World energy crisis has triggered more attention to energy saving and energy conversion systems. Enhanced surfaces for boiling are among the applications of great interest since they can improve the energy efficiency of heat pumping equipment (i.e., air conditioners, heat pumps, refrigeration machines). Methods that are used to make the state‐of‐the‐art enhanced surfaces are often based on complicated mechanical machine tools, are quite material‐consuming and give limited enhancement of the boiling heat transfer. Here, we present a new approach to fabricate enhanced surfaces by using a simple electrodeposition method with in‐situ grown dynamic gas bubble templates. As a result, a well‐ordered 3D macro‐porous metallic surface layer with nanostructured porosity is obtained. Since the structure is built based on the dynamic bubbles, it is perfect for the bubble generation applications such as nucleate boiling. At heat flux of 1 W  cm‐2, the heat transfer coefficient is enhanced over 17 times compared to a plain reference surface. It's estimated that such an effective boiling surface would improve the energy efficiency of many heat pumping machines with 10–30%. The extraordinary boiling performance is explained based on the structure characteristics.

This paper seeks to shed light on the question whether a magnetic household refrigerator with permanent magnets is more environmentally friendly than a conventional, vapor-compression refrigerator. Life cycle assessment has been used as a tool to investigate the environmental impacts associated with the life cycle of a magnetic refrigerator. The results of the assessment have been compared with those of a conventional, vapor-compression refrigerator with the same functionality. The comparison reveals that the magnetic refrigeration has higher environmental impacts mainly due to the use of rare-earth metals used in the magnet material. The possibility of compensating for this shortcoming through reuse of the magnetic materials or improving the design and efficiency of the magnetic refrigerator has been examined. In addition, the effect of the electricity mix consumed during the use phase, as one of the key factors determining the life cycle environmental impacts, has been investigated.

A visualization study was conducted with the aim of deepening the understanding of the boiling mechanism in a dendritic and microporous copper structure for enhanced boiling heat transfer. The unique structure has earlier been shown to enhance heat transfer in pool boiling applications as well as in convective boiling in both small and large channels. Pool boiling tests were conducted in R134a and in the dielectric fluid FC-72 and were visualized with a high speed imaging system. Data on bubble size, bubble frequency density, heat transfer coefficient and the latent and sensible heat flux contributions were collected and calculated at heat flux varying between 2 and 15 W/cm 2 . The enhanced surface produces smaller bubbles and sustains a high bubble frequency density in both fluids, even at low heat flux. An enhanced latent heat transfer mechanism of up to 10 times, compared to that of a plain reference surface, is the main reason for the improved boiling heat transfer performance on the enhanced surface. The data also suggests that the high nucleation bubble frequency density leads to increased bubble pumping action and thus enhancing single phase convection of up to 6 times. The results in this study highlight the importance of both two and single-phase heat transfer within the porous structure. KEYWORDS

Presented research is an experimental study of the performance of a standard plate heat exchanger evaporator, both with and without a novel nano- and microporous copper structure, used to enhance the boiling heat transfer mechanism in the refrigerant channel. Various distance frames in the refrigerant channel were also employed to study the influence of the refrigerant mass flux on two-phase flow heat transfer. The tests were conducted at heat fluxes ranging between 4.5 kW/m2 and 17 kW/m2 with 134a as refrigerant. Pool boiling tests of the enhancement structure, under similar conditions and at various surface inclination angles, were also performed for reasons of comparison. The plate heat exchanger with the enhancement structure displayed up to ten times enhanced heat transfer coefficient in the refrigerant channel, resulting in an improvement in the overall heat transfer coefficient with over 100%. This significant boiling enhancement is in agreement with previous pool boiling experiments and confirms that the enhancement structure may be used to enhance the performance of plate heat exchangers. A simple superposition model was used to evaluate the results, and it was found that, primarily, the convective boiling mechanism was affected by the distance frames in the standard heat exchanger. On the other hand, with the enhanced boiling structure, variations in hydraulic diameter in the refrigerant channel caused a significant change in the nucleate boiling mechanism, which accounted for the largest effect on the heat transfer performance.

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