Heat Transfer Enhancement Using Shaped Polymer Tubes: Fin Analysis

2004 ◽  
Vol 126 (2) ◽  
pp. 211-218 ◽  
Author(s):  
Zhihua Li ◽  
Jane H. Davidson ◽  
Susan C. Mantell
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Transfer Rate ◽  
Polymeric Materials ◽  
Transfer Enhancement ◽  
Transfer Rates ◽  
Shaped Tube ◽  
Polymer Tubes

The use of polymer tubes for heat exchanger tube bundles is of interest in many applications where corrosion, mineral build-up and/or weight are important. The challenge of overcoming the low thermal conductivity of polymers may be met by using many small-diameter, thin-walled polymer tubes and this route is being pursued by industry. We propose the use of unique shaped tubes that are easily extruded using polymeric materials. The shaped tubes are streamlined to reduce form drag yet the inside flow passage is kept circular to maintain the pressure capability of the tube. Special treatment is required to predict convective heat transfer rates because the temperature distribution along the outer surface of the shaped tubes is nonuniform. The average forced convection Nusselt number correlations developed for these noncircular tubes can not be used directly to determine heat transfer rate. In this paper, heat transfer rates of shaped tubes are characterized by treating the tubes as a base circular tube to which longitudinal fin(s) are added. Numerical solution of an energy balance on the fin provides the surface temperature distribution and a shaped tube efficiency, which can be used in the same manner as a fin efficiency to determine the outside convective resistance. The approach is illustrated for three streamlined shapes with fins of lenticular and oval profile. The presentation highlights the effects of the geometry and the Biot number on the tube efficiency and heat transfer enhancement. Convective heat transfer is enhanced for the oval shaped tube for 2000⩽Re⩽20,000 when Bi<0.3. For polymeric materials, the Biot number in most applications will be greater than 0.3, and adding material to the base tube reduces the heat transfer rate. The potential benefit of reduced form drag remains.

Heat transfer enhancement in microchannels using ribs and secondary flows

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Karthikeyan Paramanandam ◽  
Venkatachalapathy S. ◽  
Balamurugan Srinivasan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method. Findings The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate. Practical implications The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible. Originality/value The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

Scaling of Convective Heat Transfer Enhancement Due to Flow Pulsation in an Axisymmetric Impinging Jet

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Tim Persoons ◽  
Kuanysh Balgazin ◽  
Karl Brown ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Impinging Jets ◽  
Pulsation Frequency ◽  
Transfer Enhancement ◽  
Air Jet

Impinging jets are widely used to achieve a high local convective heat flux, with applications in high power density electronics and various other industrial fields. The heat transfer to steady impinging jets has been extensively researched, yet the understanding of pulsating impinging jets remains incomplete. Although some studies have shown a significant enhancement compared to steady jets, others have shown reductions in heat transfer rate, without consensus on the heat transfer mechanisms that determine this behavior. This study investigates the local convective heat transfer to a pulsating air jet from a long straight circular pipe nozzle impinging onto a smooth planar surface (nozzle-to-surface spacing 1 ≤ H/D ≤ 6, Reynolds numbers 6000 ≤ Re ≤ 14,000, pulsation frequency 9 Hz ≤ f ≤ 55Hz, Strouhal number 0.007 ≤ Sr = fD/Um ≤ 0.1). A different behavior is observed for the heat transfer enhancement in (i) the stagnation zone, (ii) the wall jet region and overall area average. Two different modified Strouhal numbers have been identified to scale the heat transfer enhancement in both regions: (i) Sr(H/D) and (ii) SrRe0.5. The average heat transfer rate increases by up to 75–85% for SrRe0.5 ≅ 8 (Sr = 0.1, Re = 6000), independent of nozzle-to-surface spacing. The stagnation heat transfer rate increases with nozzle-to-surface distance H/D. For H/D = 1 and low pulsation frequency (Sr < 0.025), a reduction in stagnation point heat transfer rate by 13% is observed, increasing to positive enhancements for Sr(H/D) > 0.1 up to a maximum enhancement of 48% at Sr(H/D) = 0.6.

Heat Transfer Enhancement Using Shaped Polymer Tubes: Fin Analysis

2003 ◽  
Author(s):  
Zhihua Li ◽  
Jane H. Davidson ◽  
Susan C. Mantell
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Fluid Pressure ◽  
Small Diameter ◽  
Transfer Rates ◽  
Fin Efficiency ◽  
Shaped Tube ◽  
Linear Differential ◽  
Polymer Tubes

Uniquely shaped tubes extruded with an inner circular flow passage and an outer streamlined profile are proposed to withstand the inside fluid pressure and simultaneously to reduce the pressure drop across heat exchanger tube bundles comprising hundreds of small-diameter, thin-walled polymer tubes. Heat transfer rates are characterized by treating the tubes as the combination of a base circular tube and longitudinal fin(s) of oval or lenticular profile. Numerical solution of the non-linear differential equation for surface temperature provides the shaped tube efficiency, similar in function to fin efficiency. The effects of Biot number and a dimensionless shape factor on the tube efficiency and the convective heat transfer rate are discussed. A comparison of a circular to an oval shaped tube indicates that convective heat transfer is enhanced for 2000 ≤ Re ≤ 20,000 when Bi < 0.3.

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