Roesle, M. L., V. Coskun, A. Steinfeld, 2011, "Numerical analysis of heat loss from a parabolic trough absorber tube with active vacuum system", Journal of Solar Energy Engineering 133(3), p. 031015. doi: 10.1115/1.4004276.
I was involved with a project whose goal was to develop a new receiver for parabolic trough CSP systems. One feature of the new design was that the vacuum in the annulus between the absorber tube and vacuum jacket would be actively maintained by a vacuum pump system, which would allow the design to tolerate outgassing and small leaks. The purpose of the model described in this paper was to predict the heat loss by conduction/convection across the annulus as a function of the gas and the gas pressure in the annulus. The approach used here was to incorporate slip flow correlations in a commercial CFD code. The radiation heat transfer was somewhat simplified, as the goal was to investigate the conduction/convection heat loss.
Roesle, M. L., P. Good, V. Coskun, A. Steinfeld, 2012, "Analysis of conduction heat loss from a parabolic trough solar receiver with active vacuum by direct simulation Monte Carlo", Numerical Heat Transfer, Part A 62(5), pp. 432-444. doi: 10.1080/10407782.2012.672868.
This paper addresses the same problem as the previous one, but uses direct simulation Monte Carlo (DSMC) to model the behavior of the rarefied gas in the annulus. The up-shot is that the slip flow model worked pretty well and is probably good enough. When the pressure gets low enough that the slip flow model isn't valid any more and the relative error using the slip flow model becomes large, the heat loss by conduction is so low that it isn't really important. The slip flow boundary conditions are also much easier to incorporate into commercial numerical modeling software.
Wirz, M., M. L. Roesle, A. Steinfeld, 2012, "Three-dimensional optical and thermal numerical model of solar tubular receivers in parabolic trough concentrators", Journal of Solar Energy Engineering 134(4), p. 041012. doi: 10.1115/1.4007494.
This paper presents a detailed overall model of heat transfer in parabolic trough concentrators. It uses spectral Monte Carlo ray tracing to handle radiation heat transfer (both incoming solar radiation and thermally emitted radiation) and accounts for conduction in the solid elements of the receiver. Based on the previous paper, a rather simple model of conduction through the rarefied gas in the annulus of the receiver is used.
Wirz, M., M. L. Roesle, A. Steinfeld, 2013, "Design point for predicting year-round performance of solar parabolic trough concentrator systems", paper number ES2013-18055, in Proceedings of the ASME 2013 7th International Conference on Energy Sustainability, July 14-19, Minneapolis MN.
Wirz, M., M. L. Roesle, A. Steinfeld, 2013, "Design Point for Predicting Year-Round Performance of Solar Parabolic Trough Concentrator Systems", Journal of Solar Energy Engineering 136(2), p. 021019. doi: 10.1115/1.4025709
This paper grew from a desire to determine what conditions to use when running the model described in the previous paper. Usually one wants to know how well a given design of solar concentrator will work in a given location on the earth over the course of a typical year, but the model developed in the previous paper is time-consuming to run, so it would not be practical to run it repeatedly for the hour-by-hour conditions. This paper defines an averaging process that can be applied to the hour-by-hour conditions in a location to get a single set of parameters to use as inputs for the detailed heat transfer model. When these averaged parameters are used the model results are a good approximation of the yearly averaged performance of the receiver.
Marti, J., M. L. Roesle, A. Steinfeld, 2013, "Experimental determination of the radiative properties of particle suspensions for high-temperature solar receiver applications", Heat Transfer Engineering 35(3), pp. 272-280. doi: 10.1080/01457632.2013.825173.
This paper describes our measurement of the radiative properties (extinction coefficient, scattering albedo, scattering phase function) of suspensions of green silica particles. Thin samples of the particle suspensions were made by mixing the particles with a clear epoxy, then pressing samples of the epoxy between pieces of clear glass (with a controlled gap width between them) and letting the epoxy cure. Measurements were made of the transmitted and scattered radiation through the samples using a goniometer. A model of the experimental setup was created with suspension represented as a continuous scattering medium with specified radiative properties, and Monte Carlo ray tracing used to determine how the modeled suspension would behave. The radiative properties in the model were then adjusted iteratively until they fit the measured data.
Marti, J., M. L. Roesle, A. Steinfeld, 2013, "Combined experimental-numerical approach to determine radiation properties of particle suspensions", paper number HT2013-17015, in Proceedings of the ASME 2013 Summer Heat Transfer Conference, July 14-19, Minneapolis MN.
Marti, J., M. L. Roesle, A. Steinfeld, 2014, "Combined Experimental-Numerical Approach to Determine Radiation Properties of Particle Suspensions", Journal of Heat Transfer 136(9), p. 092701. doi: 10.1115/1.4027768.
This paper is on the same topic as the previous one, and examines suspensions of both green and black silica particles. The goniometer was also calibrated carefully, so the results with the green particles differ slightly from the previous paper. (oops.) The double Henyey-Greenstein (DHG) function is found to fit the scattering phase function well, and changes in the extinction coefficient with particle loading are captured well by Kaviany and Singh's scaling factor for dependent scattering. There is a slight change in the scattering albedo and the parameters of the DHG function with particle loading.