Primary Air Inlet Research Articles

Cooling performance measurement of two cross-flow indirect evaporative coolers in general and regenerative operation modes

The main purpose of this study was to evaluate the cooling performances of two different types of cross-flow indirect evaporative coolers (IECs) operated in two different operation modes: general and regenerative. The cooling performances of the IECs were tested in each operation mode in an environmental chamber. In the general mode, the secondary air stream passing through the wet channels was the return air from the conditioned zone; whereas, in the regenerative mode, a portion of the primary air leaving the dry channels was redirected to the secondary channels. The IEC performances were measured under constant primary air inlet temperature and humidity ratio with variations of the primary airflow. As indexes of the IEC performance, the wet-bulb effectiveness and cooling capacity of both IECs in each operation mode were estimated based on the measurement data. The experimental results revealed that, in the general operation mode, both IECs exhibited higher sensible cooling performances in terms of wet-bulb effectiveness than in the regenerative mode in a 100% outdoor air system application.

Experimental study on the fouling behaviour of an underfeed fixed-bed biomass combustor

One of the most important problems occurring in biomass combustion is the appearance of fouling on heat exchangers which reduces the efficiency and lifetime of the facility. In this experimental work, wood pellets were burned in a small-scale biomass underfed fixed-bed combustor (12kWth) using low primary to secondary air ratios (15/85, 20/80, 25/75, 30/70). A water-refrigerated sampling probe was placed in the cross-flow above the bed to measure the fouling layer build-up rates. The water temperature inside the tube was varied between 20 and 95°C. This research proposes a test methodology to mimic the behaviour of a real heat exchanger of a commercial boiler.The measured deposition rates fluctuated between 7 and 28g/m2h. A greater amount of total airflow, an increase in the primary air inlet and a lower water temperature increased the deposition mass. In addition, the deposition rate decreased with time and did not appear to follow a linear pattern, which likely indicates that after a strong initial fouling rate, removal and collapse mechanisms begin to counter-balance the arrival of particles, which stabilizes the fouling layer.

Evaluation of biomass based combustor for hot air genration using maize cobs

Agriculture and energy have always been tied by close links, but the nature and strength of the relationship have changed over time. Biomass is considered as a renewable source of energy, because it is renewable in nature unlike fossil fuel like coal, oil and natural gas. Biomass is the third primary energy sources after coal and oil, accounting for about 14 per cent of the world's total energy supply. A biomass based combustor was developed and evaluated to meet the heat requirements for thermal application (drying, cooking, etc.) and power application through turbo charging. The biomass based combustor consists of combustion chamber, heat exchanger, chimney, hot air outlet and ambient air inlet, fuel hopper, primary air inlet with control, grate for proper combustion of the combustible gas. The developed biomass combustor was tested with maize cobs, three air flow rate and five fuel consumption rate. The experimental investigations show that the maximum efficiency of biomass combustor using maize cobs was 66.97 per cent in case of 1 kg/h fuel consumption rate and 400 m 3 /h air flow rate. The hot air temperature varied in between 51.55 to 142.35oC at three air flow rates i.e. 200, 300 and 400 m 3 /h and five fuel consumption rate i.e. 1 to 5 kg/h using maize cob as a fuel in the system.

Comparison of performance characteristics of SCR and ECM controlled series fan powered terminal units

Airflow, efficiency, power, and power quality characteristics were evaluated for two variable air volume series fan powered terminal units. The power and power quality data included real power, power/airflow, apparent power, harmonic frequencies, and total harmonic distortion. Each unit had the same sized primary air inlet and were provided by the same manufacturer. One unit had a motor controlled by a silicon controlled rectifier and the other had an electronically commutated motor. Data were collected at a fixed downstream static pressure and a range of upstream static pressures, primary inlet damper positions, and input controller voltages. Both controllers maintained a nearly constant fan airflow as the primary air was varied. Fan/motor efficiencies were low (below 35%) and increased with fan static pressures. The electronically commutated motor unit had efficiencies as much as four times higher than the silicon controlled rectifier controlled unit which was reflected in much lower power draws. The electronically commuted fan/motor unit had the lowest apparent power at airflows below approximately 1000 ft3/min (0.47 m3/s). For both units, the total power harmonic distortion was less than 1%. The performance data indicated a major advantage of units with electronically commutated motors.

Capacity Mapping for Optimum Utilization of Pulverizers for Coal Fired Boilers

Pulverizers play a pivotal role in coal-based thermal power generation. Improper coal fineness or drying reflects a qualitywise deterioration. This results in flame instability, unburnt combustible loss, and a propensity to slagging or clinker formation. Simultaneously, an improper air-coal ratio may result in either coal pipe choking or flame impingement, an unbalanced heat release, an excessive furnace exit gas temperature, overheating of the tube metal, etc., resulting in reduced output and excessive mill rejects. In general, the base capacity of a pulverizer is a function of coal and air quality, conditions of grinding elements, classifier, and other internals. Capacity mapping is a process of comparison of standard inputs with actual fired inputs to assess the available standard output capacity of a pulverizer. In fact, this will provide a standard guideline over the operational adjustment and maintenance requirement of the pulverizer. The base capacity is a function of grindability; fineness requirement may vary depending on the volatile matter (VM) content of the coal and the input coal size. The quantity and the inlet temperature of primary air (PA) limit the drying capacity. The base airflow requirement will change depending on the quality of raw coal and output requirement. It should be sufficient to dry pulverized coal (PC). Drying capacity is also limited by utmost PA fan power to supply air. The PA temperature is limited by air preheater (APH) inlet flue gas temperature; an increase in this will result in efficiency loss of the boiler. Besides, the higher PA inlet temperature can be attained through the economizer gas bypass, the steam coiled APH, and the partial flue gas recirculation. The PA/coal ratio, a variable quantity within the mill operating range, increases with a decrease in grindability or pulverizer output and decreases with a decrease in VM. Again, the flammability of mixture has to be monitored on explosion limit. Through calibration, the PA flow and efficiency of conveyance can be verified. The velocities of coal/air mixture to prevent fallout or to avoid erosion in the coal carrier pipe are dependent on the PC particle size distribution. Metal loss of grinding elements inversely depends on the YGP index of coal. Besides that, variations of dynamic loading and wearing of grinding elements affect the available milling capacity and percentage rejects. Therefore, capacity mapping is necessary to ensure the available pulverizer capacity to avoid overcapacity or undercapacity running of the pulverizing system, optimizing auxiliary power consumption. This will provide a guideline on the distribution of raw coal feeding in different pulverizers of a boiler to maximize system efficiency and control, resulting in a more cost effective heat rate.

An experimental study of a cross-flow type plate heat exchanger for dehumidification/cooling

The thermal and dehumidification behaviour of a standard cross-flow type plate heat exchanger, intended for use as a dehumidifier/cooler, has been investigated both experimentally and numerically. Three sets of experiments have been carried out where air is blown into the primary and secondary sides of the exchanger, while water and liquid desiccant were being sprayed in a counter flow arrangement. The first set represents the indirect evaporative cooling of the primary stream by the secondary air stream. The second set is with liquid desiccant only and no indirect evaporative cooling. In the third set of experiments the primary air stream is indirectly evaporatively cooled by the secondary air stream and dehumidified by the liquid desiccant sprayed into the primary side of the exchanger. The above experiments indicate that the heat exchanger performs well when used with liquid desiccant. Furthermore, for an exchanger angle of 45°, there is an optimum value of air mass flow rate at which the effectiveness and dehumidification efficiency of the plate heat exchanger are maxima. To investigate the effect of the ambient air conditions on the PHE performance, further experiments were carried out using a heater element and a humidifier. The results show that under laboratory conditions the exchanger effectiveness and dehumidification efficiency increase with increasing primary air inlet temperature and humidity ratio. The experimental results were used to validate a computer model developed for the cross-flow type plate heat exchanger/dehumidifier. Comparison indicates that the numerical results are in good agreement with the experiments.

Modeling and simulation of co-current moving bed gasification reactors — Part II. A detailed gasifier model

A detailed modeling program was developed for the simulation of co-current moving bed (down-draft) reactors fed carbonaceous materials. The model development consisted of formulating a non-isothermal particle model and applying the principles of thermodynamics, transport processes, hydrodynamics of solid and gas flows, and the mass and energy balances. The completed gasifier modeling program was used to simulate the reactor performance and to evolve the design criterion, specifically the dimension of the gasification zone. The gasifier model was validated using literature data. The dependence of reactor performance on operating variables (such as feedstock moisture contents, particle sizes, reactor insulation, input air temperatures and gasifier loads) has been studied with poplar wood chips as a feedstock. An increasing moisture content causes the feedstock conversion efficiency to decrease because of lower oxidation temperatures. Smaller particle size (not less than 0·5 cm), reactor insulation, and high input air temperature were all proven beneficial to gasifier operation. An increase of reactor load, causing a reduced residence time, resulted in declined efficiencies. However, the reactor can meet the demand variation by varying the air input rates. As for the design of the reactor dimension, a length of 100 cm below the primary air inlet is recommended for various gasifier operating and feedstock conditions.

Results of Field Measurements on Some Runup Noise Suppressors

Detailed acoustical measurements have been conducted on several types of runup noise suppressors, including: (1) a coupled exhaust unit, (2) separately coupled intake and exhaust units, (3) a complete enclosure, and (4) a runup pen. In most instances, the measurement procedure consisted of recording sound pressure levels as a function of octave bands of frequency both on a close-in rectangle and on a 250-ft semicircle about the aircraft, with and without the suppressor in place. The results of these measurements will be compared, particularly to point out the noise reduction characteristics as a function of both angle and frequency for each type of suppressor. In addition to noise reduction per se, the suppressor designer is also interested in how his design may be improved. Toward this end analyses have been performed to determine the relative contributions of the various “noise sources” of an aircraft-suppressor combination (suppressor exhaust opening, primary air inlet opening, secondary air inlet opening, etc.) to the noise levels at 250 ft. An example of such an analysis is described, and calculated, and measured sound pressure levels at 250 ft are compared. [Supported in part by the U. S. Air Force under Contract Nos. AF 33(616)-2151, AF 33(616)-3335, and AF 33(616)-3938.]

A Study of Burner Oscillations of the Organ-Pipe Type

Abstract Three simplified combustion systems have been investigated for acoustical oscillations. The systems are: (a) a mixing chamber and multiple-port burner mounted in a combustion tube open at both ends; (b) a similar mixing chamber and multiple-port burner which completely blocked the secondary-air inlet of the combustion tube; and (c) a system similar to (b), but utilizing separate fuel and primary-air inlets, giving a diffusion flame rather than a premixed-gas flame. Oscillations were found to occur only for certain ranges of the variables. In the first system, the pitch differed significantly in adjacent ranges of oscillation. In the two latter systems, the frequency of the oscillations remained fairly uniform and close to the fundamental of the combustion tube, although breaks occurred in the data as the configurations of the inlet supply systems were varied. These results are explained on the basis of (a) the time of feedback of pressure pulses which ultimately cause changes in the heat-release rate, and (b) the location of the flame relative to a section of maximum pressure amplitude in the combustion tube. In further substantiation of the implications of the test results, the Appendix presents a thermodynamic treatment of the phase requirement between rate of heat release and pressure.