Size Of Heating Surface Research Articles

Structure of High‐Performance Evaporators for Space Application

A new structure of cold plates, where an unheated auxiliary channel is installed to supply liquid directly to the bottom of coalesced flattened bubbles in a narrow heated channel, is tested to investigate the increase in critical heat flux. Assuming the application to the laser solar power system, a large heating surface with a length of 150 mm in the flow direction is employed, and a narrow channel structure is adopted to reduce the size of cold plates, where the gap sizes are selected as 5 mm and 2 mm. Experiments are performed for water as a test liquid at inlet subcooling of 15 K under near atmospheric pressure. Inlet liquid velocity is varied from 0.065 m/s to 0.6m/s for the upward flow on ground. A value of critical heat flux of 2.2 x 10(6) W/m2 is obtained for 5-mm gap size at the inlet velocity of 0.2 m/s. At low liquid flow rate, the structure realizes the CHF values larger by 2.5 times than those for the normal heated channel without additional liquid supply. A new method to evaluate the performance of cold plates is proposed to take account of the variation in the size of heating surface, inlet liquid velocity, and subcooling that influence the CHF values. The validity of the proposed structure of the cold plate for the increase in critical heat flux is confirmed.

Investigation of Surface Film Boiling under Free Convection : (1st Report, An Experiment on Small Wires)

The experimental study on film boiling was undertaken to clarify how the behavior of bubble formation on the liquid-vapor interface depends upon the degree of subcooling and the size of heating surface, and to determine the influence of the stirring action of bubbles on film boiling heat transfer. The ranges of the experiment are as follows. Heating surface : horizontal platinum-wire of 0.5, 0.7 and 1.0 mm in diameter Test fluid : H2O, CCl4 Heat flux : (20∼80)×104 kcal/m2hr for H2O, (8∼50)×104 kcal/m2hr for CCl4 Degree of subcooling : 0∼15°C From the experiment performed, the following facts were found : (I) the assumption of smooth liquid-vapor interface, as often adopted in the theoretical analysis, can not be applied for low degree of subcooling ; (II) the behavior of bubble formation is affected by the size of heating surface ; (III) the distance between the bubble formation sites is larger than the critical and dangerous wave length determined by Taylor's instability ; and (IV) the effect of the size of heating surface on heat transfer coefficient can be correlated in a unified law by introducing the concept of equivalent Prandtl number.

Growth and Collapse of Bubbles in Nucleate Boiling

A number of theoretical and experimental studies on the growth and collapse of bubbles have been made in order to clarify the boiling phenomena. Most of those experiments, however, have been made with heating surfaces of smaller size than bubble diameter. Authors have been doubtful of the validity of applying such experimental results to boiling with a larger heating surface. In order to clarify the dependence of the bubble growth and collapse upon the shape and size of heating surface, they carried out experiments by means of the heating surfaces of horizontal circular brass plates 100 mm and 140 mm in diameter respectively and of horizontal small platinum wire 0.5 mm in diameter and found that : (1) Bubble growth and collapse are independent of heat flux. (2) Bubble collapse is strongly influenced by the degree of subcooling. (3) Bubble growth and collapse which essentially dominate the boiling heat transfer are considerably affected by the size of heating surface.

Growth and Collapse of Bubbles in Nucleate Boiling

A number of theoretical and experimental studies on growth and collapse of bubbles have been made in order to clarify the boiling phenomena. Almost of those experiments, however, have been made with heating surface of smaller size than bubble diameter. Authors have been doubtful of the validity of applying such experimental results to boiling with larger heating surface. In order to clarify the dependence of the bubble growth and collapse upon the shape and size of heating surface, they carried out experiments by means of heating surfaces of horizontal circular brass plates 10 cm and 14 cm in diameter respectively and of horizontal small platinum wire 0.5 nm in diameter. From their experiments following facts were made clear. (1) Bubble growth and collapse are independent of heat flux. (2) Bubble collapse is strongly influenced by the degree of subcooling. (3) Bubble growth and collapse which essentially dominate boiling heat transfer are considerab1y affected by the size of heating surface. According to the above-mentioned facts, it may be concluded that one must be careful of applying the experimental results with a heating surface of a size smaller than bubble diameter to boiling with a larger heating surface.