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  • 201.
    Su, Chang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Potential of natural refrigerant in China, the case of the heat pump market2016In: Refrigeration Science and Technology, International Institute of Refrigeration , 2016, p. 341-347Conference paper (Refereed)
    Abstract [en]

    Heat pumps is regarded as renewable technology for heating systems in China. Phasing out traditional HCFC and HFC refrigerants is compulsory under various international conventions and protocols. This paper presents the current application status for R744 (carbon dioxide / CO2), R290 (propane) and R717 (ammonia / NH3). The potential of each natural refrigerant in the heat pump market is analyzed from the perspective of policy makers, manufacturers and end-users. The analysis shows that CO2, propane and ammonia are still at early stage of commercialization, while propane is the most promising candidate among the three. Finally, this paper concludes that there is a significant potential for natural refrigerant on the Chinese heat pump market. As technology advances, national regulations are enforced and national standards revised, choosing natural refrigerant will become both technically and economically feasible.

  • 202. Utomo, Adi T.
    et al.
    Haghighi, Ehsan B.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Zavareh, Ashkan I. T.
    Ghanbarpourgeravi, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Poth, Heiko
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pacek, Andrzej W.
    The effect of nanoparticles on laminar heat transfer in a horizontal tube2014In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 69, p. 77-91Article in journal (Refereed)
    Abstract [en]

    Heat transfer coefficient in laminar flow of water-based alumina, titania and carbon nanotube nanofluids in a straight pipe with constant heat flux at the wall have been investigated independently by two universities. The nanoparticles affect the thermo-physical properties of the suspensions, however, nanopartides presence and movement due to Brownian diffusion and thermophoresis seemed to have insignificant effect on heat transfer coefficient. The Nusselt number of all investigated nanofluids followed standard heat transfer correlations developed for liquids within +/- 10% suggesting that all investigated nanofluids can be treated as homogenous fluids. Different methods of comparison between heat transfer coefficient in nanofluids and base fluid are also critically discussed.

  • 203.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. KTH.
    Chiu, Justin NingWei
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Experimental investigation on cylindrically macro-encapsulated latent heat storage for space heating applications2019In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 182, p. 166-177Article in journal (Refereed)
    Abstract [en]

    The integration of latent heat thermal energy storage (LHTES) units with heating systems in buildings is regarded as a promising technology for heating load management; however, so far a limited number of experimental studies have been reported that focus on space heating applications on a representative scale. In this study, we develop and test a 0.38 m3 LHTES unit containing cylindrically macro-encapsulated phase change materials (PCMs) with a melting temperature range of 44–53 °C and with gross mass of 154 kg. The unit has been tested with two tank orientations, horizontal and vertical. In the horizontal orientation tests, parametric studies show that increasing the difference between heat transfer fluid (HTF) supply temperatures and phase-change temperatures of PCMs, as well as increasing HTF flowrates, can both reduce the complete melting/solidification and complete charging/discharging time. Non-linear charging/discharging rates in PCMs are observed. The vertical orientation enables the forming of either a stratified or mixed flow regime in the tank. For charging, the stratified flow provides higher charging rates in PCMs compared to the mixed flow. When discharging the unit with a stratified HTF flow at 35 °C, lower HTF flowrates prolong the discharging time during which the released heat sustains an outlet temperature above 45 °C. Finally, comparisons between horizontal and vertical orientation tests reveal that although the vertical orientation can shorten the charging/discharging time by up to 20% for the entire unit to reach an energy density of 30 kWh/m3, it leads to decrease in PCM thermal capacity by at most 8.2%. The speculated cause of this loss is phase segregation suggested by observed fluid motions in PCM cylinders. This study comprehensively characterizes an LHTES unit providing insights to optimizing its operating strategies considering its coupling with space heating systems.

  • 204.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Navarro-Peris, Emilio
    Piscopiello, Salvatore
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Corberán, José M.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Large-Capacity Propane Heat Pumps for DHW Production in Residential Buildings2018In: Refrigeration Science and Technology, Valencia, Spain, 2018, p. 1222-1230Conference paper (Refereed)
    Abstract [en]

    Using heat pump technology to provide Space Heating (SH) and to produce Domestic Hot Water (DHW) for residential buildings has been widely applied during past decades. In this study, two scenarios adopting large-capacity propane heat pumps are defined and evaluated. These two scenarios, which are named after Scenario A and Scenario B respectively, provide SH and DHW either separately by two units or integrally by one unit. The COP1s of two scenarios are compared based on the simulation results from experimentally validated models. The results show that two scenarios have almost equal efficiency; the relative difference is within 6%. In the optimization analysis of Scenario B, varying DHW heating capacity produced by the desuperheater in the heat pump is modelled. The DHW demand ratio varies from approximately 9% to 20% with no detectable influences on the COP1. The corresponding COP1s and temperature profiles in the heat exchangers are demonstrated. The simulation results indicate that increasing DHW capacity in Scenario B can narrow down the temperature approach in the condenser and insignificantly improves the overall COP1s.

  • 205.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mazzotti, Willem
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Björn, Palm
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Performance Evaluation of a Large Capacity Air-Water Heat Pump Using Propane as Refrigerant2016Conference paper (Refereed)
    Abstract [en]

    Heat pump applications working with hydrocarbons as refrigerant have been under significant development along with the gradual phasing-out of conventional HFC systems. In this study, a large capacity air-water heat pump prototype using propane as refrigerant is tested to evaluate its heating performance under different operating conditions. The experimental set-up is briefly explained. The results of the experimental investigations of the heat pump prototype are presented in terms of the COP1, heating capacity and the compressor efficiency. At the design point, the experimental COP1 and heating capacity are 3.43 and 36.59 kW respectively. Experimental results for all test conditions are compared to simulation results generated from the model, which is created by the software IMST-ART. The model is validated through comparisons of those parameters since a good agreement between simulated and experimental data have been found. The maximum discrepancies of COP1 and heating capacity are around 5% and 10% respectively.

  • 206. Yang, Z. L.
    et al.
    Kazachkov, Ivan
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn E.
    KTH, Superseded Departments, Energy Technology.
    An analytical model on the instability of thin film flow dynamics in a micro-gap channel2001In: Journal of Enhanced Heat Transfer, ISSN 1065-5131, E-ISSN 1563-5074, Vol. 8, no 3, p. 175-184Article in journal (Refereed)
    Abstract [en]

    In this paper, a mathematical model is developed to investigate the liquid film dynamics in micro-gap channels, in which a liquid film flows along the wall surfaces and gas flows in the channel core. It is assumed that the Reynolds numbers for both gas and liquid flow are very low and there is no mass transfer at the interface. The instability behavior of the interface of two-phase flow is analysed by employing Stoke's equations, which are solved by non-linear boundary conditions. The solution shows that if the perturbations at the interface are small, they do not grow, however, kinematic waves still exist. All perturbations on the film surface are convoyed by gas flow without growing or decreasing. From the analytical results it is also found that in a micro-gap-channel in the case of constant pressure gradient, the perturbations on both sides of the gap interface are strictly interconnected, and their relationship has been obtained.

  • 207. Yang, Z. L.
    et al.
    Palm, Björn E.
    KTH, Superseded Departments, Energy Technology.
    Sehgal, B. R.
    Numerical simulation of bubbly two-phase flow in a narrow channel2002In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 45, no 3, p. 631-639Article in journal (Refereed)
    Abstract [en]

    An advanced numerical simulation method on fluid dynamics - lattice-Boltzmann (LB) method is employed to simulate the movement of Taylor bubbles in a narrow channel, and to investigate the flow regimes of two-phase flow in narrow channels under adiabatic conditions. The calculated average thickness of the fluid film between the Taylor bubble and the channel wall agree well with the classical analytical correlation developed by Bretherton. The numerical simulation of the behavior of the flow regime transition in a narrow channel shows that the body force has significant effect on the movement of bubbles with different sizes. Smaller body force always leads to the later coalescence of the bubbles, and decreases the flow regime transition time. The calculations show that the surface tension of the fluid has little effect on the flow regime transition behavior within the assumed range of the surface tension. The bubbly flow with different bubble sizes will gradually change into the slug flow regime. However, the bubbly flow regime with the same bubble size may be maintained if no perturbations on the bubble movement occur. The slug flow regime will not change if no phase change occurs at the two-phase interface.

2345 201 - 207 of 207
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