  Compression of greenhouse gases still dominates the market of refrigeration
devices. Although well stablished and efficient, this technology is neither
safe for the environment nor able to be scaled down to nanoscale. Solid-state
cooling technologies are being developed to overcome these limitations,
including studies at nanoscale. Among them, the so-called elastocaloric effect
(eC) consists of the thermal response, $\Delta T$, of a material under strain
deformation. In this work, fully atomistic molecular dynamics simulations of
the eC in carbon nanotubes (CNTs) are presented over a large temperature span.
The efficiency of the CNTs as solid refrigerators is investigated by simulating
their eC in a model of refrigerator machine running under Otto-like
thermodynamic cycles (two adiabatic expansion/contraction plus two isochoric
heat exchange processes) operating at temperatures, $T_\mbox{O}$, ranging from
300 to 2000 K. The coefficient-of-performance (COP), defined as the ratio of
heat removed from the cold region to the total work performed by the system per
thermodynamic cycle, is calculated for each value of $T_\mbox{O}$. Our results
show a non-linear dependence of $\Delta T$ on $T_\mbox{O}$, reaching a minimum
value of about 30 K for $T_\mbox{O}$ between 500 and 600 K, then growing and
converging to a linear dependence on $T_\mbox{O}$ for large temperatures. The
COP of CNTs is shown to remain about the same and approximately equal to 8.
These results are shown to be weakly depend on CNT diameter and chirality but
not on length. The isothermal entropy change of the CNTs due to the eC is also
estimated and shown to depend non-linearly on $T_\mbox{O}$ values. These
results predict that CNTs can be considered versatile nanoscale solid
refrigerators able to efficiently work over a large temperature span.
