Numerical model of a parallel flow minichannel evaporator with new flow boiling heat transfer correlation

2016 ◽  
Vol 63 ◽  
pp. 1-13 ◽  
Author(s):  
Zhen Tian ◽  
Lei Ma ◽  
Bo Gu ◽  
Lin Yang ◽  
Fen Liu
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Parallel Flow ◽  
Heat Transfer Correlation ◽  
Flow Boiling Heat Transfer

Numerical Simulation of Saturated Flow Boiling Heat Transfer of Ammonia/Water Mixture in Bubble Pumps for Absorption–Diffusion Refrigerators

2013 ◽  
Vol 6 (1) ◽  
Author(s):  
Soo W. Jo ◽  
S. A. Sherif ◽  
W. E. Lear
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Numerical Model ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Water Mixture ◽  
Saturated Flow ◽  
Ammonia Water ◽  
Flow Boiling Heat Transfer ◽  
Bubble Pump

This paper addresses a multidimensional numerical simulation of the saturated flow boiling heat transfer in bubble pumps of absorption–diffusion refrigeration cycles. The bubble pump with a shape of vertical tube is subjected to a uniform heat flux from the tube outer wall surface along the entire pump length. As the bubble pump wall is heated, a nonazeotropic mixture of saturated strong ammonia/water entering into the bubble pump transforms to ammonia vapor and diluted ammonia/water mixture. The weaker ammonia/water mixture is lifted by the buoyant force created by the ammonia vapor. The present multidimensional numerical simulation was performed using the two-fluid model with the equilibrium phase change model and the standard k-ε turbulence model. The numerical model designed for the present simulation was validated through a comparative study referring to available experimental data. The present numerical model was compared with the one-dimensional model to assess its applicability for numerical simulation of the saturated flow boiling heat transfer in bubble pumps. As a result, it is seen that the present numerical model predicts the performance of ammonia/water bubble pumps more realistically than the one-dimensional model. In addition, the effects of the bubble pump's geometrical dimension and heat input on the pump performance were investigated using the present numerical approach.

A Heat Transfer Correlation of Flow Boiling In Micro-Finned Helically Coiled Tube

2005 ◽  
Author(s):  
Wenzhi Cui ◽  
Longjian Li ◽  
Mingdao Xin ◽  
Tien-Chien Jen ◽  
Qinghua Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Straight Tube ◽  
Heat Transfer Correlation ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Helically Coiled Tube ◽  
Flow Boiling Heat Transfer

In the research of intube flow boiling, a widely accepted factor is that there are two main mechanisms participating in the heat transfer. One is nucleate boiling, which is dependent on the presence of active nuclei on the heated wall and the heat transfer coefficient is much influenced by the heat flux, much similar to pool boiling. In the other heat transfer mode, the boiling nuclei are fully suppressed and heat is transferred by the liquid evaporation through the interface of liquid film and vapor core. This is also called forced convective evaporation or convective boiling. In the evaporation region, the dependence of heat transfer on heat flux is not distinct and governed mainly by the mass flux and vapor quality. In the open literature on convective boiling heat transfer of refrigerant researches have been extensively conducted in straight tube. The studies, however, on two-phase flow boiling heat transfer in helically coiled tube are far less than that in straight tube. Because of the high efficiency in heat transfer and compactness in volume, helically coiled tubes are used extensively in practical industries. Therefore, it is important for application to obtain the correlations of flow boiling heat transfer coefficient in helically coiled tube. A new kind of micro-finned helically coiled tube was developed by the present authors and the flow boiling heat transfer characteristics are experimental studied in this paper, using R134a, an environment-friendly refrigerant as experimental fluid. By introducing convective boiling number NCB, as suggested by V. V. Klimenko (in Ref. [8]), the transition boundary between nucleate boiling and forced convective boiling in helically coiled tube is examined, which is much different with that in straight tube. Based on the analysis of the mechanisms of flow boiling, heat transfer correlation of the specific micro-finned helically coiled tubes is obtained, which has a mean absolute deviation of 13.8%.

Heat Transfer Correlation for Boiling Flows in Vertical Rectangular Narrow Channel

2013 ◽  
Author(s):  
Chong Chen ◽  
Puzhen Gao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Narrow Channel ◽  
Heat Transfer Correlation ◽  
Two Phase ◽  
Narrow Channels ◽  
Flow Boiling Heat Transfer

In view of the practical significance of a correlation of heat transfer coefficient in the aspect of such applications as engineering and predictive, some efforts towards correlating flow boiling heat transfer correlation for vertical rectangular narrow channels have been made in this paper. Based on analyses of existing general correlations for flow boiling heat transfer, it is found that general correlations are not suitable to predict heat transfer coefficients in narrow channels. By considering the suppression factor S and two-phase pool boiling heat transfer coefficient hnb, introducing boiling number Bo and two-phase friction multiplier ϕtt2, the Chen correlation has been modified to be used for narrow channels. The flow boiling heat transfer was the function of boiling number Bo and two-phase friction multiplier ϕtt2, the coefficients have a regular change with the increase of boiling number Bo or two-phase friction multiplier ϕtt2. A comparison of the newly developed correlation with the existing data for narrow channels shows a satisfactory agreement. The heat transfer coefficient of the narrow channel was well predicted by the new correlation and the deviation within ±20%.

Sign in / Sign up

Export Citation Format

Share Document