Topic
Heat transfer
About: Heat transfer is a research topic. Over the lifetime, 181795 publications have been published within this topic receiving 2923586 citations. The topic is also known as: heat exchange.
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TL;DR: In this article, the authors used a trans-critical CO 2 process for tap water heating and achieved a heating-COP of 4.3 for an Oslo climate, using ambient air as heat source.
Abstract: CO 2 is one of the few non-toxic and non-flammable working fluids that do not contribute to ozone depletion or global warming, if leaked to the atmosphere. Tap water heating is one promising application for a trans-critical CO 2 process. The temperature glide at heat rejection contributes to a very good temperature adaptation when heating tap water, which inherits a large temperature glide. This, together with efficient compression and good heat transfer characteristics of CO 2 , makes it possible to design very efficient systems. A heating-COP of 4.3 is achieved for the prototype when heating tap water from 9°C to 60°C, at an evaporation temperature of 0°C. The results lead to a seasonal performance factor of about 4 for an Oslo climate, using ambient air as heat source. Thus, the primary energy consumption can be reduced with more than 75% compared with electrical or gas fired systems. Another significant advantage of this system, compared with conventional heat pump water heaters, is that hot water with temperatures up to 90°C can be produced without operational difficulties.
306 citations
TL;DR: The basic nonlinear differential equation for the velocity field f and the differential equation with variable coefficient for the temperature field @q are solved numerically by using a fourth-order Runge-Kutta integration scheme and it is shown that the heat flow is always from the stretching sheet to the fluid.
306 citations
TL;DR: In this article, the fundamental heat transfer mechanisms at PEMFC component level (including polymer electrolyte, catalyst layers, gas diffusion media and bipolar plates) are briefly reviewed and the current status of PEMF cooling technology is also reviewed and research needs are identified.
306 citations
TL;DR: In this paper, a Poisson equation is solved with appropriate boundary conditions of zero normal heat flux through the continental boundaries to obtain the ocean heat transport, and results indicate lower ocean transports than in previous residual calculations which are therefore more compatible with direct ocean estimates.
Abstract: The heat budget has been computed locally over the entire globe for each month of 1988 using compatible top-of-the-atmosphere radiation from the Earth Radiation Budget Experiment combined with European Centre for Medium Range Weather Forecasts atmospheric data. The effective heat sources and sinks (diabatic heating) and effective moisture sources and sinks for the atmosphere are computed and combined to produce overall estimates of the atmospheric energy divergence and the net flux through the Earth's surface. On an annual mean basis, this is directly related to the divergence of the ocean heat transport, and new computations of the ocean heat transport are made for the ocean basins. Results are presented for January and July, and the annual mean for 1988, along with a comprehensive discussion of errors. While the current results are believed to be the best available at present, there are substantial shortcomings remaining in the estimates of the atmospheric heat and moisture budgets. The issues, which are also present in all previous studies, arise from the diurnal cycle, problems with atmospheric divergence, vertical resolution, spurious mass imbalances, initialized versus uninitialized atmospheric analyses, and postprocessing to produce the atmospheric archive on pressure surfaces. Over land, additional problems arise from the complex surface topography, so that computed surface fluxes are more reliable over the oceans. The use of zonal means to compute ocean transports is shown to produce misleading results because a considerable part of the implied ocean transports is through the land. The need to compute the heat budget locally is demonstrated and results indicate lower ocean transports than in previous residual calculations which are therefore more compatible with direct ocean estimates. A Poisson equation is solved with appropriate boundary conditions of zero normal heat flux through the continental boundaries to obtain the ocean heat transport. Because of the poor observational data base, adjustments to the surface fluxes are necessary over the southern oceans. Error bars are estimated based on the large-scale spurious residuals over land of 30 W m−2 over 1000 km scales (1012 m2). In the Atlantic Ocean, a northward transport emerges at all latitudes with peak values of 1.1±0.2 PW (1 standard error) at 20 to 30°N. Comparable values are achieved in the Pacific at 20°N, so that the total is 2.1±0.3 PW. The peak southward transport is at 15 to 20°S of 1.9±0.3 PW made up of strong components from both the Pacific and Indian Oceans and with a heat flux from the Pacific into the Indian Ocean in the Indonesian throughflow. The pattern of poleward heat fluxes is suggestive of a strong role for Ekman transports in the tropical regions.
306 citations