Development of an Outdoor Test Facility for Wind Convectors

1990 ◽  
Vol 112 (4) ◽  
pp. 287-292 ◽  
Author(s):  
P. F. Monaghan ◽  
D. P. Finn ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Heat Pumps ◽  
Test Facility ◽  
Transfer Performance ◽  
Test Results ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Outdoor Test

This paper deals with measurement of heat transfer performance of wind convectors, an alternative air source evaporator system for heat pumps. An automatically controlled and monitored outdoor wind convector test facility that is capable of measuring heat transfer rates and overall heat-transfer coefficients to within ± 5 percent measurement uncertainty for up to three wind convectors has been designed, built, and tested. Data on air temperature and humidity, solar radiation, and wind speed and direction are simultaneously collected. The choice of measurement technique for each variable and an error analysis for each sensor is discussed. Typical graphical test results are presented.

scholarly journals Experimental Study on the Evaporation and Condensation Heat Transfer Characteristics of a Vapor Chamber

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 11
Author(s):  
Yanfei Liu ◽  
Xiaotian Han ◽  
Chaoqun Shen ◽  
Feng Yao ◽  
Mengchen Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Condensation Heat Transfer ◽  
Transfer Performance ◽  
Vapor Chamber ◽  
Filling Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporation And Condensation

A vapor chamber can meet the cooling requirements of high heat flux electronic equipment. In this paper, based on a proposed vapor chamber with a side window, a vapor chamber experimental system was designed to visually study its evaporation and condensation heat transfer performance. Using infrared thermal imaging technology, the temperature distribution and the vapor–liquid two-phase interface evolution inside the cavity were experimentally observed. Furthermore, the evaporation and condensation heat transfer coefficients were obtained according to the measured temperature of the liquid near the evaporator surface and the vapor near the condenser surface. The effects of heat load and filling rate on the thermal resistance and the evaporation and condensation heat transfer coefficients are analyzed and discussed. The results indicate that the liquid filling rate that maximized the evaporation heat transfer coefficient was different from the liquid filling rate that maximized the condensation heat transfer coefficient. The vapor chamber showed good heat transfer performance with a liquid filling rate of 33%. According to the infrared thermal images, it was observed that the evaporation/boiling heat transfer could be strengthened by the interference of easily broken bubbles and boiling liquid. When the heat input increased, the uniformity of temperature distribution was improved due to the intensified heat transfer on the evaporator surface.

Heat Transfer Performance of Micro-Porous Copper Foams with Homogeneous and Hybrid Structures Manufactured by Lost Carbonate Sintering

2015 ◽  
Vol 1779 ◽  
pp. 39-44 ◽  
Author(s):  
Jan Mary Baloyo ◽  
Yuyuan Zhao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Hybrid Structures ◽  
High Porosity ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Porous Copper

ABSTRACTThe heat transfer coefficients of homogeneous and hybrid micro-porous copper foams, produced by the Lost Carbonate Sintering (LCS) process, were measured under one-dimensional forced convection conditions using water coolant. In general, increasing the water flow rate led to an increase in the heat transfer coefficients. For homogeneous samples, the optimum heat transfer performance was observed for samples with 60% porosity. Different trends in the heat transfer coefficients were found in samples with hybrid structures. Firstly, for horizontal bilayer structures, placing the high porosity layer by the heater gave a higher heat transfer coefficient than the other way round. Secondly, for integrated vertical bilayer structures, having the high porosity layer by the water inlet gave a better heat transfer performance. Lastly, for segmented vertical bilayer samples, having the low porosity layer by the water inlet offered the greatest heat transfer coefficient overall, which is five times higher than its homogeneous counterpart.

Effect of Nano-Particles on Pool Boiling Heat Transfer of Refrigerant 141b

2007 ◽  
Author(s):  
Da-Wei Liu ◽  
Chien-Yuh Yang
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nano Particles ◽  
Test Results ◽  
Tube Surface ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients

Fluids with nano-sized particles have been proved that may effectively enhance the single-phase convective heat transfer performance. For pool boiling heat transfer, the published test results seems conflicted to each other. Some measured heat transfer coefficient decreased with increasing particle concentration but some showed no appreciable difference. This study provides an experimental investigation on pool boiling heat transfer performance of refrigerants R-141b with and without nano-sized Au particles on horizontal plain tubes. The test results show that the boiling heat transfer coefficients increase with increasing nano-particles concentration. At particles concentration of 1.0%, the heat transfer coefficient is more than twice higher than those without nano-particles. However, the heat transfer coefficients decreased for each test after every 5 days and finally close to those of R-141b without nano-particles. The SPM investigation shows that the test tube surface roughness decreased from 0.317 μm before boiling test to 0.162 μm after test. Further investigation by TEM and Dynamic Light Scattering particle analyzer shows that the nano-particles aggregated from 3 μm before test to 110 μm after test. This results show that the nano-sized Au particles are able to significantly increase pool boiling heat transfer of refrigerant R-141b on plain tube surface. The tube surface roughness and particle size changed after boiling test. Both of these effects degrade the boiling heat transfer coefficients.

The Effects of Wettability and Surface Morphology on Heat Transfer for Zinc Oxide Nanostructured Aluminum Surfaces

2017 ◽  
Author(s):  
Claire M. Kunkle ◽  
Jordan P. Mizerak ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Heat Transfer Performance ◽  
Nucleate Boiling ◽  
Contact Angles ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wetted Area ◽  
Aluminum Surfaces

The development of hydrophilic surface coatings for enhanced wetting characteristics has led to improvement in heat transfer metrics like impinging droplet vaporization time and the heat transfer coefficient. Hydrothermal synthesis, a method of developing hydrophilic surfaces, has been previously shown to produce high performing heat transfer surfaces on copper substrates [1]. Our study applied this production method to aluminum substrates, which have the advantage of being cheaper, lighter, and a more widely used for heat sinks than copper. Previous experiments have shown that water droplets on ZnO nanostructure coated surfaces, at low superheats, evaporate via thin film evaporation rather than nucleate boiling. This leads to heat transfer coefficients as much as three times higher than nucleate boiling models for the same superheat. Our nanocoated aluminum surfaces exhibit superhydrophilicity with an average droplet liquid film thickness of 20–30 microns, which can produce heat transfer coefficients of over 25 kW/m2K. This study discusses characterization of ZnO nanostructured aluminum surfaces to better understand the related mechanisms which lead to such high heat transfer performance. All ZnO nanostructured aluminum surfaces produced for this study exhibited superhydrophilicity, with sessile droplet contact angles of less than 5 degrees. The challenge of achieving accuracy for such low contact angles led to the development of a new wetting metric related to the droplet’s wetted area on a surface rather than the contact angle. This new metric is predicated on the the fact that heat transfer performance is directly related to this wetted area, thickens, and shape of the expanding droplet footprint. Shape irregularity of droplets on these superhydrophilic surfaces is discussed in this study, where there appears to be advantages to irregular spreading compared with surfaces that produce symmetric radial spreading. One form of irregular spreading consists of liquid droplets spreading out both on top of the surface and within the microstructure of the surface coating. The liquid within the microstructure forms films less than 5 microns thick, making local heat transfer coefficients of greater than 100 kW/m2K possible. SEM microscope imaging provided additional insight to the underlying mechanisms which cause these surfaces to produce such exceptional spreading as well as irregular spreading, resulting in very good heat transfer performance. Experimental work was coupled with computational analysis to model the contact line of the droplet footprint. Image processing of experimental photos helps to analyze spreading characteristics, which can be directly related to heat transfer due to film thickness at various points during spreading. Approaches used to characterize these superhydrophilic surfaces advance understanding of the connections between nanoscale structural elements and macroscale performance characteristics in heat transfer. This understanding can reveal key insights for developing even better high performance surfaces for a broad range of applications.

Experimental Investigation of Single-Phase Microjet Array Impingement Cooling

2009 ◽  
Author(s):  
Eric A. Browne ◽  
Gregory J. Michna ◽  
Michael K. Jensen ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Single Phase ◽  
Heat Transfer Performance ◽  
Deionized Water ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Average Heat ◽  
Heat Transfer Coefficients

The heat transfer performance of two microjet arrays using degassed deionized water was investigated. The in-line jet arrays had a spacing of 250 μm, a standoff of 200 μm, and diameters of 54 and 112 μm. Average heat transfer coefficients were obtained for 150 < Red < 3300 and ranged from 80,000 to 414,000 W/m2-K. A heat flux of 1,110 W/cm2 was attained with 23 °C water and a surface temperature of 50 °C.

Experimental Investigation of Single-Phase Microjet Array Heat Transfer

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Eric A. Browne ◽  
Gregory J. Michna ◽  
Michael K. Jensen ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Heat Transfer Performance ◽  
Deionized Water ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Number Range ◽  
Average Heat ◽  
Submerged Jet ◽  
Heat Transfer Coefficients

The heat transfer performance of two microjet arrays was investigated using degassed deionized water and air. The inline jet arrays had diameters of 54 μm and 112 μm, a spacing of 250 μm, a standoff of 200 μm (S/d=2.2 and 4.6, H/d=1.8 and 3.7), and jet-to-heater area ratios from 0.036 to 0.16. Average heat transfer coefficients with deionized water were obtained for 150≤Red≤3300 and ranged from 80,000 W/m2 K to 414,000 W/m2 K. A heat flux of 1110 W/cm2 was attained with 23°C inlet water and an average surface temperature of 50°C. The Reynolds number range for the same arrays with air was 300≤Red≤4900 with average heat transfer coefficients of 2500 W/m2 K to 15,000 W/m2 K. The effect of the Mach number on the area-averaged Nusselt number was found to be negligible. The data were compared with available correlations for submerged jet array heat transfer.

Enhanced Flow Boiling Over Open Microchannels With Uniform and Tapered Gap Manifolds

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Satish G. Kandlikar ◽  
Theodore Widger ◽  
Ankit Kalani ◽  
Valentina Mejia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Flow boiling in microchannels has been extensively studied in the past decade. Instabilities, low critical heat flux (CHF) values, and low heat transfer coefficients have been identified as the major shortcomings preventing its implementation in practical high heat flux removal systems. A novel open microchannel design with uniform and tapered manifolds (OMM) is presented to provide stable and highly enhanced heat transfer performance. The effects of the gap height and flow rate on the heat transfer performance have been experimentally studied with water. The critical heat fluxes (CHFs) and heat transfer coefficients obtained with the OMM are significantly higher than the values reported by previous researchers for flow boiling with water in microchannels. A record heat flux of 506 W/cm2 with a wall superheat of 26.2 °C was obtained for a gap size of 0.127 mm. The CHF was not reached due to heater power limitation in the current design. A maximum effective heat transfer coefficient of 290,000 W/m2 °C was obtained at an intermediate heat flux of 319 W/cm2 with a gap of 0.254 mm at 225 mL/min. The flow boiling heat transfer was found to be insensitive to flow rates between 40–333 mL/min and gap sizes between 0.127–1.016 mm, indicating the dominance of nucleate boiling. The OMM geometry is promising to provide exceptional performance that is particularly attractive in meeting the challenges of high heat flux removal in electronics cooling applications.

Experimental Investigation of Evaporation Heat Transfer Inside Horizontal Micro-Fin Tubes

2016 ◽  
Author(s):  
Xu Chen ◽  
Pengfei Mi ◽  
Peter R. N. Childs ◽  
Ekaterina Sokolova ◽  
Wei Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Geometric Parameters ◽  
Transfer Performance ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Fin Tubes

Tubes with their features optimized to enhance heat transfer are routinely used in industry. A series of experimental investigations of evaporation heat transfer of widely used refrigerants inside a horizontal micro-fin cooper tube have been conducted and are reported here. The micro-fin tubes have different geometric parameters with inner diameter ranging from 4.98mm to 7.14mm. The helix angle of the tested tubes ranges from 18.858° to 35°. The apex angle of the tested tubes ranges from 11° to 40°. In addition, other geometric parameters of the tubes vary, such as the fin height, fin pitch and starts. Evaporation heat transfer experiments were conducted with the tubes and the working fluids include R22, R32 and R410A. The evaporation experiments were taken at a constant temperature of 6 °C for R22 and R410A, but 10 °C for R32. Moreover, the working conditions of the experiments varied with the mass flux ranging from 100 kg/(m2.s) to 400 kg/(m2.s). For the evaporation experiments, the inlet vapor quality is set as 0.1, while the outlet vapor quality is set as 0.9. The experimental data reveals that tubes with different geometric parameters have different heat transfer performance. The heat transfer coefficients, the reduced pressure and the changing trend of the heat transfer coefficients vary among these tubes. The experimental data has been compared with available models in the literature and an analysis of the effect of geometric parameters on the performance of the tubes undertaken. The influence of each geometric parameter on the heat transfer performance of the micro-fin tube has been analyzed and is reported.

Heat Transfer Performance for Helium Gas Flowing in a Minichannel With Different Inner Diameters

2021 ◽  
Author(s):  
Feng Xu ◽  
Qiusheng Liu ◽  
Makoto Shibahara
Keyword(s):  
Heat Transfer ◽  
Transfer Process ◽  
Heat Transfer Performance ◽  
Heat Transfer Process ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Helium Gas ◽  
Inner Diameter

Abstract The high heat load on the first wall of the helium cooled blanket is removed by tube flow of helium gas. Heat transfer augmentation is considered to be acquired by downsizing of channels. Therefore, this paper experimentally studied the influence of inner diameter on the heat transfer performance of helium gas flowing in a minichannel. The helium gas flowed in the small platinum tubes with the inner diameters of 0.8 mm and 1.8 mm, respectively. The heat generation rate of the tube was controlled by a heat input subsystem and raised with an exponential equation. The surface temperature and heat flux of the tubes were obtained under a wide range of e-folding time at different flow velocities. The heat transfer coefficients of different inner diameter tubes were compared at the same conditions. The heat transfer performance of the 0.8 mm-diameter tube was compared with a classical correlation. The experimental results showed that the heat transfer performance in the minichannel is better than a conventional large-diameter tube. The heat transfer coefficients of the 0.8 mm-diameter tube were higher than those of the 1.8 mm-diameter tube. The heat transfer process was enhanced with reducing the inner diameter of the minichannel. The heat transfer process was divided into two parts including transient and quasi-steady-state regions.

Local Heat Transfer in a Rotating Serpentine Flow Passage

1992 ◽  
Vol 114 (2) ◽  
pp. 354-361 ◽  
Author(s):  
Wen-Jei Yang ◽  
Nengli Zhang ◽  
Jeff Chiou
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Flow Passage ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation

An experimental study is performed on the internal cooling of a rotating serpentine flow passage of square cross section with throughflow. The test section is not proceeded by a hydrodynamic calming region, i.e., a leading arm, and is rotated at low Rossby numbers. The local heat transfer coefficients along the flow passage, including the leading wall, trailing wall, and sidewalls, are determined together with the circumferentially averaged values. The Reynolds, Rossby, and rotating Rayleigh numbers are varied to determine their effects on heat transfer performance. It is disclosed that heat transfer augmentation is significant at all sharp turns due to the presence of strong secondary flow. The rotational effect is very obvious and complicated in the local heat transfer performance but it is very minor on the average heat transfer performance. The throughflow rate plays an important role on the heat transfer performance. The results may serve as a baseline for comparison with the results from a model with a leading arm to determine the effects of a hydrodynamic calming section on the heat transfer performance of a rotating serpentine flow passage.

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