Advanced Loop Thermosiphon With Check Valve (ALT/CV): Thermal Performance and Behavior

2020 ◽  
Vol 10 (2) ◽  
pp. 283-295
Author(s):  
Khridsadakhon Booddachan ◽  
Nipon Bhuwakietkumjohn ◽  
Thanya Parameethanuwat

Nanofluids (NFs) are an attractive alternative to traditional working fluids for thermosiphons, but the solid nanoparticles (NPs) within the NF can agglomerate and reduce the thermal performance. This study focused on clarifying the effect of a NF with surfactants on the heat transfer characteristics of an advanced loop thermosiphon with a check valve (ALT/CV). In an experiment, the ALT/CV was filled with different working fluids at filling ratios of 30%, 50%, and 80% with respect to the evaporator volume. Heat was supplied at 20%, 40%, 60%, 80%, and 100% of the heater output (2000 W). Five working fluids were considered: deionized (DI) water, a DI water-based NF with 0.5 wt% silver NPs, and the same NF containing 0.5, 1, and 1.5 wt% oleic acid (OA) and potassium oleate (OAK+) as surfactants. The results showed that the ALT/CV provided a better heat transfer performance than a normal thermosiphon. The maximum heat transfer rate was achieved with the NF containing 0.5 wt% silver NPs and 1 wt% OAK+. The NF containing OAK+ demonstrated a heat transfer rate approximately 80% higher than that of the DI water

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3711
Author(s):  
Asifa ◽  
Talha Anwar ◽  
Poom Kumam ◽  
Zahir Shah ◽  
Kanokwan Sitthithakerngkiet

In this modern era, nanofluids are considered one of the advanced kinds of heat transferring fluids due to their enhanced thermal features. The present study is conducted to investigate that how the suspension of molybdenum-disulfide (MoS2) nanoparticles boosts the thermal performance of a Casson-type fluid. Sodium alginate (NaAlg) based nanofluid is contained inside a vertical channel of width d and it exhibits a flow due to the movement of the left wall. The walls are nested in a permeable medium, and a uniform magnetic field and radiation flux are also involved in determining flow patterns and thermal behavior of the nanofluid. Depending on velocity boundary conditions, the flow phenomenon is examined for three different situations. To evaluate the influence of shape factor, MoS2 nanoparticles of blade, cylinder, platelet, and brick shapes are considered. The mathematical modeling is performed in the form of non-integer order operators, and a double fractional analysis is carried out by separately solving Caputo-Fabrizio and Atangana-Baleanu operators based fractional models. The system of coupled PDEs is converted to ODEs by operating the Laplace transformation, and Zakian’s algorithm is applied to approximate the Laplace inversion numerically. The solutions of flow and energy equations are presented in terms of graphical illustrations and tables to discuss important physical aspects of the observed problem. Moreover, a detailed inspection on shear stress and Nusselt number is carried out to get a deep insight into skin friction and heat transfer mechanisms. It is analyzed that the suspension of MoS2 nanoparticles leads to ameliorating the heat transfer rate up to 9.5%. To serve the purpose of achieving maximum heat transfer rate and reduced skin friction, the Atangana-Baleanu operator based fractional model is more effective. Furthermore, it is perceived that velocity and energy functions of the nanofluid exhibit significant variations because of the different shapes of nanoparticles.


Author(s):  
M. Favre-Marinet ◽  
S. Le Person ◽  
A. Bejan

Experimental investigations of the flow and the associated heat transfer were conducted in two-dimensional microchannels in order to test possible size effects on the laws of hydrodynamics and heat transfer and to infer optimal conditions of use from the measurements. The test section was designed to modify easily the channel height e between 1 mm and 0.1 mm. Measurements of the overall friction factor and local Nusselt numbers show that the classical laws of hydrodynamics and heat transfer are verified for e > 0.4 mm. For lower values of e, a significant decrease of the Nusselt number is observed, whereas the Poiseuille number continues to have the conventional value of laminar developed flow. The transition to turbulence is not affected by the channel size. For fixed pressure drop across the channel, a maximum of heat transfer rate density is found for a particular value of e. The corresponding dimensionless optimal spacing and heat transfer rate density are in very good agreement with the predictions of Bejan and Sciubba (1992). This paper is the first time that the optimal spacing between parallel plates is determined experimentally.


2019 ◽  
Vol 25 (8) ◽  
pp. 39-51
Author(s):  
Nassr Fadhil Hussein ◽  
Abdulrahman Shakir Mahmood

Enhancement of heat transfer in the tube heat exchanger is studied experimentally by using discrete twisted tapes. Three different positions were selected for inserting turbulators along tube section (horizontal position by α= 00, inclined position by α= 45 0 and vertical position by α= 900). The space between turbulators was fixed by distributing 5 pieces of these turbulators with pitch ratio    PR = (0.44). Also, the factor of constant heat flux was applied as a boundary condition around the tube test section for all experiments of this investigation, while the flow rates were selected as a variable factor (Reynolds number values vary from 5000 to 15000). The results show that using discrete twisted tapes enhances the heat transfer rate by about 60.7-103.7 % compared with plane tube case. Also, inserting turbulators with inclined position offers maximum heat transfer rate by 103.7%.  


Author(s):  
Kieran Hanly ◽  
Edmond Walsh ◽  
Ronan Grimes

Demands for increased functionality from mobile electronic products have led to an increase in the amount of heat that needs to be dissipated. The authors propose a novel mini-heatsink to meet the growing power density needs of the miniature electronics market. This paper looks at the optimisation of a miniature radial flow heatsink with laminar forced convection flow originating from the center. Two single length scale fins positioned at different angles were used to simulate a segment of the heatsink. A Labview PID program was used to monitor and maintain the temperature of these fins. The optimum angle at which maximum heat transfer occurred was determined as a function of pressure drop. The design was varied using the multiscale approach by inserting fins of a smaller length scale into regions of underutilised flow at the exit to achieve the highest heat transfer rate while simultaneously minimising the viscous drag. This method is in contrast to previous work where investigators inserted smaller length scales into the inlet of the original architecture in the regions of unused (isothermal) flow. Non-dimensional results are presented which show increased heat transfer with the addition of smaller length scales. This paper concludes that the multiscale design feature increased the heat transfer rate.


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