| 1. |
- Arslan, Muhammad, et al.
(författare)
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Impact of Varying Load Conditions and Cooling Energy Comparison of a Double-Inlet Pulse Tube Refrigerator
- 2020
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Ingår i: Processes. - : MDPI. - 2227-9717. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- Modeling and optimization of a double-inlet pulse tube refrigerator (DIPTR) is very difficult due to its geometry and nature. The objective of this paper was to optimize-DIPTR through experiments with the cold heat exchanger (CHX) along the comparison of cooling load with experimental data using different boundary conditions. To predict its performance, a detailed two-dimensional DIPTR model was developed. A double-drop pulse pipe cooler was used for solving continuity, dynamic and power calculations. External conditions for applicable boundaries include sinusoidal pressure from an end of the tube from a user-defined function and constant temperature or limitations of thermal flux within the outer walls of exchanger walls under colder conditions. The results of the system's cooling behavior were reported, along with the connection between the mass flow rates, heat distribution along pulse tube and cold-end pressure, the cooler load's wall temp profile and cooler loads with varied boundary conditions i.e. opening of 20% double-inlet and 40-60% orifice valves, respectively. Different loading conditions of 1 and 5W were applied on the CHX. At 150 K temperature of the cold-end heat exchanger, a maximum load of 3.7 W was achieved. The results also reveal a strong correlation between computational fluid dynamics modeling results and experimental results of the DIPTR.
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| 2. |
- Ullah, Zia, et al.
(författare)
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Towards the development of sustainable tourism in pakistan : A study of the role of tour operators
- 2021
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Ingår i: Sustainability (Switzerland). - : MDPI AG. - 2071-1050. ; 13:9
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Tidskriftsartikel (refereegranskat)abstract
- The literature on sustainable tourism is scant, particularly in the least developed countries. Very few studies touch upon the concept and no holistic theoretical or conceptual frameworks around the idea of sustainable tourism have been formulated. This study aims at exploring the role of tour operators in developing sustainable tourism in Pakistan and how the tour operators (TOs) conceive their role in this regard. TOs were reached through phone calls, emails, and virtual sources as face-to-face interviews were not possible due to COVID-19 pandemic and restrictions on travel by the government. In-depth interviews were conducted to gather data. Results suggest that the TOs although realize the importance of social, environmental, and economic dimensions of tourism on the communities but have no management systems in place to cater accordingly. There are no incentives in place by the government facilitate TOs to design and implement such systems. The TOs do not select a destination based on Global Sustainable Tourism Council criterion, but rather the selection of destination is mostly demand-based and profit-oriented. The study suggests that corporate profit motive is the sole criterion for decision making and is one of the major causes impeding sustainable tourism in Pakistan. The role of TOs in developing sustainable tourism is vague as the TOs do not have any systems in place to implement sustainable models. The study recommends that efforts need to be put in place to incentivize sustainable tourism in Pakistan and proper laws should be set forth by the authorities to comply by the TOs. The role of TOs is important and understood, however, there is a need to put proper systems in place.
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