Effect of the Richardson Number on Flow and Heat Transfer in a Cylinder Filled with Cu-Water Nano-fluid at Different Nanoparticle Concentrations

Fluid circulation and thermal exchange properties via integrated natural and artificial convection within a container have attracted considerable interest due to its many industrial uses. This present work concentrates on determining the effect of the Richardson number on flow and heat transfer in a cylinder filled with Cu-Water nanofluid at different nanoparticle concentrations. The governing equations: continuity and Navier Stoke fields were discretized using the finite difference approach and simulated in C++ programming language. In this work, the Richardson parameter ranged from 2.6*104 to 2.8*104, while the concentration of Cu nanoparticles ranged from 1% to 10%, and the results are presented as Nusselt number, vorticity, and stream function profiles. The results reveal that the maximum Richardson value is 2.76 x 104 at the nanoparticle volume of 0.04, resulting in a considerable increase in the convective heat transfer rate. Furthermore, as the Richardson parameters increase, the Nusselt number in the nanofluid increases exponentially while the local drag coefficient decreases. The stream function, longitudinal velocity and circulation increase as the Richardson parameters grow. The technical design for air turbulence prediction involves an understanding of the Richardson-driven connection as a mix of wind speed and convective stability variables

Development of Mathematical Models for Thermal Conductivities of Some Engineering Materials

Thermal conductivity equipment was developed using locally available materials. The equipment consists of the sample holder, the thermometer probe cavity, the heating cavity and the structural wooden frame, performance evaluation was carried out using four different materials (iron, brass, mild steel and aluminum). The experimental studies were carried out at different time; 300 seconds interval (from 300 through 1500seconds) on the four materials and temperatures reading were recorded. The results of experimental studies were modeled to develop regression equations for predicting thermal conductivities of the materials. Analysis of Variance (ANOVA) and statistical t-test were carried out to validate the models at 5% level of significance. The experimental results show that Aluminum has highest thermal conductivity with respect to temperature while a linear model with coefficient of determination, R2 (0.9097) was obtained. Statistical tests for each of models developed and the experimental results show that there is no significant difference at 5% level of significance. It is concluded that the models developed could be used to predict thermal conductivity for the four materials with good accuracy with respect to time. Keywords: Performance evaluation, thermal conductivity, ANOV

COMPARATIVE STUDY OF THERMAL CHARACTERISTICS OF METALLIC AND NONMETALLIC WATER-BASED NANOFLUIDS IN A SQUARE CAVITY

Heat transfer fluids are a dynamic factor that affects the costs and size of heat exchangers. However, low thermal properties of accessible coolants like water and oils place a setback on the growth of heat transfer to attain high-performance cooling. The paper presents a numerical analysis of a comparative study on thermal characteristics of Al2O3, CuO, AlN, and SiC water-based nanofluids in a square cavity. The cavity is surrounded by a hot moving horizontal plate, an adiabatic vertical wall on the right, and the left vertical and lower horizontal sides by cold isothermal walls. The governing equations were solved using finite approximation techniques to assess the thermal characteristics of the four different nanofluids in the enclosure with varying sizes of nanoparticles in the range of 1% ≤ φ ≤ 10%. The results reveal that CuO has a different pattern of heat characteristics compared to other nanofluids. CuO has the highest Nusselt number of 58.4715, and Al2O3 has the least value of 58.4634 at a 10 % volume fraction. Nanoparticle size has a substantial influence on the thermal attributes of the four nanofluids. This work indicates that different nanofluids have satisfactory thermal characteristics than based fluid water, which determines its applications. Keywords Cavity, Nanofluids, Natural convection, Heat transfer enhancement DOI: 10.7176/JIEA/11-2-08 Publication date: September 30th 202

Numerical Investigation of Buoyancy Effect Associated with a Continuously Moving Horizontal plate

This work presents numerical studies of the effects of buoyancy force parameter, Bf, coupled with viscous dissipation on the convective heat transfer in a fluid-filled rectangular cavity. The cavity is bounded by a hot horizontal plate maintained at temperature Tw and moving continuously at velocity Uw. It is also bounded on the left vertical and lower horizontal sides by cold isothermal walls and an adiabatic vertical wall on the right. The cavity was filled with quenching medium. The study was carried out for different quenching media such as oil with Prandtl number, Pr = 10, air with Prandtl number, Pr = 0.7 and liquid metal with Prandtl number, Pr = 0.01, for various bouyancy parameters in the range 5 x 10-3 ≤ Bf ≤ 10-2, fixed Eckert numbers, Ec = 1.0 and mixed convection parameter, Gr/Re2 = 1.0, in order to characterize the nature of the flow patterns and energy distribution. The flow governing equations including the momentum and energy equations were thereby solved using the finite difference method. The results are presented in the form of profiles for temperature, velocity and local Nusselt numbers. The results show that the buoyancy force parameter has significant influence on the velocity and temperature profile for a Prandtl number higher than unity at fixed viscous dissipation. Further results show that an increase in the buoyancy force parameter for a Prandtl number greater than unity leads to a significant increase in the maximum velocity attainable in the cavity. The results would be useful as baseline data for manufacturing and material processing industries involved with wire drawing, continuous rolling and glass fiber productions. Keywords: Buoyancy effect, Finite difference scheme, Heat transfer, Isotherms, Mixed Convectio

Investigation of Some Factors Influencing Corrosion on Refrigerator

The corrosion of steel reinforcing bar can proceed out of sight and eventually result in failure of a section of the highway. The collapse of electrical towers, damage to building, leakages in refrigerator all these result in significant repair cost, endangering public safety and health. This paper presents investigation of some factors influencing corrosion on refrigerator, such as presence of dissolved mineral, organic impurities and dissolved gasses in the water. The survey results are presented using graphs. T-test and Anova were used to ascertain the significance of the factors. The result of alternative Hypothesis and null Hypothesis on the T-test and Anova test were carried out on the factors causing corrosion and responsible for the corrosion were able to be identified. The results revealed that the corrosive effect of fresh water varies from locality to locality due to the wide variety of dissolved impurities, the organism causing the greatest corrosion problems are bacteria and fungi, time of exposure to a corrosive environment influences metal corrosion, most salt solution is good electrolyte and can promote corrosive attack and corrosion effects reduce the life span of refrigerator. The result of this research would guide environmental and material engineers in better planning to minimize corrosion

Experimental Evaluation of a Thermally Driven Adsorption Refrigeration System in Ogbomoso Environs

Solar energy is the most promising among the available green energy sources and also the remedy to the increasing global warming potential and ozone depletion. This paper presents an experimental evaluation of an adsorption refrigeration system uses solar energy as a source of heat gain to drive the refrigeration system. It consists of a solar collector, an adsorbent bed, a condenser and an evaporator. The effect of variation of the ambient, condenser, evaporator and desorption temperatures on the COP system and SCP cycle with local weather parameters were investigated. A parabolic solar concentrator was built to collect the solar energy to heat the combination of adsorbent, Activated carbon and adsorbate, methanol and the system employed solar energy as the main power supply. The experimental results revealed that the ambient, condenser, evaporator and desorption temperatures were increased by 25%, 4%, 13% and 265% respectively with solar time from 9hr to 13hr. The response of COP and SCP with variation in solar radiation and desorption temperature had higher influence compare to other weather parameters. The collector and thermal efficiencies were 0.014 and 6.98% respectively at the peak inner adsorber temperature of 114.1 oC. The respective cycle and net solar COPs of the ARS were 0.408 and 0.00080 at an evaporator temperature of 17.1 oC. This study showed that the solar thermal-driven ARS performed well in south-western climatic conditions of Nigeria and can be used to replace conventional refrigeration system to reduce the effect of global warming and environmental pollutions caused chlorofloro-refrigerants. Keywords: Solar, Adsorption, Refrigeration, COP, Concentrator

Development of a System Framework that Estimate Cooling Loads for Air-Conditioning System for Residential and Non-residential Buildings

Cooling Load estimation for air conditioning systems is done either by manual calculation or judgmental estimation based on experience of the air conditioning practitioner. While manual calculation is laborious, estimate based on judgment is liable to error due to gigantic, complex and dynamic nature of present day architectural designs. Load calculation through computer automation is likely to make a positive impact in the dynamic nature of air conditioning applications. This study developed computer software to handle simple and typical load estimate for air conditioning in Nigeria. The study has developed a system framework that estimate cooling loads for air-conditioning system for residential and non-residential buildings. It provides an effective and user-friendly way of introducing a residential cooling load calculation program to users. This software results compare favourably with the previous works and it can be used for educational purposes in air conditioning laboratory. Keywords: Air-conditioning, Cooling loads, Residential buildings, Syste

Thermal Evaluation of a Parabolic Trough Solar Concentrator Using Three Different Receivers

Energy demand, global warming from the fossil fuels and attempt to reduce greenhouse gas emission have placed the centre of attention on how to utilize an alternative sources of energy such as renewable energy technology This work presents the design, fabrication, and evaluation of the performance of Parabolic Trough Solar Concentrator (PTSC) as a source of heat energy. The PTSC is built, having the Supporting stand made of mild steel and reflector is made of the segmented mirror having a reflectivity of 0.85, a rim angle of 90o and aperture area of 2.5 m2 and with a concentration ratio of 11.7. The receiver pipes are made of three different materials; copper, aluminum, and stainless steel. The effects of shifts in focal lengths on the performance of the PTSC with three different receivers were investigated. The results reveal copper as a receiver tube conducts heat to the heat transfer fluid better than aluminum and stainless steel receivers. The focal length of 30 cm gave the best results compared to other values of 27 and 35 cm with a maximum temperature of 114.4 oC. The experimental results revealed that useful heat gained, overall heat loss coefficient, collector efficiency factor, heat removal factor, collector and thermal efficiency were 147.8 J, 5.04 W/m2K, 0.05, 15.05, 0.032% and 15.5% respectively. The study shows that the Parabolic Trough Solar Concentrator as a source of heat energy gives a promising performance. This concentrator will reduce the dependence on the electric power supply, and it controls pollution emanating from fossil fuel, thereby reducing environmental problems. Keywords: Parabolic Trough Solar Collector, Segmented Mirror, Efficiency, Receivers. DOI: 10.7176/JETP/9-5-03 Publication date:June 30th 201

Effect of Climatic Governing Parameters on the Performance of Solar Adsorption Refrigeration System

Solar energy is a renewable resource, clean and ecologically friendly. Solar thermal energy is attractive alternative energy to drive the adsorption of refrigeration machines. This work presents a numerical investigation of the effect of climatic governing parameters such as ambient temperature and component temperatures on the performance of solar adsorption refrigeration systems using methanol/activated charcoal pairs. Activated carbon as adsorbent and methanol as a refrigerant is selected. Some predictive empirical equations accounting for heat balance in the solar collector components, instantaneous heat and mass transfer in adsorbent bed, and performance parameters were presented. Interactive C++ programming was developed to carry out the parametric study of some climatic factors such as ambient temperature and solar radiation intensity with aperture width of 0.14 m, collector length of 2.1m on the system performance. The effect of ambient temperature and component temperatures with aperture width, collector length, on specific cooling power (SCP), refrigeration cycle COP (COPcycle), and solar coefficient of performance (COPs) are being investigated. The results are presented in form of profiles such as pressure developed in the generator, specific cooling power and system coefficient of performance profiles, under varying weather conditions and ambient temperature, operating conditions of evaporating temperature, Tev = 0 oC, condensing temperature, Tcon = 30 oC and desorption temperature of 100 oC, The influences of operating and design parameters on the system performance are significant. The system performance shows no appreciable changes with varying condenser temperature with significant effect with varying evaporation and desorption temperature. It is shown clearly that for different desorption temperatures below 120 oC there is an appreciable effect on the system performance parameters. The study has revealed the system attains a promising performance of the adsorption refrigeration system using AC / methanol pair driven by solar energy. Keywords: Adsorption; Refrigeration; Activated carbon/methanol; Simulatio