LAMINAR MIXING IN SMX STATIC MIXERS

This paper experimentally examines the performance of a commercial static mixer (SMX). Experiments were carried out to obtain the pressure drop across different numbers of mixing elements (4, 8, 12 and 16). The quality of mixing was visually assessed using flow visualization techniques. Experiments were performed for Reynolds number between 50 and 3000 (based on the unobstructed pipe diameter). The presence of the mixing elements in the flow stream promotes a non-laminar, turbulent-like flow which considerably enhances the mixing. Addition of more mixing elements triggered mixing in the flow at lower Reynolds numbers but this was achieved at the expense of higher pressure drop. This work represents the first stage of an on going work to develop correlations to assess the mixing quality and pressure loss in the SMX static mixers

EXPERIMENTAL EVALUATION OF A CONICAL-SCREW BRIQUETTING MACHINE FOR THE BRIQUETTING OF CARBONIZED COTTON STALKS IN SUDAN

Briquetting of the carbonized agricultural residues represents one of the possible solutions to the local energy shortages in many developing countries. It constitutes a positive solution to the problem of increasing rates of desertification in many areas worldwide. Agricultural residues are not attractive as a household fuel source for urban areas because they are very bulky and have low energy intensity. Also, to eliminate the smoke generation when burning agricultural residues requires processing it by carbonization before being used as a house-hold indoor fuel. Previously investigated, briquetting machines lacked high productivity and were of complicated designs. The present study puts forward a machine of simple design which could be manufactured locally in Sudan and of much higher productivity. The local Sudanese briquetting experience was overviewed, studying all the alternative available options and the market potential. The study presents a detailed design study of the new briquetting machine. The prototype was made and tested in the field at Al-Gazeera area in Sudan. The investigation results show that the new machine has a production rate better than all the previous alternatives. This low pressure screw briquetting machine was found to have a production rate equivalent to about eight times better than the production rate of the best local competitor. The production cost was found to be lower due to the lower binder requirement for the new machine, which is lower by about 65%. The initial moisture content of the feed stock required for this machine is lower by about 30 % compared to the best alternative, which results in shorter drying time for the fuel briquettes produced. The quality of the produced briquettes was found to be better and of lower smoke generation when burned due to the lower binder content

THE INFLUENCE OF WAVE PATTERNS AND FREQUENCY ON THERMO-ACOUSTIC COOLING EFFECT

With the increasing environmental challenges, the search for an environmentally benign cooling technology that has simple and robust architecture continues. Thermo-acoustic refrigeration seems to be a promising candidate to fulfil these requirements. In this study, a simple thermo-acoustic refrigeration system was fabricated and tested. The thermo-acoustic refrigerator consists of acoustic driver (loudspeaker), resonator, stack, vacuum system and testing system. The effect of wave patterns and frequency on thermo-acoustic cooling effect was studied. It was found that a square wave pattern would yield superior cooling effects compared to other wave patterns tested

EXPERIMENTAL INVESTIGATION OF OPEN LOOP MULTI-STAGE IMPEDANCE PUMPING SYSTEM

Impedance pump is a simple valveless pumping mechanism, where an elastic tube is joined to a more rigid one; a periodic asymmetrical pinching on the elastic tube will produce a unidirectional flow. This pumping concept offers a low energy, low noise alternative at both micro and macro scales. This paper describes an experimental investigation of the performance of a two-stage, open loop impedance pump. The results show that, when compared to a single stage open loop impedance pump, the two-stage impedance pump can achieve a significant pressure head and flow rate increment. A pressure head increment of 240 Pa is obtained in the single stage system compared to 480 Pa for the two-stage system. The corresponding flow rates were 5 mL/s and 8 mL/s respectively. This is an indication that impedance pumping system can be scaled up to achieve a variety of pumping assignments

Effect of vegetation and waterbody on the garden city concept: an evaluation study using a newly developed city, Putrajaya, Malaysia

The garden city concept was adopted in the development of a new tropical city, Putrajaya, aimed at mitigating the effect of urban thermal modification associated with urbanisation, such as urban heat island (UHI). WRF/Noah/UCM coupled system was used to estimate the urban environment over the area and the individual thermal contributions of natural land use classes (vegetation and waterbody). A control experiment including all land use types describing the urban conditions of Putrajaya city agreed well with the observations in the region. A series of experiments was then conducted, in which vegetation and waterbody were successively replaced with an urban land use type, providing the basis for an assessment of their respective effect on urban thermal mitigation. Surface energy components, 2-m air temperature (T2m) and mixing ratio (Q2m), relative humidity (RH) and UHI intensity (UHII) showed variations for each land use class. Overall, an increase in urban surfaces caused a corresponding increase in the thermal conditions of the city. Conversely, waterbody and vegetation induced a daily reduction of 0.14 and 0.39 °C of T2m, respectively. RH, UHI and T2m also showed variations with urban fractions. A thermal reduction effect of vegetation is visible during mornings and nights, while that of water is minimally shown during daytime. However, during nights and mornings, canopy layer thermal conditions above waterbody remain relatively high, with a rather undesirable effect on the surrounding microclimate, because of its high heat capacity and thermal inertia

A comparison of energy absorbing capabilities of paper and steel structures subjected to progressive failure under free falling objects

An inverted paper cup of 0.26 mm thickness was subjected to deformation under a freely falling steel ball at a velocity of 2.77 m/sec. The deformed features of the paper cup were measured. The dynamic loading event was simulated using piecewise linear plasticity material model in LSDYNA. Deformed shape of the paper cup in finite element model matched closely with experimental results with ignorable small discrepancies. The paper cup was able to absorb all the kinetic energy of the falling steel ball for the above mentioned falling speed and the ball did not bounce out of the cavity generated by the impact. In LSDYNA a similar size steel cup was also subjected to a freely falling ball with same speed and the energy absorbed was compared to the energy absorbed by the paper cup. It was found that under similar onditions a paper cup would undergo a significant progressive failure and absorb all the energy of the falling object

EFFECT OF DIFFERENT HEAT EXCHANGERS ON THE WASTE-HEAT DRIVEN THERMOACOUSTIC ENGINE

To enhance the efficiency of the SCORE thermoacoustic engine, it is important to investigate the heat transfer between the bulge or theconvolution and the regenerator. Heat transfer due to convection has greatinfluence on performance of the thermoacoustic engine. The total heat transfer from the bulge or the convolution to the first few layers of the regenerator is mainly due to convection and radiation. In this paper, the two modes of heat transfers, convection and radiation are under investigation numerically. The main objective of the present study is to find an ideal shape of the bulge which transports heat from the cooking stove to regenerator. Four different designs of the bulge are proposed in this work. Numerical method FluentTM CFD modelling with surface to surface (S2S) radiation method is chosen to study the radiation effect. The main challenge in the development of the models of such system is to simulate the coupled heat transfer effect and the temperature gradient across both the bulge and porous media surfaces. The results show a very limited amount of heat transfer by convection on all the bulge simulated cases, with a dominant radiative heat transfer over the convective heat transfer while convection was found to be dominant in the convolution simulated case. By looking at the heat fluxes solely, convolution design is recommended to improve the engine performance as it possesses higher total heat flux comparatively but most of it was found to be by convection rather than radiation. The results were validated analytically in a recent accepted paper and found to be in good agreement. To accurately predict the heat transfer in the model, conduction must also be included in future studies as well

CFD Investigation of the Heat Transfer between an External Heat Source and the Regenerator of a Thermoacoustic Engine

AbstractThe heat transfer between an external source to the regenerator of a thermoacoustic engine involves both convection and radiation heat transfer. In order to enhance the efficiency of the thermoacoustic engine, it is very important to investigate the heat transferred by the two modes to the regenerator. In this paper, the two modes of heat transfer, convection and radiation are under investigation numerically. This work considers the two modes of heat transfer under oscillating flow through the porous medium of the regenerator, the oscillating flow is moving in front of the hot surface of the external heat source resulting in strong convection currents. The CFD modelling and simulation was conducted using Ansys_FluentTM CFD software. The results show the strong influence of the convection currents and its strong relations to the amplitude and frequency of the vibrations of the oscillating flow. The results also show the importance of radiation heattransfer between the hot surface and the regenerator and the role it may play on the performance of the engine

Radiation Heat Transfer between the Externally Heated Surface and the Regenerator of the Thermoacoustic Engine

AbstractThe SCORE thermoacoustic engine (TAE) depends of an external heat source from the waste heat of wood burning stove or propane gas. The overall efficiency of TAE depends a lot on the efficiency of the heat transfer process from the cooking stove to the regenerator. It is important to supply most of the heat to the engine directly to the regenerator top surface for best performance of the engine. The combined and complex mode of heat transfer from the cooking stove to the engine makes this task extremely difficult to be achieved. In this work analytical calculations are used to calculate from the fundamentals the radiation heat transfer from two types of heat exchangers used by the SCORE project to transfer heat from the external heat source to the engine. The objective of this study is to understand and evaluate the proportions of heat transferred from the inner side of the external hot surface to the engine. A detailed analysis of the view factors, the surface and space resistances were conducted to calculate the radiation heat transfer in each case at different temperatures. The results obtained showed the actual radiation performance of each part of the convolution and the bulge. Although the convolution performed better in terms of the total heat transfer, but the bulge showed higher radiation. The analytical results were compared with the published numerical results