**5. Experimental methods**

Precise measurement results in good outcome in every research work. In heat transfer, measurement plays a pivotal role in the analysis of thermal system. Even after the numerical modeling of a heat flow system, it is not possible to define all the parameters with full accuracy leading to the failure of many thermal systems. This includes most of the engineering devices such as spacecraft, cryogenic engines, satellites, etc. Modeling of a turbulent flow and transition zone is very complicated, and hence it is difficult to predict very accurately. For the accuracy and relevancy of data, precise measurement is required which gives rise to the development of precise system with better accuracy.

#### **5.1 Heat transfer**

Heat flux measurement is an important aspect for understanding the physics related to transport of heat; distinguish among conduction, convection, and radiation mechanism; analyze energy balance; derive material properties; and understand the flow regimes, etc. The physical and mathematical models are presented to investigate the evolution of surface waves for free-falling turbulent wavy films with varying Reynolds number [56]. Thermochromic liquid crystal (TLC) is one of the best techniques to visualize the transient heat flow over the surface. The change in color of TLC from red to green to blue helps understand the flow of heat flux over a surface in supersonic wind tunnel [57]. Luminescent coating is another option for measurement of heat flow over a surface. The method has been used to determine the heat flow in shorter duration of less than 10 ms hypersonic flow [58]. Heater foils can be used to measure the bulk temperature development in time-based heat flow measurement by using a simplified model in which temperature development has been characterized [59].

#### **5.2 Temperature measurement**

For the temperature measurement during rapid contact solidification at the surface of substrate, an interfacial temperature sensor of 1 μm diameter has been fabricated [60]. A telecentric objective has been used for the first time to phase out the dependence on the angles in color determination in fluid-based TLCs for precision measurement [61]. An acoustic thermal scan has been evaluated using numerical methodology to evaluate the spatial resolution [62].

**9**

*Applications of Heat Transfer Enhancement Techniques: A State-of-the-Art Review*

the measurement of sudden shift in the velocity in turbulent flow.

A multiple hot-film sensor (MHFS) arrays were used to evaluate the skin friction along the surfaces of two-dimensional streamlined objects (circular cylinder) [63]. A high time resolution ultrasonic velocity profiler (UVP) system has been developed to determine 1D velocity profile on an ultrasonic beamline [64]. A numerical investigation [65] was conducted to determine the thermal response of hot wire for

Bubble cluster pattern has been reported in the turbulent bubbly flow using

This part of the chapter deals with melting and freezing of materials. The section is divided into several subsections such as phase change materials (PCMs); formation of ice and its melting; melting and freezing of radial objects; melting and solidification of metals, nonmetals, and composites; crystallization; and globule,

The inability to recover latent heat after super cooling of PCMs has been pointed

Researches on the formation of ice and its melting include the thermal behavior

of ice under constant heat flow per unit area and melt removal, melting of ice using natural convection, ice making by cooling water-oil emulsion with stirring, and numerical simulation of melting of ice in water under the influence of natural

A lot of work has been presented on phase change in radial objects such as sphere, cylinders, and slabs. A mathematical model using numerical analysis has been developed to study the melting process of PCMs in sphere [76]. A novel

convection and cooling effect produced by melting of ice [73–75].

out, and the method to recover latent heat has been discussed [71]. The melting mechanism of PCMs in magnetic field in low-gravity atmosphere has been discussed [72]. Other works include fabrication of carbon brushes which can be used to enhance the thermal conductivity in phase change materials, the role of ultrasonic vibration on melting characterization of PCMs, and detailed examination of

spray, and plunge cooling for better understanding.

solid liquid phase change heat flow enhancement.

**6.2 Formation of ice and its melting**

**6.3 Melting and freezing of radial objects**

rake of resistive flow and signal processing associated with it [66]. Air and liquid flows have been measured individually in two-phase air liquid flow [67]. Ultrasound Doppler velocimetry has been used to measure the thickness and velocity of the liquid film [68]. A novel pressure-sensitive paint (PSP) has been formulated and used for pressure measurement in cryogenic wind tunnel [69]. A high-sensitivity thermal conductivity detector has been developed from different materials which can be used in the diagnosis of fault in transformer,

*DOI: http://dx.doi.org/10.5772/intechopen.92873*

**5.3 Velocity measurement**

**5.4 Miscellaneous**

oil exploration, etc. [70].

**6.1 Phase change materials**

**6. Phase change**

*Applications of Heat Transfer Enhancement Techniques: A State-of-the-Art Review DOI: http://dx.doi.org/10.5772/intechopen.92873*

### **5.3 Velocity measurement**

*Inverse Heat Conduction and Heat Exchangers*

A study showing the separation of energy in free shear zone was carried out, and the role of pressure in the flow separation was studied [50]. In vertical ducts and other cross sections, mixed convection was investigated numerically [51]. Three-dimensional flow studies for understanding the effect of step height were also available. Large eddy simulation (LES) was undertaken for the turbulent flow over a backward-facing step [52]. A laminar airfoil was taken, and adiabatic and heating conditions were investigated at modest subsonic Mach numbers [53]. Correlations among the heat transfer coefficients of dull-edged flat plates and square channels were studied [54]. A finite volume method was used to investigate the 2D natural convection in a heated cylinder, and the significance of aspect ratio, Prandtl number, and boundary conditions on thermal characteristics were

Precise measurement results in good outcome in every research work. In heat transfer, measurement plays a pivotal role in the analysis of thermal system. Even after the numerical modeling of a heat flow system, it is not possible to define all the parameters with full accuracy leading to the failure of many thermal systems. This includes most of the engineering devices such as spacecraft, cryogenic engines, satellites, etc. Modeling of a turbulent flow and transition zone is very complicated, and hence it is difficult to predict very accurately. For the accuracy and relevancy of data, precise measurement is required which gives rise to the development of

Heat flux measurement is an important aspect for understanding the physics related to transport of heat; distinguish among conduction, convection, and radiation mechanism; analyze energy balance; derive material properties; and understand the flow regimes, etc. The physical and mathematical models are presented to investigate the evolution of surface waves for free-falling turbulent wavy films with varying Reynolds number [56]. Thermochromic liquid crystal (TLC) is one of the best techniques to visualize the transient heat flow over the surface. The change in color of TLC from red to green to blue helps understand the flow of heat flux over a surface in supersonic wind tunnel [57]. Luminescent coating is another option for measurement of heat flow over a surface. The method has been used to determine the heat flow in shorter duration of less than 10 ms hypersonic flow [58]. Heater foils can be used to measure the bulk temperature development in time-based heat flow measurement by using a simplified model in which temperature development

For the temperature measurement during rapid contact solidification at the surface of substrate, an interfacial temperature sensor of 1 μm diameter has been fabricated [60]. A telecentric objective has been used for the first time to phase out the dependence on the angles in color determination in fluid-based TLCs for precision measurement [61]. An acoustic thermal scan has been evaluated using

numerical methodology to evaluate the spatial resolution [62].

**4. Flow separation**

studied [55].

**5. Experimental methods**

precise system with better accuracy.

has been characterized [59].

**5.2 Temperature measurement**

**5.1 Heat transfer**

**8**

A multiple hot-film sensor (MHFS) arrays were used to evaluate the skin friction along the surfaces of two-dimensional streamlined objects (circular cylinder) [63]. A high time resolution ultrasonic velocity profiler (UVP) system has been developed to determine 1D velocity profile on an ultrasonic beamline [64]. A numerical investigation [65] was conducted to determine the thermal response of hot wire for the measurement of sudden shift in the velocity in turbulent flow.

### **5.4 Miscellaneous**

Bubble cluster pattern has been reported in the turbulent bubbly flow using rake of resistive flow and signal processing associated with it [66]. Air and liquid flows have been measured individually in two-phase air liquid flow [67]. Ultrasound Doppler velocimetry has been used to measure the thickness and velocity of the liquid film [68]. A novel pressure-sensitive paint (PSP) has been formulated and used for pressure measurement in cryogenic wind tunnel [69]. A high-sensitivity thermal conductivity detector has been developed from different materials which can be used in the diagnosis of fault in transformer, oil exploration, etc. [70].
