Publication Date

8-2023

Date of Final Oral Examination (Defense)

4-21-2023

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Mechanical Engineering

Department

Mechanical and Biomechanical Engineering

Major Advisor

Todd Otanicar, Ph.D.

Advisor

Krishna Pakala, Ph.D.

Advisor

Nirmala Kandadai, Ph.D.

Abstract

Solid particles have recently attracted substantial interest as a thermal transport medium in high-temperature energy storage and thermal energy conversion systems due to their ability to operate at high temperatures (up to 1000 °C). This is especially useful in the concentrating solar power (CSP) industry where solid particles are utilized as heat transfer media. Thermal conductivity of particles in CSP is critically important to the overall heat transfer that occurs within a heat exchanger. A cheap and effective avenue to increase the thermal conductivity of a particle distribution is by reducing its porosity by employing 2 differently sized particles. The thermal conductivity can be increased further by applying a load to the particles. At lower temperatures (20-300 °C), previous work has demonstrated a binary particle distribution has superior thermal conductivity. In this work, the thermal conductivities of HSP binary particle distributions under load are explored at ambient temperatures revealing enhanced thermal conductivity. Furthermore, high temperature (from 300-700 °C) analysis of HSP binary particle distributions are also explored with results being that monodispersed distributions yield higher thermal conductivities due to enhanced surface radiation in larger particles. A bimodal distribution increases packed-bed thermal conductivity only up to around ~400 °C at which monodisperse distributions with larger particles then yield higher thermal conductivities. HSP binary particle thermal conductivity results are compared to current models demonstrating inadequate characterization at high temperatures (> 400 °C) due to the dominant heat transfer mechanism of radiation in larger particles at high temperature. These models are implemented in a numerical model of the Gen3 Particle Pilot Plant (G3P3) 20 kWt prototype heat exchanger constructed by Sandia National Laboratory (SNL) where they can then be validated using SNL’s experimental data from the prototype. From SNL’s experimental data, the ZBS thermal conductivity method is confirmed to be accurate at working G3P3 20 kWt prototype heat exchanger temperatures (290-500 °C) at particle and sCO2 mass flow rates of 100 g/s while the Yagi and Kunii thermal conductivity method is not. Utilizing the validated numerical model and ZBS thermal conductivity method, various binary particle mixtures are simulated at working G3P3 20 kWt prototype heat exchanger temperatures revealing increases in the overall heat transfer coefficient of up to 25% in HSP 16/30-40/70 mixtures as well as increases as high as 40% in CP 20/40-70/140 mixtures when compared to monodispersed particle distributions of the respective mixtures’ large particles. Solid particle thermal conductivity enhancement with binary particle distributions in this way has the potential to be a significant step forward towards the CSP industry’s goal of developing the world’s first 1 MWt heat exchanger through the G3P3 program.

DOI

https://doi.org/10.18122/td.2136.boisestate

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