Advanced Materials Research Vols. 984-985

Abstract: Heat transfer fluids are indispensable in heat transfer and exchange equipment. They determine the ability of the system to dissipate thermal energy. However, they are limited by their low convective heat transfer rates. Nanofluids are suspensions of nanomaterial and most of them are elements with a high thermal conductivity suspended (immersed) in conventional fluids. This enhances the heat transfer rates while also changing the property of the fluid and is a new opportunity for thermal sciences provided by the advances in nanoscience. The nanofluids are expected to be the next generation of heat transfer fluids because of their unique thermal properties and enhanced heat transfer rate in comparison to conventional cooling fluids. This study provides a review of research in this field with focus on heat transfer characteristics and potential applications of nanofluids. The paper also identifies opportunities for future research on nanofluids’ heat transfer application in internal combustion engines.

Abstract: Efficient, compact centrifugal compressor with higher pressure ratios along with adequate surge margins necessitates developing non-conventional diffuser designs. A method of reducing shear losses on the stationary vaneless diffuser sidewalls is by rotating the side walls of vaneless diffuser. Forced rotating vaneless diffuser, a type in which the diffuser is integral with impeller and rotates at same speed, is obtained by extending the impeller disks beyond the blades. In this paper, the conventional stationary vaneless diffuser is redesigned to act as a ‘forced’ rotating vaneless diffuser. The effect of shroud extension is analyzed for the backward curved centrifugal impeller with shrouds extended by 40% with impeller exit diameter on flow diffusion and compared to an impeller with stationary vaneless diffuser. A higher static pressure rise by around 10% along with reduced losses is achieved by shroud extension configuration, RVD-ES. This indicates that the rate of diffusion is higher in the extended shroud configuration.

Abstract: The main aim of this article is to evaluate the performance of an air conditioner working with R22 and the new ternary mixture which comprises R32/R125/ R600a (0.4:0.4:0.2, by mass). The energy performance assessment of the air conditioner is made for four different condensing temperatures such as 30, 35, 40 and 45 ^°C with evaporator temperatures 22 and 25 ^°C respectively. The experimental tests are performed with secondary fluids like water and air in the condenser and in the evaporator respectively. The experimental tests are performed and comparative exergy analysis has been presented. REFPROP is utilized to find the thermodynamic properties of the mixture. The overall exergetic performance of R22 is comparatively better than that of the mixture. The performances of the individual components are also examined. The exergy destruction of compressor is larger for the mixture, followed by condenser then evaporator and ended with expansion valve. Thus to improve the performance of the system the compressor design has to be reformed.

Abstract: Jet Impingement is used in many applications where extensive heating (or) cooling is necessary to produce high heat transfer rate in a localized region. Those applications include glass production, drying of papers, annealing of metals and cooling of electronic equipments. Present work is involved with the experimental investigation of single jet impingement on Aluminium block. The effect of Reynolds number and the distance between the jet and block (H/d ratio) are considered as the interesting variable parameters. The heat transfer rate and reattachment length are reported in detailed for the various Reynolds number and various jet to block ratio. The flow physics revealed that when the Reynolds number increases the reattachment length also increases. The heat transfer rate increases with increase in Reynolds number up to critical heat flux and then further increase of Reynolds number leads to decrease in heat transfer.

Abstract: Heat transfer improvement in solar operated devices is one of the key issues of energy saving and compact designs. Researches in heat transfer have been carried out over the past several decades, culminating in the development of the heat transfer techniques used at present. The use of additives is a technique employed to enhance the heat transfer performance of base fluids. Recently, an innovative material, nanosized particle has been used in suspension in conventional heat transfer fluids that changes the heat transfer characteristic. In this project, an attempt has been made to verify change in heat transfer behavior while using nanofluids. For this purpose, a conical solar collector has been designed, constructed using locally available sheet steel. Polyurethane foam material is used as a insulating liner inside the cone. Thin reflective aluminum sheet is used to focus the solar radiation onto the absorbing surface. The main objective of this paper is to study the heat transfer behavior of Al₂O₃, Cu₂O and ZnO nanofluid and especially Al₂O₃ nanofluid of various concentrations in absorber space of conical solar collector. Experimental study was conducted on different days and the data were recorded. The results obtained show that addition of nanoparticles in the base fluid, improve the heat transfer rate.

Abstract: The main objective of our work is to analysis the heat transfer rate for various fluids with different matrix heat exchanger (MHE) models and flow characteristic in matrix heat exchanger by using computational fluid dynamics (CFD) package with small car. The amount of heat carried by the cold fluid from hot fluid is mainly depends upon the mass flow rate of the working fluid. The heat transfer area per unit volume of tube is more. So, it increases the temperature of the cold fluid. Here, the hot and cold fluids are moving in the alternate tubes of heat exchanger in the counter flow direction. The small amounts of pressure drop are occurred but which is less compared to existing model. Flow disturbances are rectified in the MHE through the modifications made. Since, silicon carbide material is used as a polishing material to avoid the deposit of carbon at the inner side of the flow passage and this waste heat energy is used for heating passenger cabin during winter season. The wood is used as an insulating material to avoid the heat flow from fluid to atmosphere. Keywords-Heat transfer rate, Matrix heat exchanger, Working fluid, Polishing material.

Abstract: Solar photovoltaic (PV) plays a major role in the renewable energy sector in the field of power production. Production of electricity from solar PV is gaining rapid importance due to its cleaner energy production capacity and it’s adaptability to various climatic conditions. PV cells suffer noticeable drop in efficiency as their operating temperature increases beyond a certain limit. In such cases cooling of the PV cells becomes mandatory. Since the efficiencies of PV cells are in the lower range (a maximum of 18%), a highly effective, inexpensive cooling system is necessary to be employed. Air cooling provides a solution to this cause and is meant to be an better counterpart to water cooling since it overcomes the problems of water cooling such as silt formation, evaporation, soiling and reflection losses. This paper presents a simple mathematical PV/T model to design the cooling system using plate-pin fin extended surface heat exchanger model. A relationship between the heat dissipated and the number of fins along with its dependence on individual fin area is also developed. This model will provide the researchers to design their cooling system according to their PV system geometry.

Abstract: The present study proposes a numerical model to analyze the effect of four dimensional parameters on performance characteristics such as Coefficient of performance (COP), of the Inertance-Type Pulse Tube Refrigerator (ITPTR). The numerical model is validated by comparing with previously published results. The detail analysis of cool down behaviour, heat transfer at the cold end and the pressure variation inside the whole system has been carried out by using the most powerful computational fluid dynamic software package ANSYS FLUENT 13. The operating frequency for all the studied cases is (34 Hz). In fact, to get an optimum parameter experimentally is a very tedious for iterance pulse tube refrigerator job, so that the CFD approach gives a better solution. Finally, an artificial neural network (ANN) based process model is proposed to establish relation between input parameters and the responses. The model provides an inexpensive and time saving substitute to study the performance of ITPTR. The model can be used for selecting ideal process states to improve ITPTR performance.

Abstract: A computational fluid dynamic approach has been utilized to optimize the fin shape inside a circular tube having different shape of fins attached internal circumference of the tube. Total three type shape (rectangular shape, T-Shape, triangular shape) of fins is utilized for this numerical analysis. The tube length is taken 5m and dimeter of 0.07m. For all case volume of fins remains constant factor with Reynolds number 1200 and constant wall heat flux of 200 W/m2. For this analysis a commercial package FLUENT is used. The present paper shows how the fluid temperature, pressure and velocity changes in axial direction for changing the fin shape. Result shows that for triangular fin shape there optimum heat transfer between other configuration of fin.

Abstract: With the growing energy command due to growing world people and industrialization, utilizing strenuous solar energy for thermal and electrical power production will be the future renewable power source to decrease the confidence on fossil fuel and reduce carbon dioxide discharge. Besides by means of determined Photovoltaic (CPV) system, Concentrated Thermoelectric generator (CTEG) will be another possible option for sustainable power generation. The CTEG system utilizes concentrated solar flux as a heat source to the thermoelectric generating (TEG) module in generating direct current thermoelectricity which can be easily converted to alternating power using an inverter. By maintaining a temperature difference between the hot and cold sides of the thermoelectric cells (Seebeck effect), thermoelectricity is generated where its magnitude is a function of temperature difference. The main challenge is the effectiveness of excess heat removal which accumulated at the cold side of the thermoelectric cell to achieve greater power generation. Using acting cooling mechanisms are not energy efficient proposal as it requires power in operating them and significantly reduces the total power output generated. They are planned in the paper for working CTEG system through passive cooling and achieving invariable cooling. Two-phase closed thermosyphon is implement as an helpful heat transporting device for transfer excess heat from heated TEG part to the frozen PCM storeroom reservoir for heat luggage compartment. This investigation is to evaluate the thermal presentation of the proposed system.. The working fluid used in the thermosyphon was Acetone and its filling ratio was designated at 40% of the evaporator volume. Paraffin wax was selected as PCM with melting point of 47oC and acceptably high latent heat storage was selected in the thermal storage. The passive cooling mechanisms consist of PCM storage tank, heat pipe-based heat transfer system for transporting heat from TEG modules to the PCM thermal storage during the daytime and a similar heat pipe-based system for discharging heat from PCM storage tank to the cooler ambient during the night time.