Last updated: 2/1/2016
Heat Transfer Today -
engineering students in understanding the
Computer System Requirements
In the past most instructional-software packages for heat & mass transfer were based on the "computerization" of existing analytical solutions and experimental correlations. Often the result was a facility for doing more conventional calculations, only faster; and usually the computed result was just a single "answer" -- such as an overall convective heat-transfer coefficient or fin efficiency.
By contrast, our software uses modern numerical algorithms to solve the fundamental governing ordinary or partial-differential equations in real time. By combining this more fundamental approach with enhanced color-visualization techniques, our new software modules allow a student to "see" -- and thus perhaps to understand -- the physics underlying a particular process.
To date, we have developed software modules for eleven (11) fundamental topics in heat transfer. About a twenty (20) "mini-modules," which use a combination of an Excel Spreadsheet for input and graphical display of output and Visual Basic for Applications (VBA) macros for the serious calculations, have also been developed and may be downloaded here.
All software and a manual (Heat Transfer Tools) consisting of about 100 pages of documentation were originally published by McGraw-Hill in July 2001. In addition to the software, the CD-Rom includes about 60 additional pages in "pdf" files detailing the numerical modeling used "behind the scenes," making these materials very appropriate for use at the graduate level as well as by undergraduates. A few copies of the book and CD may still be available through Amazon.
A complete heat transfer textbook (Heat Transfer Today) with totally updated and integrated software is in preparation now and may be published by Pearson in 2016. For now several sample modules and many of the Excel/VBA workbooks may be downloaded below.
While originally developed strictly for use in a Windows environment, all modules have been installed in the University’s “cloud” system and work equally well in Macintosh and Unix environments as well as on mobile (Ipad and Android-based) devices.
The algorithms and interfaces for each module are uniquely tailored for the particular application - thus avoiding the frequently-steep learning curves associated with much more powerful, commercially available and often costly CFD packages. In most cases specific techniques were derived from the authors' research, as well as from experience in graduate and undergraduate teaching. All modules were used extensively for the first time by some sixty university students taking undergraduate Heat and Mass Transfer during the Spring 1996 semester and then fifteen more times in the Spring 1997-2012 semesters. All modules have been enhanced continuously and extensively as a result of these experiences.
Many of the original Fortran programs were developed and used as lecture demonstrations in distance education courses in Computational Fluid Dynamics and Heat Transfer taught through the Virginia Commonwealth Graduate Engineering Program.
1 Early Years in the Broadcast Studio
Then as facilities became available, they were used in a similar mode for a number of years in a projector-equipped, local classroom. The development of the graphical-user-interfaces during the 1995-96 academic year made them appropriate for student use as well, both on their own, or as we use them, in a scheduled "studio" session. Students attend two 50-minute-long, traditional classes a week, but also have a two-hour working session in one of our computer classrooms.
2 Two-person Teams Working in the Studio Session
Originally Watcom Fortran 77 was used for the intense numerical computations and for generation of the color plots, while a tailored Visual Basic executable was used for the user interface. Later all modules were ported to Visual Basic 6, allowing for much more interactivity than in the past. Now in 2016 all modules are written in VB 2013 and have been installed and tested in the “cloud.”
The development of the underlying computational routines, the user-interface, on-line help file, the supporting documentation, the student exercises, and in many cases a journal article is extremely time-consuming. Consequently the topics for modules were chosen with great care. Only fundamental subjects that cover at least ten pages in a typical textbook were selected. In several cases virtually all the concepts from a whole chapter in a graduate-level text can be illustrated using one module. In addition, several of the modules are sufficiently general that they may be used in a variety of related courses, both graduate and undergraduate, in mathematics, science and engineering.
Ribando, R.J., Heat Transfer Tools,
Ribando, R.J., Richards, L.G., and O'Leary,G.W., "A "Hands-On" Approach to Teaching Undergraduate Heat Transfer," Symposium on Mechanical Engineering Education, Paper IMECE2004-61165, ASME IMECE '04, Anaheim, CA, Nov. 14-19, 2004.
Ribando, R.J., Scott, T.C., Richards, L.G. and O'Leary, G.W., "Using Software with Visualization to Teach Heat Transfer Concepts," Paper # 2002-1536, Proceedings of the ASEE Annual Conference and Exposition, Montreal, Canada, June 16-19,2002.
Ribando, R.J., Scott, T.C., and O'Leary, G.W.,
"Application of the Studio Model to Teaching Heat Transfer," Proceedings
of the 2001 American Society for Engineering Education Annual Conference &
Ribando, R.J., Scott, T.C. and O'Leary, G.W., "Teaching Heat Transfer in a Studio Mode," Session on Energy Systems Education, 1999 ASME IMECE, Nashville, TN, HTD - Vol. 364-4, Edited by L.C.Witte, Nov. 1999, pp. 397-407.
Ribando, R.J., "Teaching Modules for Heat
Transfer," Workshop on Advanced Technology for Engineering Education,
Feb. 24-25, 1998,
Ribando, R.J. and O'Leary, G.W., "Teaching Modules for Heat Transfer," ASME Proceedings of the 32nd National Heat Transfer Conference, HTD-Vol.344, Volume 6, Innovations in Heat Transfer Education, pp. 75-82, August 1997.
New Free Update – 7/27/2015
New Free Update – 2/1/2016
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New Free Update – 9/24/2015
New Free Update – 9/24/2015
This module covers natural convection in a fluid-saturated, porous material, a topic covered in a number of recent graduate-level heat transfer texts. The problem is analogous to classical Rayleigh-Benard natural convection in homogeneous fluid layers. The fluid is assumed to be "Boussinesq," i.e., the fluid density is considered only a function of temperature and variable only in the body force term, and to completely fill all interstices. Fluid motion is assumed governed by the Darcy equations. Heating may be either from the bottom of the layer or from side to side.
Before any run the user selects the aspect ratio of the layer and the number of grid points to be used in the vertical direction. The same grid spacing is used in both directions, so different aspect ratios are obtained simply by adding or subtracting columns of grid points in the horizontal direction. These two parameters may not be changed once a calculation is begun. Before as well during a run the user may set the Rayleigh number for the calculation and also change the heating mode from either bottom-to-top or side-to-side. (The remaining sides are taken as adiabatic.)
5. Natural Convection in a Saturated Permeable Layer
Unless the user elects to stop prematurely, the program runs to a prescribed non-dimensional time. During that interval a succession of 200 color contour plots of temperature are drawn in the left-hand window creating an animation effect. Contours of streamfunction are superimposed on top if the user selects that option. The Nusselt number computed at both the bottom and top (or at the left and right sides if that heating option has been selected) is plotted in the right hand window as a function of time. Switching the heating direction or changing the Rayleigh number in the midst of a run produces interesting transients which may be monitored in both windows.
Unless one has selected a very large number of grid points (which may happen especially with a low height/width ratio), performance is satisfactory on most current platforms. Very thorough implementation instructions of this algorithm are included on the HTT CD-ROM, making it suitable as a several-week-long project in a graduate-level computational methods or convection heat transfer course.
New Free Update – 8/19/2015
New Free Update – 10/7/2015
The usual treatment of heat exchanger thermal design and analysis is based on two analytically-based solution methods applied to the governing, coupled heat balance equations for the two fluids. Because the solution of these differential equations by analytical means is challenging for all but the simplest configurations, the numerical results have been graphed in non-dimensional form and the resulting charts have been used routinely for the last half century. The LMTD method is commonly used for heat exchanger design, that is, determining the required thermal size, while the Effectiveness - NTU method is used for performance calculations. Unfortunately the charts and equations associated with these two methods do not give a complete picture of what is happening inside the exchanger, only a single overall measure. In these two modules, the same governing heat balance equations are solved in discretized form using modern numerical techniques, yielding not only the same "bottom line" results as the traditional methods, but giving a complete picture of what is happening within the device.
Our software for heat-exchanger education consists of one module that covers both “1-D” and “2-D” exchangers:
Both algorithms solve discretized, coupled heat-balance equations along the paths of the two fluids as they each traverse the heat exchanger. Separate algorithms (on the two tabs) have been developed because in one case, a coupled set of ordinary differential equations apply, while in the other a coupled set of partial differential equations govern. The detailed temperature distribution is presented to the user in both tabs, and the performance and design numbers associated with the conventional (LMTD and effectiveness-NTU) methods are reported in both cases for comparison. Samples of the main user-interface for both algorithms are shown below.
Both algorithms allow for several geometric options. The single pass, cross-flow heat exchanger module allows the four generic textbook options: neither fluid mixed, both fluids mixed and either one or the other, but not both mixed. A fifth selection, a two-pass geometry related to an experiment we have done in our undergraduate lab, is also included. The user selects this option in the top left corner and a small schematic of the selected geometry appears.
6 Interface for Cross-Flow Heat Exchanger Option
The 1-D option (tab seen below) allows for several generic geometries, including double pipe designs (parallel and counterflow), shell-and-tube designs and 2-pass, 2-pass plate configurations. After selection of the "Configuration" option, the user specifies a few other inputs relevant to that particular case. In the case of a shell-and-tube configuration, the baffle arrangement is used as a convenient means of discretizing the shell for the numerical solution.
7 The Interface for a Shell-and-Tube Arrangement
In both modules after the geometry has been selected, the user specifies the heat-capacity rates for both fluids and indicates which of the two calculation methods to use. For the “Design” option, the user then specifies the desired outlet temperature of the hot fluid. For the Performance option the user inputs the product of the overall heat transfer coefficient and area (UA product). (Input boxes are shown in white on all user interfaces while numbers appearing on the gray background are program outputs.)
Based on this user input, the temperature distributions in both fluids are computed and displayed in a fraction of a second. For the cross-flow module the temperature distribution in both fluids is depicted in the form of color contour plots as seen above. The hot fluid is shown flowing vertically in the leftmost plot. The cold fluid flows from left to right and is shown in the center. The local difference between the two fluids, which can be helpful in assessing the quality of a design, is shown in the right hand plot.
For one-dimensional geometries HTT_HX returns a plot of the temperatures of both fluids as a function of position. In fact three curves are plotted. In the interface seen above, the temperature of the shell fluid is shown in light blue. That of the tube fluid is plotted twice; the yellow line shows the tube fluid temperature plotted in the conventional way; i.e., as counterflow. The third (green line) shows the tube temperature as "seen" by the shell fluid as it passes through the exchanger. So for instance, shell fluid entering the top of the three shells used in this example first encounters fluid that is exiting the shell, then fluid that has just entered that shell, then fluid that is nearly ready to exit, etc. This accounts for what appears to be a "ringing" behavior in the curves. (The analytical solutions are based on the exchange of heat between the shell fluid and the mean of the two local pipe fluid temperatures at that horizontal position.)
In addition to the detailed temperature distributions, both interfaces return all the design and performance measures used with the traditional methods so that all results may be verified by comparison with the conventional charts. While not currently configured, either module could be adapted to handle situations which inherently cannot be handled by the analytically-based methods, including non-uniform thermal properties, non-uniform overall heat transfer coefficient and condensation or evaporation of either fluid occurring in only a portion of the device. Such capability is available in commercial HX design software.
A complete description of the numerical algorithm used in these two modules may be found in: Ribando, R.J., O'Leary,G.W., and Carlson-Skalak,S.E., "A General, Numerical Scheme for Heat Exchanger Thermal Analysis and Design," Computer Applications in Engineering Education, Vol. 5, No. 4, 1997, pp 231-242.
New Free Update – 8/19/2015
The View Factor from one surface to another (also known as the Shape Factor and the Configuration Factor) is the fraction of radiation leaving the first surface that is intercepted by the second. For some very simple geometries this quantity can be determined by geometric arguments. The reciprocity theorem and shape factor algebra may be useful for other arrangements. For a very few geometries, e.g., perpendicular rectangles with a common edge, coaxial parallel disks, coaxial cylinders and aligned parallel rectangles, the very complicated quadruple integral defining the view factor between two surfaces may be integrated analytically. The resulting values are given in the form of charts in virtually every heat transfer book. An Excel spreadsheet that evaluates these analytical solutions for any of the four geometries listed above may be downloaded by clicking on any of the links above. View factors for still other geometries are tabulated in many sources. Several modern applications of radiation heat transfer, including the thermal analysis of large space structures and the rendering of complex three-dimensional scenes on computers using the radiosity method, require the computation of the view factors between thousands of pairs of surfaces. The numerical scheme used in this module is typical of modern means developed for such applications.
This module computes the view factor between two parallelograms arbitrarily positioned in three-dimensional space using a numerical implementation of the Nusselt unit sphere method based on the NASA TRASYS code. Users enter the x, y and z coordinates of three corners of each plate into an on-screen table (contained on a separate sheet not seen in the interface below); the coordinates for the fourth corner of each plate are computed automatically. To aid in verifying the geometric input data, the plates are drawn on the screen in a perspective view with hidden surface removal. The slider bars seen in the upper right of the interface seen below may be used to select any desired viewing angle - - also giving student engineers some much-needed reinforcement of training in 3-D visualization. On a modern PC the recomputation and refresh of the figure and the calculation of the viewfactor itself is nearly instantaneous. In addition to the conventional arrangements covered by viewfactor charts and equations which may be used for program verification, this program computes completely arbitrary arrangements in 3-D space. In the event that either surface cannot "see" the other surface completely, a warning is returned.
In addition to the experience with 3-D visualization, the radiation view factor module exposes students to a modern analysis technique, which is used in industry, but simple enough for students to implement in an elective, undergraduate computer graphics course.
A discussion of the verification process for this module may be found in: Ribando, R.J. and Weller, E.A., "The Verification of an Analytical Solution - An Important Engineering Lesson," Journal of Engineering Education, Vol. 88, No. 3, July 1999, pp. 281-283.
About 20 "mini-modules" implemented using a combination of the Excel spreadsheet and Visual Basic for Applications (VBA) may be downloaded here. Some of these are for heat transfer; others cover thermodynamics, computational methods and fluid mechanics.
Descriptions of eight projects intended for student implementation are described here. Six were included in the first edition of Heat Transfer Tools; two more, one of which may be downloaded, have been prepared for the second edition.
It has been said that "the purpose of computing is insight, not numbers." An online quiz that tests understanding of the physical principles that may be learned partly through computer "experimentation" using the HTT modules may be taken here.
The original development of the interfaces
during the 1995-96 academic year was supported by a fellowship from
Professor Robert J. Ribando
122 Engineer's Way
e-mail: rjr at virginia.edu