Begell House Inc.
Heat Transfer Research
HTR
1064-2285
49
13
2018
EXPERIMENTAL AND NUMERICAL ANALYSES OF A HEAT PUMP-DRIVEN CHILLED CEILING SYSTEMS
1219-1229
Deniz
Yilmaz
Mechanical Engineering Department, Istanbul Arel University, Istanbul, Turkey
Ali
Ozyurt
Mechanical Engineering Department, Marmara University, Istanbul, Turkey
Passive cooling covers the natural processes of heat dissipation and heat gain operations and provides a highly effi cient, comfortable environment around. As commonly known, when air is heated, it rises, when cooled, it descends. Natural
cooling and heating use this physical property of air to provide the best thermal conditions. In this study, an air-to-water heat pump system used for chilled ceiling operations was analyzed numerically and experimentally. Main objective of this
study is to obtain COP of the heat pump system. In order to determine the effi ciency, test room was established with heat
pump-driven passive chilled ceiling panels. The test room was constructed of 120-mm polyurethane panels to minimize heat
losses. All the data obtained from the system is recorded on a time period of per-second based during the processes.
UNSTEADY CONVECTION HEAT AND MASS TRANSFER OF A FRACTIONAL OLDROYD-B FLUID WITH CHEMICAL REACTION AND HEAT SOURCE/SINK EFFECT
1231-1246
Jinhu
Zhao
School of Mathematics and Statistics, Fuyang Normal College, Fuyang 236037, Anhui, China
Liancun
Zheng
School of Mathematics and Physics, University of Science and Technology Beĳing, Beĳing 100083,
China
Xinxin
Zhang
School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China; Beijing Key Laboratory of Energy Saving and Emission Reduction for Metallurgical Industry, University of Science and Technology Beijing, Beijing 100083, China
Fawang
Liu
School of Mathematical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane,
Qld. 4001, Australia
This paper studies unsteady convection heat and mass transfer of a fractional Oldroyd-B fluid in the presence of chemical
reaction and heat source/sink. Nonlinear coupled governing equations with time−space derivatives are derived and solved numerically. The effects of involved parameters on velocity, temperature, and concentration fields are analyzed. The results show that fractional derivative parameters have a remarkable influence on the viscoelastic properties of the fluid and play an opposite role in the boundary layer. With increase of the buoyancy ratio number, the velocity distributions rise, but the temperature distributions decline. Moreover, the heat source generates energy causing the temperature of the fluid to increase, while the heat sink absorbs energy which leads to the decrease of the temperature. Chemical reaction reduces the concentration boundary-layer thickness and improves the rate of mass transfer.
THERMAL PERFORMANCE OF A PIN FIN WITH UNEQUAL CONVECTIVE COEFFICIENTS OVER ITS TIP AND SURFACE
1247-1273
Sunil S.
Mehendale
Michigan Technological University, Houghton, Michigan 49931, USA
It is generally understood that heat transfer of a fin increases with its length. In cases where the fin tip experiences significantly higher convective coefficients, a situation exists where the heat transfer decreases with its length. Applications of this situation may exist in air conditioning, refrigeration, and electronics cooling. Analytical results for one-dimensional temperature distribution and heat transfer rate are presented for such a pin fin. A critical tip-to-surface coefficient ratio h(= hcrit) depending only on the transverse Biot number Bi exists, for which the heat transfer is independent of length. For "subcritical" conditions (h < hcrit), fin heat transfer increases with length, as is commonly known. In this case, long fins will be necessary for maximizing heat transfer. For "supercritical" situations (h > hcrit), however, the heat transfer
rate decreases with length, asymptotically approaching that for an infinitely long fin. Here, short fins will suffice to provide near-maximum heat duty. Compared to the unfinned base exposed to the tip coefficient, subcritical fins will enhance heat transfer; under supercritical situations, they will insulate the surface. However, compared to the finless base exposed to the surface coefficient, fins will always increase heat transfer. If the fin tip is employed to accurately measure the fluid temperature, the dimensionless fin length L must be no less than Lmin, which is a function only of Bi and h/hcrit . An analytical expression for Lmin necessary to keep the relative error within one percent has been developed. Whether the fin is used to enhance heat transfer or measure fluid temperature, the fin cross section should have as high surface area-to-volume ratio as possible.
NUMERICAL CHARACTERIZATION AND VALIDATION OF THE THERMAL RESPONSE OF AN EMPTY ISO CONTAINER EXPOSED TO REAL WEATHER CONDITIONS
1275-1297
Brian
Hunter
U.S. Army ARDEC, RDAR-MEA-A, Building 94, Picatinny Arsenal, NJ 07806
Heather
Pacella
U.S. Army ARDEC, RDAR-MEA-A, Building 94, Picatinny Arsenal, NJ 07806
Kenneth
Blecker
U.S. Army ARDEC, RDAR-EIL-F, Building 455, Picatinny Arsenal, NJ 07806
The purpose of this study was to develop and validate a computational model of the thermal behavior of an ISO container
exposed to real weather conditions. A thorough understanding of this process can allow for the design or orientation of
ISO containers to minimize exposure and maximize lifespan of its contents. Currently, the thermal history of assets in
storage cannot be determined without continuous monitoring of individual items, and there is no method to provide a
detailed estimate of the exposure by analyzing existing data when continuous data was not collected. This work describes
the experimental and initial numerical investigations of an instrumented empty ISO container to characterize the thermal
response. Thermocouple data collected through long-term field experiments of an empty ISO container were used to develop
and validate the numerical model, which includes combined effects from natural convection and radiation inside a 3D
enclosure, as well as external forced convection, conduction, and solar radiation. It is found that the numerical model has
the capability to validate broad trends observed from the experimental data over two noncontinuous days of varying cloud
cover in a computationally efficient manner. The overall accuracy and computational efficiency afforded by the numerical
model will advance the understanding of the implications of storage environment selection, as well as provide key predictive information for future investigations into the thermal exposure of contents in a loaded ISO container.
EFFECTS OF HEAT FLUX ON NATURAL CONVECTION OF WATER-BASED NANOFLUIDS IN A TRAPEZOIDAL ENCLOSURE
1299-1321
Xiaofeng
Wang
School of Mathematical Sciences, Henan Institute of Science and Technology, Xinxiang, Henan 453003, PR China; School of Mathematics and Statistics, Minnan Normal University, Zhangzhou, Fujian 363000, PR China
Juntao
Wang
School of Mathematical Sciences, Henan Institute of Science and Technology, Xinxiang, Henan
453003, PR China
Weizhong
Dai
Mathematics and Statistics, College of Engineering and Science, Louisiana Tech University, Ruston, LA 71272, USA
This study investigates natural convection heat transfer of water-based nanofluids in a trapezoidal enclosure where the
left vertical side is heated with constant heat flux both partially and throughout the entire wall, the inclined wall is
cooled, and the rest walls are kept adiabatic. The dimensionless governing equations were solved using a higher-order compact finite difference method, and solutions for algebraic equations were obtained through pesudo-time algorithms. Investigations of four types of nanofluids were made at different values of Rayleigh number Ra in the range 102 ≤ Ra ≤ 105, for the heat flux Ht lying in the range 0.2 ≤ Ht ≤ 0.8, enclosure aspect ratio AR within 1.5 ≤ AR ≤ 3.0, center position of a heater Υp in 0.3 ≤ Υp ≤ 0.7, solid volume fraction parameter Φ of nanofluids in the range
0% ≤ Φ ≤ 20%, and at the fixed angle φ = 45°. The results show that the maximum value of the local Nusselt number NuΥ and average Nusselt number Nu can be achieved for the highest Rayleigh number Ra, the smallest center position of the heater Υp, and the smallest enclosure aspect ratio AR. In addition, it was observed that the enhancement in heat transfer in the trapezoidal enclosure is much improved with increase of the solid volume fraction parameter Φ of nanofluids at a low volume fraction (Φ ≤ 10%), but opposite effects appear when the solid volume fraction parameter
Φ is high (Φ > 10%). Moreover, multiple correlations in terms of the Rayleigh number Ra and the solid volume fraction Φ of nanoparticles have been established.