Increasing Air Mass Flow Rate Research Articles

Flame Dynamics in an Optically Accessible Solid Fuel Ramjet Combustor

Flow–flame interactions were investigated in an optically accessible solid fuel ramjet combustor. Experiments were performed with a single hydroxyl-terminated polybutadiene fuel slab located downstream of a backward-facing step in a rectangular chamber. To emulate flight-relevant combustor conditions, unvitiated heated air was directed through the combustion chamber with an inlet temperature of , chamber pressures of 450–690 kPa, and port Reynolds number of . To characterize the heat-release distribution and velocity field, 20 kHz -chemiluminescence and 10 kHz particle imaging velocimetry measurements were used. Comparison between the mean chemiluminescence images acquired at three flow conditions indicates reduction in flame height above the grain with increasing air mass flow rate. Dominant heat-release coherent structures in the statistically stationary flow are identified using the spectral proper orthogonal decomposition technique implemented on time series of instantaneous images. The spatial mode shapes of the chemiluminescence and velocity field measurements indicated that the flow–flame interactions were dominated by vortex shedding generated at the backward-facing step in the combustor, at Strouhal numbers of 0.06–0.10. The frequency corresponding to these modes is shown to be invariant of air mass flux, indicating that system dynamics are primarily dependent on the backward-facing step geometry and the bulk velocity in the combustor.

Combustion Characteristics and Visualization Analysis of a Biomass Pellet Oriented in Different Positions in a Fixed-Bed Reactor at Different Operating Conditions

For all real-world applications, such as fluidized-bed and packed-bed combustion, it is essential to understand the combustion characteristics of an individual solid biomass particle. Under a variety of operating circumstances, investigations on the combustion and mass loss of single pellets of sugarcane (SC) and guava leaves (GL) were conducted. A visualization technique was used to capture the combustion processes of volatile and char. Both homogeneous ignition and hetero–homogeneous simultaneous ignition of both volatiles and char were found. When compared to the material composition and particle-size distribution of the pellet, the brightness of the pellet changed differently with increasing air mass flow rate and hot air temperature. By increasing the hot air temperature and air mass flow rate, the volatile flame of biomass pellets was made shorter and brighter, which lowered the volatile burnout duration. The majority of the entire conversion time is spent on char burning. Compared to other angles, the pellet orientation angle of 30° has a shorter ignition time, a lower surface temperature, and a lower burnout temperature.

A new method for continuous measurement of residence time distribution in spray drying

The residence time distribution of particles is one of the most important parameters during spray drying, since it directly impacts the thermal damage of a potential product. Due to insufficiencies of previous approaches for measuring the residence time distribution, a new method for continuous measurements was developed. This method simultaneously allows the determination of the residence time distribution of individual particle size fractions. The impact of air mass flow rate and particle size on the residence time distribution during spray drying was investigated. The mean particle residence time decreased with increasing air mass flow rate from 15.8 s for 190 kg/h, to 13.0 s for 210 kg/h and to 7.1 s for 230 kg/h, which is significantly shorter than the mean air residence time of 35.3 s, 31.9 s and 29.1 s, respectively. The mean particle residence time decreased with increasing particle size, with this effect being more pronounced for lower air flow rates. If the particle size is smaller than 105 µm, the presented technique can be transferred to any kind of single-stage spray dryer.

Thermal Performance of Single Glazing Flat Plate Photovoltaic Thermal Hybrid System with Various Air Channels

Abstract The present study attempts to investigate the thermal performance of five types of mild steel air channels in the photovoltaic thermal hybrid system. This system has been designed, fabricated, and tested in the tropical climatic condition of Chennai, India. There are five kinds of air channels studied in this work, namely, reference air channel, single-fin channel, multifin channel, fin with T baffle channel, and fin with V baffle channel. These channels are studied and compared. The experiments were accomplished with two mass flow rates, m˙: 0.00565 and 0.00847 kg/s. The photovoltaic thermal hybrid system performance was enhanced by increased air velocity, enhanced heat transfer between the absorber surface and air, and physical geometry of the channel. This optimal performance has been attained in the present study, with strong agreement with previously published findings. The photovoltaic thermal hybrid system experimentally proved to enhance thermal and photovoltaic efficiencies with increasing air mass flow rate, and the maximum electrical efficiency was found to be 13.70 % at the mass flow rate of 0.00565 kg/s and 14.27 % at the mass flow rate of 0.00847 kg/s; similarly, the thermal efficiency was 14.12 % at m˙ = 0.00565 kg/s and 20.81 % at m˙ = 0.00847 kg/s.

Theoretical analysis and experimental study on a low-temperature heat pump sludge drying system

A low-temperature heat pump sludge drying system was constructed and experimentally studied in the present study. The initial and final moisture contents on dry basis of sludge are 1.53 and 0.2, and the drying duration is 5 h. Theoretical models for heat pump circulation and moist air circulation are established and validated with the experimental results. Based on the validated theoretical models, sensitivity analysis of evaporating temperature, condensing temperature, and air mass flow rate on the temperature and humidity of moist air at the outlet of drying closet, drying rate and specific power consumption (SPC) are carried out. The temperature of moist air at the outlet of drying closet increases with increasing evaporating temperature and condensing temperature, while decreases with increasing air mass flow rate. The drying rate decreases with increasing evaporating temperature while increases with increasing condensing temperature, and first increases and then decreases with increasing air mass flow rate. The appreciated air mass flow rate ranges between 0.8 and 1.0 kg/s, and the drying rate around 6.0 kg/10min can be achieved under these conditions. The relative humidity of moist air at the outlet of drying closet shares a similar trend with the drying rate while SPC shows a contrary trend.

Design Strategies and Control Methods for a Thermally Driven Heat Pump System Based on Combined Cycles

Heating sector is one of the key emitters of greenhouse gas, and thus innovations are needed to improve the energy efficiency of heating technologies. In this paper, a recently proposed gas fuelled heat pump system that integrates an Organic Rankine Cycle (ORC) with an air-sourced heat pump (ASHP) has been further investigated. The heat produced by the gas burner is used to drive an ORC power system to produce mechanical power, which is then directly used to drive a vapour compression heat pump. Two different designs of the combined system were modelled, and their performances were compared and analysed. In the first design, the cold water is firstly heated in the heat pump condenser and then further heated in the ORC condenser to achieve the required final temperature. In the second design, the water is firstly heated in the ORC condenser and then further heated in the heat pump condenser. The results showed that the first design can achieve better overall fuel-to-heat efficiency. Using Aspen Plus, a dynamic model has then been developed to study the optimal control strategies for this design when ambient air temperature changes. The results revealed that, for the ambient temperature ranging from 7 ˚C to 15 ˚C, increasing air mass flow rate is sufficient to maintain the overall system performance. While when ambient temperature is below 7 ˚C, more heat is required from the gas burner that would reduce the fuel-to-heat efficiency.

Investigation of the condensation process of moist air around horizontal pipe

The condensation process of water vapor from moist air flowing around horizontal pipe is investigated theoretically and experimentally. This process involved in many engineering applications, such as refrigeration and air conditioning. In the theoretical analysis, the flow is assumed to be laminar, steady and with constant physical properties. The condensation process is described by continuity, momentum, energy and mass in the form of dimensionless ordinary differential equations using similarity variables. The dimensionless governing equations are solved by Runge Kutta fourth order integration technique accompanied with shooting method. The boundary layer thickness of mass, thermal and hydrodynamic, in addition to Nusselt and Sherwood numbers are investigated at different Reynolds numbers, and condensation and position parameters. In the experimental work, the effects of air inlet conditions (i.e. relative humidity, and mass flow rate) are varied and examined on the condensation process. The findings show that the average heat and mass transfer coefficients increase with increasing air mass flow rate and air relative humidity, and decrease with increasing the temperature difference between the air dew point and pipe surface temperature. Comparisons between the present theoretical and experimental work with previous theoretical study are accomplished within accepted error.

A qualitative study on the pulsatile flow phenomenon in a dense fly ash pneumatic conveyor

Understanding of the dynamic particulate flow structures within a dense gas-fly ash pneumatic conveyor must be improved in order to better aid its design guidance. The complex pulsatile movement of the gas-fly ash mixture dominates the flow performance within the pipeline, and historically, non-invasive measurement devices such as the electrical capacitance tomography (ECT) were often used to sufficiently capture the flow dynamics. However, inadequate studies have been conducted on the pulsatile flow phenomenon, which directly relate to the gas-fly ash two-phase flow performance. This paper aims to investigate the pulsatile flows using an ECT device. Initially, pulsatile flow patterns under various experimental conditions were obtained through ECT. Pulses within a flow were then characterised into pulse growth and decay segments, which represent the superficial fluidisation and deaeration processes during conveying. Subsequently, structural and statistical analyses were performed on the pulse growth and decay segments. Results suggested that the increasing air mass flow rate led to the decrease of the superficial fluidisation/deaeration magnitude, however, the increase of the superficial fluidisation/deaeration durations. Also, the air mass flow rate was indicated as the dominant factor in determining the pulsing statistical parameters. This research provides fundamental insights for further modelling the dense fly ash pneumatic flows.

A hybrid solar desalination system of air humidification, dehumidification and water flashing evaporation: Part II. Experimental investigation

This paper describes laboratory experiments with a hybrid solar desalination system consisting of a humidification–dehumidification unit and single stage flashing evaporation unit configured by a (Al2O3/H2O) nano-fluid solar water heater under the climatological conditions of Tanta City, Egypt. The laboratory work has been carried out in actual thermal environment in August 2013. The validation has an emphasis on the main parameters with impact on the water production capacity. These are the solar radiation, feed water mass flow rate, inlet cooling water temperature, mass flow rate of cooling water and nano-particle volume fraction. The main conclusion is that good agreement is obtained between simulated and measured variations of water production and performance ratio values for variations of these parameters. The performance ratio of SSF unit is varied between 0.32 and 1.4 and flashing ranges between 3 and 9°C. The maximum productivity of the system reached 41.8kg/day according to test and operation conditions. The solar water heater efficiency is affected by the nano-particle volume fraction. The humidifier efficiency is affected by increasing water mass flow rate more than the increasing air mass flow rate and reaches about 98%. Finally, collector's efficiencies are about 55% and 56% for solar water heater and solar air heater respectively.

The Performance of Solar Air Heater with High Density Polyethylene Paper as Top Cover and Brown Sand Layer as an Absorber

Experimental investigations on the performance of a flat plate solar air heater (SAH) with brown sand as absorber and clear HDPE paper as top cover was done. The efficiency, heat gain factor and heat loss coefficient were determined for the collector. The effects of air mass flow rate and thermal efficiency was also studied. The SAH model was placed outdoors and tests were conducted in an open field between 0900 and 1500 Hrs. and parameters including solar radiation, temperature and air mass flow rates were recorded after every 20 minutes for 100 hours. Results show that, the efficiency increase with increasing air mass flow rate. The highest efficiency obtained was 54% at air mass flow rate of 1.22xl0 -5 Kg/s. The temperature difference between the outlet flow and the ambient reduces as the air mass flow rate increases with a maximum difference of 31°C at air mass flow rate of 6.83X10 -6 Kg/s which occurred at 1240 Hrs.

Development of a Small Scale Concentrating Parabolic trough Solar Collector for Drying Purposes

A high performance solar collector was developed to modify agricultural building environment such as dairy, poultry farm buildings and greenhouses. Moreover it should be efficiently utilized as a solar dryer for drying various agricultural products and by products. The materials used include steel sheet with high performance of reflecting light, absorber tube, and angle iron and fully insulated drying chamber. A CPTSC was a tilted at 340south (Equivalent to the latitude of Peshawar) Pakistan. A CPTSC a total reflecting surface area was 2.9 m2 respectively. The absorber tube having a surface of 0.376 m2 was fixed in front of the reflector at the distance equal to the focal length. The total volume of drying chamber was 0.3135 m3. An experiment was conducted to enhance the efficiency of the CPTSC and two air mass flow rate treatments were tested with normal and convective mass air flow rate, 0.6 kg. Min-1 and 1.72 kg. Min-1 under the average temperature of the month (January, February and March, 2012). Moreover, the process was replicated three times under the completely randomized design. The result showed that both air mass flow rate and average temperature of the month significantly effected the efficiency of a concentrating parabolic trough solar collector. The new model of a CPTSC increased the efficiency from 8 to 25 % with increase in both air mass flow rates and average temperature of the months. Therefore it is concluded that the solar collector efficiency increased with increasing air mass flow rate.

Development of a Small Scale Concentrating Parabolic trough Solar Collector for Drying Purposes

A high performance solar collector was developed to modify agricultural building environment such as dairy, poultry farm buildings and greenhouses. Moreover it should be efficiently utilized as a solar dryer for drying various agricultural products and by products. The materials used include steel sheet with high performance of reflecting light, absorber tube, and angle iron and fully insulated drying chamber. A CPTSC was a tilted at 340south (Equivalent to the latitude of Peshawar) Pakistan. A CPTSC a total reflecting surface area was 2.9 m2 respectively. The absorber tube having a surface of 0.376 m2 was fixed in front of the reflector at the distance equal to the focal length. The total volume of drying chamber was 0.3135 m3. An experiment was conducted to enhance the efficiency of the CPTSC and two air mass flow rate treatments were tested with normal and convective mass air flow rate, 0.6 kg. Min-1 and 1.72 kg. Min-1 under the average temperature of the month (January, February and March, 2012). Moreover, the process was replicated three times under the completely randomized design. The result showed that both air mass flow rate and average temperature of the month significantly effected the efficiency of a concentrating parabolic trough solar collector. The new model of a CPTSC increased the efficiency from 8 to 25 % with increase in both air mass flow rates and average temperature of the months. Therefore it is concluded that the solar collector efficiency increased with increasing air mass flow rate.

Maximising the energy output of a PVT air system

Simultaneously generating both electricity and low grade heat, photovoltaic thermal (PVT) systems maximise the solar energy extracted per unit of collector area and have the added benefit of increasing the photovoltaic (PV) electrical output by reducing the PV operating temperature. A graphical representation of the temperature rise and rate of heat output as a function of the number of transfer units NTUs illustrates the influence of fundamental parameter values on the thermal performance of the PVT collector. With the aim of maximising the electrical and thermal energy outputs, a whole of system approach was used to design an experimental, unglazed, single pass, open loop PVT air system in Sydney. The PVT collector is oriented towards the north with a tilt angle of 34°, and used six 110Wp frameless PV modules. A unique result was achieved whereby the additional electrical PV output was in excess of the fan energy requirement for air mass flow rates in the range of 0.03–0.05kg/sm2. This was made possible through energy efficient hydraulic design using large ducts to minimise the pressure loss and selection of a fan that produces high air mass flow rates (0.02–0.1kg/sm2) at a low input power (4–85W). The experimental PVT air system demonstrated increasing thermal and electrical PV efficiencies with increasing air mass flow rate, with thermal efficiencies in the range of 28–55% and electrical PV efficiencies between 10.6% and 12.2% at midday.

Experimental performance of single and double pass solar air heater with fins and steel wire mesh as absorber

Thermal performance of a single and double pass solar air heater with fins attached and using a steel wire mesh as absorber plate was investigated experimentally. The effects of air mass flow rate range between 0.012 kg/s and 0.038 kg/s on the outlet temperature and thermal efficiency was studied. The bed heights were 7 cm and 3 cm for the lower and upper channels respectively. Result shows that, the efficiency increase with increasing air mass flow rate. For the same flow rate, the efficiency of the double pass is found to be higher than the single pass by 7–19.4%. Maximum efficiency obtained for the single and double pass air heater was 59.62% and 63.74% respectively for air mass flow rate of 0.038 kg/s. Moreover, the thermal efficiency further decreases by increasing the height of the first pass of the double pass solar air heater. The temperature difference between the outlet flow and the ambient, Δ T, reduces as the air mass flow rate increase The result of a single or double solar air heater using steel wire mesh arrange in layers as an absorber plate and packing material when compared with a conventional solar air heater shows a much more substantial enhancement in the thermal efficiency.

Thermal performance analysis of a closed wet cooling tower

A detailed model was developed and employed to examine the thermal performance of a closed wet cooling tower. The model is capable of predicting the variation of air thermodynamic properties, sprayed and serpentine water temperature as well as heat transfer rates exchanged between air and falling water stream inside the indirect wet cooling tower. The reliability of simulations was tested against experimental data obtained from the literature. A parametric study was conducted to evaluate the thermal behaviour of the indirect cooling tower under various air mass flowrates, serpentine water mass flowrates and inlet temperatures. The results of the theoretical investigation revealed an increase in cooling capacity and percentage loss of sprayed water due to evaporation, with increasing air mass flowrate. On the other hand, the increase of serpentine water mass flowrate resulted in slight increase in the overall temperature reduction of serpentine water. The effect of variable serpentine water inlet temperature on thermal performance of the indirect wet cooling tower was insignificant compared to other cases.

Heat Transfer and Flow Friction Characteristics for Compact Cold Plates

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.

Steady-state and transient performance of a shrouded longitudinal fin array

Experiments were conducted with a forced-convection cooled, shrouded array of longitudinal fins in the steady-state and transient mode of operation. The parameters varied during the experiments were the air blowing rate and power input. Steady-state, instantaneous and time average values of the fin efficiency and average Nusselt number were calculated and compared. Experimentally found time-average fin efficiencies were found to be relatively lower than the corresponding steady-state values with the difference increasing with increasing power and decreasing with increasing air mass flow rate.