News Letter on Heat Transfer Research: February -2019

Impingement heat transfer of quadruple synthetic jets

In this work, the warmth transfer performance of natural event quadruple artificial jets is through an experiment investigated by means that of infrared diagnostic technique and also the heated skinny foil technique. Four configurations (monopole-like, dipole-like, quadrupole-like and 90-degrees-circularly-shifted-jets), obtained by introducing totally different part shifts between the only artificial jets, are relatively studied at constant values of the Reynolds and Strouhal numbers, up to 4000 and zero.2, severally. it’s shown that the warmth transfer behavior is strictly associated with the dynamics of the coherent vortex structures that type once the interaction of the vortex rings inherent to the only jets. The signature of those vortical structures on the warmth transfer distributions is clear at short impingement distances, wherever the foremost important variations between the investigated configurations are so found. within the comparison, the 90-degrees-circularly-shifted-jets configuration is ascertained to supply the very best heat transfer rates, though with all-time low degree of uniformity, whereas the monopole-like jet is characterised by all-time low Nusselt range values and also the highest uniformity. because the impingement distance will increase, these variations are increasingly smudgy out and also the four configurations exhibit equivalent performance from the viewpoints of each magnitude and uniformity of the warmth transfer rate. [1]

Experimental investigation of the warmth transfer performance of microchannel heat exchangers with fan-shaped cavities

The microchannel device has been applied in several field due to its blessings, like miniaturisation, giant specific area, and high heat and mass transfer rate. during this work, a microchannel device with fan-shaped cavities (FSCs) was developed, and wont to conduct comparative experimental studies with the standard rectangular straight microchannel device. the consequences of structural parameters, like the deviation degree, coincidence degree and distribution of FSCs, on the warmth transfer performance of the microchannel device were investigated. The results indicate that the performance of the microchannel device with FSCs is healthier than that while not FSCs and therefore the pressure drop is smaller. it’s conjointly unconcealed that the deviation degree, coincidence degree and distribution of the FSCs have necessary effects on the warmth transfer performance. [2]

The result of wire-coil inserts on the warmth transfer and pressure drop of R1234yf flow boiling

Due to growing environmental issues regarding warming, eco-friendly HFO refrigerants like R1234yf are recently introduced as another to traditional HFC ones. the current analysis work investigates the boiling heat transfer constant and pressure drop of R1234yf flow as a replacement refrigerant for R134a in horizontal plain and wire-coil inserted tubes of eight.7 mm within diameter. Meanwhile, the accuracy of some well-known correlations to predict R1234yf flow boiling thermo-hydraulic properties are evaluated. The results show that the studied correlations might predict the warmth transfer constant and pressure drop of R1234yf flow boiling in plain tubes with a suitable accuracy. The impact of main operative parameters together with the vapor quality, the warmth flux, and therefore the mass rate is additionally completely studied employing a well-instrumented check equipment. in line with the results, at constant vapor quality, the warmth transfer constant will increase with each the heat flux and therefore the mass rate. additionally, inserting a wire-coil within the tube might enhance the warmth transfer constant the maximum amount as seventy two whereas leads up to eighty five increment in the pressure drop. This study and its result’s useful in style of next generation of warmth exchangers use R1234yf refrigerant as a operating fluid. [3]

Heat transfer surprise could lead to thermal transistors

As much as a hundred times a lot of heat than expected by the quality radiation theory will flow between 2 nanoscale objects, even at bigger-than-nanoscale distances, researchers at the University of Michigan and also the school of William and Blessed Virgin have reported  within the journal Nature. [4]

Augmentation of Natural Convection Heat Transfer from a Fin by Lateral polygonal shape Perforations

In this study the improvement of warmth transfer from a horizontal rectangular fin subjected to natural convection given lateral hexangular perforations is investigated exploitation one dimensional finite component technique. The orientation of those perforations is delineate as they need 2 sides parallel to the bottom and tip of the fin. The perforated fin is compared with its equivalent solid one. The parameters thought of are geometrical dimensions and thermal properties of the fin and these of the perforations. This study involves increased heat transfer surfaces that give exaggerated turbulence and a more robust flow distribution. Also, it thought of the gain in fin space and of warmth transfer coefficients thanks to perforations. From this study and sure as shooting values of hexangular dimension and areas between perforations, it’s found that there’s Associate in Nursing augmentation in heat transfer dissipation of the perforated fin over than that of the equivalent solid one. Moreover, the warmth transfer improvement of the perforated fin will increase because the thickness and thermal physical phenomenon of the fin are exaggerated. [5]

Reference

[1] Paolillo G, Greco CS, Cardone G. Impingement heat transfer of quadruple synthetic jets. International Journal of Heat and Mass Transfer. 2019 Jun 1;135:1192-206. (web link)

[2] Pan M, Wang H, Zhong Y, Hu M, Zhou X, Dong G, Huang P. Experimental investigation of the heat transfer performance of microchannel heat exchangers with fan-shaped cavities. International Journal of Heat and Mass Transfer. 2019 May 1;134:1199-208. (web link)

[3] Sajadi B, Najafizadeh MM, Soleimani M, Behabadi MA, Naserinejad J. The effect of wire-coil inserts on the heat transfer and pressure drop of R1234yf flow boiling. Applied Thermal Engineering. 2019 Feb 25. (web link)

[4] Heat transfer surprise could lead to thermal transistors

Date: September 5, 2018

Source: University of Michigan (web link)

[5] Augmentation of Natural Convection Heat Transfer from a Fin by Lateral Hexagonal Perforations

Abdullah H. AlEssa

Al-Balqa Applied University, Al-Husn University College, Al-Husn, Irbid, Jordan.

Isam H. E. Qasem

Al-Balqa Applied University, Al-Husn University College, Al-Husn, Irbid, Jordan