Krishpersad Manohar

Measurement of Apparent Thermal Conductivity by the Thermal Probe Method

Three thermal probes were constructed in accordance with ASTM D 5334 and calibrated using heat-flow metre data. The temperature-time response of the thermal probes for determining apparent thermal conductivity λ under transient state conditions was logged at 1 s intervals. The instrumentation used reduced the determinate error associated with voltage and current measurements to a negligibly small value that made the uncertainty in λ dependent on the uncertainty of the slope dT/dlnt. A test method was run in 1000 s, in which a criterion of 2.5% spread among three consecutive slope values was used to determine the extent of the linear segment of the T–ln t curve. The probes demonstrated repeatability within ±3.5% but had definite individual bias indicating a need for individual calibration. Using individual probe calibration factors, the experimentally de termined λs for all-purpose sand, sifted sand, and soil were deter mined to be 0.520, 0.445, and 2.11 W/moK, respectively.

Biodegradable fibrous thermal insulation

This study investigates the potential of naturally occurring biodegradable fibers for use as building thermal insulation. The use of biodegradable building thermal insulation would alleviate the environmental problems presently associated with the disposal of currently used man-made non-biodegradable thermal insulations. The apparent thermal conductivity(l) for biodegradable coconut and sugarcane fiber were investigated in accordance with ASTM C 518 over the density ranges 40 kg/m3 to 90 kg/m3 and 70 kg/m3 to 120 kg/m3 for the test temperature ranges 13.2oC to 21.8oC and 18oC to 32oC, respectively. The experimental data were used to determine empirical equations for l variation with density and temperature for both coconut and sugarcane fiber. Comparison of l at 24oC for coconut and sugarcane fiber were made with seven different conventional insulation from published data. The results indicated that the minimum l for both coconut and sugarcane fiber are within the range normally associated with building thermal insulation. The l variation with density and mean temperature for both coconut and sugarcane fiber were consistent with the behavior of loose-fill thermal insulation.

Self-Starting Hybrid ‘H’ Type Wind Turbine

Wind energy is one of the fastest growing alternative energy resources being taped into worldwide. Vertical axis Darrieus ‘H’ type lift turbines have the potential to compete effectively with the more widely used conventional horizontal axis wind turbines. However, a disadvantage is when the rotor is stationary, no net rotational force arises, even at high wind speed. The rotor must already be spinning to generate torque and the design is normally not self-starting. In this study a hybrid Darrieus ‘H’ type lift turbine was designed to operate as a self-starting drag type turbine at low rotational speed. With increasing rotational velocity the centrifugal force converted the drag type blades to full symmetrical airfoil sections making the turbine lift type. Design calculations, construction and testing of a two-blade prototype with 43 cm long blades, 14 cm wide, which formed a symmetrical airfoil of NACA 0018 profile when closed. The diameter for the turbine was 1.448 m and tests were conducted at six pitch angles with respect to the closed blade section (0°, 15°, 22.5°, 30°, 37.5° and 45°). Test results showed that the wind turbine was self-starting and the shaft speed increased linearly with wind speed at all angles of attack for moderate wind speed up to 10 m/s. However, the rate of change in shaft speed with wind speed showed an increase from 0° angle of attack to a critical 37.5° angle of attack and then decreased at 45° angle of attack. This observation is consistent with airfoil theory that greater drag forces exist at smaller angles of attack. A similar trend was observed for shaft power and turbine efficiency with maximum values of 49.5 W and 24%, respectively, at a wind speed of 8.29 m/s for the 37.5° angle of attack. The tip speed ratio increased from a minimum of 0.83 at 0° to a maximum of 2.66 at 37.5° and then decreased at 45°. This indicated drag type operation (t.s.r. 1) at higher angle of attack. This trend was consistent with theory as the drag force decreased the aerodynamic lift force increased with increasing attack angle, causing the blade speed to exceed that of the wind speed.Copyright

Use of coconut fiber as a low-cost thermal insulator

Cost is one of the major factors to be considered when choosing a thermal insulator. Design engineers continuously strive to provide the best at the lowest possible cost. In the tropics climatic conditions are essentiallyhot and humid and a cause for daily discomfort. To some extent, air-conditioning of buildings has solved this problem. The major deterrent to air-conditioning is the exorbitant cost of imported thermal insulation materials. This has prompted a search for local, low-cost but effective thermal insulation for buildings. Coconut fiber is available at minimal cost from the copra industry in Trinidad, as it is a waste product from the coconut. The viability of using coconut fiber as building thermal insulation was explored by conducting thermal conductivity tests on 200 mm X 400 mm X 60 mm thick slab-like specimens. The test equipment used was a locally designed constant temperature hot box apparatus. This apparatus was designed to test slab-like specimens under steady-state conditions. The reliability if this experimental set up was checked using Gypsum Plaster. The thermal conductivity test results for coconut fiber over the density range 30 kg/m 3 to 115 kg/m 3 showed the characteristic hooked shape graph for fibrous material. For the 60 mm thick specimens at a mean temperature of 39 °C, a minimum thermal conductivity of 0.058 W/mK occurred at an optimum density of 85 kg/m 3 . The thermal conductivity of commonly used industrial insulators, namely loose-fill expanded vermiculite, cellular glass and blanket fiber glass, at a mean temperature of 38 °C are 0.066 W/mK, 0.061 W/mK and 0.052 W/mK respectively [13]. When compared, these results show that air dried coconut fiber has far reaching potential for use as an effective building thermal insulation.

Low Cost Laboratory Built Wind Tunnel

Laboratory wind tunnel made it possible to observe from a stationary position and measure the aerodynamic forces and associated parameters in a controlled environment the behaviour of objects that would normally be moving through the air. A conventional non-return type wind tunnel with one closed working section was designed, constructed and calibrated for wind speed up to 16 m/s. Test results indicated that the boundary layer effects on the air flow within the wind tunnel penetrated the velocity profile to a depth of approximately 60 mm over the test range 3 m/s to 16 m/s. The cost of construction totaled US

Economical Darrieus straight bladed vertical axis wind turbine for renewable energy applications

1354 which is a fraction of the cost for purchasing an off the shelf laboratory testing wind tunnel of comparative size.

Laminar Forced Convection for Flow Across a Cylinder With Longitudinal Fins of Finite Thickness

AbstractIn remote and stand alone applications, the simple straight bladed Darrieus type vertical axis wind turbine is very practical due to its simple design and low cost of construction. It has the potential to compete effectively with the more widely used horizontal axis wind turbines. This project explores a Darrieus type vertical axis wind turbine, adapted for domestic electricity generation. Design, construction and modelling of a three-blade vertical axis wind turbine with 305 cm long blades, 55 cm chord length, which formed a symmetrical airfoil of National Advisory Committee for Aeronautics (NACA 0018) profile, was performed in this study to demonstrate how used materials can be recycled to produce an economically feasible Darrieus type vertical axis wind turbine that can be utilised to produce usable electrical power. The double multiple streamtube model was used to reproduce this turbine. Materials used were chosen for practicality, availability within the southern Caribbean islands of Trinidad...

Simulating Drag and Lift Coefficient Variation of the MI VAWT1 airfoil with Angle of Attack at Low Reynolds Number

Conjugate numerical solution of laminar forced convection for cross-flow over a cylinder with external longitudinal fins of finite thickness has been carried out. The rate of heat transfer from the fins increases and that from the free area of the cylinder marginally decreases with an increase in thickness, length, and number of fins. The rate of heat transfer from the fins alone is usually much higher than that from the cylinder surface. As a consequence, the net result of these two opposing effects is an increase in the total heat transfer over that of the smooth cylinder, the amount increasing with an increase in thickness, length, and number of fins but with diminishing returns. The fins are more effective at high Re values than at low ones.

Experimental Investigation of End PlateEffects on the Vertical Axis Wind TurbineAirfoil Blade

Due to the complexity of shear layer development over an airfoil surface, measurements of time-resolved fluctuating surface pressure within the separated flow region are difficulty. Modelling the flow characteristics with computer generated simulations is an alternative for overcoming this difficulty. The DesignFoil simulation served as a tool in analysing the flow regime across the MIVAWT1 airfoil. The results showed that the point at which transition from laminar to turbulent flow occurred moved progressively up towards the leading edge as the angle of attack increased from 0 o to 15 o . Also, within this range the change in drag coefficient was small and the lift coefficient increased linearly up to 10 o and then started decreasing. The results are consistent with published work.

Horizontal Strut-Arm Optimization Effects onDrag Coefficient

An experimental investigation of the variation of lift coefficient at low wind speeds comparative to the operation of a vertical axis wind turbine operation was undertaken. Data was recorded at angle of attack for±0, 5, -5, 10, -10, 15, -15 degrees and the wind speed was varied for Reynolds number ranging from 3.32 x105 to 9.64 x 105. Pressure taps on the airfoil skin collected the stagnation pressures which were converted to lift coefficient values. Experiments were conducted with and without end plate attachment to the MI-VAWT1 airfoil.Results indicated that the addition of the endplates increased the lift coefficient at all angle of attack over the range of Reynolds number tested. Similar trends were observed with and without endplate.The flow regime boundary layer separation point advanced toward the leading-edge with an increase in the angle of attack up to ±10o.As the angle of attack increased above ±10o the stall angle was approached. This resulted in the separation bubble bursting, which created a suction peak and the lift coefficient decreased.