Graduation Year

2005

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Muhammad Mustafizur Rahman, Ph.D.

Committee Member

Autar K. Kaw, Ph.D.

Committee Member

Venkat R. Bhethanabotla, Ph.D.

Keywords

Zero boil-off, Cryocooler, Multi-layer insulation, Ammonia, Uniform and discrete heating

Abstract

The study presents a systematic single and two-phase analysis of fluid flow and heat transfer in a liquid hydrogen storage vessel for both earth and space applications.The study considered a cylindrical tank with elliptical top and bottom. The tank wall ismade of aluminum and a multi-layered blanket of cryogenic insulation (MLI) has been attached on the top of the aluminum. The tank is connected to a cryocooler to dissipate the heat leak through the insulation and tank wall into the fluid within the tank. The cryocooler has not been modeled; only the flow in and out of the tank to the cryocooler system has been included. The primary emphasis of this research has been the fluid circulation within the tank for different fluid distribution scenario and for different level of gravity to simulate all potential earth and space based applications. The equations solved in the liquid region included the conservation of mass, conservation of energy, and conservation of momentum. For the solid region only the heat conduction equation was solved. The steady-state velocity, temperature and pressure distributions were calculated for different inlet positions, inlet opening sizes, inlet velocities and for different gravity values. The above simulations were carried out for constant heat flux and constant wall temperature cases. It was observed from single-phase analysis that a good flow circulation can be obtained when the cold entering fluid was made to flow in radial direction and the inlet opening was placed close to the tank wall. For a two-phase analysis the mass and energy balance at the evaporating interface was taken into account by incorporating the change in specific volume and latent heat of evaporation. A good flow circulation in the liquid region was observed when the cold entering fluid was made to flow at an angle to the axis of the tank or aligned to the bottom surface of the tank. The fluid velocity in the vapor region was found to be higher compared to the liquid region.

The focus of the study for the later part of the present investigation was the conjugate heat transfer during a confined liquid jet impingement on a uniform and discrete heating source. Equations governing the conservation of mass, momentum, and energy were solved in the fluid region. In the solid region, the heat conduction equation was solved. The solid-fluid interface temperature shows a strong dependence on several geometric, fluid flow, and heat transfer parameters. For uniform and discrete heat sources the Nusselt number increased with Reynolds number. For a given flow rate, a higher heat transfer coefficient was obtained with smaller slot width and lower impingement height.The average Nusselt number and average heat transfer coefficient are greater for a lower thermal conductivity substrate. A higher heat transfer coefficient at the impingement location was seen at a smaller thickness, whereas a thicker plate or a higher thermal conductivity plate material provided a more uniform distribution of heat transfer coefficient. Compared to Mil-7808 and FC-77, ammonia provided much smaller solidfluid interface temperature and higher heat transfer coefficient whereas FC-77 provided lower Nusselt number. In case of discrete heat sources calculations were done for two different physical conditions, namely, when the total input power is constant and when the magnitude of heat flux at the sources are constant. There was a periodic rise and fall of interface temperature along the heated and unheated regions of the plate when the plate thickness was negligible. The average Nusselt number and average local heat transfer coefficient were highest for uniform heating case and it increased with number of heat sources during discrete heating.

Download

Share

COinS