Heat transfer in a low latitude flat-plate solar collector

Study of rate of heat transfer in a flat-plate solar collector is the main subject of this paper. Measurements of collector and working fluid temperatures were carried out for one year covering the harmattan and rainy seasons in Port Harcourt, Nigeria, which is situated at the latitude of 4.858oN and longitude of 8.372oE. Energy balance equations for heat exchanger were employed to develop a mathematical model which relates the working fluid temperature with the vital collector geometric and physical design parameters. The exit fluid temperature was used to compute the rate of heat transfer to the working fluid and the efficiency of the transfer. The optimum fluid temperatures obtained for the harmattan, rainy and yearly (or combined) seasons were: 317.4, 314.9 and 316.2 [K], respectively. The corresponding insolation utilized were: 83.23, 76.61 and 79.92 [W/m2], respectively, with the corresponding mean collector efficiency of 0.190, 0.205 and 0.197 [-], respectively. The working fluid flowrate, the collector length and the range of time that gave rise to maximum results were: 0.0093 [kg/s], 2.0 [m] and 12PM - 13.00PM, respectively. There was good agreement between the computed and the measured working fluid temperatures. The results obtained are useful for the optimal design of the solar collector and its operations

GENERATION OF A TYPICAL METEOROLOGICAL YEAR FOR PORT HARCOURT ZONE

This paper presents data for the typical meteorological year (TMY) for the Port Harcourt climatic zone based on the hourly meteorological data recorded during the period 1983–2002, using the Finkelstein-Schafer statistical method. The data are the global solar radiation, wind velocity, dry bulb temperature, relative humidity, and others. The HVAC outside design conditions for the Port Harcourt climatic zone (latitude 4.44oN, longitude 7.1oE, elevation 20 m) were found to be 26.7oC, 78.6% and 3.5 m/s for the dry bulb temperature, relative humidity and wind speed, respectively, and 13.5 MJ/m2/day for the global solar radiation. The TMY data for the zone are shown to be sufficiently reliable for engineering practice

Analysis of air-conditioning and drying processes using spreadsheet add-in for psychrometric data

A spreadsheet add-in for the psychrometric data at any barometric pressure and in the air-conditioning and drying temperatureranges was developed using appropriate correlations. It was then used to simulate and analyse air-conditioning and dryingprocesses in the Microsoft Excel environment by exploiting its spreadsheet and graphic potentials. The package allowsone to determine the properties of humid air at any desired state, and to simulate and analyse air-conditioning as well asdrying processes. This, as a teaching tool, evokes the intellectual curiosity of students and enhances their interest and abilityin the thermodynamics of humid-air processes

Exergy analysis of a gas turbine power plant

Exergy analysis of a 100MW gas turbine power plant that works on theBrayton cycle is presented. The average increase in the thermodynamicdegradation of the plant over the period of six (6) years at three differentlevels of load was assessed. The exergy analysis of the plant was done ontwo sets of data: one from the start-up report at the commissioning of theplant and the other from the log sheets for operation of the plant in theperiod considered. The later set of data was processed using statistical tools. The result shows that at full load, 259.216 MW of exergy is lost on the average, and that exergy loss is most prevalent in the combustion chamber, followed by the exhaust system, and is lowest in the compressor. Both the rational and thermal efficiencies of the plant reduce in value over the period considered, but not significantly. The fuel consumption rate also increased on the average by 0.24%.Keywords: Exergy analysis, gas turbine power plant, irreversibility

Exergoeconomic analysis of cascaded organic power plant for the Port Harcourt climatic zone, Nigeria

This paper presents the exergoeconomic analysis of a 100 kW solar driven organic Rankine cycle (ORC) power plant for the Port Harcourt climatic zone, latitude 4.5–5.5°N and longitude 6.5–7.5°E, at an ambient temperature range of 23–31°C. A cascade cycle of R134a and R290 working fluids was considered for the proposed plant. The relationships between thermodynamic properties and characteristics were formulated and numerical solutions obtained in the Microsoft Excel and MATLAB environments for the assessment of the performance of the plant. The size and mass flow rate of water through the flat plate solar collector, mass flow rates, efficiencies, and other relevant parameters of the cycles were determined. The energy and exergy efficiencies of the proposed plant, at the optimal collector operation, are 18.92 and 21.61%, respectively. The total capital investment, levelized cost of energy, payback time and the earning power of the investment were estimated to be 352 US$/kW, 0.0072 US$/kWh, 2 years 7 months, and 14.3%, respectively. The unit cost of electricity obtained did not consider energy storage, which would have significantly increase the unit cost of electricity. The component exergoeconomic factors, the relative cost difference and the average specific cost of revenue of the plant were also determined. These results might be particularly useful to researchers and energy engineers who might wish to optimize the system for effective electricity generation. From simulations performed, it is viable to install an ORC power plant in the climatic zone considered in this study

Determination of the thermal conductivity and specific heat capacity of neem seeds by inverse problem method

Determination of the thermal conductivity and the specific heat capacity of neem seeds (Azadirachta indica A. Juss) usingthe inverse method is the main subject of this work. One-dimensional formulation of heat conduction problem in a spherewas used. Finite difference method was adopted for the solution of the heat conduction problem. The thermal conductivityand the specific heat capacity were determined by least square method in conjunction with Levenberg-Marquardt algorithm.The results obtained compare favourably with those obtained experimentally. These results are useful in the analysis ofneem seeds drying and leaching processes

Performance evaluation of a combined cycle power plant integrated with organic Rankine cycle and absorption refrigeration system

This study presents the performance evaluation of a combined gas- and steam- turbine cycle power plant (CCPP) integrated with organic Rankine cycle (ORC) and absorption refrigeration cycle (ARC). The attached ORC and ARC units are powered with the flue gas exhaust heat from the CCPP. The evaluation was conducted by performing energy, exergy and environmental sustainability index analysis of the integrated power plant (IPP) and its components. Based on the operating data of an existing CCPP operating in the tropical rain forest region of Nigeria, results of the analysis showed that by utilizing exhaust heat of the CCPP to power an ORC, using R113 as the working fluid, extra 7.5 MW of electricity was generated and by powering an ARC to cool inlet air streams to 15°C in the gas turbine plants, additional 51.1 MW of electricity was generated. The overall effect of integrating ORC and ARC to the CCPP showed that the net power output of the integrated power plant was increased by 9.1%, thermal and exergy efficiencies by 8.7% and 8.8%, respectively, while the total exergy destruction rate and specific fuel consumption reduced by 13.3% and 8.4% respectively. Sustainability index increased by 8.4% which means that the integrated plant has greater environmental sustainability potential over the combined cycle plant

Mathematical analysis of interconnected photovoltaic arrays under different shading conditions

A comprehensive mathematical analysis of interconnected photovoltaic arrays under different shading conditions (opacity) and patterns (column, row, diagonal and corner) has been carried out in this work. The equivalent circuit models for the different shading conditions and patterns, and pseudocode algorithm were developed upon which the performance characteristics of the interconnected arrays were analyzed. Five different interconnections were inclusively considered in this work: series-parallel, total-cross-tied (TCT), bridge-linked, ladder and honey-comb interconnection. The emerging analytical results revealed that TCT is most dominant interconnection and shading patterns across the strings (row and diagonal) have detrimental effect on output power, especially when the opacity is one (signifying perfect shading condition) but shading patterns along the string (column or corner shadings) are less severe to power generation. The formation of double peaks sequel to the presence of shadings are inimical to power generated from the interconnected arrays. Moreover, increasing the interconnections enhances the output power and further serves as a means of bypassing current in the event of threats to the modules. Thus, the results obtained provide vital information for smooth operation and maximization of output power in interconnected arrays by avoiding shades on the strings