CHAPTER THREE – METHODOLOGY
3.1 Introduction 37
3.2 Development of Model 38 3.2.1 Equation solution for modelling 40 3.2.2 Development of mesh modelling 42 3.2.3 Boundary conditions 43 3.2.4 Grid independency 44 3.3 Experiment setup 45 3.3.1 Equipment setup 45 3.3.2 Nanofluids preparation 51 3.4 Work flow of experimental and simulation analysis 53
process. Figure 2.3 shows an overview of the molded copper and aluminum block containing arrays of microchannel. Working fluids will flow through the microchannel and absorb heat in the heatsink. Previous study by (Parida, 2007) investigated heat transfer is higher at copper based microchannel compared to aluminum. It is speculated that the presence of significant surface roughness within the microchannel resulted the increasing of flow mixing. The thermalperformance for metal based microchannelheatsink devices has enormous potential in many heat transfer problem primarily in electronic cooling. The heat transfer in microchannel is not only significantly reduces the weight load but also increase the capability to remove much greater amount of heat than any of large scale of cooling systems. There are many design of microchannel from past researchers based on their purpose and objectives.
As today’s electronic devices have become compact, the modern techniques of cooling are substituted for the conventional ones. The heat sinks and heat exchangers are benefited from the developments achieved in electronics and material science, which makes it possible to construct such devices in miniature. Microchannelheat sinks, are a new class of heat sinks first proposed by Tuckerman and Pease . They revealed to be very efficient and suitable for high heat removal from small surfaces. The channel hydraulic diameter is usually less than 1 mm, and this microscopic size reduces and thins the thermal boundary layer, which reduces thermal resistance and, consequently, increases the amount of heat transfer [2, 3]. In the issue of heat transfer efficiency in equipment such as heat exchangers, thermal conductivity of the working fluid plays a major role . Common fluids in heat transfer used in industries are usually fluids such as water, oils, and ethylene glycol. With increasing global competition in various industries and the role of energy in production costs, these industries are increasingly moving towards the development of advanced and new fluids with high thermalperformance. Nanofluids increase thermophysical properties (thermal conductivity, thermal diffusivity, viscosity and convective heat transfer coefficient) in comparison with base fluids such as water or oil [5-8]. Due to the ability of the nanoparticles in increasing the heat tran -
This section describes the mathematical formulation of the problem. The constant wall heat flux (H) was considered as thermal boundary conditions. It covers the effect of brinkman number on laminar forced convection of nanofluid flowing between two parallel plates (wide rectangular cross section). The problem which was considered is depicted schematically in Fig. 1. A wide rectangular microchannel (high width to height) permits that the computational domain of solution restricts to two dimensions. Corcione  proposed a correlation were used to calculate the effective viscosity and thermal conductivity of nanofluid. To focus on the effect on the heatsinkperformance due to the brinkman number, following assumptions were made:
A common approach for cooling computer chips with high performance is to join the chip to a circular microchannal heatsink. During operation, a chip generates a uniform heat flux at its interface with heatsink, while a fluid coolant (NEPCM slurry) is flown through the channels. A chip and a heatsink are considered each 10×5.1 mm on a side as show in Figure 1. Heatsink meshed shows in Figure 2. The fluid is supplied in the inlet temperature, heat flux and inlet velocity equals to 298 k, 1W and 2m/s respectively.
PG Scholar, Department of Mechanical Engineering, Bhabha Engineering Research Institute, Bhopal (M.P.), India 1 Asst. Professor, Department of Mechanical Engineering, Bhabha Engineering Research Institute, Bhopal (M.P.), India 2 Principal, Department of Computer Science Engineering, Bhabha Engineering Research Institute, Bhopal (M.P.), India 3 ABSTRACT: Technological evolution in application of small-scale electronic devices have led to increase in cooling demand to accomplish this microchannelheatsink is decent option for removal of heat generated. In this numerical study by CFD analysis consequence of pin fin with hexagonal microchamber on performance of microchannelheatsink has been examined. Water, silicone oil, potassium formate solution and transformer oil were employed as coolant. Performance of MCHS was calculated in the basis of Nusselt no., pressure drop and thermalperformance index at different values of Reynolds no. From this analysis it is found that use of hexagonal microchamber successfully lowers the pressure drop generated form application of pin fin.
The heat produced in the integrated circuits should be effec- tively removed and the temperature should be maintained below a particular value in order for the electronic systems to function properly and with better life span. In this regard, Hassan et al.  had made an state-of-the-art literature review on the microchannelheat sinks developed for removing the heat produced in the integrated circuits. They had briefly explained about various progresses of removing the heat gen- erated in the integrated circuits over a decade. The effect of cir- cular, square and trapezoidal grooved tubes in the heat transfer characteristics was analyzed numerically with the help of computational fluid dynamics code and the results were compared with the plain tube by Selvaraj et al.  and they reported the analysis can be extended to micro channel heat sinks also. Zhang et al.  had reported from their studies that the micro channel heatsink with liquid metal possesses relatively lower thermal resistance compared to water as work- ing fluid. Thus they reported that liquid metals may be an alternate source for water with better heat transfer characteris- tics but with slightly higher pressure drop across the channel. Salimpour et al.  had studied the effect of non-circular shapes in the optimization of heat transfer characteristics of micro channel heat sinks. They have analyzed the rectangular, elliptic and isosceles triangular cross sections of the micro channel heat sinks and found that both rectangular and ellip- tical micro channel heat sinks have similar performance and the isosceles triangle MCHS had shown weaker performance. Dharaiya and Kandlikar  had developed correlations for Nusselt number for heat transfer in rectangular micro channels for both developing and fully developed laminar flows and this technique was very much useful for the design and optimiza- tion of micro channel heat sinks and other microfluidic devices. Xie et al.  had carried out numerical study in the mini channel heat sinks to study the heat transfer characteris- tics for laminar flow. They had optimized the geometry using water as the working fluid for effective heat dissipation and les- ser pressure drop. Xie et al.  had numerically analyzed the influence of bifurcations on the thermalperformance of micro channel heat sinks using CFD code. They had designed five various types of MCHS with bifurcation and one plane MCHS without bifurcation. They examined and reported that the bifurcation model gives better heat transfer characteristics with
Although microchannel cooling is well-suited to thermal management of electronics, its use can be extended to other technological fields where there is also demand for high heat flux dissipation. The present work investigates the applicability of microchannelheat sinks to Concentrating Photovoltaic/Thermal (CPVT) systems. Such systems utilize optical devices to concentrate solar irradiation onto a small receiver area which is occupied by highly efficient solar cells. The presence of a high heat flux can cause excess increase on the solar cell temperature, which leads to efficiency loss and long-term degradation. Therefore, the incorporation of an efficient and compact heatsink is vital, so as to maintain the operating cell temperature within allowable ranges and moreover to extract surplus heat, which can be exploited in other applications. More specifically, this study focuses on the cooling of a linear parabolic trough CPVT system using two microchannel configurations employing fixed- and variable-width microchannels respectively. A complete methodology for the heatsink geometry optimization is presented. Initially, a one-dimensional thermal resistance model and pressure drop correlations are utilized, in order to approximate the overall performance of each configuration. In a second step, the objective
In the practical application of a micro-channel heatsink (e.g. in cooling a micro-processor chip), as was the motivation for the present study, a vital quantity of interest is the actual surface temperature that can be achieved with a given micro-channel geometry, under a given heat load. Therefore, as a final observation, this chapter present the data in terms of energy management. In previous chapters, the heat transfer performance has been presented primarily in terms of thermal resistance and pressure drop. However, as indicated in the introduction of this work, a key motivation for the present study is the cooling of electronic chips producing a certain heat flux through their surface. Since there is an upper limit of the temperature at which a chip can operate reliably, key practical questions about the cooling system are (a) can a sufficiently low chip temperature be achieved for a given heat flux, and (b) how much energy is needed to achieve an acceptable temperature? Hence this chapter revisits the findings of earlier chapters focusing on the temperatures of the base of the heatsink where the heat flux is applied and the pumping power required to achieve them. One of the ways to evaluate the energy management in a system is to consider the heat transfer performance based on the maximum and/or average temperature. Therefore, the results of chapter 4 are represented in terms of average and maximum temperatures with water as a coolant, and this will be the first section in this chapter. To develop the investigation a further step, chapter 5 is also revisited to explore the average and maximum temperatures of the best VGs that offer high thermalperformance (see Fig. 5.16). The VG configurations are end gap model with gap=150 µm (E2), central gap model with gap=100 µm (C2), central and end gaps with gap=250 µm (CE1), no gap (full-span) and the uniform channel (seeTable6.1). The second section of this work studies the effect of heat transfer and fluid flow performance.
Nanofluids are gaining lot of importance in thermal applications due to its excellent heat transfer characteristics. Micro-scale heat transfer devices are used on large scale in electronics industry which leads to the development of compact size heat exchanger with high heat transfer coefficient. Recent development in the field of nanotechnology involves the use of suspended nanoparticles in base fluids which leads to the improvement in the heat transfer coefficient of base fluids. This paper summarizes the articles published on enhancement of convective heat transfer in microchannelheat exchanger usingnanofluids and effect of various thermophysical properties on heat transfer performance. Theoretical and experimental results for different geometries and effects on Nusselt number are reported in this paper. The results show outstanding increase in the importance of nanofluid application in microchannels. The effects of use of different nanofluids and their performance as compared to base fluids are shown.
Advancement in micro and nano fabrication technologies eases to manufacture compact heat exchanger devices. The compact heat exchanger and heat transfer devices performance can drastically improved by usingmicrochannel arrays along with use of nanofluids. The parametric analysis of semicircular microchannelheatsink with distilled water and different concentrations of Multiwalled carbon nanotubes is carried out theoretically along with experimentation. The theoretical design is carried out for Minimum thermal resistance, maximum heat transfer coefficient, minimum friction factor and pressure drop along with minimum entropy generation. The microchannels with 200 µm hydraulic diameters are prototyped on accurate wire cut EDM. The effect of heat fluxes and Reynolds number is observed on heat transfer coefficient and pressure drop in laminar region. The performance of IC system is achieved best under Reynolds number 550 to 750. The heat transfer enhancement is observed 39 % over pure water with concentration of 0.1 % carbon nanofluids. The exact comparison theoretical calculation is done with experimental results and they are further validated with correlations in journal papers. Reynolds number increases then heat transfer coefficient, pressure drop, thermal resistance increases.
A previous model, the WANic 3850, utilized an active heatsink for cooling the Cavium component. However, GE Intelligent Platforms’ design team wanted a complete and thorough thermal examination of the WANic 3860, so that a passive cooling solution could be used, offering much greater reliability, reductions in cost and implementation time. In response, ATS provided several thermal management analysis and design services for GE Fanuc Intelligent Platforms, including:
4.3.3. Two-phase ﬂow with instabilities (regime ‘c’)
In contrast to the decrease in heat transfer coefﬁcients with increasing heat ﬂux in the boiling regime ‘b’, the heat transfer coef- ﬁcients in the boiling regime ‘c’ tend to remain relatively constant, which suggests a different heat transfer mechanism. Flow instabil- ities are responsible for the transition from the boiling regime ‘b’ to the boiling regime ‘c’. As ﬂow instabilities occur, the ﬂow patterns both downstream and upstream are dramatically changed. The ﬂow in the upstream region is intermittently reversed and alter- nates with time between reversed ﬂow and non-reversed ﬂow. Such ﬂow reversals were visually observed and documented by the authors in  via high-speed visualization. The corresponding instabilities were also reﬂected as sharp increases in the magni- tude of ﬂuctuations recorded in the pressure drop across the microchannels. Stronger instabilities at higher heat ﬂuxes result in bubbles being pushed back into the inlet plenum during the per- iod of reversed ﬂow; as a result, the ﬂow upstream is changed to pulsating two-phase ﬂow. Corresponding to the alternating re- versed and non-reversed ﬂow in the upstream region, the ﬂow in the downstream region alternates with time between wispy-annu- lar ﬂow and churn ﬂow. As detailed in  , the ﬂow reversal in the upstream region causes a periodic change in ﬂow rate in the down- stream region of the microchannels. The periodic change in ﬂow rate downstream at a constant heat input leads to the alternating wispy-annular and churn ﬂow; the vapor quality in the former is much higher than that in the latter ﬂow pattern. The photograph in Fig. 10 , captured at a heat ﬂux of 65 W/cm 2 and ﬂow rate of 60 ml/min, shows the vapor cores in the microchannels during the wispy-annular ﬂow; the liquid ﬁlm on the channel walls breaks up into liquid patches that may coil up into liquid droplets. Fig. 11 (a) presents the pressure drop measurements over a period of time (at four heat ﬂux levels and a ﬂow rate of 60 ml/min) show- ing the pressure drop ﬂuctuations before and after the commence- ment of ﬂow instabilities in the microchannels. The standard deviations of the ﬂuctuations in pressure drop, deﬁned as
Objective of this study is controlling the thermal deformation from laser transformation hardening process. Unlike the laser forming process, thermal deformation behavior in laser heat treatment has rarely been studied. It is important that there is no deformation on specimen when heat treatment process is conducted. So this study was conducted. In this study, Thermal deformation tendency after laser heat treatment of steel sheets is investigated. Laser heat treatment experiments were conducted by a 3 kW diode laser on 2 mm thick DP590 dual phase steel and boron steel sheets. Also, in these experiments, there are four types of heatsink were used: steel, stainless steel 316, copper and no heatsink were considered. For each kind of heatsink, four interaction time and six levels of intensity were used for both types of steel. After experiments, deflection angle were measured by three dimension coordinate system and cross section of all specimen was captured, microstructure distribution such as martensite, bainite, ferrite and pearlite within heat treated region for all specimen were analyzed. All of deflection angle was distributed within interaction time and intensity. From this study, thermal deformation is reduced from positive value to negative value when a heatsink is used. Between positive value and negative value, zero deflection regimes, which are considered good conditions for heat treat process, are observed. In these different appearance of deflection angle, two different thermal deformation mechanisms are involved, which are plastic deformation and phase transformation. Plastic deformation cause positive deflection angle and the phase transformation cause negative bending angle. It was also observed that heat affected zone depth from surface of specimen with respect to the specimen thickness is an important factor for deciding deformation. The heat affected zone depth is approached half of specimen, the thermal deformation angle is located in zero regime region as heatsink was used.
This study experimentally investigates single phase heat transfer and pressure drop characteristics of a shallow rectangular microchannelheatsink whose surface is enhanced with copper nanowires (CuNWs). The hydraulic diameter of the channel is 672 μm and the bottom wall is coated with Cu nanowires (CuNWs) of 200 nm in diameter and 50 μm in length. CuNWs are grown on the Cu heatsink by electrochemical synthesis technique which is inexpensive and readily scalable. The heat transfer and pressure drop results of CuNWs enhanced heatsink are compared with that of bare copper surface heatsinkusing deionized (DI) water as the working fluid at Reynolds Number (Re) ranging from 106-636. The experimental results indicate an enhancement in Nusselt Number (Nu) at all Re with a maximum enhancement of 24% at Re = 106. An increase in pressure drop is also observed in all test cases due to enhanced roughness. The enhanced thermalperformance is attributed to the enhanced wettability and the increased heat transfer surface area due to the addition of CuNWs arrays. The surface morphology of the heatsink has also been studied before and after heat transfer experiments through SEM to determine the effect of fluid flow on CuNWs arrays. The SEM results demonstrate no notable changes in surface morphology for the Re range in which experiments have been conducted and for single phase flow.
nanoparticles (1-10 Vol. %) and 0.1 Vol. % Triton X-100 as stabilizer to distillated water as base fluid. The prepared mixture is homogenized by using an ultrasonic bath (model) for 10 hours. The produced stable nanofluid is used for thermal analysis. In the last step of experiments, for investigation of the effect of base fluid composition, ethylene glycol is mixed with water involving different volume concentrations (10, 20 and 40 Vol. %). The produced mixture is agitated in a flask and used for preparation of nanofluids. The Physical properties of Al 2 O 3
channel structure. Influence of corrugated amplitude, wave length, volumetric flow rate & fraction of various nanofluids are shown. Three different class of nanofluids have been applied with a volume concentration of 1% to 5%. It has been observed that if the purest form of water is used then MCHS heat transfer has improved significantly compared to the conventional channel . Vinodhan & Rajan 2014 has carried out computational experiments for heat transfer & flow pattern in four new nnel MCHS configurations to compare it with a traditional heatsink. Higher heat transfer and Nusselt number rates were achieved in new designs due to the presence of many regions of development flow . Kuppusamy et al. In 2015, studied the influence of the triangular micro-mixers adjusted between main current channels in MCHS. For simulation, a unit wall with simple MCHS and a triangular microcomputer (MTM) is selected. Results revealed that the heat transfer of MTM depends on changes in all geometric parameters . Vafai & Zhu 1999 revealed that double-layer MCHS is a major improvement over a traditional single-layer MCHS because less temperature rise of the base surface has been noticed competed to a single layer heatsink . Balasubramanian et al. 2011 have conducted a test for straight and expandable micro channels having same dimensions & similar working conditions using demineralized water as a refrigerant. Results demonstrated that the expanding MCHS has preferable heat transfer over the regular MCHS also heat transfer coefficient in expandable channels is nearly consistent while straight channel heat transfer coefficient shows large variation throughout the range of G due to better bubble stability  which is demonstrated in Fig.6. Mohammed et al. 2011 observed that the MCHS zigzag has less temperature and a higher value of h between straight, sinuous and undulating channels for the same cross-sectional area of MCHS when numerical simulations were performed using 3D model FVM for water .
Many researchers investigated the enhancement design or calculation of different heat sinks using numerical and experimental methods. Bejan and Sciubba (1992) obtained the optimal rib spacing for maximum heat transfer from a package of parallel plates that was cooled by forced convection. Knight et al. (1992) developed a rib optimization method for a heatsink with micro channels by iterative solution of nonlinear equations. Bessaih and Kadja (2000) carried out the numerical simulation of air turbulence on several electronic components in a vertical channel, and the influence of the heat dissipation of the components was obtained and a method of heat dissipation was proposed. Etemoglu (2007) had experimented with and analyzed the new technologies of cooling the electronic equipment such as jet-flow and
Figure 11 shows the variation of effectiveness with inlet fluid velocity for different values of volume fraction. (c = 0 refer to pure water). From this figure it can be seen that the effectiveness decreased with increase of velocity. Also the large difference between different cases of volume fractions is occurred in low values of velocities and this difference is decreased with increase of fluid velocity. This is due to the effect of usingnanofluids which appear in low flow rate while in high flow rate the flow is dominated by volume flow rate and the effect of sold particles on the developing of boundary layer.