Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
17
1
2010
Thermal and Friction Characteristics of Laminar Flow through Square and Rectangular Ducts with Transverse Ribs and Twisted Tapes with and without Oblique Teeth
1-21
10.1615/JEnhHeatTransf.v17.i1.10
Sujoy
Saha
Department of Mechanical Engineering, Indian Maritime University, Kolkata Campus, Kolkata- 700088, ( A central University, Govt. of India)
P. K.
Pal
Department of Mechanical Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103
laminar swirl flow; forced convection; transverse ribs; twisted tape; square and rectangular ducts
Thermal and friction characteristics of a laminar flow through square and rectangular ducts with periodic transverse ribs and different types of twisted tapes with and without oblique teeth have been studied experimentally. Correlations for predicting the friction factor and Nusselt number have been developed and performance has been evaluated. Although both friction factor and Nusselt number are the highest for the case of all types of twisted tapes with oblique teeth in combination with transverse ribs, the performance evaluation has shown that the ducts with transverse ribs and regularly spaced twisted-tape elements with oblique teeth are the best and this is recommended. However, where the pressure drop in a heat exchanger is a small fraction of the total system pressure drop; the heat transfer being higher, full-length and short-length twisted tapes in combination with transverse ribs can be recommended since the heat exchanging surface area requirement will be less.
Flow Impingement onto a Conical Cavity at Elevated Wall Temperature: Effects of Conical Nozzle Cone Angle and Flow Velocities on Heat Transfer Rates
23-43
10.1615/JEnhHeatTransf.v17.i1.20
S. Z.
Shuja
Mechanical Engineering Department, KFUPM Box 1913, Dhahran 31261, Saudi Arabia
Bekir S.
Yilbas
Mechanical Engineering Department, KFUPM Box 1913, Dhahran 31261, Saudi Arabia
conical nozzle; conical cavity; jet impingement; heat transfer
Conical nozzles are used for laser processing of engineering materials. The process parameters including the assisting gas jet velocity and the nozzle configuration influence the end product quality. The heat transfer rates and the skin friction in the laser-processed region depend on the flow structures developed in this region. In the present study, the flow structure around the conical cavity due to the jet is investigated numerically. The cavity wall temperatures are kept at 1500 K to resemble the laser-produced cavity. The effect of the jet velocity on the heat transfer rates from the cavity surface and the skin friction along the cavity wall are examined for two cone angles of the conical nozzle. The Reynolds stress turbulence model is accommodated to account for the turbulence while air is used as the working fluid in the simulations. It is found that the nozzle outer angle and the jet velocity alter the heat transfer rates from the cavity surface.
Forced Convective Flow Drag and Heat Transfer Characteristics of CuO Nanoparticle Suspensions and Nanofluids in a Small Tube
45-57
10.1615/JEnhHeatTransf.v17.i1.30
Liang
Liao
School of Mechanical Engineering, Shanghai Jiaotong University
Zhenhua
Liu
Shanghai Jiao Tong University, 800 Dong Chuan Rd. Minhang District, Shanghai 200240, China
Ran
Bao
School of Mechanical Engineering, Shanghai Jiaotong University
nanofluid; forced convection; enhanced heat transfer; flow drag
The present experiment investigates the forced convective flow drag and enhanced heat transfer of water−CuO nanoparticle suspensions and nanofluids in a steel tube with an inner diameter of 1.02 mm. The nanoparticle suspension consists of a base fluid and nanoparticles, while the nanofluid consists of a base fluid, nanoparticles, and a surfactant. Previous studies were all concerned with nanofluids without any research attention paid to nanoparticle suspensions yet. The effect of fluid temperature on heat transfer and flow drag has never been considered as well. This study aims to understand how surfactant and fluid temperature affect forced convective flow drag and heat transfer. The experimental results show that: fluid temperature has a great effect on the heat transfer of both nanoparticle suspensions and nanofluids; for both of them, the heat transfer coefficient enhancement comes mainly from the increasing effective thermal conductivity. The surfactant has no influence on the heat transfer. However, it does affect the flow drag characteristic. For suspensions, flow drag is greater than that of water in the laminar flow region, while it is obviously lower than that of water in the turbulent flow region. For nanofluids, the flow drag is greater than that of water in the whole flow region. Fluid temperature has no obvious effect on flow drag of both suspensions and nanofluid.
Two-Phase Refrigerant Distribution in a Parallel-Flow Heat Exchanger
59-75
10.1615/JEnhHeatTransf.v17.i1.40
Nae-Hyun
Kim
Department of Mechanical Engineering, Incheon National University, Incheon 406-772, Republic of Korea
D. Y.
Kim
Graduate School, University of Incheon, #177 Dohwa-Dong, Nam-Gu, Incheon, 402-749, Korea
parallel flow heat exchanger; header; two-phase distribution; R-134a; air−water
The distribution of R-134a flow is experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as mass flux and quality are investigated. The flow at the header inlet is stratified. The results are compared with the previous air−water results, where the flow at the header inlet is annular. For the downward flow configuration, most of the liquid flows through the frontal part of the header. The distribution of liquid improves as the protrusion depth or the mass flux increases, or the quality decreases. For the upward configuration, most of the liquid flow through rear part of the header. The liquid distribution improves as the mass flux or quality decreases. The protrusion depth has a minimal effect. Comparison of the present data on a stratified inlet flow with those of the previous annular inlet flow reveals that an inlet flow pattern has a significant effect on flow distribution. Generally, the effect of a tube protrusion depth, mass flux or quality on liquid distribution is much stronger for an annular inlet flow, probably due to a high gas velocity. Liquid distribution of the stratified inlet flow is better than that of the annular inlet flow. For the downward flow, the effect of quality on liquid distribution of the stratified inlet flow is opposite to that of the annular inlet flow. For the upward flow, the effect of the mass flux or quality of the stratified inlet flow is opposite to that of the annular inlet flow. Possible explanation is provided from the flow visualization results.
Experimental Study of Heat Transfer and Friction in Annular Ducts with a Heated Tube Having a Spirally Wound Helical Spring
77-92
10.1615/JEnhHeatTransf.v17.i1.50
B. K.
Maheshwari
Department of Mechanical Engineering, Faculty of Engineering and Architecture, Jai Narain Vyas University, Jodhpur 342 011, India
Shailesh K.
Patel
Department of Mechanical Engineering, Faculty of Engineering and Architecture, Jai Narain Vyas University, Jodhpur 342 011, India
Rajendra
Karwa
Department of Mechanical Engineering, Faculty of Engineering and Architecture, Jai Narain Vyas University, Jodhpur 342 011, India
asymmetrically heated annular duct; spirally wound helical spring; heat transfer enhancement; thermohydraulic performance
The paper presents results of an experimental investigation carried out to study the effect of relative roughness pitch and perforation of the spring roughness (by changing coil pitch of the helical spring) on heat transfer and friction factor for turbulent flow in an asymmetrically heated annular duct (radius ratio = 0.39) with a heated tube having a spirally wound helical spring. The spring diameter to hydraulic diameter ratio is 0.11. The relative roughness pitch ranges from 4.09 to 8.18, while the relative coil pitch is 2.66−4.5. The maximum enhancement in the Nusselt number over the smooth annulus ranges from 95 to 172% for Spring 2 (with a relative coil pitch, pc/d, of 2.66 arranged at a relative roughness pitch, p/e, of 4) while the lowest enhancement of 54−81% is seen for Spring 12 (pc/d = 4.5; p/e = 8) in the flow Reynolds number range of about 4000−14,000; the Nusselt number ratio, Nu/Nus, has been found first to increase with an increase in the Reynolds number up to about 10,000 and then decrease. The corresponding enhancement in the friction factor values is 193−307% and 116−137%, respectively. Thermal performance comparison at equal pumping power for the roughened and smooth annuli shows performance advantage of 32−83% for Spring 2. Nusselt number and friction factor correlations have been developed for the most preferred type of roughness.
Numerical Simulation of the Improvement to the Heat Transfer within the Internal Combustion Engine by the Application of Nanofluids
93-109
10.1615/JEnhHeatTransf.v17.i1.60
Jizu
Lv
School of Energy and Power Engineering & Key Laboratory of Ocean Energy Utilization and Energy Conservation of the Ministry of Education, Dalian University of Technology, Dalian 116023
Long
Zhou
School of Energy and Power Engineering & Key Laboratory of Ocean Energy Utilization and Energy Conservation of the Ministry of Education, Dalian University of Technology, Dalian 116023
Minli
Bai
School of Energy and Power Engineering & Key Laboratory of Ocean Energy Utilization and Energy Conservation of the Ministry of Education, Dalian University of Technology, Dalian 116023
Jia Wei
Liu
School of Energy and Power Engineering, Dalian University of Technology, Dalian 116023
Zhe
Xu
School of Energy and Power Engineering, Dalian University of Technology, Dalian 116023
nanofluid; internal combustion engine; heat transfer enhancement
A numerical simulation method has been employed to study the use of nanofluids for cooling of an internal combustion engine. The heat transfer enhancement due to nanofluids has been studied from two aspects; the flow and heat transfer in the cooling system and the heat transfer between the sliding-contact components of the combustion chamber (e.g., piston rings and cylinder liner). The results showed that the application of nanofluids significantly enhanced the heat transfer, and the effect was larger with an increasing concentration of nanoparticles. The pumping power of the cooling system was increased by the use of nanofluids, but this can be accepted by considering the enhanced heat transfer. The heat transfer between the piston rings and cylinder liner, and the cooling of the piston and cooling jacket were improved by adding nanoparticles to the lubrication. Meanwhile, Cu−oil nanofluids also showed potential for improving the lubrication itself.