A practical guide to specifying an undergraduate thermal laboratory in Bangladesh: which experiments earn their floor space, how to instrument them, why steady state breaks your timetable, and what safety around heated equipment actually requires.
A heat exchanger demonstration unit arrives, is uncrated, is plugged in, and then sits idle for a semester because nobody specified where the cold stream comes from. The hot side has its own heater and pump. The cold side expects a supply at a temperature and flow rate that the building simply does not have in April, when the roof tank water is warm. This is the characteristic failure of thermal laboratories: the rig works, the utilities around it do not.
Thermal teaching equipment is less physically demanding than a fluids laboratory but more demanding on instrumentation and time. The three constraints that shape it are heat rejection, steady state and safety.
Undergraduate thermal courses in Bangladesh divide into three teaching blocks, and a laboratory that covers all three properly is doing its job. Applied thermodynamics and heat transfer are usually separate papers, but they share a room, a technician and often a rig.
| Teaching block | Experiment | Rig type |
|---|---|---|
| Conduction | Linear conduction along a bar, radial conduction through a disc, thermal conductivity of insulating materials, contact resistance across a joint | Bench-top module, low utility demand |
| Convection | Free and forced convection from a flat plate, a pinned surface and a finned surface, effect of air velocity | Bench-top with a small fan or duct |
| Radiation | Stefan-Boltzmann relation, inverse square law, emissivity of different surfaces | Bench-top, needs a darkened corner |
| Heat exchangers | Concentric tube, shell and tube, plate and cross-flow units; parallel against counter flow; overall heat transfer coefficient and effectiveness | Floor-standing or trolley, needs hot and cold streams, for example the EDIBON ICHE |
| Boiling and condensation | Pool boiling regimes, filmwise against dropwise condensation | Bench-top, glass shrouded, needs care |
| Refrigeration | Vapour compression cycle on the pressure-enthalpy chart, coefficient of performance, effect of condenser and evaporator conditions | Trolley unit, for example the EDIBON TRVCC |
| Alternative cycles | Absorption refrigeration, heat driven rather than work driven | Trolley unit, for example the EDIBON TRAB |
| Fuels and combustion | Calorific value of solid and liquid fuels, flue gas analysis, air to fuel ratio, flame stability | Bomb calorimeter such as the EDIBON TBCF; combustion unit such as the TVCC |
| Air conditioning | Psychrometric processes, sensible and latent load, cooling and dehumidification | Floor-standing duct rig |
| Gas laws and cycles | Perfect gas relations, expansion processes, engine indicator diagrams | Bench-top and engine test bed |
If the budget cannot buy all of it in one year, the block to protect is heat exchangers. It is the only one that connects thermodynamics, fluid mechanics, instrumentation and process design in a single afternoon, and it is the experiment most likely to be examined and most likely to be asked about at an accreditation visit.
Thermal rigs are mostly temperature measurement with a little flow and pressure attached. The instrumentation choices decide whether students learn measurement or just copy numbers off a screen.
Computer-controlled units with a data acquisition system such as EDIBON EDAS/VIS record every channel at a chosen interval, export to a spreadsheet and let a class of sixty produce comparable results. That is a real gain. The loss is that a student who has never watched a temperature creep towards steady state has no feel for thermal time constants at all.
The practical compromise most departments settle on: first year and second year read instruments by hand and plot on graph paper, third year and final year use the logger and are assessed on what they do with the data. Specify the rig so both are possible. A unit whose sensor outputs are only visible inside proprietary software is a poorer teaching instrument than one with a panel display and a logged output.
Ask the supplier, in writing, how cold junction compensation is handled and how a thermocouple channel is calibrated in the field. Keep a dated calibration record for every temperature channel, even if the interval is annual and the method is an ice point and a boiling point check.
This is the scheduling problem nobody warns a new lecturer about. A conduction bar reaches steady state slowly. A shell and tube exchanger needs both streams stable before any reading means anything. A refrigeration unit needs the compressor to settle. In a three-hour slot with sixty students rotating through stations, a rig that takes forty minutes to stabilise will produce one usable data set, not five.
Thermal laboratories injure people in ordinary ways: contact burns, steam, pressurised glass and, occasionally, an oxygen cylinder handled carelessly. None of it is exotic, and all of it is preventable with a specification written before purchase.
Write these into the tender as requirements the supplier must meet, not as things you will sort out afterwards. Retrofit guarding is always uglier and usually gets removed.
Use the same arithmetic as any other teaching laboratory: cohort divided by working group size gives the number of stations that must run simultaneously, and the number of distinct experiments sets the rotation length. A section of sixty in groups of five needs twelve stations; a twelve-week rotation then covers twelve experiments once each.
Thermal work has one extra constraint. Some rigs cannot be run side by side without interfering with each other. A radiation experiment next to a hot air duct, or a free convection module beside a doorway with a ceiling fan above it, will give results that do not match theory and students will conclude the theory is wrong. Zone the room: still-air experiments in one area away from fans and openings, forced-flow and combustion rigs near the extract.
The room also gains heat. A dozen heated rigs running for three hours in a Dhaka April will make the space uncomfortable and will shift the ambient reference temperature that half the experiments depend on. Size the room ventilation or cooling for the connected heat load of the rigs, not for the number of occupants.
Three failure modes recur in this climate and all three are cheap to design out.