Experimental Study on Flow and Heat Transfer Characteristics in a Microscale Heat Exchanger

2007 ◽  
Author(s):  
Tao Wang ◽  
Xuegong Hu ◽  
Dawei Tang
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Exchanger ◽  
Thermal Resistance ◽  
Flow Rate ◽  
Laser Cooling ◽  
Cooling System ◽  
Volumetric Flow Rate ◽  
Distilled Water ◽  
Total Thermal Resistance

To solve the questions of the middle heat exchanger of space-based laser cooling system such as large heat transfer area and operating mode instability, a MC-MG (Microchannel-Microgroove) microscale heat exchanger is proposed and experimental study is carried out. The experimental results indicate that as the Reynolds number increases, the Nusselt number originally increases and then keeps constant. While adding the volumetric flow rate of distilled water in the microchannels, the total thermal resistance is first reduced and then becomes steady. With increasing the volumetric flow rate of distilled water, the total quantity of heat transfer increases first, then decreases and finally tends to be constant. The average heat transfer coefficient of the heat exchanger reaches to 1.6 × 104W/ (m2-K) and total thermal resistance is less than 0.21K/W. Therefore the solution to cooling laser with the heat exchanger is preferable.

Development of Cooling System for a Large Area at High Heat Flux by Using Flow Boiling in Narrow Channels

2009 ◽  
Author(s):  
Shinichi Miura ◽  
Yukihiro Inada ◽  
Yasuhisa Shinmoto ◽  
Haruhiko Ohta
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Mass Velocity ◽  
Cooling System ◽  
Volumetric Flow Rate ◽  
High Heat ◽  
High Heat Flux ◽  
Gap Size ◽  
Heated Channel

Advance of an electronic technology has caused the increase of heat generation density for semiconductors densely integrated. Thermal management becomes more important, and a cooling system for high heat flux is required. It is extremely effective to such a demand using flow boiling heat transfer because of its high heat removal ability. To develop the cooling system for a large area at high heat flux, the cold plate structure of narrow channels with auxiliary unheated channel for additional liquid supply was devised and confirmed its validity by experiments. A large surface of 150mm in heated length and 30mm in width with grooves of an apex angle of 90 deg, 0.5mm depth and 1mm in pitch was employed. A structure of narrow rectangular heated channel between parallel plates with an unheated auxiliary channel was employed and the heat transfer characteristics were examined by using water for different combinations of gap sizes and volumetric flow rates. Five different liquid distribution modes were tested and their data were compared. The values of CHF larger than 1.9×106W/m2 for gap size of 2mm under mass velocity based on total volumetric flow rate and on the cross section area of main heated channel 720kg/m2s or 1.7×106W/m2 for gap size of 5mm under 290kg/m2s were obtained under total volumetric flow rate 4.5×10−5m3/s regardless of the liquid distribution modes. Under several conditions, the extensions of dry-patches were observed at the upstream location of the main heated channel resulting burnout not at the downstream but at the upstream. High values of CHF larger than 2×106W/m2 were obtained only for gap size of 2mm. The result indicates that higher mass velocity in the main heated channel is more effective for the increase in CHF. It was clarified that there is optimum flow rate distribution to obtain the highest values of CHF. For gap size of 2mm, high heat transfer coefficient as much as 7.4×104W/m2K were obtained at heat flux 1.5×106W/m2 under mass velocity 720kg/m2s based on total volumetric flow rate and on the cross section area of main heated channel. Also to obtain high heat transfer coefficient, it is more useful to supply the cooling liquid from the auxiliary unheated channel for additional liquid supply in the transverse direction perpendicular to the flow in the main heated channel.

Experimental Investigation of a Packed-Bed Latent Heat Thermal Storage System With Encapsulated Phase Change Material

2014 ◽  
Author(s):  
Tanvir E. Alam ◽  
Jaspreet Dhau ◽  
D. Y. Goswami ◽  
M. M. Rahman ◽  
Elias Stefankos
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Latent Heat ◽  
Flow Rate ◽  
Storage System ◽  
Volumetric Flow Rate ◽  
Packed Bed ◽  
Heat Transfer Fluid ◽  
Encapsulated Phase Change Material ◽  
Change Material

An experimental study on a laboratory scale prototype packed-bed latent heat thermal energy storage (TES) system is presented. Spherical capsules of sodium nitrate melting point of 306°C were used as the PCM and air was used as the heat transfer fluid (HTF). The storage system was operated between 286°C to 326°C and the volumetric flow rate of the HTF was varied from 110 m3/hr to 151 m3/hr. Temperature distribution along the bed and inside the capsules was monitored continuously during charging and discharging of the system. The effect of mass flow rate of the HTF on the charging and discharging time and on the pressure drop across the bed was also evaluated.

Experimental Investigation of Spray Cooling Heat Transfer on Circular Grooved Surface

2017 ◽  
Author(s):  
Azzam S. Salman ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Cooling System ◽  
Volumetric Flow Rate ◽  
Target Surface ◽  
Spray Cooling ◽  
Operating Conditions ◽  
Low Flow ◽  
Inlet Temperature ◽  
Flow Rates

An experimental study was conducted in a closed loop spray cooling system working with deionized water as a cooling medium, to investigate the effects of surface modification on the spray cooling heat transfer enhancement in the single-phase region. Plain copper surface with diameter 1.5 cm and an enhanced surface with circular grooves were tested under different operating conditions. The volumetric flow rate of the coolant ranged from 115 mL/min to 177 mL/min., and the water inlet temperature was kept between 21–23 °C. Also, the distances between the nozzle and the target surface were varied at 8, 10, and 12 mm respectively. The results show that the distance between the nozzle and the target surface did not have a significant effect on the heat transfer performance for the low flow rates, while it has a slight effect on high flow rates for both surfaces. Also, increasing the liquid volumetric flow rate increases the amount of heat removed, and the heat transfer coefficient for both surfaces. Moreover, the maximum enhancement ratios achieved were 23.4% and 31% with volumetric flow rates of 153 mL/min, and 177 mL/min respectively.

Comprehensive Reduction of Thermal Resistance in Air Cooled Condensers

2015 ◽  
Author(s):  
Ahmad Saleh ◽  
Jayanta Kapat
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Transfer Process ◽  
Cooling System ◽  
Ambient Air ◽  
Heat Transfer Process ◽  
Air Cooling ◽  
Total Thermal Resistance ◽  
Fin Efficiency

Restriction on water consumption is becoming an increasing problem for the power generation industry. As an alternative both to once-through cooling and to surface condenser/wet-cooling tower combination, utility companies and equipment manufacturers are considering, and even implementing, air-cooled condenser (ACC). However, the industry is quite reluctant to switch over to ACC for three important reasons: (a) lower power output, (b) higher capital cost, and (c) larger physical foot-print, all because of the same reason — it is not as efficient to transfer heat from condensing steam to air as it is to transfer to water. In other words, overall thermal resistance from condensing steam to the ambient air is significantly higher than to cooling water. To get a clear and full understanding of the heat transfer process occur in air-cooling condenser, Detailed mathematical equations were derived to model the heat transfer process through the fined-tubes of the ACC. The total thermal resistance model was analyzed and investigated to identify the design components with highest affect in the process. The paper proposes a viable cooling system based on novel heat pipe technology which addresses these problems. This technology employs boiling as the means to store and transfer heat energy. A detailed mathematical set of equations was derived to model the heat pipe thermal resistance. A comparison of the heat transfer performances of the ACC technology and the proposed method is presented. The proposed cooling system suggests a solution for each of the three components of the thermal resistance, the super-hydrophobic coating of the steam ducts internal surfaces increased the condensing heat transfer rate by an order of magnitude, the proposed design of the heat pipes improved the external heat transfer, and the installation mechanism improves the fin efficiency by eliminating the contact resistance between steam duct and the heat pipe.

Effect of Additional MnFe2O4 on a Combination of EG-Water Nanofluid and Volumetric Flowrate Variations towards Heat Transfer in Shell and Tube Heat Exchanger System

2020 ◽  
Vol 851 ◽  
pp. 38-46
Author(s):  
Avita Ayu Permanasari ◽  
Fadel Fadillah ◽  
Poppy Puspitasari ◽  
Sukarni Sukarni
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Base Fluid ◽  
Volume Fraction ◽  
Volumetric Flow Rate ◽  
Shell And Tube ◽  
Water Base ◽  
Volumetric Flowrate

Nanofluid is an efficient fluid when used in heat exchanger system because of its larger thermal conductivity compared to conventional fluids such as water, oil, and ethylene glycol (EG). This research used MnFe2O4 nanoparticle due to its higher magnetic sensitivity compared to other ferrite nanoparticles and larger thermal conductivity than TiO2. This research used the MnFe2O4 nanoparticle with a combination of EG-Water base fluids in ratios of 40:60, 60:40, and 80:20. MnFe2O4 nanofluid mixed with EG-Water base fluids was made using the two-step method with 0.05% MnFe2O4 volume fraction in each base fluid ratio. This research used shell and tube type heat exchanger with heat temperature of 60°C and cold temperature of 26°C that were carried out at volumetric flowrate in each base fluid ratio for 0.22 l/m, 0.44 l/m, and 0.66 l/m. This research aimed to find the best combination ratio of EG-Water in thermophysical (thermal conductivity, specific heat, density, and viscosity) and to find the effect of volumetric flowrate variations on the heat exchange characteristics (the Reynold number, the Nusselt number, ∆T LMTD, convection coefficient, heat transfer, and overall heat transfer coefficient). The results of this research were that the sample of EG-Water with 40:60 ratio had the best heat transfer characteristics compared to samples with 60:40 and 80:20 ratios. Meanwhile, for the volumetric flow rate, a higher volumetric flow rate resulted in a larger result.

Combined Microstructure and Heat Transfer Modeling of Carbon Nanotube Thermal Interface Materials1

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Sridhar Sadasivam ◽  
Stephen L. Hodson ◽  
Matthew R. Maschmann ◽  
Timothy S. Fisher
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Finite Volume ◽  
Pressure Dependence ◽  
Matrix Material ◽  
Three Dimensional ◽  
Coarse Grain ◽  
Total Thermal Resistance ◽  
Thermal Interface ◽  
Cnt Arrays

A microstructure-sensitive thermomechanical simulation framework is developed to predict the mechanical and heat transfer properties of vertically aligned CNT (VACNT) arrays used as thermal interface materials (TIMs). The model addresses the gap between atomistic thermal transport simulations of individual CNTs (carbon nanotubes) and experimental measurements of thermal resistance of CNT arrays at mesoscopic length scales. Energy minimization is performed using a bead–spring coarse-grain model to obtain the microstructure of the CNT array as a function of the applied load. The microstructures obtained from the coarse-grain simulations are used as inputs to a finite volume solver that solves one-dimensional and three-dimensional Fourier heat conduction in the CNTs and filler matrix, respectively. Predictions from the finite volume solver are fitted to experimental data on the total thermal resistance of CNT arrays to obtain an individual CNT thermal conductivity of 12 W m−1 K−1 and CNT–substrate contact conductance of 7 × 107 W m−2 K−1. The results also indicate that the thermal resistance of the CNT array shows a weak dependence on the CNT–CNT contact resistance. Embedding the CNT array in wax is found to reduce the total thermal resistance of the array by almost 50%, and the pressure dependence of thermal resistance nearly vanishes when a matrix material is introduced. Detailed microstructural information such as the topology of CNT–substrate contacts and the pressure dependence of CNT–opposing substrate contact area are also reported.

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