Nandy Putra

Temperature Dependence of Thermal Conductivity Enhancement for Nanofluids

Usual heat transfer fluids with suspended ultra fine particles of nanometer size are named as nanofluids, which have opened a new dimension in heat transfer processes. The recent investigations confirm the potential of nanofluids in enhancing heat transfer required for present age technology. The present investigation goes detailed into investigating the increase of thermal conductivity with temperature for nano fluids with water as base fluid and particles of Al 2 O 3 or CuO as suspension material. A temperature oscillation technique is utilized for the measurement of thermal diffusivity and thermal conductivity is calculated from it

Pool boiling characteristics of nano-fluids

Abstract Common fluids with particles of the order of nanometers in size are termed as ‘nano-fluids’ which have created considerable interest in recent times for their improved heat transfer capabilities. With very small volume fraction of such particles the thermal conductivity and convective heat transfer capability of these suspensions are significantly enhanced without the problems encountered in common slurries such as clogging, erosion, sedimentation and increase in pressure drop. This naturally brings out the question whether such fluids can be used for two phase applications or in other words phase change in such suspensions will be assistant or detrimental to the process of heat transfer. The present paper investigates into this question through experimental study of pool boiling in water–Al 2 O 3 nano-fluids. The results indicate that the nano-particles have pronounced and significant influence on the boiling process deteriorating the boiling characteristics of the fluid. It has been observed that with increasing particle concentration, the degradation in boiling performance takes place which increases the heating surface temperature. This indicates that the role of transient conduction in pool boiling is overshadowed by some other effect. Since the particles under consideration are one to two orders of magnitude smaller than the surface roughness it was concluded that the change of surface characteristics during boiling due to trapped particles on the surface is the cause for the shift of the boiling characteristics in the negative direction. The results serve as a guidance for the design of cooling systems with nano-fluids where an overheating may occur if saturation temperature is attained. It also indicates the possibility of such engineered fluids to be used in material processing or heat treatment applications where a higher pre-assigned surface temperature is required to be maintained without changing the fluid temperature.

Pool boiling of nano-fluids on horizontal narrow tubes

Abstract The search for new cooling medium does not limit itself to liquids alone. Liquid–solid suspensions have got a good promise in convective cooling applications. Suspension of common fluids with particles of the order of nanometers (typically 10–100 nm) in size are called ‘nano-fluids’ which have been found to enhance the heat transfer capability of the base fluid to a considerable extent. With very small volume fraction, such particles are capable of increasing the thermal conductivity and convective heat transfer significantly without the known problems encountered in common slurries such as clogging, erosion, sedimentation and increase in pressure drop. A recent study on pool boiling on a tube of large diameter (20 mm) shows that the nano-particles degrade the boiling performance with increasing particle concentration pushing up the wall superheat for a given heat flux. The present investigation focuses on an experimental study of pool boiling in water–Al2O3 nano-fluids on horizontal tubes of small diameter. Tubes of small diameter are of interest in efficient cooling applications such as those in electronic modules or LASER devices where miniaturisation is taking place at a rapid pace. However pool boiling of narrow horizontal tubes (4 and 6.5 mm diameter) is qualitatively different from the large diameter tubes due to difference in bubble sliding mechanism. It is found that at the range of narrow tubes the deterioration in performance in boiling is less compared to large industrial tubes which makes it less susceptible to local overheating in convective applications. Thus, the present study on boiling of nano-fluids can act as a guidance for the use of these engineered fluids in the above applications.

Experiment and analysis for non-Fourier conduction in materials with non-homogeneous inner structure

Abstract The proposition of hyperbolic conduction (also known as the second sound wave) for materials with non-homogeneous inner structure has run into a serious controversy in recent times. While one group of investigators has observed very strong evidence of hyperbolic nature of conduction in such materials and experimentally determined the corresponding relaxation times to be of the order of tens of seconds, the other group proclaims that their experiments do not show any such relaxation behaviour and the conventional Fourier law of conduction is good enough to describe conduction in them. This paper is an effort towards resolving this controversy. In the first place the experimental philosophies and techniques of both the groups have been thoroughly examined. It has been observed that determination of thermophysical properties independent of the relaxation time measurement is an inherent inconsistency in all these experiments. Additionally the assumptions regarding temperature input might have also played a role to arrive at diverging conclusions. Based on these observations an experimental method has been suggested in this study which uses temperature oscillation in semi infinite medium to determine the thermal diffusivity and the relaxation time simultaneously from a single experiment. Using this technique the wide range of experiments conducted reveal that there exists a definite hyperbolic effect in the “bulk” conduction behaviour of such materials although it is somewhat less in extent to those reported by investigators claiming existence of hyperbolic conduction. Also a wide range of experiments with variation of parameters such as packing material, its particle size, filling gas used and its pressure and temperature have been conducted. The data presented here for the wide range of parameters can be useful for further investigations and plausible explanation of “bulk conduction” in materials with non-homogeneous inner structure.

Design, manufacturing and testing of a portable vaccine carrier box employing thermoelectric module and heat pipe.

Vaccination is a highly effective method and a cheap tool for preventing certain infectious diseases. Routine immunization programs protect most of the worlds children from diseases that claim millions of lives each year. There are many practical problems impeding vaccine delivery, especially to maintain the cold chain system, which is the means for storing and transporting vaccines in a potent state from the manufacturer to the person being immunized at a temperature of 2–8°C. The development of the solid state thermoelectric cooling system has permitted newly developed packages that are capable of meeting many requirements and applications where environmental concern, size, weight, performance and noise are an issue. This paper describes the development of a vaccine carrier box. A combination of a thermoelectric module and a heat pipe is used for the cooling system. The position of the heat pipe as a heat sink on the hot side of the thermoelectric module will enhance the thermoelectric performance. The minimum temperature in the cabin of the vaccine carrier box reached −10°C, which indicates that the design of the vaccine carrier box can maintain the vaccine at desired temperatures.

An experimental investigation of pool boiling on narrow horizontal tubes

Pool boiling characteristics on horizontal tubes with diameter lying between wires and industrial tubes have been investigated experimentally. Boiling experiments are carried out at near atmospheric pressures with water and R-123 as boiling liquids. The experimental results show quite a different boiling behavior compared to larger tubes or plates. The commonly used correlations are found to be ineffective over this range of diameters. A developing sliding bubble mechanism can be attributed to such behavior which shows a strong diameter effect. The heat transfer is found to increase with diameter which is contrary to that on industrial size tubes. Useful boiling data are presented in this range of diameters in which experimental data are scarce. The need for more investigations is stressed in view of emerging applications in this area.

Application of Al2O3 Nanofluid on Sintered Copper-Powder Vapor Chamber for Electronic Cooling

The development of electronic devices pushes manufacturers to create smaller microchips with higher performance than ever before. Microchip with higher working load produces more heat. This leads to the need of cooling system that able to dissipate high heat flux. Vapor chamber is one of highly effective heat spreading device. Its ability to dissipate high heat flux density in limited space made it potential for electronic cooling application, like Central Processing Unit (CPU) cooling system. The purpose of this paper is to study the application of Al2O3 Nanofluid as working fluid for vapor chamber. Vapor chamber performance was measured in real CPU working condition. Al2O3 Nanofluid with concentration of 0.1%, 0.3%, 0.5%, 1%, 2% and 3% as working fluid of the vapor chamber were tested and compared with its base fluid, water. Al2O3 nanofluid shows better thermal performance than its base fluid due to the interaction of particle enhancing the thermal conductivity. The result showed that the effect of working fluid is significant to the performance of vapor chamber at high heat load, and the application of Al2O3 nanofluid as working fluid would enhance thermal performance of vapor chamber, compared to other conventional working fluid being used before.

Influence of stack plate thickness and voltage input on the performance of loudspeaker-driven thermoacoustic refrigerator

A loudspeaker-driven thermoacoustic refrigerator has been built and tested to gain understanding of its thermal performance and the cooling rate. The influence of plate thickness made of acrylic sheet was experimentally investigated by varying plate thickness of the stack, 0.15 mm, 0.5 mm and 1 mm, respectively. The experiments were conducted with various voltage input to the driver starting from setting 4 to 9 voltage peak-to-peak. The temperatures at both ends of the stack were acquired. For all variations, thermoacoustic cooling effect occurred in seconds and escalated rapidly in two minutes and became stable in ten-minute time. The experimental results showed that higher voltage input yielded higher thermal performance and faster cooling rate. For each set of experiment, the operating frequency and other parameters of the stack were kept unchanged. The experimental results show that the thermal performance and cooling rate increase with the decrease of plate thickness. The largest temperature difference, 14.8°C, was achieved with 0.1 mm plate thickness at voltage setting 9. However, the thermal performance gained for 0.5 mm plate thickness voltage setting of 9, was arguably the optimum thickness in terms of advantages in the ease of fabricating the stack and more consistent cooling.

Simulation of Heat Flux Effect in Straight Heat Pipe as Passive Residual Heat Removal System in Light Water Reactor Using RELAP5 Mod 3.2

Heat pipe is considered being used as a passive system to remove residual heat that generated from reactor core when incident occur or from spent fuel pool. The present research is aimed to studying the characteristics of straight heat pipe as passive residual heat removal system. As an initial step, a numerical simulation was conducted to simulate the best experimental design set up being prepared for the next step of the research. The objective is to get the thermal hydraulic characteristic due to variation of heat flux of heat source. The thermal hydraulic RELAP5 MOD 3.2 code is used to simulate and analyze the straight heat pipe characteristics. Variations of heat flux are 1567 Watt/m2, 3134 Watt/m2, 4701 Watt/m2, 6269 Watt/m2, and 7837 Watt/m2. Water as working fluid is heated on evaporation section with filling ratio 60%. Environmental air with variation 5 m/s and 10 m/s of velocity are used as external cooler. Straight heat pipe used in the simulation is wickless with 0.1 m of diameter and 6 m of length. The results show that higher heat flux given to the evaporator section will lead to more rapid heat transfer and achievement of steady state condition. The increasing of heat flux leads to an increase of evaporation of the working fluid and of pressure built in the heat pipe affecting higher saturation temperature of working fluid. Heat flux loading must consider the velocity of air as heat removal in the condenser to prevent dry out phenomenon in the evaporator. Based on the results, given the experimental set-up, the optimum range of experimental parameters could be determined.

The Effect of CuO-Water Nanofluid and Biomaterial Wick on Loop Heat Pipe Performance

The determinants of heat pipe performances are its wick and working fluid, instead of controlled by the material, dimension, and the shape of heat pipe. This study aimed to determine the effect of using nanofluid on the performance of Loop heat pipes (LHP) with CuO-water nanofluid that using biomaterials wick. LHP was made of 8 mm diameter copper pipe, with the diameter of evaporator and the condenser was 20 mm respectively and the length of the heat pipe was 100 mm. The wick was made of biomaterials Collaria Tabulate and the working fluid was CuO-water nanofluids where the CuO nanoparticles were synthesized by sol-gel method. The characteristic of the Tabulate Collaria biomaterial as a wick in LHP was also investigated in this experiment. The results of the experiments showed that the temperature differences between the evaporator and condenser sections with the biomaterial wick and CuO-water nanofluid were less than those using pure water. These results make the biomaterial (Collar) and nanofluids are attractive both as wick and working fluid in LHP technology. Keywords: loop heat pipe, wick, biomaterial, nanofluid.