**4. Results and discussions**

The new spiral was sized by considering the same instal space than the actual radiator. The features were 0.4 m of height, 0.15 m of depth and 0.4 m of width.

## *Designing Spiral Plate Heat Exchangers to Extend Its Service and Enhance the Thermal… DOI: http://dx.doi.org/10.5772/intechopen.85345*

A suggested car cooling system performance must cool down the hot fluid 10°C or maximum 20°C. The results were achieved by implementing the thermal and hydraulic model, where one of the fundamental variables to measure was the hot outlet temperature. The difference between hot inlet and hot outlet was 6.4°C. The thermal and hydraulic method is an option to design heat exchangers. One of its goals is to find the lowest heat transfer area because the permissible pressure drop was fixed as a parameter to use completely. Then, from this value, the method seeks for some geometrical configuration to satisfy the required pressure drop. The method determined the heat transfer area, and the numeric value was of 2.04 m<sup>2</sup> (**Tables 6** and **7**).

The permissible pressure drop was set by 1 psi for the two passages. The simulation calculated a value of 0.975 psi for the hot channel. The value for cold channel was 0.00013 psi because the cold channel has a length of 0.15 m. This flow section was considered as an open channel. This hydraulic behaviour was determined by the spiral diameter of 0.387 m, a plate length of 6.7 m, 10 spiral turns and the plate


#### **Table 6.**

**Figure 3** shows the virtual spiral plate heat exchanger designed by the software workbench, the mesh was structured with 97,250 control volumes and the geometrical features (plate width, plate spacing, plate length, thickness, etc.) are shown in

Flow (kg/h) 4200 5200 Inlet temperatures (°C) 98 20 Viscosity (cp) 0.3 0.2 Maximum pressure drop (kPa) 6.89 6.89 Thermal conductivity (W/m K) 0.6 0.0259 Heat capacity (J/Kg K) 4270.53 544.28

Plate width (m) 0.152 0.152

Specific gravity 0.97 1 Channel spacing (m) 0.0043 0.0088

Thermal conductivity (aluminium, W/m K) 205

Core diameter (m) 0.0508

Plate thickness (m) 0.0787

**Water Air**

The boundary conditions such as the inlet velocity, inlet temperatures, fluid properties, flow rates and metal properties were considered from the results shown

In order to demonstrate the rating and the design method, a case study was proposed. The example consists of two streams, water (hot stream) and air (cold stream), where the hot fluid flows by a spiral channel and the cold fluid flows through a cross-flow arrangement. **Table 5** explains the operational conditions for the first case study. This data was taken from a normal operation of a car radiator where they proposed to design an equipment to cool down a hot stream by 17

Table 5 summarizes the operational conditions. The plate width is set by a numeric value of 0.1524 m. The initial plate spacing for the hot stream is 0.0043 m

The second case study consists of designing a condenser for a cryogenic process. The data were taken from a case study to design a compact heat exchanger [13]. The hot temperature must cool down by 9°C to transfer a latent heat to the cold fluid. The cold temperature is 15°C. The initial core spiral diameter was 0.5 m. A plate width of 0.076 m was assumed to find the optimal plate length for the spacing

The new spiral was sized by considering the same instal space than the actual radiator. The features were 0.4 m of height, 0.15 m of depth and 0.4 m of width.

and for the cold stream is 0.0088 m, and the core diameter is 0.0508 m.

plates of 0.00254 and 0.00635 m for cold and hot stream, respectively.

degrees. **Table 4** shows the operational data for the car radiator.

**Tables 5** and **8**.

*Low-temperature Technologies*

**Table 5.** *Second case study.*

in **Tables 5** and **8**.

**3. Case study**

**4. Results and discussions**

**214**

*Second case study [13].*


**Table 7.** *Results for case study 1.*

### *Low-temperature Technologies*

spacing for both channels. To achieve a pressure drop close to the ideal value, it should be necessary to increase the plate length, but the spiral diameter would be higher than the delimited value of 0.4 m. The thermal performance remained with no significantly variations.

The compact heat exchanger was implemented to handle three stages: superheated phase, condensed phase and subcooling phase. The spiral plate heat exchanger has the same purpose, which is to condensate the refrigerant and cooling until the target temperature is reached. Though the compact exchanger has more heat transfer area than spiral exchanger, the compact used completely its maximum area to achieve the duty, but the spiral heat exchanger achieved the service using less heat transfer area. This feature is demonstrated by a pressure drop for R134a, because the maximum pressure drop was fixed to 6.89 kPa. If the pressure drop increased, the result will be a larger spiral exchanger. The hot outlet temperature could be minor than 31.72°C. These results validate the use of spiral plate heat exchangers as a part of a

*Designing Spiral Plate Heat Exchangers to Extend Its Service and Enhance the Thermal…*

Spiral plate heat exchangers have a potential participation in the cryogenic process. Heat exchangers are 30% approximately of the total cost of the cryogenic plant [14, 15]. Only two types of heat exchangers are considered for cryogenic applications: tubes (concentric tubes and coil wounded tubes) and plates (perfo-

exchangers in the refrigeration process is the high thermal efficiency. Then, spiral plate heat exchangers are capable of dealing with that situation. The thermal and hydraulic model presented in this work showed a suitable precision since the pro-

exchanger. It is possible to size spiral plate exchangers even with poor flow distribution and axial thermal behaviour and think forward to design a multi-stream

The numerical and computational results were collected by colours which they represent a profile of the measured variables, the inlet and outlet temperatures mainly. Colour red means the hottest temperature and colour blue represents the coldest temperature. **Figure 4** describes the temperature profile for the water and the air and the arrangement of the inlet and the outlet streams. The hot liquid (water) enters at the centre of the spiral moving out along the plate, and the cold

rated plates and plate-fin) [14]. The principal duty that must fill the heat

cedure does not support the traditional design such as shell and tube heat

spiral plate heat exchanger for cryogenic challenges.

stream (air) crosses the plate width.

*The temperature profile for the cold and the hot streams.*

**Figure 4.**

**217**

cryogenic process.

*DOI: http://dx.doi.org/10.5772/intechopen.85345*

For the improvement of the spiral design, only the plate spacings for the cold stream and the hot stream were reduced to 4 and 4.2 mm, respectively. The results are shown in **Table 8**.

The results in **Table 8** show that the thermal and hydraulic performance was improved, by decreasing the plate gap, because the flow distribution along the channel enhances the heat transfer, and the hot outlet temperature increased the difference by 9.4°C. The available pressure drop for the hot stream was used fully, while the cold pressure drop presented the variation of 0.00072 psi. The heat transfer area continued as 2.04 m, the number of turns raised by 1.5 rounds and the spiral outside diameter was modified to 0.32 and 0.06 m lower than the first case study.

The results for the second design were compared with the compact heat exchanger design, and they are shown in **Table 9**.

The results are similar regarding the hot outlet temperature; however, there was a significant difference between the heat transfer areas. The compact heat exchanger was designed to use fins to increase the thermal effectiveness.


#### **Table 8.**

*Results for an improvement design.*


**Table 9.** *Results for a condenser design.*

### *Designing Spiral Plate Heat Exchangers to Extend Its Service and Enhance the Thermal… DOI: http://dx.doi.org/10.5772/intechopen.85345*

The compact heat exchanger was implemented to handle three stages: superheated phase, condensed phase and subcooling phase. The spiral plate heat exchanger has the same purpose, which is to condensate the refrigerant and cooling until the target temperature is reached. Though the compact exchanger has more heat transfer area than spiral exchanger, the compact used completely its maximum area to achieve the duty, but the spiral heat exchanger achieved the service using less heat transfer area. This feature is demonstrated by a pressure drop for R134a, because the maximum pressure drop was fixed to 6.89 kPa. If the pressure drop increased, the result will be a larger spiral exchanger. The hot outlet temperature could be minor than 31.72°C. These results validate the use of spiral plate heat exchangers as a part of a cryogenic process.

Spiral plate heat exchangers have a potential participation in the cryogenic process. Heat exchangers are 30% approximately of the total cost of the cryogenic plant [14, 15]. Only two types of heat exchangers are considered for cryogenic applications: tubes (concentric tubes and coil wounded tubes) and plates (perforated plates and plate-fin) [14]. The principal duty that must fill the heat exchangers in the refrigeration process is the high thermal efficiency. Then, spiral plate heat exchangers are capable of dealing with that situation. The thermal and hydraulic model presented in this work showed a suitable precision since the procedure does not support the traditional design such as shell and tube heat exchanger. It is possible to size spiral plate exchangers even with poor flow distribution and axial thermal behaviour and think forward to design a multi-stream spiral plate heat exchanger for cryogenic challenges.

The numerical and computational results were collected by colours which they represent a profile of the measured variables, the inlet and outlet temperatures mainly. Colour red means the hottest temperature and colour blue represents the coldest temperature. **Figure 4** describes the temperature profile for the water and the air and the arrangement of the inlet and the outlet streams. The hot liquid (water) enters at the centre of the spiral moving out along the plate, and the cold stream (air) crosses the plate width.

**Figure 4.** *The temperature profile for the cold and the hot streams.*

spacing for both channels. To achieve a pressure drop close to the ideal value, it should be necessary to increase the plate length, but the spiral diameter would be higher than the delimited value of 0.4 m. The thermal performance remained with

For the improvement of the spiral design, only the plate spacings for the cold stream and the hot stream were reduced to 4 and 4.2 mm, respectively. The results

The results in **Table 8** show that the thermal and hydraulic performance was improved, by decreasing the plate gap, because the flow distribution along the channel enhances the heat transfer, and the hot outlet temperature increased the difference by 9.4°C. The available pressure drop for the hot stream was used fully, while the cold pressure drop presented the variation of 0.00072 psi. The heat transfer area continued as 2.04 m, the number of turns raised by 1.5 rounds and the spiral outside diameter was modified to 0.32 and 0.06 m lower than the first case

The results for the second design were compared with the compact heat

Tout (°C) 88.6 79.4 Maximum pressure drop (kPa) 6.89 0.004826

HTC (W/m<sup>2</sup> K) 12577.35 628.41

Plate length (m) 6.7 6.7

Tout (°C) 31.72 16.7 32.85 Pressure drop (kPa) 0.875 5.38 84.5

) 0.0929 1.46

) 2.04

Diameter (m) 0.32

U (W/m<sup>2</sup> K) 105.37 Effectiveness 0.76 Number of rounds 11.5

a significant difference between the heat transfer areas. The compact heat exchanger was designed to use fins to increase the thermal effectiveness.

The results are similar regarding the hot outlet temperature; however, there was

**Water Air**

**R134a Water Compact HE**

exchanger design, and they are shown in **Table 9**.

Diameter (m) 0.120

U (W/m<sup>2</sup> K) 3185.5 Effectiveness 0.38 Number of rounds 2.43 Plate length (m) 0.609

HTC (W/m<sup>2</sup> K) 69098.78 18091.41

no significantly variations.

*Low-temperature Technologies*

are shown in **Table 8**.

study.

Area (m<sup>2</sup>

**Table 8.**

Area (m<sup>2</sup>

**Table 9.**

**216**

*Results for a condenser design.*

*Results for an improvement design.*


**Nomenclature**

Ac free flow area (m<sup>2</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.85345*

C core diameter (m) Cp heat capacity (J/Kg K) De equivalent diameter (m) Dh helix diameter (m) ds spacing plate (m) F flow (kg/hr)

H plate width (m)

L plate length (m) Pr Prandtl number q heat load (W) Re Reynolds number

s specific gravity T temperature (°C)

A heat transfer area (m<sup>2</sup>

Ap plate area (m<sup>2</sup>

)

*Designing Spiral Plate Heat Exchangers to Extend Its Service and Enhance the Thermal…*

)

)

)

h film heat transfer coefficient (W/m<sup>2</sup> K)

U overall heat transfer coefficient (W/m<sup>2</sup> K)

k thermal conductivity (W/m K)

Rec critical Reynolds number

G fluid velocity (kg/hr. m<sup>2</sup>

x plate thickness (m)

ΔP pressure drop (kPa) μ viscosity (cp)

f film fluid properties b bulk fluid properties

h hot side c cold side in inlet out outlet

**Greek symbols**

**Subindices**

**219**

#### **Table 10.**

*Thermal and hydraulic performance.*

The numerical study determined an appreciable accuracy between the method design and the computational simulation. **Table 10** shows the approximation of the outlet temperatures. The hydraulic performance was measured by calculating the outlet pressure for both streams. The results determined that the maximum pressure drop was observed at the hot section. The design method calculated a pressure drop of 6.89 kPa, and the numerical result was 17.23 kPa, because the spiral flow section has the less wide spacing between the plates. The minimum pressure drop was expected for the cold stream. The method reported 0.004826 kPa. The simulation determined a value of 3.4 kPa, due to the cross-flow section that has a spacing wider than the spiral section and furthermore because the channel is open.
