SIMULATION OF ADSORPTION GENERATORS FOR OPTIMAL PERFORMANCE

Transcription

1 SIMULATION OF ADSORPTION GENERATORS FOR OPTIMAL PERFORMANCE Bob Critoph, Steven Metcalf, Ángeles Rivero Pacho University of Warwick Heat Powered Cycles, Nottingham, June 2016

2 Contents Introduction Plate designs Shell and tube designs to date Adsorbent material Simulation of shell and tube adsorbers Simulation of finned tubes Shell and tube results Finned tube results Conclusions

3 Plate designs Topmacs project for car air conditioning: Nominal bed conductivity was 0.4 W/mK but thermal mass of steel too high.

4 Past shell and tube designs Recommended by consultants Beware consultants! Output power low due to lower than expected heat transfer in shell and tube generators. Measured conductivity approx 0.2 W/mK. Carbon packed between 1.2 mm tubes

5 400 mm Past shell and tube designs Shell and tube heat exchanger 150 mm 1.2 mm 3 mm 0.8 mm

6 Past shell and tube designs What is the optimum tube diameter and pitch? Could it be made better?? Carbon packed between 1.2 mm tubes

7 Past shell and tube designs What is the optimum tube diameter and pitch? Could it be made better?? What is the optimum tube diameter and pitch? Could it be made better?? Simulate heat pump cycles in Matlab, using a range of carbon adsorbents.

8 Adsorbent material ADSORBENT Density Specific heat Conductivity (kg m -3 ) (J kg -1 K -1 ) (W m -1 K -1 ) x 0 n K Granular 208C *T(K) C + lignin *T(K) C + silane *T(K) C Grain monolith *T(K) % 208C + 25% ENG *T(K) * % 208C + 50% ENG *T(K) * T x x0 exp K 1 T sat n

9 Adsorbent material ADSORBENT Density Specific heat Conductivity (kg m -3 ) (J kg -1 K -1 ) (W m -1 K -1 ) x 0 n K Granular 208C *T(K) C + lignin *T(K) C + silane *T(K) C Grain monolith *T(K) % 208C + 25% ENG *T(K) * % 208C + 50% ENG *T(K) * T x x0 exp K 1 T sat n

10 Adsorbent material ADSORBENT Density Specific heat Conductivity (kg m -3 ) (J kg -1 K -1 ) (W m -1 K -1 ) x 0 n K Granular 208C *T(K) C + lignin *T(K) C + silane *T(K) C Grain monolith *T(K) % 208C + 25% ENG *T(K) * % 208C + 50% ENG *T(K) * T x x0 exp K 1 T sat n

11 Adsorbent material ADSORBENT Density Specific heat Conductivity (kg m -3 ) (J kg -1 K -1 ) (W m -1 K -1 ) x 0 n K Granular 208C *T(K) C + lignin *T(K) C + silane *T(K) C Grain monolith *T(K) % 208C + 25% ENG *T(K) * % 208C + 50% ENG *T(K) * T x x0 exp K 1 T sat n

12 Adsorbent material ADSORBENT Density Specific heat Conductivity (kg m -3 ) (J kg -1 K -1 ) (W m -1 K -1 ) x 0 n K Granular 208C *T(K) C + lignin *T(K) C + silane *T(K) C Grain monolith *T(K) % 208C + 25% ENG *T(K) * % 208C + 50% ENG *T(K) * T x x0 exp K 1 T sat n

13 Adsorbent material ADSORBENT Density Specific heat Conductivity (kg m -3 ) (J kg -1 K -1 ) (W m -1 K -1 ) x 0 n K Granular 208C *T(K) C + lignin *T(K) C + silane *T(K) C Grain monolith *T(K) % 208C + 25% ENG *T(K) * % 208C + 50% ENG *T(K) * T x x0 exp K 1 T sat n

14 Simulation of shell and tube adsorbers Radial direction Adiabatic surface Carbon Steel Water flow nr nodes Axial direction nl nodes 2-bed cycle with heat recovery 3 cycles for periodicity Typical time step 0.02 s

15 Simulation of shell finned tube adsorbers Aluminium Carbon Steel Water flow Radial direction Adiabatic surface nr nodes Axial direction nl nodes 2-bed cycle with heat recovery 3 cycles for periodicity Time step in metal 1/20 x carbon

16 COPh Shell and tube results Range of heat recovery times Existing 1.2 mm tube diameter Existing 3 mm tube pitch 208C carbon with lignin Output power per unit volume (kw/m 3 ) time 20 time 30 time 40 time 50 time 60 time 70 time 90 time 110 time 130 time 150 time 170 time 200 Envelope Return water from load 50C Heating, cooling times High temperature water 170C T EVAP 5C

17 COPh Shell and tube results materials comparison ENG + carbon (50%) ENG + carbon (75%) Lignin + carbon Monolithic grains Silane block Vibrated grains Envelope - ENG + carbon (50%) Envelope - ENG + carbon (75%) Envelope - Lignin + carbon Envelope - Monolithic grains Envelope - Silane + carbon Envelope - Vibrated grains Conclusion: Examine different restrict tube further analysis diameters to and 208C pitches + lignin Output power per unit volume (kw/m 3 )

18 COPh Shell and tube results pitch comparison with 1.2 mm tube Conclusion: Could finned Present tubes offer pitch an not far from improvement? optimum 2.5 to 4 mm Pitch = 2.5 mm Pitch = 3 mm Pitch = 4 mm Pitch = 5 mm Envelope - Pitch = 2.5 mm Envelope - Pitch = 3 mm Envelope - Pitch = 4 mm Envelope - Pitch = 5 mm Output power per unit volume (kw/m 3 )

19 Output heating power per unit volume (kw/m3) Finned tube results (3 mm diameter) COPh Half heating/cooling time (s) Power - Time rec. = 0s - Low hw Power - Time rec. = 50s - Low hw Power - Time rec. = 0s - High hw Power - Time rec. = 50s - High hw COPh - Time rec. = 0s - Low hw COPh - Time rec. = 50s - Low hw COPh - Time rec. = 0s - High hw COPh - Time rec. = 50s - High hw

20 Finned tube results Output heating power per unit volume (kw/m 3 ) COPh Higher pitches are feasible, desirable Higher pitches lead to water side heat transfer becoming dominant. Graph shows effect of increasing water side heat transfer x Half heating/cooling time (s) Power - Time rec. = 0s - Low hw Power - Time rec. = 0s - High hw COPh - Time rec. = 0s - Low hw COPh - Time rec. = 0s - High hw Power - Time rec. = 50s - Low hw Power - Time rec. = 50s - High hw COPh - Time rec. = 50s - Low hw COPh - Time rec. = 50s - High hw

21 COPh Finned tube, 3 mm dia., high water H.T Output power per unit volume (kw/m3) Pitch = 6 mm Pitch = 8 mm Pitch = 10 mm Pitch = 12 mm Pitch = 16 mm Envelope - Pitch = 6 mm Envelope - Pitch = 8 mm Envelope - Pitch = 10 mm Envelope - Pitch = 12 mm Envelope - Pitch = 16 mm 3 mm diameter is not necessarily optimal Higher pitches mean easier manufacturing Changing cycle times allow good modulation

22 Conclusions Control strategies provide a useful degree of modulation with acceptable COP variation Existing shell and tube design is not far from optimal Finned tube designs should be easier to manufacture and have better performance Water side heat transfer will be limiting Future work will identify desired tube and fin dimensions

23 Thanks for your attention!