Sliding bubble dynamics and the effects on surface heat transfer
An investigation into the effects of a single sliding air bubble on heat transfer from a submerged, inclined surface has been undertaken. Existing literature has shown that both vapour and gas bubbles can increase heat transfer rates from adjacent heated surfaces. However, the mechanisms involved are complex and dynamic and in some cases poorly understood. The present study utilises high speed, high resolution, infrared thermography and video photography to measure two dimensional surface heat transfer and three dimensional bubble position and shape. This provides a unique insight into the complex interactions at the heated surface. Bubbles of volume 0.05, 0.1, 0.2 and 0.4 ml were released onto a surface inclined at 30 degrees to horizontal. Results confirmed that sliding bubbles can enhance heat transfer rates up to a factor of 9 and further insight was gained about the mechanisms behind this phenomenon. The enhancement effects were observed over large areas and persisted for a long duration with the bubble exhibiting complex shape and path oscillations. It is believed that the periodic wake structure present behind the sliding bubble affects the bubble motion and is responsible for the heat transfer effects observed. The nature of this wake is proposed to be that of a chain of horseshoe vortices.
A modified wall boiling model considering sliding bubbles based on the RPI wall boiling model
Abstract The bubble sliding is an important phenomenon in subcooled boiling flow, which has a significant influence to heat transfer, while the RPI wall boiling model does not consider the influence of sliding bubbles directly. This paper proposes a modified wall boiling model considering the sliding bubbles, and the simulation results of the modified model are compared with the experimental data to verify the accuracy of the model. According to the results, the modified model is applicable for the mass flux from 648.4 to 1630 kg/(m2•s), with the heat flux range of 227 to 306 kW/m2, the inlet subcooled temperature range of 30 to 50 K and the pressure range of 0.2 to 0.4 MPa. In addition, bubble departure diameter, bubble lift-off diameter, bubble sliding distance and the distribution of heat flux are discussed in this paper.
Warm Hands in Cold Age – On the Need of a New World Order of Care
The world is aging as fertility and mortality are both decreasing. This article focuses on practical care work for the elderly. Such work is done primarily by women even though a larger portion than previously is paid rather than unpaid. All over the world, most elderly care work is organized within the family, most often unpaid. Men receive more care from partners than women, while women receive more care from female relatives. When care work is paid, the payment is generally low. A comparison between Germany, Spain, and Sweden demonstrates similar gender patterns, even though the role of the state in supporting care differs considerably as do care workers' conditions. The sustainability of today's distribution and organization of care work is questioned as the need for care increases, and the possibility of more equal sharing of care work between women and men is explored.