Exergy, Performance And Environmental Impact Analysis Of Compression Refrigeration Systems

Major concern in refrigeration hinges largely on energy conservation, environmental safety and efficient cooling system. The concept of quality of useful energy which invariably leads to energy conservation is naturally related to exergy. This study therefore experimentally conducts exergy, performance and environmental impact analysis of compression refrigeration systems using R134a, R410a and R407c, refrigerants. The experiment was performed using a modified exiting R134a refrigerating system. The refrigerator was built with Scroll compressor, 48m3 evaporator space, 1m throttle length and 0.2mm array of rods in the condensing unit coupled with thermocouple K attached at the various components and a digital 10^-3 accuracy weighing scale for charging refrigerant in the required grams. The results show that for 100 grams charge of the refrigerants, the exergetic efficiency, coefficient of performance (COP) and the degree of environmentally friendliness of each of the refrigerants are of order R410a > R407c,> R134a and for 80 grams charge of the refrigerants, the order of performance is R410a > R134a> R407c. While for 60 grams charge of the refrigerants, the exergetic efficiency, coefficient of performance and the degree of environmentally friendliness of each of the refrigerants are of order R407c> R410a > R134a, that of 40 grams charge of the refrigerants is of order R134a> R407c> R410a. The study therefore established that irrespective of the grams charge values of the investigated refrigerants used, R410a is the best, closely followed by R134a and lastly R407c

Design of Fuzzy Logic Based Relay for Distance Protection

The safe generation and distribution of power is the most desirable factor targeted by utility companies.  Therefore, there is a serious concern for protection of the transmission line as well as the equipment involved.  Several works have been carried out on protection to protect mostly human lives while some aimed at the use of microcontrollers to optimize the performance of a relay.  Part of the conventional relay operation works was the work by IEEE Working Group I17 Incorrect Operation Reporting in which for 20 total events, for voltage above 400V, unnecessary trips during fault is 30%, unnecessary trip other than fault is 5%, and total misoperation is 35%.  These results could be improved upon.  As new technology surfaces more application areas also evolve such as the use of artificial intelligence tool like fuzzy logic to enhance the performance of a relay which is the key element in the switching operation of a power network.  This fuzzy logic based relay shows considerable improvement on false trip phenomenon usually associated with the operations of a relay in which a total of 25 events were used to form the rule base for voltage ranging from 480V to 15kV, unnecessary trip fault is 2%, and total misoperation is less than 10%. In this work, the protection scheme proposed is for transmission line's distance protections relay whose operation is adaptive and directly controlled using fuzzy logic controller which is fault tolerant, directional, and least affected by power swing

Experimental performance of LPG refrigerant charges with varied concentration of TiO2 nano-lubricants in a domestic refrigerator

This article present an experimental investigation of varied mass charges of Liquefied Petroleum Gas (40 g, 50 g, 60 g and 70 g) enhanced with varied TiO2 nanoparticle/mineral oil concentrations (0.2 g/L, 0.4 g/L and 0.6 g/L nanolubricants) in a R134a compressor of a domestic refrigerator. Performance tests investigated at steady state included: pull down time, power consumption, compressor power input, cooling capacity and coefficient of performance (COP). Analysis was based on temperature and pressure readings obtained from appropriate gauges attached to the test rig. Refrigerant property characteristics were obtained using Ref-Prop NIST 9.0 software. Results obtained showed almost equal evaporator air temperatures and reduction in power consumption for all tested nano-lubricant concentrations except at 70 g charge of LPG using 0.6 g/L nano-lubricant. Furthermore, the lowest compressor power input was found to be 21 W and obtained using 70 g of LPG with either of 0.2 g/L or 0.4 g/L nano-lubricants. At 70 g of LPG using 0.6 g/L concentration of nano-lubricant, highest cooling capacity index of 65 W was obtained while the highest COP of 2.8 was obtained with 40 g charge of LPG using 0.4 g/L concentration of nanolubricant. In conclusion, LPG-TiO2 nano-lubricant mixture works safely and efficiently in domestic refrigerators without modification of capillary tube length, but requires adequate optimization

Thermodynamic Performance Analysis and Optimization of Domestic Refrigerator with Varying Refrigerant Charge and Capillary Tube Lengths

In this paper, thermodynamic performance analysis and optimization of a domestic refrigerator were experimentally carried out by simultaneously varying the refrigerant charge (wr) and the capillary tube length (L). Continuous running and cycling tests were performed on a domestic refrigerator under tropical conditions using three refrigerants (R12, LPG and R600A) with different capillary tube lengths and various charges. The results show that the design temperature and pull-down time set by ISO for small refrigerator are achieved earlier using refrigerant charge 60g of LPG with 1.5m capillary tube length. The highest COP (4.8) was obtained using 60g charge of LPG with L = 1.5m. The average COP obtained using LPG was 1.14% and 15.09 % higher than that of R600a and R12 respectively. Based on the results of this study, R600a offered lowest power consumption. The compressor consumed 20 % less power compared to LPG and 32% less power than R12 in the system. In conclusion, the system performed best with LPG in terms of COP and cooling capacity. In term of power consumption R600a performed best.This shows that both LPG and R600A can be used as replacement for R12 in domestic refrigerator

A COMPARATIVE STUDY ON THE PERFORMANCE OF THE DOMESTIC REFRIGERATOR USINGR600A AND LPG WITH VARYING REFRIGERANT CHARGE AND CAPILLARY TUBE LENGTH

A comparative experimental study on the performance of a domestic refrigerator using R600A and LPG with a varying refrigerant charge (wr) and capillary tube length (L) was carried out. The enthalpy of the refrigerants R600A and LPG for each data set for the experimental conditions were obtained by using REFPROP soft ware (version 9.0). The results show that the design temperature and pull-down time set by ISO for a small refrigerator are achieved earlier using refrigerant charge 60 g of LPG with a 1.5 m capillary tube length. The highest COP (4.8) was obtained using 60-g charge of LPG with L of 1.5-m. The average COP obtained using LPG was 1.14% higher than that of R600A. Based on the result of electric power consumption, R600A off ered lowest power consumption. The compressor consumed 20% less power compared to LPG in the system. The system performed best with LPG in terms of COP and cooling capacity, while in terms of power consumption R600A performed best

Design and Implementation of a Compact Home Security System

This paper presents the design and implementation of a compact home security system. The use of security systems in today’s home where safety is an important issue cannot be over emphasized. The high crime rates and domestic hazards has brought up the need to take proper measures to prevent intrusions and hazards. It is in this regard that the design and implementation of a compact home security system based on the Global System for Mobile communication (GSM) comes in. Previous designs have used finger print protection, password protection, speech recognition, sensors with buzzer alarms, SMS and e-mail alerts but the designs were with so much complexities as well as at a cost disadvantage. The system presented here is of a minimal cost and simple design, it consists of one motion sensor, one temperature sensor, and one gas sensor.  The system was designed using the ATMEGA 8 microcontroller which controls the sending of SMS to the authorized number. The motion sensor (infrared) detects the movement of people entering the house and when there is a detection of an intruder the owner is notified through an SMS. The temperature sensor in this system also initiates an SMS to the owner when the temperature exceeds a particular value. The gas sensor also works in similar manner when it detects smoke and gas thereby sending SMS alert to the owner of the house. The respective sensors detected the compromise in each situation and sent the corresponding SMS to the user. This device therefore helps to prevent intruders, accidents arising from harmful gases and fire outbreaks in  homes, offices and industries

Design and Implementation of a Cost Effective Real Time Vehicle Tracking System Using Telit GM862

This paper gives the description of the design and implementation of a Real Time Cost Effective Vehicle Tracking System making use of Telit GM862 Module. The Module was installed in a vehicle as the Vehicle Unit while a mobile hand set was used as the Remote Tracking Device. The Module was configured using hyper-terminal on a computer system where the necessary properties and parameters were set. SMSATRUN service was also activated on the module. The SMS information to query the location was sent from the Remote Tracking Device using GSM/GPRS modem on any chosen GSM network to the Vehicle Unit (Module). The Vehicle Unit responds with an SMS message of the location information to the Tracking Device with an authorized mobile number on the GSM Network. The coordinates of the location received are then displayed on Google Map

Effect of Capillary Tube Length and Refrigerant Charge on the Performance of Domestic Refrigerator with R12 and R600a

In this work, the thermodynamic performance of a domestic refrigerator was experimentally studied by simultaneously varying the refrigerant charge (mr) and the capillary tube length (L). The potential of replacing R12 by R600a was also investigated. The test rig for the experiment was a vapor compression refrigerator designed to work with R12. The enthalpy of the refrigerants R600a and R12 for each data set for the experimental conditions were obtained by using REFPROP software (version 9.0). The results show that the design temperature of -120C (according to ISO - 8187 standard) and pull – down time of 135 minutes are achieved by using 60g of R600a with L= 1.2m and 1.5m. For R12, the design temperature is achieved at pull – down time of 165 minutes with mr = 40g and L = 0.9m. The appropriate combination of L and mr for R600a to be used as a drop-in refrigerant for R12 is found to be 1.5m and 60g on the basis of power consumption per day, pull-down time and COP, whereas by considering the cooling capacity, it is 0.9 m and 60g. The cooling capacity of R600a was about 9.18% higher than that of R12, the power consumed by R600a was about 24 % lower than that of R12 and the COP of R600a was about 6.3% higher than that of R12. In conclusion, the proposed R600a seems to be an appropriate long-term candidate to replace R-12 in the existing refrigerator in terms of power consumption, cooling capacity and COP

Professional development in teaching and learning for early career academic geographers: Contexts, practices and tensions

This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Geography in Higher Education on 16th May 2011, available online: doi: 10.1080/03098265.2011.563380This paper provides a review of the practices and tensions informing approaches to professional development for early career academic geographers who are teaching in higher education. We offer examples from Britain, Canada, Nigeria and the USA. The tensions include: institutional and departmental cultures; models that offer generic and discipline-specific approaches; the credibility of alternative settings for professional development in teaching and learning; the valuing of professional development and of teaching in academic systems of reward and recognition; and the challenges of balancing professional and personal life. We summarize concepts of good practice and suggest opportunities for future research

Using antenatal care as a platform for malaria surveillance data collection: study protocol

BACKGROUND: While many malaria-endemic countries have health management information systems that can measure and report malaria trends in a timely manner, these routine systems have limitations. Periodic community cross-sectional household surveys are used to estimate malaria prevalence and intervention coverage but lack geographic granularity and are resource intensive. Incorporating malaria testing for all women at their first antenatal care (ANC) visit (i.e., ANC1) could provide a more timely and granular source of data for monitoring trends in malaria burden and intervention coverage. This article describes a protocol designed to assess if ANC-based surveillance could be a pragmatic tool to monitor malaria. METHODS: This is an observational, cross-sectional study conducted in Benin, Burkina Faso, Mozambique, Nigeria, Tanzania, and Zambia. Pregnant women attending ANC1 in selected health facilities will be tested for malaria infection by rapid diagnostic test and administered a brief questionnaire to capture key indicators of malaria control intervention coverage and care-seeking behaviour. In each location, contemporaneous cross-sectional household surveys will be leveraged to assess correlations between estimates obtained using each method, and the use of ANC data as a tool to track trends in malaria burden and intervention coverage will be validated. RESULTS: This study will assess malaria prevalence at ANC1 aggregated at health facility and district levels, and by gravidity relative to current pregnancy (i.e., gravida 1, gravida 2, and gravida 3 +). ANC1 malaria prevalence will be presented as monthly trends. Additionally, correlation between ANC1 and household survey-derived estimates of malaria prevalence, bed net ownership and use, and care-seeking will be assessed. CONCLUSION: ANC1-based surveillance has the potential to provide a cost-effective, localized measure of malaria prevalence that is representative of the general population and useful for tracking monthly changes in parasite prevalence, as well as providing population-representative estimates of intervention coverage and care-seeking behavior. This study will evaluate the representativeness of these measures and collect information on operational feasibility, usefulness for programmatic decision-making, and potential for scale-up of malaria ANC1 surveillance