D.L. Hofeldt

Bio: D.L. Hofeldt is an academic researcher from University of Minnesota. The author has contributed to research in topics: Heat transfer & Countercurrent exchange. The author has an hindex of 4, co-authored 6 publications receiving 92 citations.

Experimental and numerical investigation of thermal energy storage with a finned tube

Abstract: A latent heat thermal energy storage system using a phase change material (PCM) is an efficient way of storing or releasing a large amount of heat during melting or solidification. It has been determined that the shell-and-tube type heat exchanger is the most promising device as a latent heat system that requires high efficiency for a minimum volume. In this type of heat exchanger, the PCM fills the annular shell space around the finned tube while the heat transfer fluid flows within the tube. One of the methods used for increasing the rate of energy storage is to increase the heat transfer surface area by employing finned surfaces. In this study, energy storage by phase change around a radially finned tube is investigated numerically and experimentally. The solution of the system consists of the solving governing equations for the heat transfer fluid (HTF), pipe wall and phase change material. Numerical simulations are performed to investigate the effect of several fin parameters (fin spacing and fin diameter) and flow parameter (Re number and inlet temperature of HTF) and compare with experimental results. The effect of each variable on energy storage and amount of solidification are presented graphically. Copyright © 2005 John Wiley & Sons, Ltd.

Experimental Investigation of Micro HeatPipes Fabricated in Silicon Wafers

Abstract: An experimental investigation was conducted to determine the thermal behavior of arrays of micro heat pipes fabricated in silicon wafers. Two types of micro heat pipe arrays were evaluated, one that utilized machined rectangular channels and the other that used an anisotropic etching process to produce triangular channels. Once fabricated, a clear pyrex cover plate was bonded to the top surface of each wafer using an ultraviolet bonding technique to form the micro heat pipe array. These micro heat pipe arrays were then evacuated and charged with a predetermined amount of methanol. Using an infrared thermal imaging unit, the temperature gradients and maximum localized temperatures were measured and an effective thermal conductivity was computed. The experimental results were compared with those obtained for a plain silicon wafer

A thermodynamic review on solar box type cookers

Abstract: Globally there is profuse literature on the continuous developments of box type solar cookers and solar ovens. A lot of research work has been carried out in recent passed years in the world which clearly shown the utilization of solar energy towards the greatest needs of mankind obviously solar cooking, fuel saving, non-polluting environment and to save and produce electricity. In the present literature the efforts have been made to focus on diverse developments of box type solar cooker till now. An attempt has been made to optimize the various major parameters such as geometries of box-cooker, glazing system, cooking vessels design, heat storage, insulation, mirror boosters and financial feasibility of solar cooker box. All the discussed factors have been taken into account in the fabrication of a simple solar box cooker and a good improvement has been found in the performance of box cooker with efficient working in low ambient temperatures. A wiper type mechanism to remove vapor droplets from the bottom of glazing, during the cooking process has been introduced and discussed with a new designed cooking vessel. The investigational testing of the fabricated box cooker has been carried out under the climate conditions of Moradabad (latitude – 28°58′north and longitude – 78°47′east) Uttar Pradesh.