Recovering private key from Secp256k1 signatures I've seen many answers here and many articles that says we can recover the private key from reused R signatures.
But, what if the r,s signatures are different in transaction of bitcoin then is there a way we could find the ephemeral Key k used in both the cases and find the private key?
In ECDSA, each signature has its own ephemeral key $k$. If $k$ is generated properly, then no amount of signatures will help you recover the private key. "Proper" generation here means either random uniform selection in the proper range, or an appropriate derandomization process such as the one described in RFC 6979.

If the very same $k$ value is used in two signatures, on two distinct messages, but with the same private key $x$, then the private key is revealed. This is the deadly mistake of Sony back in early 2011 (and the initial motivation for RFC 6979, btw). Indeed, if the two messages are $m_1$ and $m_2$, and both values use the same $k$ values, then the two signatures are $(r,s_1)$ and $(r,s_2)$:
\begin{eqnarray}
  s_1 &amp;=&amp; (h(m_1) + xr) / k \\
  s_2 &amp;=&amp; (h(m_2) + xr) / k \\
\end{eqnarray}
The ephemeral key $k$, and the private key $x$, can then be computed as:
\begin{eqnarray}
  k &amp;=&amp; \frac{h(m_1) - h(m_2)}{s_1 - s_2} \\
  x &amp;=&amp; \frac{ks_1 - h(m_1)}{r} \\
\end{eqnarray}

If the values of $k$ are not reused, but are generated with some bias (i.e. not all values in the $[1,q-1]$ range are selected with the same probability), then the private key $x$ can still be recovered from a set of signatures. If for instance $q$ has size 256 bits, but values of $k$ are always lower than $2^{253}$ (i.e. the top three bits are always zero), then a few hundreds of signatures suffice.

If the values of $k$ are generated with a strong, cryptographically secure source, and with no bias, then there is no known attack against ECDSA that would recover the private key $x$, even if many signatures are known. The first reuse of $k$ out of pure back luck is expected to happen after an average of $2^{n/2}$ signatures for an $n$-bit curve, i.e. never in practice if you use a decent curve.

Also, in Bitcoin, people tend not to sign a lot with any given key. For privacy reason, address reuse is discouraged.