Numerical and experimental investigation of free convective heat transport for subsea heat exchangers (completed)
The goal of this project is to reach a higher level of understanding of the physics involved in heat exchange processes caused by free convection and how to maximize these. We then want to use this knowledge to improve the efficiency of the cooler.
About the project
For gas fields, sooner or later the reservoir pressure becomes too low to maintain natural flow at a satisfactory production rate. Substantial additional reserves can be secured by enhancing recovery from fields already in operation by using increased gas recovery measures. Subsea gas compression has matured as a field development element, the benefit potential of this technology is that it eliminates the need for surface production facilities and supports production from reservoirs otherwise not seen economically attractive. As a part of the subsea gas compression systems, subsea gas cooling is identified as an area with requirements to be developed. Natural convection is the motor behind the cooling, movable parts are therefore not necessary. A draft velocity is induced by the density differences due to the temperature differences in the fluid which are caused by local heating of seawater. The main idea is to take advantage of the draft velocity and use this effect to enhance the cooling. One of the main technology gaps in the development of a passive cooler is the heat transfer between the cooler pipes and the seawater. This is due to uncertainties in the calculations of the draft effect and estimation thereof, uncertainties in the transition to turbulence caused by the interaction between the pipes, and in general the complexity of the physical problem. The idea of the cooler concept is to find a geometry where natural convection from the lower cylinders is used to enhance the heat transport from the upper cylinders with a mixed free and natural convective heat transport approach. Secondly is the idea to use multiple arrays of vertical aligned horizontal cylinders in order to reduce the shear forces between the natural convective flow and the fluid at rest. This will consequently increase the buoyancy induced flow velocity which again will increase the heat transfer from the pipes, giving a more efficient subsea cooler. This project addresses to build conf
The goal is to reach a higher level of understanding of the physics involved in heat exchange processes caused by free convection and how to maximize these, thereafter to use this knowledge to improve the efficiency of the cooler. The main deliverable will be engineering models for design work, a best practice on how to model free convective flow using CFD tools, in addition to input on how to design an efficient cooler. The delivery will be obtained by; 1. Understanding free convection phenomena to help select modeling strategy 2. Develop predictive flow models for 3D CFD work. 3. Use numerical models as a development tool for improvement of cooler efficiency 4. Develop simple 1D or 2D engineering models for design work Both numerical simulations and physical tests shall be carried out initially out on a fairly simple geometry. The results will be compared and the gained knowledge will be used to model free convective heat transport as correct as possible. High resolution LES
Project number 193215/S60 of the Research Council of Norway (RCN).
Research and conference papers
Grafsrønningen, S., Jensen, A. and Pettersson-Reif, “B.A. PIV investigation of a buoyant plume above heated horizontal cylinder”, European Turbulence Conference, Warsaw, 2011
S. Grafsrønningen, A. Jensen & A. Reif :"PIV investigation of buoyant plume from natural convection heat transfer above horizontal heated cylinder", International Journal of Heat and Mass Transfer, Volume 54, Issues 23-24, November 2011, Pages 4975-4987
S. Grafsrønningen og A. Jensen: “Simultanous PIV/LIF measurements of laminar-turbulent transitional plume above horizontal cylinder”, submitted 2011