A very low Nano fluid concentration was used as the first Nano **heat** **transfer** experiment. An increase in **heat** **transfer** **rate** is observed at any given flow **rate**. The plot of mass flow **rate** vs. **heat** **transfer** **rate** is shown in Fig.3. There is an improvement in **heat** flow **rate** due to the addition of nanoparticles even at very low concentrations. For example at a mass flow **rate** of 0.005 kg/s, a 5.5% increase in **heat** **transfer** **rate** is observed.

Maximum **heat** **transfer** **rate** is an important parameter in **heat** pipe performance. In the present study the maximum **heat** **transfer** **rate** has been calculated by using C++ program for the different operating temperature of a particular **heat** pipe dimension. For this purpose the selected fluids is water. Taking the dimension as constant and varying the temperature, the maximum **heat** **transfer** **rate** has been calculated.

13 Read more

Any type of nanoparticles mixed with bases fluid is called nanofluid. Nanofluid sometimes called an emulsion. Nanofluids are having several advantages. Due to nano size particles, pressure losses during flow will be less. Higher thermal conductivity of nano particles will increase the **heat** **transfer** **rate**. Successful employment of nanofluid will lead to lighter and smaller **heat** exchanger. There will be a drastic change in the properties of the base fluid after introducing suspending nanofluids. **Heat** **transfer** **rate** increases due to large surface area of the nano particles in the base fluid. Nanofluids are most suitable for rapid heating and cooling systems.

A **heat** exchanger is a device used for affecting the process of **heat** exchange between two fluids that are at two different temperatures. **Heat** exchangers are useful in engineering process like those in refrigeration and air conditioning systems, power systems, food processing systems, chemical reactors and space or aeronautical applications. In **heat** exchangers the temperature of each fluid changes as it passes through the exchanger and hence the temperature of the dividing wall between the fluids also changes along the length of the exchanger. **Heat** exchangers are designed to deliver a certain **heat** **transfer** **rate** for a certain specified condition of flow rates and temperatures. Shell and tube **heat** exchangers are used when a process requires large amounts of fluid to be heated or cooled, is suited for higher pressure applications. Nano particles research is gaining increasing interest due to their unique properties, such as increased thermal conductivity, toughness and ductility, increased hardness and strength of metals and alloys, luminescent efficiency of semiconductors, formability of ceramics. In order to enhance the **heat** **transfer** **rate** of the **heat** exchanger, a new category of fluids are used along with the conventional fluids like water, those fluids are called as nano fluids. Nano fluids are those fluids which exhibit significantly novel properties when compared to conventional fluids. Nano fluids are suspensions containing particles that are less than 100nm and have a bulk solids thermal conductivity of orders of magnitude higher than the base fluids.

1.1 FINS:In study of **heat** **transfer**, a fin is a surface that it is extends from an object to increase the **rate** of **heat** **transfer**. Fin act as the important part that help to reduce the distribution of overheat by the engine block. In Many thermal applications **heat** has to be removed from a small area to the surrounding (or) Environment to maintain it in a steady state condition.

through a partially filled pipe with porous material. The results showed that the location of the porous medium affects the performance of the composite pipe, the thermal conductivity ratio has a considerable effect on the **heat** **transfer** enhancement in case 1 for all porous thicknesses. While, in case 2, its effect on the enhanced **heat** **transfer** is more obvious at higher porous thicknesses. Guo, Shi Zhang, and Rong [6] investigated numerically the enhancement of the **heat** **transfer** for fluid flow in pipe partially filled with porous medium. The results show that changing the thickness of porous medium affect the **rate** of **heat** **transfer** and flow resistance, small effect of porosity on temperature and flow field ( other parameters were fixed) and at the same parameter values, pipe partially filled with porous media enchanted the **rate** of **heat** **transfer** effect comparing with blank pipe. Aziz, Kundu, and Bhanja [7] investigated numerically the **rate** of **heat** **transfer** on fixed and moving porous fin material by studying the temperature distribution, optimum design parameters and efficiency of the moving porous fin. The investigation shows that the results of both decomposition method and finite difference method approach with each other and the moving porous fin better than fixed ones in the **rate** of **heat** **transfer**. Mehrizi, Farhadi, Sedighi, and Delavar [8] studied the extent of enhancement of the **heat** **transfer** at a ventilated porous media plate **heat** exchanger by using method of Boltzmann which was designed by square cavity with thermal insulated inlet and outlet and three fins with constant hot temperature. The study shows that the **rate** of **heat** **transfer** enhanced due to adding porous medium to the **heat** exchanger, at high Reynolds number, the porous medium has high effect in Nusselt number, the position of the fin affects sensibly on Nusselt number

15 Read more

By observing the CFD analysis the pressure drop & velocity values are more for water fluid at solar parabolic trough collectors compared with flat plate collector. The more **heat** **transfer** **rate** at fluid water. By observing the thermal analysis **Heat** flux value is less for steel material than aluminum and copper material at solar collectors and **Heat** flux value is more for copper material than aluminum and steel material at solar absorber

Abstract - For the enhancement in performance of the **heat** exchanger, it is decided to increase the turbulence and intermixing of flow of hot fluid inside the hot fluid pipe by means of specially design delta winglets that will be placed within the inner tube and these winglets are produced by the 3-d printing process .The winglet serve dual purpose namely- one to increase the surface area and other to improve the interaction between particles and thereby increasing the **heat** **transfer**. In this work, 3-D printed delta winglet holder used in Inline, 5 degree inclined and 10degree inclined staggered position in double pipe **heat** exchanger. It is observed that **heat** **transfer** **rate** of the 10 degree inclined configuration of counter flow is better than that of parallel flow configuration. The thermal analysis shows that the maximum **heat** flux is 31.80W/mm². The increased **heat** **transfer** **rate** can be attributed to higher turbulence and closer interaction of the working fluids. This is achieved with the complex design of delta winglet to create turbulence. The comparative results also displayed in the paper.

10 Read more

**Heat** **transfer** can be defined as the exchange of thermal energy between physical systems. The **rate** of **heat** **transfer** is dependent on the properties of the intervening medium and temperatures of the systems through which the **heat** is transferred. The three basic fundamental modes of **heat** **transfer** are conduction, convection and radiation. **Heat** **transfer** is a process by which a system changes its internal energy. Hence it plays a vital role in applications of the First Law of Thermodynamics. Conduction is also known as diffusion. The direction of **heat** **transfer** is from a region of high temperature to another region of lower temperature, and is governed by the Second Law of Thermodynamics. **Heat** **transfer** changes the internal of the systems from which and to which the energy is transferred. **Heat** **transfer** occur in a direction that increases the entropy of the collection of systems. When all involved bodies and the surroundings reach the same temperature, thermal equilibrium is achieved. Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.

different techniques have been used. One of the advanced techniques among them is suspension of nanoparticle in the base fluids as water, ethylene glycol, oil. In last few years so many research has been done for enhancing the **heat** **transfer** **rate** like inserting baffles, twisted tapes, brushes, etc. This leads to increase in weight of **heat** exchangers and also cost of manufacturing. The worldwide researchers are making hard efforts to find out suitable alternatives for **heat** exchangers with different geometry and varying parameters which effects on performance of **heat** exchanger. Now days Nano fluid has become blessings for researchers. Nano fluid increases the **heat** **transfer** **rate** when suspended in base fluids water, ethylene glycol. With the fast track development of nanotechnology, particles of nanometer size are used for enhancing **heat** **transfer** **rate** are called Nano fluids. This work is focused on study of **heat** **transfer** **rate** enhancement at low concentration.

The **heat** exchangers have many applications in the industry. Its performance depends on its design, **heat** **transfer** **rate**, type of medium, pressure drop etc. Its **heat** **transfer** **rate** can be increased my changing the fluid stream inside the **heat** exchanger. It is done by placing the obstacle in the flow called as insert. **Heat** **transfer** **rate** can be enhanced by using different methods. Those are as follows: 1)Active Techniques: These techniques are more complicated for the design and use point of view. It requires external power source to enhance the **heat** **transfer** **rate**. It has limited application due to requirement of external power source. 3) Passive Techniques: These techniques use surface of geometrical modifications to the flow channel by incorporating inserts or additional devices. This technique does not require any external power; rather they use power form system itself. Ultimately leads into a rise in fluid pressure drop. This method gives higher **heat** **transfer** **rate** as compared with the extended surface. 4) Compound Techniques: It is a hybrid method where both active and passive techniques are combined to increase the **heat** **transfer** **rate**. As this method uses passive technique since it doesn’t require any external power source. Due to this advantage it is widely used in the industries. 5)Extended Surface: They provide effective **heat** **transfer** enlargement. The new research led to modify the fin surface that also tends to improve the **heat** **transfer** coefficient. 6)Treated surface: These are the **heat** **transfer** surfaces which have thin alteration on their finish or coating.

The electrical power generation is observed to be a strong function of flow **rate** and inlet exhaust temperature. The implications of varying inlet con- ditions could be very severe if proper conditioning of output power is not carried out. The ZT value of high-temperature skutterudites decreases consid- erably along the flow direction due to decreasing DT and temperatures at the hot-side junction. The thermoelectric modules close to the inlet are exposed to much higher gas temperatures and hence generate higher electrical power output per unit area. By optimizing the fin spacing and thick- ness, the **heat** **transfer** **rate** can be enhanced con- 0

10 Read more

Variation of **heat** **transfer** **rate** with Q Reynolds number are shown in figure 5.5 and it is observed that for all the cases **heat** **transfer** **rate** increases as Reynolds number increases and it is maximum in outer corrugated tube for all values of Reynolds number. Variation of h with Reynold number are as shown in Fig 5.3. As seen from the figure h increases as Re increases. At low Reynold.no h of internally corrugated tube is higher as compared to externally corrugated tube and plain tube but at high Reynold number it is lesser than the other two.

13 Read more

Variation of **heat** **transfer** **rate** with Q Reynolds number are shown in figure 5.5 and it is observed that for all the cases **heat** **transfer** **rate** increases as Reynolds number increases and it is maximum in outer corrugated tube for all values of Reynolds number. Variation of h with Reynold number are as shown in Fig 5.3. As seen from the figure h increases as Re increases. At low Reynold.no h of internally corrugated tube is higher as compared to externally corrugated tube and plain tube but at high Reynold number it is lesser than the other two.

13 Read more

Thermal conductivity can be defined as amount of **heat** transferred through unit thickness of material in a direction normal to a surface of unit area. Thermal conductivity refers to the amount/speed of **heat** transmitted through a material. **Heat** **transfer** occurs at a higher **rate** across materials of high thermal conductivity than those of low thermal conductivity. Thermal conductivity of nanofluid is determined by following equation,

Due to rapid demand on the thermoelectric cooler box, an investigation concerning the effect of water volume on a thermoelectric cooler box performance and its COP has been conducted. The aim of this study is to know the performance and the COP of the cooler box with water volume variations. The conduction **heat** **transfer** **rate** flowing from the ambient to the cooler box space is discussed deeply as this type of **heat** **transfer** **rate** is seldom to be elucidated in the published literature and it can be the dominant of the **heat** load when there is no water volume inside the cooler box. The cooler box size was 390 mm x 320 mm x 530 mm and the water volume variations employed were ranging from 0 to 4500 ml. The power used was of approximately 51.27 W. The results indicate that increasing the water volume raises the cooler box space temperature and the COP but decreases the conduction **heat** **transfer** **rate**. At 0 ml water volume, the conduction **heat** **transfer** **rate** increases and it gets constant, while at higher water volumes the COP decreases with the time. The effect of the water volume on the **heat** **transfer** **rate** of the air is negligible but it is significant on the total **heat** **transfer** and conduction **heat** **transfer**.

Ahmet Tandiroglu studied effect of the flow geometry parameters on transient forced convection **heat** **transfer** for turbulent flow in circular tube with baffle inserts. The characteristic parameter of the tubes was different range of pitch to inlet diameter ratio H/D=1, 2, 3and the baffle orientation angle β=45 0 , 90 0 and 180 0 . Air was used as working fluid in the range of Reynolds number 3000 to 20,000. It was varied different geometrical parameter such as baffle spacing H and the baffle orientation angel β. It was conclude that the tubes with baffle inserts give higher **heat** **transfer** **rate** than smooth tube. The time averaged Nusselt number increases with increasing Reynolds number. The **rate** of pressure drop increases with increasing Reynolds number for transient flow conditions but decreases with increasing Reynolds number for the steady state flow conditions. The **rate** of average pressure drop in the baffle inserted tubes for transient flow conditions was higher than that of steady state flow conditions.

Equations (23) to (26) are solved by an in-house USTREAM code developed by the third named author to obtain the three-dimensional numerical **heat** **transfer** results. In order to check if the numerical results are reliable, an insulated sphere is analyzed to determine how many cells are needed to obtain a satisfactory result. It was found that a model of an insulated sphere, which consists of 26600 cells, gave a satisfactory solution of **heat** **transfer** **rate** within ±0.01% compared with that from exact analytic solution. Therefore, in the case of analyzing an insulated oblate spheroid, the numerical solutions obtained by the model with same number of cells can be expected to be highly accurate.

A. M. &, the other. Treats the natural convection **heat** **transfer** from perforated fins. The temperature distribution was examined for an array of rectangular fins (15 fins) with uniform cross-sectional area(100x270 mm) embedded with different vertical body perforations that extend through the fin thickness. The patterns of perforations include 18 circular perforations (holes). Experiments were carried out in an experimental facility that was specifically design and constructed for this purpose. The **heat** **transfer** **rate** and the coefficient of **heat** **transfer** increases with perforation diameter increased.

The Passive **heat** **transfer** augmentation methods does not need any external power input. In the convective **heat** **transfer**, one of the ways to enhance **heat** **transfer** **rate** is to increase the effective surface area and residence time of the **heat** **transfer** fluids. By Using, this technique causes the swirl in the bulk of the fluids and disturbs the actual boundary layers, which increase effective surface area, residence time and simultaneously **heat** **transfer** coefficient increases in an existing system. Methods generally used are, extended surface, displaced enhancements devices, rough surfaces surface tension devices, Inserts requires additional arrangements to make to fluid flow which enhance and augment the **heat** **transfer**. The types of inserts are twisted tape, wire coils, ribs, baffles, plates, helical screw insert, mesh inserts, convergent – divergent conical rings, conical rings etc. Twisted tapes are the metallic strips twisted using some of the suitable techniques as per the required shape and dimension, which are inserted in the flow to enhance the **heat** **transfer**. The twisted tape inserts are most suitable and widely used in **heat** exchangers to enhance the **heat** **transfer**. Twisted tape inserts increase **heat** **transfer** rates with less friction factor. The use of twisted tapes in a tube gives simple passive technique for enhancing the convective **heat** **transfer** by making swirl into the heavy flow which disrupting the boundary layer at the tube surface due to rapidly changes in the surface geometry. Which means to say that such type of tapes induce turbulence and swirl flow which induces inside the boundary layer and which gives better results of **heat** **transfer** coefficient and Nusselt number due to the changes in geometry of twisted tape inserts. Simultaneously, the pressure drop inside the tube will be increases when using twisted-tape as an insert. For this a many researchers have been done by experimentally and numerically to investigate the desired design to achieve the better thermal performance with less frictional losses. The **heat** **transfer** enhancement of twisted tapes inserts depends on the Pitch In addition, twist ratio.

15 Read more