*3.1.3.2 Concept 2: solar-thermal hydraulics (STH): water replaces R140a*

After discarding the concept of using a chloro-hydrocarbon, water was considered. The immediate problem however, was that it was less dense and had a much lower vapour pressure at the envisaged working temperatures. Most importantly, its enthalpy of evaporation was an order of magnitude higher than that of R140a. These limitations were to be overcome in a series of solutions still using STH principles (i.e., evaporate the liquid, raise it to some height and condense it there to provide a head that will reset the mechanism at the end of the day). A summary of the salient 'solutions' up to the time the STH system was discarded is given below.


• A redesign of the mechanical linear to rotary motion inter-conversion system. A light weight semi cylindrical rack was to be in rectilinear motion, atop a rigid stem. The stem was to be attached to the spring loaded piston. The rack would then drive a fixed axis spur gear, mounted on the solar collector's axis of rotation (**Figure 5**). For locations say in the southern hemisphere, one side of the rack would be used. The other half would be used in the northern hemisphere, where the orientation of the axis and relative position of evaporator would have to be switched to still enable east to west day tracking. In this way, no internal readjustments would be necessary, if the device was moved across the equator.

**Figure 5** illustrates the mechanism at this stage. The mechanical valves have also been replaced with solenoid valves by now.

STH systems had been attractive mainly because they looked novel and relied entirely on 'free' solar energy for their operation most of the time. They had a simple backup plan of burning biomass in case of cloudy days. The evaporator, the vapour evacuation system, the cylinder-piston-spring assembly were designed and constructed. A 200 mm × 200 mm × 100 mm aluminium block for manufacture of the semi cylindrical rack was also purchased. Meanwhile, a separate experiment to verify findings of a theoretical analysis on water evaporation rate yields in an evacuated collector gave 'unwanted' results. Whereas water seemed to evaporate fast enough at the low pressures, most of the vapour re-condensed on the collector glazing and in the evacuation piping before reaching the condenser. It was clear that a more elaborate evacuation system would have to be used if STH were to progress further.

A second 'unwanted' result came from the workshop. Machining of the cylindrical rack in the CNC workshop encountered problems when the purchased block was being resized for actual machining (it had not been exactly 200 mm × 200 mm × 100 mm). These problems forced a re-examination of the 'needs' of Section 3.1.2. It became apparent that the manufacturing problems being encountered, together with the possibility of vacuum leaks in the field would make the product not only 'too expensive', but would also affect its reliability. Moreover, as seen in **Figure 5**, the mechanism would be bulky, and perhaps less marketable than substitutes which could come on the scene later. Thus, STH on this product was discarded. Use was however to be made of almost all components and learnings from it in this and other off shoot products.

**77**

**Figure 6.**

*Reorientation of the hydro-mechanism.*

*Mechanical Engineering Design: Going over the Analysis-Synthesis Mountain to Seed Creativity*

Although STH was now out of the question, the idea of a hydraulic head provided by an oversized 100 L condenser in **Figure 5** still remained attractive. The condenser had intentionally been oversized to provide sufficient heat transfer area, and also to hold reserve water in case of bad weather and inability to light a fire under the evaporator for whatever reason. The piston-cylinder assembly had been designed to discharge about 5 L a day—which would have easily been evaporated by energy incident on a 1.8 m × 1.2 m collection surface. It was therefore reasoned that with 100 L initially filled into the condenser tank (by whatever means), there could be a 20 day pumping head capacity to reset the mechanism at night. The 50 L tank of **Figure 4** was also revisited to hold daily discharges from the mechanism. This would therefore hold slightly more than a week's discharge (as it could not be filled to capacity). This, at last seemed to settle the hydraulics part—if only the cylindri-

*3.1.3.4 The double rack replaces the cylindrical rack: a Hooke joint appears; the* 

facilitated by a double rack-gear set such as shown in **Figure 6**.

Because of manufacturing difficulties mentioned above, the aluminium rack design was reconsidered. Moreover, in absence of the evaporator, the stem sticking out of part of the cylinder looked neither a safe nor an aesthetically 'correct' design. Therefore, it was decided to use an ordinary straight rack-gear set completely housed within the cylinder. The rack would now be part of the piston rod, while the gear shaft axis would be fixed. The gear shaft would protrude slightly out of the cylinder to connect to the collector shaft. Minding about the 'Needs' in Section 3.1.2 on deployment anywhere in sub-Saharan Africa and the now user-inaccessible gearing, the gear shaft was to be standardized as horizontal, normal to the cylinder axis. Variable slope collector shaft axes for different locations were to be joined to this horizontal shaft with a Hooke coupling. Bi-hemispherical installation was to be

This selection of elements would affect the geometry of the mechanism-collector connection of **Figure 5**. Either the collector would have to be lowered, or a horizontally oriented spring-piston-cylinder assembly would need to be raised. The former was considered impractical because a collector-ground clearance must be maintained

*DOI: http://dx.doi.org/10.5772/intechopen.85174*

cal rack could be made. It was not made.

*cylinder orientation changes*

*3.1.3.3 Other concepts: genesis of the hydro-mechanism*

**Figure 5.** *The last of the STH concepts.*

*Mechanical Engineering Design: Going over the Analysis-Synthesis Mountain to Seed Creativity DOI: http://dx.doi.org/10.5772/intechopen.85174*

### *3.1.3.3 Other concepts: genesis of the hydro-mechanism*

*New Innovations in Engineering Education and Naval Engineering*

been replaced with solenoid valves by now.

• A redesign of the mechanical linear to rotary motion inter-conversion system. A light weight semi cylindrical rack was to be in rectilinear motion, atop a rigid stem. The stem was to be attached to the spring loaded piston. The rack would then drive a fixed axis spur gear, mounted on the solar collector's axis of rotation (**Figure 5**). For locations say in the southern hemisphere, one side of the rack would be used. The other half would be used in the northern hemisphere, where the orientation of the axis and relative position of evaporator would have to be switched to still enable east to west day tracking. In this way, no internal readjustments would be necessary, if the device was moved across the equator.

**Figure 5** illustrates the mechanism at this stage. The mechanical valves have also

STH systems had been attractive mainly because they looked novel and relied entirely on 'free' solar energy for their operation most of the time. They had a simple backup plan of burning biomass in case of cloudy days. The evaporator, the vapour evacuation system, the cylinder-piston-spring assembly were designed and constructed. A 200 mm × 200 mm × 100 mm aluminium block for manufacture of the semi cylindrical rack was also purchased. Meanwhile, a separate experiment to verify findings of a theoretical analysis on water evaporation rate yields in an evacuated collector gave 'unwanted' results. Whereas water seemed to evaporate fast enough at the low pressures, most of the vapour re-condensed on the collector glazing and in the evacuation piping before reaching the condenser. It was clear that a more elaborate evacuation system would have to be used if STH were to progress further.

A second 'unwanted' result came from the workshop. Machining of the cylindrical rack in the CNC workshop encountered problems when the purchased block was being resized for actual machining (it had not been exactly 200 mm × 200 mm × 100 mm). These problems forced a re-examination of the 'needs' of Section 3.1.2. It became apparent that the manufacturing problems being encountered, together with the possibility of vacuum leaks in the field would make the product not only 'too expensive', but would also affect its reliability. Moreover, as seen in **Figure 5**, the mechanism would be bulky, and perhaps less marketable than substitutes which could come on the scene later. Thus, STH on this product was discarded. Use was however to be made of almost all components and learnings from it in this and other

**76**

**Figure 5.**

*The last of the STH concepts.*

off shoot products.

Although STH was now out of the question, the idea of a hydraulic head provided by an oversized 100 L condenser in **Figure 5** still remained attractive. The condenser had intentionally been oversized to provide sufficient heat transfer area, and also to hold reserve water in case of bad weather and inability to light a fire under the evaporator for whatever reason. The piston-cylinder assembly had been designed to discharge about 5 L a day—which would have easily been evaporated by energy incident on a 1.8 m × 1.2 m collection surface. It was therefore reasoned that with 100 L initially filled into the condenser tank (by whatever means), there could be a 20 day pumping head capacity to reset the mechanism at night. The 50 L tank of **Figure 4** was also revisited to hold daily discharges from the mechanism. This would therefore hold slightly more than a week's discharge (as it could not be filled to capacity). This, at last seemed to settle the hydraulics part—if only the cylindrical rack could be made. It was not made.

### *3.1.3.4 The double rack replaces the cylindrical rack: a Hooke joint appears; the cylinder orientation changes*

Because of manufacturing difficulties mentioned above, the aluminium rack design was reconsidered. Moreover, in absence of the evaporator, the stem sticking out of part of the cylinder looked neither a safe nor an aesthetically 'correct' design. Therefore, it was decided to use an ordinary straight rack-gear set completely housed within the cylinder. The rack would now be part of the piston rod, while the gear shaft axis would be fixed. The gear shaft would protrude slightly out of the cylinder to connect to the collector shaft. Minding about the 'Needs' in Section 3.1.2 on deployment anywhere in sub-Saharan Africa and the now user-inaccessible gearing, the gear shaft was to be standardized as horizontal, normal to the cylinder axis. Variable slope collector shaft axes for different locations were to be joined to this horizontal shaft with a Hooke coupling. Bi-hemispherical installation was to be facilitated by a double rack-gear set such as shown in **Figure 6**.

This selection of elements would affect the geometry of the mechanism-collector connection of **Figure 5**. Either the collector would have to be lowered, or a horizontally oriented spring-piston-cylinder assembly would need to be raised. The former was considered impractical because a collector-ground clearance must be maintained

**Figure 6.** *Reorientation of the hydro-mechanism.*

during all phases of rotation of the collector. The latter was considered aesthetically unsound and required more ground space to effect. Therefore, the orientation of the cylinder was now changed to vertical as in **Figure 6**.
