be reduced and the water temperature can be increased to provide the required cooling capacity. The results of this study would be able to offer fundamental data about cooling capacity of open-type CRCP.

Selection of turbulence models in case of numerical simulation of heat-, air- and mass exchange processes

Numerical experiment with the use of software products, such as Ansis, Star–CD, Star-CCM+ and other, helps get the fields of distributing parameters in different environments. In case of conducting numerical simulation one of the main tasks is to select the most appropriate turbulence model. This work presents analysis of results of numerical simulation of ventilation processes in production premises with spatial heat sources located on the platforms above floor level with the use of Spalart-Allmaras (SA) and k-ε turbulence models as well as LES method. A comparison of results of full-scale experiment and numerical simulation has been performed. A turbulence model k-ε has been used in numerical investigations of heat-and mass exchange processes in the nozzle of cellular humidifier of system of processing plenum air. The analysis of results of calculation and experimental data acquired at experimental installation is shown. The condition of microclimate in the working zone of premises significantly depends on the peculiarities of heat exchange through external building structures. This work presents results of numerical simulation of heat exchange through cold floors on the ground and in case of presence of underlining in the production premises with sources of heat emissions with the use of k-ε turbulence model.

Integrated Solution in an Office Room with Diffuse Ceiling Ventilation and Thermally Activated Building Constructions

An integrated system is proposed in this study to combine diffuse ceiling ventilation with a thermally activated building construction (TABS), aiming to provide cooling/ heating and ventilation to an office room all year around. The performance of the integrated system is evaluated by full-scale experiments in a climate chamber. The experimental results indicate that diffuse ceiling can significantly improve thermal comfort in the occupied zone, by reducing draught risk and vertical temperature gradient. The linear function between pressure drop and air change rate points out that the air flow through diffuse ceiling is laminar. A thermal decay is found in the plenum air and the thermal performance of TABS may be influenced by water flow and air flow direction.

Application of an ice thermal energy storage system as ways of energy management in a multi-functional building

Peak-hour tariff typically troubles commercial office buildings in hot and humid climates where cooling demands are high during summer. Because the local power company rate structure strongly favors the practice of load shift and conversely penalizes peak load demand during peak hours, a multi-functional office building in Taipei seeks to reduce its cooling cost by ways of an ice thermal energy storage system in which harvested ice is stored during cheaper off-peak hours and thawing the storage medium during peak hours. The system uses partial storage approach to satisfy off-peak cooling demand while peak-hour cooling burden is relieved by chilled water built the previous night. Two screw chillers would be integrated with each other for the implementation to allow feeding chill water to the air-handler coils while producing ice for storage at the same time. The refrigeration cycle of water chilling operates under two modes, the ice mode for thermal storage, and the chill water mode for instantaneous air cooling. Super-cooled air from melted ice-water makes humidity levels to be lower than conditioned with conventional systems, as well as load shift incentives. Cool air is introduced to variable air volume terminal boxes and is mixed with induced plenum air to bypass any reheat, yielding additional saving.

Design of an ice thermal energy storage system for a building of hospitality operation

Large chunk of cooling load is typically demanded during hospitality operation. In the pursuit of reducing its energy cost, a multi-functional commercial building incorporates ice thermal energy storage (TES) concept for storing harvested ice at off-peak hours and thawing the storage medium at peak hours. Ice built during off-peak hours is used to relief the cooling burden of hospitality operation at peak hours. The refrigeration cycle of water chilling would operate under two modes, the ice mode for thermal storage, and the chill water mode for instantaneous air cooling. The TES design uses a partial storage approach to satisfy off-peak hour cooling demands. Two screw chillers are integrated with each other for the implementation to allow feeding chill water to the air-handler coils while producing ice for storage at the same time. Not only does the TES system take advantage of the electric rate structure, super-cooled air also makes humidity levels to be lower than buildings with conventional cooling systems. Cool air is introduced to VAV (variable air volume) terminal boxes and is mixed with induced plenum air to bypass any reheat, yielding additional saving. The TES system saves electricity cost while providing thermal comfort to occupants. Indoor air quality may have been sacrificed when only 5L/s per person of fresh ventilation is introduced into the building.

An experimental investigation of a two-dimensional prototype of a transparent transpired collector

This paper presents an experimental investigation of the thermal performance of a two-dimensional reduced scale prototype designed to simulate the essential features of a novel type of solar air collector involving a transparent transpired cover. Another objective is to analyze the effects of varying key parameters such as plenum thicknesses, pitch spacing, slots width, irradiation, and air mass flow rate in term of collector efficiency. A multi-level factorial design of experiments is used for this investigation. It is found that the air mass flow rate has the strongest effect on the efficiency of the transparent transpired collector. The irradiation, slots width, pitch spacing and plenum thicknesses seems to have a moderate effect.

A Sampler for Total Suspended Particulates with Size Resolution and high sampling efficiency for large particles

AbstractFor a field intercomparison of various widely used dust samplers, a reference instrument was needed. Based on a Wide Range Aerosol Classifier (WRAC), several improvements were introduced compared with the original design including mass flow control of the samplers and the plenum air, brushless threephase blowers, hyperbolic inlets and generally a more compact design, allowing for more comfortable operation. In addition, for measurement of small particle size distributions, a Hauke high‐volume, low‐pressure impactor (LPI 150/0.15) was included, so that size distribution information with cuts at 0.12, 0.30, 1.19, 3.14, 10.2, 20.4, 37.4 and 60 μm could be obtained. In addition, the aspiration efficiency was measured under in situconditions and parallel measurements were performed with the two reference samplers built so that the performance was well characterized.

Levels of airborne chlordane and chlorpyrifos in two plenum houses: Saranex S-15 as a vapor barrier

In the 1960's the wood industry developed a plenum-type structure that used a down-flow furnace and air-conditioning unit to distribute heated or cooled air to a plenum underneath a wood floor from which air was circulated throughout the house by air vents in the floor or baseboards. The most efficient means of protecting these structures from termite damage is the treatment of the footings and the soil adjacent to the foundation with termiticides such as chlordane or chlorpyrifos. However, several studies have shown that chlordane residues are measureable in conventional houses treated with chlordane by subslab injection or post-constructio n exterior ditching (Lillie 1981; Wright and Leidy 1982). Because treatment of plenum houses involves the application of termiticide both inside and outside of the plenum air space, attention in the present study was directed to the use of a plastic film barrier to impede the movement of volatilized termiticides from treated soil into the plenum air space. The results of pilot studies in this laboratory, which examined films of polyethylene (i and 6 mils thick) polyvinylidene chloride and polyethylene (Saranex S-14, 2 mils thick), and polyamide (Capran 77-C, i mil thick) for their effectiveness as barriers to chlordane and chlorpyrifos penetration, indicated that the Saranex film was the most effective of these. For this reason it was selected as the film barrier to be used in this study of plenum houses which were constructed, treated and monitored to determine its effectiveness in preventing vapors of the termiticides chlordane and chlorpyrifos from appearing in the ambient air of the house.

Reply by Author to P. A. Sullivan

Hullender, D.A., Wormley, D.N., and Richardson, H.H., Active Control of Vehicle Air Cushion Suspensions, Journal of Dynamic Measurement and Control, Vol. 94, March 1972, pp.41-48. Genin, J., Ginsberg, J.H., and Ting, B.C., Fluid Suspension Model for Air Cushioned Vehicle, Journal of Sound and Vibration, Vol. 25, Nov. 1972, pp. 83-93. Sweet, L.M., Richardson, H.H., and Wormley, D.N., Air Cushion/Compfessor-Duct Dynamic Interactions, Journal of Dynamic Measurement and Control, Vol. 97, Sept. 1975 pp. 283-292. Goldschmied, F.R. and Wormley, D.N., Frequency Response of Blower-Duct-Plenum Systems, Journal of Hydronautics, Vol. 11, Jan. 1977, pp. 18-27. Thompson, W.C., Boghani, A.B., and Leland, T.J.W., Experimental and Analytical Dynamic Flow Characteristics of an Axial Flow Fan from an Air Cushion Landing System Model, NASA TN D8413, July 1977. Hinchey, M.J. and Sullivan, P.A., Duct on the Stability of Plenum Air Cushions, Journal of Sound and Vibration, Vol. 60, Sept. 1978, pp. 87-99. Hinchey, M.J. and Sullivan, P.A., Duct on the Dynamic Fan Characteristics of Air Cushion Systems, Journal of Hydronautics, Vol. 13, Jan. 1979, pp. 28-29. Hinchey, M.J., Heave Instabilities of Amphibious Air Cushion Suspension Systems, Institute for Aerospace Studies, University of Toronto, Report No. 246, Nov. 1980. Hinchey, M.J. and Sullivan, P.A., A Theoretical Study of Limit Cycle Oscillations of Plenum Air Cushions, Journal of Sound and Vibration, Vol. 79, Nov. 1981, pp. 61-78. 17 Graham, T.A., Effects of Skirt Material Choice on the Stability of an Air Cushion, Institute for Aerospace Studies, University of Toronto, M. A.Sc. Thesis, Oct. 1980.

A theoretical study of limit cycle oscillations of plenum air cushions

Air cushion vehicles (ACV) are prone to the occurrence of dynamic instabilities which frequently appear as stable finite amplitude oscillations. The aim of this work is to ascertain if the non-linearities characteristics of ACV dynamics generate limit cycle oscillations for cushion systems operating at conditions for which a linear theory predicts instability. The types of non-linearity that can occur are discussed, and an analysis is presented for a single cell flexible skirted plenum chamber constrained to move in pure heave only. Two cushion feed cases are considered: a plenum box supply and a duct. The results obtained by a Galerkin/describing function analysis are compared with those generated by a full numerical simulation. For the plenum box supply system, it is shown that the limit cycles can be suppressed by using a piston to introduce high frequency small amplitude volume oscillations into the plenum chamber.

Duct effects on the heave stability of plenum air cushions

Linear heave stability boundaries for a fun-duct-plenum air cushion suspension system are presented. These were obtained by using a quasi-static pressure-flow relationship for the fan, a finite element discretization for one dimensional unsteady duct flow, and a lumped capacitance model for the plenum. They indicate that even relatively short ducts can have a major effect at practical flow rates on the stability of cushion systems typically used for amphibious and overland operations. Some results obtained from a non-linear analysis, in which the method of characteristics was used for the duct flow, suggest that the linear approach should be adequate for practical stability calculations. Comparisons with lumped parameter models indicate that here the duct effect is associated primarily with the inertance of the air in the duct. It is also shown that for some operating conditions the duct-plenum system behaves as an Helmholtz resonator. Good agreement is obtained with an earlier transmission line analysis based on the wave equation.

Analysis, testing and design of plenum air cushion suspensions, including feeding system dynamics

Analysis, testing and design of plenum air cushion suspensions, including feeding system dynamics

The Roles of Skirt Planform and Deflection in Hovercraft Response

A linearized theory of hovercraft response while moving over regular waves is modified to account for, firstly, a cushion planform other than rectangular and, secondly, deflections of the skirt enclosing the supporting cushion as a result of wave-induced variations in the internal pressures. Consideration is given to the pitching and heaving of a hovercraft whose plenum air chamber is divided into two compartments by a transverse barrier. Detailed calculations are carried out for a cushion planform whose forward part is hexagonal and for a vertically deflecting skirt hemline, but the results are more widely useful in suggesting the general nature of the roles of cushion planform and skirt dynamics. A method of representing the overall effect of skirt deflection is proposed, involving four dimensionless coefficients, and the effect of these coefficients on the dynamic characteristics is investigated.

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.

Heaving and Pitching Response of a Hovercraft Moving over Regular Waves

Consideration is given to the pitching and heaving of a hovercraft whose plenum air cushion is divided into two compartments by a transverse barrier. Linearized equations of motion are developed, subject to the assumption that the skirt hem does not contact the surface beneath; the coefficients can be calculated in terms of craft geometry, weight and lift-fan characteristics, or in terms of natural frequencies and damping ratios for pitch and heave. In considering the response to regular head and following seas, particular attention is given to accelerations experienced at the bow and to the position of the pitch centre, where the vertical accelerations are least. The behaviour of a realistic craft is examined for waves of various lengths and for different craft speeds, and consideration is given to the effects of moving the mass centre and of modifying the barrier between cushion compartments. A relatively vigorous response is predicted for certain distinct ratios of craft length to wave length, as was the case for the pure heaving response studied earlier. Once again, it is possible to relate this maximum response to conditions at which rapid changes occur in cushion volume and escape area, but now the changes for the individual compartments must be considered as well.

Effect of plenum air flow on fire resistance ratings

It has been the practice to test the effects of air handling plenums in floor ceiling assemblies under static conditions, but what are the effects under dynamic conditions? The test results reported here provide some guidelines that may be used for predicting the effects of active air handling plenums.

Performance testing of an air cushion vehicle on the greenland ice cap

Abstract : During the summer of 1964, performance tests were conducted on the Greenland Ice Cap to determine and evaluate the feasibility of the air cushion vehicle concept as a transportation method in polar regions. Results from tests with the Bell Tri-Cell Plenum Air Cushion Vehicle indicated that the test vehicle can cruise over an undisturbed snow surface at speeds up to 35 mph and produce a maximum speed of 42 mph. The test vehicle was capable of ascending a 6 to 10% slope against a 15-knot wind, traveling over soft snow drifts up to 30 inches high, and crossing ditches of at least a 5-ft width. The payload capacity of the vehicle was approximately 1000 lb, not including the operator and fuel. The skirt lifting sideforce concept and the harrow disk attachment proved to be very effective for control and maneuverability of the vehicle. (Author)